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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
4 *
5 * Swap reorganised 29.12.95, Stephen Tweedie.
6 * kswapd added: 7.1.96 sct
7 * Removed kswapd_ctl limits, and swap out as many pages as needed
8 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
9 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
10 * Multiqueue VM started 5.8.00, Rik van Riel.
11 */
12
13#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
14
15#include <linux/mm.h>
16#include <linux/sched/mm.h>
17#include <linux/module.h>
18#include <linux/gfp.h>
19#include <linux/kernel_stat.h>
20#include <linux/swap.h>
21#include <linux/pagemap.h>
22#include <linux/init.h>
23#include <linux/highmem.h>
24#include <linux/vmpressure.h>
25#include <linux/vmstat.h>
26#include <linux/file.h>
27#include <linux/writeback.h>
28#include <linux/blkdev.h>
29#include <linux/buffer_head.h> /* for try_to_release_page(),
30 buffer_heads_over_limit */
31#include <linux/mm_inline.h>
32#include <linux/backing-dev.h>
33#include <linux/rmap.h>
34#include <linux/topology.h>
35#include <linux/cpu.h>
36#include <linux/cpuset.h>
37#include <linux/compaction.h>
38#include <linux/notifier.h>
39#include <linux/rwsem.h>
40#include <linux/delay.h>
41#include <linux/kthread.h>
42#include <linux/freezer.h>
43#include <linux/memcontrol.h>
44#include <linux/delayacct.h>
45#include <linux/sysctl.h>
46#include <linux/oom.h>
47#include <linux/pagevec.h>
48#include <linux/prefetch.h>
49#include <linux/printk.h>
50#include <linux/dax.h>
51#include <linux/psi.h>
52
53#include <asm/tlbflush.h>
54#include <asm/div64.h>
55
56#include <linux/swapops.h>
57#include <linux/balloon_compaction.h>
58
59#include "internal.h"
60
61#define CREATE_TRACE_POINTS
62#include <trace/events/vmscan.h>
63
64struct scan_control {
65 /* How many pages shrink_list() should reclaim */
66 unsigned long nr_to_reclaim;
67
68 /*
69 * Nodemask of nodes allowed by the caller. If NULL, all nodes
70 * are scanned.
71 */
72 nodemask_t *nodemask;
73
74 /*
75 * The memory cgroup that hit its limit and as a result is the
76 * primary target of this reclaim invocation.
77 */
78 struct mem_cgroup *target_mem_cgroup;
79
80 /*
81 * Scan pressure balancing between anon and file LRUs
82 */
83 unsigned long anon_cost;
84 unsigned long file_cost;
85
86 /* Can active pages be deactivated as part of reclaim? */
87#define DEACTIVATE_ANON 1
88#define DEACTIVATE_FILE 2
89 unsigned int may_deactivate:2;
90 unsigned int force_deactivate:1;
91 unsigned int skipped_deactivate:1;
92
93 /* Writepage batching in laptop mode; RECLAIM_WRITE */
94 unsigned int may_writepage:1;
95
96 /* Can mapped pages be reclaimed? */
97 unsigned int may_unmap:1;
98
99 /* Can pages be swapped as part of reclaim? */
100 unsigned int may_swap:1;
101
102 /*
103 * Cgroup memory below memory.low is protected as long as we
104 * don't threaten to OOM. If any cgroup is reclaimed at
105 * reduced force or passed over entirely due to its memory.low
106 * setting (memcg_low_skipped), and nothing is reclaimed as a
107 * result, then go back for one more cycle that reclaims the protected
108 * memory (memcg_low_reclaim) to avert OOM.
109 */
110 unsigned int memcg_low_reclaim:1;
111 unsigned int memcg_low_skipped:1;
112
113 unsigned int hibernation_mode:1;
114
115 /* One of the zones is ready for compaction */
116 unsigned int compaction_ready:1;
117
118 /* There is easily reclaimable cold cache in the current node */
119 unsigned int cache_trim_mode:1;
120
121 /* The file pages on the current node are dangerously low */
122 unsigned int file_is_tiny:1;
123
124 /* Allocation order */
125 s8 order;
126
127 /* Scan (total_size >> priority) pages at once */
128 s8 priority;
129
130 /* The highest zone to isolate pages for reclaim from */
131 s8 reclaim_idx;
132
133 /* This context's GFP mask */
134 gfp_t gfp_mask;
135
136 /* Incremented by the number of inactive pages that were scanned */
137 unsigned long nr_scanned;
138
139 /* Number of pages freed so far during a call to shrink_zones() */
140 unsigned long nr_reclaimed;
141
142 struct {
143 unsigned int dirty;
144 unsigned int unqueued_dirty;
145 unsigned int congested;
146 unsigned int writeback;
147 unsigned int immediate;
148 unsigned int file_taken;
149 unsigned int taken;
150 } nr;
151
152 /* for recording the reclaimed slab by now */
153 struct reclaim_state reclaim_state;
154};
155
156#ifdef ARCH_HAS_PREFETCHW
157#define prefetchw_prev_lru_page(_page, _base, _field) \
158 do { \
159 if ((_page)->lru.prev != _base) { \
160 struct page *prev; \
161 \
162 prev = lru_to_page(&(_page->lru)); \
163 prefetchw(&prev->_field); \
164 } \
165 } while (0)
166#else
167#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
168#endif
169
170/*
171 * From 0 .. 200. Higher means more swappy.
172 */
173int vm_swappiness = 60;
174
175static void set_task_reclaim_state(struct task_struct *task,
176 struct reclaim_state *rs)
177{
178 /* Check for an overwrite */
179 WARN_ON_ONCE(rs && task->reclaim_state);
180
181 /* Check for the nulling of an already-nulled member */
182 WARN_ON_ONCE(!rs && !task->reclaim_state);
183
184 task->reclaim_state = rs;
185}
186
187static LIST_HEAD(shrinker_list);
188static DECLARE_RWSEM(shrinker_rwsem);
189
190#ifdef CONFIG_MEMCG
191static int shrinker_nr_max;
192
193/* The shrinker_info is expanded in a batch of BITS_PER_LONG */
194static inline int shrinker_map_size(int nr_items)
195{
196 return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
197}
198
199static inline int shrinker_defer_size(int nr_items)
200{
201 return (round_up(nr_items, BITS_PER_LONG) * sizeof(atomic_long_t));
202}
203
204static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
205 int nid)
206{
207 return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
208 lockdep_is_held(&shrinker_rwsem));
209}
210
211static int expand_one_shrinker_info(struct mem_cgroup *memcg,
212 int map_size, int defer_size,
213 int old_map_size, int old_defer_size)
214{
215 struct shrinker_info *new, *old;
216 struct mem_cgroup_per_node *pn;
217 int nid;
218 int size = map_size + defer_size;
219
220 for_each_node(nid) {
221 pn = memcg->nodeinfo[nid];
222 old = shrinker_info_protected(memcg, nid);
223 /* Not yet online memcg */
224 if (!old)
225 return 0;
226
227 new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
228 if (!new)
229 return -ENOMEM;
230
231 new->nr_deferred = (atomic_long_t *)(new + 1);
232 new->map = (void *)new->nr_deferred + defer_size;
233
234 /* map: set all old bits, clear all new bits */
235 memset(new->map, (int)0xff, old_map_size);
236 memset((void *)new->map + old_map_size, 0, map_size - old_map_size);
237 /* nr_deferred: copy old values, clear all new values */
238 memcpy(new->nr_deferred, old->nr_deferred, old_defer_size);
239 memset((void *)new->nr_deferred + old_defer_size, 0,
240 defer_size - old_defer_size);
241
242 rcu_assign_pointer(pn->shrinker_info, new);
243 kvfree_rcu(old, rcu);
244 }
245
246 return 0;
247}
248
249void free_shrinker_info(struct mem_cgroup *memcg)
250{
251 struct mem_cgroup_per_node *pn;
252 struct shrinker_info *info;
253 int nid;
254
255 for_each_node(nid) {
256 pn = memcg->nodeinfo[nid];
257 info = rcu_dereference_protected(pn->shrinker_info, true);
258 kvfree(info);
259 rcu_assign_pointer(pn->shrinker_info, NULL);
260 }
261}
262
263int alloc_shrinker_info(struct mem_cgroup *memcg)
264{
265 struct shrinker_info *info;
266 int nid, size, ret = 0;
267 int map_size, defer_size = 0;
268
269 down_write(&shrinker_rwsem);
270 map_size = shrinker_map_size(shrinker_nr_max);
271 defer_size = shrinker_defer_size(shrinker_nr_max);
272 size = map_size + defer_size;
273 for_each_node(nid) {
274 info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid);
275 if (!info) {
276 free_shrinker_info(memcg);
277 ret = -ENOMEM;
278 break;
279 }
280 info->nr_deferred = (atomic_long_t *)(info + 1);
281 info->map = (void *)info->nr_deferred + defer_size;
282 rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
283 }
284 up_write(&shrinker_rwsem);
285
286 return ret;
287}
288
289static inline bool need_expand(int nr_max)
290{
291 return round_up(nr_max, BITS_PER_LONG) >
292 round_up(shrinker_nr_max, BITS_PER_LONG);
293}
294
295static int expand_shrinker_info(int new_id)
296{
297 int ret = 0;
298 int new_nr_max = new_id + 1;
299 int map_size, defer_size = 0;
300 int old_map_size, old_defer_size = 0;
301 struct mem_cgroup *memcg;
302
303 if (!need_expand(new_nr_max))
304 goto out;
305
306 if (!root_mem_cgroup)
307 goto out;
308
309 lockdep_assert_held(&shrinker_rwsem);
310
311 map_size = shrinker_map_size(new_nr_max);
312 defer_size = shrinker_defer_size(new_nr_max);
313 old_map_size = shrinker_map_size(shrinker_nr_max);
314 old_defer_size = shrinker_defer_size(shrinker_nr_max);
315
316 memcg = mem_cgroup_iter(NULL, NULL, NULL);
317 do {
318 ret = expand_one_shrinker_info(memcg, map_size, defer_size,
319 old_map_size, old_defer_size);
320 if (ret) {
321 mem_cgroup_iter_break(NULL, memcg);
322 goto out;
323 }
324 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
325out:
326 if (!ret)
327 shrinker_nr_max = new_nr_max;
328
329 return ret;
330}
331
332void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
333{
334 if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
335 struct shrinker_info *info;
336
337 rcu_read_lock();
338 info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
339 /* Pairs with smp mb in shrink_slab() */
340 smp_mb__before_atomic();
341 set_bit(shrinker_id, info->map);
342 rcu_read_unlock();
343 }
344}
345
346static DEFINE_IDR(shrinker_idr);
347
348static int prealloc_memcg_shrinker(struct shrinker *shrinker)
349{
350 int id, ret = -ENOMEM;
351
352 if (mem_cgroup_disabled())
353 return -ENOSYS;
354
355 down_write(&shrinker_rwsem);
356 /* This may call shrinker, so it must use down_read_trylock() */
357 id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
358 if (id < 0)
359 goto unlock;
360
361 if (id >= shrinker_nr_max) {
362 if (expand_shrinker_info(id)) {
363 idr_remove(&shrinker_idr, id);
364 goto unlock;
365 }
366 }
367 shrinker->id = id;
368 ret = 0;
369unlock:
370 up_write(&shrinker_rwsem);
371 return ret;
372}
373
374static void unregister_memcg_shrinker(struct shrinker *shrinker)
375{
376 int id = shrinker->id;
377
378 BUG_ON(id < 0);
379
380 lockdep_assert_held(&shrinker_rwsem);
381
382 idr_remove(&shrinker_idr, id);
383}
384
385static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
386 struct mem_cgroup *memcg)
387{
388 struct shrinker_info *info;
389
390 info = shrinker_info_protected(memcg, nid);
391 return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
392}
393
394static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
395 struct mem_cgroup *memcg)
396{
397 struct shrinker_info *info;
398
399 info = shrinker_info_protected(memcg, nid);
400 return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
401}
402
403void reparent_shrinker_deferred(struct mem_cgroup *memcg)
404{
405 int i, nid;
406 long nr;
407 struct mem_cgroup *parent;
408 struct shrinker_info *child_info, *parent_info;
409
410 parent = parent_mem_cgroup(memcg);
411 if (!parent)
412 parent = root_mem_cgroup;
413
414 /* Prevent from concurrent shrinker_info expand */
415 down_read(&shrinker_rwsem);
416 for_each_node(nid) {
417 child_info = shrinker_info_protected(memcg, nid);
418 parent_info = shrinker_info_protected(parent, nid);
419 for (i = 0; i < shrinker_nr_max; i++) {
420 nr = atomic_long_read(&child_info->nr_deferred[i]);
421 atomic_long_add(nr, &parent_info->nr_deferred[i]);
422 }
423 }
424 up_read(&shrinker_rwsem);
425}
426
427static bool cgroup_reclaim(struct scan_control *sc)
428{
429 return sc->target_mem_cgroup;
430}
431
432/**
433 * writeback_throttling_sane - is the usual dirty throttling mechanism available?
434 * @sc: scan_control in question
435 *
436 * The normal page dirty throttling mechanism in balance_dirty_pages() is
437 * completely broken with the legacy memcg and direct stalling in
438 * shrink_page_list() is used for throttling instead, which lacks all the
439 * niceties such as fairness, adaptive pausing, bandwidth proportional
440 * allocation and configurability.
441 *
442 * This function tests whether the vmscan currently in progress can assume
443 * that the normal dirty throttling mechanism is operational.
444 */
445static bool writeback_throttling_sane(struct scan_control *sc)
446{
447 if (!cgroup_reclaim(sc))
448 return true;
449#ifdef CONFIG_CGROUP_WRITEBACK
450 if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
451 return true;
452#endif
453 return false;
454}
455#else
456static int prealloc_memcg_shrinker(struct shrinker *shrinker)
457{
458 return -ENOSYS;
459}
460
461static void unregister_memcg_shrinker(struct shrinker *shrinker)
462{
463}
464
465static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
466 struct mem_cgroup *memcg)
467{
468 return 0;
469}
470
471static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
472 struct mem_cgroup *memcg)
473{
474 return 0;
475}
476
477static bool cgroup_reclaim(struct scan_control *sc)
478{
479 return false;
480}
481
482static bool writeback_throttling_sane(struct scan_control *sc)
483{
484 return true;
485}
486#endif
487
488static long xchg_nr_deferred(struct shrinker *shrinker,
489 struct shrink_control *sc)
490{
491 int nid = sc->nid;
492
493 if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
494 nid = 0;
495
496 if (sc->memcg &&
497 (shrinker->flags & SHRINKER_MEMCG_AWARE))
498 return xchg_nr_deferred_memcg(nid, shrinker,
499 sc->memcg);
500
501 return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
502}
503
504
505static long add_nr_deferred(long nr, struct shrinker *shrinker,
506 struct shrink_control *sc)
507{
508 int nid = sc->nid;
509
510 if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
511 nid = 0;
512
513 if (sc->memcg &&
514 (shrinker->flags & SHRINKER_MEMCG_AWARE))
515 return add_nr_deferred_memcg(nr, nid, shrinker,
516 sc->memcg);
517
518 return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
519}
520
521/*
522 * This misses isolated pages which are not accounted for to save counters.
523 * As the data only determines if reclaim or compaction continues, it is
524 * not expected that isolated pages will be a dominating factor.
525 */
526unsigned long zone_reclaimable_pages(struct zone *zone)
527{
528 unsigned long nr;
529
530 nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
531 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
532 if (get_nr_swap_pages() > 0)
533 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
534 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
535
536 return nr;
537}
538
539/**
540 * lruvec_lru_size - Returns the number of pages on the given LRU list.
541 * @lruvec: lru vector
542 * @lru: lru to use
543 * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list)
544 */
545static unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru,
546 int zone_idx)
547{
548 unsigned long size = 0;
549 int zid;
550
551 for (zid = 0; zid <= zone_idx && zid < MAX_NR_ZONES; zid++) {
552 struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
553
554 if (!managed_zone(zone))
555 continue;
556
557 if (!mem_cgroup_disabled())
558 size += mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
559 else
560 size += zone_page_state(zone, NR_ZONE_LRU_BASE + lru);
561 }
562 return size;
563}
564
565/*
566 * Add a shrinker callback to be called from the vm.
567 */
568int prealloc_shrinker(struct shrinker *shrinker)
569{
570 unsigned int size;
571 int err;
572
573 if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
574 err = prealloc_memcg_shrinker(shrinker);
575 if (err != -ENOSYS)
576 return err;
577
578 shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
579 }
580
581 size = sizeof(*shrinker->nr_deferred);
582 if (shrinker->flags & SHRINKER_NUMA_AWARE)
583 size *= nr_node_ids;
584
585 shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
586 if (!shrinker->nr_deferred)
587 return -ENOMEM;
588
589 return 0;
590}
591
592void free_prealloced_shrinker(struct shrinker *shrinker)
593{
594 if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
595 down_write(&shrinker_rwsem);
596 unregister_memcg_shrinker(shrinker);
597 up_write(&shrinker_rwsem);
598 return;
599 }
600
601 kfree(shrinker->nr_deferred);
602 shrinker->nr_deferred = NULL;
603}
604
605void register_shrinker_prepared(struct shrinker *shrinker)
606{
607 down_write(&shrinker_rwsem);
608 list_add_tail(&shrinker->list, &shrinker_list);
609 shrinker->flags |= SHRINKER_REGISTERED;
610 up_write(&shrinker_rwsem);
611}
612
613int register_shrinker(struct shrinker *shrinker)
614{
615 int err = prealloc_shrinker(shrinker);
616
617 if (err)
618 return err;
619 register_shrinker_prepared(shrinker);
620 return 0;
621}
622EXPORT_SYMBOL(register_shrinker);
623
624/*
625 * Remove one
626 */
627void unregister_shrinker(struct shrinker *shrinker)
628{
629 if (!(shrinker->flags & SHRINKER_REGISTERED))
630 return;
631
632 down_write(&shrinker_rwsem);
633 list_del(&shrinker->list);
634 shrinker->flags &= ~SHRINKER_REGISTERED;
635 if (shrinker->flags & SHRINKER_MEMCG_AWARE)
636 unregister_memcg_shrinker(shrinker);
637 up_write(&shrinker_rwsem);
638
639 kfree(shrinker->nr_deferred);
640 shrinker->nr_deferred = NULL;
641}
642EXPORT_SYMBOL(unregister_shrinker);
643
644#define SHRINK_BATCH 128
645
646static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
647 struct shrinker *shrinker, int priority)
648{
649 unsigned long freed = 0;
650 unsigned long long delta;
651 long total_scan;
652 long freeable;
653 long nr;
654 long new_nr;
655 long batch_size = shrinker->batch ? shrinker->batch
656 : SHRINK_BATCH;
657 long scanned = 0, next_deferred;
658
659 freeable = shrinker->count_objects(shrinker, shrinkctl);
660 if (freeable == 0 || freeable == SHRINK_EMPTY)
661 return freeable;
662
663 /*
664 * copy the current shrinker scan count into a local variable
665 * and zero it so that other concurrent shrinker invocations
666 * don't also do this scanning work.
667 */
668 nr = xchg_nr_deferred(shrinker, shrinkctl);
669
670 if (shrinker->seeks) {
671 delta = freeable >> priority;
672 delta *= 4;
673 do_div(delta, shrinker->seeks);
674 } else {
675 /*
676 * These objects don't require any IO to create. Trim
677 * them aggressively under memory pressure to keep
678 * them from causing refetches in the IO caches.
679 */
680 delta = freeable / 2;
681 }
682
683 total_scan = nr >> priority;
684 total_scan += delta;
685 total_scan = min(total_scan, (2 * freeable));
686
687 trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
688 freeable, delta, total_scan, priority);
689
690 /*
691 * Normally, we should not scan less than batch_size objects in one
692 * pass to avoid too frequent shrinker calls, but if the slab has less
693 * than batch_size objects in total and we are really tight on memory,
694 * we will try to reclaim all available objects, otherwise we can end
695 * up failing allocations although there are plenty of reclaimable
696 * objects spread over several slabs with usage less than the
697 * batch_size.
698 *
699 * We detect the "tight on memory" situations by looking at the total
700 * number of objects we want to scan (total_scan). If it is greater
701 * than the total number of objects on slab (freeable), we must be
702 * scanning at high prio and therefore should try to reclaim as much as
703 * possible.
704 */
705 while (total_scan >= batch_size ||
706 total_scan >= freeable) {
707 unsigned long ret;
708 unsigned long nr_to_scan = min(batch_size, total_scan);
709
710 shrinkctl->nr_to_scan = nr_to_scan;
711 shrinkctl->nr_scanned = nr_to_scan;
712 ret = shrinker->scan_objects(shrinker, shrinkctl);
713 if (ret == SHRINK_STOP)
714 break;
715 freed += ret;
716
717 count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
718 total_scan -= shrinkctl->nr_scanned;
719 scanned += shrinkctl->nr_scanned;
720
721 cond_resched();
722 }
723
724 /*
725 * The deferred work is increased by any new work (delta) that wasn't
726 * done, decreased by old deferred work that was done now.
727 *
728 * And it is capped to two times of the freeable items.
729 */
730 next_deferred = max_t(long, (nr + delta - scanned), 0);
731 next_deferred = min(next_deferred, (2 * freeable));
732
733 /*
734 * move the unused scan count back into the shrinker in a
735 * manner that handles concurrent updates.
736 */
737 new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
738
739 trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
740 return freed;
741}
742
743#ifdef CONFIG_MEMCG
744static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
745 struct mem_cgroup *memcg, int priority)
746{
747 struct shrinker_info *info;
748 unsigned long ret, freed = 0;
749 int i;
750
751 if (!mem_cgroup_online(memcg))
752 return 0;
753
754 if (!down_read_trylock(&shrinker_rwsem))
755 return 0;
756
757 info = shrinker_info_protected(memcg, nid);
758 if (unlikely(!info))
759 goto unlock;
760
761 for_each_set_bit(i, info->map, shrinker_nr_max) {
762 struct shrink_control sc = {
763 .gfp_mask = gfp_mask,
764 .nid = nid,
765 .memcg = memcg,
766 };
767 struct shrinker *shrinker;
768
769 shrinker = idr_find(&shrinker_idr, i);
770 if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
771 if (!shrinker)
772 clear_bit(i, info->map);
773 continue;
774 }
775
776 /* Call non-slab shrinkers even though kmem is disabled */
777 if (!memcg_kmem_enabled() &&
778 !(shrinker->flags & SHRINKER_NONSLAB))
779 continue;
780
781 ret = do_shrink_slab(&sc, shrinker, priority);
782 if (ret == SHRINK_EMPTY) {
783 clear_bit(i, info->map);
784 /*
785 * After the shrinker reported that it had no objects to
786 * free, but before we cleared the corresponding bit in
787 * the memcg shrinker map, a new object might have been
788 * added. To make sure, we have the bit set in this
789 * case, we invoke the shrinker one more time and reset
790 * the bit if it reports that it is not empty anymore.
791 * The memory barrier here pairs with the barrier in
792 * set_shrinker_bit():
793 *
794 * list_lru_add() shrink_slab_memcg()
795 * list_add_tail() clear_bit()
796 * <MB> <MB>
797 * set_bit() do_shrink_slab()
798 */
799 smp_mb__after_atomic();
800 ret = do_shrink_slab(&sc, shrinker, priority);
801 if (ret == SHRINK_EMPTY)
802 ret = 0;
803 else
804 set_shrinker_bit(memcg, nid, i);
805 }
806 freed += ret;
807
808 if (rwsem_is_contended(&shrinker_rwsem)) {
809 freed = freed ? : 1;
810 break;
811 }
812 }
813unlock:
814 up_read(&shrinker_rwsem);
815 return freed;
816}
817#else /* CONFIG_MEMCG */
818static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
819 struct mem_cgroup *memcg, int priority)
820{
821 return 0;
822}
823#endif /* CONFIG_MEMCG */
824
825/**
826 * shrink_slab - shrink slab caches
827 * @gfp_mask: allocation context
828 * @nid: node whose slab caches to target
829 * @memcg: memory cgroup whose slab caches to target
830 * @priority: the reclaim priority
831 *
832 * Call the shrink functions to age shrinkable caches.
833 *
834 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
835 * unaware shrinkers will receive a node id of 0 instead.
836 *
837 * @memcg specifies the memory cgroup to target. Unaware shrinkers
838 * are called only if it is the root cgroup.
839 *
840 * @priority is sc->priority, we take the number of objects and >> by priority
841 * in order to get the scan target.
842 *
843 * Returns the number of reclaimed slab objects.
844 */
845static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
846 struct mem_cgroup *memcg,
847 int priority)
848{
849 unsigned long ret, freed = 0;
850 struct shrinker *shrinker;
851
852 /*
853 * The root memcg might be allocated even though memcg is disabled
854 * via "cgroup_disable=memory" boot parameter. This could make
855 * mem_cgroup_is_root() return false, then just run memcg slab
856 * shrink, but skip global shrink. This may result in premature
857 * oom.
858 */
859 if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
860 return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
861
862 if (!down_read_trylock(&shrinker_rwsem))
863 goto out;
864
865 list_for_each_entry(shrinker, &shrinker_list, list) {
866 struct shrink_control sc = {
867 .gfp_mask = gfp_mask,
868 .nid = nid,
869 .memcg = memcg,
870 };
871
872 ret = do_shrink_slab(&sc, shrinker, priority);
873 if (ret == SHRINK_EMPTY)
874 ret = 0;
875 freed += ret;
876 /*
877 * Bail out if someone want to register a new shrinker to
878 * prevent the registration from being stalled for long periods
879 * by parallel ongoing shrinking.
880 */
881 if (rwsem_is_contended(&shrinker_rwsem)) {
882 freed = freed ? : 1;
883 break;
884 }
885 }
886
887 up_read(&shrinker_rwsem);
888out:
889 cond_resched();
890 return freed;
891}
892
893void drop_slab_node(int nid)
894{
895 unsigned long freed;
896
897 do {
898 struct mem_cgroup *memcg = NULL;
899
900 if (fatal_signal_pending(current))
901 return;
902
903 freed = 0;
904 memcg = mem_cgroup_iter(NULL, NULL, NULL);
905 do {
906 freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
907 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
908 } while (freed > 10);
909}
910
911void drop_slab(void)
912{
913 int nid;
914
915 for_each_online_node(nid)
916 drop_slab_node(nid);
917}
918
919static inline int is_page_cache_freeable(struct page *page)
920{
921 /*
922 * A freeable page cache page is referenced only by the caller
923 * that isolated the page, the page cache and optional buffer
924 * heads at page->private.
925 */
926 int page_cache_pins = thp_nr_pages(page);
927 return page_count(page) - page_has_private(page) == 1 + page_cache_pins;
928}
929
930static int may_write_to_inode(struct inode *inode)
931{
932 if (current->flags & PF_SWAPWRITE)
933 return 1;
934 if (!inode_write_congested(inode))
935 return 1;
936 if (inode_to_bdi(inode) == current->backing_dev_info)
937 return 1;
938 return 0;
939}
940
941/*
942 * We detected a synchronous write error writing a page out. Probably
943 * -ENOSPC. We need to propagate that into the address_space for a subsequent
944 * fsync(), msync() or close().
945 *
946 * The tricky part is that after writepage we cannot touch the mapping: nothing
947 * prevents it from being freed up. But we have a ref on the page and once
948 * that page is locked, the mapping is pinned.
949 *
950 * We're allowed to run sleeping lock_page() here because we know the caller has
951 * __GFP_FS.
952 */
953static void handle_write_error(struct address_space *mapping,
954 struct page *page, int error)
955{
956 lock_page(page);
957 if (page_mapping(page) == mapping)
958 mapping_set_error(mapping, error);
959 unlock_page(page);
960}
961
962/* possible outcome of pageout() */
963typedef enum {
964 /* failed to write page out, page is locked */
965 PAGE_KEEP,
966 /* move page to the active list, page is locked */
967 PAGE_ACTIVATE,
968 /* page has been sent to the disk successfully, page is unlocked */
969 PAGE_SUCCESS,
970 /* page is clean and locked */
971 PAGE_CLEAN,
972} pageout_t;
973
974/*
975 * pageout is called by shrink_page_list() for each dirty page.
976 * Calls ->writepage().
977 */
978static pageout_t pageout(struct page *page, struct address_space *mapping)
979{
980 /*
981 * If the page is dirty, only perform writeback if that write
982 * will be non-blocking. To prevent this allocation from being
983 * stalled by pagecache activity. But note that there may be
984 * stalls if we need to run get_block(). We could test
985 * PagePrivate for that.
986 *
987 * If this process is currently in __generic_file_write_iter() against
988 * this page's queue, we can perform writeback even if that
989 * will block.
990 *
991 * If the page is swapcache, write it back even if that would
992 * block, for some throttling. This happens by accident, because
993 * swap_backing_dev_info is bust: it doesn't reflect the
994 * congestion state of the swapdevs. Easy to fix, if needed.
995 */
996 if (!is_page_cache_freeable(page))
997 return PAGE_KEEP;
998 if (!mapping) {
999 /*
1000 * Some data journaling orphaned pages can have
1001 * page->mapping == NULL while being dirty with clean buffers.
1002 */
1003 if (page_has_private(page)) {
1004 if (try_to_free_buffers(page)) {
1005 ClearPageDirty(page);
1006 pr_info("%s: orphaned page\n", __func__);
1007 return PAGE_CLEAN;
1008 }
1009 }
1010 return PAGE_KEEP;
1011 }
1012 if (mapping->a_ops->writepage == NULL)
1013 return PAGE_ACTIVATE;
1014 if (!may_write_to_inode(mapping->host))
1015 return PAGE_KEEP;
1016
1017 if (clear_page_dirty_for_io(page)) {
1018 int res;
1019 struct writeback_control wbc = {
1020 .sync_mode = WB_SYNC_NONE,
1021 .nr_to_write = SWAP_CLUSTER_MAX,
1022 .range_start = 0,
1023 .range_end = LLONG_MAX,
1024 .for_reclaim = 1,
1025 };
1026
1027 SetPageReclaim(page);
1028 res = mapping->a_ops->writepage(page, &wbc);
1029 if (res < 0)
1030 handle_write_error(mapping, page, res);
1031 if (res == AOP_WRITEPAGE_ACTIVATE) {
1032 ClearPageReclaim(page);
1033 return PAGE_ACTIVATE;
1034 }
1035
1036 if (!PageWriteback(page)) {
1037 /* synchronous write or broken a_ops? */
1038 ClearPageReclaim(page);
1039 }
1040 trace_mm_vmscan_writepage(page);
1041 inc_node_page_state(page, NR_VMSCAN_WRITE);
1042 return PAGE_SUCCESS;
1043 }
1044
1045 return PAGE_CLEAN;
1046}
1047
1048/*
1049 * Same as remove_mapping, but if the page is removed from the mapping, it
1050 * gets returned with a refcount of 0.
1051 */
1052static int __remove_mapping(struct address_space *mapping, struct page *page,
1053 bool reclaimed, struct mem_cgroup *target_memcg)
1054{
1055 unsigned long flags;
1056 int refcount;
1057 void *shadow = NULL;
1058
1059 BUG_ON(!PageLocked(page));
1060 BUG_ON(mapping != page_mapping(page));
1061
1062 xa_lock_irqsave(&mapping->i_pages, flags);
1063 /*
1064 * The non racy check for a busy page.
1065 *
1066 * Must be careful with the order of the tests. When someone has
1067 * a ref to the page, it may be possible that they dirty it then
1068 * drop the reference. So if PageDirty is tested before page_count
1069 * here, then the following race may occur:
1070 *
1071 * get_user_pages(&page);
1072 * [user mapping goes away]
1073 * write_to(page);
1074 * !PageDirty(page) [good]
1075 * SetPageDirty(page);
1076 * put_page(page);
1077 * !page_count(page) [good, discard it]
1078 *
1079 * [oops, our write_to data is lost]
1080 *
1081 * Reversing the order of the tests ensures such a situation cannot
1082 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
1083 * load is not satisfied before that of page->_refcount.
1084 *
1085 * Note that if SetPageDirty is always performed via set_page_dirty,
1086 * and thus under the i_pages lock, then this ordering is not required.
1087 */
1088 refcount = 1 + compound_nr(page);
1089 if (!page_ref_freeze(page, refcount))
1090 goto cannot_free;
1091 /* note: atomic_cmpxchg in page_ref_freeze provides the smp_rmb */
1092 if (unlikely(PageDirty(page))) {
1093 page_ref_unfreeze(page, refcount);
1094 goto cannot_free;
1095 }
1096
1097 if (PageSwapCache(page)) {
1098 swp_entry_t swap = { .val = page_private(page) };
1099 mem_cgroup_swapout(page, swap);
1100 if (reclaimed && !mapping_exiting(mapping))
1101 shadow = workingset_eviction(page, target_memcg);
1102 __delete_from_swap_cache(page, swap, shadow);
1103 xa_unlock_irqrestore(&mapping->i_pages, flags);
1104 put_swap_page(page, swap);
1105 } else {
1106 void (*freepage)(struct page *);
1107
1108 freepage = mapping->a_ops->freepage;
1109 /*
1110 * Remember a shadow entry for reclaimed file cache in
1111 * order to detect refaults, thus thrashing, later on.
1112 *
1113 * But don't store shadows in an address space that is
1114 * already exiting. This is not just an optimization,
1115 * inode reclaim needs to empty out the radix tree or
1116 * the nodes are lost. Don't plant shadows behind its
1117 * back.
1118 *
1119 * We also don't store shadows for DAX mappings because the
1120 * only page cache pages found in these are zero pages
1121 * covering holes, and because we don't want to mix DAX
1122 * exceptional entries and shadow exceptional entries in the
1123 * same address_space.
