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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/mm/compaction.c
4 *
5 * Memory compaction for the reduction of external fragmentation. Note that
6 * this heavily depends upon page migration to do all the real heavy
7 * lifting
8 *
9 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
10 */
11#include <linux/cpu.h>
12#include <linux/swap.h>
13#include <linux/migrate.h>
14#include <linux/compaction.h>
15#include <linux/mm_inline.h>
16#include <linux/sched/signal.h>
17#include <linux/backing-dev.h>
18#include <linux/sysctl.h>
19#include <linux/sysfs.h>
20#include <linux/page-isolation.h>
21#include <linux/kasan.h>
22#include <linux/kthread.h>
23#include <linux/freezer.h>
24#include <linux/page_owner.h>
25#include <linux/psi.h>
26#include "internal.h"
27
28#ifdef CONFIG_COMPACTION
29static inline void count_compact_event(enum vm_event_item item)
30{
31 count_vm_event(item);
32}
33
34static inline void count_compact_events(enum vm_event_item item, long delta)
35{
36 count_vm_events(item, delta);
37}
38#else
39#define count_compact_event(item) do { } while (0)
40#define count_compact_events(item, delta) do { } while (0)
41#endif
42
43#if defined CONFIG_COMPACTION || defined CONFIG_CMA
44
45#define CREATE_TRACE_POINTS
46#include <trace/events/compaction.h>
47
48#define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
49#define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
50#define pageblock_start_pfn(pfn) block_start_pfn(pfn, pageblock_order)
51#define pageblock_end_pfn(pfn) block_end_pfn(pfn, pageblock_order)
52
53/*
54 * Fragmentation score check interval for proactive compaction purposes.
55 */
56static const unsigned int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
57
58/*
59 * Page order with-respect-to which proactive compaction
60 * calculates external fragmentation, which is used as
61 * the "fragmentation score" of a node/zone.
62 */
63#if defined CONFIG_TRANSPARENT_HUGEPAGE
64#define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER
65#elif defined CONFIG_HUGETLBFS
66#define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER
67#else
68#define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT)
69#endif
70
71static unsigned long release_freepages(struct list_head *freelist)
72{
73 struct page *page, *next;
74 unsigned long high_pfn = 0;
75
76 list_for_each_entry_safe(page, next, freelist, lru) {
77 unsigned long pfn = page_to_pfn(page);
78 list_del(&page->lru);
79 __free_page(page);
80 if (pfn > high_pfn)
81 high_pfn = pfn;
82 }
83
84 return high_pfn;
85}
86
87static void split_map_pages(struct list_head *list)
88{
89 unsigned int i, order, nr_pages;
90 struct page *page, *next;
91 LIST_HEAD(tmp_list);
92
93 list_for_each_entry_safe(page, next, list, lru) {
94 list_del(&page->lru);
95
96 order = page_private(page);
97 nr_pages = 1 << order;
98
99 post_alloc_hook(page, order, __GFP_MOVABLE);
100 if (order)
101 split_page(page, order);
102
103 for (i = 0; i < nr_pages; i++) {
104 list_add(&page->lru, &tmp_list);
105 page++;
106 }
107 }
108
109 list_splice(&tmp_list, list);
110}
111
112#ifdef CONFIG_COMPACTION
113
114int PageMovable(struct page *page)
115{
116 struct address_space *mapping;
117
118 VM_BUG_ON_PAGE(!PageLocked(page), page);
119 if (!__PageMovable(page))
120 return 0;
121
122 mapping = page_mapping(page);
123 if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
124 return 1;
125
126 return 0;
127}
128EXPORT_SYMBOL(PageMovable);
129
130void __SetPageMovable(struct page *page, struct address_space *mapping)
131{
132 VM_BUG_ON_PAGE(!PageLocked(page), page);
133 VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
134 page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
135}
136EXPORT_SYMBOL(__SetPageMovable);
137
138void __ClearPageMovable(struct page *page)
139{
140 VM_BUG_ON_PAGE(!PageMovable(page), page);
141 /*
142 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
143 * flag so that VM can catch up released page by driver after isolation.
144 * With it, VM migration doesn't try to put it back.
145 */
146 page->mapping = (void *)((unsigned long)page->mapping &
147 PAGE_MAPPING_MOVABLE);
148}
149EXPORT_SYMBOL(__ClearPageMovable);
150
151/* Do not skip compaction more than 64 times */
152#define COMPACT_MAX_DEFER_SHIFT 6
153
154/*
155 * Compaction is deferred when compaction fails to result in a page
156 * allocation success. 1 << compact_defer_shift, compactions are skipped up
157 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
158 */
159static void defer_compaction(struct zone *zone, int order)
160{
161 zone->compact_considered = 0;
162 zone->compact_defer_shift++;
163
164 if (order < zone->compact_order_failed)
165 zone->compact_order_failed = order;
166
167 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
168 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
169
170 trace_mm_compaction_defer_compaction(zone, order);
171}
172
173/* Returns true if compaction should be skipped this time */
174static bool compaction_deferred(struct zone *zone, int order)
175{
176 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
177
178 if (order < zone->compact_order_failed)
179 return false;
180
181 /* Avoid possible overflow */
182 if (++zone->compact_considered >= defer_limit) {
183 zone->compact_considered = defer_limit;
184 return false;
185 }
186
187 trace_mm_compaction_deferred(zone, order);
188
189 return true;
190}
191
192/*
193 * Update defer tracking counters after successful compaction of given order,
194 * which means an allocation either succeeded (alloc_success == true) or is
195 * expected to succeed.
196 */
197void compaction_defer_reset(struct zone *zone, int order,
198 bool alloc_success)
199{
200 if (alloc_success) {
201 zone->compact_considered = 0;
202 zone->compact_defer_shift = 0;
203 }
204 if (order >= zone->compact_order_failed)
205 zone->compact_order_failed = order + 1;
206
207 trace_mm_compaction_defer_reset(zone, order);
208}
209
210/* Returns true if restarting compaction after many failures */
211static bool compaction_restarting(struct zone *zone, int order)
212{
213 if (order < zone->compact_order_failed)
214 return false;
215
216 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
217 zone->compact_considered >= 1UL << zone->compact_defer_shift;
218}
219
220/* Returns true if the pageblock should be scanned for pages to isolate. */
221static inline bool isolation_suitable(struct compact_control *cc,
222 struct page *page)
223{
224 if (cc->ignore_skip_hint)
225 return true;
226
227 return !get_pageblock_skip(page);
228}
229
230static void reset_cached_positions(struct zone *zone)
231{
232 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
233 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
234 zone->compact_cached_free_pfn =
235 pageblock_start_pfn(zone_end_pfn(zone) - 1);
236}
237
238/*
239 * Compound pages of >= pageblock_order should consistently be skipped until
240 * released. It is always pointless to compact pages of such order (if they are
241 * migratable), and the pageblocks they occupy cannot contain any free pages.
242 */
243static bool pageblock_skip_persistent(struct page *page)
244{
245 if (!PageCompound(page))
246 return false;
247
248 page = compound_head(page);
249
250 if (compound_order(page) >= pageblock_order)
251 return true;
252
253 return false;
254}
255
256static bool
257__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
258 bool check_target)
259{
260 struct page *page = pfn_to_online_page(pfn);
261 struct page *block_page;
262 struct page *end_page;
263 unsigned long block_pfn;
264
265 if (!page)
266 return false;
267 if (zone != page_zone(page))
268 return false;
269 if (pageblock_skip_persistent(page))
270 return false;
271
272 /*
273 * If skip is already cleared do no further checking once the
274 * restart points have been set.
275 */
276 if (check_source && check_target && !get_pageblock_skip(page))
277 return true;
278
279 /*
280 * If clearing skip for the target scanner, do not select a
281 * non-movable pageblock as the starting point.
282 */
283 if (!check_source && check_target &&
284 get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
285 return false;
286
287 /* Ensure the start of the pageblock or zone is online and valid */
288 block_pfn = pageblock_start_pfn(pfn);
289 block_pfn = max(block_pfn, zone->zone_start_pfn);
290 block_page = pfn_to_online_page(block_pfn);
291 if (block_page) {
292 page = block_page;
293 pfn = block_pfn;
294 }
295
296 /* Ensure the end of the pageblock or zone is online and valid */
297 block_pfn = pageblock_end_pfn(pfn) - 1;
298 block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
299 end_page = pfn_to_online_page(block_pfn);
300 if (!end_page)
301 return false;
302
303 /*
304 * Only clear the hint if a sample indicates there is either a
305 * free page or an LRU page in the block. One or other condition
306 * is necessary for the block to be a migration source/target.
307 */
308 do {
309 if (pfn_valid_within(pfn)) {
310 if (check_source && PageLRU(page)) {
311 clear_pageblock_skip(page);
312 return true;
313 }
314
315 if (check_target && PageBuddy(page)) {
316 clear_pageblock_skip(page);
317 return true;
318 }
319 }
320
321 page += (1 << PAGE_ALLOC_COSTLY_ORDER);
322 pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
323 } while (page <= end_page);
324
325 return false;
326}
327
328/*
329 * This function is called to clear all cached information on pageblocks that
330 * should be skipped for page isolation when the migrate and free page scanner
331 * meet.
332 */
333static void __reset_isolation_suitable(struct zone *zone)
334{
335 unsigned long migrate_pfn = zone->zone_start_pfn;
336 unsigned long free_pfn = zone_end_pfn(zone) - 1;
337 unsigned long reset_migrate = free_pfn;
338 unsigned long reset_free = migrate_pfn;
339 bool source_set = false;
340 bool free_set = false;
341
342 if (!zone->compact_blockskip_flush)
343 return;
344
345 zone->compact_blockskip_flush = false;
346
347 /*
348 * Walk the zone and update pageblock skip information. Source looks
349 * for PageLRU while target looks for PageBuddy. When the scanner
350 * is found, both PageBuddy and PageLRU are checked as the pageblock
351 * is suitable as both source and target.
352 */
353 for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
354 free_pfn -= pageblock_nr_pages) {
355 cond_resched();
356
357 /* Update the migrate PFN */
358 if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
359 migrate_pfn < reset_migrate) {
360 source_set = true;
361 reset_migrate = migrate_pfn;
362 zone->compact_init_migrate_pfn = reset_migrate;
363 zone->compact_cached_migrate_pfn[0] = reset_migrate;
364 zone->compact_cached_migrate_pfn[1] = reset_migrate;
365 }
366
367 /* Update the free PFN */
368 if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
369 free_pfn > reset_free) {
370 free_set = true;
371 reset_free = free_pfn;
372 zone->compact_init_free_pfn = reset_free;
373 zone->compact_cached_free_pfn = reset_free;
374 }
375 }
376
377 /* Leave no distance if no suitable block was reset */
378 if (reset_migrate >= reset_free) {
379 zone->compact_cached_migrate_pfn[0] = migrate_pfn;
380 zone->compact_cached_migrate_pfn[1] = migrate_pfn;
381 zone->compact_cached_free_pfn = free_pfn;
382 }
383}
384
385void reset_isolation_suitable(pg_data_t *pgdat)
386{
387 int zoneid;
388
389 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
390 struct zone *zone = &pgdat->node_zones[zoneid];
391 if (!populated_zone(zone))
392 continue;
393
394 /* Only flush if a full compaction finished recently */
395 if (zone->compact_blockskip_flush)
396 __reset_isolation_suitable(zone);
397 }
398}
399
400/*
401 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
402 * locks are not required for read/writers. Returns true if it was already set.
403 */
404static bool test_and_set_skip(struct compact_control *cc, struct page *page,
405 unsigned long pfn)
406{
407 bool skip;
408
409 /* Do no update if skip hint is being ignored */
410 if (cc->ignore_skip_hint)
411 return false;
412
413 if (!IS_ALIGNED(pfn, pageblock_nr_pages))
414 return false;
415
416 skip = get_pageblock_skip(page);
417 if (!skip && !cc->no_set_skip_hint)
418 set_pageblock_skip(page);
419
420 return skip;
421}
422
423static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
424{
425 struct zone *zone = cc->zone;
426
427 pfn = pageblock_end_pfn(pfn);
428
429 /* Set for isolation rather than compaction */
430 if (cc->no_set_skip_hint)
431 return;
432
433 if (pfn > zone->compact_cached_migrate_pfn[0])
434 zone->compact_cached_migrate_pfn[0] = pfn;
435 if (cc->mode != MIGRATE_ASYNC &&
436 pfn > zone->compact_cached_migrate_pfn[1])
437 zone->compact_cached_migrate_pfn[1] = pfn;
438}
439
440/*
441 * If no pages were isolated then mark this pageblock to be skipped in the
442 * future. The information is later cleared by __reset_isolation_suitable().
443 */
444static void update_pageblock_skip(struct compact_control *cc,
445 struct page *page, unsigned long pfn)
446{
447 struct zone *zone = cc->zone;
448
449 if (cc->no_set_skip_hint)
450 return;
451
452 if (!page)
453 return;
454
455 set_pageblock_skip(page);
456
457 /* Update where async and sync compaction should restart */
458 if (pfn < zone->compact_cached_free_pfn)
459 zone->compact_cached_free_pfn = pfn;
460}
461#else
462static inline bool isolation_suitable(struct compact_control *cc,
463 struct page *page)
464{
465 return true;
466}
467
468static inline bool pageblock_skip_persistent(struct page *page)
469{
470 return false;
471}
472
473static inline void update_pageblock_skip(struct compact_control *cc,
474 struct page *page, unsigned long pfn)
475{
476}
477
478static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
479{
480}
481
482static bool test_and_set_skip(struct compact_control *cc, struct page *page,
483 unsigned long pfn)
484{
485 return false;
486}
487#endif /* CONFIG_COMPACTION */
488
489/*
490 * Compaction requires the taking of some coarse locks that are potentially
491 * very heavily contended. For async compaction, trylock and record if the
492 * lock is contended. The lock will still be acquired but compaction will
493 * abort when the current block is finished regardless of success rate.
494 * Sync compaction acquires the lock.
495 *
496 * Always returns true which makes it easier to track lock state in callers.
497 */
498static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
499 struct compact_control *cc)
500 __acquires(lock)
501{
502 /* Track if the lock is contended in async mode */
503 if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
504 if (spin_trylock_irqsave(lock, *flags))
505 return true;
506
507 cc->contended = true;
508 }
509
510 spin_lock_irqsave(lock, *flags);
511 return true;
512}
513
514/*
515 * Compaction requires the taking of some coarse locks that are potentially
516 * very heavily contended. The lock should be periodically unlocked to avoid
517 * having disabled IRQs for a long time, even when there is nobody waiting on
518 * the lock. It might also be that allowing the IRQs will result in
519 * need_resched() becoming true. If scheduling is needed, async compaction
520 * aborts. Sync compaction schedules.
521 * Either compaction type will also abort if a fatal signal is pending.
522 * In either case if the lock was locked, it is dropped and not regained.
