1 // SPDX-License-Identifier: GPL-2.0
3 * linux/mm/compaction.c
5 * Memory compaction for the reduction of external fragmentation. Note that
6 * this heavily depends upon page migration to do all the real heavy
9 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
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>
28 #ifdef CONFIG_COMPACTION
29 static inline void count_compact_event(enum vm_event_item item)
34 static inline void count_compact_events(enum vm_event_item item, long delta)
36 count_vm_events(item, delta);
39 #define count_compact_event(item) do { } while (0)
40 #define count_compact_events(item, delta) do { } while (0)
43 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
45 #define CREATE_TRACE_POINTS
46 #include <trace/events/compaction.h>
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)
54 * Fragmentation score check interval for proactive compaction purposes.
56 static const unsigned int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
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.
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
68 #define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT)
71 static unsigned long release_freepages(struct list_head *freelist)
73 struct page *page, *next;
74 unsigned long high_pfn = 0;
76 list_for_each_entry_safe(page, next, freelist, lru) {
77 unsigned long pfn = page_to_pfn(page);
87 static void split_map_pages(struct list_head *list)
89 unsigned int i, order, nr_pages;
90 struct page *page, *next;
93 list_for_each_entry_safe(page, next, list, lru) {
96 order = page_private(page);
97 nr_pages = 1 << order;
99 post_alloc_hook(page, order, __GFP_MOVABLE);
101 split_page(page, order);
103 for (i = 0; i < nr_pages; i++) {
104 list_add(&page->lru, &tmp_list);
109 list_splice(&tmp_list, list);
112 #ifdef CONFIG_COMPACTION
114 int PageMovable(struct page *page)
116 struct address_space *mapping;
118 VM_BUG_ON_PAGE(!PageLocked(page), page);
119 if (!__PageMovable(page))
122 mapping = page_mapping(page);
123 if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
128 EXPORT_SYMBOL(PageMovable);
130 void __SetPageMovable(struct page *page, struct address_space *mapping)
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);
136 EXPORT_SYMBOL(__SetPageMovable);
138 void __ClearPageMovable(struct page *page)
140 VM_BUG_ON_PAGE(!PageLocked(page), page);
141 VM_BUG_ON_PAGE(!PageMovable(page), page);
143 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
144 * flag so that VM can catch up released page by driver after isolation.
145 * With it, VM migration doesn't try to put it back.
147 page->mapping = (void *)((unsigned long)page->mapping &
148 PAGE_MAPPING_MOVABLE);
150 EXPORT_SYMBOL(__ClearPageMovable);
152 /* Do not skip compaction more than 64 times */
153 #define COMPACT_MAX_DEFER_SHIFT 6
156 * Compaction is deferred when compaction fails to result in a page
157 * allocation success. 1 << compact_defer_shift, compactions are skipped up
158 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
160 static void defer_compaction(struct zone *zone, int order)
162 zone->compact_considered = 0;
163 zone->compact_defer_shift++;
165 if (order < zone->compact_order_failed)
166 zone->compact_order_failed = order;
168 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
169 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
171 trace_mm_compaction_defer_compaction(zone, order);
174 /* Returns true if compaction should be skipped this time */
175 static bool compaction_deferred(struct zone *zone, int order)
177 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
179 if (order < zone->compact_order_failed)
182 /* Avoid possible overflow */
183 if (++zone->compact_considered >= defer_limit) {
184 zone->compact_considered = defer_limit;
188 trace_mm_compaction_deferred(zone, order);
194 * Update defer tracking counters after successful compaction of given order,
195 * which means an allocation either succeeded (alloc_success == true) or is
196 * expected to succeed.
198 void compaction_defer_reset(struct zone *zone, int order,
202 zone->compact_considered = 0;
203 zone->compact_defer_shift = 0;
205 if (order >= zone->compact_order_failed)
206 zone->compact_order_failed = order + 1;
208 trace_mm_compaction_defer_reset(zone, order);
211 /* Returns true if restarting compaction after many failures */
212 static bool compaction_restarting(struct zone *zone, int order)
214 if (order < zone->compact_order_failed)
217 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
218 zone->compact_considered >= 1UL << zone->compact_defer_shift;
221 /* Returns true if the pageblock should be scanned for pages to isolate. */
222 static inline bool isolation_suitable(struct compact_control *cc,
225 if (cc->ignore_skip_hint)
228 return !get_pageblock_skip(page);
231 static void reset_cached_positions(struct zone *zone)
233 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
234 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
235 zone->compact_cached_free_pfn =
236 pageblock_start_pfn(zone_end_pfn(zone) - 1);
240 * Compound pages of >= pageblock_order should consistently be skipped until
241 * released. It is always pointless to compact pages of such order (if they are
242 * migratable), and the pageblocks they occupy cannot contain any free pages.
244 static bool pageblock_skip_persistent(struct page *page)
246 if (!PageCompound(page))
249 page = compound_head(page);
251 if (compound_order(page) >= pageblock_order)
258 __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
261 struct page *page = pfn_to_online_page(pfn);
262 struct page *block_page;
263 struct page *end_page;
264 unsigned long block_pfn;
268 if (zone != page_zone(page))
270 if (pageblock_skip_persistent(page))
274 * If skip is already cleared do no further checking once the
275 * restart points have been set.
277 if (check_source && check_target && !get_pageblock_skip(page))
281 * If clearing skip for the target scanner, do not select a
282 * non-movable pageblock as the starting point.
284 if (!check_source && check_target &&
285 get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
288 /* Ensure the start of the pageblock or zone is online and valid */
289 block_pfn = pageblock_start_pfn(pfn);
290 block_pfn = max(block_pfn, zone->zone_start_pfn);
291 block_page = pfn_to_online_page(block_pfn);
297 /* Ensure the end of the pageblock or zone is online and valid */
298 block_pfn = pageblock_end_pfn(pfn) - 1;
299 block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
300 end_page = pfn_to_online_page(block_pfn);
305 * Only clear the hint if a sample indicates there is either a
306 * free page or an LRU page in the block. One or other condition
307 * is necessary for the block to be a migration source/target.
310 if (pfn_valid_within(pfn)) {
311 if (check_source && PageLRU(page)) {
312 clear_pageblock_skip(page);
316 if (check_target && PageBuddy(page)) {
317 clear_pageblock_skip(page);
322 page += (1 << PAGE_ALLOC_COSTLY_ORDER);
323 pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
324 } while (page <= end_page);
330 * This function is called to clear all cached information on pageblocks that
331 * should be skipped for page isolation when the migrate and free page scanner
334 static void __reset_isolation_suitable(struct zone *zone)
336 unsigned long migrate_pfn = zone->zone_start_pfn;
337 unsigned long free_pfn = zone_end_pfn(zone) - 1;
338 unsigned long reset_migrate = free_pfn;
339 unsigned long reset_free = migrate_pfn;
340 bool source_set = false;
341 bool free_set = false;
343 if (!zone->compact_blockskip_flush)
346 zone->compact_blockskip_flush = false;
349 * Walk the zone and update pageblock skip information. Source looks
350 * for PageLRU while target looks for PageBuddy. When the scanner
351 * is found, both PageBuddy and PageLRU are checked as the pageblock
352 * is suitable as both source and target.