1124 */
1125 if (reclaimed && page_is_file_lru(page) &&
1126 !mapping_exiting(mapping) && !dax_mapping(mapping))
1127 shadow = workingset_eviction(page, target_memcg);
1128 __delete_from_page_cache(page, shadow);
1129 xa_unlock_irqrestore(&mapping->i_pages, flags);
1130
1131 if (freepage != NULL)
1132 freepage(page);
1133 }
1134
1135 return 1;
1136
1137cannot_free:
1138 xa_unlock_irqrestore(&mapping->i_pages, flags);
1139 return 0;
1140}
1141
1142/*
1143 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
1144 * someone else has a ref on the page, abort and return 0. If it was
1145 * successfully detached, return 1. Assumes the caller has a single ref on
1146 * this page.
1147 */
1148int remove_mapping(struct address_space *mapping, struct page *page)
1149{
1150 if (__remove_mapping(mapping, page, false, NULL)) {
1151 /*
1152 * Unfreezing the refcount with 1 rather than 2 effectively
1153 * drops the pagecache ref for us without requiring another
1154 * atomic operation.
1155 */
1156 page_ref_unfreeze(page, 1);
1157 return 1;
1158 }
1159 return 0;
1160}
1161
1162/**
1163 * putback_lru_page - put previously isolated page onto appropriate LRU list
1164 * @page: page to be put back to appropriate lru list
1165 *
1166 * Add previously isolated @page to appropriate LRU list.
1167 * Page may still be unevictable for other reasons.
1168 *
1169 * lru_lock must not be held, interrupts must be enabled.
1170 */
1171void putback_lru_page(struct page *page)
1172{
1173 lru_cache_add(page);
1174 put_page(page); /* drop ref from isolate */
1175}
1176
1177enum page_references {
1178 PAGEREF_RECLAIM,
1179 PAGEREF_RECLAIM_CLEAN,
1180 PAGEREF_KEEP,
1181 PAGEREF_ACTIVATE,
1182};
1183
1184static enum page_references page_check_references(struct page *page,
1185 struct scan_control *sc)
1186{
1187 int referenced_ptes, referenced_page;
1188 unsigned long vm_flags;
1189
1190 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
1191 &vm_flags);
1192 referenced_page = TestClearPageReferenced(page);
1193
1194 /*
1195 * Mlock lost the isolation race with us. Let try_to_unmap()
1196 * move the page to the unevictable list.
1197 */
1198 if (vm_flags & VM_LOCKED)
1199 return PAGEREF_RECLAIM;
1200
1201 if (referenced_ptes) {
1202 /*
1203 * All mapped pages start out with page table
1204 * references from the instantiating fault, so we need
1205 * to look twice if a mapped file page is used more
1206 * than once.
1207 *
1208 * Mark it and spare it for another trip around the
1209 * inactive list. Another page table reference will
1210 * lead to its activation.
1211 *
1212 * Note: the mark is set for activated pages as well
1213 * so that recently deactivated but used pages are
1214 * quickly recovered.
1215 */
1216 SetPageReferenced(page);
1217
1218 if (referenced_page || referenced_ptes > 1)
1219 return PAGEREF_ACTIVATE;
1220
1221 /*
1222 * Activate file-backed executable pages after first usage.
1223 */
1224 if ((vm_flags & VM_EXEC) && !PageSwapBacked(page))
1225 return PAGEREF_ACTIVATE;
1226
1227 return PAGEREF_KEEP;
1228 }
1229
1230 /* Reclaim if clean, defer dirty pages to writeback */
1231 if (referenced_page && !PageSwapBacked(page))
1232 return PAGEREF_RECLAIM_CLEAN;
1233
1234 return PAGEREF_RECLAIM;
1235}
1236
1237/* Check if a page is dirty or under writeback */
1238static void page_check_dirty_writeback(struct page *page,
1239 bool *dirty, bool *writeback)
1240{
1241 struct address_space *mapping;
1242
1243 /*
1244 * Anonymous pages are not handled by flushers and must be written
1245 * from reclaim context. Do not stall reclaim based on them
1246 */
1247 if (!page_is_file_lru(page) ||
1248 (PageAnon(page) && !PageSwapBacked(page))) {
1249 *dirty = false;
1250 *writeback = false;
1251 return;
1252 }
1253
1254 /* By default assume that the page flags are accurate */
1255 *dirty = PageDirty(page);
1256 *writeback = PageWriteback(page);
1257
1258 /* Verify dirty/writeback state if the filesystem supports it */
1259 if (!page_has_private(page))
1260 return;
1261
1262 mapping = page_mapping(page);
1263 if (mapping && mapping->a_ops->is_dirty_writeback)
1264 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
1265}
1266
1267/*
1268 * shrink_page_list() returns the number of reclaimed pages
1269 */
1270static unsigned int shrink_page_list(struct list_head *page_list,
1271 struct pglist_data *pgdat,
1272 struct scan_control *sc,
1273 struct reclaim_stat *stat,
1274 bool ignore_references)
1275{
1276 LIST_HEAD(ret_pages);
1277 LIST_HEAD(free_pages);
1278 unsigned int nr_reclaimed = 0;
1279 unsigned int pgactivate = 0;
1280
1281 memset(stat, 0, sizeof(*stat));
1282 cond_resched();
1283
1284 while (!list_empty(page_list)) {
1285 struct address_space *mapping;
1286 struct page *page;
1287 enum page_references references = PAGEREF_RECLAIM;
1288 bool dirty, writeback, may_enter_fs;
1289 unsigned int nr_pages;
1290
1291 cond_resched();
1292
1293 page = lru_to_page(page_list);
1294 list_del(&page->lru);
1295
1296 if (!trylock_page(page))
1297 goto keep;
1298
1299 VM_BUG_ON_PAGE(PageActive(page), page);
1300
1301 nr_pages = compound_nr(page);
1302
1303 /* Account the number of base pages even though THP */
1304 sc->nr_scanned += nr_pages;
1305
1306 if (unlikely(!page_evictable(page)))
1307 goto activate_locked;
1308
1309 if (!sc->may_unmap && page_mapped(page))
1310 goto keep_locked;
1311
1312 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
1313 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
1314
1315 /*
1316 * The number of dirty pages determines if a node is marked
1317 * reclaim_congested which affects wait_iff_congested. kswapd
1318 * will stall and start writing pages if the tail of the LRU
1319 * is all dirty unqueued pages.
1320 */
1321 page_check_dirty_writeback(page, &dirty, &writeback);
1322 if (dirty || writeback)
1323 stat->nr_dirty++;
1324
1325 if (dirty && !writeback)
1326 stat->nr_unqueued_dirty++;
1327
1328 /*
1329 * Treat this page as congested if the underlying BDI is or if
1330 * pages are cycling through the LRU so quickly that the
1331 * pages marked for immediate reclaim are making it to the
1332 * end of the LRU a second time.
1333 */
1334 mapping = page_mapping(page);
1335 if (((dirty || writeback) && mapping &&
1336 inode_write_congested(mapping->host)) ||
1337 (writeback && PageReclaim(page)))
1338 stat->nr_congested++;
1339
1340 /*
1341 * If a page at the tail of the LRU is under writeback, there
1342 * are three cases to consider.
1343 *
1344 * 1) If reclaim is encountering an excessive number of pages
1345 * under writeback and this page is both under writeback and
1346 * PageReclaim then it indicates that pages are being queued
1347 * for IO but are being recycled through the LRU before the
1348 * IO can complete. Waiting on the page itself risks an
1349 * indefinite stall if it is impossible to writeback the
1350 * page due to IO error or disconnected storage so instead
1351 * note that the LRU is being scanned too quickly and the
1352 * caller can stall after page list has been processed.
1353 *
1354 * 2) Global or new memcg reclaim encounters a page that is
1355 * not marked for immediate reclaim, or the caller does not
1356 * have __GFP_FS (or __GFP_IO if it's simply going to swap,
1357 * not to fs). In this case mark the page for immediate
1358 * reclaim and continue scanning.
1359 *
1360 * Require may_enter_fs because we would wait on fs, which
1361 * may not have submitted IO yet. And the loop driver might
1362 * enter reclaim, and deadlock if it waits on a page for
1363 * which it is needed to do the write (loop masks off
1364 * __GFP_IO|__GFP_FS for this reason); but more thought
1365 * would probably show more reasons.
1366 *
1367 * 3) Legacy memcg encounters a page that is already marked
1368 * PageReclaim. memcg does not have any dirty pages
1369 * throttling so we could easily OOM just because too many
1370 * pages are in writeback and there is nothing else to
1371 * reclaim. Wait for the writeback to complete.
1372 *
1373 * In cases 1) and 2) we activate the pages to get them out of
1374 * the way while we continue scanning for clean pages on the
1375 * inactive list and refilling from the active list. The
1376 * observation here is that waiting for disk writes is more
1377 * expensive than potentially causing reloads down the line.
1378 * Since they're marked for immediate reclaim, they won't put
1379 * memory pressure on the cache working set any longer than it
1380 * takes to write them to disk.
1381 */
1382 if (PageWriteback(page)) {
1383 /* Case 1 above */
1384 if (current_is_kswapd() &&
1385 PageReclaim(page) &&
1386 test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1387 stat->nr_immediate++;
1388 goto activate_locked;
1389
1390 /* Case 2 above */
1391 } else if (writeback_throttling_sane(sc) ||
1392 !PageReclaim(page) || !may_enter_fs) {
1393 /*
1394 * This is slightly racy - end_page_writeback()
1395 * might have just cleared PageReclaim, then
1396 * setting PageReclaim here end up interpreted
1397 * as PageReadahead - but that does not matter
1398 * enough to care. What we do want is for this
1399 * page to have PageReclaim set next time memcg
1400 * reclaim reaches the tests above, so it will
1401 * then wait_on_page_writeback() to avoid OOM;
1402 * and it's also appropriate in global reclaim.
1403 */
1404 SetPageReclaim(page);
1405 stat->nr_writeback++;
1406 goto activate_locked;
1407
1408 /* Case 3 above */
1409 } else {
1410 unlock_page(page);
1411 wait_on_page_writeback(page);
1412 /* then go back and try same page again */
1413 list_add_tail(&page->lru, page_list);
1414 continue;
1415 }
1416 }
1417
1418 if (!ignore_references)
1419 references = page_check_references(page, sc);
1420
1421 switch (references) {
1422 case PAGEREF_ACTIVATE:
1423 goto activate_locked;
1424 case PAGEREF_KEEP:
1425 stat->nr_ref_keep += nr_pages;
1426 goto keep_locked;
1427 case PAGEREF_RECLAIM:
1428 case PAGEREF_RECLAIM_CLEAN:
1429 ; /* try to reclaim the page below */
1430 }
1431
1432 /*
1433 * Anonymous process memory has backing store?
1434 * Try to allocate it some swap space here.
1435 * Lazyfree page could be freed directly
1436 */
1437 if (PageAnon(page) && PageSwapBacked(page)) {
1438 if (!PageSwapCache(page)) {
1439 if (!(sc->gfp_mask & __GFP_IO))
1440 goto keep_locked;
1441 if (page_maybe_dma_pinned(page))
1442 goto keep_locked;
1443 if (PageTransHuge(page)) {
1444 /* cannot split THP, skip it */
1445 if (!can_split_huge_page(page, NULL))
1446 goto activate_locked;
1447 /*
1448 * Split pages without a PMD map right
1449 * away. Chances are some or all of the
1450 * tail pages can be freed without IO.
1451 */
1452 if (!compound_mapcount(page) &&
1453 split_huge_page_to_list(page,
1454 page_list))
1455 goto activate_locked;
1456 }
1457 if (!add_to_swap(page)) {
1458 if (!PageTransHuge(page))
1459 goto activate_locked_split;
1460 /* Fallback to swap normal pages */
1461 if (split_huge_page_to_list(page,
1462 page_list))
1463 goto activate_locked;
1464#ifdef CONFIG_TRANSPARENT_HUGEPAGE
1465 count_vm_event(THP_SWPOUT_FALLBACK);
1466#endif
1467 if (!add_to_swap(page))
1468 goto activate_locked_split;
1469 }
1470
1471 may_enter_fs = true;
1472
1473 /* Adding to swap updated mapping */
1474 mapping = page_mapping(page);
1475 }
1476 } else if (unlikely(PageTransHuge(page))) {
1477 /* Split file THP */
1478 if (split_huge_page_to_list(page, page_list))
1479 goto keep_locked;
1480 }
1481
1482 /*
1483 * THP may get split above, need minus tail pages and update
1484 * nr_pages to avoid accounting tail pages twice.
1485 *
1486 * The tail pages that are added into swap cache successfully
1487 * reach here.
1488 */
1489 if ((nr_pages > 1) && !PageTransHuge(page)) {
1490 sc->nr_scanned -= (nr_pages - 1);
1491 nr_pages = 1;
1492 }
1493
1494 /*
1495 * The page is mapped into the page tables of one or more
1496 * processes. Try to unmap it here.
1497 */
1498 if (page_mapped(page)) {
1499 enum ttu_flags flags = TTU_BATCH_FLUSH;
1500 bool was_swapbacked = PageSwapBacked(page);
1501
1502 if (unlikely(PageTransHuge(page)))
1503 flags |= TTU_SPLIT_HUGE_PMD;
1504
1505 try_to_unmap(page, flags);
1506 if (page_mapped(page)) {
1507 stat->nr_unmap_fail += nr_pages;
1508 if (!was_swapbacked && PageSwapBacked(page))
1509 stat->nr_lazyfree_fail += nr_pages;
1510 goto activate_locked;
1511 }
1512 }
1513
1514 if (PageDirty(page)) {
1515 /*
1516 * Only kswapd can writeback filesystem pages
1517 * to avoid risk of stack overflow. But avoid
1518 * injecting inefficient single-page IO into
1519 * flusher writeback as much as possible: only
1520 * write pages when we've encountered many
1521 * dirty pages, and when we've already scanned
1522 * the rest of the LRU for clean pages and see
1523 * the same dirty pages again (PageReclaim).
1524 */
1525 if (page_is_file_lru(page) &&
1526 (!current_is_kswapd() || !PageReclaim(page) ||
1527 !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1528 /*
1529 * Immediately reclaim when written back.
1530 * Similar in principal to deactivate_page()
1531 * except we already have the page isolated
1532 * and know it's dirty
1533 */
1534 inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1535 SetPageReclaim(page);
1536
1537 goto activate_locked;
1538 }
1539
1540 if (references == PAGEREF_RECLAIM_CLEAN)
1541 goto keep_locked;
1542 if (!may_enter_fs)
1543 goto keep_locked;
1544 if (!sc->may_writepage)
1545 goto keep_locked;
1546
1547 /*
1548 * Page is dirty. Flush the TLB if a writable entry
1549 * potentially exists to avoid CPU writes after IO
1550 * starts and then write it out here.
1551 */
1552 try_to_unmap_flush_dirty();
1553 switch (pageout(page, mapping)) {
1554 case PAGE_KEEP:
1555 goto keep_locked;
1556 case PAGE_ACTIVATE:
1557 goto activate_locked;
1558 case PAGE_SUCCESS:
1559 stat->nr_pageout += thp_nr_pages(page);
1560
1561 if (PageWriteback(page))
1562 goto keep;
1563 if (PageDirty(page))
1564 goto keep;
1565
1566 /*
1567 * A synchronous write - probably a ramdisk. Go
1568 * ahead and try to reclaim the page.
1569 */
1570 if (!trylock_page(page))
1571 goto keep;
1572 if (PageDirty(page) || PageWriteback(page))
1573 goto keep_locked;
1574 mapping = page_mapping(page);
1575 fallthrough;
1576 case PAGE_CLEAN:
1577 ; /* try to free the page below */
1578 }
1579 }
1580
1581 /*
1582 * If the page has buffers, try to free the buffer mappings
1583 * associated with this page. If we succeed we try to free
1584 * the page as well.
1585 *
1586 * We do this even if the page is PageDirty().
1587 * try_to_release_page() does not perform I/O, but it is
1588 * possible for a page to have PageDirty set, but it is actually
1589 * clean (all its buffers are clean). This happens if the
1590 * buffers were written out directly, with submit_bh(). ext3
1591 * will do this, as well as the blockdev mapping.
1592 * try_to_release_page() will discover that cleanness and will
1593 * drop the buffers and mark the page clean - it can be freed.
1594 *
1595 * Rarely, pages can have buffers and no ->mapping. These are
1596 * the pages which were not successfully invalidated in
1597 * truncate_cleanup_page(). We try to drop those buffers here
1598 * and if that worked, and the page is no longer mapped into
1599 * process address space (page_count == 1) it can be freed.
1600 * Otherwise, leave the page on the LRU so it is swappable.
1601 */
1602 if (page_has_private(page)) {
1603 if (!try_to_release_page(page, sc->gfp_mask))
1604 goto activate_locked;
1605 if (!mapping && page_count(page) == 1) {
1606 unlock_page(page);
1607 if (put_page_testzero(page))
1608 goto free_it;
1609 else {
1610 /*
1611 * rare race with speculative reference.
1612 * the speculative reference will free
1613 * this page shortly, so we may
1614 * increment nr_reclaimed here (and
1615 * leave it off the LRU).
1616 */
1617 nr_reclaimed++;
1618 continue;
1619 }
1620 }
1621 }
1622
1623 if (PageAnon(page) && !PageSwapBacked(page)) {
1624 /* follow __remove_mapping for reference */
1625 if (!page_ref_freeze(page, 1))
1626 goto keep_locked;
1627 if (PageDirty(page)) {
1628 page_ref_unfreeze(page, 1);
1629 goto keep_locked;
1630 }
1631
1632 count_vm_event(PGLAZYFREED);
1633 count_memcg_page_event(page, PGLAZYFREED);
1634 } else if (!mapping || !__remove_mapping(mapping, page, true,
1635 sc->target_mem_cgroup))
1636 goto keep_locked;
1637
1638 unlock_page(page);
1639free_it:
1640 /*
1641 * THP may get swapped out in a whole, need account
1642 * all base pages.
1643 */
1644 nr_reclaimed += nr_pages;
1645
1646 /*
1647 * Is there need to periodically free_page_list? It would
1648 * appear not as the counts should be low
1649 */
1650 if (unlikely(PageTransHuge(page)))
1651 destroy_compound_page(page);
1652 else
1653 list_add(&page->lru, &free_pages);
1654 continue;
1655
1656activate_locked_split:
1657 /*
1658 * The tail pages that are failed to add into swap cache
1659 * reach here. Fixup nr_scanned and nr_pages.
1660 */
1661 if (nr_pages > 1) {
1662 sc->nr_scanned -= (nr_pages - 1);
1663 nr_pages = 1;
1664 }
1665activate_locked:
1666 /* Not a candidate for swapping, so reclaim swap space. */
1667 if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
1668 PageMlocked(page)))
1669 try_to_free_swap(page);
1670 VM_BUG_ON_PAGE(PageActive(page), page);
1671 if (!PageMlocked(page)) {
1672 int type = page_is_file_lru(page);
1673 SetPageActive(page);
1674 stat->nr_activate[type] += nr_pages;
1675 count_memcg_page_event(page, PGACTIVATE);
1676 }
1677keep_locked:
1678 unlock_page(page);
1679keep:
1680 list_add(&page->lru, &ret_pages);
1681 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1682 }
1683
1684 pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
1685
1686 mem_cgroup_uncharge_list(&free_pages);
1687 try_to_unmap_flush();
1688 free_unref_page_list(&free_pages);
1689
1690 list_splice(&ret_pages, page_list);
1691 count_vm_events(PGACTIVATE, pgactivate);
1692
1693 return nr_reclaimed;
1694}
1695
1696unsigned int reclaim_clean_pages_from_list(struct zone *zone,
1697 struct list_head *page_list)
1698{
1699 struct scan_control sc = {
1700 .gfp_mask = GFP_KERNEL,
1701 .priority = DEF_PRIORITY,
1702 .may_unmap = 1,
1703 };
1704 struct reclaim_stat stat;
1705 unsigned int nr_reclaimed;
1706 struct page *page, *next;
1707 LIST_HEAD(clean_pages);
1708 unsigned int noreclaim_flag;
1709
1710 list_for_each_entry_safe(page, next, page_list, lru) {
1711 if (!PageHuge(page) && page_is_file_lru(page) &&
1712 !PageDirty(page) && !__PageMovable(page) &&
1713 !PageUnevictable(page)) {
1714 ClearPageActive(page);
1715 list_move(&page->lru, &clean_pages);
1716 }
1717 }
1718
1719 /*
1720 * We should be safe here since we are only dealing with file pages and
1721 * we are not kswapd and therefore cannot write dirty file pages. But
1722 * call memalloc_noreclaim_save() anyway, just in case these conditions
1723 * change in the future.
1724 */
1725 noreclaim_flag = memalloc_noreclaim_save();
1726 nr_reclaimed = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
1727 &stat, true);
1728 memalloc_noreclaim_restore(noreclaim_flag);
1729
1730 list_splice(&clean_pages, page_list);
1731 mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE,
1732 -(long)nr_reclaimed);
1733 /*
1734 * Since lazyfree pages are isolated from file LRU from the beginning,
1735 * they will rotate back to anonymous LRU in the end if it failed to
1736 * discard so isolated count will be mismatched.
1737 * Compensate the isolated count for both LRU lists.
1738 */
1739 mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON,
1740 stat.nr_lazyfree_fail);
1741 mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE,
1742 -(long)stat.nr_lazyfree_fail);
1743 return nr_reclaimed;
1744}
1745
1746/*
1747 * Attempt to remove the specified page from its LRU. Only take this page
1748 * if it is of the appropriate PageActive status. Pages which are being
1749 * freed elsewhere are also ignored.
1750 *
1751 * page: page to consider
1752 * mode: one of the LRU isolation modes defined above
1753 *
1754 * returns true on success, false on failure.
1755 */
1756bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
1757{
1758 /* Only take pages on the LRU. */
1759 if (!PageLRU(page))
1760 return false;
1761
1762 /* Compaction should not handle unevictable pages but CMA can do so */
1763 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1764 return false;
1765
1766 /*
1767 * To minimise LRU disruption, the caller can indicate that it only
1768 * wants to isolate pages it will be able to operate on without
1769 * blocking - clean pages for the most part.
1770 *
1771 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1772 * that it is possible to migrate without blocking
1773 */
1774 if (mode & ISOLATE_ASYNC_MIGRATE) {
1775 /* All the caller can do on PageWriteback is block */
1776 if (PageWriteback(page))
1777 return false;
1778
1779 if (PageDirty(page)) {
1780 struct address_space *mapping;
1781 bool migrate_dirty;
1782
1783 /*
1784 * Only pages without mappings or that have a
1785 * ->migratepage callback are possible to migrate
1786 * without blocking. However, we can be racing with
1787 * truncation so it's necessary to lock the page
1788 * to stabilise the mapping as truncation holds
1789 * the page lock until after the page is removed
1790 * from the page cache.
1791 */
1792 if (!trylock_page(page))
1793 return false;
1794
1795 mapping = page_mapping(page);
1796 migrate_dirty = !mapping || mapping->a_ops->migratepage;
1797 unlock_page(page);
1798 if (!migrate_dirty)
1799 return false;
1800 }
1801 }
1802
1803 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1804 return false;
1805
1806 return true;
1807}
1808
1809/*
1810 * Update LRU sizes after isolating pages. The LRU size updates must
1811 * be complete before mem_cgroup_update_lru_size due to a sanity check.
1812 */
1813static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1814 enum lru_list lru, unsigned long *nr_zone_taken)
1815{
1816 int zid;
1817
1818 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1819 if (!nr_zone_taken[zid])
1820 continue;
1821
1822 update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1823 }
1824
1825}
1826
1827/*
1828 * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
1829 *
1830 * lruvec->lru_lock is heavily contended. Some of the functions that
1831 * shrink the lists perform better by taking out a batch of pages
1832 * and working on them outside the LRU lock.
1833 *
1834 * For pagecache intensive workloads, this function is the hottest
1835 * spot in the kernel (apart from copy_*_user functions).
1836 *
1837 * Lru_lock must be held before calling this function.
1838 *
1839 * @nr_to_scan: The number of eligible pages to look through on the list.
1840 * @lruvec: The LRU vector to pull pages from.
1841 * @dst: The temp list to put pages on to.
1842 * @nr_scanned: The number of pages that were scanned.
1843 * @sc: The scan_control struct for this reclaim session
1844 * @lru: LRU list id for isolating
1845 *
1846 * returns how many pages were moved onto *@dst.
1847 */
1848static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1849 struct lruvec *lruvec, struct list_head *dst,
1850 unsigned long *nr_scanned, struct scan_control *sc,
1851 enum lru_list lru)
1852{
1853 struct list_head *src = &lruvec->lists[lru];
1854 unsigned long nr_taken = 0;
1855 unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1856 unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1857 unsigned long skipped = 0;
1858 unsigned long scan, total_scan, nr_pages;
1859 LIST_HEAD(pages_skipped);
1860 isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
1861
1862 total_scan = 0;
1863 scan = 0;
1864 while (scan < nr_to_scan && !list_empty(src)) {
1865 struct page *page;
1866
1867 page = lru_to_page(src);
1868 prefetchw_prev_lru_page(page, src, flags);
1869
1870 nr_pages = compound_nr(page);
1871 total_scan += nr_pages;
1872
1873 if (page_zonenum(page) > sc->reclaim_idx) {
1874 list_move(&page->lru, &pages_skipped);
1875 nr_skipped[page_zonenum(page)] += nr_pages;
1876 continue;
1877 }
1878
1879 /*
1880 * Do not count skipped pages because that makes the function
1881 * return with no isolated pages if the LRU mostly contains
1882 * ineligible pages. This causes the VM to not reclaim any
1883 * pages, triggering a premature OOM.
1884 *
1885 * Account all tail pages of THP. This would not cause
1886 * premature OOM since __isolate_lru_page() returns -EBUSY
1887 * only when the page is being freed somewhere else.
1888 */
1889 scan += nr_pages;
1890 if (!__isolate_lru_page_prepare(page, mode)) {
1891 /* It is being freed elsewhere */
1892 list_move(&page->lru, src);
1893 continue;
1894 }
1895 /*
1896 * Be careful not to clear PageLRU until after we're
1897 * sure the page is not being freed elsewhere -- the
1898 * page release code relies on it.
1899 */
1900 if (unlikely(!get_page_unless_zero(page))) {
1901 list_move(&page->lru, src);
1902 continue;
1903 }
1904
1905 if (!TestClearPageLRU(page)) {
1906 /* Another thread is already isolating this page */
1907 put_page(page);
1908 list_move(&page->lru, src);
1909 continue;
1910 }
1911
1912 nr_taken += nr_pages;
1913 nr_zone_taken[page_zonenum(page)] += nr_pages;
1914 list_move(&page->lru, dst);
1915 }
1916
1917 /*
1918 * Splice any skipped pages to the start of the LRU list. Note that
1919 * this disrupts the LRU order when reclaiming for lower zones but
1920 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
1921 * scanning would soon rescan the same pages to skip and put the
1922 * system at risk of premature OOM.
1923 */
1924 if (!list_empty(&pages_skipped)) {
1925 int zid;
1926
1927 list_splice(&pages_skipped, src);
1928 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1929 if (!nr_skipped[zid])
1930 continue;
1931
1932 __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1933 skipped += nr_skipped[zid];
1934 }
1935 }
1936 *nr_scanned = total_scan;
1937 trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
1938 total_scan, skipped, nr_taken, mode, lru);
1939 update_lru_sizes(lruvec, lru, nr_zone_taken);
1940 return nr_taken;
1941}
1942
1943/**
1944 * isolate_lru_page - tries to isolate a page from its LRU list
1945 * @page: page to isolate from its LRU list
1946 *
1947 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1948 * vmstat statistic corresponding to whatever LRU list the page was on.
1949 *
1950 * Returns 0 if the page was removed from an LRU list.
1951 * Returns -EBUSY if the page was not on an LRU list.
1952 *
1953 * The returned page will have PageLRU() cleared. If it was found on
1954 * the active list, it will have PageActive set. If it was found on
1955 * the unevictable list, it will have the PageUnevictable bit set. That flag
1956 * may need to be cleared by the caller before letting the page go.
1957 *
1958 * The vmstat statistic corresponding to the list on which the page was
1959 * found will be decremented.
1960 *
1961 * Restrictions:
1962 *
1963 * (1) Must be called with an elevated refcount on the page. This is a
1964 * fundamental difference from isolate_lru_pages (which is called
1965 * without a stable reference).
1966 * (2) the lru_lock must not be held.
1967 * (3) interrupts must be enabled.
1968 */
1969int isolate_lru_page(struct page *page)
1970{
1971 int ret = -EBUSY;
1972
1973 VM_BUG_ON_PAGE(!page_count(page), page);
1974 WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1975
1976 if (TestClearPageLRU(page)) {
1977 struct lruvec *lruvec;
1978
1979 get_page(page);
1980 lruvec = lock_page_lruvec_irq(page);
1981 del_page_from_lru_list(page, lruvec);
1982 unlock_page_lruvec_irq(lruvec);
1983 ret = 0;
1984 }
1985
1986 return ret;
1987}
1988
1989/*
1990 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1991 * then get rescheduled. When there are massive number of tasks doing page
1992 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1993 * the LRU list will go small and be scanned faster than necessary, leading to
1994 * unnecessary swapping, thrashing and OOM.
1995 */
1996static int too_many_isolated(struct pglist_data *pgdat, int file,
1997 struct scan_control *sc)
1998{
1999 unsigned long inactive, isolated;
2000
2001 if (current_is_kswapd())
2002 return 0;
2003
2004 if (!writeback_throttling_sane(sc))
2005 return 0;
2006
2007 if (file) {
2008 inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
2009 isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
2010 } else {
2011 inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
2012 isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
2013 }
2014
2015 /*
2016 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
2017 * won't get blocked by normal direct-reclaimers, forming a circular
2018 * deadlock.
2019 */
2020 if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
2021 inactive >>= 3;
2022
2023 return isolated > inactive;
2024}
2025
2026/*
2027 * move_pages_to_lru() moves pages from private @list to appropriate LRU list.
2028 * On return, @list is reused as a list of pages to be freed by the caller.
2029 *
2030 * Returns the number of pages moved to the given lruvec.
2031 */
2032static unsigned int move_pages_to_lru(struct lruvec *lruvec,
2033 struct list_head *list)
2034{
2035 int nr_pages, nr_moved = 0;
2036 LIST_HEAD(pages_to_free);
2037 struct page *page;
2038
2039 while (!list_empty(list)) {
2040 page = lru_to_page(list);
2041 VM_BUG_ON_PAGE(PageLRU(page), page);
2042 list_del(&page->lru);
2043 if (unlikely(!page_evictable(page))) {
2044 spin_unlock_irq(&lruvec->lru_lock);
2045 putback_lru_page(page);
2046 spin_lock_irq(&lruvec->lru_lock);
2047 continue;
2048 }
2049
2050 /*
2051 * The SetPageLRU needs to be kept here for list integrity.
2052 * Otherwise:
2053 * #0 move_pages_to_lru #1 release_pages
2054 * if !put_page_testzero
2055 * if (put_page_testzero())
2056 * !PageLRU //skip lru_lock
2057 * SetPageLRU()
2058 * list_add(&page->lru,)
2059 * list_add(&page->lru,)
2060 */
2061 SetPageLRU(page);
2062
2063 if (unlikely(put_page_testzero(page))) {
2064 __clear_page_lru_flags(page);
2065
2066 if (unlikely(PageCompound(page))) {
2067 spin_unlock_irq(&lruvec->lru_lock);
2068 destroy_compound_page(page);
2069 spin_lock_irq(&lruvec->lru_lock);
2070 } else
2071 list_add(&page->lru, &pages_to_free);
2072
2073 continue;
2074 }
2075
2076 /*
2077 * All pages were isolated from the same lruvec (and isolation
2078 * inhibits memcg migration).
2079 */
2080 VM_BUG_ON_PAGE(!page_matches_lruvec(page, lruvec), page);
2081 add_page_to_lru_list(page, lruvec);
2082 nr_pages = thp_nr_pages(page);
2083 nr_moved += nr_pages;
2084 if (PageActive(page))
2085 workingset_age_nonresident(lruvec, nr_pages);
2086 }
2087
2088 /*
2089 * To save our caller's stack, now use input list for pages to free.
2090 */
2091 list_splice(&pages_to_free, list);
2092
2093 return nr_moved;
2094}
2095
2096/*
2097 * If a kernel thread (such as nfsd for loop-back mounts) services
2098 * a backing device by writing to the page cache it sets PF_LOCAL_THROTTLE.
2099 * In that case we should only throttle if the backing device it is
2100 * writing to is congested. In other cases it is safe to throttle.
