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