523 *
524 * Returns true if compaction should abort due to fatal signal pending, or
525 * async compaction due to need_resched()
526 * Returns false when compaction can continue (sync compaction might have
527 * scheduled)
528 */
529static bool compact_unlock_should_abort(spinlock_t *lock,
530 unsigned long flags, bool *locked, struct compact_control *cc)
531{
532 if (*locked) {
533 spin_unlock_irqrestore(lock, flags);
534 *locked = false;
535 }
536
537 if (fatal_signal_pending(current)) {
538 cc->contended = true;
539 return true;
540 }
541
542 cond_resched();
543
544 return false;
545}
546
547/*
548 * Isolate free pages onto a private freelist. If @strict is true, will abort
549 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
550 * (even though it may still end up isolating some pages).
551 */
552static unsigned long isolate_freepages_block(struct compact_control *cc,
553 unsigned long *start_pfn,
554 unsigned long end_pfn,
555 struct list_head *freelist,
556 unsigned int stride,
557 bool strict)
558{
559 int nr_scanned = 0, total_isolated = 0;
560 struct page *cursor;
561 unsigned long flags = 0;
562 bool locked = false;
563 unsigned long blockpfn = *start_pfn;
564 unsigned int order;
565
566 /* Strict mode is for isolation, speed is secondary */
567 if (strict)
568 stride = 1;
569
570 cursor = pfn_to_page(blockpfn);
571
572 /* Isolate free pages. */
573 for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
574 int isolated;
575 struct page *page = cursor;
576
577 /*
578 * Periodically drop the lock (if held) regardless of its
579 * contention, to give chance to IRQs. Abort if fatal signal
580 * pending or async compaction detects need_resched()
581 */
582 if (!(blockpfn % SWAP_CLUSTER_MAX)
583 && compact_unlock_should_abort(&cc->zone->lock, flags,
584 &locked, cc))
585 break;
586
587 nr_scanned++;
588 if (!pfn_valid_within(blockpfn))
589 goto isolate_fail;
590
591 /*
592 * For compound pages such as THP and hugetlbfs, we can save
593 * potentially a lot of iterations if we skip them at once.
594 * The check is racy, but we can consider only valid values
595 * and the only danger is skipping too much.
596 */
597 if (PageCompound(page)) {
598 const unsigned int order = compound_order(page);
599
600 if (likely(order < MAX_ORDER)) {
601 blockpfn += (1UL << order) - 1;
602 cursor += (1UL << order) - 1;
603 }
604 goto isolate_fail;
605 }
606
607 if (!PageBuddy(page))
608 goto isolate_fail;
609
610 /*
611 * If we already hold the lock, we can skip some rechecking.
612 * Note that if we hold the lock now, checked_pageblock was
613 * already set in some previous iteration (or strict is true),
614 * so it is correct to skip the suitable migration target
615 * recheck as well.
616 */
617 if (!locked) {
618 locked = compact_lock_irqsave(&cc->zone->lock,
619 &flags, cc);
620
621 /* Recheck this is a buddy page under lock */
622 if (!PageBuddy(page))
623 goto isolate_fail;
624 }
625
626 /* Found a free page, will break it into order-0 pages */
627 order = buddy_order(page);
628 isolated = __isolate_free_page(page, order);
629 if (!isolated)
630 break;
631 set_page_private(page, order);
632
633 total_isolated += isolated;
634 cc->nr_freepages += isolated;
635 list_add_tail(&page->lru, freelist);
636
637 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
638 blockpfn += isolated;
639 break;
640 }
641 /* Advance to the end of split page */
642 blockpfn += isolated - 1;
643 cursor += isolated - 1;
644 continue;
645
646isolate_fail:
647 if (strict)
648 break;
649 else
650 continue;
651
652 }
653
654 if (locked)
655 spin_unlock_irqrestore(&cc->zone->lock, flags);
656
657 /*
658 * There is a tiny chance that we have read bogus compound_order(),
659 * so be careful to not go outside of the pageblock.
660 */
661 if (unlikely(blockpfn > end_pfn))
662 blockpfn = end_pfn;
663
664 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
665 nr_scanned, total_isolated);
666
667 /* Record how far we have got within the block */
668 *start_pfn = blockpfn;
669
670 /*
671 * If strict isolation is requested by CMA then check that all the
672 * pages requested were isolated. If there were any failures, 0 is
673 * returned and CMA will fail.
674 */
675 if (strict && blockpfn < end_pfn)
676 total_isolated = 0;
677
678 cc->total_free_scanned += nr_scanned;
679 if (total_isolated)
680 count_compact_events(COMPACTISOLATED, total_isolated);
681 return total_isolated;
682}
683
684/**
685 * isolate_freepages_range() - isolate free pages.
686 * @cc: Compaction control structure.
687 * @start_pfn: The first PFN to start isolating.
688 * @end_pfn: The one-past-last PFN.
689 *
690 * Non-free pages, invalid PFNs, or zone boundaries within the
691 * [start_pfn, end_pfn) range are considered errors, cause function to
692 * undo its actions and return zero.
693 *
694 * Otherwise, function returns one-past-the-last PFN of isolated page
695 * (which may be greater then end_pfn if end fell in a middle of
696 * a free page).
697 */
698unsigned long
699isolate_freepages_range(struct compact_control *cc,
700 unsigned long start_pfn, unsigned long end_pfn)
701{
702 unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
703 LIST_HEAD(freelist);
704
705 pfn = start_pfn;
706 block_start_pfn = pageblock_start_pfn(pfn);
707 if (block_start_pfn < cc->zone->zone_start_pfn)
708 block_start_pfn = cc->zone->zone_start_pfn;
709 block_end_pfn = pageblock_end_pfn(pfn);
710
711 for (; pfn < end_pfn; pfn += isolated,
712 block_start_pfn = block_end_pfn,
713 block_end_pfn += pageblock_nr_pages) {
714 /* Protect pfn from changing by isolate_freepages_block */
715 unsigned long isolate_start_pfn = pfn;
716
717 block_end_pfn = min(block_end_pfn, end_pfn);
718
719 /*
720 * pfn could pass the block_end_pfn if isolated freepage
721 * is more than pageblock order. In this case, we adjust
722 * scanning range to right one.
723 */
724 if (pfn >= block_end_pfn) {
725 block_start_pfn = pageblock_start_pfn(pfn);
726 block_end_pfn = pageblock_end_pfn(pfn);
727 block_end_pfn = min(block_end_pfn, end_pfn);
728 }
729
730 if (!pageblock_pfn_to_page(block_start_pfn,
731 block_end_pfn, cc->zone))
732 break;
733
734 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
735 block_end_pfn, &freelist, 0, true);
736
737 /*
738 * In strict mode, isolate_freepages_block() returns 0 if
739 * there are any holes in the block (ie. invalid PFNs or
740 * non-free pages).
741 */
742 if (!isolated)
743 break;
744
745 /*
746 * If we managed to isolate pages, it is always (1 << n) *
747 * pageblock_nr_pages for some non-negative n. (Max order
748 * page may span two pageblocks).
749 */
750 }
751
752 /* __isolate_free_page() does not map the pages */
753 split_map_pages(&freelist);
754
755 if (pfn < end_pfn) {
756 /* Loop terminated early, cleanup. */
757 release_freepages(&freelist);
758 return 0;
759 }
760
761 /* We don't use freelists for anything. */
762 return pfn;
763}
764
765/* Similar to reclaim, but different enough that they don't share logic */
766static bool too_many_isolated(pg_data_t *pgdat)
767{
768 unsigned long active, inactive, isolated;
769
770 inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
771 node_page_state(pgdat, NR_INACTIVE_ANON);
772 active = node_page_state(pgdat, NR_ACTIVE_FILE) +
773 node_page_state(pgdat, NR_ACTIVE_ANON);
774 isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
775 node_page_state(pgdat, NR_ISOLATED_ANON);
776
777 return isolated > (inactive + active) / 2;
778}
779
780/**
781 * isolate_migratepages_block() - isolate all migrate-able pages within
782 * a single pageblock
783 * @cc: Compaction control structure.
784 * @low_pfn: The first PFN to isolate
785 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
786 * @isolate_mode: Isolation mode to be used.
787 *
788 * Isolate all pages that can be migrated from the range specified by
789 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
790 * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
791 * -ENOMEM in case we could not allocate a page, or 0.
792 * cc->migrate_pfn will contain the next pfn to scan.
793 *
794 * The pages are isolated on cc->migratepages list (not required to be empty),
795 * and cc->nr_migratepages is updated accordingly.
796 */
797static int
798isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
799 unsigned long end_pfn, isolate_mode_t isolate_mode)
800{
801 pg_data_t *pgdat = cc->zone->zone_pgdat;
802 unsigned long nr_scanned = 0, nr_isolated = 0;
803 struct lruvec *lruvec;
804 unsigned long flags = 0;
805 struct lruvec *locked = NULL;
806 struct page *page = NULL, *valid_page = NULL;
807 unsigned long start_pfn = low_pfn;
808 bool skip_on_failure = false;
809 unsigned long next_skip_pfn = 0;
810 bool skip_updated = false;
811 int ret = 0;
812
813 cc->migrate_pfn = low_pfn;
814
815 /*
816 * Ensure that there are not too many pages isolated from the LRU
817 * list by either parallel reclaimers or compaction. If there are,
818 * delay for some time until fewer pages are isolated
819 */
820 while (unlikely(too_many_isolated(pgdat))) {
821 /* stop isolation if there are still pages not migrated */
822 if (cc->nr_migratepages)
823 return -EAGAIN;
824
825 /* async migration should just abort */
826 if (cc->mode == MIGRATE_ASYNC)
827 return -EAGAIN;
828
829 congestion_wait(BLK_RW_ASYNC, HZ/10);
830
831 if (fatal_signal_pending(current))
832 return -EINTR;
833 }
834
835 cond_resched();
836
837 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
838 skip_on_failure = true;
839 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
840 }
841
842 /* Time to isolate some pages for migration */
843 for (; low_pfn < end_pfn; low_pfn++) {
844
845 if (skip_on_failure && low_pfn >= next_skip_pfn) {
846 /*
847 * We have isolated all migration candidates in the
848 * previous order-aligned block, and did not skip it due
849 * to failure. We should migrate the pages now and
850 * hopefully succeed compaction.
851 */
852 if (nr_isolated)
853 break;
854
855 /*
856 * We failed to isolate in the previous order-aligned
857 * block. Set the new boundary to the end of the
858 * current block. Note we can't simply increase
859 * next_skip_pfn by 1 << order, as low_pfn might have
860 * been incremented by a higher number due to skipping
861 * a compound or a high-order buddy page in the
862 * previous loop iteration.
863 */
864 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
865 }
866
867 /*
868 * Periodically drop the lock (if held) regardless of its
869 * contention, to give chance to IRQs. Abort completely if
870 * a fatal signal is pending.
871 */
872 if (!(low_pfn % SWAP_CLUSTER_MAX)) {
873 if (locked) {
874 unlock_page_lruvec_irqrestore(locked, flags);
875 locked = NULL;
876 }
877
878 if (fatal_signal_pending(current)) {
879 cc->contended = true;
880 ret = -EINTR;
881
882 goto fatal_pending;
883 }
884
885 cond_resched();
886 }
887
888 if (!pfn_valid_within(low_pfn))
889 goto isolate_fail;
890 nr_scanned++;
891
892 page = pfn_to_page(low_pfn);
893
894 /*
895 * Check if the pageblock has already been marked skipped.
896 * Only the aligned PFN is checked as the caller isolates
897 * COMPACT_CLUSTER_MAX at a time so the second call must
898 * not falsely conclude that the block should be skipped.
899 */
900 if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
901 if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
902 low_pfn = end_pfn;
903 page = NULL;
904 goto isolate_abort;
905 }
906 valid_page = page;
907 }
908
909 if (PageHuge(page) && cc->alloc_contig) {
910 ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
911
912 /*
913 * Fail isolation in case isolate_or_dissolve_huge_page()
914 * reports an error. In case of -ENOMEM, abort right away.
915 */
916 if (ret < 0) {
917 /* Do not report -EBUSY down the chain */
918 if (ret == -EBUSY)
919 ret = 0;
920 low_pfn += (1UL << compound_order(page)) - 1;
921 goto isolate_fail;
922 }
923
924 if (PageHuge(page)) {
925 /*
926 * Hugepage was successfully isolated and placed
927 * on the cc->migratepages list.
928 */
929 low_pfn += compound_nr(page) - 1;
930 goto isolate_success_no_list;
931 }
932
933 /*
934 * Ok, the hugepage was dissolved. Now these pages are
935 * Buddy and cannot be re-allocated because they are
936 * isolated. Fall-through as the check below handles
937 * Buddy pages.
938 */
939 }
940
941 /*
942 * Skip if free. We read page order here without zone lock
943 * which is generally unsafe, but the race window is small and
944 * the worst thing that can happen is that we skip some
945 * potential isolation targets.
946 */
947 if (PageBuddy(page)) {
948 unsigned long freepage_order = buddy_order_unsafe(page);
949
950 /*
951 * Without lock, we cannot be sure that what we got is
952 * a valid page order. Consider only values in the
953 * valid order range to prevent low_pfn overflow.
954 */
955 if (freepage_order > 0 && freepage_order < MAX_ORDER)
956 low_pfn += (1UL << freepage_order) - 1;
957 continue;
958 }
959
960 /*
961 * Regardless of being on LRU, compound pages such as THP and
962 * hugetlbfs are not to be compacted unless we are attempting
963 * an allocation much larger than the huge page size (eg CMA).
964 * We can potentially save a lot of iterations if we skip them
965 * at once. The check is racy, but we can consider only valid
966 * values and the only danger is skipping too much.
967 */
968 if (PageCompound(page) && !cc->alloc_contig) {
969 const unsigned int order = compound_order(page);
970
971 if (likely(order < MAX_ORDER))
972 low_pfn += (1UL << order) - 1;
973 goto isolate_fail;
974 }
975
976 /*
977 * Check may be lockless but that's ok as we recheck later.
978 * It's possible to migrate LRU and non-lru movable pages.
979 * Skip any other type of page
980 */
981 if (!PageLRU(page)) {
982 /*
983 * __PageMovable can return false positive so we need
984 * to verify it under page_lock.
985 */
986 if (unlikely(__PageMovable(page)) &&
987 !PageIsolated(page)) {
988 if (locked) {
989 unlock_page_lruvec_irqrestore(locked, flags);
990 locked = NULL;
991 }
992
993 if (!isolate_movable_page(page, isolate_mode))
994 goto isolate_success;
995 }
996
997 goto isolate_fail;
998 }
999
1000 /*
1001 * Migration will fail if an anonymous page is pinned in memory,
1002 * so avoid taking lru_lock and isolating it unnecessarily in an
1003 * admittedly racy check.