2101 */
2102static int current_may_throttle(void)
2103{
2104 return !(current->flags & PF_LOCAL_THROTTLE) ||
2105 current->backing_dev_info == NULL ||
2106 bdi_write_congested(current->backing_dev_info);
2107}
2108
2109/*
2110 * shrink_inactive_list() is a helper for shrink_node(). It returns the number
2111 * of reclaimed pages
2112 */
2113static unsigned long
2114shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
2115 struct scan_control *sc, enum lru_list lru)
2116{
2117 LIST_HEAD(page_list);
2118 unsigned long nr_scanned;
2119 unsigned int nr_reclaimed = 0;
2120 unsigned long nr_taken;
2121 struct reclaim_stat stat;
2122 bool file = is_file_lru(lru);
2123 enum vm_event_item item;
2124 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2125 bool stalled = false;
2126
2127 while (unlikely(too_many_isolated(pgdat, file, sc))) {
2128 if (stalled)
2129 return 0;
2130
2131 /* wait a bit for the reclaimer. */
2132 msleep(100);
2133 stalled = true;
2134
2135 /* We are about to die and free our memory. Return now. */
2136 if (fatal_signal_pending(current))
2137 return SWAP_CLUSTER_MAX;
2138 }
2139
2140 lru_add_drain();
2141
2142 spin_lock_irq(&lruvec->lru_lock);
2143
2144 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
2145 &nr_scanned, sc, lru);
2146
2147 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
2148 item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
2149 if (!cgroup_reclaim(sc))
2150 __count_vm_events(item, nr_scanned);
2151 __count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
2152 __count_vm_events(PGSCAN_ANON + file, nr_scanned);
2153
2154 spin_unlock_irq(&lruvec->lru_lock);
2155
2156 if (nr_taken == 0)
2157 return 0;
2158
2159 nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, &stat, false);
2160
2161 spin_lock_irq(&lruvec->lru_lock);
2162 move_pages_to_lru(lruvec, &page_list);
2163
2164 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
2165 item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
2166 if (!cgroup_reclaim(sc))
2167 __count_vm_events(item, nr_reclaimed);
2168 __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
2169 __count_vm_events(PGSTEAL_ANON + file, nr_reclaimed);
2170 spin_unlock_irq(&lruvec->lru_lock);
2171
2172 lru_note_cost(lruvec, file, stat.nr_pageout);
2173 mem_cgroup_uncharge_list(&page_list);
2174 free_unref_page_list(&page_list);
2175
2176 /*
2177 * If dirty pages are scanned that are not queued for IO, it
2178 * implies that flushers are not doing their job. This can
2179 * happen when memory pressure pushes dirty pages to the end of
2180 * the LRU before the dirty limits are breached and the dirty
2181 * data has expired. It can also happen when the proportion of
2182 * dirty pages grows not through writes but through memory
2183 * pressure reclaiming all the clean cache. And in some cases,
2184 * the flushers simply cannot keep up with the allocation
2185 * rate. Nudge the flusher threads in case they are asleep.
2186 */
2187 if (stat.nr_unqueued_dirty == nr_taken)
2188 wakeup_flusher_threads(WB_REASON_VMSCAN);
2189
2190 sc->nr.dirty += stat.nr_dirty;
2191 sc->nr.congested += stat.nr_congested;
2192 sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
2193 sc->nr.writeback += stat.nr_writeback;
2194 sc->nr.immediate += stat.nr_immediate;
2195 sc->nr.taken += nr_taken;
2196 if (file)
2197 sc->nr.file_taken += nr_taken;
2198
2199 trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
2200 nr_scanned, nr_reclaimed, &stat, sc->priority, file);
2201 return nr_reclaimed;
2202}
2203
2204/*
2205 * shrink_active_list() moves pages from the active LRU to the inactive LRU.
2206 *
2207 * We move them the other way if the page is referenced by one or more
2208 * processes.
2209 *
2210 * If the pages are mostly unmapped, the processing is fast and it is
2211 * appropriate to hold lru_lock across the whole operation. But if
2212 * the pages are mapped, the processing is slow (page_referenced()), so
2213 * we should drop lru_lock around each page. It's impossible to balance
2214 * this, so instead we remove the pages from the LRU while processing them.
2215 * It is safe to rely on PG_active against the non-LRU pages in here because
2216 * nobody will play with that bit on a non-LRU page.
2217 *
2218 * The downside is that we have to touch page->_refcount against each page.
2219 * But we had to alter page->flags anyway.
2220 */
2221static void shrink_active_list(unsigned long nr_to_scan,
2222 struct lruvec *lruvec,
2223 struct scan_control *sc,
2224 enum lru_list lru)
2225{
2226 unsigned long nr_taken;
2227 unsigned long nr_scanned;
2228 unsigned long vm_flags;
2229 LIST_HEAD(l_hold); /* The pages which were snipped off */
2230 LIST_HEAD(l_active);
2231 LIST_HEAD(l_inactive);
2232 struct page *page;
2233 unsigned nr_deactivate, nr_activate;
2234 unsigned nr_rotated = 0;
2235 int file = is_file_lru(lru);
2236 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2237
2238 lru_add_drain();
2239
2240 spin_lock_irq(&lruvec->lru_lock);
2241
2242 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
2243 &nr_scanned, sc, lru);
2244
2245 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
2246
2247 if (!cgroup_reclaim(sc))
2248 __count_vm_events(PGREFILL, nr_scanned);
2249 __count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
2250
2251 spin_unlock_irq(&lruvec->lru_lock);
2252
2253 while (!list_empty(&l_hold)) {
2254 cond_resched();
2255 page = lru_to_page(&l_hold);
2256 list_del(&page->lru);
2257
2258 if (unlikely(!page_evictable(page))) {
2259 putback_lru_page(page);
2260 continue;
2261 }
2262
2263 if (unlikely(buffer_heads_over_limit)) {
2264 if (page_has_private(page) && trylock_page(page)) {
2265 if (page_has_private(page))
2266 try_to_release_page(page, 0);
2267 unlock_page(page);
2268 }
2269 }
2270
2271 if (page_referenced(page, 0, sc->target_mem_cgroup,
2272 &vm_flags)) {
2273 /*
2274 * Identify referenced, file-backed active pages and
2275 * give them one more trip around the active list. So
2276 * that executable code get better chances to stay in
2277 * memory under moderate memory pressure. Anon pages
2278 * are not likely to be evicted by use-once streaming
2279 * IO, plus JVM can create lots of anon VM_EXEC pages,
2280 * so we ignore them here.
2281 */
2282 if ((vm_flags & VM_EXEC) && page_is_file_lru(page)) {
2283 nr_rotated += thp_nr_pages(page);
2284 list_add(&page->lru, &l_active);
2285 continue;
2286 }
2287 }
2288
2289 ClearPageActive(page); /* we are de-activating */
2290 SetPageWorkingset(page);
2291 list_add(&page->lru, &l_inactive);
2292 }
2293
2294 /*
2295 * Move pages back to the lru list.
2296 */
2297 spin_lock_irq(&lruvec->lru_lock);
2298
2299 nr_activate = move_pages_to_lru(lruvec, &l_active);
2300 nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
2301 /* Keep all free pages in l_active list */
2302 list_splice(&l_inactive, &l_active);
2303
2304 __count_vm_events(PGDEACTIVATE, nr_deactivate);
2305 __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
2306
2307 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
2308 spin_unlock_irq(&lruvec->lru_lock);
2309
2310 mem_cgroup_uncharge_list(&l_active);
2311 free_unref_page_list(&l_active);
2312 trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
2313 nr_deactivate, nr_rotated, sc->priority, file);
2314}
2315
2316unsigned long reclaim_pages(struct list_head *page_list)
2317{
2318 int nid = NUMA_NO_NODE;
2319 unsigned int nr_reclaimed = 0;
2320 LIST_HEAD(node_page_list);
2321 struct reclaim_stat dummy_stat;
2322 struct page *page;
2323 unsigned int noreclaim_flag;
2324 struct scan_control sc = {
2325 .gfp_mask = GFP_KERNEL,
2326 .priority = DEF_PRIORITY,
2327 .may_writepage = 1,
2328 .may_unmap = 1,
2329 .may_swap = 1,
2330 };
2331
2332 noreclaim_flag = memalloc_noreclaim_save();
2333
2334 while (!list_empty(page_list)) {
2335 page = lru_to_page(page_list);
2336 if (nid == NUMA_NO_NODE) {
2337 nid = page_to_nid(page);
2338 INIT_LIST_HEAD(&node_page_list);
2339 }
2340
2341 if (nid == page_to_nid(page)) {
2342 ClearPageActive(page);
2343 list_move(&page->lru, &node_page_list);
2344 continue;
2345 }
2346
2347 nr_reclaimed += shrink_page_list(&node_page_list,
2348 NODE_DATA(nid),
2349 &sc, &dummy_stat, false);
2350 while (!list_empty(&node_page_list)) {
2351 page = lru_to_page(&node_page_list);
2352 list_del(&page->lru);
2353 putback_lru_page(page);
2354 }
2355
2356 nid = NUMA_NO_NODE;
2357 }
2358
2359 if (!list_empty(&node_page_list)) {
2360 nr_reclaimed += shrink_page_list(&node_page_list,
2361 NODE_DATA(nid),
2362 &sc, &dummy_stat, false);
2363 while (!list_empty(&node_page_list)) {
2364 page = lru_to_page(&node_page_list);
2365 list_del(&page->lru);
2366 putback_lru_page(page);
2367 }
2368 }
2369
2370 memalloc_noreclaim_restore(noreclaim_flag);
2371
2372 return nr_reclaimed;
2373}
2374
2375static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2376 struct lruvec *lruvec, struct scan_control *sc)
2377{
2378 if (is_active_lru(lru)) {
2379 if (sc->may_deactivate & (1 << is_file_lru(lru)))
2380 shrink_active_list(nr_to_scan, lruvec, sc, lru);
2381 else
2382 sc->skipped_deactivate = 1;
2383 return 0;
2384 }
2385
2386 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2387}
2388
2389/*
2390 * The inactive anon list should be small enough that the VM never has
2391 * to do too much work.
2392 *
2393 * The inactive file list should be small enough to leave most memory
2394 * to the established workingset on the scan-resistant active list,
2395 * but large enough to avoid thrashing the aggregate readahead window.
2396 *
2397 * Both inactive lists should also be large enough that each inactive
2398 * page has a chance to be referenced again before it is reclaimed.
2399 *
2400 * If that fails and refaulting is observed, the inactive list grows.
2401 *
2402 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2403 * on this LRU, maintained by the pageout code. An inactive_ratio
2404 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2405 *
2406 * total target max
2407 * memory ratio inactive
2408 * -------------------------------------
2409 * 10MB 1 5MB
2410 * 100MB 1 50MB
2411 * 1GB 3 250MB
2412 * 10GB 10 0.9GB
2413 * 100GB 31 3GB
2414 * 1TB 101 10GB
2415 * 10TB 320 32GB
2416 */
2417static bool inactive_is_low(struct lruvec *lruvec, enum lru_list inactive_lru)
2418{
2419 enum lru_list active_lru = inactive_lru + LRU_ACTIVE;
2420 unsigned long inactive, active;
2421 unsigned long inactive_ratio;
2422 unsigned long gb;
2423
2424 inactive = lruvec_page_state(lruvec, NR_LRU_BASE + inactive_lru);
2425 active = lruvec_page_state(lruvec, NR_LRU_BASE + active_lru);
2426
2427 gb = (inactive + active) >> (30 - PAGE_SHIFT);
2428 if (gb)
2429 inactive_ratio = int_sqrt(10 * gb);
2430 else
2431 inactive_ratio = 1;
2432
2433 return inactive * inactive_ratio < active;
2434}
2435
2436enum scan_balance {
2437 SCAN_EQUAL,
2438 SCAN_FRACT,
2439 SCAN_ANON,
2440 SCAN_FILE,
2441};
2442
2443/*
2444 * Determine how aggressively the anon and file LRU lists should be
2445 * scanned. The relative value of each set of LRU lists is determined
2446 * by looking at the fraction of the pages scanned we did rotate back
2447 * onto the active list instead of evict.
2448 *
2449 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
2450 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
2451 */
2452static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
2453 unsigned long *nr)
2454{
2455 struct mem_cgroup *memcg = lruvec_memcg(lruvec);
2456 unsigned long anon_cost, file_cost, total_cost;
2457 int swappiness = mem_cgroup_swappiness(memcg);
2458 u64 fraction[ANON_AND_FILE];
2459 u64 denominator = 0; /* gcc */
2460 enum scan_balance scan_balance;
2461 unsigned long ap, fp;
2462 enum lru_list lru;
2463
2464 /* If we have no swap space, do not bother scanning anon pages. */
2465 if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2466 scan_balance = SCAN_FILE;
2467 goto out;
2468 }
2469
2470 /*
2471 * Global reclaim will swap to prevent OOM even with no
2472 * swappiness, but memcg users want to use this knob to
2473 * disable swapping for individual groups completely when
2474 * using the memory controller's swap limit feature would be
2475 * too expensive.
2476 */
2477 if (cgroup_reclaim(sc) && !swappiness) {
2478 scan_balance = SCAN_FILE;
2479 goto out;
2480 }
2481
2482 /*
2483 * Do not apply any pressure balancing cleverness when the
2484 * system is close to OOM, scan both anon and file equally
2485 * (unless the swappiness setting disagrees with swapping).
2486 */
2487 if (!sc->priority && swappiness) {
2488 scan_balance = SCAN_EQUAL;
2489 goto out;
2490 }
2491
2492 /*
2493 * If the system is almost out of file pages, force-scan anon.
2494 */
2495 if (sc->file_is_tiny) {
2496 scan_balance = SCAN_ANON;
2497 goto out;
2498 }
2499
2500 /*
2501 * If there is enough inactive page cache, we do not reclaim
2502 * anything from the anonymous working right now.
2503 */
2504 if (sc->cache_trim_mode) {
2505 scan_balance = SCAN_FILE;
2506 goto out;
2507 }
2508
2509 scan_balance = SCAN_FRACT;
2510 /*
2511 * Calculate the pressure balance between anon and file pages.
2512 *
2513 * The amount of pressure we put on each LRU is inversely
2514 * proportional to the cost of reclaiming each list, as
2515 * determined by the share of pages that are refaulting, times
2516 * the relative IO cost of bringing back a swapped out
2517 * anonymous page vs reloading a filesystem page (swappiness).
2518 *
2519 * Although we limit that influence to ensure no list gets
2520 * left behind completely: at least a third of the pressure is
2521 * applied, before swappiness.
2522 *
2523 * With swappiness at 100, anon and file have equal IO cost.
2524 */
2525 total_cost = sc->anon_cost + sc->file_cost;
2526 anon_cost = total_cost + sc->anon_cost;
2527 file_cost = total_cost + sc->file_cost;
2528 total_cost = anon_cost + file_cost;
2529
2530 ap = swappiness * (total_cost + 1);
2531 ap /= anon_cost + 1;
2532
2533 fp = (200 - swappiness) * (total_cost + 1);
2534 fp /= file_cost + 1;
2535
2536 fraction[0] = ap;
2537 fraction[1] = fp;
2538 denominator = ap + fp;
2539out:
2540 for_each_evictable_lru(lru) {
2541 int file = is_file_lru(lru);
2542 unsigned long lruvec_size;
2543 unsigned long low, min;
2544 unsigned long scan;
2545
2546 lruvec_size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
2547 mem_cgroup_protection(sc->target_mem_cgroup, memcg,
2548 &min, &low);
2549
2550 if (min || low) {
2551 /*
2552 * Scale a cgroup's reclaim pressure by proportioning
2553 * its current usage to its memory.low or memory.min
2554 * setting.
2555 *
2556 * This is important, as otherwise scanning aggression
2557 * becomes extremely binary -- from nothing as we
2558 * approach the memory protection threshold, to totally
2559 * nominal as we exceed it. This results in requiring
2560 * setting extremely liberal protection thresholds. It
2561 * also means we simply get no protection at all if we
2562 * set it too low, which is not ideal.
2563 *
2564 * If there is any protection in place, we reduce scan
2565 * pressure by how much of the total memory used is
2566 * within protection thresholds.
2567 *
2568 * There is one special case: in the first reclaim pass,
2569 * we skip over all groups that are within their low
2570 * protection. If that fails to reclaim enough pages to
2571 * satisfy the reclaim goal, we come back and override
2572 * the best-effort low protection. However, we still
2573 * ideally want to honor how well-behaved groups are in
2574 * that case instead of simply punishing them all
2575 * equally. As such, we reclaim them based on how much
2576 * memory they are using, reducing the scan pressure
2577 * again by how much of the total memory used is under
2578 * hard protection.
2579 */
2580 unsigned long cgroup_size = mem_cgroup_size(memcg);
2581 unsigned long protection;
2582
2583 /* memory.low scaling, make sure we retry before OOM */
2584 if (!sc->memcg_low_reclaim && low > min) {
2585 protection = low;
2586 sc->memcg_low_skipped = 1;
2587 } else {
2588 protection = min;
2589 }
2590
2591 /* Avoid TOCTOU with earlier protection check */
2592 cgroup_size = max(cgroup_size, protection);
2593
2594 scan = lruvec_size - lruvec_size * protection /
2595 (cgroup_size + 1);
2596
2597 /*
2598 * Minimally target SWAP_CLUSTER_MAX pages to keep
2599 * reclaim moving forwards, avoiding decrementing
2600 * sc->priority further than desirable.
2601 */
2602 scan = max(scan, SWAP_CLUSTER_MAX);
2603 } else {
2604 scan = lruvec_size;
2605 }
2606
2607 scan >>= sc->priority;
2608
2609 /*
2610 * If the cgroup's already been deleted, make sure to
2611 * scrape out the remaining cache.
2612 */
2613 if (!scan && !mem_cgroup_online(memcg))
2614 scan = min(lruvec_size, SWAP_CLUSTER_MAX);
2615
2616 switch (scan_balance) {
2617 case SCAN_EQUAL:
2618 /* Scan lists relative to size */
2619 break;
2620 case SCAN_FRACT:
2621 /*
2622 * Scan types proportional to swappiness and
2623 * their relative recent reclaim efficiency.
2624 * Make sure we don't miss the last page on
2625 * the offlined memory cgroups because of a
2626 * round-off error.
2627 */
2628 scan = mem_cgroup_online(memcg) ?
2629 div64_u64(scan * fraction[file], denominator) :
2630 DIV64_U64_ROUND_UP(scan * fraction[file],
2631 denominator);
2632 break;
2633 case SCAN_FILE:
2634 case SCAN_ANON:
2635 /* Scan one type exclusively */
2636 if ((scan_balance == SCAN_FILE) != file)
2637 scan = 0;
2638 break;
2639 default:
2640 /* Look ma, no brain */
2641 BUG();
2642 }
2643
2644 nr[lru] = scan;
2645 }
2646}
2647
2648static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
2649{
2650 unsigned long nr[NR_LRU_LISTS];
2651 unsigned long targets[NR_LRU_LISTS];
2652 unsigned long nr_to_scan;
2653 enum lru_list lru;
2654 unsigned long nr_reclaimed = 0;
2655 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2656 struct blk_plug plug;
2657 bool scan_adjusted;
2658
2659 get_scan_count(lruvec, sc, nr);
2660
2661 /* Record the original scan target for proportional adjustments later */
2662 memcpy(targets, nr, sizeof(nr));
2663
2664 /*
2665 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2666 * event that can occur when there is little memory pressure e.g.
2667 * multiple streaming readers/writers. Hence, we do not abort scanning
2668 * when the requested number of pages are reclaimed when scanning at
2669 * DEF_PRIORITY on the assumption that the fact we are direct
2670 * reclaiming implies that kswapd is not keeping up and it is best to
2671 * do a batch of work at once. For memcg reclaim one check is made to
2672 * abort proportional reclaim if either the file or anon lru has already
2673 * dropped to zero at the first pass.
2674 */
2675 scan_adjusted = (!cgroup_reclaim(sc) && !current_is_kswapd() &&
2676 sc->priority == DEF_PRIORITY);
2677
2678 blk_start_plug(&plug);
2679 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2680 nr[LRU_INACTIVE_FILE]) {
2681 unsigned long nr_anon, nr_file, percentage;
2682 unsigned long nr_scanned;
2683
2684 for_each_evictable_lru(lru) {
2685 if (nr[lru]) {
2686 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2687 nr[lru] -= nr_to_scan;
2688
2689 nr_reclaimed += shrink_list(lru, nr_to_scan,
2690 lruvec, sc);
2691 }
2692 }
2693
2694 cond_resched();
2695
2696 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2697 continue;
2698
2699 /*
2700 * For kswapd and memcg, reclaim at least the number of pages
2701 * requested. Ensure that the anon and file LRUs are scanned
2702 * proportionally what was requested by get_scan_count(). We
2703 * stop reclaiming one LRU and reduce the amount scanning
2704 * proportional to the original scan target.
2705 */
2706 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2707 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2708
2709 /*
2710 * It's just vindictive to attack the larger once the smaller
2711 * has gone to zero. And given the way we stop scanning the
2712 * smaller below, this makes sure that we only make one nudge
2713 * towards proportionality once we've got nr_to_reclaim.
2714 */
2715 if (!nr_file || !nr_anon)
2716 break;
2717
2718 if (nr_file > nr_anon) {
2719 unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2720 targets[LRU_ACTIVE_ANON] + 1;
2721 lru = LRU_BASE;
2722 percentage = nr_anon * 100 / scan_target;
2723 } else {
2724 unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2725 targets[LRU_ACTIVE_FILE] + 1;
2726 lru = LRU_FILE;
2727 percentage = nr_file * 100 / scan_target;
2728 }
2729
2730 /* Stop scanning the smaller of the LRU */
2731 nr[lru] = 0;
2732 nr[lru + LRU_ACTIVE] = 0;
2733
2734 /*
2735 * Recalculate the other LRU scan count based on its original
2736 * scan target and the percentage scanning already complete
2737 */
2738 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2739 nr_scanned = targets[lru] - nr[lru];
2740 nr[lru] = targets[lru] * (100 - percentage) / 100;
2741 nr[lru] -= min(nr[lru], nr_scanned);
2742
2743 lru += LRU_ACTIVE;
2744 nr_scanned = targets[lru] - nr[lru];
2745 nr[lru] = targets[lru] * (100 - percentage) / 100;
2746 nr[lru] -= min(nr[lru], nr_scanned);
2747
2748 scan_adjusted = true;
2749 }
2750 blk_finish_plug(&plug);
2751 sc->nr_reclaimed += nr_reclaimed;
2752
2753 /*
2754 * Even if we did not try to evict anon pages at all, we want to
2755 * rebalance the anon lru active/inactive ratio.
2756 */
2757 if (total_swap_pages && inactive_is_low(lruvec, LRU_INACTIVE_ANON))
2758 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2759 sc, LRU_ACTIVE_ANON);
2760}
2761
2762/* Use reclaim/compaction for costly allocs or under memory pressure */
2763static bool in_reclaim_compaction(struct scan_control *sc)
2764{
2765 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2766 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2767 sc->priority < DEF_PRIORITY - 2))
2768 return true;
2769
2770 return false;
2771}
2772
2773/*
2774 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2775 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2776 * true if more pages should be reclaimed such that when the page allocator
2777 * calls try_to_compact_pages() that it will have enough free pages to succeed.
2778 * It will give up earlier than that if there is difficulty reclaiming pages.
2779 */
2780static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2781 unsigned long nr_reclaimed,
2782 struct scan_control *sc)
2783{
2784 unsigned long pages_for_compaction;
2785 unsigned long inactive_lru_pages;
2786 int z;
2787
2788 /* If not in reclaim/compaction mode, stop */
2789 if (!in_reclaim_compaction(sc))
2790 return false;
2791
2792 /*
2793 * Stop if we failed to reclaim any pages from the last SWAP_CLUSTER_MAX
2794 * number of pages that were scanned. This will return to the caller
2795 * with the risk reclaim/compaction and the resulting allocation attempt
2796 * fails. In the past we have tried harder for __GFP_RETRY_MAYFAIL
2797 * allocations through requiring that the full LRU list has been scanned
2798 * first, by assuming that zero delta of sc->nr_scanned means full LRU
2799 * scan, but that approximation was wrong, and there were corner cases
2800 * where always a non-zero amount of pages were scanned.
2801 */
2802 if (!nr_reclaimed)
2803 return false;
2804
2805 /* If compaction would go ahead or the allocation would succeed, stop */
2806 for (z = 0; z <= sc->reclaim_idx; z++) {
2807 struct zone *zone = &pgdat->node_zones[z];
2808 if (!managed_zone(zone))
2809 continue;
2810
2811 switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2812 case COMPACT_SUCCESS:
2813 case COMPACT_CONTINUE:
2814 return false;
2815 default:
2816 /* check next zone */
2817 ;
2818 }
2819 }
2820
2821 /*
2822 * If we have not reclaimed enough pages for compaction and the
2823 * inactive lists are large enough, continue reclaiming
2824 */
2825 pages_for_compaction = compact_gap(sc->order);
2826 inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2827 if (get_nr_swap_pages() > 0)
2828 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2829
2830 return inactive_lru_pages > pages_for_compaction;
2831}
2832
2833static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
2834{
2835 struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
2836 struct mem_cgroup *memcg;
2837
2838 memcg = mem_cgroup_iter(target_memcg, NULL, NULL);
2839 do {
2840 struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
2841 unsigned long reclaimed;
2842 unsigned long scanned;
2843
2844 /*
2845 * This loop can become CPU-bound when target memcgs
2846 * aren't eligible for reclaim - either because they
2847 * don't have any reclaimable pages, or because their
2848 * memory is explicitly protected. Avoid soft lockups.
2849 */
2850 cond_resched();
2851
2852 mem_cgroup_calculate_protection(target_memcg, memcg);
2853
2854 if (mem_cgroup_below_min(memcg)) {
2855 /*
2856 * Hard protection.
2857 * If there is no reclaimable memory, OOM.
2858 */
2859 continue;
2860 } else if (mem_cgroup_below_low(memcg)) {
2861 /*
2862 * Soft protection.
2863 * Respect the protection only as long as
2864 * there is an unprotected supply
2865 * of reclaimable memory from other cgroups.
2866 */
2867 if (!sc->memcg_low_reclaim) {
2868 sc->memcg_low_skipped = 1;
2869 continue;
2870 }
2871 memcg_memory_event(memcg, MEMCG_LOW);
2872 }
2873
2874 reclaimed = sc->nr_reclaimed;
2875 scanned = sc->nr_scanned;
2876
2877 shrink_lruvec(lruvec, sc);
2878
2879 shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
2880 sc->priority);
2881
2882 /* Record the group's reclaim efficiency */
2883 vmpressure(sc->gfp_mask, memcg, false,
2884 sc->nr_scanned - scanned,
2885 sc->nr_reclaimed - reclaimed);
2886
2887 } while ((memcg = mem_cgroup_iter(target_memcg, memcg, NULL)));
2888}
2889
2890static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
2891{
2892 struct reclaim_state *reclaim_state = current->reclaim_state;
2893 unsigned long nr_reclaimed, nr_scanned;
2894 struct lruvec *target_lruvec;
2895 bool reclaimable = false;
2896 unsigned long file;
2897
2898 target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
2899
2900again:
2901 memset(&sc->nr, 0, sizeof(sc->nr));
2902
2903 nr_reclaimed = sc->nr_reclaimed;
2904 nr_scanned = sc->nr_scanned;
2905
2906 /*
2907 * Determine the scan balance between anon and file LRUs.
2908 */
2909 spin_lock_irq(&target_lruvec->lru_lock);
2910 sc->anon_cost = target_lruvec->anon_cost;
2911 sc->file_cost = target_lruvec->file_cost;
2912 spin_unlock_irq(&target_lruvec->lru_lock);
2913
2914 /*
2915 * Target desirable inactive:active list ratios for the anon
2916 * and file LRU lists.
2917 */
2918 if (!sc->force_deactivate) {
2919 unsigned long refaults;
2920
2921 refaults = lruvec_page_state(target_lruvec,
2922 WORKINGSET_ACTIVATE_ANON);
2923 if (refaults != target_lruvec->refaults[0] ||
2924 inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
2925 sc->may_deactivate |= DEACTIVATE_ANON;
2926 else
2927 sc->may_deactivate &= ~DEACTIVATE_ANON;
2928
2929 /*
2930 * When refaults are being observed, it means a new
2931 * workingset is being established. Deactivate to get
2932 * rid of any stale active pages quickly.
2933 */
2934 refaults = lruvec_page_state(target_lruvec,
2935 WORKINGSET_ACTIVATE_FILE);
2936 if (refaults != target_lruvec->refaults[1] ||
2937 inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
2938 sc->may_deactivate |= DEACTIVATE_FILE;
2939 else
2940 sc->may_deactivate &= ~DEACTIVATE_FILE;
2941 } else
2942 sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
2943
2944 /*
2945 * If we have plenty of inactive file pages that aren't
2946 * thrashing, try to reclaim those first before touching
2947 * anonymous pages.
2948 */
2949 file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
2950 if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
2951 sc->cache_trim_mode = 1;
2952 else
2953 sc->cache_trim_mode = 0;
2954
2955 /*
2956 * Prevent the reclaimer from falling into the cache trap: as
2957 * cache pages start out inactive, every cache fault will tip
2958 * the scan balance towards the file LRU. And as the file LRU
2959 * shrinks, so does the window for rotation from references.
2960 * This means we have a runaway feedback loop where a tiny
2961 * thrashing file LRU becomes infinitely more attractive than
2962 * anon pages. Try to detect this based on file LRU size.
2963 */
2964 if (!cgroup_reclaim(sc)) {
2965 unsigned long total_high_wmark = 0;
2966 unsigned long free, anon;
2967 int z;
2968
2969 free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
2970 file = node_page_state(pgdat, NR_ACTIVE_FILE) +
2971 node_page_state(pgdat, NR_INACTIVE_FILE);
2972
2973 for (z = 0; z < MAX_NR_ZONES; z++) {
2974 struct zone *zone = &pgdat->node_zones[z];
2975 if (!managed_zone(zone))
2976 continue;
2977
2978 total_high_wmark += high_wmark_pages(zone);
2979 }
2980
2981 /*
2982 * Consider anon: if that's low too, this isn't a
2983 * runaway file reclaim problem, but rather just
2984 * extreme pressure. Reclaim as per usual then.
2985 */
2986 anon = node_page_state(pgdat, NR_INACTIVE_ANON);
2987
2988 sc->file_is_tiny =
2989 file + free <= total_high_wmark &&
2990 !(sc->may_deactivate & DEACTIVATE_ANON) &&
2991 anon >> sc->priority;
2992 }
2993
2994 shrink_node_memcgs(pgdat, sc);
2995
2996 if (reclaim_state) {
2997 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2998 reclaim_state->reclaimed_slab = 0;
2999 }
3000
3001 /* Record the subtree's reclaim efficiency */
3002 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
3003 sc->nr_scanned - nr_scanned,
3004 sc->nr_reclaimed - nr_reclaimed);
3005
3006 if (sc->nr_reclaimed - nr_reclaimed)
3007 reclaimable = true;
3008
3009 if (current_is_kswapd()) {
3010 /*
3011 * If reclaim is isolating dirty pages under writeback,
3012 * it implies that the long-lived page allocation rate
3013 * is exceeding the page laundering rate. Either the
3014 * global limits are not being effective at throttling
3015 * processes due to the page distribution throughout
3016 * zones or there is heavy usage of a slow backing
3017 * device. The only option is to throttle from reclaim
3018 * context which is not ideal as there is no guarantee
3019 * the dirtying process is throttled in the same way
3020 * balance_dirty_pages() manages.
3021 *
3022 * Once a node is flagged PGDAT_WRITEBACK, kswapd will
3023 * count the number of pages under pages flagged for
3024 * immediate reclaim and stall if any are encountered
3025 * in the nr_immediate check below.
3026 */
3027 if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
3028 set_bit(PGDAT_WRITEBACK, &pgdat->flags);
3029
3030 /* Allow kswapd to start writing pages during reclaim.*/
3031 if (sc->nr.unqueued_dirty == sc->nr.file_taken)
3032 set_bit(PGDAT_DIRTY, &pgdat->flags);
3033
3034 /*
3035 * If kswapd scans pages marked for immediate
3036 * reclaim and under writeback (nr_immediate), it
3037 * implies that pages are cycling through the LRU
3038 * faster than they are written so also forcibly stall.
3039 */
3040 if (sc->nr.immediate)
3041 congestion_wait(BLK_RW_ASYNC, HZ/10);
3042 }
3043
3044 /*
3045 * Tag a node/memcg as congested if all the dirty pages
3046 * scanned were backed by a congested BDI and
3047 * wait_iff_congested will stall.
3048 *
3049 * Legacy memcg will stall in page writeback so avoid forcibly
3050 * stalling in wait_iff_congested().
3051 */
3052 if ((current_is_kswapd() ||
3053 (cgroup_reclaim(sc) && writeback_throttling_sane(sc))) &&
3054 sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
3055 set_bit(LRUVEC_CONGESTED, &target_lruvec->flags);
3056
3057 /*
3058 * Stall direct reclaim for IO completions if underlying BDIs
3059 * and node is congested. Allow kswapd to continue until it
3060 * starts encountering unqueued dirty pages or cycling through
3061 * the LRU too quickly.
3062 */
3063 if (!current_is_kswapd() && current_may_throttle() &&
3064 !sc->hibernation_mode &&
3065 test_bit(LRUVEC_CONGESTED, &target_lruvec->flags))
3066 wait_iff_congested(BLK_RW_ASYNC, HZ/10);
3067
3068 if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
3069 sc))
3070 goto again;
3071
3072 /*
3073 * Kswapd gives up on balancing particular nodes after too
3074 * many failures to reclaim anything from them and goes to
3075 * sleep. On reclaim progress, reset the failure counter. A
3076 * successful direct reclaim run will revive a dormant kswapd.
3077 */
3078 if (reclaimable)
3079 pgdat->kswapd_failures = 0;
3080}
3081
3082/*
3083 * Returns true if compaction should go ahead for a costly-order request, or
3084 * the allocation would already succeed without compaction. Return false if we
3085 * should reclaim first.