354 for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
355 free_pfn -= pageblock_nr_pages) {
358 /* Update the migrate PFN */
359 if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
360 migrate_pfn < reset_migrate) {
362 reset_migrate = migrate_pfn;
363 zone->compact_init_migrate_pfn = reset_migrate;
364 zone->compact_cached_migrate_pfn[0] = reset_migrate;
365 zone->compact_cached_migrate_pfn[1] = reset_migrate;
368 /* Update the free PFN */
369 if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
370 free_pfn > reset_free) {
372 reset_free = free_pfn;
373 zone->compact_init_free_pfn = reset_free;
374 zone->compact_cached_free_pfn = reset_free;
378 /* Leave no distance if no suitable block was reset */
379 if (reset_migrate >= reset_free) {
380 zone->compact_cached_migrate_pfn[0] = migrate_pfn;
381 zone->compact_cached_migrate_pfn[1] = migrate_pfn;
382 zone->compact_cached_free_pfn = free_pfn;
386 void reset_isolation_suitable(pg_data_t *pgdat)
390 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
391 struct zone *zone = &pgdat->node_zones[zoneid];
392 if (!populated_zone(zone))
395 /* Only flush if a full compaction finished recently */
396 if (zone->compact_blockskip_flush)
397 __reset_isolation_suitable(zone);
402 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
403 * locks are not required for read/writers. Returns true if it was already set.
405 static bool test_and_set_skip(struct compact_control *cc, struct page *page,
410 /* Do no update if skip hint is being ignored */
411 if (cc->ignore_skip_hint)
414 if (!IS_ALIGNED(pfn, pageblock_nr_pages))
417 skip = get_pageblock_skip(page);
418 if (!skip && !cc->no_set_skip_hint)
419 set_pageblock_skip(page);
424 static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
426 struct zone *zone = cc->zone;
428 pfn = pageblock_end_pfn(pfn);
430 /* Set for isolation rather than compaction */
431 if (cc->no_set_skip_hint)
434 if (pfn > zone->compact_cached_migrate_pfn[0])
435 zone->compact_cached_migrate_pfn[0] = pfn;
436 if (cc->mode != MIGRATE_ASYNC &&
437 pfn > zone->compact_cached_migrate_pfn[1])
438 zone->compact_cached_migrate_pfn[1] = pfn;
442 * If no pages were isolated then mark this pageblock to be skipped in the
443 * future. The information is later cleared by __reset_isolation_suitable().
445 static void update_pageblock_skip(struct compact_control *cc,
446 struct page *page, unsigned long pfn)
448 struct zone *zone = cc->zone;
450 if (cc->no_set_skip_hint)
456 set_pageblock_skip(page);
458 /* Update where async and sync compaction should restart */
459 if (pfn < zone->compact_cached_free_pfn)
460 zone->compact_cached_free_pfn = pfn;
463 static inline bool isolation_suitable(struct compact_control *cc,
469 static inline bool pageblock_skip_persistent(struct page *page)
474 static inline void update_pageblock_skip(struct compact_control *cc,
475 struct page *page, unsigned long pfn)
479 static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
483 static bool test_and_set_skip(struct compact_control *cc, struct page *page,
488 #endif /* CONFIG_COMPACTION */
491 * Compaction requires the taking of some coarse locks that are potentially
492 * very heavily contended. For async compaction, trylock and record if the
493 * lock is contended. The lock will still be acquired but compaction will
494 * abort when the current block is finished regardless of success rate.
495 * Sync compaction acquires the lock.
497 * Always returns true which makes it easier to track lock state in callers.
499 static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
500 struct compact_control *cc)
503 /* Track if the lock is contended in async mode */
504 if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
505 if (spin_trylock_irqsave(lock, *flags))
508 cc->contended = true;
511 spin_lock_irqsave(lock, *flags);
516 * Compaction requires the taking of some coarse locks that are potentially
517 * very heavily contended. The lock should be periodically unlocked to avoid
518 * having disabled IRQs for a long time, even when there is nobody waiting on
519 * the lock. It might also be that allowing the IRQs will result in
520 * need_resched() becoming true. If scheduling is needed, async compaction
521 * aborts. Sync compaction schedules.
522 * Either compaction type will also abort if a fatal signal is pending.
523 * In either case if the lock was locked, it is dropped and not regained.
525 * Returns true if compaction should abort due to fatal signal pending, or
526 * async compaction due to need_resched()
527 * Returns false when compaction can continue (sync compaction might have
530 static bool compact_unlock_should_abort(spinlock_t *lock,
531 unsigned long flags, bool *locked, struct compact_control *cc)
534 spin_unlock_irqrestore(lock, flags);
538 if (fatal_signal_pending(current)) {
539 cc->contended = true;
549 * Isolate free pages onto a private freelist. If @strict is true, will abort
550 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
551 * (even though it may still end up isolating some pages).
553 static unsigned long isolate_freepages_block(struct compact_control *cc,
554 unsigned long *start_pfn,
555 unsigned long end_pfn,
556 struct list_head *freelist,
560 int nr_scanned = 0, total_isolated = 0;
562 unsigned long flags = 0;
564 unsigned long blockpfn = *start_pfn;
567 /* Strict mode is for isolation, speed is secondary */
571 cursor = pfn_to_page(blockpfn);
573 /* Isolate free pages. */
574 for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
576 struct page *page = cursor;
579 * Periodically drop the lock (if held) regardless of its
580 * contention, to give chance to IRQs. Abort if fatal signal
581 * pending or async compaction detects need_resched()
583 if (!(blockpfn % SWAP_CLUSTER_MAX)
584 && compact_unlock_should_abort(&cc->zone->lock, flags,
589 if (!pfn_valid_within(blockpfn))
593 * For compound pages such as THP and hugetlbfs, we can save
594 * potentially a lot of iterations if we skip them at once.
595 * The check is racy, but we can consider only valid values
596 * and the only danger is skipping too much.
598 if (PageCompound(page)) {
599 const unsigned int order = compound_order(page);
601 if (likely(order < MAX_ORDER)) {
602 blockpfn += (1UL << order) - 1;
603 cursor += (1UL << order) - 1;
608 if (!PageBuddy(page))
612 * If we already hold the lock, we can skip some rechecking.
613 * Note that if we hold the lock now, checked_pageblock was
614 * already set in some previous iteration (or strict is true),
615 * so it is correct to skip the suitable migration target
619 locked = compact_lock_irqsave(&cc->zone->lock,
622 /* Recheck this is a buddy page under lock */
623 if (!PageBuddy(page))
627 /* Found a free page, will break it into order-0 pages */
628 order = buddy_order(page);
629 isolated = __isolate_free_page(page, order);
632 set_page_private(page, order);
634 total_isolated += isolated;
635 cc->nr_freepages += isolated;
636 list_add_tail(&page->lru, freelist);
638 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
639 blockpfn += isolated;
642 /* Advance to the end of split page */
643 blockpfn += isolated - 1;
644 cursor += isolated - 1;
656 spin_unlock_irqrestore(&cc->zone->lock, flags);
659 * There is a tiny chance that we have read bogus compound_order(),
660 * so be careful to not go outside of the pageblock.
662 if (unlikely(blockpfn > end_pfn))
665 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
666 nr_scanned, total_isolated);
668 /* Record how far we have got within the block */
669 *start_pfn = blockpfn;
672 * If strict isolation is requested by CMA then check that all the
673 * pages requested were isolated. If there were any failures, 0 is
674 * returned and CMA will fail.