1004 */
1005 if (!page_mapping(page) &&
1006 page_count(page) > page_mapcount(page))
1007 goto isolate_fail;
1008
1009 /*
1010 * Only allow to migrate anonymous pages in GFP_NOFS context
1011 * because those do not depend on fs locks.
1012 */
1013 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
1014 goto isolate_fail;
1015
1016 /*
1017 * Be careful not to clear PageLRU until after we're
1018 * sure the page is not being freed elsewhere -- the
1019 * page release code relies on it.
1020 */
1021 if (unlikely(!get_page_unless_zero(page)))
1022 goto isolate_fail;
1023
1024 if (!__isolate_lru_page_prepare(page, isolate_mode))
1025 goto isolate_fail_put;
1026
1027 /* Try isolate the page */
1028 if (!TestClearPageLRU(page))
1029 goto isolate_fail_put;
1030
1031 lruvec = mem_cgroup_page_lruvec(page);
1032
1033 /* If we already hold the lock, we can skip some rechecking */
1034 if (lruvec != locked) {
1035 if (locked)
1036 unlock_page_lruvec_irqrestore(locked, flags);
1037
1038 compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
1039 locked = lruvec;
1040
1041 lruvec_memcg_debug(lruvec, page);
1042
1043 /* Try get exclusive access under lock */
1044 if (!skip_updated) {
1045 skip_updated = true;
1046 if (test_and_set_skip(cc, page, low_pfn))
1047 goto isolate_abort;
1048 }
1049
1050 /*
1051 * Page become compound since the non-locked check,
1052 * and it's on LRU. It can only be a THP so the order
1053 * is safe to read and it's 0 for tail pages.
1054 */
1055 if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
1056 low_pfn += compound_nr(page) - 1;
1057 SetPageLRU(page);
1058 goto isolate_fail_put;
1059 }
1060 }
1061
1062 /* The whole page is taken off the LRU; skip the tail pages. */
1063 if (PageCompound(page))
1064 low_pfn += compound_nr(page) - 1;
1065
1066 /* Successfully isolated */
1067 del_page_from_lru_list(page, lruvec);
1068 mod_node_page_state(page_pgdat(page),
1069 NR_ISOLATED_ANON + page_is_file_lru(page),
1070 thp_nr_pages(page));
1071
1072isolate_success:
1073 list_add(&page->lru, &cc->migratepages);
1074isolate_success_no_list:
1075 cc->nr_migratepages += compound_nr(page);
1076 nr_isolated += compound_nr(page);
1077
1078 /*
1079 * Avoid isolating too much unless this block is being
1080 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1081 * or a lock is contended. For contention, isolate quickly to
1082 * potentially remove one source of contention.
1083 */
1084 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
1085 !cc->rescan && !cc->contended) {
1086 ++low_pfn;
1087 break;
1088 }
1089
1090 continue;
1091
1092isolate_fail_put:
1093 /* Avoid potential deadlock in freeing page under lru_lock */
1094 if (locked) {
1095 unlock_page_lruvec_irqrestore(locked, flags);
1096 locked = NULL;
1097 }
1098 put_page(page);
1099
1100isolate_fail:
1101 if (!skip_on_failure && ret != -ENOMEM)
1102 continue;
1103
1104 /*
1105 * We have isolated some pages, but then failed. Release them
1106 * instead of migrating, as we cannot form the cc->order buddy
1107 * page anyway.
1108 */
1109 if (nr_isolated) {
1110 if (locked) {
1111 unlock_page_lruvec_irqrestore(locked, flags);
1112 locked = NULL;
1113 }
1114 putback_movable_pages(&cc->migratepages);
1115 cc->nr_migratepages = 0;
1116 nr_isolated = 0;
1117 }
1118
1119 if (low_pfn < next_skip_pfn) {
1120 low_pfn = next_skip_pfn - 1;
1121 /*
1122 * The check near the loop beginning would have updated
1123 * next_skip_pfn too, but this is a bit simpler.
1124 */
1125 next_skip_pfn += 1UL << cc->order;
1126 }
1127
1128 if (ret == -ENOMEM)
1129 break;
1130 }
1131
1132 /*
1133 * The PageBuddy() check could have potentially brought us outside
1134 * the range to be scanned.
1135 */
1136 if (unlikely(low_pfn > end_pfn))
1137 low_pfn = end_pfn;
1138
1139 page = NULL;
1140
1141isolate_abort:
1142 if (locked)
1143 unlock_page_lruvec_irqrestore(locked, flags);
1144 if (page) {
1145 SetPageLRU(page);
1146 put_page(page);
1147 }
1148
1149 /*
1150 * Updated the cached scanner pfn once the pageblock has been scanned
1151 * Pages will either be migrated in which case there is no point
1152 * scanning in the near future or migration failed in which case the
1153 * failure reason may persist. The block is marked for skipping if
1154 * there were no pages isolated in the block or if the block is
1155 * rescanned twice in a row.
1156 */
1157 if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
1158 if (valid_page && !skip_updated)
1159 set_pageblock_skip(valid_page);
1160 update_cached_migrate(cc, low_pfn);
1161 }
1162
1163 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1164 nr_scanned, nr_isolated);
1165
1166fatal_pending:
1167 cc->total_migrate_scanned += nr_scanned;
1168 if (nr_isolated)
1169 count_compact_events(COMPACTISOLATED, nr_isolated);
1170
1171 cc->migrate_pfn = low_pfn;
1172
1173 return ret;
1174}
1175
1176/**
1177 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1178 * @cc: Compaction control structure.
1179 * @start_pfn: The first PFN to start isolating.
1180 * @end_pfn: The one-past-last PFN.
1181 *
1182 * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
1183 * in case we could not allocate a page, or 0.
1184 */
1185int
1186isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1187 unsigned long end_pfn)
1188{
1189 unsigned long pfn, block_start_pfn, block_end_pfn;
1190 int ret = 0;
1191
1192 /* Scan block by block. First and last block may be incomplete */
1193 pfn = start_pfn;
1194 block_start_pfn = pageblock_start_pfn(pfn);
1195 if (block_start_pfn < cc->zone->zone_start_pfn)
1196 block_start_pfn = cc->zone->zone_start_pfn;
1197 block_end_pfn = pageblock_end_pfn(pfn);
1198
1199 for (; pfn < end_pfn; pfn = block_end_pfn,
1200 block_start_pfn = block_end_pfn,
1201 block_end_pfn += pageblock_nr_pages) {
1202
1203 block_end_pfn = min(block_end_pfn, end_pfn);
1204
1205 if (!pageblock_pfn_to_page(block_start_pfn,
1206 block_end_pfn, cc->zone))
1207 continue;
1208
1209 ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
1210 ISOLATE_UNEVICTABLE);
1211
1212 if (ret)
1213 break;
1214
1215 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
1216 break;
1217 }
1218
1219 return ret;
1220}
1221
1222#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1223#ifdef CONFIG_COMPACTION
1224
1225static bool suitable_migration_source(struct compact_control *cc,
1226 struct page *page)
1227{
1228 int block_mt;
1229
1230 if (pageblock_skip_persistent(page))
1231 return false;
1232
1233 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1234 return true;
1235
1236 block_mt = get_pageblock_migratetype(page);
1237
1238 if (cc->migratetype == MIGRATE_MOVABLE)
1239 return is_migrate_movable(block_mt);
1240 else
1241 return block_mt == cc->migratetype;
1242}
1243
1244/* Returns true if the page is within a block suitable for migration to */
1245static bool suitable_migration_target(struct compact_control *cc,
1246 struct page *page)
1247{
1248 /* If the page is a large free page, then disallow migration */
1249 if (PageBuddy(page)) {
1250 /*
1251 * We are checking page_order without zone->lock taken. But
1252 * the only small danger is that we skip a potentially suitable
1253 * pageblock, so it's not worth to check order for valid range.
1254 */
1255 if (buddy_order_unsafe(page) >= pageblock_order)
1256 return false;
1257 }
1258
1259 if (cc->ignore_block_suitable)
1260 return true;
1261
1262 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1263 if (is_migrate_movable(get_pageblock_migratetype(page)))
1264 return true;
1265
1266 /* Otherwise skip the block */
1267 return false;
1268}
1269
1270static inline unsigned int
1271freelist_scan_limit(struct compact_control *cc)
1272{
1273 unsigned short shift = BITS_PER_LONG - 1;
1274
1275 return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1276}
1277
1278/*
1279 * Test whether the free scanner has reached the same or lower pageblock than
1280 * the migration scanner, and compaction should thus terminate.
1281 */
1282static inline bool compact_scanners_met(struct compact_control *cc)
1283{
1284 return (cc->free_pfn >> pageblock_order)
1285 <= (cc->migrate_pfn >> pageblock_order);
1286}
1287
1288/*
1289 * Used when scanning for a suitable migration target which scans freelists
1290 * in reverse. Reorders the list such as the unscanned pages are scanned
1291 * first on the next iteration of the free scanner
1292 */
1293static void
1294move_freelist_head(struct list_head *freelist, struct page *freepage)
1295{
1296 LIST_HEAD(sublist);
1297
1298 if (!list_is_last(freelist, &freepage->lru)) {
1299 list_cut_before(&sublist, freelist, &freepage->lru);
1300 list_splice_tail(&sublist, freelist);
1301 }
1302}
1303
1304/*
1305 * Similar to move_freelist_head except used by the migration scanner
1306 * when scanning forward. It's possible for these list operations to
1307 * move against each other if they search the free list exactly in
1308 * lockstep.
1309 */
1310static void
1311move_freelist_tail(struct list_head *freelist, struct page *freepage)
1312{
1313 LIST_HEAD(sublist);
1314
1315 if (!list_is_first(freelist, &freepage->lru)) {
1316 list_cut_position(&sublist, freelist, &freepage->lru);
1317 list_splice_tail(&sublist, freelist);
1318 }
1319}
1320
1321static void
1322fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
1323{
1324 unsigned long start_pfn, end_pfn;
1325 struct page *page;
1326
1327 /* Do not search around if there are enough pages already */
1328 if (cc->nr_freepages >= cc->nr_migratepages)
1329 return;
1330
1331 /* Minimise scanning during async compaction */
1332 if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1333 return;
1334
1335 /* Pageblock boundaries */
1336 start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
1337 end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
1338
1339 page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
1340 if (!page)
1341 return;
1342
1343 /* Scan before */
1344 if (start_pfn != pfn) {
1345 isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
1346 if (cc->nr_freepages >= cc->nr_migratepages)
1347 return;
1348 }
1349
1350 /* Scan after */
1351 start_pfn = pfn + nr_isolated;
1352 if (start_pfn < end_pfn)
1353 isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
1354
1355 /* Skip this pageblock in the future as it's full or nearly full */
1356 if (cc->nr_freepages < cc->nr_migratepages)
1357 set_pageblock_skip(page);
1358}
1359
1360/* Search orders in round-robin fashion */
1361static int next_search_order(struct compact_control *cc, int order)
1362{
1363 order--;
1364 if (order < 0)
1365 order = cc->order - 1;
1366
1367 /* Search wrapped around? */
1368 if (order == cc->search_order) {
1369 cc->search_order--;
1370 if (cc->search_order < 0)
1371 cc->search_order = cc->order - 1;
1372 return -1;
1373 }
1374
1375 return order;
1376}
1377
1378static unsigned long
1379fast_isolate_freepages(struct compact_control *cc)
1380{
1381 unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1);
1382 unsigned int nr_scanned = 0;
1383 unsigned long low_pfn, min_pfn, highest = 0;
1384 unsigned long nr_isolated = 0;
1385 unsigned long distance;
1386 struct page *page = NULL;
1387 bool scan_start = false;
1388 int order;
1389
1390 /* Full compaction passes in a negative order */
1391 if (cc->order <= 0)
1392 return cc->free_pfn;
1393
1394 /*
1395 * If starting the scan, use a deeper search and use the highest
1396 * PFN found if a suitable one is not found.
1397 */
1398 if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1399 limit = pageblock_nr_pages >> 1;
1400 scan_start = true;
1401 }
1402
1403 /*
1404 * Preferred point is in the top quarter of the scan space but take
1405 * a pfn from the top half if the search is problematic.
1406 */
1407 distance = (cc->free_pfn - cc->migrate_pfn);
1408 low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1409 min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1410
1411 if (WARN_ON_ONCE(min_pfn > low_pfn))
1412 low_pfn = min_pfn;
1413
1414 /*
1415 * Search starts from the last successful isolation order or the next
1416 * order to search after a previous failure
1417 */
1418 cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1419
1420 for (order = cc->search_order;
1421 !page && order >= 0;
1422 order = next_search_order(cc, order)) {
1423 struct free_area *area = &cc->zone->free_area[order];
1424 struct list_head *freelist;
1425 struct page *freepage;
1426 unsigned long flags;
1427 unsigned int order_scanned = 0;
1428 unsigned long high_pfn = 0;
1429
1430 if (!area->nr_free)
1431 continue;
1432
1433 spin_lock_irqsave(&cc->zone->lock, flags);
1434 freelist = &area->free_list[MIGRATE_MOVABLE];
1435 list_for_each_entry_reverse(freepage, freelist, lru) {
1436 unsigned long pfn;
1437
1438 order_scanned++;
1439 nr_scanned++;
1440 pfn = page_to_pfn(freepage);
1441
1442 if (pfn >= highest)
1443 highest = max(pageblock_start_pfn(pfn),
1444 cc->zone->zone_start_pfn);
1445
1446 if (pfn >= low_pfn) {
1447 cc->fast_search_fail = 0;
1448 cc->search_order = order;
1449 page = freepage;
1450 break;
1451 }
1452
1453 if (pfn >= min_pfn && pfn > high_pfn) {
1454 high_pfn = pfn;
1455
1456 /* Shorten the scan if a candidate is found */
1457 limit >>= 1;
1458 }
1459
1460 if (order_scanned >= limit)
1461 break;
1462 }
1463
1464 /* Use a minimum pfn if a preferred one was not found */
1465 if (!page && high_pfn) {
1466 page = pfn_to_page(high_pfn);
1467
1468 /* Update freepage for the list reorder below */
1469 freepage = page;
1470 }
1471
1472 /* Reorder to so a future search skips recent pages */
1473 move_freelist_head(freelist, freepage);
1474
1475 /* Isolate the page if available */
1476 if (page) {
1477 if (__isolate_free_page(page, order)) {
1478 set_page_private(page, order);
1479 nr_isolated = 1 << order;
1480 cc->nr_freepages += nr_isolated;
1481 list_add_tail(&page->lru, &cc->freepages);
1482 count_compact_events(COMPACTISOLATED, nr_isolated);
1483 } else {
1484 /* If isolation fails, abort the search */
1485 order = cc->search_order + 1;
1486 page = NULL;
1487 }
1488 }
1489
1490 spin_unlock_irqrestore(&cc->zone->lock, flags);
1491
1492 /*
1493 * Smaller scan on next order so the total scan is related
1494 * to freelist_scan_limit.