3086 */
3087static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
3088{
3089 unsigned long watermark;
3090 enum compact_result suitable;
3091
3092 suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
3093 if (suitable == COMPACT_SUCCESS)
3094 /* Allocation should succeed already. Don't reclaim. */
3095 return true;
3096 if (suitable == COMPACT_SKIPPED)
3097 /* Compaction cannot yet proceed. Do reclaim. */
3098 return false;
3099
3100 /*
3101 * Compaction is already possible, but it takes time to run and there
3102 * are potentially other callers using the pages just freed. So proceed
3103 * with reclaim to make a buffer of free pages available to give
3104 * compaction a reasonable chance of completing and allocating the page.
3105 * Note that we won't actually reclaim the whole buffer in one attempt
3106 * as the target watermark in should_continue_reclaim() is lower. But if
3107 * we are already above the high+gap watermark, don't reclaim at all.
3108 */
3109 watermark = high_wmark_pages(zone) + compact_gap(sc->order);
3110
3111 return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
3112}
3113
3114/*
3115 * This is the direct reclaim path, for page-allocating processes. We only
3116 * try to reclaim pages from zones which will satisfy the caller's allocation
3117 * request.
3118 *
3119 * If a zone is deemed to be full of pinned pages then just give it a light
3120 * scan then give up on it.
3121 */
3122static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
3123{
3124 struct zoneref *z;
3125 struct zone *zone;
3126 unsigned long nr_soft_reclaimed;
3127 unsigned long nr_soft_scanned;
3128 gfp_t orig_mask;
3129 pg_data_t *last_pgdat = NULL;
3130
3131 /*
3132 * If the number of buffer_heads in the machine exceeds the maximum
3133 * allowed level, force direct reclaim to scan the highmem zone as
3134 * highmem pages could be pinning lowmem pages storing buffer_heads
3135 */
3136 orig_mask = sc->gfp_mask;
3137 if (buffer_heads_over_limit) {
3138 sc->gfp_mask |= __GFP_HIGHMEM;
3139 sc->reclaim_idx = gfp_zone(sc->gfp_mask);
3140 }
3141
3142 for_each_zone_zonelist_nodemask(zone, z, zonelist,
3143 sc->reclaim_idx, sc->nodemask) {
3144 /*
3145 * Take care memory controller reclaiming has small influence
3146 * to global LRU.
3147 */
3148 if (!cgroup_reclaim(sc)) {
3149 if (!cpuset_zone_allowed(zone,
3150 GFP_KERNEL | __GFP_HARDWALL))
3151 continue;
3152
3153 /*
3154 * If we already have plenty of memory free for
3155 * compaction in this zone, don't free any more.
3156 * Even though compaction is invoked for any
3157 * non-zero order, only frequent costly order
3158 * reclamation is disruptive enough to become a
3159 * noticeable problem, like transparent huge
3160 * page allocations.
3161 */
3162 if (IS_ENABLED(CONFIG_COMPACTION) &&
3163 sc->order > PAGE_ALLOC_COSTLY_ORDER &&
3164 compaction_ready(zone, sc)) {
3165 sc->compaction_ready = true;
3166 continue;
3167 }
3168
3169 /*
3170 * Shrink each node in the zonelist once. If the
3171 * zonelist is ordered by zone (not the default) then a
3172 * node may be shrunk multiple times but in that case
3173 * the user prefers lower zones being preserved.
3174 */
3175 if (zone->zone_pgdat == last_pgdat)
3176 continue;
3177
3178 /*
3179 * This steals pages from memory cgroups over softlimit
3180 * and returns the number of reclaimed pages and
3181 * scanned pages. This works for global memory pressure
3182 * and balancing, not for a memcg's limit.
3183 */
3184 nr_soft_scanned = 0;
3185 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
3186 sc->order, sc->gfp_mask,
3187 &nr_soft_scanned);
3188 sc->nr_reclaimed += nr_soft_reclaimed;
3189 sc->nr_scanned += nr_soft_scanned;
3190 /* need some check for avoid more shrink_zone() */
3191 }
3192
3193 /* See comment about same check for global reclaim above */
3194 if (zone->zone_pgdat == last_pgdat)
3195 continue;
3196 last_pgdat = zone->zone_pgdat;
3197 shrink_node(zone->zone_pgdat, sc);
3198 }
3199
3200 /*
3201 * Restore to original mask to avoid the impact on the caller if we
3202 * promoted it to __GFP_HIGHMEM.
3203 */
3204 sc->gfp_mask = orig_mask;
3205}
3206
3207static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat)
3208{
3209 struct lruvec *target_lruvec;
3210 unsigned long refaults;
3211
3212 target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
3213 refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON);
3214 target_lruvec->refaults[0] = refaults;
3215 refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_FILE);
3216 target_lruvec->refaults[1] = refaults;
3217}
3218
3219/*
3220 * This is the main entry point to direct page reclaim.
3221 *
3222 * If a full scan of the inactive list fails to free enough memory then we
3223 * are "out of memory" and something needs to be killed.
3224 *
3225 * If the caller is !__GFP_FS then the probability of a failure is reasonably
3226 * high - the zone may be full of dirty or under-writeback pages, which this
3227 * caller can't do much about. We kick the writeback threads and take explicit
3228 * naps in the hope that some of these pages can be written. But if the
3229 * allocating task holds filesystem locks which prevent writeout this might not
3230 * work, and the allocation attempt will fail.
3231 *
3232 * returns: 0, if no pages reclaimed
3233 * else, the number of pages reclaimed
3234 */
3235static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
3236 struct scan_control *sc)
3237{
3238 int initial_priority = sc->priority;
3239 pg_data_t *last_pgdat;
3240 struct zoneref *z;
3241 struct zone *zone;
3242retry:
3243 delayacct_freepages_start();
3244
3245 if (!cgroup_reclaim(sc))
3246 __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
3247
3248 do {
3249 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
3250 sc->priority);
3251 sc->nr_scanned = 0;
3252 shrink_zones(zonelist, sc);
3253
3254 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
3255 break;
3256
3257 if (sc->compaction_ready)
3258 break;
3259
3260 /*
3261 * If we're getting trouble reclaiming, start doing
3262 * writepage even in laptop mode.
3263 */
3264 if (sc->priority < DEF_PRIORITY - 2)
3265 sc->may_writepage = 1;
3266 } while (--sc->priority >= 0);
3267
3268 last_pgdat = NULL;
3269 for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
3270 sc->nodemask) {
3271 if (zone->zone_pgdat == last_pgdat)
3272 continue;
3273 last_pgdat = zone->zone_pgdat;
3274
3275 snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
3276
3277 if (cgroup_reclaim(sc)) {
3278 struct lruvec *lruvec;
3279
3280 lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup,
3281 zone->zone_pgdat);
3282 clear_bit(LRUVEC_CONGESTED, &lruvec->flags);
3283 }
3284 }
3285
3286 delayacct_freepages_end();
3287
3288 if (sc->nr_reclaimed)
3289 return sc->nr_reclaimed;
3290
3291 /* Aborted reclaim to try compaction? don't OOM, then */
3292 if (sc->compaction_ready)
3293 return 1;
3294
3295 /*
3296 * We make inactive:active ratio decisions based on the node's
3297 * composition of memory, but a restrictive reclaim_idx or a
3298 * memory.low cgroup setting can exempt large amounts of
3299 * memory from reclaim. Neither of which are very common, so
3300 * instead of doing costly eligibility calculations of the
3301 * entire cgroup subtree up front, we assume the estimates are
3302 * good, and retry with forcible deactivation if that fails.
3303 */
3304 if (sc->skipped_deactivate) {
3305 sc->priority = initial_priority;
3306 sc->force_deactivate = 1;
3307 sc->skipped_deactivate = 0;
3308 goto retry;
3309 }
3310
3311 /* Untapped cgroup reserves? Don't OOM, retry. */
3312 if (sc->memcg_low_skipped) {
3313 sc->priority = initial_priority;
3314 sc->force_deactivate = 0;
3315 sc->memcg_low_reclaim = 1;
3316 sc->memcg_low_skipped = 0;
3317 goto retry;
3318 }
3319
3320 return 0;
3321}
3322
3323static bool allow_direct_reclaim(pg_data_t *pgdat)
3324{
3325 struct zone *zone;
3326 unsigned long pfmemalloc_reserve = 0;
3327 unsigned long free_pages = 0;
3328 int i;
3329 bool wmark_ok;
3330
3331 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
3332 return true;
3333
3334 for (i = 0; i <= ZONE_NORMAL; i++) {
3335 zone = &pgdat->node_zones[i];
3336 if (!managed_zone(zone))
3337 continue;
3338
3339 if (!zone_reclaimable_pages(zone))
3340 continue;
3341
3342 pfmemalloc_reserve += min_wmark_pages(zone);
3343 free_pages += zone_page_state(zone, NR_FREE_PAGES);
3344 }
3345
3346 /* If there are no reserves (unexpected config) then do not throttle */
3347 if (!pfmemalloc_reserve)
3348 return true;
3349
3350 wmark_ok = free_pages > pfmemalloc_reserve / 2;
3351
3352 /* kswapd must be awake if processes are being throttled */
3353 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
3354 if (READ_ONCE(pgdat->kswapd_highest_zoneidx) > ZONE_NORMAL)
3355 WRITE_ONCE(pgdat->kswapd_highest_zoneidx, ZONE_NORMAL);
3356
3357 wake_up_interruptible(&pgdat->kswapd_wait);
3358 }
3359
3360 return wmark_ok;
3361}
3362
3363/*
3364 * Throttle direct reclaimers if backing storage is backed by the network
3365 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
3366 * depleted. kswapd will continue to make progress and wake the processes
3367 * when the low watermark is reached.
3368 *
3369 * Returns true if a fatal signal was delivered during throttling. If this
3370 * happens, the page allocator should not consider triggering the OOM killer.
3371 */
3372static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
3373 nodemask_t *nodemask)
3374{
3375 struct zoneref *z;
3376 struct zone *zone;
3377 pg_data_t *pgdat = NULL;
3378
3379 /*
3380 * Kernel threads should not be throttled as they may be indirectly
3381 * responsible for cleaning pages necessary for reclaim to make forward
3382 * progress. kjournald for example may enter direct reclaim while
3383 * committing a transaction where throttling it could forcing other
3384 * processes to block on log_wait_commit().
3385 */
3386 if (current->flags & PF_KTHREAD)
3387 goto out;
3388
3389 /*
3390 * If a fatal signal is pending, this process should not throttle.
3391 * It should return quickly so it can exit and free its memory
3392 */
3393 if (fatal_signal_pending(current))
3394 goto out;
3395
3396 /*
3397 * Check if the pfmemalloc reserves are ok by finding the first node
3398 * with a usable ZONE_NORMAL or lower zone. The expectation is that
3399 * GFP_KERNEL will be required for allocating network buffers when
3400 * swapping over the network so ZONE_HIGHMEM is unusable.
3401 *
3402 * Throttling is based on the first usable node and throttled processes
3403 * wait on a queue until kswapd makes progress and wakes them. There
3404 * is an affinity then between processes waking up and where reclaim
3405 * progress has been made assuming the process wakes on the same node.
3406 * More importantly, processes running on remote nodes will not compete
3407 * for remote pfmemalloc reserves and processes on different nodes
3408 * should make reasonable progress.
3409 */
3410 for_each_zone_zonelist_nodemask(zone, z, zonelist,
3411 gfp_zone(gfp_mask), nodemask) {
3412 if (zone_idx(zone) > ZONE_NORMAL)
3413 continue;
3414
3415 /* Throttle based on the first usable node */
3416 pgdat = zone->zone_pgdat;
3417 if (allow_direct_reclaim(pgdat))
3418 goto out;
3419 break;
3420 }
3421
3422 /* If no zone was usable by the allocation flags then do not throttle */
3423 if (!pgdat)
3424 goto out;
3425
3426 /* Account for the throttling */
3427 count_vm_event(PGSCAN_DIRECT_THROTTLE);
3428
3429 /*
3430 * If the caller cannot enter the filesystem, it's possible that it
3431 * is due to the caller holding an FS lock or performing a journal
3432 * transaction in the case of a filesystem like ext[3|4]. In this case,
3433 * it is not safe to block on pfmemalloc_wait as kswapd could be
3434 * blocked waiting on the same lock. Instead, throttle for up to a
3435 * second before continuing.
3436 */
3437 if (!(gfp_mask & __GFP_FS)) {
3438 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
3439 allow_direct_reclaim(pgdat), HZ);
3440
3441 goto check_pending;
3442 }
3443
3444 /* Throttle until kswapd wakes the process */
3445 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
3446 allow_direct_reclaim(pgdat));
3447
3448check_pending:
3449 if (fatal_signal_pending(current))
3450 return true;
3451
3452out:
3453 return false;
3454}
3455
3456unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
3457 gfp_t gfp_mask, nodemask_t *nodemask)
3458{
3459 unsigned long nr_reclaimed;
3460 struct scan_control sc = {
3461 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3462 .gfp_mask = current_gfp_context(gfp_mask),
3463 .reclaim_idx = gfp_zone(gfp_mask),
3464 .order = order,
3465 .nodemask = nodemask,
3466 .priority = DEF_PRIORITY,
3467 .may_writepage = !laptop_mode,
3468 .may_unmap = 1,
3469 .may_swap = 1,
3470 };
3471
3472 /*
3473 * scan_control uses s8 fields for order, priority, and reclaim_idx.
3474 * Confirm they are large enough for max values.
3475 */
3476 BUILD_BUG_ON(MAX_ORDER > S8_MAX);
3477 BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
3478 BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);
3479
3480 /*
3481 * Do not enter reclaim if fatal signal was delivered while throttled.
3482 * 1 is returned so that the page allocator does not OOM kill at this
3483 * point.
3484 */
3485 if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
3486 return 1;
3487
3488 set_task_reclaim_state(current, &sc.reclaim_state);
3489 trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
3490
3491 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3492
3493 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
3494 set_task_reclaim_state(current, NULL);
3495
3496 return nr_reclaimed;
3497}
3498
3499#ifdef CONFIG_MEMCG
3500
3501/* Only used by soft limit reclaim. Do not reuse for anything else. */
3502unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
3503 gfp_t gfp_mask, bool noswap,
3504 pg_data_t *pgdat,
3505 unsigned long *nr_scanned)
3506{
3507 struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
3508 struct scan_control sc = {
3509 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3510 .target_mem_cgroup = memcg,
3511 .may_writepage = !laptop_mode,
3512 .may_unmap = 1,
3513 .reclaim_idx = MAX_NR_ZONES - 1,
3514 .may_swap = !noswap,
3515 };
3516
3517 WARN_ON_ONCE(!current->reclaim_state);
3518
3519 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3520 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3521
3522 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3523 sc.gfp_mask);
3524
3525 /*
3526 * NOTE: Although we can get the priority field, using it
3527 * here is not a good idea, since it limits the pages we can scan.
3528 * if we don't reclaim here, the shrink_node from balance_pgdat
3529 * will pick up pages from other mem cgroup's as well. We hack
3530 * the priority and make it zero.
3531 */
3532 shrink_lruvec(lruvec, &sc);
3533
3534 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
3535
3536 *nr_scanned = sc.nr_scanned;
3537
3538 return sc.nr_reclaimed;
3539}
3540
3541unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3542 unsigned long nr_pages,
3543 gfp_t gfp_mask,
3544 bool may_swap)
3545{
3546 unsigned long nr_reclaimed;
3547 unsigned int noreclaim_flag;
3548 struct scan_control sc = {
3549 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3550 .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
3551 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3552 .reclaim_idx = MAX_NR_ZONES - 1,
3553 .target_mem_cgroup = memcg,
3554 .priority = DEF_PRIORITY,
3555 .may_writepage = !laptop_mode,
3556 .may_unmap = 1,
3557 .may_swap = may_swap,
3558 };
3559 /*
3560 * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
3561 * equal pressure on all the nodes. This is based on the assumption that
3562 * the reclaim does not bail out early.
3563 */
3564 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3565
3566 set_task_reclaim_state(current, &sc.reclaim_state);
3567 trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
3568 noreclaim_flag = memalloc_noreclaim_save();
3569
3570 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3571
3572 memalloc_noreclaim_restore(noreclaim_flag);
3573 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
3574 set_task_reclaim_state(current, NULL);
3575
3576 return nr_reclaimed;
3577}
3578#endif
3579
3580static void age_active_anon(struct pglist_data *pgdat,
3581 struct scan_control *sc)
3582{
3583 struct mem_cgroup *memcg;
3584 struct lruvec *lruvec;
3585
3586 if (!total_swap_pages)
3587 return;
3588
3589 lruvec = mem_cgroup_lruvec(NULL, pgdat);
3590 if (!inactive_is_low(lruvec, LRU_INACTIVE_ANON))
3591 return;
3592
3593 memcg = mem_cgroup_iter(NULL, NULL, NULL);
3594 do {
3595 lruvec = mem_cgroup_lruvec(memcg, pgdat);
3596 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3597 sc, LRU_ACTIVE_ANON);
3598 memcg = mem_cgroup_iter(NULL, memcg, NULL);
3599 } while (memcg);
3600}
3601
3602static bool pgdat_watermark_boosted(pg_data_t *pgdat, int highest_zoneidx)
3603{
3604 int i;
3605 struct zone *zone;
3606
3607 /*
3608 * Check for watermark boosts top-down as the higher zones
3609 * are more likely to be boosted. Both watermarks and boosts
3610 * should not be checked at the same time as reclaim would
3611 * start prematurely when there is no boosting and a lower
3612 * zone is balanced.
3613 */
3614 for (i = highest_zoneidx; i >= 0; i--) {
3615 zone = pgdat->node_zones + i;
3616 if (!managed_zone(zone))
3617 continue;
3618
3619 if (zone->watermark_boost)
3620 return true;
3621 }
3622
3623 return false;
3624}
3625
3626/*
3627 * Returns true if there is an eligible zone balanced for the request order
3628 * and highest_zoneidx
3629 */
3630static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)
3631{
3632 int i;
3633 unsigned long mark = -1;
3634 struct zone *zone;
3635
3636 /*
3637 * Check watermarks bottom-up as lower zones are more likely to
3638 * meet watermarks.
3639 */
3640 for (i = 0; i <= highest_zoneidx; i++) {
3641 zone = pgdat->node_zones + i;
3642
3643 if (!managed_zone(zone))
3644 continue;
3645
3646 mark = high_wmark_pages(zone);
3647 if (zone_watermark_ok_safe(zone, order, mark, highest_zoneidx))
3648 return true;
3649 }
3650
3651 /*
3652 * If a node has no populated zone within highest_zoneidx, it does not
3653 * need balancing by definition. This can happen if a zone-restricted
3654 * allocation tries to wake a remote kswapd.
3655 */
3656 if (mark == -1)
3657 return true;
3658
3659 return false;
3660}
3661
3662/* Clear pgdat state for congested, dirty or under writeback. */
3663static void clear_pgdat_congested(pg_data_t *pgdat)
3664{
3665 struct lruvec *lruvec = mem_cgroup_lruvec(NULL, pgdat);
3666
3667 clear_bit(LRUVEC_CONGESTED, &lruvec->flags);
3668 clear_bit(PGDAT_DIRTY, &pgdat->flags);
3669 clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
3670}
3671
3672/*
3673 * Prepare kswapd for sleeping. This verifies that there are no processes
3674 * waiting in throttle_direct_reclaim() and that watermarks have been met.
3675 *
3676 * Returns true if kswapd is ready to sleep
3677 */
3678static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order,
3679 int highest_zoneidx)
3680{
3681 /*
3682 * The throttled processes are normally woken up in balance_pgdat() as
3683 * soon as allow_direct_reclaim() is true. But there is a potential
3684 * race between when kswapd checks the watermarks and a process gets
3685 * throttled. There is also a potential race if processes get
3686 * throttled, kswapd wakes, a large process exits thereby balancing the
3687 * zones, which causes kswapd to exit balance_pgdat() before reaching
3688 * the wake up checks. If kswapd is going to sleep, no process should
3689 * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
3690 * the wake up is premature, processes will wake kswapd and get
3691 * throttled again. The difference from wake ups in balance_pgdat() is
3692 * that here we are under prepare_to_wait().
3693 */
3694 if (waitqueue_active(&pgdat->pfmemalloc_wait))
3695 wake_up_all(&pgdat->pfmemalloc_wait);
3696
3697 /* Hopeless node, leave it to direct reclaim */
3698 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
3699 return true;
3700
3701 if (pgdat_balanced(pgdat, order, highest_zoneidx)) {
3702 clear_pgdat_congested(pgdat);
3703 return true;
3704 }
3705
3706 return false;
3707}
3708
3709/*
3710 * kswapd shrinks a node of pages that are at or below the highest usable
3711 * zone that is currently unbalanced.
3712 *
3713 * Returns true if kswapd scanned at least the requested number of pages to
3714 * reclaim or if the lack of progress was due to pages under writeback.
3715 * This is used to determine if the scanning priority needs to be raised.
3716 */
3717static bool kswapd_shrink_node(pg_data_t *pgdat,
3718 struct scan_control *sc)
3719{
3720 struct zone *zone;
3721 int z;
3722
3723 /* Reclaim a number of pages proportional to the number of zones */
3724 sc->nr_to_reclaim = 0;
3725 for (z = 0; z <= sc->reclaim_idx; z++) {
3726 zone = pgdat->node_zones + z;
3727 if (!managed_zone(zone))
3728 continue;
3729
3730 sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
3731 }
3732
3733 /*
3734 * Historically care was taken to put equal pressure on all zones but
3735 * now pressure is applied based on node LRU order.
3736 */
3737 shrink_node(pgdat, sc);
3738
3739 /*
3740 * Fragmentation may mean that the system cannot be rebalanced for
3741 * high-order allocations. If twice the allocation size has been
3742 * reclaimed then recheck watermarks only at order-0 to prevent
3743 * excessive reclaim. Assume that a process requested a high-order
3744 * can direct reclaim/compact.
3745 */
3746 if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3747 sc->order = 0;
3748
3749 return sc->nr_scanned >= sc->nr_to_reclaim;
3750}
3751
3752/* Page allocator PCP high watermark is lowered if reclaim is active. */
3753static inline void
3754update_reclaim_active(pg_data_t *pgdat, int highest_zoneidx, bool active)
3755{
3756 int i;
3757 struct zone *zone;
3758
3759 for (i = 0; i <= highest_zoneidx; i++) {
3760 zone = pgdat->node_zones + i;
3761
3762 if (!managed_zone(zone))
3763 continue;
3764
3765 if (active)
3766 set_bit(ZONE_RECLAIM_ACTIVE, &zone->flags);
3767 else
3768 clear_bit(ZONE_RECLAIM_ACTIVE, &zone->flags);
3769 }
3770}
3771
3772static inline void
3773set_reclaim_active(pg_data_t *pgdat, int highest_zoneidx)
3774{
3775 update_reclaim_active(pgdat, highest_zoneidx, true);
3776}
3777
3778static inline void
3779clear_reclaim_active(pg_data_t *pgdat, int highest_zoneidx)
3780{
3781 update_reclaim_active(pgdat, highest_zoneidx, false);
3782}
3783
3784/*
3785 * For kswapd, balance_pgdat() will reclaim pages across a node from zones
3786 * that are eligible for use by the caller until at least one zone is
3787 * balanced.
3788 *
3789 * Returns the order kswapd finished reclaiming at.
3790 *
3791 * kswapd scans the zones in the highmem->normal->dma direction. It skips
3792 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3793 * found to have free_pages <= high_wmark_pages(zone), any page in that zone
3794 * or lower is eligible for reclaim until at least one usable zone is
3795 * balanced.
3796 */
3797static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
3798{
3799 int i;
3800 unsigned long nr_soft_reclaimed;
3801 unsigned long nr_soft_scanned;
3802 unsigned long pflags;
3803 unsigned long nr_boost_reclaim;
3804 unsigned long zone_boosts[MAX_NR_ZONES] = { 0, };
3805 bool boosted;
3806 struct zone *zone;
3807 struct scan_control sc = {
3808 .gfp_mask = GFP_KERNEL,
3809 .order = order,
3810 .may_unmap = 1,
3811 };
3812
3813 set_task_reclaim_state(current, &sc.reclaim_state);
3814 psi_memstall_enter(&pflags);
3815 __fs_reclaim_acquire();
3816
3817 count_vm_event(PAGEOUTRUN);
3818
3819 /*
3820 * Account for the reclaim boost. Note that the zone boost is left in
3821 * place so that parallel allocations that are near the watermark will
3822 * stall or direct reclaim until kswapd is finished.
3823 */
3824 nr_boost_reclaim = 0;
3825 for (i = 0; i <= highest_zoneidx; i++) {
3826 zone = pgdat->node_zones + i;
3827 if (!managed_zone(zone))
3828 continue;
3829
3830 nr_boost_reclaim += zone->watermark_boost;
3831 zone_boosts[i] = zone->watermark_boost;
3832 }
3833 boosted = nr_boost_reclaim;
3834
3835restart:
3836 set_reclaim_active(pgdat, highest_zoneidx);
3837 sc.priority = DEF_PRIORITY;
3838 do {
3839 unsigned long nr_reclaimed = sc.nr_reclaimed;
3840 bool raise_priority = true;
3841 bool balanced;
3842 bool ret;
3843
3844 sc.reclaim_idx = highest_zoneidx;
3845
3846 /*
3847 * If the number of buffer_heads exceeds the maximum allowed
3848 * then consider reclaiming from all zones. This has a dual
3849 * purpose -- on 64-bit systems it is expected that
3850 * buffer_heads are stripped during active rotation. On 32-bit
3851 * systems, highmem pages can pin lowmem memory and shrinking
3852 * buffers can relieve lowmem pressure. Reclaim may still not
3853 * go ahead if all eligible zones for the original allocation
3854 * request are balanced to avoid excessive reclaim from kswapd.
3855 */
3856 if (buffer_heads_over_limit) {
3857 for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
3858 zone = pgdat->node_zones + i;
3859 if (!managed_zone(zone))
3860 continue;
3861
3862 sc.reclaim_idx = i;
3863 break;
3864 }
3865 }
3866
3867 /*
3868 * If the pgdat is imbalanced then ignore boosting and preserve
3869 * the watermarks for a later time and restart. Note that the
3870 * zone watermarks will be still reset at the end of balancing
3871 * on the grounds that the normal reclaim should be enough to
3872 * re-evaluate if boosting is required when kswapd next wakes.
3873 */
3874 balanced = pgdat_balanced(pgdat, sc.order, highest_zoneidx);
3875 if (!balanced && nr_boost_reclaim) {
3876 nr_boost_reclaim = 0;
3877 goto restart;
3878 }
3879
3880 /*
3881 * If boosting is not active then only reclaim if there are no
3882 * eligible zones. Note that sc.reclaim_idx is not used as
3883 * buffer_heads_over_limit may have adjusted it.
3884 */
3885 if (!nr_boost_reclaim && balanced)
3886 goto out;
3887
3888 /* Limit the priority of boosting to avoid reclaim writeback */
3889 if (nr_boost_reclaim && sc.priority == DEF_PRIORITY - 2)
3890 raise_priority = false;
3891
3892 /*
3893 * Do not writeback or swap pages for boosted reclaim. The
3894 * intent is to relieve pressure not issue sub-optimal IO
3895 * from reclaim context. If no pages are reclaimed, the
3896 * reclaim will be aborted.
3897 */
3898 sc.may_writepage = !laptop_mode && !nr_boost_reclaim;
3899 sc.may_swap = !nr_boost_reclaim;
3900
3901 /*
3902 * Do some background aging of the anon list, to give
3903 * pages a chance to be referenced before reclaiming. All
3904 * pages are rotated regardless of classzone as this is
3905 * about consistent aging.
3906 */
3907 age_active_anon(pgdat, &sc);
3908
3909 /*
3910 * If we're getting trouble reclaiming, start doing writepage
3911 * even in laptop mode.
3912 */
3913 if (sc.priority < DEF_PRIORITY - 2)
3914 sc.may_writepage = 1;
3915
3916 /* Call soft limit reclaim before calling shrink_node. */
3917 sc.nr_scanned = 0;
3918 nr_soft_scanned = 0;
3919 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3920 sc.gfp_mask, &nr_soft_scanned);
3921 sc.nr_reclaimed += nr_soft_reclaimed;
3922
3923 /*
3924 * There should be no need to raise the scanning priority if
3925 * enough pages are already being scanned that that high
3926 * watermark would be met at 100% efficiency.
3927 */
3928 if (kswapd_shrink_node(pgdat, &sc))
3929 raise_priority = false;
3930
3931 /*
3932 * If the low watermark is met there is no need for processes
3933 * to be throttled on pfmemalloc_wait as they should not be
3934 * able to safely make forward progress. Wake them
3935 */
3936 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3937 allow_direct_reclaim(pgdat))
3938 wake_up_all(&pgdat->pfmemalloc_wait);
3939
3940 /* Check if kswapd should be suspending */
3941 __fs_reclaim_release();
3942 ret = try_to_freeze();
3943 __fs_reclaim_acquire();
3944 if (ret || kthread_should_stop())
3945 break;
3946
3947 /*
3948 * Raise priority if scanning rate is too low or there was no
3949 * progress in reclaiming pages
3950 */
3951 nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
3952 nr_boost_reclaim -= min(nr_boost_reclaim, nr_reclaimed);
3953
3954 /*
3955 * If reclaim made no progress for a boost, stop reclaim as
3956 * IO cannot be queued and it could be an infinite loop in
3957 * extreme circumstances.
3958 */
3959 if (nr_boost_reclaim && !nr_reclaimed)
3960 break;
3961
3962 if (raise_priority || !nr_reclaimed)
3963 sc.priority--;
3964 } while (sc.priority >= 1);
3965
3966 if (!sc.nr_reclaimed)
3967 pgdat->kswapd_failures++;
3968
3969out:
3970 clear_reclaim_active(pgdat, highest_zoneidx);
3971
3972 /* If reclaim was boosted, account for the reclaim done in this pass */
3973 if (boosted) {
3974 unsigned long flags;
3975
3976 for (i = 0; i <= highest_zoneidx; i++) {
3977 if (!zone_boosts[i])
3978 continue;
3979
3980 /* Increments are under the zone lock */
3981 zone = pgdat->node_zones + i;
3982 spin_lock_irqsave(&zone->lock, flags);
3983 zone->watermark_boost -= min(zone->watermark_boost, zone_boosts[i]);
3984 spin_unlock_irqrestore(&zone->lock, flags);
3985 }
3986
3987 /*
3988 * As there is now likely space, wakeup kcompact to defragment
3989 * pageblocks.
3990 */
3991 wakeup_kcompactd(pgdat, pageblock_order, highest_zoneidx);
3992 }
3993
3994 snapshot_refaults(NULL, pgdat);
3995 __fs_reclaim_release();
3996 psi_memstall_leave(&pflags);
3997 set_task_reclaim_state(current, NULL);
3998
3999 /*
4000 * Return the order kswapd stopped reclaiming at as
4001 * prepare_kswapd_sleep() takes it into account. If another caller
4002 * entered the allocator slow path while kswapd was awake, order will
4003 * remain at the higher level.
4004 */
4005 return sc.order;
4006}
4007
4008/*
4009 * The pgdat->kswapd_highest_zoneidx is used to pass the highest zone index to
4010 * be reclaimed by kswapd from the waker. If the value is MAX_NR_ZONES which is
4011 * not a valid index then either kswapd runs for first time or kswapd couldn't
4012 * sleep after previous reclaim attempt (node is still unbalanced). In that
4013 * case return the zone index of the previous kswapd reclaim cycle.
4014 */
4015static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
4016 enum zone_type prev_highest_zoneidx)
4017{
4018 enum zone_type curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
4019
4020 return curr_idx == MAX_NR_ZONES ? prev_highest_zoneidx : curr_idx;
4021}
4022
4023static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
4024 unsigned int highest_zoneidx)
4025{
4026 long remaining = 0;
4027 DEFINE_WAIT(wait);
4028
4029 if (freezing(current) || kthread_should_stop())
4030 return;
4031
4032 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
4033
4034 /*
4035 * Try to sleep for a short interval. Note that kcompactd will only be
4036 * woken if it is possible to sleep for a short interval. This is
4037 * deliberate on the assumption that if reclaim cannot keep an
4038 * eligible zone balanced that it's also unlikely that compaction will
4039 * succeed.
4040 */
4041 if (prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
4042 /*
4043 * Compaction records what page blocks it recently failed to
4044 * isolate pages from and skips them in the future scanning.
4045 * When kswapd is going to sleep, it is reasonable to assume
4046 * that pages and compaction may succeed so reset the cache.
4047 */
4048 reset_isolation_suitable(pgdat);
4049
4050 /*
4051 * We have freed the memory, now we should compact it to make
4052 * allocation of the requested order possible.
4053 */
4054 wakeup_kcompactd(pgdat, alloc_order, highest_zoneidx);
4055
4056 remaining = schedule_timeout(HZ/10);
4057
4058 /*
4059 * If woken prematurely then reset kswapd_highest_zoneidx and
4060 * order. The values will either be from a wakeup request or
4061 * the previous request that slept prematurely.
4062 */
4063 if (remaining) {
4064 WRITE_ONCE(pgdat->kswapd_highest_zoneidx,
4065 kswapd_highest_zoneidx(pgdat,
4066 highest_zoneidx));
4067
4068 if (READ_ONCE(pgdat->kswapd_order) < reclaim_order)
4069 WRITE_ONCE(pgdat->kswapd_order, reclaim_order);
4070 }
4071
4072 finish_wait(&pgdat->kswapd_wait, &wait);
4073 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
4074 }
4075
4076 /*
4077 * After a short sleep, check if it was a premature sleep. If not, then
4078 * go fully to sleep until explicitly woken up.