676 if (strict && blockpfn < end_pfn)
679 cc->total_free_scanned += nr_scanned;
681 count_compact_events(COMPACTISOLATED, total_isolated);
682 return total_isolated;
686 * isolate_freepages_range() - isolate free pages.
687 * @cc: Compaction control structure.
688 * @start_pfn: The first PFN to start isolating.
689 * @end_pfn: The one-past-last PFN.
691 * Non-free pages, invalid PFNs, or zone boundaries within the
692 * [start_pfn, end_pfn) range are considered errors, cause function to
693 * undo its actions and return zero.
695 * Otherwise, function returns one-past-the-last PFN of isolated page
696 * (which may be greater then end_pfn if end fell in a middle of
700 isolate_freepages_range(struct compact_control *cc,
701 unsigned long start_pfn, unsigned long end_pfn)
703 unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
707 block_start_pfn = pageblock_start_pfn(pfn);
708 if (block_start_pfn < cc->zone->zone_start_pfn)
709 block_start_pfn = cc->zone->zone_start_pfn;
710 block_end_pfn = pageblock_end_pfn(pfn);
712 for (; pfn < end_pfn; pfn += isolated,
713 block_start_pfn = block_end_pfn,
714 block_end_pfn += pageblock_nr_pages) {
715 /* Protect pfn from changing by isolate_freepages_block */
716 unsigned long isolate_start_pfn = pfn;
718 block_end_pfn = min(block_end_pfn, end_pfn);
721 * pfn could pass the block_end_pfn if isolated freepage
722 * is more than pageblock order. In this case, we adjust
723 * scanning range to right one.
725 if (pfn >= block_end_pfn) {
726 block_start_pfn = pageblock_start_pfn(pfn);
727 block_end_pfn = pageblock_end_pfn(pfn);
728 block_end_pfn = min(block_end_pfn, end_pfn);
731 if (!pageblock_pfn_to_page(block_start_pfn,
732 block_end_pfn, cc->zone))
735 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
736 block_end_pfn, &freelist, 0, true);
739 * In strict mode, isolate_freepages_block() returns 0 if
740 * there are any holes in the block (ie. invalid PFNs or
747 * If we managed to isolate pages, it is always (1 << n) *
748 * pageblock_nr_pages for some non-negative n. (Max order
749 * page may span two pageblocks).
753 /* __isolate_free_page() does not map the pages */
754 split_map_pages(&freelist);
757 /* Loop terminated early, cleanup. */
758 release_freepages(&freelist);
762 /* We don't use freelists for anything. */
766 /* Similar to reclaim, but different enough that they don't share logic */
767 static bool too_many_isolated(pg_data_t *pgdat)
769 unsigned long active, inactive, isolated;
771 inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
772 node_page_state(pgdat, NR_INACTIVE_ANON);
773 active = node_page_state(pgdat, NR_ACTIVE_FILE) +
774 node_page_state(pgdat, NR_ACTIVE_ANON);
775 isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
776 node_page_state(pgdat, NR_ISOLATED_ANON);
778 return isolated > (inactive + active) / 2;
782 * isolate_migratepages_block() - isolate all migrate-able pages within
784 * @cc: Compaction control structure.
785 * @low_pfn: The first PFN to isolate
786 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
787 * @isolate_mode: Isolation mode to be used.
789 * Isolate all pages that can be migrated from the range specified by
790 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
791 * Returns zero if there is a fatal signal pending, otherwise PFN of the
792 * first page that was not scanned (which may be both less, equal to or more
795 * The pages are isolated on cc->migratepages list (not required to be empty),
796 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
797 * is neither read nor updated.
800 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
801 unsigned long end_pfn, isolate_mode_t isolate_mode)
803 pg_data_t *pgdat = cc->zone->zone_pgdat;
804 unsigned long nr_scanned = 0, nr_isolated = 0;
805 struct lruvec *lruvec;
806 unsigned long flags = 0;
807 struct lruvec *locked = NULL;
808 struct page *page = NULL, *valid_page = NULL;
809 unsigned long start_pfn = low_pfn;
810 bool skip_on_failure = false;
811 unsigned long next_skip_pfn = 0;
812 bool skip_updated = false;
815 * Ensure that there are not too many pages isolated from the LRU
816 * list by either parallel reclaimers or compaction. If there are,
817 * delay for some time until fewer pages are isolated
819 while (unlikely(too_many_isolated(pgdat))) {
820 /* stop isolation if there are still pages not migrated */
821 if (cc->nr_migratepages)
824 /* async migration should just abort */
825 if (cc->mode == MIGRATE_ASYNC)
828 congestion_wait(BLK_RW_ASYNC, HZ/10);
830 if (fatal_signal_pending(current))
836 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
837 skip_on_failure = true;
838 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
841 /* Time to isolate some pages for migration */
842 for (; low_pfn < end_pfn; low_pfn++) {
844 if (skip_on_failure && low_pfn >= next_skip_pfn) {
846 * We have isolated all migration candidates in the
847 * previous order-aligned block, and did not skip it due
848 * to failure. We should migrate the pages now and
849 * hopefully succeed compaction.
855 * We failed to isolate in the previous order-aligned
856 * block. Set the new boundary to the end of the
857 * current block. Note we can't simply increase
858 * next_skip_pfn by 1 << order, as low_pfn might have
859 * been incremented by a higher number due to skipping
860 * a compound or a high-order buddy page in the
861 * previous loop iteration.
863 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
867 * Periodically drop the lock (if held) regardless of its
868 * contention, to give chance to IRQs. Abort completely if
869 * a fatal signal is pending.
871 if (!(low_pfn % SWAP_CLUSTER_MAX)) {
873 unlock_page_lruvec_irqrestore(locked, flags);
877 if (fatal_signal_pending(current)) {
878 cc->contended = true;
887 if (!pfn_valid_within(low_pfn))
891 page = pfn_to_page(low_pfn);
894 * Check if the pageblock has already been marked skipped.
895 * Only the aligned PFN is checked as the caller isolates
896 * COMPACT_CLUSTER_MAX at a time so the second call must
897 * not falsely conclude that the block should be skipped.
899 if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
900 if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
909 * Skip if free. We read page order here without zone lock
910 * which is generally unsafe, but the race window is small and
911 * the worst thing that can happen is that we skip some
912 * potential isolation targets.
914 if (PageBuddy(page)) {
915 unsigned long freepage_order = buddy_order_unsafe(page);
918 * Without lock, we cannot be sure that what we got is
919 * a valid page order. Consider only values in the
920 * valid order range to prevent low_pfn overflow.
922 if (freepage_order > 0 && freepage_order < MAX_ORDER)
923 low_pfn += (1UL << freepage_order) - 1;
928 * Regardless of being on LRU, compound pages such as THP and
929 * hugetlbfs are not to be compacted unless we are attempting
930 * an allocation much larger than the huge page size (eg CMA).
931 * We can potentially save a lot of iterations if we skip them
932 * at once. The check is racy, but we can consider only valid
933 * values and the only danger is skipping too much.
935 if (PageCompound(page) && !cc->alloc_contig) {
936 const unsigned int order = compound_order(page);
938 if (likely(order < MAX_ORDER))
939 low_pfn += (1UL << order) - 1;
944 * Check may be lockless but that's ok as we recheck later.
945 * It's possible to migrate LRU and non-lru movable pages.