1495 */
1496 if (order_scanned >= limit)
1497 limit = max(1U, limit >> 1);
1498 }
1499
1500 if (!page) {
1501 cc->fast_search_fail++;
1502 if (scan_start) {
1503 /*
1504 * Use the highest PFN found above min. If one was
1505 * not found, be pessimistic for direct compaction
1506 * and use the min mark.
1507 */
1508 if (highest) {
1509 page = pfn_to_page(highest);
1510 cc->free_pfn = highest;
1511 } else {
1512 if (cc->direct_compaction && pfn_valid(min_pfn)) {
1513 page = pageblock_pfn_to_page(min_pfn,
1514 min(pageblock_end_pfn(min_pfn),
1515 zone_end_pfn(cc->zone)),
1516 cc->zone);
1517 cc->free_pfn = min_pfn;
1518 }
1519 }
1520 }
1521 }
1522
1523 if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1524 highest -= pageblock_nr_pages;
1525 cc->zone->compact_cached_free_pfn = highest;
1526 }
1527
1528 cc->total_free_scanned += nr_scanned;
1529 if (!page)
1530 return cc->free_pfn;
1531
1532 low_pfn = page_to_pfn(page);
1533 fast_isolate_around(cc, low_pfn, nr_isolated);
1534 return low_pfn;
1535}
1536
1537/*
1538 * Based on information in the current compact_control, find blocks
1539 * suitable for isolating free pages from and then isolate them.
1540 */
1541static void isolate_freepages(struct compact_control *cc)
1542{
1543 struct zone *zone = cc->zone;
1544 struct page *page;
1545 unsigned long block_start_pfn; /* start of current pageblock */
1546 unsigned long isolate_start_pfn; /* exact pfn we start at */
1547 unsigned long block_end_pfn; /* end of current pageblock */
1548 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1549 struct list_head *freelist = &cc->freepages;
1550 unsigned int stride;
1551
1552 /* Try a small search of the free lists for a candidate */
1553 isolate_start_pfn = fast_isolate_freepages(cc);
1554 if (cc->nr_freepages)
1555 goto splitmap;
1556
1557 /*
1558 * Initialise the free scanner. The starting point is where we last
1559 * successfully isolated from, zone-cached value, or the end of the
1560 * zone when isolating for the first time. For looping we also need
1561 * this pfn aligned down to the pageblock boundary, because we do
1562 * block_start_pfn -= pageblock_nr_pages in the for loop.
1563 * For ending point, take care when isolating in last pageblock of a
1564 * zone which ends in the middle of a pageblock.
1565 * The low boundary is the end of the pageblock the migration scanner
1566 * is using.
1567 */
1568 isolate_start_pfn = cc->free_pfn;
1569 block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1570 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1571 zone_end_pfn(zone));
1572 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1573 stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1574
1575 /*
1576 * Isolate free pages until enough are available to migrate the
1577 * pages on cc->migratepages. We stop searching if the migrate
1578 * and free page scanners meet or enough free pages are isolated.
1579 */
1580 for (; block_start_pfn >= low_pfn;
1581 block_end_pfn = block_start_pfn,
1582 block_start_pfn -= pageblock_nr_pages,
1583 isolate_start_pfn = block_start_pfn) {
1584 unsigned long nr_isolated;
1585
1586 /*
1587 * This can iterate a massively long zone without finding any
1588 * suitable migration targets, so periodically check resched.
1589 */
1590 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1591 cond_resched();
1592
1593 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1594 zone);
1595 if (!page)
1596 continue;
1597
1598 /* Check the block is suitable for migration */
1599 if (!suitable_migration_target(cc, page))
1600 continue;
1601
1602 /* If isolation recently failed, do not retry */
1603 if (!isolation_suitable(cc, page))
1604 continue;
1605
1606 /* Found a block suitable for isolating free pages from. */
1607 nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1608 block_end_pfn, freelist, stride, false);
1609
1610 /* Update the skip hint if the full pageblock was scanned */
1611 if (isolate_start_pfn == block_end_pfn)
1612 update_pageblock_skip(cc, page, block_start_pfn);
1613
1614 /* Are enough freepages isolated? */
1615 if (cc->nr_freepages >= cc->nr_migratepages) {
1616 if (isolate_start_pfn >= block_end_pfn) {
1617 /*
1618 * Restart at previous pageblock if more
1619 * freepages can be isolated next time.
1620 */
1621 isolate_start_pfn =
1622 block_start_pfn - pageblock_nr_pages;
1623 }
1624 break;
1625 } else if (isolate_start_pfn < block_end_pfn) {
1626 /*
1627 * If isolation failed early, do not continue
1628 * needlessly.
1629 */
1630 break;
1631 }
1632
1633 /* Adjust stride depending on isolation */
1634 if (nr_isolated) {
1635 stride = 1;
1636 continue;
1637 }
1638 stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1639 }
1640
1641 /*
1642 * Record where the free scanner will restart next time. Either we
1643 * broke from the loop and set isolate_start_pfn based on the last
1644 * call to isolate_freepages_block(), or we met the migration scanner
1645 * and the loop terminated due to isolate_start_pfn < low_pfn
1646 */
1647 cc->free_pfn = isolate_start_pfn;
1648
1649splitmap:
1650 /* __isolate_free_page() does not map the pages */
1651 split_map_pages(freelist);
1652}
1653
1654/*
1655 * This is a migrate-callback that "allocates" freepages by taking pages
1656 * from the isolated freelists in the block we are migrating to.
1657 */
1658static struct page *compaction_alloc(struct page *migratepage,
1659 unsigned long data)
1660{
1661 struct compact_control *cc = (struct compact_control *)data;
1662 struct page *freepage;
1663
1664 if (list_empty(&cc->freepages)) {
1665 isolate_freepages(cc);
1666
1667 if (list_empty(&cc->freepages))
1668 return NULL;
1669 }
1670
1671 freepage = list_entry(cc->freepages.next, struct page, lru);
1672 list_del(&freepage->lru);
1673 cc->nr_freepages--;
1674
1675 return freepage;
1676}
1677
1678/*
1679 * This is a migrate-callback that "frees" freepages back to the isolated
1680 * freelist. All pages on the freelist are from the same zone, so there is no
1681 * special handling needed for NUMA.
1682 */
1683static void compaction_free(struct page *page, unsigned long data)
1684{
1685 struct compact_control *cc = (struct compact_control *)data;
1686
1687 list_add(&page->lru, &cc->freepages);
1688 cc->nr_freepages++;
1689}
1690
1691/* possible outcome of isolate_migratepages */
1692typedef enum {
1693 ISOLATE_ABORT, /* Abort compaction now */
1694 ISOLATE_NONE, /* No pages isolated, continue scanning */
1695 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1696} isolate_migrate_t;
1697
1698/*
1699 * Allow userspace to control policy on scanning the unevictable LRU for
1700 * compactable pages.
1701 */
1702#ifdef CONFIG_PREEMPT_RT
1703int sysctl_compact_unevictable_allowed __read_mostly = 0;
1704#else
1705int sysctl_compact_unevictable_allowed __read_mostly = 1;
1706#endif
1707
1708static inline void
1709update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1710{
1711 if (cc->fast_start_pfn == ULONG_MAX)
1712 return;
1713
1714 if (!cc->fast_start_pfn)
1715 cc->fast_start_pfn = pfn;
1716
1717 cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1718}
1719
1720static inline unsigned long
1721reinit_migrate_pfn(struct compact_control *cc)
1722{
1723 if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1724 return cc->migrate_pfn;
1725
1726 cc->migrate_pfn = cc->fast_start_pfn;
1727 cc->fast_start_pfn = ULONG_MAX;
1728
1729 return cc->migrate_pfn;
1730}
1731
1732/*
1733 * Briefly search the free lists for a migration source that already has
1734 * some free pages to reduce the number of pages that need migration
1735 * before a pageblock is free.
1736 */
1737static unsigned long fast_find_migrateblock(struct compact_control *cc)
1738{
1739 unsigned int limit = freelist_scan_limit(cc);
1740 unsigned int nr_scanned = 0;
1741 unsigned long distance;
1742 unsigned long pfn = cc->migrate_pfn;
1743 unsigned long high_pfn;
1744 int order;
1745 bool found_block = false;
1746
1747 /* Skip hints are relied on to avoid repeats on the fast search */
1748 if (cc->ignore_skip_hint)
1749 return pfn;
1750
1751 /*
1752 * If the migrate_pfn is not at the start of a zone or the start
1753 * of a pageblock then assume this is a continuation of a previous
1754 * scan restarted due to COMPACT_CLUSTER_MAX.
1755 */
1756 if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1757 return pfn;
1758
1759 /*
1760 * For smaller orders, just linearly scan as the number of pages
1761 * to migrate should be relatively small and does not necessarily
1762 * justify freeing up a large block for a small allocation.
1763 */
1764 if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1765 return pfn;
1766
1767 /*
1768 * Only allow kcompactd and direct requests for movable pages to
1769 * quickly clear out a MOVABLE pageblock for allocation. This
1770 * reduces the risk that a large movable pageblock is freed for
1771 * an unmovable/reclaimable small allocation.
1772 */
1773 if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1774 return pfn;
1775
1776 /*
1777 * When starting the migration scanner, pick any pageblock within the
1778 * first half of the search space. Otherwise try and pick a pageblock
1779 * within the first eighth to reduce the chances that a migration
1780 * target later becomes a source.
1781 */
1782 distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1783 if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1784 distance >>= 2;
1785 high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1786
1787 for (order = cc->order - 1;
1788 order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
1789 order--) {
1790 struct free_area *area = &cc->zone->free_area[order];
1791 struct list_head *freelist;
1792 unsigned long flags;
1793 struct page *freepage;
1794
1795 if (!area->nr_free)
1796 continue;
1797
1798 spin_lock_irqsave(&cc->zone->lock, flags);
1799 freelist = &area->free_list[MIGRATE_MOVABLE];
1800 list_for_each_entry(freepage, freelist, lru) {
1801 unsigned long free_pfn;
1802
1803 if (nr_scanned++ >= limit) {
1804 move_freelist_tail(freelist, freepage);
1805 break;
1806 }
1807
1808 free_pfn = page_to_pfn(freepage);
1809 if (free_pfn < high_pfn) {
1810 /*
1811 * Avoid if skipped recently. Ideally it would
1812 * move to the tail but even safe iteration of
1813 * the list assumes an entry is deleted, not
1814 * reordered.
1815 */
1816 if (get_pageblock_skip(freepage))
1817 continue;
1818
1819 /* Reorder to so a future search skips recent pages */
1820 move_freelist_tail(freelist, freepage);
1821
1822 update_fast_start_pfn(cc, free_pfn);
1823 pfn = pageblock_start_pfn(free_pfn);
1824 cc->fast_search_fail = 0;
1825 found_block = true;
1826 set_pageblock_skip(freepage);
1827 break;
1828 }
1829 }
1830 spin_unlock_irqrestore(&cc->zone->lock, flags);
1831 }
1832
1833 cc->total_migrate_scanned += nr_scanned;
1834
1835 /*
1836 * If fast scanning failed then use a cached entry for a page block
1837 * that had free pages as the basis for starting a linear scan.
1838 */
1839 if (!found_block) {
1840 cc->fast_search_fail++;
1841 pfn = reinit_migrate_pfn(cc);
1842 }
1843 return pfn;
1844}
1845
1846/*
1847 * Isolate all pages that can be migrated from the first suitable block,
1848 * starting at the block pointed to by the migrate scanner pfn within
1849 * compact_control.
1850 */
1851static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1852{
1853 unsigned long block_start_pfn;
1854 unsigned long block_end_pfn;
1855 unsigned long low_pfn;
1856 struct page *page;
1857 const isolate_mode_t isolate_mode =
1858 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1859 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1860 bool fast_find_block;
1861
1862 /*
1863 * Start at where we last stopped, or beginning of the zone as
1864 * initialized by compact_zone(). The first failure will use
1865 * the lowest PFN as the starting point for linear scanning.
1866 */
1867 low_pfn = fast_find_migrateblock(cc);
1868 block_start_pfn = pageblock_start_pfn(low_pfn);
1869 if (block_start_pfn < cc->zone->zone_start_pfn)
1870 block_start_pfn = cc->zone->zone_start_pfn;
1871
1872 /*
1873 * fast_find_migrateblock marks a pageblock skipped so to avoid
1874 * the isolation_suitable check below, check whether the fast
1875 * search was successful.
1876 */
1877 fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
1878
1879 /* Only scan within a pageblock boundary */
1880 block_end_pfn = pageblock_end_pfn(low_pfn);
1881
1882 /*
1883 * Iterate over whole pageblocks until we find the first suitable.
1884 * Do not cross the free scanner.
1885 */
1886 for (; block_end_pfn <= cc->free_pfn;
1887 fast_find_block = false,
1888 cc->migrate_pfn = low_pfn = block_end_pfn,
1889 block_start_pfn = block_end_pfn,
1890 block_end_pfn += pageblock_nr_pages) {
1891
1892 /*
1893 * This can potentially iterate a massively long zone with
1894 * many pageblocks unsuitable, so periodically check if we
1895 * need to schedule.
1896 */
1897 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1898 cond_resched();
1899
1900 page = pageblock_pfn_to_page(block_start_pfn,
1901 block_end_pfn, cc->zone);
1902 if (!page)
1903 continue;
1904
1905 /*
1906 * If isolation recently failed, do not retry. Only check the
1907 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1908 * to be visited multiple times. Assume skip was checked
1909 * before making it "skip" so other compaction instances do
1910 * not scan the same block.
1911 */
1912 if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
1913 !fast_find_block && !isolation_suitable(cc, page))
1914 continue;
1915
1916 /*
1917 * For async compaction, also only scan in MOVABLE blocks
1918 * without huge pages. Async compaction is optimistic to see
1919 * if the minimum amount of work satisfies the allocation.
1920 * The cached PFN is updated as it's possible that all
1921 * remaining blocks between source and target are unsuitable
1922 * and the compaction scanners fail to meet.
1923 */
1924 if (!suitable_migration_source(cc, page)) {
1925 update_cached_migrate(cc, block_end_pfn);
1926 continue;
1927 }
1928
1929 /* Perform the isolation */
1930 if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,
1931 isolate_mode))
1932 return ISOLATE_ABORT;
1933
1934 /*
1935 * Either we isolated something and proceed with migration. Or
1936 * we failed and compact_zone should decide if we should
1937 * continue or not.
1938 */
1939 break;
1940 }
1941
1942 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1943}
1944
1945/*
1946 * order == -1 is expected when compacting via
1947 * /proc/sys/vm/compact_memory
1948 */
1949static inline bool is_via_compact_memory(int order)
1950{
1951 return order == -1;
1952}
1953
1954static bool kswapd_is_running(pg_data_t *pgdat)
1955{
1956 return pgdat->kswapd && task_is_running(pgdat->kswapd);
1957}
1958
1959/*
1960 * A zone's fragmentation score is the external fragmentation wrt to the
1961 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
1962 */
1963static unsigned int fragmentation_score_zone(struct zone *zone)
1964{
1965 return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
1966}
1967
1968/*
1969 * A weighted zone's fragmentation score is the external fragmentation
1970 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
1971 * returns a value in the range [0, 100].