4079 */
4080 if (!remaining &&
4081 prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
4082 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
4083
4084 /*
4085 * vmstat counters are not perfectly accurate and the estimated
4086 * value for counters such as NR_FREE_PAGES can deviate from the
4087 * true value by nr_online_cpus * threshold. To avoid the zone
4088 * watermarks being breached while under pressure, we reduce the
4089 * per-cpu vmstat threshold while kswapd is awake and restore
4090 * them before going back to sleep.
4091 */
4092 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
4093
4094 if (!kthread_should_stop())
4095 schedule();
4096
4097 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
4098 } else {
4099 if (remaining)
4100 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
4101 else
4102 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
4103 }
4104 finish_wait(&pgdat->kswapd_wait, &wait);
4105}
4106
4107/*
4108 * The background pageout daemon, started as a kernel thread
4109 * from the init process.
4110 *
4111 * This basically trickles out pages so that we have _some_
4112 * free memory available even if there is no other activity
4113 * that frees anything up. This is needed for things like routing
4114 * etc, where we otherwise might have all activity going on in
4115 * asynchronous contexts that cannot page things out.
4116 *
4117 * If there are applications that are active memory-allocators
4118 * (most normal use), this basically shouldn't matter.
4119 */
4120static int kswapd(void *p)
4121{
4122 unsigned int alloc_order, reclaim_order;
4123 unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
4124 pg_data_t *pgdat = (pg_data_t *)p;
4125 struct task_struct *tsk = current;
4126 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
4127
4128 if (!cpumask_empty(cpumask))
4129 set_cpus_allowed_ptr(tsk, cpumask);
4130
4131 /*
4132 * Tell the memory management that we're a "memory allocator",
4133 * and that if we need more memory we should get access to it
4134 * regardless (see "__alloc_pages()"). "kswapd" should
4135 * never get caught in the normal page freeing logic.
4136 *
4137 * (Kswapd normally doesn't need memory anyway, but sometimes
4138 * you need a small amount of memory in order to be able to
4139 * page out something else, and this flag essentially protects
4140 * us from recursively trying to free more memory as we're
4141 * trying to free the first piece of memory in the first place).
4142 */
4143 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
4144 set_freezable();
4145
4146 WRITE_ONCE(pgdat->kswapd_order, 0);
4147 WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
4148 for ( ; ; ) {
4149 bool ret;
4150
4151 alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
4152 highest_zoneidx = kswapd_highest_zoneidx(pgdat,
4153 highest_zoneidx);
4154
4155kswapd_try_sleep:
4156 kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
4157 highest_zoneidx);
4158
4159 /* Read the new order and highest_zoneidx */
4160 alloc_order = READ_ONCE(pgdat->kswapd_order);
4161 highest_zoneidx = kswapd_highest_zoneidx(pgdat,
4162 highest_zoneidx);
4163 WRITE_ONCE(pgdat->kswapd_order, 0);
4164 WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
4165
4166 ret = try_to_freeze();
4167 if (kthread_should_stop())
4168 break;
4169
4170 /*
4171 * We can speed up thawing tasks if we don't call balance_pgdat
4172 * after returning from the refrigerator
4173 */
4174 if (ret)
4175 continue;
4176
4177 /*
4178 * Reclaim begins at the requested order but if a high-order
4179 * reclaim fails then kswapd falls back to reclaiming for
4180 * order-0. If that happens, kswapd will consider sleeping
4181 * for the order it finished reclaiming at (reclaim_order)
4182 * but kcompactd is woken to compact for the original
4183 * request (alloc_order).
4184 */
4185 trace_mm_vmscan_kswapd_wake(pgdat->node_id, highest_zoneidx,
4186 alloc_order);
4187 reclaim_order = balance_pgdat(pgdat, alloc_order,
4188 highest_zoneidx);
4189 if (reclaim_order < alloc_order)
4190 goto kswapd_try_sleep;
4191 }
4192
4193 tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
4194
4195 return 0;
4196}
4197
4198/*
4199 * A zone is low on free memory or too fragmented for high-order memory. If
4200 * kswapd should reclaim (direct reclaim is deferred), wake it up for the zone's
4201 * pgdat. It will wake up kcompactd after reclaiming memory. If kswapd reclaim
4202 * has failed or is not needed, still wake up kcompactd if only compaction is
4203 * needed.
4204 */
4205void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
4206 enum zone_type highest_zoneidx)
4207{
4208 pg_data_t *pgdat;
4209 enum zone_type curr_idx;
4210
4211 if (!managed_zone(zone))
4212 return;
4213
4214 if (!cpuset_zone_allowed(zone, gfp_flags))
4215 return;
4216
4217 pgdat = zone->zone_pgdat;
4218 curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
4219
4220 if (curr_idx == MAX_NR_ZONES || curr_idx < highest_zoneidx)
4221 WRITE_ONCE(pgdat->kswapd_highest_zoneidx, highest_zoneidx);
4222
4223 if (READ_ONCE(pgdat->kswapd_order) < order)
4224 WRITE_ONCE(pgdat->kswapd_order, order);
4225
4226 if (!waitqueue_active(&pgdat->kswapd_wait))
4227 return;
4228
4229 /* Hopeless node, leave it to direct reclaim if possible */
4230 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ||
4231 (pgdat_balanced(pgdat, order, highest_zoneidx) &&
4232 !pgdat_watermark_boosted(pgdat, highest_zoneidx))) {
4233 /*
4234 * There may be plenty of free memory available, but it's too
4235 * fragmented for high-order allocations. Wake up kcompactd
4236 * and rely on compaction_suitable() to determine if it's
4237 * needed. If it fails, it will defer subsequent attempts to
4238 * ratelimit its work.
4239 */
4240 if (!(gfp_flags & __GFP_DIRECT_RECLAIM))
4241 wakeup_kcompactd(pgdat, order, highest_zoneidx);
4242 return;
4243 }
4244
4245 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, highest_zoneidx, order,
4246 gfp_flags);
4247 wake_up_interruptible(&pgdat->kswapd_wait);
4248}
4249
4250#ifdef CONFIG_HIBERNATION
4251/*
4252 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
4253 * freed pages.
4254 *
4255 * Rather than trying to age LRUs the aim is to preserve the overall
4256 * LRU order by reclaiming preferentially
4257 * inactive > active > active referenced > active mapped
4258 */
4259unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
4260{
4261 struct scan_control sc = {
4262 .nr_to_reclaim = nr_to_reclaim,
4263 .gfp_mask = GFP_HIGHUSER_MOVABLE,
4264 .reclaim_idx = MAX_NR_ZONES - 1,
4265 .priority = DEF_PRIORITY,
4266 .may_writepage = 1,
4267 .may_unmap = 1,
4268 .may_swap = 1,
4269 .hibernation_mode = 1,
4270 };
4271 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
4272 unsigned long nr_reclaimed;
4273 unsigned int noreclaim_flag;
4274
4275 fs_reclaim_acquire(sc.gfp_mask);
4276 noreclaim_flag = memalloc_noreclaim_save();
4277 set_task_reclaim_state(current, &sc.reclaim_state);
4278
4279 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
4280
4281 set_task_reclaim_state(current, NULL);
4282 memalloc_noreclaim_restore(noreclaim_flag);
4283 fs_reclaim_release(sc.gfp_mask);
4284
4285 return nr_reclaimed;
4286}
4287#endif /* CONFIG_HIBERNATION */
4288
4289/*
4290 * This kswapd start function will be called by init and node-hot-add.
4291 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
4292 */
4293int kswapd_run(int nid)
4294{
4295 pg_data_t *pgdat = NODE_DATA(nid);
4296 int ret = 0;
4297
4298 if (pgdat->kswapd)
4299 return 0;
4300
4301 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
4302 if (IS_ERR(pgdat->kswapd)) {
4303 /* failure at boot is fatal */
4304 BUG_ON(system_state < SYSTEM_RUNNING);
4305 pr_err("Failed to start kswapd on node %d\n", nid);
4306 ret = PTR_ERR(pgdat->kswapd);
4307 pgdat->kswapd = NULL;
4308 }
4309 return ret;
4310}
4311
4312/*
4313 * Called by memory hotplug when all memory in a node is offlined. Caller must
4314 * hold mem_hotplug_begin/end().
4315 */
4316void kswapd_stop(int nid)
4317{
4318 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
4319
4320 if (kswapd) {
4321 kthread_stop(kswapd);
4322 NODE_DATA(nid)->kswapd = NULL;
4323 }
4324}
4325
4326static int __init kswapd_init(void)
4327{
4328 int nid;
4329
4330 swap_setup();
4331 for_each_node_state(nid, N_MEMORY)
4332 kswapd_run(nid);
4333 return 0;
4334}
4335
4336module_init(kswapd_init)
4337
4338#ifdef CONFIG_NUMA
4339/*
4340 * Node reclaim mode
4341 *
4342 * If non-zero call node_reclaim when the number of free pages falls below
4343 * the watermarks.
4344 */
4345int node_reclaim_mode __read_mostly;
4346
4347/*
4348 * Priority for NODE_RECLAIM. This determines the fraction of pages
4349 * of a node considered for each zone_reclaim. 4 scans 1/16th of
4350 * a zone.
4351 */
4352#define NODE_RECLAIM_PRIORITY 4
4353
4354/*
4355 * Percentage of pages in a zone that must be unmapped for node_reclaim to
4356 * occur.
4357 */
4358int sysctl_min_unmapped_ratio = 1;
4359
4360/*
4361 * If the number of slab pages in a zone grows beyond this percentage then
4362 * slab reclaim needs to occur.
4363 */
4364int sysctl_min_slab_ratio = 5;
4365
4366static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
4367{
4368 unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
4369 unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
4370 node_page_state(pgdat, NR_ACTIVE_FILE);
4371
4372 /*
4373 * It's possible for there to be more file mapped pages than
4374 * accounted for by the pages on the file LRU lists because
4375 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
4376 */
4377 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
4378}
4379
4380/* Work out how many page cache pages we can reclaim in this reclaim_mode */
4381static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
4382{
4383 unsigned long nr_pagecache_reclaimable;
4384 unsigned long delta = 0;
4385
4386 /*
4387 * If RECLAIM_UNMAP is set, then all file pages are considered
4388 * potentially reclaimable. Otherwise, we have to worry about
4389 * pages like swapcache and node_unmapped_file_pages() provides
4390 * a better estimate
4391 */
4392 if (node_reclaim_mode & RECLAIM_UNMAP)
4393 nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
4394 else
4395 nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
4396
4397 /* If we can't clean pages, remove dirty pages from consideration */
4398 if (!(node_reclaim_mode & RECLAIM_WRITE))
4399 delta += node_page_state(pgdat, NR_FILE_DIRTY);
4400
4401 /* Watch for any possible underflows due to delta */
4402 if (unlikely(delta > nr_pagecache_reclaimable))
4403 delta = nr_pagecache_reclaimable;
4404
4405 return nr_pagecache_reclaimable - delta;
4406}
4407
4408/*
4409 * Try to free up some pages from this node through reclaim.
4410 */
4411static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
4412{
4413 /* Minimum pages needed in order to stay on node */
4414 const unsigned long nr_pages = 1 << order;
4415 struct task_struct *p = current;
4416 unsigned int noreclaim_flag;
4417 struct scan_control sc = {
4418 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
4419 .gfp_mask = current_gfp_context(gfp_mask),
4420 .order = order,
4421 .priority = NODE_RECLAIM_PRIORITY,
4422 .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
4423 .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
4424 .may_swap = 1,
4425 .reclaim_idx = gfp_zone(gfp_mask),
4426 };
4427 unsigned long pflags;
4428
4429 trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
4430 sc.gfp_mask);
4431
4432 cond_resched();
4433 psi_memstall_enter(&pflags);
4434 fs_reclaim_acquire(sc.gfp_mask);
4435 /*
4436 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
4437 * and we also need to be able to write out pages for RECLAIM_WRITE
4438 * and RECLAIM_UNMAP.
4439 */
4440 noreclaim_flag = memalloc_noreclaim_save();
4441 p->flags |= PF_SWAPWRITE;
4442 set_task_reclaim_state(p, &sc.reclaim_state);
4443
4444 if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
4445 /*
4446 * Free memory by calling shrink node with increasing
4447 * priorities until we have enough memory freed.
4448 */
4449 do {
4450 shrink_node(pgdat, &sc);
4451 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
4452 }
4453
4454 set_task_reclaim_state(p, NULL);
4455 current->flags &= ~PF_SWAPWRITE;
4456 memalloc_noreclaim_restore(noreclaim_flag);
4457 fs_reclaim_release(sc.gfp_mask);
4458 psi_memstall_leave(&pflags);
4459
4460 trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
4461
4462 return sc.nr_reclaimed >= nr_pages;
4463}
4464
4465int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
4466{
4467 int ret;
4468
4469 /*
4470 * Node reclaim reclaims unmapped file backed pages and
4471 * slab pages if we are over the defined limits.
4472 *
4473 * A small portion of unmapped file backed pages is needed for
4474 * file I/O otherwise pages read by file I/O will be immediately
4475 * thrown out if the node is overallocated. So we do not reclaim
4476 * if less than a specified percentage of the node is used by
4477 * unmapped file backed pages.
4478 */
4479 if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
4480 node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B) <=
4481 pgdat->min_slab_pages)
4482 return NODE_RECLAIM_FULL;
4483
4484 /*
4485 * Do not scan if the allocation should not be delayed.
4486 */
4487 if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
4488 return NODE_RECLAIM_NOSCAN;
4489
4490 /*
4491 * Only run node reclaim on the local node or on nodes that do not
4492 * have associated processors. This will favor the local processor
4493 * over remote processors and spread off node memory allocations
4494 * as wide as possible.
4495 */
4496 if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
4497 return NODE_RECLAIM_NOSCAN;
4498
4499 if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
4500 return NODE_RECLAIM_NOSCAN;
4501
4502 ret = __node_reclaim(pgdat, gfp_mask, order);
4503 clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
4504
4505 if (!ret)
4506 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
4507
4508 return ret;
4509}
4510#endif
4511
4512/**
4513 * check_move_unevictable_pages - check pages for evictability and move to
4514 * appropriate zone lru list
4515 * @pvec: pagevec with lru pages to check
4516 *
4517 * Checks pages for evictability, if an evictable page is in the unevictable
4518 * lru list, moves it to the appropriate evictable lru list. This function
4519 * should be only used for lru pages.
4520 */
4521void check_move_unevictable_pages(struct pagevec *pvec)
4522{
4523 struct lruvec *lruvec = NULL;
4524 int pgscanned = 0;
4525 int pgrescued = 0;
4526 int i;
4527
4528 for (i = 0; i < pvec->nr; i++) {
4529 struct page *page = pvec->pages[i];
4530 int nr_pages;
4531
4532 if (PageTransTail(page))
4533 continue;
4534
4535 nr_pages = thp_nr_pages(page);
4536 pgscanned += nr_pages;
4537
4538 /* block memcg migration during page moving between lru */
4539 if (!TestClearPageLRU(page))
4540 continue;
4541
4542 lruvec = relock_page_lruvec_irq(page, lruvec);
4543 if (page_evictable(page) && PageUnevictable(page)) {
4544 del_page_from_lru_list(page, lruvec);
4545 ClearPageUnevictable(page);
4546 add_page_to_lru_list(page, lruvec);
4547 pgrescued += nr_pages;
4548 }
4549 SetPageLRU(page);
4550 }
4551
4552 if (lruvec) {
4553 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
4554 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
4555 unlock_page_lruvec_irq(lruvec);
4556 } else if (pgscanned) {
4557 count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
4558 }
4559}
4560EXPORT_SYMBOL_GPL(check_move_unevictable_pages);
1/*
2 * linux/mm/vmscan.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 *
6 * Swap reorganised 29.12.95, Stephen Tweedie.
7 * kswapd added: 7.1.96 sct
8 * Removed kswapd_ctl limits, and swap out as many pages as needed
9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11 * Multiqueue VM started 5.8.00, Rik van Riel.
12 */
13
14#include <linux/mm.h>
15#include <linux/module.h>
16#include <linux/gfp.h>
17#include <linux/kernel_stat.h>
18#include <linux/swap.h>
19#include <linux/pagemap.h>
20#include <linux/init.h>
21#include <linux/highmem.h>
22#include <linux/vmpressure.h>
23#include <linux/vmstat.h>
24#include <linux/file.h>
25#include <linux/writeback.h>
26#include <linux/blkdev.h>
27#include <linux/buffer_head.h> /* for try_to_release_page(),
28 buffer_heads_over_limit */
29#include <linux/mm_inline.h>
30#include <linux/backing-dev.h>
31#include <linux/rmap.h>
32#include <linux/topology.h>
33#include <linux/cpu.h>
34#include <linux/cpuset.h>
35#include <linux/compaction.h>
36#include <linux/notifier.h>
37#include <linux/rwsem.h>
38#include <linux/delay.h>
39#include <linux/kthread.h>
40#include <linux/freezer.h>
41#include <linux/memcontrol.h>
42#include <linux/delayacct.h>
43#include <linux/sysctl.h>
44#include <linux/oom.h>
45#include <linux/prefetch.h>
46
47#include <asm/tlbflush.h>
48#include <asm/div64.h>
49
50#include <linux/swapops.h>
51#include <linux/balloon_compaction.h>
52
53#include "internal.h"
54
55#define CREATE_TRACE_POINTS
56#include <trace/events/vmscan.h>
57
58struct scan_control {
59 /* Incremented by the number of inactive pages that were scanned */
60 unsigned long nr_scanned;
61
62 /* Number of pages freed so far during a call to shrink_zones() */
63 unsigned long nr_reclaimed;
64
65 /* How many pages shrink_list() should reclaim */
66 unsigned long nr_to_reclaim;
67
68 unsigned long hibernation_mode;
69
70 /* This context's GFP mask */
71 gfp_t gfp_mask;
72
73 int may_writepage;
74
75 /* Can mapped pages be reclaimed? */
76 int may_unmap;
77
78 /* Can pages be swapped as part of reclaim? */
79 int may_swap;
80
81 int order;
82
83 /* Scan (total_size >> priority) pages at once */
84 int priority;
85
86 /*
87 * The memory cgroup that hit its limit and as a result is the
88 * primary target of this reclaim invocation.
89 */
90 struct mem_cgroup *target_mem_cgroup;
91
92 /*
93 * Nodemask of nodes allowed by the caller. If NULL, all nodes
94 * are scanned.
95 */
96 nodemask_t *nodemask;
97};
98
99#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
100
101#ifdef ARCH_HAS_PREFETCH
102#define prefetch_prev_lru_page(_page, _base, _field) \
103 do { \
104 if ((_page)->lru.prev != _base) { \
105 struct page *prev; \
106 \
107 prev = lru_to_page(&(_page->lru)); \
108 prefetch(&prev->_field); \
109 } \
110 } while (0)
111#else
112#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
113#endif
114
115#ifdef ARCH_HAS_PREFETCHW
116#define prefetchw_prev_lru_page(_page, _base, _field) \
117 do { \
118 if ((_page)->lru.prev != _base) { \
119 struct page *prev; \
120 \
121 prev = lru_to_page(&(_page->lru)); \
122 prefetchw(&prev->_field); \
123 } \
124 } while (0)
125#else
126#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
127#endif
128
129/*
130 * From 0 .. 100. Higher means more swappy.
131 */
132int vm_swappiness = 60;
133unsigned long vm_total_pages; /* The total number of pages which the VM controls */
134
135static LIST_HEAD(shrinker_list);
136static DECLARE_RWSEM(shrinker_rwsem);
137
138#ifdef CONFIG_MEMCG
139static bool global_reclaim(struct scan_control *sc)
140{
141 return !sc->target_mem_cgroup;
142}
143#else
144static bool global_reclaim(struct scan_control *sc)
145{
146 return true;
147}
148#endif
149
150static unsigned long zone_reclaimable_pages(struct zone *zone)
151{
152 int nr;
153
154 nr = zone_page_state(zone, NR_ACTIVE_FILE) +
155 zone_page_state(zone, NR_INACTIVE_FILE);
156
157 if (get_nr_swap_pages() > 0)
158 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
159 zone_page_state(zone, NR_INACTIVE_ANON);
160
161 return nr;
162}
163
164bool zone_reclaimable(struct zone *zone)
165{
166 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
167}
168
169static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
170{
171 if (!mem_cgroup_disabled())
172 return mem_cgroup_get_lru_size(lruvec, lru);
173
174 return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
175}
176
177/*
178 * Add a shrinker callback to be called from the vm.
179 */
180int register_shrinker(struct shrinker *shrinker)
181{
182 size_t size = sizeof(*shrinker->nr_deferred);
183
184 /*
185 * If we only have one possible node in the system anyway, save
186 * ourselves the trouble and disable NUMA aware behavior. This way we
187 * will save memory and some small loop time later.
188 */
189 if (nr_node_ids == 1)
190 shrinker->flags &= ~SHRINKER_NUMA_AWARE;
191
192 if (shrinker->flags & SHRINKER_NUMA_AWARE)
193 size *= nr_node_ids;
194
195 shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
196 if (!shrinker->nr_deferred)
197 return -ENOMEM;
198
199 down_write(&shrinker_rwsem);
200 list_add_tail(&shrinker->list, &shrinker_list);
201 up_write(&shrinker_rwsem);
202 return 0;
203}
204EXPORT_SYMBOL(register_shrinker);
205
206/*
207 * Remove one
208 */
209void unregister_shrinker(struct shrinker *shrinker)
210{
211 down_write(&shrinker_rwsem);
212 list_del(&shrinker->list);
213 up_write(&shrinker_rwsem);
214 kfree(shrinker->nr_deferred);
215}
216EXPORT_SYMBOL(unregister_shrinker);
217
218#define SHRINK_BATCH 128
219
220static unsigned long
221shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker,
222 unsigned long nr_pages_scanned, unsigned long lru_pages)
223{
224 unsigned long freed = 0;
225 unsigned long long delta;
226 long total_scan;
227 long freeable;
228 long nr;
229 long new_nr;
230 int nid = shrinkctl->nid;
231 long batch_size = shrinker->batch ? shrinker->batch
232 : SHRINK_BATCH;
233
234 freeable = shrinker->count_objects(shrinker, shrinkctl);
235 if (freeable == 0)
236 return 0;
237
238 /*
239 * copy the current shrinker scan count into a local variable
240 * and zero it so that other concurrent shrinker invocations
241 * don't also do this scanning work.
242 */
243 nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
244
245 total_scan = nr;
246 delta = (4 * nr_pages_scanned) / shrinker->seeks;
247 delta *= freeable;
248 do_div(delta, lru_pages + 1);
249 total_scan += delta;
250 if (total_scan < 0) {
251 printk(KERN_ERR
252 "shrink_slab: %pF negative objects to delete nr=%ld\n",
253 shrinker->scan_objects, total_scan);
254 total_scan = freeable;
255 }
256
257 /*
258 * We need to avoid excessive windup on filesystem shrinkers
259 * due to large numbers of GFP_NOFS allocations causing the
260 * shrinkers to return -1 all the time. This results in a large
261 * nr being built up so when a shrink that can do some work
262 * comes along it empties the entire cache due to nr >>>
263 * freeable. This is bad for sustaining a working set in
264 * memory.
265 *
266 * Hence only allow the shrinker to scan the entire cache when
267 * a large delta change is calculated directly.
268 */
269 if (delta < freeable / 4)
270 total_scan = min(total_scan, freeable / 2);
271
272 /*
273 * Avoid risking looping forever due to too large nr value:
274 * never try to free more than twice the estimate number of
275 * freeable entries.
276 */
277 if (total_scan > freeable * 2)
278 total_scan = freeable * 2;
279
280 trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
281 nr_pages_scanned, lru_pages,
282 freeable, delta, total_scan);
283
284 /*
285 * Normally, we should not scan less than batch_size objects in one
286 * pass to avoid too frequent shrinker calls, but if the slab has less
287 * than batch_size objects in total and we are really tight on memory,
288 * we will try to reclaim all available objects, otherwise we can end
289 * up failing allocations although there are plenty of reclaimable
290 * objects spread over several slabs with usage less than the
291 * batch_size.
292 *
293 * We detect the "tight on memory" situations by looking at the total
294 * number of objects we want to scan (total_scan). If it is greater
295 * than the total number of objects on slab (freeable), we must be
296 * scanning at high prio and therefore should try to reclaim as much as
297 * possible.
298 */
299 while (total_scan >= batch_size ||
300 total_scan >= freeable) {
301 unsigned long ret;
302 unsigned long nr_to_scan = min(batch_size, total_scan);
303
304 shrinkctl->nr_to_scan = nr_to_scan;
305 ret = shrinker->scan_objects(shrinker, shrinkctl);
306 if (ret == SHRINK_STOP)
307 break;
308 freed += ret;
309
310 count_vm_events(SLABS_SCANNED, nr_to_scan);
311 total_scan -= nr_to_scan;
312
313 cond_resched();
314 }
315
316 /*
317 * move the unused scan count back into the shrinker in a
318 * manner that handles concurrent updates. If we exhausted the
319 * scan, there is no need to do an update.
320 */
321 if (total_scan > 0)
322 new_nr = atomic_long_add_return(total_scan,
323 &shrinker->nr_deferred[nid]);
324 else
325 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
326
327 trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr);
328 return freed;
329}
330
331/*
332 * Call the shrink functions to age shrinkable caches
333 *
334 * Here we assume it costs one seek to replace a lru page and that it also
335 * takes a seek to recreate a cache object. With this in mind we age equal
336 * percentages of the lru and ageable caches. This should balance the seeks
337 * generated by these structures.
338 *
339 * If the vm encountered mapped pages on the LRU it increase the pressure on
340 * slab to avoid swapping.
341 *
342 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
343 *
344 * `lru_pages' represents the number of on-LRU pages in all the zones which
345 * are eligible for the caller's allocation attempt. It is used for balancing
346 * slab reclaim versus page reclaim.
347 *
348 * Returns the number of slab objects which we shrunk.
349 */
350unsigned long shrink_slab(struct shrink_control *shrinkctl,
351 unsigned long nr_pages_scanned,
352 unsigned long lru_pages)
353{
354 struct shrinker *shrinker;
355 unsigned long freed = 0;
356
357 if (nr_pages_scanned == 0)
358 nr_pages_scanned = SWAP_CLUSTER_MAX;
359
360 if (!down_read_trylock(&shrinker_rwsem)) {
361 /*
362 * If we would return 0, our callers would understand that we
363 * have nothing else to shrink and give up trying. By returning
364 * 1 we keep it going and assume we'll be able to shrink next
365 * time.
366 */
367 freed = 1;
368 goto out;
369 }
370
371 list_for_each_entry(shrinker, &shrinker_list, list) {
372 if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) {
373 shrinkctl->nid = 0;
374 freed += shrink_slab_node(shrinkctl, shrinker,
375 nr_pages_scanned, lru_pages);
376 continue;
377 }
378
379 for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) {
380 if (node_online(shrinkctl->nid))
381 freed += shrink_slab_node(shrinkctl, shrinker,
382 nr_pages_scanned, lru_pages);
383
384 }
385 }
386 up_read(&shrinker_rwsem);
387out:
388 cond_resched();
389 return freed;
390}
391
392static inline int is_page_cache_freeable(struct page *page)
393{
394 /*
395 * A freeable page cache page is referenced only by the caller
396 * that isolated the page, the page cache radix tree and
397 * optional buffer heads at page->private.
398 */
399 return page_count(page) - page_has_private(page) == 2;
400}
401
402static int may_write_to_queue(struct backing_dev_info *bdi,
403 struct scan_control *sc)
404{
405 if (current->flags & PF_SWAPWRITE)
406 return 1;
407 if (!bdi_write_congested(bdi))
408 return 1;
409 if (bdi == current->backing_dev_info)
410 return 1;
411 return 0;
412}
413
414/*
415 * We detected a synchronous write error writing a page out. Probably
416 * -ENOSPC. We need to propagate that into the address_space for a subsequent
417 * fsync(), msync() or close().
418 *
419 * The tricky part is that after writepage we cannot touch the mapping: nothing
420 * prevents it from being freed up. But we have a ref on the page and once
421 * that page is locked, the mapping is pinned.
422 *
423 * We're allowed to run sleeping lock_page() here because we know the caller has
424 * __GFP_FS.
425 */
426static void handle_write_error(struct address_space *mapping,
427 struct page *page, int error)
428{
429 lock_page(page);
430 if (page_mapping(page) == mapping)
431 mapping_set_error(mapping, error);
432 unlock_page(page);
433}
434
435/* possible outcome of pageout() */
436typedef enum {
437 /* failed to write page out, page is locked */
438 PAGE_KEEP,
439 /* move page to the active list, page is locked */
440 PAGE_ACTIVATE,
441 /* page has been sent to the disk successfully, page is unlocked */
442 PAGE_SUCCESS,
443 /* page is clean and locked */
444 PAGE_CLEAN,
445} pageout_t;
446
447/*
448 * pageout is called by shrink_page_list() for each dirty page.
449 * Calls ->writepage().
450 */
451static pageout_t pageout(struct page *page, struct address_space *mapping,
452 struct scan_control *sc)
453{
454 /*
455 * If the page is dirty, only perform writeback if that write
456 * will be non-blocking. To prevent this allocation from being
457 * stalled by pagecache activity. But note that there may be
458 * stalls if we need to run get_block(). We could test
459 * PagePrivate for that.
460 *
461 * If this process is currently in __generic_file_aio_write() against
462 * this page's queue, we can perform writeback even if that
463 * will block.
464 *
465 * If the page is swapcache, write it back even if that would
466 * block, for some throttling. This happens by accident, because
467 * swap_backing_dev_info is bust: it doesn't reflect the
468 * congestion state of the swapdevs. Easy to fix, if needed.
469 */
470 if (!is_page_cache_freeable(page))
471 return PAGE_KEEP;
472 if (!mapping) {
473 /*
474 * Some data journaling orphaned pages can have
475 * page->mapping == NULL while being dirty with clean buffers.
476 */
477 if (page_has_private(page)) {
478 if (try_to_free_buffers(page)) {
479 ClearPageDirty(page);
480 printk("%s: orphaned page\n", __func__);
481 return PAGE_CLEAN;
482 }
483 }
484 return PAGE_KEEP;
485 }
486 if (mapping->a_ops->writepage == NULL)
487 return PAGE_ACTIVATE;
488 if (!may_write_to_queue(mapping->backing_dev_info, sc))
489 return PAGE_KEEP;
490
491 if (clear_page_dirty_for_io(page)) {
492 int res;
493 struct writeback_control wbc = {
494 .sync_mode = WB_SYNC_NONE,
495 .nr_to_write = SWAP_CLUSTER_MAX,
496 .range_start = 0,
497 .range_end = LLONG_MAX,
498 .for_reclaim = 1,
499 };
500
501 SetPageReclaim(page);
502 res = mapping->a_ops->writepage(page, &wbc);
503 if (res < 0)
504 handle_write_error(mapping, page, res);
505 if (res == AOP_WRITEPAGE_ACTIVATE) {
506 ClearPageReclaim(page);
507 return PAGE_ACTIVATE;
508 }
509
510 if (!PageWriteback(page)) {
511 /* synchronous write or broken a_ops? */
512 ClearPageReclaim(page);
513 }
514 trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
515 inc_zone_page_state(page, NR_VMSCAN_WRITE);
516 return PAGE_SUCCESS;
517 }
518
519 return PAGE_CLEAN;
520}
521
522/*
523 * Same as remove_mapping, but if the page is removed from the mapping, it
524 * gets returned with a refcount of 0.
525 */
526static int __remove_mapping(struct address_space *mapping, struct page *page,
527 bool reclaimed)
528{
529 BUG_ON(!PageLocked(page));
530 BUG_ON(mapping != page_mapping(page));
531
532 spin_lock_irq(&mapping->tree_lock);
533 /*
534 * The non racy check for a busy page.
535 *
536 * Must be careful with the order of the tests. When someone has
537 * a ref to the page, it may be possible that they dirty it then
538 * drop the reference. So if PageDirty is tested before page_count
539 * here, then the following race may occur:
540 *
541 * get_user_pages(&page);
542 * [user mapping goes away]
543 * write_to(page);
544 * !PageDirty(page) [good]
545 * SetPageDirty(page);
546 * put_page(page);
547 * !page_count(page) [good, discard it]
548 *
549 * [oops, our write_to data is lost]
550 *
551 * Reversing the order of the tests ensures such a situation cannot
552 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
553 * load is not satisfied before that of page->_count.
554 *
555 * Note that if SetPageDirty is always performed via set_page_dirty,
556 * and thus under tree_lock, then this ordering is not required.
557 */
558 if (!page_freeze_refs(page, 2))
559 goto cannot_free;
560 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
561 if (unlikely(PageDirty(page))) {
562 page_unfreeze_refs(page, 2);
563 goto cannot_free;
564 }
565
566 if (PageSwapCache(page)) {
567 swp_entry_t swap = { .val = page_private(page) };
568 __delete_from_swap_cache(page);
569 spin_unlock_irq(&mapping->tree_lock);
570 swapcache_free(swap, page);
571 } else {
572 void (*freepage)(struct page *);
573 void *shadow = NULL;
574
575 freepage = mapping->a_ops->freepage;
576 /*
577 * Remember a shadow entry for reclaimed file cache in
578 * order to detect refaults, thus thrashing, later on.
579 *
580 * But don't store shadows in an address space that is
581 * already exiting. This is not just an optizimation,
582 * inode reclaim needs to empty out the radix tree or
583 * the nodes are lost. Don't plant shadows behind its
584 * back.