946 * Skip any other type of page
948 if (!PageLRU(page)) {
950 * __PageMovable can return false positive so we need
951 * to verify it under page_lock.
953 if (unlikely(__PageMovable(page)) &&
954 !PageIsolated(page)) {
956 unlock_page_lruvec_irqrestore(locked, flags);
960 if (!isolate_movable_page(page, isolate_mode))
961 goto isolate_success;
968 * Migration will fail if an anonymous page is pinned in memory,
969 * so avoid taking lru_lock and isolating it unnecessarily in an
970 * admittedly racy check.
972 if (!page_mapping(page) &&
973 page_count(page) > page_mapcount(page))
977 * Only allow to migrate anonymous pages in GFP_NOFS context
978 * because those do not depend on fs locks.
980 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
984 * Be careful not to clear PageLRU until after we're
985 * sure the page is not being freed elsewhere -- the
986 * page release code relies on it.
988 if (unlikely(!get_page_unless_zero(page)))
991 if (__isolate_lru_page_prepare(page, isolate_mode) != 0)
992 goto isolate_fail_put;
994 /* Try isolate the page */
995 if (!TestClearPageLRU(page))
996 goto isolate_fail_put;
999 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1001 /* If we already hold the lock, we can skip some rechecking */
1002 if (lruvec != locked) {
1004 unlock_page_lruvec_irqrestore(locked, flags);
1006 compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
1010 lruvec_memcg_debug(lruvec, page);
1012 /* Try get exclusive access under lock */
1013 if (!skip_updated) {
1014 skip_updated = true;
1015 if (test_and_set_skip(cc, page, low_pfn))
1020 * Page become compound since the non-locked check,
1021 * and it's on LRU. It can only be a THP so the order
1022 * is safe to read and it's 0 for tail pages.
1024 if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
1025 low_pfn += compound_nr(page) - 1;
1027 goto isolate_fail_put;
1032 /* The whole page is taken off the LRU; skip the tail pages. */
1033 if (PageCompound(page))
1034 low_pfn += compound_nr(page) - 1;
1036 /* Successfully isolated */
1037 del_page_from_lru_list(page, lruvec, page_lru(page));
1038 mod_node_page_state(page_pgdat(page),
1039 NR_ISOLATED_ANON + page_is_file_lru(page),
1040 thp_nr_pages(page));
1043 list_add(&page->lru, &cc->migratepages);
1044 cc->nr_migratepages += compound_nr(page);
1045 nr_isolated += compound_nr(page);
1048 * Avoid isolating too much unless this block is being
1049 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1050 * or a lock is contended. For contention, isolate quickly to
1051 * potentially remove one source of contention.
1053 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
1054 !cc->rescan && !cc->contended) {
1062 /* Avoid potential deadlock in freeing page under lru_lock */
1064 unlock_page_lruvec_irqrestore(locked, flags);
1070 if (!skip_on_failure)
1074 * We have isolated some pages, but then failed. Release them
1075 * instead of migrating, as we cannot form the cc->order buddy
1080 unlock_page_lruvec_irqrestore(locked, flags);
1083 putback_movable_pages(&cc->migratepages);
1084 cc->nr_migratepages = 0;
1088 if (low_pfn < next_skip_pfn) {
1089 low_pfn = next_skip_pfn - 1;
1091 * The check near the loop beginning would have updated
1092 * next_skip_pfn too, but this is a bit simpler.
1094 next_skip_pfn += 1UL << cc->order;
1099 * The PageBuddy() check could have potentially brought us outside
1100 * the range to be scanned.
1102 if (unlikely(low_pfn > end_pfn))
1109 unlock_page_lruvec_irqrestore(locked, flags);
1116 * Updated the cached scanner pfn once the pageblock has been scanned
1117 * Pages will either be migrated in which case there is no point
1118 * scanning in the near future or migration failed in which case the
1119 * failure reason may persist. The block is marked for skipping if
1120 * there were no pages isolated in the block or if the block is
1121 * rescanned twice in a row.
1123 if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
1124 if (valid_page && !skip_updated)
1125 set_pageblock_skip(valid_page);
1126 update_cached_migrate(cc, low_pfn);
1129 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1130 nr_scanned, nr_isolated);
1133 cc->total_migrate_scanned += nr_scanned;
1135 count_compact_events(COMPACTISOLATED, nr_isolated);
1141 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1142 * @cc: Compaction control structure.
1143 * @start_pfn: The first PFN to start isolating.
1144 * @end_pfn: The one-past-last PFN.
1146 * Returns zero if isolation fails fatally due to e.g. pending signal.
1147 * Otherwise, function returns one-past-the-last PFN of isolated page
1148 * (which may be greater than end_pfn if end fell in a middle of a THP page).
1151 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1152 unsigned long end_pfn)
1154 unsigned long pfn, block_start_pfn, block_end_pfn;
1156 /* Scan block by block. First and last block may be incomplete */
1158 block_start_pfn = pageblock_start_pfn(pfn);
1159 if (block_start_pfn < cc->zone->zone_start_pfn)
1160 block_start_pfn = cc->zone->zone_start_pfn;
1161 block_end_pfn = pageblock_end_pfn(pfn);
1163 for (; pfn < end_pfn; pfn = block_end_pfn,
1164 block_start_pfn = block_end_pfn,
1165 block_end_pfn += pageblock_nr_pages) {
1167 block_end_pfn = min(block_end_pfn, end_pfn);
1169 if (!pageblock_pfn_to_page(block_start_pfn,
1170 block_end_pfn, cc->zone))
1173 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
1174 ISOLATE_UNEVICTABLE);
1179 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
1186 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
1187 #ifdef CONFIG_COMPACTION
1189 static bool suitable_migration_source(struct compact_control *cc,
1194 if (pageblock_skip_persistent(page))
1197 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1200 block_mt = get_pageblock_migratetype(page);
1202 if (cc->migratetype == MIGRATE_MOVABLE)
1203 return is_migrate_movable(block_mt);
1205 return block_mt == cc->migratetype;
1208 /* Returns true if the page is within a block suitable for migration to */
1209 static bool suitable_migration_target(struct compact_control *cc,
1212 /* If the page is a large free page, then disallow migration */
1213 if (PageBuddy(page)) {
1215 * We are checking page_order without zone->lock taken. But
1216 * the only small danger is that we skip a potentially suitable
1217 * pageblock, so it's not worth to check order for valid range.
1219 if (buddy_order_unsafe(page) >= pageblock_order)
1223 if (cc->ignore_block_suitable)
1226 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1227 if (is_migrate_movable(get_pageblock_migratetype(page)))
1230 /* Otherwise skip the block */
1234 static inline unsigned int
1235 freelist_scan_limit(struct compact_control *cc)
1237 unsigned short shift = BITS_PER_LONG - 1;
1239 return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1243 * Test whether the free scanner has reached the same or lower pageblock than
1244 * the migration scanner, and compaction should thus terminate.