1972 *
1973 * The scaling factor ensures that proactive compaction focuses on larger
1974 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
1975 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
1976 * and thus never exceeds the high threshold for proactive compaction.
1977 */
1978static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
1979{
1980 unsigned long score;
1981
1982 score = zone->present_pages * fragmentation_score_zone(zone);
1983 return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
1984}
1985
1986/*
1987 * The per-node proactive (background) compaction process is started by its
1988 * corresponding kcompactd thread when the node's fragmentation score
1989 * exceeds the high threshold. The compaction process remains active till
1990 * the node's score falls below the low threshold, or one of the back-off
1991 * conditions is met.
1992 */
1993static unsigned int fragmentation_score_node(pg_data_t *pgdat)
1994{
1995 unsigned int score = 0;
1996 int zoneid;
1997
1998 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1999 struct zone *zone;
2000
2001 zone = &pgdat->node_zones[zoneid];
2002 score += fragmentation_score_zone_weighted(zone);
2003 }
2004
2005 return score;
2006}
2007
2008static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
2009{
2010 unsigned int wmark_low;
2011
2012 /*
2013 * Cap the low watermark to avoid excessive compaction
2014 * activity in case a user sets the proactiveness tunable
2015 * close to 100 (maximum).
2016 */
2017 wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
2018 return low ? wmark_low : min(wmark_low + 10, 100U);
2019}
2020
2021static bool should_proactive_compact_node(pg_data_t *pgdat)
2022{
2023 int wmark_high;
2024
2025 if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
2026 return false;
2027
2028 wmark_high = fragmentation_score_wmark(pgdat, false);
2029 return fragmentation_score_node(pgdat) > wmark_high;
2030}
2031
2032static enum compact_result __compact_finished(struct compact_control *cc)
2033{
2034 unsigned int order;
2035 const int migratetype = cc->migratetype;
2036 int ret;
2037
2038 /* Compaction run completes if the migrate and free scanner meet */
2039 if (compact_scanners_met(cc)) {
2040 /* Let the next compaction start anew. */
2041 reset_cached_positions(cc->zone);
2042
2043 /*
2044 * Mark that the PG_migrate_skip information should be cleared
2045 * by kswapd when it goes to sleep. kcompactd does not set the
2046 * flag itself as the decision to be clear should be directly
2047 * based on an allocation request.
2048 */
2049 if (cc->direct_compaction)
2050 cc->zone->compact_blockskip_flush = true;
2051
2052 if (cc->whole_zone)
2053 return COMPACT_COMPLETE;
2054 else
2055 return COMPACT_PARTIAL_SKIPPED;
2056 }
2057
2058 if (cc->proactive_compaction) {
2059 int score, wmark_low;
2060 pg_data_t *pgdat;
2061
2062 pgdat = cc->zone->zone_pgdat;
2063 if (kswapd_is_running(pgdat))
2064 return COMPACT_PARTIAL_SKIPPED;
2065
2066 score = fragmentation_score_zone(cc->zone);
2067 wmark_low = fragmentation_score_wmark(pgdat, true);
2068
2069 if (score > wmark_low)
2070 ret = COMPACT_CONTINUE;
2071 else
2072 ret = COMPACT_SUCCESS;
2073
2074 goto out;
2075 }
2076
2077 if (is_via_compact_memory(cc->order))
2078 return COMPACT_CONTINUE;
2079
2080 /*
2081 * Always finish scanning a pageblock to reduce the possibility of
2082 * fallbacks in the future. This is particularly important when
2083 * migration source is unmovable/reclaimable but it's not worth
2084 * special casing.
2085 */
2086 if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
2087 return COMPACT_CONTINUE;
2088
2089 /* Direct compactor: Is a suitable page free? */
2090 ret = COMPACT_NO_SUITABLE_PAGE;
2091 for (order = cc->order; order < MAX_ORDER; order++) {
2092 struct free_area *area = &cc->zone->free_area[order];
2093 bool can_steal;
2094
2095 /* Job done if page is free of the right migratetype */
2096 if (!free_area_empty(area, migratetype))
2097 return COMPACT_SUCCESS;
2098
2099#ifdef CONFIG_CMA
2100 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2101 if (migratetype == MIGRATE_MOVABLE &&
2102 !free_area_empty(area, MIGRATE_CMA))
2103 return COMPACT_SUCCESS;
2104#endif
2105 /*
2106 * Job done if allocation would steal freepages from
2107 * other migratetype buddy lists.
2108 */
2109 if (find_suitable_fallback(area, order, migratetype,
2110 true, &can_steal) != -1) {
2111
2112 /* movable pages are OK in any pageblock */
2113 if (migratetype == MIGRATE_MOVABLE)
2114 return COMPACT_SUCCESS;
2115
2116 /*
2117 * We are stealing for a non-movable allocation. Make
2118 * sure we finish compacting the current pageblock
2119 * first so it is as free as possible and we won't
2120 * have to steal another one soon. This only applies
2121 * to sync compaction, as async compaction operates
2122 * on pageblocks of the same migratetype.
2123 */
2124 if (cc->mode == MIGRATE_ASYNC ||
2125 IS_ALIGNED(cc->migrate_pfn,
2126 pageblock_nr_pages)) {
2127 return COMPACT_SUCCESS;
2128 }
2129
2130 ret = COMPACT_CONTINUE;
2131 break;
2132 }
2133 }
2134
2135out:
2136 if (cc->contended || fatal_signal_pending(current))
2137 ret = COMPACT_CONTENDED;
2138
2139 return ret;
2140}
2141
2142static enum compact_result compact_finished(struct compact_control *cc)
2143{
2144 int ret;
2145
2146 ret = __compact_finished(cc);
2147 trace_mm_compaction_finished(cc->zone, cc->order, ret);
2148 if (ret == COMPACT_NO_SUITABLE_PAGE)
2149 ret = COMPACT_CONTINUE;
2150
2151 return ret;
2152}
2153
2154static enum compact_result __compaction_suitable(struct zone *zone, int order,
2155 unsigned int alloc_flags,
2156 int highest_zoneidx,
2157 unsigned long wmark_target)
2158{
2159 unsigned long watermark;
2160
2161 if (is_via_compact_memory(order))
2162 return COMPACT_CONTINUE;
2163
2164 watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2165 /*
2166 * If watermarks for high-order allocation are already met, there
2167 * should be no need for compaction at all.
2168 */
2169 if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2170 alloc_flags))
2171 return COMPACT_SUCCESS;
2172
2173 /*
2174 * Watermarks for order-0 must be met for compaction to be able to
2175 * isolate free pages for migration targets. This means that the
2176 * watermark and alloc_flags have to match, or be more pessimistic than
2177 * the check in __isolate_free_page(). We don't use the direct
2178 * compactor's alloc_flags, as they are not relevant for freepage
2179 * isolation. We however do use the direct compactor's highest_zoneidx
2180 * to skip over zones where lowmem reserves would prevent allocation
2181 * even if compaction succeeds.
2182 * For costly orders, we require low watermark instead of min for
2183 * compaction to proceed to increase its chances.
2184 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2185 * suitable migration targets
2186 */
2187 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2188 low_wmark_pages(zone) : min_wmark_pages(zone);
2189 watermark += compact_gap(order);
2190 if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2191 ALLOC_CMA, wmark_target))
2192 return COMPACT_SKIPPED;
2193
2194 return COMPACT_CONTINUE;
2195}
2196
2197/*
2198 * compaction_suitable: Is this suitable to run compaction on this zone now?
2199 * Returns
2200 * COMPACT_SKIPPED - If there are too few free pages for compaction
2201 * COMPACT_SUCCESS - If the allocation would succeed without compaction
2202 * COMPACT_CONTINUE - If compaction should run now
2203 */
2204enum compact_result compaction_suitable(struct zone *zone, int order,
2205 unsigned int alloc_flags,
2206 int highest_zoneidx)
2207{
2208 enum compact_result ret;
2209 int fragindex;
2210
2211 ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
2212 zone_page_state(zone, NR_FREE_PAGES));
2213 /*
2214 * fragmentation index determines if allocation failures are due to
2215 * low memory or external fragmentation
2216 *
2217 * index of -1000 would imply allocations might succeed depending on
2218 * watermarks, but we already failed the high-order watermark check
2219 * index towards 0 implies failure is due to lack of memory
2220 * index towards 1000 implies failure is due to fragmentation
2221 *
2222 * Only compact if a failure would be due to fragmentation. Also
2223 * ignore fragindex for non-costly orders where the alternative to
2224 * a successful reclaim/compaction is OOM. Fragindex and the
2225 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2226 * excessive compaction for costly orders, but it should not be at the
2227 * expense of system stability.
2228 */
2229 if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
2230 fragindex = fragmentation_index(zone, order);
2231 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
2232 ret = COMPACT_NOT_SUITABLE_ZONE;
2233 }
2234
2235 trace_mm_compaction_suitable(zone, order, ret);
2236 if (ret == COMPACT_NOT_SUITABLE_ZONE)
2237 ret = COMPACT_SKIPPED;
2238
2239 return ret;
2240}
2241
2242bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2243 int alloc_flags)
2244{
2245 struct zone *zone;
2246 struct zoneref *z;
2247
2248 /*
2249 * Make sure at least one zone would pass __compaction_suitable if we continue
2250 * retrying the reclaim.
2251 */
2252 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2253 ac->highest_zoneidx, ac->nodemask) {
2254 unsigned long available;
2255 enum compact_result compact_result;
2256
2257 /*
2258 * Do not consider all the reclaimable memory because we do not
2259 * want to trash just for a single high order allocation which
2260 * is even not guaranteed to appear even if __compaction_suitable
2261 * is happy about the watermark check.
2262 */
2263 available = zone_reclaimable_pages(zone) / order;
2264 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2265 compact_result = __compaction_suitable(zone, order, alloc_flags,
2266 ac->highest_zoneidx, available);
2267 if (compact_result != COMPACT_SKIPPED)
2268 return true;
2269 }
2270
2271 return false;
2272}
2273
2274static enum compact_result
2275compact_zone(struct compact_control *cc, struct capture_control *capc)
2276{
2277 enum compact_result ret;
2278 unsigned long start_pfn = cc->zone->zone_start_pfn;
2279 unsigned long end_pfn = zone_end_pfn(cc->zone);
2280 unsigned long last_migrated_pfn;
2281 const bool sync = cc->mode != MIGRATE_ASYNC;
2282 bool update_cached;
2283
2284 /*
2285 * These counters track activities during zone compaction. Initialize
2286 * them before compacting a new zone.
2287 */
2288 cc->total_migrate_scanned = 0;
2289 cc->total_free_scanned = 0;
2290 cc->nr_migratepages = 0;
2291 cc->nr_freepages = 0;
2292 INIT_LIST_HEAD(&cc->freepages);
2293 INIT_LIST_HEAD(&cc->migratepages);
2294
2295 cc->migratetype = gfp_migratetype(cc->gfp_mask);
2296 ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
2297 cc->highest_zoneidx);
2298 /* Compaction is likely to fail */
2299 if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
2300 return ret;
2301
2302 /* huh, compaction_suitable is returning something unexpected */
2303 VM_BUG_ON(ret != COMPACT_CONTINUE);
2304
2305 /*
2306 * Clear pageblock skip if there were failures recently and compaction
2307 * is about to be retried after being deferred.
2308 */
2309 if (compaction_restarting(cc->zone, cc->order))
2310 __reset_isolation_suitable(cc->zone);
2311
2312 /*
2313 * Setup to move all movable pages to the end of the zone. Used cached
2314 * information on where the scanners should start (unless we explicitly
2315 * want to compact the whole zone), but check that it is initialised
2316 * by ensuring the values are within zone boundaries.
2317 */
2318 cc->fast_start_pfn = 0;
2319 if (cc->whole_zone) {
2320 cc->migrate_pfn = start_pfn;
2321 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2322 } else {
2323 cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2324 cc->free_pfn = cc->zone->compact_cached_free_pfn;
2325 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2326 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2327 cc->zone->compact_cached_free_pfn = cc->free_pfn;
2328 }
2329 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2330 cc->migrate_pfn = start_pfn;
2331 cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2332 cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2333 }
2334
2335 if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2336 cc->whole_zone = true;
2337 }
2338
2339 last_migrated_pfn = 0;
2340
2341 /*
2342 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2343 * the basis that some migrations will fail in ASYNC mode. However,
2344 * if the cached PFNs match and pageblocks are skipped due to having
2345 * no isolation candidates, then the sync state does not matter.
2346 * Until a pageblock with isolation candidates is found, keep the
2347 * cached PFNs in sync to avoid revisiting the same blocks.
2348 */
2349 update_cached = !sync &&
2350 cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2351
2352 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
2353 cc->free_pfn, end_pfn, sync);
2354
2355 /* lru_add_drain_all could be expensive with involving other CPUs */
2356 lru_add_drain();
2357
2358 while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2359 int err;
2360 unsigned long iteration_start_pfn = cc->migrate_pfn;
2361
2362 /*
2363 * Avoid multiple rescans which can happen if a page cannot be
2364 * isolated (dirty/writeback in async mode) or if the migrated
2365 * pages are being allocated before the pageblock is cleared.
2366 * The first rescan will capture the entire pageblock for
2367 * migration. If it fails, it'll be marked skip and scanning
2368 * will proceed as normal.
2369 */
2370 cc->rescan = false;
2371 if (pageblock_start_pfn(last_migrated_pfn) ==
2372 pageblock_start_pfn(iteration_start_pfn)) {
2373 cc->rescan = true;
2374 }
2375
2376 switch (isolate_migratepages(cc)) {
2377 case ISOLATE_ABORT:
2378 ret = COMPACT_CONTENDED;
2379 putback_movable_pages(&cc->migratepages);
2380 cc->nr_migratepages = 0;
2381 goto out;
2382 case ISOLATE_NONE:
2383 if (update_cached) {
2384 cc->zone->compact_cached_migrate_pfn[1] =
2385 cc->zone->compact_cached_migrate_pfn[0];
2386 }
2387
2388 /*
2389 * We haven't isolated and migrated anything, but
2390 * there might still be unflushed migrations from
2391 * previous cc->order aligned block.