585 */
586 if (reclaimed && page_is_file_cache(page) &&
587 !mapping_exiting(mapping))
588 shadow = workingset_eviction(mapping, page);
589 __delete_from_page_cache(page, shadow);
590 spin_unlock_irq(&mapping->tree_lock);
591 mem_cgroup_uncharge_cache_page(page);
592
593 if (freepage != NULL)
594 freepage(page);
595 }
596
597 return 1;
598
599cannot_free:
600 spin_unlock_irq(&mapping->tree_lock);
601 return 0;
602}
603
604/*
605 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
606 * someone else has a ref on the page, abort and return 0. If it was
607 * successfully detached, return 1. Assumes the caller has a single ref on
608 * this page.
609 */
610int remove_mapping(struct address_space *mapping, struct page *page)
611{
612 if (__remove_mapping(mapping, page, false)) {
613 /*
614 * Unfreezing the refcount with 1 rather than 2 effectively
615 * drops the pagecache ref for us without requiring another
616 * atomic operation.
617 */
618 page_unfreeze_refs(page, 1);
619 return 1;
620 }
621 return 0;
622}
623
624/**
625 * putback_lru_page - put previously isolated page onto appropriate LRU list
626 * @page: page to be put back to appropriate lru list
627 *
628 * Add previously isolated @page to appropriate LRU list.
629 * Page may still be unevictable for other reasons.
630 *
631 * lru_lock must not be held, interrupts must be enabled.
632 */
633void putback_lru_page(struct page *page)
634{
635 bool is_unevictable;
636 int was_unevictable = PageUnevictable(page);
637
638 VM_BUG_ON_PAGE(PageLRU(page), page);
639
640redo:
641 ClearPageUnevictable(page);
642
643 if (page_evictable(page)) {
644 /*
645 * For evictable pages, we can use the cache.
646 * In event of a race, worst case is we end up with an
647 * unevictable page on [in]active list.
648 * We know how to handle that.
649 */
650 is_unevictable = false;
651 lru_cache_add(page);
652 } else {
653 /*
654 * Put unevictable pages directly on zone's unevictable
655 * list.
656 */
657 is_unevictable = true;
658 add_page_to_unevictable_list(page);
659 /*
660 * When racing with an mlock or AS_UNEVICTABLE clearing
661 * (page is unlocked) make sure that if the other thread
662 * does not observe our setting of PG_lru and fails
663 * isolation/check_move_unevictable_pages,
664 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
665 * the page back to the evictable list.
666 *
667 * The other side is TestClearPageMlocked() or shmem_lock().
668 */
669 smp_mb();
670 }
671
672 /*
673 * page's status can change while we move it among lru. If an evictable
674 * page is on unevictable list, it never be freed. To avoid that,
675 * check after we added it to the list, again.
676 */
677 if (is_unevictable && page_evictable(page)) {
678 if (!isolate_lru_page(page)) {
679 put_page(page);
680 goto redo;
681 }
682 /* This means someone else dropped this page from LRU
683 * So, it will be freed or putback to LRU again. There is
684 * nothing to do here.
685 */
686 }
687
688 if (was_unevictable && !is_unevictable)
689 count_vm_event(UNEVICTABLE_PGRESCUED);
690 else if (!was_unevictable && is_unevictable)
691 count_vm_event(UNEVICTABLE_PGCULLED);
692
693 put_page(page); /* drop ref from isolate */
694}
695
696enum page_references {
697 PAGEREF_RECLAIM,
698 PAGEREF_RECLAIM_CLEAN,
699 PAGEREF_KEEP,
700 PAGEREF_ACTIVATE,
701};
702
703static enum page_references page_check_references(struct page *page,
704 struct scan_control *sc)
705{
706 int referenced_ptes, referenced_page;
707 unsigned long vm_flags;
708
709 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
710 &vm_flags);
711 referenced_page = TestClearPageReferenced(page);
712
713 /*
714 * Mlock lost the isolation race with us. Let try_to_unmap()
715 * move the page to the unevictable list.
716 */
717 if (vm_flags & VM_LOCKED)
718 return PAGEREF_RECLAIM;
719
720 if (referenced_ptes) {
721 if (PageSwapBacked(page))
722 return PAGEREF_ACTIVATE;
723 /*
724 * All mapped pages start out with page table
725 * references from the instantiating fault, so we need
726 * to look twice if a mapped file page is used more
727 * than once.
728 *
729 * Mark it and spare it for another trip around the
730 * inactive list. Another page table reference will
731 * lead to its activation.
732 *
733 * Note: the mark is set for activated pages as well
734 * so that recently deactivated but used pages are
735 * quickly recovered.
736 */
737 SetPageReferenced(page);
738
739 if (referenced_page || referenced_ptes > 1)
740 return PAGEREF_ACTIVATE;
741
742 /*
743 * Activate file-backed executable pages after first usage.
744 */
745 if (vm_flags & VM_EXEC)
746 return PAGEREF_ACTIVATE;
747
748 return PAGEREF_KEEP;
749 }
750
751 /* Reclaim if clean, defer dirty pages to writeback */
752 if (referenced_page && !PageSwapBacked(page))
753 return PAGEREF_RECLAIM_CLEAN;
754
755 return PAGEREF_RECLAIM;
756}
757
758/* Check if a page is dirty or under writeback */
759static void page_check_dirty_writeback(struct page *page,
760 bool *dirty, bool *writeback)
761{
762 struct address_space *mapping;
763
764 /*
765 * Anonymous pages are not handled by flushers and must be written
766 * from reclaim context. Do not stall reclaim based on them
767 */
768 if (!page_is_file_cache(page)) {
769 *dirty = false;
770 *writeback = false;
771 return;
772 }
773
774 /* By default assume that the page flags are accurate */
775 *dirty = PageDirty(page);
776 *writeback = PageWriteback(page);
777
778 /* Verify dirty/writeback state if the filesystem supports it */
779 if (!page_has_private(page))
780 return;
781
782 mapping = page_mapping(page);
783 if (mapping && mapping->a_ops->is_dirty_writeback)
784 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
785}
786
787/*
788 * shrink_page_list() returns the number of reclaimed pages
789 */
790static unsigned long shrink_page_list(struct list_head *page_list,
791 struct zone *zone,
792 struct scan_control *sc,
793 enum ttu_flags ttu_flags,
794 unsigned long *ret_nr_dirty,
795 unsigned long *ret_nr_unqueued_dirty,
796 unsigned long *ret_nr_congested,
797 unsigned long *ret_nr_writeback,
798 unsigned long *ret_nr_immediate,
799 bool force_reclaim)
800{
801 LIST_HEAD(ret_pages);
802 LIST_HEAD(free_pages);
803 int pgactivate = 0;
804 unsigned long nr_unqueued_dirty = 0;
805 unsigned long nr_dirty = 0;
806 unsigned long nr_congested = 0;
807 unsigned long nr_reclaimed = 0;
808 unsigned long nr_writeback = 0;
809 unsigned long nr_immediate = 0;
810
811 cond_resched();
812
813 mem_cgroup_uncharge_start();
814 while (!list_empty(page_list)) {
815 struct address_space *mapping;
816 struct page *page;
817 int may_enter_fs;
818 enum page_references references = PAGEREF_RECLAIM_CLEAN;
819 bool dirty, writeback;
820
821 cond_resched();
822
823 page = lru_to_page(page_list);
824 list_del(&page->lru);
825
826 if (!trylock_page(page))
827 goto keep;
828
829 VM_BUG_ON_PAGE(PageActive(page), page);
830 VM_BUG_ON_PAGE(page_zone(page) != zone, page);
831
832 sc->nr_scanned++;
833
834 if (unlikely(!page_evictable(page)))
835 goto cull_mlocked;
836
837 if (!sc->may_unmap && page_mapped(page))
838 goto keep_locked;
839
840 /* Double the slab pressure for mapped and swapcache pages */
841 if (page_mapped(page) || PageSwapCache(page))
842 sc->nr_scanned++;
843
844 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
845 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
846
847 /*
848 * The number of dirty pages determines if a zone is marked
849 * reclaim_congested which affects wait_iff_congested. kswapd
850 * will stall and start writing pages if the tail of the LRU
851 * is all dirty unqueued pages.
852 */
853 page_check_dirty_writeback(page, &dirty, &writeback);
854 if (dirty || writeback)
855 nr_dirty++;
856
857 if (dirty && !writeback)
858 nr_unqueued_dirty++;
859
860 /*
861 * Treat this page as congested if the underlying BDI is or if
862 * pages are cycling through the LRU so quickly that the
863 * pages marked for immediate reclaim are making it to the
864 * end of the LRU a second time.
865 */
866 mapping = page_mapping(page);
867 if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
868 (writeback && PageReclaim(page)))
869 nr_congested++;
870
871 /*
872 * If a page at the tail of the LRU is under writeback, there
873 * are three cases to consider.
874 *
875 * 1) If reclaim is encountering an excessive number of pages
876 * under writeback and this page is both under writeback and
877 * PageReclaim then it indicates that pages are being queued
878 * for IO but are being recycled through the LRU before the
879 * IO can complete. Waiting on the page itself risks an
880 * indefinite stall if it is impossible to writeback the
881 * page due to IO error or disconnected storage so instead
882 * note that the LRU is being scanned too quickly and the
883 * caller can stall after page list has been processed.
884 *
885 * 2) Global reclaim encounters a page, memcg encounters a
886 * page that is not marked for immediate reclaim or
887 * the caller does not have __GFP_IO. In this case mark
888 * the page for immediate reclaim and continue scanning.
889 *
890 * __GFP_IO is checked because a loop driver thread might
891 * enter reclaim, and deadlock if it waits on a page for
892 * which it is needed to do the write (loop masks off
893 * __GFP_IO|__GFP_FS for this reason); but more thought
894 * would probably show more reasons.
895 *
896 * Don't require __GFP_FS, since we're not going into the
897 * FS, just waiting on its writeback completion. Worryingly,
898 * ext4 gfs2 and xfs allocate pages with
899 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
900 * may_enter_fs here is liable to OOM on them.
901 *
902 * 3) memcg encounters a page that is not already marked
903 * PageReclaim. memcg does not have any dirty pages
904 * throttling so we could easily OOM just because too many
905 * pages are in writeback and there is nothing else to
906 * reclaim. Wait for the writeback to complete.
907 */
908 if (PageWriteback(page)) {
909 /* Case 1 above */
910 if (current_is_kswapd() &&
911 PageReclaim(page) &&
912 zone_is_reclaim_writeback(zone)) {
913 nr_immediate++;
914 goto keep_locked;
915
916 /* Case 2 above */
917 } else if (global_reclaim(sc) ||
918 !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
919 /*
920 * This is slightly racy - end_page_writeback()
921 * might have just cleared PageReclaim, then
922 * setting PageReclaim here end up interpreted
923 * as PageReadahead - but that does not matter
924 * enough to care. What we do want is for this
925 * page to have PageReclaim set next time memcg
926 * reclaim reaches the tests above, so it will
927 * then wait_on_page_writeback() to avoid OOM;
928 * and it's also appropriate in global reclaim.
929 */
930 SetPageReclaim(page);
931 nr_writeback++;
932
933 goto keep_locked;
934
935 /* Case 3 above */
936 } else {
937 wait_on_page_writeback(page);
938 }
939 }
940
941 if (!force_reclaim)
942 references = page_check_references(page, sc);
943
944 switch (references) {
945 case PAGEREF_ACTIVATE:
946 goto activate_locked;
947 case PAGEREF_KEEP:
948 goto keep_locked;
949 case PAGEREF_RECLAIM:
950 case PAGEREF_RECLAIM_CLEAN:
951 ; /* try to reclaim the page below */
952 }
953
954 /*
955 * Anonymous process memory has backing store?
956 * Try to allocate it some swap space here.
957 */
958 if (PageAnon(page) && !PageSwapCache(page)) {
959 if (!(sc->gfp_mask & __GFP_IO))
960 goto keep_locked;
961 if (!add_to_swap(page, page_list))
962 goto activate_locked;
963 may_enter_fs = 1;
964
965 /* Adding to swap updated mapping */
966 mapping = page_mapping(page);
967 }
968
969 /*
970 * The page is mapped into the page tables of one or more
971 * processes. Try to unmap it here.
972 */
973 if (page_mapped(page) && mapping) {
974 switch (try_to_unmap(page, ttu_flags)) {
975 case SWAP_FAIL:
976 goto activate_locked;
977 case SWAP_AGAIN:
978 goto keep_locked;
979 case SWAP_MLOCK:
980 goto cull_mlocked;
981 case SWAP_SUCCESS:
982 ; /* try to free the page below */
983 }
984 }
985
986 if (PageDirty(page)) {
987 /*
988 * Only kswapd can writeback filesystem pages to
989 * avoid risk of stack overflow but only writeback
990 * if many dirty pages have been encountered.
991 */
992 if (page_is_file_cache(page) &&
993 (!current_is_kswapd() ||
994 !zone_is_reclaim_dirty(zone))) {
995 /*
996 * Immediately reclaim when written back.
997 * Similar in principal to deactivate_page()
998 * except we already have the page isolated
999 * and know it's dirty
1000 */
1001 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
1002 SetPageReclaim(page);
1003
1004 goto keep_locked;
1005 }
1006
1007 if (references == PAGEREF_RECLAIM_CLEAN)
1008 goto keep_locked;
1009 if (!may_enter_fs)
1010 goto keep_locked;
1011 if (!sc->may_writepage)
1012 goto keep_locked;
1013
1014 /* Page is dirty, try to write it out here */
1015 switch (pageout(page, mapping, sc)) {
1016 case PAGE_KEEP:
1017 goto keep_locked;
1018 case PAGE_ACTIVATE:
1019 goto activate_locked;
1020 case PAGE_SUCCESS:
1021 if (PageWriteback(page))
1022 goto keep;
1023 if (PageDirty(page))
1024 goto keep;
1025
1026 /*
1027 * A synchronous write - probably a ramdisk. Go
1028 * ahead and try to reclaim the page.
1029 */
1030 if (!trylock_page(page))
1031 goto keep;
1032 if (PageDirty(page) || PageWriteback(page))
1033 goto keep_locked;
1034 mapping = page_mapping(page);
1035 case PAGE_CLEAN:
1036 ; /* try to free the page below */
1037 }
1038 }
1039
1040 /*
1041 * If the page has buffers, try to free the buffer mappings
1042 * associated with this page. If we succeed we try to free
1043 * the page as well.
1044 *
1045 * We do this even if the page is PageDirty().
1046 * try_to_release_page() does not perform I/O, but it is
1047 * possible for a page to have PageDirty set, but it is actually
1048 * clean (all its buffers are clean). This happens if the
1049 * buffers were written out directly, with submit_bh(). ext3
1050 * will do this, as well as the blockdev mapping.
1051 * try_to_release_page() will discover that cleanness and will
1052 * drop the buffers and mark the page clean - it can be freed.
1053 *
1054 * Rarely, pages can have buffers and no ->mapping. These are
1055 * the pages which were not successfully invalidated in
1056 * truncate_complete_page(). We try to drop those buffers here
1057 * and if that worked, and the page is no longer mapped into
1058 * process address space (page_count == 1) it can be freed.
1059 * Otherwise, leave the page on the LRU so it is swappable.
1060 */
1061 if (page_has_private(page)) {
1062 if (!try_to_release_page(page, sc->gfp_mask))
1063 goto activate_locked;
1064 if (!mapping && page_count(page) == 1) {
1065 unlock_page(page);
1066 if (put_page_testzero(page))
1067 goto free_it;
1068 else {
1069 /*
1070 * rare race with speculative reference.
1071 * the speculative reference will free
1072 * this page shortly, so we may
1073 * increment nr_reclaimed here (and
1074 * leave it off the LRU).
1075 */
1076 nr_reclaimed++;
1077 continue;
1078 }
1079 }
1080 }
1081
1082 if (!mapping || !__remove_mapping(mapping, page, true))
1083 goto keep_locked;
1084
1085 /*
1086 * At this point, we have no other references and there is
1087 * no way to pick any more up (removed from LRU, removed
1088 * from pagecache). Can use non-atomic bitops now (and
1089 * we obviously don't have to worry about waking up a process
1090 * waiting on the page lock, because there are no references.
1091 */
1092 __clear_page_locked(page);
1093free_it:
1094 nr_reclaimed++;
1095
1096 /*
1097 * Is there need to periodically free_page_list? It would
1098 * appear not as the counts should be low
1099 */
1100 list_add(&page->lru, &free_pages);
1101 continue;
1102
1103cull_mlocked:
1104 if (PageSwapCache(page))
1105 try_to_free_swap(page);
1106 unlock_page(page);
1107 putback_lru_page(page);
1108 continue;
1109
1110activate_locked:
1111 /* Not a candidate for swapping, so reclaim swap space. */
1112 if (PageSwapCache(page) && vm_swap_full())
1113 try_to_free_swap(page);
1114 VM_BUG_ON_PAGE(PageActive(page), page);
1115 SetPageActive(page);
1116 pgactivate++;
1117keep_locked:
1118 unlock_page(page);
1119keep:
1120 list_add(&page->lru, &ret_pages);
1121 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1122 }
1123
1124 free_hot_cold_page_list(&free_pages, 1);
1125
1126 list_splice(&ret_pages, page_list);
1127 count_vm_events(PGACTIVATE, pgactivate);
1128 mem_cgroup_uncharge_end();
1129 *ret_nr_dirty += nr_dirty;
1130 *ret_nr_congested += nr_congested;
1131 *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1132 *ret_nr_writeback += nr_writeback;
1133 *ret_nr_immediate += nr_immediate;
1134 return nr_reclaimed;
1135}
1136
1137unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1138 struct list_head *page_list)
1139{
1140 struct scan_control sc = {
1141 .gfp_mask = GFP_KERNEL,
1142 .priority = DEF_PRIORITY,
1143 .may_unmap = 1,
1144 };
1145 unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1146 struct page *page, *next;
1147 LIST_HEAD(clean_pages);
1148
1149 list_for_each_entry_safe(page, next, page_list, lru) {
1150 if (page_is_file_cache(page) && !PageDirty(page) &&
1151 !isolated_balloon_page(page)) {
1152 ClearPageActive(page);
1153 list_move(&page->lru, &clean_pages);
1154 }
1155 }
1156
1157 ret = shrink_page_list(&clean_pages, zone, &sc,
1158 TTU_UNMAP|TTU_IGNORE_ACCESS,
1159 &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1160 list_splice(&clean_pages, page_list);
1161 mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
1162 return ret;
1163}
1164
1165/*
1166 * Attempt to remove the specified page from its LRU. Only take this page
1167 * if it is of the appropriate PageActive status. Pages which are being
1168 * freed elsewhere are also ignored.
1169 *
1170 * page: page to consider
1171 * mode: one of the LRU isolation modes defined above
1172 *
1173 * returns 0 on success, -ve errno on failure.
1174 */
1175int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1176{
1177 int ret = -EINVAL;
1178
1179 /* Only take pages on the LRU. */
1180 if (!PageLRU(page))
1181 return ret;
1182
1183 /* Compaction should not handle unevictable pages but CMA can do so */
1184 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1185 return ret;
1186
1187 ret = -EBUSY;
1188
1189 /*
1190 * To minimise LRU disruption, the caller can indicate that it only
1191 * wants to isolate pages it will be able to operate on without
1192 * blocking - clean pages for the most part.
1193 *
1194 * ISOLATE_CLEAN means that only clean pages should be isolated. This
1195 * is used by reclaim when it is cannot write to backing storage
1196 *
1197 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1198 * that it is possible to migrate without blocking
1199 */
1200 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1201 /* All the caller can do on PageWriteback is block */
1202 if (PageWriteback(page))
1203 return ret;
1204
1205 if (PageDirty(page)) {
1206 struct address_space *mapping;
1207
1208 /* ISOLATE_CLEAN means only clean pages */
1209 if (mode & ISOLATE_CLEAN)
1210 return ret;
1211
1212 /*
1213 * Only pages without mappings or that have a
1214 * ->migratepage callback are possible to migrate
1215 * without blocking
1216 */
1217 mapping = page_mapping(page);
1218 if (mapping && !mapping->a_ops->migratepage)
1219 return ret;
1220 }
1221 }
1222
1223 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1224 return ret;
1225
1226 if (likely(get_page_unless_zero(page))) {
1227 /*
1228 * Be careful not to clear PageLRU until after we're
1229 * sure the page is not being freed elsewhere -- the
1230 * page release code relies on it.
1231 */
1232 ClearPageLRU(page);
1233 ret = 0;
1234 }
1235
1236 return ret;
1237}
1238
1239/*
1240 * zone->lru_lock is heavily contended. Some of the functions that
1241 * shrink the lists perform better by taking out a batch of pages
1242 * and working on them outside the LRU lock.
1243 *
1244 * For pagecache intensive workloads, this function is the hottest
1245 * spot in the kernel (apart from copy_*_user functions).
1246 *
1247 * Appropriate locks must be held before calling this function.
1248 *
1249 * @nr_to_scan: The number of pages to look through on the list.
1250 * @lruvec: The LRU vector to pull pages from.
1251 * @dst: The temp list to put pages on to.
1252 * @nr_scanned: The number of pages that were scanned.
1253 * @sc: The scan_control struct for this reclaim session
1254 * @mode: One of the LRU isolation modes
1255 * @lru: LRU list id for isolating
1256 *
1257 * returns how many pages were moved onto *@dst.
1258 */
1259static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1260 struct lruvec *lruvec, struct list_head *dst,
1261 unsigned long *nr_scanned, struct scan_control *sc,
1262 isolate_mode_t mode, enum lru_list lru)
1263{
1264 struct list_head *src = &lruvec->lists[lru];
1265 unsigned long nr_taken = 0;
1266 unsigned long scan;
1267
1268 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1269 struct page *page;
1270 int nr_pages;
1271
1272 page = lru_to_page(src);
1273 prefetchw_prev_lru_page(page, src, flags);
1274
1275 VM_BUG_ON_PAGE(!PageLRU(page), page);
1276
1277 switch (__isolate_lru_page(page, mode)) {
1278 case 0:
1279 nr_pages = hpage_nr_pages(page);
1280 mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1281 list_move(&page->lru, dst);
1282 nr_taken += nr_pages;
1283 break;
1284
1285 case -EBUSY:
1286 /* else it is being freed elsewhere */
1287 list_move(&page->lru, src);
1288 continue;
1289
1290 default:
1291 BUG();
1292 }
1293 }
1294
1295 *nr_scanned = scan;
1296 trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1297 nr_taken, mode, is_file_lru(lru));
1298 return nr_taken;
1299}
1300
1301/**
1302 * isolate_lru_page - tries to isolate a page from its LRU list
1303 * @page: page to isolate from its LRU list
1304 *
1305 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1306 * vmstat statistic corresponding to whatever LRU list the page was on.
1307 *
1308 * Returns 0 if the page was removed from an LRU list.
1309 * Returns -EBUSY if the page was not on an LRU list.
1310 *
1311 * The returned page will have PageLRU() cleared. If it was found on
1312 * the active list, it will have PageActive set. If it was found on
1313 * the unevictable list, it will have the PageUnevictable bit set. That flag
1314 * may need to be cleared by the caller before letting the page go.
1315 *
1316 * The vmstat statistic corresponding to the list on which the page was
1317 * found will be decremented.
1318 *
1319 * Restrictions:
1320 * (1) Must be called with an elevated refcount on the page. This is a
1321 * fundamentnal difference from isolate_lru_pages (which is called
1322 * without a stable reference).
1323 * (2) the lru_lock must not be held.
1324 * (3) interrupts must be enabled.
1325 */
1326int isolate_lru_page(struct page *page)
1327{
1328 int ret = -EBUSY;
1329
1330 VM_BUG_ON_PAGE(!page_count(page), page);
1331
1332 if (PageLRU(page)) {
1333 struct zone *zone = page_zone(page);
1334 struct lruvec *lruvec;
1335
1336 spin_lock_irq(&zone->lru_lock);
1337 lruvec = mem_cgroup_page_lruvec(page, zone);
1338 if (PageLRU(page)) {
1339 int lru = page_lru(page);
1340 get_page(page);
1341 ClearPageLRU(page);
1342 del_page_from_lru_list(page, lruvec, lru);
1343 ret = 0;
1344 }
1345 spin_unlock_irq(&zone->lru_lock);
1346 }
1347 return ret;
1348}
1349
1350/*
1351 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1352 * then get resheduled. When there are massive number of tasks doing page
1353 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1354 * the LRU list will go small and be scanned faster than necessary, leading to
1355 * unnecessary swapping, thrashing and OOM.
1356 */
1357static int too_many_isolated(struct zone *zone, int file,
1358 struct scan_control *sc)
1359{
1360 unsigned long inactive, isolated;
1361
1362 if (current_is_kswapd())
1363 return 0;
1364
1365 if (!global_reclaim(sc))
1366 return 0;
1367
1368 if (file) {
1369 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1370 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1371 } else {
1372 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1373 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1374 }
1375
1376 /*
1377 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1378 * won't get blocked by normal direct-reclaimers, forming a circular
1379 * deadlock.
1380 */
1381 if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1382 inactive >>= 3;
1383
1384 return isolated > inactive;
1385}
1386
1387static noinline_for_stack void
1388putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1389{
1390 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1391 struct zone *zone = lruvec_zone(lruvec);
1392 LIST_HEAD(pages_to_free);
1393
1394 /*
1395 * Put back any unfreeable pages.
1396 */
1397 while (!list_empty(page_list)) {
1398 struct page *page = lru_to_page(page_list);
1399 int lru;
1400
1401 VM_BUG_ON_PAGE(PageLRU(page), page);
1402 list_del(&page->lru);
1403 if (unlikely(!page_evictable(page))) {
1404 spin_unlock_irq(&zone->lru_lock);
1405 putback_lru_page(page);
1406 spin_lock_irq(&zone->lru_lock);
1407 continue;
1408 }
1409
1410 lruvec = mem_cgroup_page_lruvec(page, zone);
1411
1412 SetPageLRU(page);
1413 lru = page_lru(page);
1414 add_page_to_lru_list(page, lruvec, lru);
1415
1416 if (is_active_lru(lru)) {
1417 int file = is_file_lru(lru);
1418 int numpages = hpage_nr_pages(page);
1419 reclaim_stat->recent_rotated[file] += numpages;
1420 }
1421 if (put_page_testzero(page)) {
1422 __ClearPageLRU(page);
1423 __ClearPageActive(page);
1424 del_page_from_lru_list(page, lruvec, lru);
1425
1426 if (unlikely(PageCompound(page))) {
1427 spin_unlock_irq(&zone->lru_lock);
1428 (*get_compound_page_dtor(page))(page);
1429 spin_lock_irq(&zone->lru_lock);
1430 } else
1431 list_add(&page->lru, &pages_to_free);
1432 }
1433 }
1434
1435 /*
1436 * To save our caller's stack, now use input list for pages to free.
1437 */
1438 list_splice(&pages_to_free, page_list);
1439}
1440
1441/*
1442 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1443 * of reclaimed pages
1444 */
1445static noinline_for_stack unsigned long
1446shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1447 struct scan_control *sc, enum lru_list lru)
1448{
1449 LIST_HEAD(page_list);
1450 unsigned long nr_scanned;
1451 unsigned long nr_reclaimed = 0;
1452 unsigned long nr_taken;
1453 unsigned long nr_dirty = 0;
1454 unsigned long nr_congested = 0;
1455 unsigned long nr_unqueued_dirty = 0;
1456 unsigned long nr_writeback = 0;
1457 unsigned long nr_immediate = 0;
1458 isolate_mode_t isolate_mode = 0;
1459 int file = is_file_lru(lru);
1460 struct zone *zone = lruvec_zone(lruvec);
1461 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1462
1463 while (unlikely(too_many_isolated(zone, file, sc))) {
1464 congestion_wait(BLK_RW_ASYNC, HZ/10);
1465
1466 /* We are about to die and free our memory. Return now. */
1467 if (fatal_signal_pending(current))
1468 return SWAP_CLUSTER_MAX;
1469 }
1470
1471 lru_add_drain();
1472
1473 if (!sc->may_unmap)
1474 isolate_mode |= ISOLATE_UNMAPPED;
1475 if (!sc->may_writepage)
1476 isolate_mode |= ISOLATE_CLEAN;
1477
1478 spin_lock_irq(&zone->lru_lock);
1479
1480 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1481 &nr_scanned, sc, isolate_mode, lru);
1482
1483 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1484 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1485
1486 if (global_reclaim(sc)) {
1487 zone->pages_scanned += nr_scanned;
1488 if (current_is_kswapd())
1489 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1490 else
1491 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1492 }
1493 spin_unlock_irq(&zone->lru_lock);
1494
1495 if (nr_taken == 0)
1496 return 0;
1497
1498 nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1499 &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1500 &nr_writeback, &nr_immediate,
1501 false);
1502
1503 spin_lock_irq(&zone->lru_lock);
1504
1505 reclaim_stat->recent_scanned[file] += nr_taken;
1506
1507 if (global_reclaim(sc)) {
1508 if (current_is_kswapd())
1509 __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1510 nr_reclaimed);
1511 else
1512 __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1513 nr_reclaimed);
1514 }
1515
1516 putback_inactive_pages(lruvec, &page_list);
1517
1518 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1519
1520 spin_unlock_irq(&zone->lru_lock);
1521
1522 free_hot_cold_page_list(&page_list, 1);
1523
1524 /*
1525 * If reclaim is isolating dirty pages under writeback, it implies
1526 * that the long-lived page allocation rate is exceeding the page
1527 * laundering rate. Either the global limits are not being effective
1528 * at throttling processes due to the page distribution throughout
1529 * zones or there is heavy usage of a slow backing device. The
1530 * only option is to throttle from reclaim context which is not ideal
1531 * as there is no guarantee the dirtying process is throttled in the
1532 * same way balance_dirty_pages() manages.
1533 *
1534 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1535 * of pages under pages flagged for immediate reclaim and stall if any
1536 * are encountered in the nr_immediate check below.
1537 */
1538 if (nr_writeback && nr_writeback == nr_taken)
1539 zone_set_flag(zone, ZONE_WRITEBACK);
1540
1541 /*
1542 * memcg will stall in page writeback so only consider forcibly
1543 * stalling for global reclaim
1544 */
1545 if (global_reclaim(sc)) {
1546 /*
1547 * Tag a zone as congested if all the dirty pages scanned were
1548 * backed by a congested BDI and wait_iff_congested will stall.
1549 */
1550 if (nr_dirty && nr_dirty == nr_congested)
1551 zone_set_flag(zone, ZONE_CONGESTED);
1552
1553 /*
1554 * If dirty pages are scanned that are not queued for IO, it
1555 * implies that flushers are not keeping up. In this case, flag
1556 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
1557 * pages from reclaim context. It will forcibly stall in the
1558 * next check.
1559 */
1560 if (nr_unqueued_dirty == nr_taken)
1561 zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
1562
1563 /*
1564 * In addition, if kswapd scans pages marked marked for
1565 * immediate reclaim and under writeback (nr_immediate), it
1566 * implies that pages are cycling through the LRU faster than
1567 * they are written so also forcibly stall.
1568 */
1569 if (nr_unqueued_dirty == nr_taken || nr_immediate)
1570 congestion_wait(BLK_RW_ASYNC, HZ/10);
1571 }
1572
1573 /*
1574 * Stall direct reclaim for IO completions if underlying BDIs or zone
1575 * is congested. Allow kswapd to continue until it starts encountering
1576 * unqueued dirty pages or cycling through the LRU too quickly.
1577 */
1578 if (!sc->hibernation_mode && !current_is_kswapd())
1579 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1580
1581 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1582 zone_idx(zone),
1583 nr_scanned, nr_reclaimed,
1584 sc->priority,
1585 trace_shrink_flags(file));
1586 return nr_reclaimed;
1587}
1588
1589/*
1590 * This moves pages from the active list to the inactive list.
1591 *
1592 * We move them the other way if the page is referenced by one or more
1593 * processes, from rmap.
1594 *
1595 * If the pages are mostly unmapped, the processing is fast and it is
1596 * appropriate to hold zone->lru_lock across the whole operation. But if
1597 * the pages are mapped, the processing is slow (page_referenced()) so we
1598 * should drop zone->lru_lock around each page. It's impossible to balance
1599 * this, so instead we remove the pages from the LRU while processing them.
1600 * It is safe to rely on PG_active against the non-LRU pages in here because
1601 * nobody will play with that bit on a non-LRU page.
1602 *
1603 * The downside is that we have to touch page->_count against each page.
1604 * But we had to alter page->flags anyway.