1246 static inline bool compact_scanners_met(struct compact_control *cc)
1248 return (cc->free_pfn >> pageblock_order)
1249 <= (cc->migrate_pfn >> pageblock_order);
1253 * Used when scanning for a suitable migration target which scans freelists
1254 * in reverse. Reorders the list such as the unscanned pages are scanned
1255 * first on the next iteration of the free scanner
1258 move_freelist_head(struct list_head *freelist, struct page *freepage)
1262 if (!list_is_last(freelist, &freepage->lru)) {
1263 list_cut_before(&sublist, freelist, &freepage->lru);
1264 if (!list_empty(&sublist))
1265 list_splice_tail(&sublist, freelist);
1270 * Similar to move_freelist_head except used by the migration scanner
1271 * when scanning forward. It's possible for these list operations to
1272 * move against each other if they search the free list exactly in
1276 move_freelist_tail(struct list_head *freelist, struct page *freepage)
1280 if (!list_is_first(freelist, &freepage->lru)) {
1281 list_cut_position(&sublist, freelist, &freepage->lru);
1282 if (!list_empty(&sublist))
1283 list_splice_tail(&sublist, freelist);
1288 fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
1290 unsigned long start_pfn, end_pfn;
1291 struct page *page = pfn_to_page(pfn);
1293 /* Do not search around if there are enough pages already */
1294 if (cc->nr_freepages >= cc->nr_migratepages)
1297 /* Minimise scanning during async compaction */
1298 if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1301 /* Pageblock boundaries */
1302 start_pfn = pageblock_start_pfn(pfn);
1303 end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)) - 1;
1306 if (start_pfn != pfn) {
1307 isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
1308 if (cc->nr_freepages >= cc->nr_migratepages)
1313 start_pfn = pfn + nr_isolated;
1314 if (start_pfn < end_pfn)
1315 isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
1317 /* Skip this pageblock in the future as it's full or nearly full */
1318 if (cc->nr_freepages < cc->nr_migratepages)
1319 set_pageblock_skip(page);
1322 /* Search orders in round-robin fashion */
1323 static int next_search_order(struct compact_control *cc, int order)
1327 order = cc->order - 1;
1329 /* Search wrapped around? */
1330 if (order == cc->search_order) {
1332 if (cc->search_order < 0)
1333 cc->search_order = cc->order - 1;
1340 static unsigned long
1341 fast_isolate_freepages(struct compact_control *cc)
1343 unsigned int limit = min(1U, freelist_scan_limit(cc) >> 1);
1344 unsigned int nr_scanned = 0;
1345 unsigned long low_pfn, min_pfn, highest = 0;
1346 unsigned long nr_isolated = 0;
1347 unsigned long distance;
1348 struct page *page = NULL;
1349 bool scan_start = false;
1352 /* Full compaction passes in a negative order */
1354 return cc->free_pfn;
1357 * If starting the scan, use a deeper search and use the highest
1358 * PFN found if a suitable one is not found.
1360 if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1361 limit = pageblock_nr_pages >> 1;
1366 * Preferred point is in the top quarter of the scan space but take
1367 * a pfn from the top half if the search is problematic.
1369 distance = (cc->free_pfn - cc->migrate_pfn);
1370 low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1371 min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1373 if (WARN_ON_ONCE(min_pfn > low_pfn))
1377 * Search starts from the last successful isolation order or the next
1378 * order to search after a previous failure
1380 cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1382 for (order = cc->search_order;
1383 !page && order >= 0;
1384 order = next_search_order(cc, order)) {
1385 struct free_area *area = &cc->zone->free_area[order];
1386 struct list_head *freelist;
1387 struct page *freepage;
1388 unsigned long flags;
1389 unsigned int order_scanned = 0;
1390 unsigned long high_pfn = 0;
1395 spin_lock_irqsave(&cc->zone->lock, flags);
1396 freelist = &area->free_list[MIGRATE_MOVABLE];
1397 list_for_each_entry_reverse(freepage, freelist, lru) {
1402 pfn = page_to_pfn(freepage);
1405 highest = pageblock_start_pfn(pfn);
1407 if (pfn >= low_pfn) {
1408 cc->fast_search_fail = 0;
1409 cc->search_order = order;
1414 if (pfn >= min_pfn && pfn > high_pfn) {
1417 /* Shorten the scan if a candidate is found */
1421 if (order_scanned >= limit)
1425 /* Use a minimum pfn if a preferred one was not found */
1426 if (!page && high_pfn) {
1427 page = pfn_to_page(high_pfn);
1429 /* Update freepage for the list reorder below */
1433 /* Reorder to so a future search skips recent pages */
1434 move_freelist_head(freelist, freepage);
1436 /* Isolate the page if available */
1438 if (__isolate_free_page(page, order)) {
1439 set_page_private(page, order);
1440 nr_isolated = 1 << order;
1441 cc->nr_freepages += nr_isolated;
1442 list_add_tail(&page->lru, &cc->freepages);
1443 count_compact_events(COMPACTISOLATED, nr_isolated);
1445 /* If isolation fails, abort the search */
1446 order = cc->search_order + 1;
1451 spin_unlock_irqrestore(&cc->zone->lock, flags);
1454 * Smaller scan on next order so the total scan ig related
1455 * to freelist_scan_limit.
1457 if (order_scanned >= limit)
1458 limit = min(1U, limit >> 1);
1462 cc->fast_search_fail++;
1465 * Use the highest PFN found above min. If one was
1466 * not found, be pessimistic for direct compaction
1467 * and use the min mark.
1470 page = pfn_to_page(highest);
1471 cc->free_pfn = highest;
1473 if (cc->direct_compaction && pfn_valid(min_pfn)) {
1474 page = pageblock_pfn_to_page(min_pfn,
1475 pageblock_end_pfn(min_pfn),
1477 cc->free_pfn = min_pfn;
1483 if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1484 highest -= pageblock_nr_pages;
1485 cc->zone->compact_cached_free_pfn = highest;
1488 cc->total_free_scanned += nr_scanned;
1490 return cc->free_pfn;
1492 low_pfn = page_to_pfn(page);
1493 fast_isolate_around(cc, low_pfn, nr_isolated);
1498 * Based on information in the current compact_control, find blocks
1499 * suitable for isolating free pages from and then isolate them.
1501 static void isolate_freepages(struct compact_control *cc)
1503 struct zone *zone = cc->zone;
1505 unsigned long block_start_pfn; /* start of current pageblock */
1506 unsigned long isolate_start_pfn; /* exact pfn we start at */
1507 unsigned long block_end_pfn; /* end of current pageblock */
1508 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1509 struct list_head *freelist = &cc->freepages;
1510 unsigned int stride;
1512 /* Try a small search of the free lists for a candidate */
1513 isolate_start_pfn = fast_isolate_freepages(cc);
1514 if (cc->nr_freepages)
1518 * Initialise the free scanner. The starting point is where we last
1519 * successfully isolated from, zone-cached value, or the end of the
1520 * zone when isolating for the first time. For looping we also need
1521 * this pfn aligned down to the pageblock boundary, because we do
1522 * block_start_pfn -= pageblock_nr_pages in the for loop.
1523 * For ending point, take care when isolating in last pageblock of a
1524 * zone which ends in the middle of a pageblock.
1525 * The low boundary is the end of the pageblock the migration scanner
1528 isolate_start_pfn = cc->free_pfn;
1529 block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1530 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1531 zone_end_pfn(zone));
1532 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1533 stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1536 * Isolate free pages until enough are available to migrate the
1537 * pages on cc->migratepages. We stop searching if the migrate
1538 * and free page scanners meet or enough free pages are isolated.