2392 */
2393 goto check_drain;
2394 case ISOLATE_SUCCESS:
2395 update_cached = false;
2396 last_migrated_pfn = iteration_start_pfn;
2397 }
2398
2399 err = migrate_pages(&cc->migratepages, compaction_alloc,
2400 compaction_free, (unsigned long)cc, cc->mode,
2401 MR_COMPACTION);
2402
2403 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
2404 &cc->migratepages);
2405
2406 /* All pages were either migrated or will be released */
2407 cc->nr_migratepages = 0;
2408 if (err) {
2409 putback_movable_pages(&cc->migratepages);
2410 /*
2411 * migrate_pages() may return -ENOMEM when scanners meet
2412 * and we want compact_finished() to detect it
2413 */
2414 if (err == -ENOMEM && !compact_scanners_met(cc)) {
2415 ret = COMPACT_CONTENDED;
2416 goto out;
2417 }
2418 /*
2419 * We failed to migrate at least one page in the current
2420 * order-aligned block, so skip the rest of it.
2421 */
2422 if (cc->direct_compaction &&
2423 (cc->mode == MIGRATE_ASYNC)) {
2424 cc->migrate_pfn = block_end_pfn(
2425 cc->migrate_pfn - 1, cc->order);
2426 /* Draining pcplists is useless in this case */
2427 last_migrated_pfn = 0;
2428 }
2429 }
2430
2431check_drain:
2432 /*
2433 * Has the migration scanner moved away from the previous
2434 * cc->order aligned block where we migrated from? If yes,
2435 * flush the pages that were freed, so that they can merge and
2436 * compact_finished() can detect immediately if allocation
2437 * would succeed.
2438 */
2439 if (cc->order > 0 && last_migrated_pfn) {
2440 unsigned long current_block_start =
2441 block_start_pfn(cc->migrate_pfn, cc->order);
2442
2443 if (last_migrated_pfn < current_block_start) {
2444 lru_add_drain_cpu_zone(cc->zone);
2445 /* No more flushing until we migrate again */
2446 last_migrated_pfn = 0;
2447 }
2448 }
2449
2450 /* Stop if a page has been captured */
2451 if (capc && capc->page) {
2452 ret = COMPACT_SUCCESS;
2453 break;
2454 }
2455 }
2456
2457out:
2458 /*
2459 * Release free pages and update where the free scanner should restart,
2460 * so we don't leave any returned pages behind in the next attempt.
2461 */
2462 if (cc->nr_freepages > 0) {
2463 unsigned long free_pfn = release_freepages(&cc->freepages);
2464
2465 cc->nr_freepages = 0;
2466 VM_BUG_ON(free_pfn == 0);
2467 /* The cached pfn is always the first in a pageblock */
2468 free_pfn = pageblock_start_pfn(free_pfn);
2469 /*
2470 * Only go back, not forward. The cached pfn might have been
2471 * already reset to zone end in compact_finished()
2472 */
2473 if (free_pfn > cc->zone->compact_cached_free_pfn)
2474 cc->zone->compact_cached_free_pfn = free_pfn;
2475 }
2476
2477 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2478 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2479
2480 trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
2481 cc->free_pfn, end_pfn, sync, ret);
2482
2483 return ret;
2484}
2485
2486static enum compact_result compact_zone_order(struct zone *zone, int order,
2487 gfp_t gfp_mask, enum compact_priority prio,
2488 unsigned int alloc_flags, int highest_zoneidx,
2489 struct page **capture)
2490{
2491 enum compact_result ret;
2492 struct compact_control cc = {
2493 .order = order,
2494 .search_order = order,
2495 .gfp_mask = gfp_mask,
2496 .zone = zone,
2497 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2498 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2499 .alloc_flags = alloc_flags,
2500 .highest_zoneidx = highest_zoneidx,
2501 .direct_compaction = true,
2502 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2503 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2504 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2505 };
2506 struct capture_control capc = {
2507 .cc = &cc,
2508 .page = NULL,
2509 };
2510
2511 /*
2512 * Make sure the structs are really initialized before we expose the
2513 * capture control, in case we are interrupted and the interrupt handler
2514 * frees a page.
2515 */
2516 barrier();
2517 WRITE_ONCE(current->capture_control, &capc);
2518
2519 ret = compact_zone(&cc, &capc);
2520
2521 VM_BUG_ON(!list_empty(&cc.freepages));
2522 VM_BUG_ON(!list_empty(&cc.migratepages));
2523
2524 /*
2525 * Make sure we hide capture control first before we read the captured
2526 * page pointer, otherwise an interrupt could free and capture a page
2527 * and we would leak it.
2528 */
2529 WRITE_ONCE(current->capture_control, NULL);
2530 *capture = READ_ONCE(capc.page);
2531 /*
2532 * Technically, it is also possible that compaction is skipped but
2533 * the page is still captured out of luck(IRQ came and freed the page).
2534 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
2535 * the COMPACT[STALL|FAIL] when compaction is skipped.
2536 */
2537 if (*capture)
2538 ret = COMPACT_SUCCESS;
2539
2540 return ret;
2541}
2542
2543int sysctl_extfrag_threshold = 500;
2544
2545/**
2546 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2547 * @gfp_mask: The GFP mask of the current allocation
2548 * @order: The order of the current allocation
2549 * @alloc_flags: The allocation flags of the current allocation
2550 * @ac: The context of current allocation
2551 * @prio: Determines how hard direct compaction should try to succeed
2552 * @capture: Pointer to free page created by compaction will be stored here
2553 *
2554 * This is the main entry point for direct page compaction.
2555 */
2556enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2557 unsigned int alloc_flags, const struct alloc_context *ac,
2558 enum compact_priority prio, struct page **capture)
2559{
2560 int may_perform_io = gfp_mask & __GFP_IO;
2561 struct zoneref *z;
2562 struct zone *zone;
2563 enum compact_result rc = COMPACT_SKIPPED;
2564
2565 /*
2566 * Check if the GFP flags allow compaction - GFP_NOIO is really
2567 * tricky context because the migration might require IO
2568 */
2569 if (!may_perform_io)
2570 return COMPACT_SKIPPED;
2571
2572 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2573
2574 /* Compact each zone in the list */
2575 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2576 ac->highest_zoneidx, ac->nodemask) {
2577 enum compact_result status;
2578
2579 if (prio > MIN_COMPACT_PRIORITY
2580 && compaction_deferred(zone, order)) {
2581 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2582 continue;
2583 }
2584
2585 status = compact_zone_order(zone, order, gfp_mask, prio,
2586 alloc_flags, ac->highest_zoneidx, capture);
2587 rc = max(status, rc);
2588
2589 /* The allocation should succeed, stop compacting */
2590 if (status == COMPACT_SUCCESS) {
2591 /*
2592 * We think the allocation will succeed in this zone,
2593 * but it is not certain, hence the false. The caller
2594 * will repeat this with true if allocation indeed
2595 * succeeds in this zone.
2596 */
2597 compaction_defer_reset(zone, order, false);
2598
2599 break;
2600 }
2601
2602 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2603 status == COMPACT_PARTIAL_SKIPPED))
2604 /*
2605 * We think that allocation won't succeed in this zone
2606 * so we defer compaction there. If it ends up
2607 * succeeding after all, it will be reset.
2608 */
2609 defer_compaction(zone, order);
2610
2611 /*
2612 * We might have stopped compacting due to need_resched() in
2613 * async compaction, or due to a fatal signal detected. In that
2614 * case do not try further zones
2615 */
2616 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2617 || fatal_signal_pending(current))
2618 break;
2619 }
2620
2621 return rc;
2622}
2623
2624/*
2625 * Compact all zones within a node till each zone's fragmentation score
2626 * reaches within proactive compaction thresholds (as determined by the
2627 * proactiveness tunable).
2628 *
2629 * It is possible that the function returns before reaching score targets
2630 * due to various back-off conditions, such as, contention on per-node or
2631 * per-zone locks.
2632 */
2633static void proactive_compact_node(pg_data_t *pgdat)
2634{
2635 int zoneid;
2636 struct zone *zone;
2637 struct compact_control cc = {
2638 .order = -1,
2639 .mode = MIGRATE_SYNC_LIGHT,
2640 .ignore_skip_hint = true,
2641 .whole_zone = true,
2642 .gfp_mask = GFP_KERNEL,
2643 .proactive_compaction = true,
2644 };
2645
2646 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2647 zone = &pgdat->node_zones[zoneid];
2648 if (!populated_zone(zone))
2649 continue;
2650
2651 cc.zone = zone;
2652
2653 compact_zone(&cc, NULL);
2654
2655 VM_BUG_ON(!list_empty(&cc.freepages));
2656 VM_BUG_ON(!list_empty(&cc.migratepages));
2657 }
2658}
2659
2660/* Compact all zones within a node */
2661static void compact_node(int nid)
2662{
2663 pg_data_t *pgdat = NODE_DATA(nid);
2664 int zoneid;
2665 struct zone *zone;
2666 struct compact_control cc = {
2667 .order = -1,
2668 .mode = MIGRATE_SYNC,
2669 .ignore_skip_hint = true,
2670 .whole_zone = true,
2671 .gfp_mask = GFP_KERNEL,
2672 };
2673
2674
2675 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2676
2677 zone = &pgdat->node_zones[zoneid];
2678 if (!populated_zone(zone))
2679 continue;
2680
2681 cc.zone = zone;
2682
2683 compact_zone(&cc, NULL);
2684
2685 VM_BUG_ON(!list_empty(&cc.freepages));
2686 VM_BUG_ON(!list_empty(&cc.migratepages));
2687 }
2688}
2689
2690/* Compact all nodes in the system */
2691static void compact_nodes(void)
2692{
2693 int nid;
2694
2695 /* Flush pending updates to the LRU lists */
2696 lru_add_drain_all();
2697
2698 for_each_online_node(nid)
2699 compact_node(nid);
2700}
2701
2702/*
2703 * Tunable for proactive compaction. It determines how
2704 * aggressively the kernel should compact memory in the
2705 * background. It takes values in the range [0, 100].
2706 */
2707unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
2708
2709/*
2710 * This is the entry point for compacting all nodes via
2711 * /proc/sys/vm/compact_memory
2712 */
2713int sysctl_compaction_handler(struct ctl_table *table, int write,
2714 void *buffer, size_t *length, loff_t *ppos)
2715{
2716 if (write)
2717 compact_nodes();
2718
2719 return 0;
2720}
2721
2722#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2723static ssize_t compact_store(struct device *dev,
2724 struct device_attribute *attr,
2725 const char *buf, size_t count)
2726{
2727 int nid = dev->id;
2728
2729 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2730 /* Flush pending updates to the LRU lists */
2731 lru_add_drain_all();
2732
2733 compact_node(nid);
2734 }
2735
2736 return count;
2737}
2738static DEVICE_ATTR_WO(compact);
2739
2740int compaction_register_node(struct node *node)
2741{
2742 return device_create_file(&node->dev, &dev_attr_compact);
2743}
2744
2745void compaction_unregister_node(struct node *node)
2746{
2747 return device_remove_file(&node->dev, &dev_attr_compact);
2748}
2749#endif /* CONFIG_SYSFS && CONFIG_NUMA */
2750
2751static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2752{
2753 return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
2754}
2755
2756static bool kcompactd_node_suitable(pg_data_t *pgdat)
2757{
2758 int zoneid;
2759 struct zone *zone;
2760 enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
2761
2762 for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
2763 zone = &pgdat->node_zones[zoneid];
2764
2765 if (!populated_zone(zone))
2766 continue;
2767
2768 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
2769 highest_zoneidx) == COMPACT_CONTINUE)
2770 return true;
2771 }
2772
2773 return false;
2774}
2775
2776static void kcompactd_do_work(pg_data_t *pgdat)
2777{
2778 /*
2779 * With no special task, compact all zones so that a page of requested
2780 * order is allocatable.
2781 */
2782 int zoneid;
2783 struct zone *zone;
2784 struct compact_control cc = {
2785 .order = pgdat->kcompactd_max_order,
2786 .search_order = pgdat->kcompactd_max_order,
2787 .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
2788 .mode = MIGRATE_SYNC_LIGHT,
2789 .ignore_skip_hint = false,
2790 .gfp_mask = GFP_KERNEL,
2791 };
2792 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2793 cc.highest_zoneidx);
2794 count_compact_event(KCOMPACTD_WAKE);
2795
2796 for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
2797 int status;
2798
2799 zone = &pgdat->node_zones[zoneid];
2800 if (!populated_zone(zone))
2801 continue;
2802
2803 if (compaction_deferred(zone, cc.order))
2804 continue;
2805
2806 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
2807 COMPACT_CONTINUE)
2808 continue;
2809
2810 if (kthread_should_stop())
2811 return;
2812
2813 cc.zone = zone;
2814 status = compact_zone(&cc, NULL);
2815
2816 if (status == COMPACT_SUCCESS) {
2817 compaction_defer_reset(zone, cc.order, false);
2818 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2819 /*
2820 * Buddy pages may become stranded on pcps that could
2821 * otherwise coalesce on the zone's free area for
2822 * order >= cc.order. This is ratelimited by the
2823 * upcoming deferral.
2824 */
2825 drain_all_pages(zone);
2826
2827 /*
2828 * We use sync migration mode here, so we defer like
2829 * sync direct compaction does.
2830 */
2831 defer_compaction(zone, cc.order);
2832 }
2833
2834 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2835 cc.total_migrate_scanned);
2836 count_compact_events(KCOMPACTD_FREE_SCANNED,
2837 cc.total_free_scanned);
2838
2839 VM_BUG_ON(!list_empty(&cc.freepages));
2840 VM_BUG_ON(!list_empty(&cc.migratepages));
2841 }
2842
2843 /*
2844 * Regardless of success, we are done until woken up next. But remember
2845 * the requested order/highest_zoneidx in case it was higher/tighter
2846 * than our current ones
2847 */
2848 if (pgdat->kcompactd_max_order <= cc.order)
2849 pgdat->kcompactd_max_order = 0;
2850 if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
2851 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2852}
2853
2854void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
2855{
2856 if (!order)
2857 return;
2858
2859 if (pgdat->kcompactd_max_order < order)
2860 pgdat->kcompactd_max_order = order;
2861
2862 if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
2863 pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
2864
2865 /*
2866 * Pairs with implicit barrier in wait_event_freezable()
2867 * such that wakeups are not missed.
2868 */
2869 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2870 return;
2871
2872 if (!kcompactd_node_suitable(pgdat))
2873 return;
2874
2875 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2876 highest_zoneidx);
2877 wake_up_interruptible(&pgdat->kcompactd_wait);
2878}
2879
2880/*
2881 * The background compaction daemon, started as a kernel thread
2882 * from the init process.