1605 */
1606
1607static void move_active_pages_to_lru(struct lruvec *lruvec,
1608 struct list_head *list,
1609 struct list_head *pages_to_free,
1610 enum lru_list lru)
1611{
1612 struct zone *zone = lruvec_zone(lruvec);
1613 unsigned long pgmoved = 0;
1614 struct page *page;
1615 int nr_pages;
1616
1617 while (!list_empty(list)) {
1618 page = lru_to_page(list);
1619 lruvec = mem_cgroup_page_lruvec(page, zone);
1620
1621 VM_BUG_ON_PAGE(PageLRU(page), page);
1622 SetPageLRU(page);
1623
1624 nr_pages = hpage_nr_pages(page);
1625 mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1626 list_move(&page->lru, &lruvec->lists[lru]);
1627 pgmoved += nr_pages;
1628
1629 if (put_page_testzero(page)) {
1630 __ClearPageLRU(page);
1631 __ClearPageActive(page);
1632 del_page_from_lru_list(page, lruvec, lru);
1633
1634 if (unlikely(PageCompound(page))) {
1635 spin_unlock_irq(&zone->lru_lock);
1636 (*get_compound_page_dtor(page))(page);
1637 spin_lock_irq(&zone->lru_lock);
1638 } else
1639 list_add(&page->lru, pages_to_free);
1640 }
1641 }
1642 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1643 if (!is_active_lru(lru))
1644 __count_vm_events(PGDEACTIVATE, pgmoved);
1645}
1646
1647static void shrink_active_list(unsigned long nr_to_scan,
1648 struct lruvec *lruvec,
1649 struct scan_control *sc,
1650 enum lru_list lru)
1651{
1652 unsigned long nr_taken;
1653 unsigned long nr_scanned;
1654 unsigned long vm_flags;
1655 LIST_HEAD(l_hold); /* The pages which were snipped off */
1656 LIST_HEAD(l_active);
1657 LIST_HEAD(l_inactive);
1658 struct page *page;
1659 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1660 unsigned long nr_rotated = 0;
1661 isolate_mode_t isolate_mode = 0;
1662 int file = is_file_lru(lru);
1663 struct zone *zone = lruvec_zone(lruvec);
1664
1665 lru_add_drain();
1666
1667 if (!sc->may_unmap)
1668 isolate_mode |= ISOLATE_UNMAPPED;
1669 if (!sc->may_writepage)
1670 isolate_mode |= ISOLATE_CLEAN;
1671
1672 spin_lock_irq(&zone->lru_lock);
1673
1674 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1675 &nr_scanned, sc, isolate_mode, lru);
1676 if (global_reclaim(sc))
1677 zone->pages_scanned += nr_scanned;
1678
1679 reclaim_stat->recent_scanned[file] += nr_taken;
1680
1681 __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1682 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1683 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1684 spin_unlock_irq(&zone->lru_lock);
1685
1686 while (!list_empty(&l_hold)) {
1687 cond_resched();
1688 page = lru_to_page(&l_hold);
1689 list_del(&page->lru);
1690
1691 if (unlikely(!page_evictable(page))) {
1692 putback_lru_page(page);
1693 continue;
1694 }
1695
1696 if (unlikely(buffer_heads_over_limit)) {
1697 if (page_has_private(page) && trylock_page(page)) {
1698 if (page_has_private(page))
1699 try_to_release_page(page, 0);
1700 unlock_page(page);
1701 }
1702 }
1703
1704 if (page_referenced(page, 0, sc->target_mem_cgroup,
1705 &vm_flags)) {
1706 nr_rotated += hpage_nr_pages(page);
1707 /*
1708 * Identify referenced, file-backed active pages and
1709 * give them one more trip around the active list. So
1710 * that executable code get better chances to stay in
1711 * memory under moderate memory pressure. Anon pages
1712 * are not likely to be evicted by use-once streaming
1713 * IO, plus JVM can create lots of anon VM_EXEC pages,
1714 * so we ignore them here.
1715 */
1716 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1717 list_add(&page->lru, &l_active);
1718 continue;
1719 }
1720 }
1721
1722 ClearPageActive(page); /* we are de-activating */
1723 list_add(&page->lru, &l_inactive);
1724 }
1725
1726 /*
1727 * Move pages back to the lru list.
1728 */
1729 spin_lock_irq(&zone->lru_lock);
1730 /*
1731 * Count referenced pages from currently used mappings as rotated,
1732 * even though only some of them are actually re-activated. This
1733 * helps balance scan pressure between file and anonymous pages in
1734 * get_scan_ratio.
1735 */
1736 reclaim_stat->recent_rotated[file] += nr_rotated;
1737
1738 move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1739 move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1740 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1741 spin_unlock_irq(&zone->lru_lock);
1742
1743 free_hot_cold_page_list(&l_hold, 1);
1744}
1745
1746#ifdef CONFIG_SWAP
1747static int inactive_anon_is_low_global(struct zone *zone)
1748{
1749 unsigned long active, inactive;
1750
1751 active = zone_page_state(zone, NR_ACTIVE_ANON);
1752 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1753
1754 if (inactive * zone->inactive_ratio < active)
1755 return 1;
1756
1757 return 0;
1758}
1759
1760/**
1761 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1762 * @lruvec: LRU vector to check
1763 *
1764 * Returns true if the zone does not have enough inactive anon pages,
1765 * meaning some active anon pages need to be deactivated.
1766 */
1767static int inactive_anon_is_low(struct lruvec *lruvec)
1768{
1769 /*
1770 * If we don't have swap space, anonymous page deactivation
1771 * is pointless.
1772 */
1773 if (!total_swap_pages)
1774 return 0;
1775
1776 if (!mem_cgroup_disabled())
1777 return mem_cgroup_inactive_anon_is_low(lruvec);
1778
1779 return inactive_anon_is_low_global(lruvec_zone(lruvec));
1780}
1781#else
1782static inline int inactive_anon_is_low(struct lruvec *lruvec)
1783{
1784 return 0;
1785}
1786#endif
1787
1788/**
1789 * inactive_file_is_low - check if file pages need to be deactivated
1790 * @lruvec: LRU vector to check
1791 *
1792 * When the system is doing streaming IO, memory pressure here
1793 * ensures that active file pages get deactivated, until more
1794 * than half of the file pages are on the inactive list.
1795 *
1796 * Once we get to that situation, protect the system's working
1797 * set from being evicted by disabling active file page aging.
1798 *
1799 * This uses a different ratio than the anonymous pages, because
1800 * the page cache uses a use-once replacement algorithm.
1801 */
1802static int inactive_file_is_low(struct lruvec *lruvec)
1803{
1804 unsigned long inactive;
1805 unsigned long active;
1806
1807 inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1808 active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1809
1810 return active > inactive;
1811}
1812
1813static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1814{
1815 if (is_file_lru(lru))
1816 return inactive_file_is_low(lruvec);
1817 else
1818 return inactive_anon_is_low(lruvec);
1819}
1820
1821static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1822 struct lruvec *lruvec, struct scan_control *sc)
1823{
1824 if (is_active_lru(lru)) {
1825 if (inactive_list_is_low(lruvec, lru))
1826 shrink_active_list(nr_to_scan, lruvec, sc, lru);
1827 return 0;
1828 }
1829
1830 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1831}
1832
1833static int vmscan_swappiness(struct scan_control *sc)
1834{
1835 if (global_reclaim(sc))
1836 return vm_swappiness;
1837 return mem_cgroup_swappiness(sc->target_mem_cgroup);
1838}
1839
1840enum scan_balance {
1841 SCAN_EQUAL,
1842 SCAN_FRACT,
1843 SCAN_ANON,
1844 SCAN_FILE,
1845};
1846
1847/*
1848 * Determine how aggressively the anon and file LRU lists should be
1849 * scanned. The relative value of each set of LRU lists is determined
1850 * by looking at the fraction of the pages scanned we did rotate back
1851 * onto the active list instead of evict.
1852 *
1853 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1854 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1855 */
1856static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1857 unsigned long *nr)
1858{
1859 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1860 u64 fraction[2];
1861 u64 denominator = 0; /* gcc */
1862 struct zone *zone = lruvec_zone(lruvec);
1863 unsigned long anon_prio, file_prio;
1864 enum scan_balance scan_balance;
1865 unsigned long anon, file;
1866 bool force_scan = false;
1867 unsigned long ap, fp;
1868 enum lru_list lru;
1869
1870 /*
1871 * If the zone or memcg is small, nr[l] can be 0. This
1872 * results in no scanning on this priority and a potential
1873 * priority drop. Global direct reclaim can go to the next
1874 * zone and tends to have no problems. Global kswapd is for
1875 * zone balancing and it needs to scan a minimum amount. When
1876 * reclaiming for a memcg, a priority drop can cause high
1877 * latencies, so it's better to scan a minimum amount there as
1878 * well.
1879 */
1880 if (current_is_kswapd() && !zone_reclaimable(zone))
1881 force_scan = true;
1882 if (!global_reclaim(sc))
1883 force_scan = true;
1884
1885 /* If we have no swap space, do not bother scanning anon pages. */
1886 if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1887 scan_balance = SCAN_FILE;
1888 goto out;
1889 }
1890
1891 /*
1892 * Global reclaim will swap to prevent OOM even with no
1893 * swappiness, but memcg users want to use this knob to
1894 * disable swapping for individual groups completely when
1895 * using the memory controller's swap limit feature would be
1896 * too expensive.
1897 */
1898 if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1899 scan_balance = SCAN_FILE;
1900 goto out;
1901 }
1902
1903 /*
1904 * Do not apply any pressure balancing cleverness when the
1905 * system is close to OOM, scan both anon and file equally
1906 * (unless the swappiness setting disagrees with swapping).
1907 */
1908 if (!sc->priority && vmscan_swappiness(sc)) {
1909 scan_balance = SCAN_EQUAL;
1910 goto out;
1911 }
1912
1913 anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1914 get_lru_size(lruvec, LRU_INACTIVE_ANON);
1915 file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1916 get_lru_size(lruvec, LRU_INACTIVE_FILE);
1917
1918 /*
1919 * Prevent the reclaimer from falling into the cache trap: as
1920 * cache pages start out inactive, every cache fault will tip
1921 * the scan balance towards the file LRU. And as the file LRU
1922 * shrinks, so does the window for rotation from references.
1923 * This means we have a runaway feedback loop where a tiny
1924 * thrashing file LRU becomes infinitely more attractive than
1925 * anon pages. Try to detect this based on file LRU size.
1926 */
1927 if (global_reclaim(sc)) {
1928 unsigned long free = zone_page_state(zone, NR_FREE_PAGES);
1929
1930 if (unlikely(file + free <= high_wmark_pages(zone))) {
1931 scan_balance = SCAN_ANON;
1932 goto out;
1933 }
1934 }
1935
1936 /*
1937 * There is enough inactive page cache, do not reclaim
1938 * anything from the anonymous working set right now.
1939 */
1940 if (!inactive_file_is_low(lruvec)) {
1941 scan_balance = SCAN_FILE;
1942 goto out;
1943 }
1944
1945 scan_balance = SCAN_FRACT;
1946
1947 /*
1948 * With swappiness at 100, anonymous and file have the same priority.
1949 * This scanning priority is essentially the inverse of IO cost.
1950 */
1951 anon_prio = vmscan_swappiness(sc);
1952 file_prio = 200 - anon_prio;
1953
1954 /*
1955 * OK, so we have swap space and a fair amount of page cache
1956 * pages. We use the recently rotated / recently scanned
1957 * ratios to determine how valuable each cache is.
1958 *
1959 * Because workloads change over time (and to avoid overflow)
1960 * we keep these statistics as a floating average, which ends
1961 * up weighing recent references more than old ones.
1962 *
1963 * anon in [0], file in [1]
1964 */
1965 spin_lock_irq(&zone->lru_lock);
1966 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1967 reclaim_stat->recent_scanned[0] /= 2;
1968 reclaim_stat->recent_rotated[0] /= 2;
1969 }
1970
1971 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1972 reclaim_stat->recent_scanned[1] /= 2;
1973 reclaim_stat->recent_rotated[1] /= 2;
1974 }
1975
1976 /*
1977 * The amount of pressure on anon vs file pages is inversely
1978 * proportional to the fraction of recently scanned pages on
1979 * each list that were recently referenced and in active use.
1980 */
1981 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1982 ap /= reclaim_stat->recent_rotated[0] + 1;
1983
1984 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1985 fp /= reclaim_stat->recent_rotated[1] + 1;
1986 spin_unlock_irq(&zone->lru_lock);
1987
1988 fraction[0] = ap;
1989 fraction[1] = fp;
1990 denominator = ap + fp + 1;
1991out:
1992 for_each_evictable_lru(lru) {
1993 int file = is_file_lru(lru);
1994 unsigned long size;
1995 unsigned long scan;
1996
1997 size = get_lru_size(lruvec, lru);
1998 scan = size >> sc->priority;
1999
2000 if (!scan && force_scan)
2001 scan = min(size, SWAP_CLUSTER_MAX);
2002
2003 switch (scan_balance) {
2004 case SCAN_EQUAL:
2005 /* Scan lists relative to size */
2006 break;
2007 case SCAN_FRACT:
2008 /*
2009 * Scan types proportional to swappiness and
2010 * their relative recent reclaim efficiency.
2011 */
2012 scan = div64_u64(scan * fraction[file], denominator);
2013 break;
2014 case SCAN_FILE:
2015 case SCAN_ANON:
2016 /* Scan one type exclusively */
2017 if ((scan_balance == SCAN_FILE) != file)
2018 scan = 0;
2019 break;
2020 default:
2021 /* Look ma, no brain */
2022 BUG();
2023 }
2024 nr[lru] = scan;
2025 }
2026}
2027
2028/*
2029 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
2030 */
2031static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
2032{
2033 unsigned long nr[NR_LRU_LISTS];
2034 unsigned long targets[NR_LRU_LISTS];
2035 unsigned long nr_to_scan;
2036 enum lru_list lru;
2037 unsigned long nr_reclaimed = 0;
2038 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2039 struct blk_plug plug;
2040 bool scan_adjusted = false;
2041
2042 get_scan_count(lruvec, sc, nr);
2043
2044 /* Record the original scan target for proportional adjustments later */
2045 memcpy(targets, nr, sizeof(nr));
2046
2047 blk_start_plug(&plug);
2048 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2049 nr[LRU_INACTIVE_FILE]) {
2050 unsigned long nr_anon, nr_file, percentage;
2051 unsigned long nr_scanned;
2052
2053 for_each_evictable_lru(lru) {
2054 if (nr[lru]) {
2055 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2056 nr[lru] -= nr_to_scan;
2057
2058 nr_reclaimed += shrink_list(lru, nr_to_scan,
2059 lruvec, sc);
2060 }
2061 }
2062
2063 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2064 continue;
2065
2066 /*
2067 * For global direct reclaim, reclaim only the number of pages
2068 * requested. Less care is taken to scan proportionally as it
2069 * is more important to minimise direct reclaim stall latency
2070 * than it is to properly age the LRU lists.
2071 */
2072 if (global_reclaim(sc) && !current_is_kswapd())
2073 break;
2074
2075 /*
2076 * For kswapd and memcg, reclaim at least the number of pages
2077 * requested. Ensure that the anon and file LRUs shrink
2078 * proportionally what was requested by get_scan_count(). We
2079 * stop reclaiming one LRU and reduce the amount scanning
2080 * proportional to the original scan target.
2081 */
2082 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2083 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2084
2085 if (nr_file > nr_anon) {
2086 unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2087 targets[LRU_ACTIVE_ANON] + 1;
2088 lru = LRU_BASE;
2089 percentage = nr_anon * 100 / scan_target;
2090 } else {
2091 unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2092 targets[LRU_ACTIVE_FILE] + 1;
2093 lru = LRU_FILE;
2094 percentage = nr_file * 100 / scan_target;
2095 }
2096
2097 /* Stop scanning the smaller of the LRU */
2098 nr[lru] = 0;
2099 nr[lru + LRU_ACTIVE] = 0;
2100
2101 /*
2102 * Recalculate the other LRU scan count based on its original
2103 * scan target and the percentage scanning already complete
2104 */
2105 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2106 nr_scanned = targets[lru] - nr[lru];
2107 nr[lru] = targets[lru] * (100 - percentage) / 100;
2108 nr[lru] -= min(nr[lru], nr_scanned);
2109
2110 lru += LRU_ACTIVE;
2111 nr_scanned = targets[lru] - nr[lru];
2112 nr[lru] = targets[lru] * (100 - percentage) / 100;
2113 nr[lru] -= min(nr[lru], nr_scanned);
2114
2115 scan_adjusted = true;
2116 }
2117 blk_finish_plug(&plug);
2118 sc->nr_reclaimed += nr_reclaimed;
2119
2120 /*
2121 * Even if we did not try to evict anon pages at all, we want to
2122 * rebalance the anon lru active/inactive ratio.
2123 */
2124 if (inactive_anon_is_low(lruvec))
2125 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2126 sc, LRU_ACTIVE_ANON);
2127
2128 throttle_vm_writeout(sc->gfp_mask);
2129}
2130
2131/* Use reclaim/compaction for costly allocs or under memory pressure */
2132static bool in_reclaim_compaction(struct scan_control *sc)
2133{
2134 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2135 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2136 sc->priority < DEF_PRIORITY - 2))
2137 return true;
2138
2139 return false;
2140}
2141
2142/*
2143 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2144 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2145 * true if more pages should be reclaimed such that when the page allocator
2146 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2147 * It will give up earlier than that if there is difficulty reclaiming pages.
2148 */
2149static inline bool should_continue_reclaim(struct zone *zone,
2150 unsigned long nr_reclaimed,
2151 unsigned long nr_scanned,
2152 struct scan_control *sc)
2153{
2154 unsigned long pages_for_compaction;
2155 unsigned long inactive_lru_pages;
2156
2157 /* If not in reclaim/compaction mode, stop */
2158 if (!in_reclaim_compaction(sc))
2159 return false;
2160
2161 /* Consider stopping depending on scan and reclaim activity */
2162 if (sc->gfp_mask & __GFP_REPEAT) {
2163 /*
2164 * For __GFP_REPEAT allocations, stop reclaiming if the
2165 * full LRU list has been scanned and we are still failing
2166 * to reclaim pages. This full LRU scan is potentially
2167 * expensive but a __GFP_REPEAT caller really wants to succeed
2168 */
2169 if (!nr_reclaimed && !nr_scanned)
2170 return false;
2171 } else {
2172 /*
2173 * For non-__GFP_REPEAT allocations which can presumably
2174 * fail without consequence, stop if we failed to reclaim
2175 * any pages from the last SWAP_CLUSTER_MAX number of
2176 * pages that were scanned. This will return to the
2177 * caller faster at the risk reclaim/compaction and
2178 * the resulting allocation attempt fails
2179 */
2180 if (!nr_reclaimed)
2181 return false;
2182 }
2183
2184 /*
2185 * If we have not reclaimed enough pages for compaction and the
2186 * inactive lists are large enough, continue reclaiming
2187 */
2188 pages_for_compaction = (2UL << sc->order);
2189 inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
2190 if (get_nr_swap_pages() > 0)
2191 inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
2192 if (sc->nr_reclaimed < pages_for_compaction &&
2193 inactive_lru_pages > pages_for_compaction)
2194 return true;
2195
2196 /* If compaction would go ahead or the allocation would succeed, stop */
2197 switch (compaction_suitable(zone, sc->order)) {
2198 case COMPACT_PARTIAL:
2199 case COMPACT_CONTINUE:
2200 return false;
2201 default:
2202 return true;
2203 }
2204}
2205
2206static void shrink_zone(struct zone *zone, struct scan_control *sc)
2207{
2208 unsigned long nr_reclaimed, nr_scanned;
2209
2210 do {
2211 struct mem_cgroup *root = sc->target_mem_cgroup;
2212 struct mem_cgroup_reclaim_cookie reclaim = {
2213 .zone = zone,
2214 .priority = sc->priority,
2215 };
2216 struct mem_cgroup *memcg;
2217
2218 nr_reclaimed = sc->nr_reclaimed;
2219 nr_scanned = sc->nr_scanned;
2220
2221 memcg = mem_cgroup_iter(root, NULL, &reclaim);
2222 do {
2223 struct lruvec *lruvec;
2224
2225 lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2226
2227 shrink_lruvec(lruvec, sc);
2228
2229 /*
2230 * Direct reclaim and kswapd have to scan all memory
2231 * cgroups to fulfill the overall scan target for the
2232 * zone.
2233 *
2234 * Limit reclaim, on the other hand, only cares about
2235 * nr_to_reclaim pages to be reclaimed and it will
2236 * retry with decreasing priority if one round over the
2237 * whole hierarchy is not sufficient.
2238 */
2239 if (!global_reclaim(sc) &&
2240 sc->nr_reclaimed >= sc->nr_to_reclaim) {
2241 mem_cgroup_iter_break(root, memcg);
2242 break;
2243 }
2244 memcg = mem_cgroup_iter(root, memcg, &reclaim);
2245 } while (memcg);
2246
2247 vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
2248 sc->nr_scanned - nr_scanned,
2249 sc->nr_reclaimed - nr_reclaimed);
2250
2251 } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
2252 sc->nr_scanned - nr_scanned, sc));
2253}
2254
2255/* Returns true if compaction should go ahead for a high-order request */
2256static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2257{
2258 unsigned long balance_gap, watermark;
2259 bool watermark_ok;
2260
2261 /* Do not consider compaction for orders reclaim is meant to satisfy */
2262 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
2263 return false;
2264
2265 /*
2266 * Compaction takes time to run and there are potentially other
2267 * callers using the pages just freed. Continue reclaiming until
2268 * there is a buffer of free pages available to give compaction
2269 * a reasonable chance of completing and allocating the page
2270 */
2271 balance_gap = min(low_wmark_pages(zone),
2272 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2273 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2274 watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
2275 watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2276
2277 /*
2278 * If compaction is deferred, reclaim up to a point where
2279 * compaction will have a chance of success when re-enabled
2280 */
2281 if (compaction_deferred(zone, sc->order))
2282 return watermark_ok;
2283
2284 /* If compaction is not ready to start, keep reclaiming */
2285 if (!compaction_suitable(zone, sc->order))
2286 return false;
2287
2288 return watermark_ok;
2289}
2290
2291/*
2292 * This is the direct reclaim path, for page-allocating processes. We only
2293 * try to reclaim pages from zones which will satisfy the caller's allocation
2294 * request.
2295 *
2296 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2297 * Because:
2298 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2299 * allocation or
2300 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2301 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2302 * zone defense algorithm.
2303 *
2304 * If a zone is deemed to be full of pinned pages then just give it a light
2305 * scan then give up on it.
2306 *
2307 * This function returns true if a zone is being reclaimed for a costly
2308 * high-order allocation and compaction is ready to begin. This indicates to
2309 * the caller that it should consider retrying the allocation instead of
2310 * further reclaim.
2311 */
2312static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2313{
2314 struct zoneref *z;
2315 struct zone *zone;
2316 unsigned long nr_soft_reclaimed;
2317 unsigned long nr_soft_scanned;
2318 unsigned long lru_pages = 0;
2319 bool aborted_reclaim = false;
2320 struct reclaim_state *reclaim_state = current->reclaim_state;
2321 gfp_t orig_mask;
2322 struct shrink_control shrink = {
2323 .gfp_mask = sc->gfp_mask,
2324 };
2325 enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
2326
2327 /*
2328 * If the number of buffer_heads in the machine exceeds the maximum
2329 * allowed level, force direct reclaim to scan the highmem zone as
2330 * highmem pages could be pinning lowmem pages storing buffer_heads
2331 */
2332 orig_mask = sc->gfp_mask;
2333 if (buffer_heads_over_limit)
2334 sc->gfp_mask |= __GFP_HIGHMEM;
2335
2336 nodes_clear(shrink.nodes_to_scan);
2337
2338 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2339 gfp_zone(sc->gfp_mask), sc->nodemask) {
2340 if (!populated_zone(zone))
2341 continue;
2342 /*
2343 * Take care memory controller reclaiming has small influence
2344 * to global LRU.
2345 */
2346 if (global_reclaim(sc)) {
2347 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2348 continue;
2349
2350 lru_pages += zone_reclaimable_pages(zone);
2351 node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2352
2353 if (sc->priority != DEF_PRIORITY &&
2354 !zone_reclaimable(zone))
2355 continue; /* Let kswapd poll it */
2356 if (IS_ENABLED(CONFIG_COMPACTION)) {
2357 /*
2358 * If we already have plenty of memory free for
2359 * compaction in this zone, don't free any more.
2360 * Even though compaction is invoked for any
2361 * non-zero order, only frequent costly order
2362 * reclamation is disruptive enough to become a
2363 * noticeable problem, like transparent huge
2364 * page allocations.
2365 */
2366 if ((zonelist_zone_idx(z) <= requested_highidx)
2367 && compaction_ready(zone, sc)) {
2368 aborted_reclaim = true;
2369 continue;
2370 }
2371 }
2372 /*
2373 * This steals pages from memory cgroups over softlimit
2374 * and returns the number of reclaimed pages and
2375 * scanned pages. This works for global memory pressure
2376 * and balancing, not for a memcg's limit.
2377 */
2378 nr_soft_scanned = 0;
2379 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2380 sc->order, sc->gfp_mask,
2381 &nr_soft_scanned);
2382 sc->nr_reclaimed += nr_soft_reclaimed;
2383 sc->nr_scanned += nr_soft_scanned;
2384 /* need some check for avoid more shrink_zone() */
2385 }
2386
2387 shrink_zone(zone, sc);
2388 }
2389
2390 /*
2391 * Don't shrink slabs when reclaiming memory from over limit cgroups
2392 * but do shrink slab at least once when aborting reclaim for
2393 * compaction to avoid unevenly scanning file/anon LRU pages over slab
2394 * pages.
2395 */
2396 if (global_reclaim(sc)) {
2397 shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2398 if (reclaim_state) {
2399 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2400 reclaim_state->reclaimed_slab = 0;
2401 }
2402 }
2403
2404 /*
2405 * Restore to original mask to avoid the impact on the caller if we
2406 * promoted it to __GFP_HIGHMEM.
2407 */
2408 sc->gfp_mask = orig_mask;
2409
2410 return aborted_reclaim;
2411}
2412
2413/* All zones in zonelist are unreclaimable? */
2414static bool all_unreclaimable(struct zonelist *zonelist,
2415 struct scan_control *sc)
2416{
2417 struct zoneref *z;
2418 struct zone *zone;
2419
2420 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2421 gfp_zone(sc->gfp_mask), sc->nodemask) {
2422 if (!populated_zone(zone))
2423 continue;
2424 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2425 continue;
2426 if (zone_reclaimable(zone))
2427 return false;
2428 }
2429
2430 return true;
2431}
2432
2433/*
2434 * This is the main entry point to direct page reclaim.
2435 *
2436 * If a full scan of the inactive list fails to free enough memory then we
2437 * are "out of memory" and something needs to be killed.
2438 *
2439 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2440 * high - the zone may be full of dirty or under-writeback pages, which this
2441 * caller can't do much about. We kick the writeback threads and take explicit
2442 * naps in the hope that some of these pages can be written. But if the
2443 * allocating task holds filesystem locks which prevent writeout this might not
2444 * work, and the allocation attempt will fail.
2445 *
2446 * returns: 0, if no pages reclaimed
2447 * else, the number of pages reclaimed
2448 */
2449static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2450 struct scan_control *sc)
2451{
2452 unsigned long total_scanned = 0;
2453 unsigned long writeback_threshold;
2454 bool aborted_reclaim;
2455
2456 delayacct_freepages_start();
2457
2458 if (global_reclaim(sc))
2459 count_vm_event(ALLOCSTALL);
2460
2461 do {
2462 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2463 sc->priority);
2464 sc->nr_scanned = 0;
2465 aborted_reclaim = shrink_zones(zonelist, sc);
2466
2467 total_scanned += sc->nr_scanned;
2468 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2469 goto out;
2470
2471 /*
2472 * If we're getting trouble reclaiming, start doing
2473 * writepage even in laptop mode.
2474 */
2475 if (sc->priority < DEF_PRIORITY - 2)
2476 sc->may_writepage = 1;
2477
2478 /*
2479 * Try to write back as many pages as we just scanned. This
2480 * tends to cause slow streaming writers to write data to the
2481 * disk smoothly, at the dirtying rate, which is nice. But
2482 * that's undesirable in laptop mode, where we *want* lumpy
2483 * writeout. So in laptop mode, write out the whole world.
2484 */
2485 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2486 if (total_scanned > writeback_threshold) {
2487 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2488 WB_REASON_TRY_TO_FREE_PAGES);
2489 sc->may_writepage = 1;
2490 }
2491 } while (--sc->priority >= 0 && !aborted_reclaim);
2492
2493out:
2494 delayacct_freepages_end();
2495
2496 if (sc->nr_reclaimed)
2497 return sc->nr_reclaimed;
2498
2499 /*
2500 * As hibernation is going on, kswapd is freezed so that it can't mark
2501 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2502 * check.
2503 */
2504 if (oom_killer_disabled)
2505 return 0;
2506
2507 /* Aborted reclaim to try compaction? don't OOM, then */
2508 if (aborted_reclaim)
2509 return 1;
2510
2511 /* top priority shrink_zones still had more to do? don't OOM, then */
2512 if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2513 return 1;
2514
2515 return 0;
2516}
2517
2518static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2519{
2520 struct zone *zone;
2521 unsigned long pfmemalloc_reserve = 0;
2522 unsigned long free_pages = 0;
2523 int i;
2524 bool wmark_ok;
2525
2526 for (i = 0; i <= ZONE_NORMAL; i++) {
2527 zone = &pgdat->node_zones[i];
2528 pfmemalloc_reserve += min_wmark_pages(zone);
2529 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2530 }
2531
2532 wmark_ok = free_pages > pfmemalloc_reserve / 2;
2533
2534 /* kswapd must be awake if processes are being throttled */
2535 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2536 pgdat->classzone_idx = min(pgdat->classzone_idx,
2537 (enum zone_type)ZONE_NORMAL);
2538 wake_up_interruptible(&pgdat->kswapd_wait);
2539 }
2540
2541 return wmark_ok;
2542}
2543
2544/*
2545 * Throttle direct reclaimers if backing storage is backed by the network
2546 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2547 * depleted. kswapd will continue to make progress and wake the processes
2548 * when the low watermark is reached.
2549 *
2550 * Returns true if a fatal signal was delivered during throttling. If this
2551 * happens, the page allocator should not consider triggering the OOM killer.
2552 */
2553static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2554 nodemask_t *nodemask)
2555{
2556 struct zone *zone;
2557 int high_zoneidx = gfp_zone(gfp_mask);
2558 pg_data_t *pgdat;
2559
2560 /*
2561 * Kernel threads should not be throttled as they may be indirectly
2562 * responsible for cleaning pages necessary for reclaim to make forward
2563 * progress. kjournald for example may enter direct reclaim while
2564 * committing a transaction where throttling it could forcing other
2565 * processes to block on log_wait_commit().
2566 */
2567 if (current->flags & PF_KTHREAD)
2568 goto out;
2569
2570 /*
2571 * If a fatal signal is pending, this process should not throttle.
2572 * It should return quickly so it can exit and free its memory
2573 */
2574 if (fatal_signal_pending(current))
2575 goto out;
2576
2577 /* Check if the pfmemalloc reserves are ok */
2578 first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2579 pgdat = zone->zone_pgdat;
2580 if (pfmemalloc_watermark_ok(pgdat))
2581 goto out;
2582
2583 /* Account for the throttling */
2584 count_vm_event(PGSCAN_DIRECT_THROTTLE);
2585
2586 /*
2587 * If the caller cannot enter the filesystem, it's possible that it
2588 * is due to the caller holding an FS lock or performing a journal
2589 * transaction in the case of a filesystem like ext[3|4]. In this case,
2590 * it is not safe to block on pfmemalloc_wait as kswapd could be
2591 * blocked waiting on the same lock. Instead, throttle for up to a
2592 * second before continuing.
2593 */
2594 if (!(gfp_mask & __GFP_FS)) {
2595 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2596 pfmemalloc_watermark_ok(pgdat), HZ);
2597
2598 goto check_pending;
2599 }
2600
2601 /* Throttle until kswapd wakes the process */
2602 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2603 pfmemalloc_watermark_ok(pgdat));
2604
2605check_pending:
2606 if (fatal_signal_pending(current))
2607 return true;
2608
2609out:
2610 return false;
2611}
2612
2613unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2614 gfp_t gfp_mask, nodemask_t *nodemask)
2615{
2616 unsigned long nr_reclaimed;
2617 struct scan_control sc = {
2618 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2619 .may_writepage = !laptop_mode,
2620 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2621 .may_unmap = 1,
2622 .may_swap = 1,
2623 .order = order,
2624 .priority = DEF_PRIORITY,
2625 .target_mem_cgroup = NULL,
2626 .nodemask = nodemask,
2627 };
2628
2629 /*
2630 * Do not enter reclaim if fatal signal was delivered while throttled.
2631 * 1 is returned so that the page allocator does not OOM kill at this
2632 * point.
2633 */
2634 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2635 return 1;
2636
2637 trace_mm_vmscan_direct_reclaim_begin(order,
2638 sc.may_writepage,
2639 gfp_mask);
2640
2641 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2642
2643 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2644
2645 return nr_reclaimed;
2646}
2647
2648#ifdef CONFIG_MEMCG
2649
2650unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2651 gfp_t gfp_mask, bool noswap,
2652 struct zone *zone,
2653 unsigned long *nr_scanned)
2654{
2655 struct scan_control sc = {
2656 .nr_scanned = 0,
2657 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2658 .may_writepage = !laptop_mode,
2659 .may_unmap = 1,
2660 .may_swap = !noswap,
2661 .order = 0,
2662 .priority = 0,
2663 .target_mem_cgroup = memcg,
2664 };
2665 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2666
2667 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2668 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2669
2670 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2671 sc.may_writepage,
2672 sc.gfp_mask);
2673
2674 /*
2675 * NOTE: Although we can get the priority field, using it
2676 * here is not a good idea, since it limits the pages we can scan.
2677 * if we don't reclaim here, the shrink_zone from balance_pgdat
2678 * will pick up pages from other mem cgroup's as well. We hack
2679 * the priority and make it zero.
2680 */
2681 shrink_lruvec(lruvec, &sc);
2682
2683 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2684
2685 *nr_scanned = sc.nr_scanned;
2686 return sc.nr_reclaimed;
2687}
2688
2689unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2690 gfp_t gfp_mask,
2691 bool noswap)
2692{
2693 struct zonelist *zonelist;
2694 unsigned long nr_reclaimed;
2695 int nid;
2696 struct scan_control sc = {
2697 .may_writepage = !laptop_mode,
2698 .may_unmap = 1,
2699 .may_swap = !noswap,
2700 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2701 .order = 0,
2702 .priority = DEF_PRIORITY,
2703 .target_mem_cgroup = memcg,
2704 .nodemask = NULL, /* we don't care the placement */
2705 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2706 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2707 };
2708
2709 /*
2710 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2711 * take care of from where we get pages. So the node where we start the
2712 * scan does not need to be the current node.