1540 for (; block_start_pfn >= low_pfn;
1541 block_end_pfn = block_start_pfn,
1542 block_start_pfn -= pageblock_nr_pages,
1543 isolate_start_pfn = block_start_pfn) {
1544 unsigned long nr_isolated;
1547 * This can iterate a massively long zone without finding any
1548 * suitable migration targets, so periodically check resched.
1550 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1553 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1558 /* Check the block is suitable for migration */
1559 if (!suitable_migration_target(cc, page))
1562 /* If isolation recently failed, do not retry */
1563 if (!isolation_suitable(cc, page))
1566 /* Found a block suitable for isolating free pages from. */
1567 nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1568 block_end_pfn, freelist, stride, false);
1570 /* Update the skip hint if the full pageblock was scanned */
1571 if (isolate_start_pfn == block_end_pfn)
1572 update_pageblock_skip(cc, page, block_start_pfn);
1574 /* Are enough freepages isolated? */
1575 if (cc->nr_freepages >= cc->nr_migratepages) {
1576 if (isolate_start_pfn >= block_end_pfn) {
1578 * Restart at previous pageblock if more
1579 * freepages can be isolated next time.
1582 block_start_pfn - pageblock_nr_pages;
1585 } else if (isolate_start_pfn < block_end_pfn) {
1587 * If isolation failed early, do not continue
1593 /* Adjust stride depending on isolation */
1598 stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1602 * Record where the free scanner will restart next time. Either we
1603 * broke from the loop and set isolate_start_pfn based on the last
1604 * call to isolate_freepages_block(), or we met the migration scanner
1605 * and the loop terminated due to isolate_start_pfn < low_pfn
1607 cc->free_pfn = isolate_start_pfn;
1610 /* __isolate_free_page() does not map the pages */
1611 split_map_pages(freelist);
1615 * This is a migrate-callback that "allocates" freepages by taking pages
1616 * from the isolated freelists in the block we are migrating to.
1618 static struct page *compaction_alloc(struct page *migratepage,
1621 struct compact_control *cc = (struct compact_control *)data;
1622 struct page *freepage;
1624 if (list_empty(&cc->freepages)) {
1625 isolate_freepages(cc);
1627 if (list_empty(&cc->freepages))
1631 freepage = list_entry(cc->freepages.next, struct page, lru);
1632 list_del(&freepage->lru);
1639 * This is a migrate-callback that "frees" freepages back to the isolated
1640 * freelist. All pages on the freelist are from the same zone, so there is no
1641 * special handling needed for NUMA.
1643 static void compaction_free(struct page *page, unsigned long data)
1645 struct compact_control *cc = (struct compact_control *)data;
1647 list_add(&page->lru, &cc->freepages);
1651 /* possible outcome of isolate_migratepages */
1653 ISOLATE_ABORT, /* Abort compaction now */
1654 ISOLATE_NONE, /* No pages isolated, continue scanning */
1655 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1656 } isolate_migrate_t;
1659 * Allow userspace to control policy on scanning the unevictable LRU for
1660 * compactable pages.
1662 #ifdef CONFIG_PREEMPT_RT
1663 int sysctl_compact_unevictable_allowed __read_mostly = 0;
1665 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1669 update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1671 if (cc->fast_start_pfn == ULONG_MAX)
1674 if (!cc->fast_start_pfn)
1675 cc->fast_start_pfn = pfn;
1677 cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1680 static inline unsigned long
1681 reinit_migrate_pfn(struct compact_control *cc)
1683 if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1684 return cc->migrate_pfn;
1686 cc->migrate_pfn = cc->fast_start_pfn;
1687 cc->fast_start_pfn = ULONG_MAX;
1689 return cc->migrate_pfn;
1693 * Briefly search the free lists for a migration source that already has
1694 * some free pages to reduce the number of pages that need migration
1695 * before a pageblock is free.
1697 static unsigned long fast_find_migrateblock(struct compact_control *cc)
1699 unsigned int limit = freelist_scan_limit(cc);
1700 unsigned int nr_scanned = 0;
1701 unsigned long distance;
1702 unsigned long pfn = cc->migrate_pfn;
1703 unsigned long high_pfn;
1706 /* Skip hints are relied on to avoid repeats on the fast search */
1707 if (cc->ignore_skip_hint)
1711 * If the migrate_pfn is not at the start of a zone or the start
1712 * of a pageblock then assume this is a continuation of a previous
1713 * scan restarted due to COMPACT_CLUSTER_MAX.
1715 if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1719 * For smaller orders, just linearly scan as the number of pages
1720 * to migrate should be relatively small and does not necessarily
1721 * justify freeing up a large block for a small allocation.
1723 if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1727 * Only allow kcompactd and direct requests for movable pages to
1728 * quickly clear out a MOVABLE pageblock for allocation. This
1729 * reduces the risk that a large movable pageblock is freed for
1730 * an unmovable/reclaimable small allocation.
1732 if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1736 * When starting the migration scanner, pick any pageblock within the
1737 * first half of the search space. Otherwise try and pick a pageblock
1738 * within the first eighth to reduce the chances that a migration
1739 * target later becomes a source.
1741 distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1742 if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1744 high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1746 for (order = cc->order - 1;
1747 order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit;
1749 struct free_area *area = &cc->zone->free_area[order];
1750 struct list_head *freelist;
1751 unsigned long flags;
1752 struct page *freepage;
1757 spin_lock_irqsave(&cc->zone->lock, flags);
1758 freelist = &area->free_list[MIGRATE_MOVABLE];
1759 list_for_each_entry(freepage, freelist, lru) {
1760 unsigned long free_pfn;
1763 free_pfn = page_to_pfn(freepage);
1764 if (free_pfn < high_pfn) {
1766 * Avoid if skipped recently. Ideally it would
1767 * move to the tail but even safe iteration of
1768 * the list assumes an entry is deleted, not
1771 if (get_pageblock_skip(freepage)) {
1772 if (list_is_last(freelist, &freepage->lru))
1778 /* Reorder to so a future search skips recent pages */
1779 move_freelist_tail(freelist, freepage);
1781 update_fast_start_pfn(cc, free_pfn);
1782 pfn = pageblock_start_pfn(free_pfn);
1783 cc->fast_search_fail = 0;
1784 set_pageblock_skip(freepage);
1788 if (nr_scanned >= limit) {
1789 cc->fast_search_fail++;
1790 move_freelist_tail(freelist, freepage);
1794 spin_unlock_irqrestore(&cc->zone->lock, flags);
1797 cc->total_migrate_scanned += nr_scanned;
1800 * If fast scanning failed then use a cached entry for a page block
1801 * that had free pages as the basis for starting a linear scan.
1803 if (pfn == cc->migrate_pfn)
1804 pfn = reinit_migrate_pfn(cc);
1810 * Isolate all pages that can be migrated from the first suitable block,
1811 * starting at the block pointed to by the migrate scanner pfn within
1814 static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1816 unsigned long block_start_pfn;
1817 unsigned long block_end_pfn;
1818 unsigned long low_pfn;
1820 const isolate_mode_t isolate_mode =
1821 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1822 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1823 bool fast_find_block;
1826 * Start at where we last stopped, or beginning of the zone as
1827 * initialized by compact_zone(). The first failure will use
1828 * the lowest PFN as the starting point for linear scanning.