2883 */
2884static int kcompactd(void *p)
2885{
2886 pg_data_t *pgdat = (pg_data_t *)p;
2887 struct task_struct *tsk = current;
2888 unsigned int proactive_defer = 0;
2889
2890 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2891
2892 if (!cpumask_empty(cpumask))
2893 set_cpus_allowed_ptr(tsk, cpumask);
2894
2895 set_freezable();
2896
2897 pgdat->kcompactd_max_order = 0;
2898 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2899
2900 while (!kthread_should_stop()) {
2901 unsigned long pflags;
2902
2903 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2904 if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
2905 kcompactd_work_requested(pgdat),
2906 msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
2907
2908 psi_memstall_enter(&pflags);
2909 kcompactd_do_work(pgdat);
2910 psi_memstall_leave(&pflags);
2911 continue;
2912 }
2913
2914 /* kcompactd wait timeout */
2915 if (should_proactive_compact_node(pgdat)) {
2916 unsigned int prev_score, score;
2917
2918 if (proactive_defer) {
2919 proactive_defer--;
2920 continue;
2921 }
2922 prev_score = fragmentation_score_node(pgdat);
2923 proactive_compact_node(pgdat);
2924 score = fragmentation_score_node(pgdat);
2925 /*
2926 * Defer proactive compaction if the fragmentation
2927 * score did not go down i.e. no progress made.
2928 */
2929 proactive_defer = score < prev_score ?
2930 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
2931 }
2932 }
2933
2934 return 0;
2935}
2936
2937/*
2938 * This kcompactd start function will be called by init and node-hot-add.
2939 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2940 */
2941int kcompactd_run(int nid)
2942{
2943 pg_data_t *pgdat = NODE_DATA(nid);
2944 int ret = 0;
2945
2946 if (pgdat->kcompactd)
2947 return 0;
2948
2949 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2950 if (IS_ERR(pgdat->kcompactd)) {
2951 pr_err("Failed to start kcompactd on node %d\n", nid);
2952 ret = PTR_ERR(pgdat->kcompactd);
2953 pgdat->kcompactd = NULL;
2954 }
2955 return ret;
2956}
2957
2958/*
2959 * Called by memory hotplug when all memory in a node is offlined. Caller must
2960 * hold mem_hotplug_begin/end().
2961 */
2962void kcompactd_stop(int nid)
2963{
2964 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2965
2966 if (kcompactd) {
2967 kthread_stop(kcompactd);
2968 NODE_DATA(nid)->kcompactd = NULL;
2969 }
2970}
2971
2972/*
2973 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2974 * not required for correctness. So if the last cpu in a node goes
2975 * away, we get changed to run anywhere: as the first one comes back,
2976 * restore their cpu bindings.
2977 */
2978static int kcompactd_cpu_online(unsigned int cpu)
2979{
2980 int nid;
2981
2982 for_each_node_state(nid, N_MEMORY) {
2983 pg_data_t *pgdat = NODE_DATA(nid);
2984 const struct cpumask *mask;
2985
2986 mask = cpumask_of_node(pgdat->node_id);
2987
2988 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2989 /* One of our CPUs online: restore mask */
2990 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2991 }
2992 return 0;
2993}
2994
2995static int __init kcompactd_init(void)
2996{
2997 int nid;
2998 int ret;
2999
3000 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3001 "mm/compaction:online",
3002 kcompactd_cpu_online, NULL);
3003 if (ret < 0) {
3004 pr_err("kcompactd: failed to register hotplug callbacks.\n");
3005 return ret;
3006 }
3007
3008 for_each_node_state(nid, N_MEMORY)
3009 kcompactd_run(nid);
3010 return 0;
3011}
3012subsys_initcall(kcompactd_init)
3013
3014#endif /* CONFIG_COMPACTION */
1/*
2 * linux/mm/compaction.c
3 *
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
6 * lifting
7 *
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
9 */
10#include <linux/swap.h>
11#include <linux/migrate.h>
12#include <linux/compaction.h>
13#include <linux/mm_inline.h>
14#include <linux/backing-dev.h>
15#include <linux/sysctl.h>
16#include <linux/sysfs.h>
17#include "internal.h"
18
19#if defined CONFIG_COMPACTION || defined CONFIG_CMA
20
21#define CREATE_TRACE_POINTS
22#include <trace/events/compaction.h>
23
24static unsigned long release_freepages(struct list_head *freelist)
25{
26 struct page *page, *next;
27 unsigned long count = 0;
28
29 list_for_each_entry_safe(page, next, freelist, lru) {
30 list_del(&page->lru);
31 __free_page(page);
32 count++;
33 }
34
35 return count;
36}
37
38static void map_pages(struct list_head *list)
39{
40 struct page *page;
41
42 list_for_each_entry(page, list, lru) {
43 arch_alloc_page(page, 0);
44 kernel_map_pages(page, 1, 1);
45 }
46}
47
48static inline bool migrate_async_suitable(int migratetype)
49{
50 return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
51}
52
53/*
54 * Isolate free pages onto a private freelist. Caller must hold zone->lock.
55 * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
56 * pages inside of the pageblock (even though it may still end up isolating
57 * some pages).
58 */
59static unsigned long isolate_freepages_block(unsigned long blockpfn,
60 unsigned long end_pfn,
61 struct list_head *freelist,
62 bool strict)
63{
64 int nr_scanned = 0, total_isolated = 0;
65 struct page *cursor;
66
67 cursor = pfn_to_page(blockpfn);
68
69 /* Isolate free pages. This assumes the block is valid */
70 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
71 int isolated, i;
72 struct page *page = cursor;
73
74 if (!pfn_valid_within(blockpfn)) {
75 if (strict)
76 return 0;
77 continue;
78 }
79 nr_scanned++;
80
81 if (!PageBuddy(page)) {
82 if (strict)
83 return 0;
84 continue;
85 }
86
87 /* Found a free page, break it into order-0 pages */
88 isolated = split_free_page(page);
89 if (!isolated && strict)
90 return 0;
91 total_isolated += isolated;
92 for (i = 0; i < isolated; i++) {
93 list_add(&page->lru, freelist);
94 page++;
95 }
96
97 /* If a page was split, advance to the end of it */
98 if (isolated) {
99 blockpfn += isolated - 1;
100 cursor += isolated - 1;
101 }
102 }
103
104 trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
105 return total_isolated;
106}
107
108/**
109 * isolate_freepages_range() - isolate free pages.
110 * @start_pfn: The first PFN to start isolating.
111 * @end_pfn: The one-past-last PFN.
112 *
113 * Non-free pages, invalid PFNs, or zone boundaries within the
114 * [start_pfn, end_pfn) range are considered errors, cause function to
115 * undo its actions and return zero.
116 *
117 * Otherwise, function returns one-past-the-last PFN of isolated page
118 * (which may be greater then end_pfn if end fell in a middle of
119 * a free page).
120 */
121unsigned long
122isolate_freepages_range(unsigned long start_pfn, unsigned long end_pfn)
123{
124 unsigned long isolated, pfn, block_end_pfn, flags;
125 struct zone *zone = NULL;
126 LIST_HEAD(freelist);
127
128 if (pfn_valid(start_pfn))
129 zone = page_zone(pfn_to_page(start_pfn));
130
131 for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
132 if (!pfn_valid(pfn) || zone != page_zone(pfn_to_page(pfn)))
133 break;
134
135 /*
136 * On subsequent iterations ALIGN() is actually not needed,
137 * but we keep it that we not to complicate the code.
138 */
139 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
140 block_end_pfn = min(block_end_pfn, end_pfn);
141
142 spin_lock_irqsave(&zone->lock, flags);
143 isolated = isolate_freepages_block(pfn, block_end_pfn,
144 &freelist, true);
145 spin_unlock_irqrestore(&zone->lock, flags);
146
147 /*
148 * In strict mode, isolate_freepages_block() returns 0 if
149 * there are any holes in the block (ie. invalid PFNs or
150 * non-free pages).
151 */
152 if (!isolated)
153 break;
154
155 /*
156 * If we managed to isolate pages, it is always (1 << n) *
157 * pageblock_nr_pages for some non-negative n. (Max order
158 * page may span two pageblocks).
159 */
160 }
161
162 /* split_free_page does not map the pages */
163 map_pages(&freelist);
164
165 if (pfn < end_pfn) {
166 /* Loop terminated early, cleanup. */
167 release_freepages(&freelist);
168 return 0;
169 }
170
171 /* We don't use freelists for anything. */
172 return pfn;
173}
174
175/* Update the number of anon and file isolated pages in the zone */
176static void acct_isolated(struct zone *zone, struct compact_control *cc)
177{
178 struct page *page;
179 unsigned int count[2] = { 0, };
180
181 list_for_each_entry(page, &cc->migratepages, lru)
182 count[!!page_is_file_cache(page)]++;
183
184 __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
185 __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
186}
187
188/* Similar to reclaim, but different enough that they don't share logic */
189static bool too_many_isolated(struct zone *zone)
190{
191 unsigned long active, inactive, isolated;
192
193 inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
194 zone_page_state(zone, NR_INACTIVE_ANON);
195 active = zone_page_state(zone, NR_ACTIVE_FILE) +
196 zone_page_state(zone, NR_ACTIVE_ANON);
197 isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
198 zone_page_state(zone, NR_ISOLATED_ANON);
199
200 return isolated > (inactive + active) / 2;
201}
202
203/**
204 * isolate_migratepages_range() - isolate all migrate-able pages in range.
205 * @zone: Zone pages are in.
206 * @cc: Compaction control structure.
207 * @low_pfn: The first PFN of the range.
208 * @end_pfn: The one-past-the-last PFN of the range.
209 *
210 * Isolate all pages that can be migrated from the range specified by
211 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
212 * pending), otherwise PFN of the first page that was not scanned
213 * (which may be both less, equal to or more then end_pfn).
214 *
215 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
216 * zero.
217 *
218 * Apart from cc->migratepages and cc->nr_migratetypes this function
219 * does not modify any cc's fields, in particular it does not modify
220 * (or read for that matter) cc->migrate_pfn.
221 */
222unsigned long
223isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
224 unsigned long low_pfn, unsigned long end_pfn)
225{
226 unsigned long last_pageblock_nr = 0, pageblock_nr;
227 unsigned long nr_scanned = 0, nr_isolated = 0;
228 struct list_head *migratelist = &cc->migratepages;
229 isolate_mode_t mode = 0;
230 struct lruvec *lruvec;
231
232 /*
233 * Ensure that there are not too many pages isolated from the LRU
234 * list by either parallel reclaimers or compaction. If there are,
235 * delay for some time until fewer pages are isolated
236 */
237 while (unlikely(too_many_isolated(zone))) {
238 /* async migration should just abort */
239 if (!cc->sync)
240 return 0;
241
242 congestion_wait(BLK_RW_ASYNC, HZ/10);
243
244 if (fatal_signal_pending(current))
245 return 0;
246 }
247
248 /* Time to isolate some pages for migration */
249 cond_resched();
250 spin_lock_irq(&zone->lru_lock);
251 for (; low_pfn < end_pfn; low_pfn++) {
252 struct page *page;
253 bool locked = true;
254
255 /* give a chance to irqs before checking need_resched() */
256 if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
257 spin_unlock_irq(&zone->lru_lock);
258 locked = false;
259 }
260 if (need_resched() || spin_is_contended(&zone->lru_lock)) {
261 if (locked)
262 spin_unlock_irq(&zone->lru_lock);
263 cond_resched();
264 spin_lock_irq(&zone->lru_lock);
265 if (fatal_signal_pending(current))
266 break;
267 } else if (!locked)
268 spin_lock_irq(&zone->lru_lock);
269
270 /*
271 * migrate_pfn does not necessarily start aligned to a
272 * pageblock. Ensure that pfn_valid is called when moving
273 * into a new MAX_ORDER_NR_PAGES range in case of large
274 * memory holes within the zone
275 */
276 if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
277 if (!pfn_valid(low_pfn)) {
278 low_pfn += MAX_ORDER_NR_PAGES - 1;
279 continue;
280 }
281 }
282
283 if (!pfn_valid_within(low_pfn))
284 continue;
285 nr_scanned++;
286
287 /*
288 * Get the page and ensure the page is within the same zone.
289 * See the comment in isolate_freepages about overlapping
290 * nodes. It is deliberate that the new zone lock is not taken
291 * as memory compaction should not move pages between nodes.
292 */
293 page = pfn_to_page(low_pfn);
294 if (page_zone(page) != zone)
295 continue;
296
297 /* Skip if free */
298 if (PageBuddy(page))
299 continue;
300
301 /*
302 * For async migration, also only scan in MOVABLE blocks. Async
303 * migration is optimistic to see if the minimum amount of work
304 * satisfies the allocation
305 */
306 pageblock_nr = low_pfn >> pageblock_order;
307 if (!cc->sync && last_pageblock_nr != pageblock_nr &&
308 !migrate_async_suitable(get_pageblock_migratetype(page))) {
309 low_pfn += pageblock_nr_pages;
310 low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
311 last_pageblock_nr = pageblock_nr;
312 continue;
313 }
314
315 if (!PageLRU(page))
316 continue;
317
318 /*
319 * PageLRU is set, and lru_lock excludes isolation,
320 * splitting and collapsing (collapsing has already
321 * happened if PageLRU is set).
322 */
323 if (PageTransHuge(page)) {
324 low_pfn += (1 << compound_order(page)) - 1;
325 continue;
326 }
327
328 if (!cc->sync)
329 mode |= ISOLATE_ASYNC_MIGRATE;
330
331 lruvec = mem_cgroup_page_lruvec(page, zone);
332
333 /* Try isolate the page */
334 if (__isolate_lru_page(page, mode) != 0)
335 continue;
336
337 VM_BUG_ON(PageTransCompound(page));
338
339 /* Successfully isolated */
340 del_page_from_lru_list(page, lruvec, page_lru(page));
341 list_add(&page->lru, migratelist);
342 cc->nr_migratepages++;
343 nr_isolated++;
344
345 /* Avoid isolating too much */
346 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
347 ++low_pfn;
348 break;
349 }
350 }
351
352 acct_isolated(zone, cc);
353
354 spin_unlock_irq(&zone->lru_lock);
355
356 trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
357
358 return low_pfn;
359}
360
361#endif /* CONFIG_COMPACTION || CONFIG_CMA */
362#ifdef CONFIG_COMPACTION
363
364/* Returns true if the page is within a block suitable for migration to */
365static bool suitable_migration_target(struct page *page)
366{
367
368 int migratetype = get_pageblock_migratetype(page);
369
370 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
371 if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
372 return false;
373
374 /* If the page is a large free page, then allow migration */
375 if (PageBuddy(page) && page_order(page) >= pageblock_order)
376 return true;
377
378 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
379 if (migrate_async_suitable(migratetype))
380 return true;
381
382 /* Otherwise skip the block */
383 return false;
384}
385
386/*
387 * Based on information in the current compact_control, find blocks
388 * suitable for isolating free pages from and then isolate them.
389 */
390static void isolate_freepages(struct zone *zone,
391 struct compact_control *cc)
392{
393 struct page *page;
394 unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
395 unsigned long flags;
396 int nr_freepages = cc->nr_freepages;
397 struct list_head *freelist = &cc->freepages;
398
399 /*
400 * Initialise the free scanner. The starting point is where we last
401 * scanned from (or the end of the zone if starting). The low point
402 * is the end of the pageblock the migration scanner is using.