2713 */
2714 nid = mem_cgroup_select_victim_node(memcg);
2715
2716 zonelist = NODE_DATA(nid)->node_zonelists;
2717
2718 trace_mm_vmscan_memcg_reclaim_begin(0,
2719 sc.may_writepage,
2720 sc.gfp_mask);
2721
2722 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2723
2724 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2725
2726 return nr_reclaimed;
2727}
2728#endif
2729
2730static void age_active_anon(struct zone *zone, struct scan_control *sc)
2731{
2732 struct mem_cgroup *memcg;
2733
2734 if (!total_swap_pages)
2735 return;
2736
2737 memcg = mem_cgroup_iter(NULL, NULL, NULL);
2738 do {
2739 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2740
2741 if (inactive_anon_is_low(lruvec))
2742 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2743 sc, LRU_ACTIVE_ANON);
2744
2745 memcg = mem_cgroup_iter(NULL, memcg, NULL);
2746 } while (memcg);
2747}
2748
2749static bool zone_balanced(struct zone *zone, int order,
2750 unsigned long balance_gap, int classzone_idx)
2751{
2752 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2753 balance_gap, classzone_idx, 0))
2754 return false;
2755
2756 if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2757 !compaction_suitable(zone, order))
2758 return false;
2759
2760 return true;
2761}
2762
2763/*
2764 * pgdat_balanced() is used when checking if a node is balanced.
2765 *
2766 * For order-0, all zones must be balanced!
2767 *
2768 * For high-order allocations only zones that meet watermarks and are in a
2769 * zone allowed by the callers classzone_idx are added to balanced_pages. The
2770 * total of balanced pages must be at least 25% of the zones allowed by
2771 * classzone_idx for the node to be considered balanced. Forcing all zones to
2772 * be balanced for high orders can cause excessive reclaim when there are
2773 * imbalanced zones.
2774 * The choice of 25% is due to
2775 * o a 16M DMA zone that is balanced will not balance a zone on any
2776 * reasonable sized machine
2777 * o On all other machines, the top zone must be at least a reasonable
2778 * percentage of the middle zones. For example, on 32-bit x86, highmem
2779 * would need to be at least 256M for it to be balance a whole node.
2780 * Similarly, on x86-64 the Normal zone would need to be at least 1G
2781 * to balance a node on its own. These seemed like reasonable ratios.
2782 */
2783static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2784{
2785 unsigned long managed_pages = 0;
2786 unsigned long balanced_pages = 0;
2787 int i;
2788
2789 /* Check the watermark levels */
2790 for (i = 0; i <= classzone_idx; i++) {
2791 struct zone *zone = pgdat->node_zones + i;
2792
2793 if (!populated_zone(zone))
2794 continue;
2795
2796 managed_pages += zone->managed_pages;
2797
2798 /*
2799 * A special case here:
2800 *
2801 * balance_pgdat() skips over all_unreclaimable after
2802 * DEF_PRIORITY. Effectively, it considers them balanced so
2803 * they must be considered balanced here as well!
2804 */
2805 if (!zone_reclaimable(zone)) {
2806 balanced_pages += zone->managed_pages;
2807 continue;
2808 }
2809
2810 if (zone_balanced(zone, order, 0, i))
2811 balanced_pages += zone->managed_pages;
2812 else if (!order)
2813 return false;
2814 }
2815
2816 if (order)
2817 return balanced_pages >= (managed_pages >> 2);
2818 else
2819 return true;
2820}
2821
2822/*
2823 * Prepare kswapd for sleeping. This verifies that there are no processes
2824 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2825 *
2826 * Returns true if kswapd is ready to sleep
2827 */
2828static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2829 int classzone_idx)
2830{
2831 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2832 if (remaining)
2833 return false;
2834
2835 /*
2836 * There is a potential race between when kswapd checks its watermarks
2837 * and a process gets throttled. There is also a potential race if
2838 * processes get throttled, kswapd wakes, a large process exits therby
2839 * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2840 * is going to sleep, no process should be sleeping on pfmemalloc_wait
2841 * so wake them now if necessary. If necessary, processes will wake
2842 * kswapd and get throttled again
2843 */
2844 if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2845 wake_up(&pgdat->pfmemalloc_wait);
2846 return false;
2847 }
2848
2849 return pgdat_balanced(pgdat, order, classzone_idx);
2850}
2851
2852/*
2853 * kswapd shrinks the zone by the number of pages required to reach
2854 * the high watermark.
2855 *
2856 * Returns true if kswapd scanned at least the requested number of pages to
2857 * reclaim or if the lack of progress was due to pages under writeback.
2858 * This is used to determine if the scanning priority needs to be raised.
2859 */
2860static bool kswapd_shrink_zone(struct zone *zone,
2861 int classzone_idx,
2862 struct scan_control *sc,
2863 unsigned long lru_pages,
2864 unsigned long *nr_attempted)
2865{
2866 int testorder = sc->order;
2867 unsigned long balance_gap;
2868 struct reclaim_state *reclaim_state = current->reclaim_state;
2869 struct shrink_control shrink = {
2870 .gfp_mask = sc->gfp_mask,
2871 };
2872 bool lowmem_pressure;
2873
2874 /* Reclaim above the high watermark. */
2875 sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
2876
2877 /*
2878 * Kswapd reclaims only single pages with compaction enabled. Trying
2879 * too hard to reclaim until contiguous free pages have become
2880 * available can hurt performance by evicting too much useful data
2881 * from memory. Do not reclaim more than needed for compaction.
2882 */
2883 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2884 compaction_suitable(zone, sc->order) !=
2885 COMPACT_SKIPPED)
2886 testorder = 0;
2887
2888 /*
2889 * We put equal pressure on every zone, unless one zone has way too
2890 * many pages free already. The "too many pages" is defined as the
2891 * high wmark plus a "gap" where the gap is either the low
2892 * watermark or 1% of the zone, whichever is smaller.
2893 */
2894 balance_gap = min(low_wmark_pages(zone),
2895 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2896 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2897
2898 /*
2899 * If there is no low memory pressure or the zone is balanced then no
2900 * reclaim is necessary
2901 */
2902 lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
2903 if (!lowmem_pressure && zone_balanced(zone, testorder,
2904 balance_gap, classzone_idx))
2905 return true;
2906
2907 shrink_zone(zone, sc);
2908 nodes_clear(shrink.nodes_to_scan);
2909 node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2910
2911 reclaim_state->reclaimed_slab = 0;
2912 shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2913 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2914
2915 /* Account for the number of pages attempted to reclaim */
2916 *nr_attempted += sc->nr_to_reclaim;
2917
2918 zone_clear_flag(zone, ZONE_WRITEBACK);
2919
2920 /*
2921 * If a zone reaches its high watermark, consider it to be no longer
2922 * congested. It's possible there are dirty pages backed by congested
2923 * BDIs but as pressure is relieved, speculatively avoid congestion
2924 * waits.
2925 */
2926 if (zone_reclaimable(zone) &&
2927 zone_balanced(zone, testorder, 0, classzone_idx)) {
2928 zone_clear_flag(zone, ZONE_CONGESTED);
2929 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2930 }
2931
2932 return sc->nr_scanned >= sc->nr_to_reclaim;
2933}
2934
2935/*
2936 * For kswapd, balance_pgdat() will work across all this node's zones until
2937 * they are all at high_wmark_pages(zone).
2938 *
2939 * Returns the final order kswapd was reclaiming at
2940 *
2941 * There is special handling here for zones which are full of pinned pages.
2942 * This can happen if the pages are all mlocked, or if they are all used by
2943 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
2944 * What we do is to detect the case where all pages in the zone have been
2945 * scanned twice and there has been zero successful reclaim. Mark the zone as
2946 * dead and from now on, only perform a short scan. Basically we're polling
2947 * the zone for when the problem goes away.
2948 *
2949 * kswapd scans the zones in the highmem->normal->dma direction. It skips
2950 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2951 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2952 * lower zones regardless of the number of free pages in the lower zones. This
2953 * interoperates with the page allocator fallback scheme to ensure that aging
2954 * of pages is balanced across the zones.
2955 */
2956static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2957 int *classzone_idx)
2958{
2959 int i;
2960 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2961 unsigned long nr_soft_reclaimed;
2962 unsigned long nr_soft_scanned;
2963 struct scan_control sc = {
2964 .gfp_mask = GFP_KERNEL,
2965 .priority = DEF_PRIORITY,
2966 .may_unmap = 1,
2967 .may_swap = 1,
2968 .may_writepage = !laptop_mode,
2969 .order = order,
2970 .target_mem_cgroup = NULL,
2971 };
2972 count_vm_event(PAGEOUTRUN);
2973
2974 do {
2975 unsigned long lru_pages = 0;
2976 unsigned long nr_attempted = 0;
2977 bool raise_priority = true;
2978 bool pgdat_needs_compaction = (order > 0);
2979
2980 sc.nr_reclaimed = 0;
2981
2982 /*
2983 * Scan in the highmem->dma direction for the highest
2984 * zone which needs scanning
2985 */
2986 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2987 struct zone *zone = pgdat->node_zones + i;
2988
2989 if (!populated_zone(zone))
2990 continue;
2991
2992 if (sc.priority != DEF_PRIORITY &&
2993 !zone_reclaimable(zone))
2994 continue;
2995
2996 /*
2997 * Do some background aging of the anon list, to give
2998 * pages a chance to be referenced before reclaiming.
2999 */
3000 age_active_anon(zone, &sc);
3001
3002 /*
3003 * If the number of buffer_heads in the machine
3004 * exceeds the maximum allowed level and this node
3005 * has a highmem zone, force kswapd to reclaim from
3006 * it to relieve lowmem pressure.
3007 */
3008 if (buffer_heads_over_limit && is_highmem_idx(i)) {
3009 end_zone = i;
3010 break;
3011 }
3012
3013 if (!zone_balanced(zone, order, 0, 0)) {
3014 end_zone = i;
3015 break;
3016 } else {
3017 /*
3018 * If balanced, clear the dirty and congested
3019 * flags
3020 */
3021 zone_clear_flag(zone, ZONE_CONGESTED);
3022 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
3023 }
3024 }
3025
3026 if (i < 0)
3027 goto out;
3028
3029 for (i = 0; i <= end_zone; i++) {
3030 struct zone *zone = pgdat->node_zones + i;
3031
3032 if (!populated_zone(zone))
3033 continue;
3034
3035 lru_pages += zone_reclaimable_pages(zone);
3036
3037 /*
3038 * If any zone is currently balanced then kswapd will
3039 * not call compaction as it is expected that the
3040 * necessary pages are already available.
3041 */
3042 if (pgdat_needs_compaction &&
3043 zone_watermark_ok(zone, order,
3044 low_wmark_pages(zone),
3045 *classzone_idx, 0))
3046 pgdat_needs_compaction = false;
3047 }
3048
3049 /*
3050 * If we're getting trouble reclaiming, start doing writepage
3051 * even in laptop mode.
3052 */
3053 if (sc.priority < DEF_PRIORITY - 2)
3054 sc.may_writepage = 1;
3055
3056 /*
3057 * Now scan the zone in the dma->highmem direction, stopping
3058 * at the last zone which needs scanning.
3059 *
3060 * We do this because the page allocator works in the opposite
3061 * direction. This prevents the page allocator from allocating
3062 * pages behind kswapd's direction of progress, which would
3063 * cause too much scanning of the lower zones.
3064 */
3065 for (i = 0; i <= end_zone; i++) {
3066 struct zone *zone = pgdat->node_zones + i;
3067
3068 if (!populated_zone(zone))
3069 continue;
3070
3071 if (sc.priority != DEF_PRIORITY &&
3072 !zone_reclaimable(zone))
3073 continue;
3074
3075 sc.nr_scanned = 0;
3076
3077 nr_soft_scanned = 0;
3078 /*
3079 * Call soft limit reclaim before calling shrink_zone.
3080 */
3081 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
3082 order, sc.gfp_mask,
3083 &nr_soft_scanned);
3084 sc.nr_reclaimed += nr_soft_reclaimed;
3085
3086 /*
3087 * There should be no need to raise the scanning
3088 * priority if enough pages are already being scanned
3089 * that that high watermark would be met at 100%
3090 * efficiency.
3091 */
3092 if (kswapd_shrink_zone(zone, end_zone, &sc,
3093 lru_pages, &nr_attempted))
3094 raise_priority = false;
3095 }
3096
3097 /*
3098 * If the low watermark is met there is no need for processes
3099 * to be throttled on pfmemalloc_wait as they should not be
3100 * able to safely make forward progress. Wake them
3101 */
3102 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3103 pfmemalloc_watermark_ok(pgdat))
3104 wake_up(&pgdat->pfmemalloc_wait);
3105
3106 /*
3107 * Fragmentation may mean that the system cannot be rebalanced
3108 * for high-order allocations in all zones. If twice the
3109 * allocation size has been reclaimed and the zones are still
3110 * not balanced then recheck the watermarks at order-0 to
3111 * prevent kswapd reclaiming excessively. Assume that a
3112 * process requested a high-order can direct reclaim/compact.
3113 */
3114 if (order && sc.nr_reclaimed >= 2UL << order)
3115 order = sc.order = 0;
3116
3117 /* Check if kswapd should be suspending */
3118 if (try_to_freeze() || kthread_should_stop())
3119 break;
3120
3121 /*
3122 * Compact if necessary and kswapd is reclaiming at least the
3123 * high watermark number of pages as requsted
3124 */
3125 if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
3126 compact_pgdat(pgdat, order);
3127
3128 /*
3129 * Raise priority if scanning rate is too low or there was no
3130 * progress in reclaiming pages
3131 */
3132 if (raise_priority || !sc.nr_reclaimed)
3133 sc.priority--;
3134 } while (sc.priority >= 1 &&
3135 !pgdat_balanced(pgdat, order, *classzone_idx));
3136
3137out:
3138 /*
3139 * Return the order we were reclaiming at so prepare_kswapd_sleep()
3140 * makes a decision on the order we were last reclaiming at. However,
3141 * if another caller entered the allocator slow path while kswapd
3142 * was awake, order will remain at the higher level
3143 */
3144 *classzone_idx = end_zone;
3145 return order;
3146}
3147
3148static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3149{
3150 long remaining = 0;
3151 DEFINE_WAIT(wait);
3152
3153 if (freezing(current) || kthread_should_stop())
3154 return;
3155
3156 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3157
3158 /* Try to sleep for a short interval */
3159 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3160 remaining = schedule_timeout(HZ/10);
3161 finish_wait(&pgdat->kswapd_wait, &wait);
3162 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3163 }
3164
3165 /*
3166 * After a short sleep, check if it was a premature sleep. If not, then
3167 * go fully to sleep until explicitly woken up.
3168 */
3169 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3170 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3171
3172 /*
3173 * vmstat counters are not perfectly accurate and the estimated
3174 * value for counters such as NR_FREE_PAGES can deviate from the
3175 * true value by nr_online_cpus * threshold. To avoid the zone
3176 * watermarks being breached while under pressure, we reduce the
3177 * per-cpu vmstat threshold while kswapd is awake and restore
3178 * them before going back to sleep.
3179 */
3180 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3181
3182 /*
3183 * Compaction records what page blocks it recently failed to
3184 * isolate pages from and skips them in the future scanning.
3185 * When kswapd is going to sleep, it is reasonable to assume
3186 * that pages and compaction may succeed so reset the cache.
3187 */
3188 reset_isolation_suitable(pgdat);
3189
3190 if (!kthread_should_stop())
3191 schedule();
3192
3193 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3194 } else {
3195 if (remaining)
3196 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3197 else
3198 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3199 }
3200 finish_wait(&pgdat->kswapd_wait, &wait);
3201}
3202
3203/*
3204 * The background pageout daemon, started as a kernel thread
3205 * from the init process.
3206 *
3207 * This basically trickles out pages so that we have _some_
3208 * free memory available even if there is no other activity
3209 * that frees anything up. This is needed for things like routing
3210 * etc, where we otherwise might have all activity going on in
3211 * asynchronous contexts that cannot page things out.
3212 *
3213 * If there are applications that are active memory-allocators
3214 * (most normal use), this basically shouldn't matter.
3215 */
3216static int kswapd(void *p)
3217{
3218 unsigned long order, new_order;
3219 unsigned balanced_order;
3220 int classzone_idx, new_classzone_idx;
3221 int balanced_classzone_idx;
3222 pg_data_t *pgdat = (pg_data_t*)p;
3223 struct task_struct *tsk = current;
3224
3225 struct reclaim_state reclaim_state = {
3226 .reclaimed_slab = 0,
3227 };
3228 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3229
3230 lockdep_set_current_reclaim_state(GFP_KERNEL);
3231
3232 if (!cpumask_empty(cpumask))
3233 set_cpus_allowed_ptr(tsk, cpumask);
3234 current->reclaim_state = &reclaim_state;
3235
3236 /*
3237 * Tell the memory management that we're a "memory allocator",
3238 * and that if we need more memory we should get access to it
3239 * regardless (see "__alloc_pages()"). "kswapd" should
3240 * never get caught in the normal page freeing logic.
3241 *
3242 * (Kswapd normally doesn't need memory anyway, but sometimes
3243 * you need a small amount of memory in order to be able to
3244 * page out something else, and this flag essentially protects
3245 * us from recursively trying to free more memory as we're
3246 * trying to free the first piece of memory in the first place).
3247 */
3248 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3249 set_freezable();
3250
3251 order = new_order = 0;
3252 balanced_order = 0;
3253 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3254 balanced_classzone_idx = classzone_idx;
3255 for ( ; ; ) {
3256 bool ret;
3257
3258 /*
3259 * If the last balance_pgdat was unsuccessful it's unlikely a
3260 * new request of a similar or harder type will succeed soon
3261 * so consider going to sleep on the basis we reclaimed at
3262 */
3263 if (balanced_classzone_idx >= new_classzone_idx &&
3264 balanced_order == new_order) {
3265 new_order = pgdat->kswapd_max_order;
3266 new_classzone_idx = pgdat->classzone_idx;
3267 pgdat->kswapd_max_order = 0;
3268 pgdat->classzone_idx = pgdat->nr_zones - 1;
3269 }
3270
3271 if (order < new_order || classzone_idx > new_classzone_idx) {
3272 /*
3273 * Don't sleep if someone wants a larger 'order'
3274 * allocation or has tigher zone constraints
3275 */
3276 order = new_order;
3277 classzone_idx = new_classzone_idx;
3278 } else {
3279 kswapd_try_to_sleep(pgdat, balanced_order,
3280 balanced_classzone_idx);
3281 order = pgdat->kswapd_max_order;
3282 classzone_idx = pgdat->classzone_idx;
3283 new_order = order;
3284 new_classzone_idx = classzone_idx;
3285 pgdat->kswapd_max_order = 0;
3286 pgdat->classzone_idx = pgdat->nr_zones - 1;
3287 }
3288
3289 ret = try_to_freeze();
3290 if (kthread_should_stop())
3291 break;
3292
3293 /*
3294 * We can speed up thawing tasks if we don't call balance_pgdat
3295 * after returning from the refrigerator
3296 */
3297 if (!ret) {
3298 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3299 balanced_classzone_idx = classzone_idx;
3300 balanced_order = balance_pgdat(pgdat, order,
3301 &balanced_classzone_idx);
3302 }
3303 }
3304
3305 current->reclaim_state = NULL;
3306 return 0;
3307}
3308
3309/*
3310 * A zone is low on free memory, so wake its kswapd task to service it.
3311 */
3312void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3313{
3314 pg_data_t *pgdat;
3315
3316 if (!populated_zone(zone))
3317 return;
3318
3319 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3320 return;
3321 pgdat = zone->zone_pgdat;
3322 if (pgdat->kswapd_max_order < order) {
3323 pgdat->kswapd_max_order = order;
3324 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3325 }
3326 if (!waitqueue_active(&pgdat->kswapd_wait))
3327 return;
3328 if (zone_balanced(zone, order, 0, 0))
3329 return;
3330
3331 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3332 wake_up_interruptible(&pgdat->kswapd_wait);
3333}
3334
3335#ifdef CONFIG_HIBERNATION
3336/*
3337 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3338 * freed pages.
3339 *
3340 * Rather than trying to age LRUs the aim is to preserve the overall
3341 * LRU order by reclaiming preferentially
3342 * inactive > active > active referenced > active mapped
3343 */
3344unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3345{
3346 struct reclaim_state reclaim_state;
3347 struct scan_control sc = {
3348 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3349 .may_swap = 1,
3350 .may_unmap = 1,
3351 .may_writepage = 1,
3352 .nr_to_reclaim = nr_to_reclaim,
3353 .hibernation_mode = 1,
3354 .order = 0,
3355 .priority = DEF_PRIORITY,
3356 };
3357 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3358 struct task_struct *p = current;
3359 unsigned long nr_reclaimed;
3360
3361 p->flags |= PF_MEMALLOC;
3362 lockdep_set_current_reclaim_state(sc.gfp_mask);
3363 reclaim_state.reclaimed_slab = 0;
3364 p->reclaim_state = &reclaim_state;
3365
3366 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3367
3368 p->reclaim_state = NULL;
3369 lockdep_clear_current_reclaim_state();
3370 p->flags &= ~PF_MEMALLOC;
3371
3372 return nr_reclaimed;
3373}
3374#endif /* CONFIG_HIBERNATION */
3375
3376/* It's optimal to keep kswapds on the same CPUs as their memory, but
3377 not required for correctness. So if the last cpu in a node goes
3378 away, we get changed to run anywhere: as the first one comes back,
3379 restore their cpu bindings. */
3380static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3381 void *hcpu)
3382{
3383 int nid;
3384
3385 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3386 for_each_node_state(nid, N_MEMORY) {
3387 pg_data_t *pgdat = NODE_DATA(nid);
3388 const struct cpumask *mask;
3389
3390 mask = cpumask_of_node(pgdat->node_id);
3391
3392 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3393 /* One of our CPUs online: restore mask */
3394 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3395 }
3396 }
3397 return NOTIFY_OK;
3398}
3399
3400/*
3401 * This kswapd start function will be called by init and node-hot-add.
3402 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3403 */
3404int kswapd_run(int nid)
3405{
3406 pg_data_t *pgdat = NODE_DATA(nid);
3407 int ret = 0;
3408
3409 if (pgdat->kswapd)
3410 return 0;
3411
3412 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3413 if (IS_ERR(pgdat->kswapd)) {
3414 /* failure at boot is fatal */
3415 BUG_ON(system_state == SYSTEM_BOOTING);
3416 pr_err("Failed to start kswapd on node %d\n", nid);
3417 ret = PTR_ERR(pgdat->kswapd);
3418 pgdat->kswapd = NULL;
3419 }
3420 return ret;
3421}
3422
3423/*
3424 * Called by memory hotplug when all memory in a node is offlined. Caller must
3425 * hold lock_memory_hotplug().
3426 */
3427void kswapd_stop(int nid)
3428{
3429 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3430
3431 if (kswapd) {
3432 kthread_stop(kswapd);
3433 NODE_DATA(nid)->kswapd = NULL;
3434 }
3435}
3436
3437static int __init kswapd_init(void)
3438{
3439 int nid;
3440
3441 swap_setup();
3442 for_each_node_state(nid, N_MEMORY)
3443 kswapd_run(nid);
3444 hotcpu_notifier(cpu_callback, 0);
3445 return 0;
3446}
3447
3448module_init(kswapd_init)
3449
3450#ifdef CONFIG_NUMA
3451/*
3452 * Zone reclaim mode
3453 *
3454 * If non-zero call zone_reclaim when the number of free pages falls below
3455 * the watermarks.
3456 */
3457int zone_reclaim_mode __read_mostly;
3458
3459#define RECLAIM_OFF 0
3460#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3461#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3462#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
3463
3464/*
3465 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3466 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3467 * a zone.
3468 */
3469#define ZONE_RECLAIM_PRIORITY 4
3470
3471/*
3472 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3473 * occur.
3474 */
3475int sysctl_min_unmapped_ratio = 1;
3476
3477/*
3478 * If the number of slab pages in a zone grows beyond this percentage then
3479 * slab reclaim needs to occur.
3480 */
3481int sysctl_min_slab_ratio = 5;
3482
3483static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3484{
3485 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3486 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3487 zone_page_state(zone, NR_ACTIVE_FILE);
3488
3489 /*
3490 * It's possible for there to be more file mapped pages than
3491 * accounted for by the pages on the file LRU lists because
3492 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3493 */
3494 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3495}
3496
3497/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3498static long zone_pagecache_reclaimable(struct zone *zone)
3499{
3500 long nr_pagecache_reclaimable;
3501 long delta = 0;
3502
3503 /*
3504 * If RECLAIM_SWAP is set, then all file pages are considered
3505 * potentially reclaimable. Otherwise, we have to worry about
3506 * pages like swapcache and zone_unmapped_file_pages() provides
3507 * a better estimate
3508 */
3509 if (zone_reclaim_mode & RECLAIM_SWAP)
3510 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3511 else
3512 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3513
3514 /* If we can't clean pages, remove dirty pages from consideration */
3515 if (!(zone_reclaim_mode & RECLAIM_WRITE))
3516 delta += zone_page_state(zone, NR_FILE_DIRTY);
3517
3518 /* Watch for any possible underflows due to delta */
3519 if (unlikely(delta > nr_pagecache_reclaimable))
3520 delta = nr_pagecache_reclaimable;
3521
3522 return nr_pagecache_reclaimable - delta;
3523}
3524
3525/*
3526 * Try to free up some pages from this zone through reclaim.
3527 */
3528static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3529{
3530 /* Minimum pages needed in order to stay on node */
3531 const unsigned long nr_pages = 1 << order;
3532 struct task_struct *p = current;
3533 struct reclaim_state reclaim_state;
3534 struct scan_control sc = {
3535 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3536 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3537 .may_swap = 1,
3538 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3539 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3540 .order = order,
3541 .priority = ZONE_RECLAIM_PRIORITY,
3542 };
3543 struct shrink_control shrink = {
3544 .gfp_mask = sc.gfp_mask,
3545 };
3546 unsigned long nr_slab_pages0, nr_slab_pages1;
3547
3548 cond_resched();
3549 /*
3550 * We need to be able to allocate from the reserves for RECLAIM_SWAP
3551 * and we also need to be able to write out pages for RECLAIM_WRITE
3552 * and RECLAIM_SWAP.
3553 */
3554 p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3555 lockdep_set_current_reclaim_state(gfp_mask);
3556 reclaim_state.reclaimed_slab = 0;
3557 p->reclaim_state = &reclaim_state;
3558
3559 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3560 /*
3561 * Free memory by calling shrink zone with increasing
3562 * priorities until we have enough memory freed.
3563 */
3564 do {
3565 shrink_zone(zone, &sc);
3566 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3567 }
3568
3569 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3570 if (nr_slab_pages0 > zone->min_slab_pages) {
3571 /*
3572 * shrink_slab() does not currently allow us to determine how
3573 * many pages were freed in this zone. So we take the current
3574 * number of slab pages and shake the slab until it is reduced
3575 * by the same nr_pages that we used for reclaiming unmapped
3576 * pages.
3577 */
3578 nodes_clear(shrink.nodes_to_scan);
3579 node_set(zone_to_nid(zone), shrink.nodes_to_scan);
3580 for (;;) {
3581 unsigned long lru_pages = zone_reclaimable_pages(zone);
3582
3583 /* No reclaimable slab or very low memory pressure */
3584 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3585 break;
3586
3587 /* Freed enough memory */
3588 nr_slab_pages1 = zone_page_state(zone,
3589 NR_SLAB_RECLAIMABLE);
3590 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3591 break;
3592 }
3593
3594 /*
3595 * Update nr_reclaimed by the number of slab pages we
3596 * reclaimed from this zone.
3597 */
3598 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3599 if (nr_slab_pages1 < nr_slab_pages0)
3600 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3601 }
3602
3603 p->reclaim_state = NULL;
3604 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3605 lockdep_clear_current_reclaim_state();
3606 return sc.nr_reclaimed >= nr_pages;
3607}
3608
3609int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3610{
3611 int node_id;
3612 int ret;
3613
3614 /*
3615 * Zone reclaim reclaims unmapped file backed pages and
3616 * slab pages if we are over the defined limits.
3617 *
3618 * A small portion of unmapped file backed pages is needed for
3619 * file I/O otherwise pages read by file I/O will be immediately
3620 * thrown out if the zone is overallocated. So we do not reclaim
3621 * if less than a specified percentage of the zone is used by
3622 * unmapped file backed pages.
3623 */
3624 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3625 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3626 return ZONE_RECLAIM_FULL;
3627
3628 if (!zone_reclaimable(zone))
3629 return ZONE_RECLAIM_FULL;
3630
3631 /*
3632 * Do not scan if the allocation should not be delayed.
3633 */
3634 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3635 return ZONE_RECLAIM_NOSCAN;
3636
3637 /*
3638 * Only run zone reclaim on the local zone or on zones that do not
3639 * have associated processors. This will favor the local processor
3640 * over remote processors and spread off node memory allocations
3641 * as wide as possible.
3642 */
3643 node_id = zone_to_nid(zone);
3644 if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3645 return ZONE_RECLAIM_NOSCAN;
3646
3647 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3648 return ZONE_RECLAIM_NOSCAN;
3649
3650 ret = __zone_reclaim(zone, gfp_mask, order);
3651 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3652
3653 if (!ret)
3654 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3655
3656 return ret;
3657}
3658#endif
3659
3660/*
3661 * page_evictable - test whether a page is evictable
3662 * @page: the page to test
3663 *
3664 * Test whether page is evictable--i.e., should be placed on active/inactive
3665 * lists vs unevictable list.
3666 *
3667 * Reasons page might not be evictable:
3668 * (1) page's mapping marked unevictable
3669 * (2) page is part of an mlocked VMA
3670 *
3671 */
3672int page_evictable(struct page *page)
3673{
3674 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3675}
3676
3677#ifdef CONFIG_SHMEM
3678/**
3679 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3680 * @pages: array of pages to check
3681 * @nr_pages: number of pages to check
3682 *
3683 * Checks pages for evictability and moves them to the appropriate lru list.
3684 *
3685 * This function is only used for SysV IPC SHM_UNLOCK.
3686 */
3687void check_move_unevictable_pages(struct page **pages, int nr_pages)
3688{
3689 struct lruvec *lruvec;
3690 struct zone *zone = NULL;
3691 int pgscanned = 0;
3692 int pgrescued = 0;
3693 int i;
3694
3695 for (i = 0; i < nr_pages; i++) {
3696 struct page *page = pages[i];
3697 struct zone *pagezone;
3698
3699 pgscanned++;
3700 pagezone = page_zone(page);
3701 if (pagezone != zone) {
3702 if (zone)
3703 spin_unlock_irq(&zone->lru_lock);
3704 zone = pagezone;
3705 spin_lock_irq(&zone->lru_lock);
3706 }
3707 lruvec = mem_cgroup_page_lruvec(page, zone);
3708
3709 if (!PageLRU(page) || !PageUnevictable(page))
3710 continue;
3711
3712 if (page_evictable(page)) {
3713 enum lru_list lru = page_lru_base_type(page);
3714
3715 VM_BUG_ON_PAGE(PageActive(page), page);
3716 ClearPageUnevictable(page);
3717 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3718 add_page_to_lru_list(page, lruvec, lru);
3719 pgrescued++;
3720 }
3721 }
3722
3723 if (zone) {
3724 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3725 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3726 spin_unlock_irq(&zone->lru_lock);
3727 }
3728}
3729#endif /* CONFIG_SHMEM */
3730
3731static void warn_scan_unevictable_pages(void)
3732{
3733 printk_once(KERN_WARNING
3734 "%s: The scan_unevictable_pages sysctl/node-interface has been "
3735 "disabled for lack of a legitimate use case. If you have "
3736 "one, please send an email to linux-mm@kvack.org.\n",
3737 current->comm);
3738}
3739
3740/*
3741 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
3742 * all nodes' unevictable lists for evictable pages
3743 */
3744unsigned long scan_unevictable_pages;
3745
3746int scan_unevictable_handler(struct ctl_table *table, int write,
3747 void __user *buffer,
3748 size_t *length, loff_t *ppos)
3749{
3750 warn_scan_unevictable_pages();
3751 proc_doulongvec_minmax(table, write, buffer, length, ppos);
3752 scan_unevictable_pages = 0;
3753 return 0;
3754}
3755
3756#ifdef CONFIG_NUMA
3757/*
3758 * per node 'scan_unevictable_pages' attribute. On demand re-scan of
3759 * a specified node's per zone unevictable lists for evictable pages.
3760 */
3761
3762static ssize_t read_scan_unevictable_node(struct device *dev,
3763 struct device_attribute *attr,
3764 char *buf)
3765{
3766 warn_scan_unevictable_pages();
3767 return sprintf(buf, "0\n"); /* always zero; should fit... */
3768}
3769
3770static ssize_t write_scan_unevictable_node(struct device *dev,
3771 struct device_attribute *attr,
3772 const char *buf, size_t count)
3773{
3774 warn_scan_unevictable_pages();
3775 return 1;
3776}
3777
3778
3779static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3780 read_scan_unevictable_node,
3781 write_scan_unevictable_node);
3782
3783int scan_unevictable_register_node(struct node *node)
3784{
3785 return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3786}
3787
3788void scan_unevictable_unregister_node(struct node *node)
3789{
3790 device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3791}
3792#endif