1830 low_pfn = fast_find_migrateblock(cc);
1831 block_start_pfn = pageblock_start_pfn(low_pfn);
1832 if (block_start_pfn < cc->zone->zone_start_pfn)
1833 block_start_pfn = cc->zone->zone_start_pfn;
1836 * fast_find_migrateblock marks a pageblock skipped so to avoid
1837 * the isolation_suitable check below, check whether the fast
1838 * search was successful.
1840 fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
1842 /* Only scan within a pageblock boundary */
1843 block_end_pfn = pageblock_end_pfn(low_pfn);
1846 * Iterate over whole pageblocks until we find the first suitable.
1847 * Do not cross the free scanner.
1849 for (; block_end_pfn <= cc->free_pfn;
1850 fast_find_block = false,
1851 low_pfn = block_end_pfn,
1852 block_start_pfn = block_end_pfn,
1853 block_end_pfn += pageblock_nr_pages) {
1856 * This can potentially iterate a massively long zone with
1857 * many pageblocks unsuitable, so periodically check if we
1860 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1863 page = pageblock_pfn_to_page(block_start_pfn,
1864 block_end_pfn, cc->zone);
1869 * If isolation recently failed, do not retry. Only check the
1870 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1871 * to be visited multiple times. Assume skip was checked
1872 * before making it "skip" so other compaction instances do
1873 * not scan the same block.
1875 if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
1876 !fast_find_block && !isolation_suitable(cc, page))
1880 * For async compaction, also only scan in MOVABLE blocks
1881 * without huge pages. Async compaction is optimistic to see
1882 * if the minimum amount of work satisfies the allocation.
1883 * The cached PFN is updated as it's possible that all
1884 * remaining blocks between source and target are unsuitable
1885 * and the compaction scanners fail to meet.
1887 if (!suitable_migration_source(cc, page)) {
1888 update_cached_migrate(cc, block_end_pfn);
1892 /* Perform the isolation */
1893 low_pfn = isolate_migratepages_block(cc, low_pfn,
1894 block_end_pfn, isolate_mode);
1897 return ISOLATE_ABORT;
1900 * Either we isolated something and proceed with migration. Or
1901 * we failed and compact_zone should decide if we should
1907 /* Record where migration scanner will be restarted. */
1908 cc->migrate_pfn = low_pfn;
1910 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1914 * order == -1 is expected when compacting via
1915 * /proc/sys/vm/compact_memory
1917 static inline bool is_via_compact_memory(int order)
1922 static bool kswapd_is_running(pg_data_t *pgdat)
1924 return pgdat->kswapd && (pgdat->kswapd->state == TASK_RUNNING);
1928 * A zone's fragmentation score is the external fragmentation wrt to the
1929 * COMPACTION_HPAGE_ORDER scaled by the zone's size. It returns a value
1930 * in the range [0, 100].
1932 * The scaling factor ensures that proactive compaction focuses on larger
1933 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
1934 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
1935 * and thus never exceeds the high threshold for proactive compaction.
1937 static unsigned int fragmentation_score_zone(struct zone *zone)
1939 unsigned long score;
1941 score = zone->present_pages *
1942 extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
1943 return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
1947 * The per-node proactive (background) compaction process is started by its
1948 * corresponding kcompactd thread when the node's fragmentation score
1949 * exceeds the high threshold. The compaction process remains active till
1950 * the node's score falls below the low threshold, or one of the back-off
1951 * conditions is met.
1953 static unsigned int fragmentation_score_node(pg_data_t *pgdat)
1955 unsigned int score = 0;
1958 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1961 zone = &pgdat->node_zones[zoneid];
1962 score += fragmentation_score_zone(zone);
1968 static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
1970 unsigned int wmark_low;
1973 * Cap the low watermak to avoid excessive compaction
1974 * activity in case a user sets the proactivess tunable
1975 * close to 100 (maximum).
1977 wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
1978 return low ? wmark_low : min(wmark_low + 10, 100U);
1981 static bool should_proactive_compact_node(pg_data_t *pgdat)
1985 if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
1988 wmark_high = fragmentation_score_wmark(pgdat, false);
1989 return fragmentation_score_node(pgdat) > wmark_high;
1992 static enum compact_result __compact_finished(struct compact_control *cc)
1995 const int migratetype = cc->migratetype;
1998 /* Compaction run completes if the migrate and free scanner meet */
1999 if (compact_scanners_met(cc)) {
2000 /* Let the next compaction start anew. */
2001 reset_cached_positions(cc->zone);
2004 * Mark that the PG_migrate_skip information should be cleared
2005 * by kswapd when it goes to sleep. kcompactd does not set the
2006 * flag itself as the decision to be clear should be directly
2007 * based on an allocation request.
2009 if (cc->direct_compaction)
2010 cc->zone->compact_blockskip_flush = true;
2013 return COMPACT_COMPLETE;
2015 return COMPACT_PARTIAL_SKIPPED;
2018 if (cc->proactive_compaction) {
2019 int score, wmark_low;
2022 pgdat = cc->zone->zone_pgdat;
2023 if (kswapd_is_running(pgdat))
2024 return COMPACT_PARTIAL_SKIPPED;
2026 score = fragmentation_score_zone(cc->zone);
2027 wmark_low = fragmentation_score_wmark(pgdat, true);
2029 if (score > wmark_low)
2030 ret = COMPACT_CONTINUE;
2032 ret = COMPACT_SUCCESS;
2037 if (is_via_compact_memory(cc->order))
2038 return COMPACT_CONTINUE;
2041 * Always finish scanning a pageblock to reduce the possibility of
2042 * fallbacks in the future. This is particularly important when
2043 * migration source is unmovable/reclaimable but it's not worth
2046 if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
2047 return COMPACT_CONTINUE;
2049 /* Direct compactor: Is a suitable page free? */
2050 ret = COMPACT_NO_SUITABLE_PAGE;
2051 for (order = cc->order; order < MAX_ORDER; order++) {
2052 struct free_area *area = &cc->zone->free_area[order];
2055 /* Job done if page is free of the right migratetype */
2056 if (!free_area_empty(area, migratetype))
2057 return COMPACT_SUCCESS;
2060 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2061 if (migratetype == MIGRATE_MOVABLE &&
2062 !free_area_empty(area, MIGRATE_CMA))
2063 return COMPACT_SUCCESS;
2066 * Job done if allocation would steal freepages from
2067 * other migratetype buddy lists.
2069 if (find_suitable_fallback(area, order, migratetype,
2070 true, &can_steal) != -1) {
2072 /* movable pages are OK in any pageblock */
2073 if (migratetype == MIGRATE_MOVABLE)
2074 return COMPACT_SUCCESS;
2077 * We are stealing for a non-movable allocation. Make
2078 * sure we finish compacting the current pageblock
2079 * first so it is as free as possible and we won't
2080 * have to steal another one soon. This only applies
2081 * to sync compaction, as async compaction operates
2082 * on pageblocks of the same migratetype.
2084 if (cc->mode == MIGRATE_ASYNC ||
2085 IS_ALIGNED(cc->migrate_pfn,
2086 pageblock_nr_pages)) {
2087 return COMPACT_SUCCESS;
2090 ret = COMPACT_CONTINUE;
2096 if (cc->contended || fatal_signal_pending(current))
2097 ret = COMPACT_CONTENDED;
2102 static enum compact_result compact_finished(struct compact_control *cc)
2106 ret = __compact_finished(cc);
2107 trace_mm_compaction_finished(cc->zone, cc->order, ret);
2108 if (ret == COMPACT_NO_SUITABLE_PAGE)
2109 ret = COMPACT_CONTINUE;
2114 static enum compact_result __compaction_suitable(struct zone *zone, int order,
2115 unsigned int alloc_flags,
2116 int highest_zoneidx,
2117 unsigned long wmark_target)
2119 unsigned long watermark;
2121 if (is_via_compact_memory(order))
2122 return COMPACT_CONTINUE;
2124 watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2126 * If watermarks for high-order allocation are already met, there
2127 * should be no need for compaction at all.