403 */
404 pfn = cc->free_pfn;
405 low_pfn = cc->migrate_pfn + pageblock_nr_pages;
406
407 /*
408 * Take care that if the migration scanner is at the end of the zone
409 * that the free scanner does not accidentally move to the next zone
410 * in the next isolation cycle.
411 */
412 high_pfn = min(low_pfn, pfn);
413
414 zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
415
416 /*
417 * Isolate free pages until enough are available to migrate the
418 * pages on cc->migratepages. We stop searching if the migrate
419 * and free page scanners meet or enough free pages are isolated.
420 */
421 for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
422 pfn -= pageblock_nr_pages) {
423 unsigned long isolated;
424
425 if (!pfn_valid(pfn))
426 continue;
427
428 /*
429 * Check for overlapping nodes/zones. It's possible on some
430 * configurations to have a setup like
431 * node0 node1 node0
432 * i.e. it's possible that all pages within a zones range of
433 * pages do not belong to a single zone.
434 */
435 page = pfn_to_page(pfn);
436 if (page_zone(page) != zone)
437 continue;
438
439 /* Check the block is suitable for migration */
440 if (!suitable_migration_target(page))
441 continue;
442
443 /*
444 * Found a block suitable for isolating free pages from. Now
445 * we disabled interrupts, double check things are ok and
446 * isolate the pages. This is to minimise the time IRQs
447 * are disabled
448 */
449 isolated = 0;
450 spin_lock_irqsave(&zone->lock, flags);
451 if (suitable_migration_target(page)) {
452 end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
453 isolated = isolate_freepages_block(pfn, end_pfn,
454 freelist, false);
455 nr_freepages += isolated;
456 }
457 spin_unlock_irqrestore(&zone->lock, flags);
458
459 /*
460 * Record the highest PFN we isolated pages from. When next
461 * looking for free pages, the search will restart here as
462 * page migration may have returned some pages to the allocator
463 */
464 if (isolated)
465 high_pfn = max(high_pfn, pfn);
466 }
467
468 /* split_free_page does not map the pages */
469 map_pages(freelist);
470
471 cc->free_pfn = high_pfn;
472 cc->nr_freepages = nr_freepages;
473}
474
475/*
476 * This is a migrate-callback that "allocates" freepages by taking pages
477 * from the isolated freelists in the block we are migrating to.
478 */
479static struct page *compaction_alloc(struct page *migratepage,
480 unsigned long data,
481 int **result)
482{
483 struct compact_control *cc = (struct compact_control *)data;
484 struct page *freepage;
485
486 /* Isolate free pages if necessary */
487 if (list_empty(&cc->freepages)) {
488 isolate_freepages(cc->zone, cc);
489
490 if (list_empty(&cc->freepages))
491 return NULL;
492 }
493
494 freepage = list_entry(cc->freepages.next, struct page, lru);
495 list_del(&freepage->lru);
496 cc->nr_freepages--;
497
498 return freepage;
499}
500
501/*
502 * We cannot control nr_migratepages and nr_freepages fully when migration is
503 * running as migrate_pages() has no knowledge of compact_control. When
504 * migration is complete, we count the number of pages on the lists by hand.
505 */
506static void update_nr_listpages(struct compact_control *cc)
507{
508 int nr_migratepages = 0;
509 int nr_freepages = 0;
510 struct page *page;
511
512 list_for_each_entry(page, &cc->migratepages, lru)
513 nr_migratepages++;
514 list_for_each_entry(page, &cc->freepages, lru)
515 nr_freepages++;
516
517 cc->nr_migratepages = nr_migratepages;
518 cc->nr_freepages = nr_freepages;
519}
520
521/* possible outcome of isolate_migratepages */
522typedef enum {
523 ISOLATE_ABORT, /* Abort compaction now */
524 ISOLATE_NONE, /* No pages isolated, continue scanning */
525 ISOLATE_SUCCESS, /* Pages isolated, migrate */
526} isolate_migrate_t;
527
528/*
529 * Isolate all pages that can be migrated from the block pointed to by
530 * the migrate scanner within compact_control.
531 */
532static isolate_migrate_t isolate_migratepages(struct zone *zone,
533 struct compact_control *cc)
534{
535 unsigned long low_pfn, end_pfn;
536
537 /* Do not scan outside zone boundaries */
538 low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
539
540 /* Only scan within a pageblock boundary */
541 end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
542
543 /* Do not cross the free scanner or scan within a memory hole */
544 if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
545 cc->migrate_pfn = end_pfn;
546 return ISOLATE_NONE;
547 }
548
549 /* Perform the isolation */
550 low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
551 if (!low_pfn)
552 return ISOLATE_ABORT;
553
554 cc->migrate_pfn = low_pfn;
555
556 return ISOLATE_SUCCESS;
557}
558
559static int compact_finished(struct zone *zone,
560 struct compact_control *cc)
561{
562 unsigned int order;
563 unsigned long watermark;
564
565 if (fatal_signal_pending(current))
566 return COMPACT_PARTIAL;
567
568 /* Compaction run completes if the migrate and free scanner meet */
569 if (cc->free_pfn <= cc->migrate_pfn)
570 return COMPACT_COMPLETE;
571
572 /*
573 * order == -1 is expected when compacting via
574 * /proc/sys/vm/compact_memory
575 */
576 if (cc->order == -1)
577 return COMPACT_CONTINUE;
578
579 /* Compaction run is not finished if the watermark is not met */
580 watermark = low_wmark_pages(zone);
581 watermark += (1 << cc->order);
582
583 if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
584 return COMPACT_CONTINUE;
585
586 /* Direct compactor: Is a suitable page free? */
587 for (order = cc->order; order < MAX_ORDER; order++) {
588 /* Job done if page is free of the right migratetype */
589 if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
590 return COMPACT_PARTIAL;
591
592 /* Job done if allocation would set block type */
593 if (order >= pageblock_order && zone->free_area[order].nr_free)
594 return COMPACT_PARTIAL;
595 }
596
597 return COMPACT_CONTINUE;
598}
599
600/*
601 * compaction_suitable: Is this suitable to run compaction on this zone now?
602 * Returns
603 * COMPACT_SKIPPED - If there are too few free pages for compaction
604 * COMPACT_PARTIAL - If the allocation would succeed without compaction
605 * COMPACT_CONTINUE - If compaction should run now
606 */
607unsigned long compaction_suitable(struct zone *zone, int order)
608{
609 int fragindex;
610 unsigned long watermark;
611
612 /*
613 * order == -1 is expected when compacting via
614 * /proc/sys/vm/compact_memory
615 */
616 if (order == -1)
617 return COMPACT_CONTINUE;
618
619 /*
620 * Watermarks for order-0 must be met for compaction. Note the 2UL.
621 * This is because during migration, copies of pages need to be
622 * allocated and for a short time, the footprint is higher
623 */
624 watermark = low_wmark_pages(zone) + (2UL << order);
625 if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
626 return COMPACT_SKIPPED;
627
628 /*
629 * fragmentation index determines if allocation failures are due to
630 * low memory or external fragmentation
631 *
632 * index of -1000 implies allocations might succeed depending on
633 * watermarks
634 * index towards 0 implies failure is due to lack of memory
635 * index towards 1000 implies failure is due to fragmentation
636 *
637 * Only compact if a failure would be due to fragmentation.
638 */
639 fragindex = fragmentation_index(zone, order);
640 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
641 return COMPACT_SKIPPED;
642
643 if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
644 0, 0))
645 return COMPACT_PARTIAL;
646
647 return COMPACT_CONTINUE;
648}
649
650static int compact_zone(struct zone *zone, struct compact_control *cc)
651{
652 int ret;
653
654 ret = compaction_suitable(zone, cc->order);
655 switch (ret) {
656 case COMPACT_PARTIAL:
657 case COMPACT_SKIPPED:
658 /* Compaction is likely to fail */
659 return ret;
660 case COMPACT_CONTINUE:
661 /* Fall through to compaction */
662 ;
663 }
664
665 /* Setup to move all movable pages to the end of the zone */
666 cc->migrate_pfn = zone->zone_start_pfn;
667 cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
668 cc->free_pfn &= ~(pageblock_nr_pages-1);
669
670 migrate_prep_local();
671
672 while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
673 unsigned long nr_migrate, nr_remaining;
674 int err;
675
676 switch (isolate_migratepages(zone, cc)) {
677 case ISOLATE_ABORT:
678 ret = COMPACT_PARTIAL;
679 goto out;
680 case ISOLATE_NONE:
681 continue;
682 case ISOLATE_SUCCESS:
683 ;
684 }
685
686 nr_migrate = cc->nr_migratepages;
687 err = migrate_pages(&cc->migratepages, compaction_alloc,
688 (unsigned long)cc, false,
689 cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
690 update_nr_listpages(cc);
691 nr_remaining = cc->nr_migratepages;
692
693 count_vm_event(COMPACTBLOCKS);
694 count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
695 if (nr_remaining)
696 count_vm_events(COMPACTPAGEFAILED, nr_remaining);
697 trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
698 nr_remaining);
699
700 /* Release LRU pages not migrated */
701 if (err) {
702 putback_lru_pages(&cc->migratepages);
703 cc->nr_migratepages = 0;
704 if (err == -ENOMEM) {
705 ret = COMPACT_PARTIAL;
706 goto out;
707 }
708 }
709 }
710
711out:
712 /* Release free pages and check accounting */
713 cc->nr_freepages -= release_freepages(&cc->freepages);
714 VM_BUG_ON(cc->nr_freepages != 0);
715
716 return ret;
717}
718
719static unsigned long compact_zone_order(struct zone *zone,
720 int order, gfp_t gfp_mask,
721 bool sync)
722{
723 struct compact_control cc = {
724 .nr_freepages = 0,
725 .nr_migratepages = 0,
726 .order = order,
727 .migratetype = allocflags_to_migratetype(gfp_mask),
728 .zone = zone,
729 .sync = sync,
730 };
731 INIT_LIST_HEAD(&cc.freepages);
732 INIT_LIST_HEAD(&cc.migratepages);
733
734 return compact_zone(zone, &cc);
735}
736
737int sysctl_extfrag_threshold = 500;
738
739/**
740 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
741 * @zonelist: The zonelist used for the current allocation
742 * @order: The order of the current allocation
743 * @gfp_mask: The GFP mask of the current allocation
744 * @nodemask: The allowed nodes to allocate from
745 * @sync: Whether migration is synchronous or not
746 *
747 * This is the main entry point for direct page compaction.
748 */
749unsigned long try_to_compact_pages(struct zonelist *zonelist,
750 int order, gfp_t gfp_mask, nodemask_t *nodemask,
751 bool sync)
752{
753 enum zone_type high_zoneidx = gfp_zone(gfp_mask);
754 int may_enter_fs = gfp_mask & __GFP_FS;
755 int may_perform_io = gfp_mask & __GFP_IO;
756 struct zoneref *z;
757 struct zone *zone;
758 int rc = COMPACT_SKIPPED;
759
760 /*
761 * Check whether it is worth even starting compaction. The order check is
762 * made because an assumption is made that the page allocator can satisfy
763 * the "cheaper" orders without taking special steps
764 */
765 if (!order || !may_enter_fs || !may_perform_io)
766 return rc;
767
768 count_vm_event(COMPACTSTALL);
769
770 /* Compact each zone in the list */
771 for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
772 nodemask) {
773 int status;
774
775 status = compact_zone_order(zone, order, gfp_mask, sync);
776 rc = max(status, rc);
777
778 /* If a normal allocation would succeed, stop compacting */
779 if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
780 break;
781 }
782
783 return rc;
784}
785
786
787/* Compact all zones within a node */
788static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
789{
790 int zoneid;
791 struct zone *zone;
792
793 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
794
795 zone = &pgdat->node_zones[zoneid];
796 if (!populated_zone(zone))
797 continue;
798
799 cc->nr_freepages = 0;
800 cc->nr_migratepages = 0;
801 cc->zone = zone;
802 INIT_LIST_HEAD(&cc->freepages);
803 INIT_LIST_HEAD(&cc->migratepages);
804
805 if (cc->order == -1 || !compaction_deferred(zone, cc->order))
806 compact_zone(zone, cc);
807
808 if (cc->order > 0) {
809 int ok = zone_watermark_ok(zone, cc->order,
810 low_wmark_pages(zone), 0, 0);
811 if (ok && cc->order > zone->compact_order_failed)
812 zone->compact_order_failed = cc->order + 1;
813 /* Currently async compaction is never deferred. */
814 else if (!ok && cc->sync)
815 defer_compaction(zone, cc->order);
816 }
817
818 VM_BUG_ON(!list_empty(&cc->freepages));
819 VM_BUG_ON(!list_empty(&cc->migratepages));
820 }
821
822 return 0;
823}
824
825int compact_pgdat(pg_data_t *pgdat, int order)
826{
827 struct compact_control cc = {
828 .order = order,
829 .sync = false,
830 };
831
832 return __compact_pgdat(pgdat, &cc);
833}
834
835static int compact_node(int nid)
836{
837 struct compact_control cc = {
838 .order = -1,
839 .sync = true,
840 };
841
842 return __compact_pgdat(NODE_DATA(nid), &cc);
843}
844
845/* Compact all nodes in the system */
846static int compact_nodes(void)
847{
848 int nid;
849
850 /* Flush pending updates to the LRU lists */
851 lru_add_drain_all();
852
853 for_each_online_node(nid)
854 compact_node(nid);
855
856 return COMPACT_COMPLETE;
857}
858
859/* The written value is actually unused, all memory is compacted */
860int sysctl_compact_memory;
861
862/* This is the entry point for compacting all nodes via /proc/sys/vm */
863int sysctl_compaction_handler(struct ctl_table *table, int write,
864 void __user *buffer, size_t *length, loff_t *ppos)
865{
866 if (write)
867 return compact_nodes();
868
869 return 0;
870}
871
872int sysctl_extfrag_handler(struct ctl_table *table, int write,
873 void __user *buffer, size_t *length, loff_t *ppos)
874{
875 proc_dointvec_minmax(table, write, buffer, length, ppos);
876
877 return 0;
878}
879
880#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
881ssize_t sysfs_compact_node(struct device *dev,
882 struct device_attribute *attr,
883 const char *buf, size_t count)
884{
885 int nid = dev->id;
886
887 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
888 /* Flush pending updates to the LRU lists */
889 lru_add_drain_all();
890
891 compact_node(nid);
892 }
893
894 return count;
895}
896static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
897
898int compaction_register_node(struct node *node)
899{
900 return device_create_file(&node->dev, &dev_attr_compact);
901}
902
903void compaction_unregister_node(struct node *node)
904{
905 return device_remove_file(&node->dev, &dev_attr_compact);
906}
907#endif /* CONFIG_SYSFS && CONFIG_NUMA */
908
909#endif /* CONFIG_COMPACTION */