2129 if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2131 return COMPACT_SUCCESS;
2134 * Watermarks for order-0 must be met for compaction to be able to
2135 * isolate free pages for migration targets. This means that the
2136 * watermark and alloc_flags have to match, or be more pessimistic than
2137 * the check in __isolate_free_page(). We don't use the direct
2138 * compactor's alloc_flags, as they are not relevant for freepage
2139 * isolation. We however do use the direct compactor's highest_zoneidx
2140 * to skip over zones where lowmem reserves would prevent allocation
2141 * even if compaction succeeds.
2142 * For costly orders, we require low watermark instead of min for
2143 * compaction to proceed to increase its chances.
2144 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2145 * suitable migration targets
2147 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2148 low_wmark_pages(zone) : min_wmark_pages(zone);
2149 watermark += compact_gap(order);
2150 if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2151 ALLOC_CMA, wmark_target))
2152 return COMPACT_SKIPPED;
2154 return COMPACT_CONTINUE;
2158 * compaction_suitable: Is this suitable to run compaction on this zone now?
2160 * COMPACT_SKIPPED - If there are too few free pages for compaction
2161 * COMPACT_SUCCESS - If the allocation would succeed without compaction
2162 * COMPACT_CONTINUE - If compaction should run now
2164 enum compact_result compaction_suitable(struct zone *zone, int order,
2165 unsigned int alloc_flags,
2166 int highest_zoneidx)
2168 enum compact_result ret;
2171 ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
2172 zone_page_state(zone, NR_FREE_PAGES));
2174 * fragmentation index determines if allocation failures are due to
2175 * low memory or external fragmentation
2177 * index of -1000 would imply allocations might succeed depending on
2178 * watermarks, but we already failed the high-order watermark check
2179 * index towards 0 implies failure is due to lack of memory
2180 * index towards 1000 implies failure is due to fragmentation
2182 * Only compact if a failure would be due to fragmentation. Also
2183 * ignore fragindex for non-costly orders where the alternative to
2184 * a successful reclaim/compaction is OOM. Fragindex and the
2185 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2186 * excessive compaction for costly orders, but it should not be at the
2187 * expense of system stability.
2189 if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
2190 fragindex = fragmentation_index(zone, order);
2191 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
2192 ret = COMPACT_NOT_SUITABLE_ZONE;
2195 trace_mm_compaction_suitable(zone, order, ret);
2196 if (ret == COMPACT_NOT_SUITABLE_ZONE)
2197 ret = COMPACT_SKIPPED;
2202 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2209 * Make sure at least one zone would pass __compaction_suitable if we continue
2210 * retrying the reclaim.
2212 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2213 ac->highest_zoneidx, ac->nodemask) {
2214 unsigned long available;
2215 enum compact_result compact_result;
2218 * Do not consider all the reclaimable memory because we do not
2219 * want to trash just for a single high order allocation which
2220 * is even not guaranteed to appear even if __compaction_suitable
2221 * is happy about the watermark check.
2223 available = zone_reclaimable_pages(zone) / order;
2224 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2225 compact_result = __compaction_suitable(zone, order, alloc_flags,
2226 ac->highest_zoneidx, available);
2227 if (compact_result != COMPACT_SKIPPED)
2234 static enum compact_result
2235 compact_zone(struct compact_control *cc, struct capture_control *capc)
2237 enum compact_result ret;
2238 unsigned long start_pfn = cc->zone->zone_start_pfn;
2239 unsigned long end_pfn = zone_end_pfn(cc->zone);
2240 unsigned long last_migrated_pfn;
2241 const bool sync = cc->mode != MIGRATE_ASYNC;
2245 * These counters track activities during zone compaction. Initialize
2246 * them before compacting a new zone.
2248 cc->total_migrate_scanned = 0;
2249 cc->total_free_scanned = 0;
2250 cc->nr_migratepages = 0;
2251 cc->nr_freepages = 0;
2252 INIT_LIST_HEAD(&cc->freepages);
2253 INIT_LIST_HEAD(&cc->migratepages);
2255 cc->migratetype = gfp_migratetype(cc->gfp_mask);
2256 ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
2257 cc->highest_zoneidx);
2258 /* Compaction is likely to fail */
2259 if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
2262 /* huh, compaction_suitable is returning something unexpected */
2263 VM_BUG_ON(ret != COMPACT_CONTINUE);
2266 * Clear pageblock skip if there were failures recently and compaction
2267 * is about to be retried after being deferred.
2269 if (compaction_restarting(cc->zone, cc->order))
2270 __reset_isolation_suitable(cc->zone);
2273 * Setup to move all movable pages to the end of the zone. Used cached
2274 * information on where the scanners should start (unless we explicitly
2275 * want to compact the whole zone), but check that it is initialised
2276 * by ensuring the values are within zone boundaries.
2278 cc->fast_start_pfn = 0;
2279 if (cc->whole_zone) {
2280 cc->migrate_pfn = start_pfn;
2281 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2283 cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2284 cc->free_pfn = cc->zone->compact_cached_free_pfn;
2285 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2286 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2287 cc->zone->compact_cached_free_pfn = cc->free_pfn;
2289 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2290 cc->migrate_pfn = start_pfn;
2291 cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2292 cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2295 if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2296 cc->whole_zone = true;
2299 last_migrated_pfn = 0;
2302 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2303 * the basis that some migrations will fail in ASYNC mode. However,
2304 * if the cached PFNs match and pageblocks are skipped due to having
2305 * no isolation candidates, then the sync state does not matter.
2306 * Until a pageblock with isolation candidates is found, keep the
2307 * cached PFNs in sync to avoid revisiting the same blocks.
2309 update_cached = !sync &&
2310 cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2312 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
2313 cc->free_pfn, end_pfn, sync);
2315 migrate_prep_local();
2317 while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2319 unsigned long iteration_start_pfn = cc->migrate_pfn;
2322 * Avoid multiple rescans which can happen if a page cannot be
2323 * isolated (dirty/writeback in async mode) or if the migrated
2324 * pages are being allocated before the pageblock is cleared.
2325 * The first rescan will capture the entire pageblock for
2326 * migration. If it fails, it'll be marked skip and scanning
2327 * will proceed as normal.
2330 if (pageblock_start_pfn(last_migrated_pfn) ==
2331 pageblock_start_pfn(iteration_start_pfn)) {
2335 switch (isolate_migratepages(cc)) {
2337 ret = COMPACT_CONTENDED;
2338 putback_movable_pages(&cc->migratepages);
2339 cc->nr_migratepages = 0;
2342 if (update_cached) {
2343 cc->zone->compact_cached_migrate_pfn[1] =
2344 cc->zone->compact_cached_migrate_pfn[0];
2348 * We haven't isolated and migrated anything, but
2349 * there might still be unflushed migrations from
2350 * previous cc->order aligned block.
2353 case ISOLATE_SUCCESS:
2354 update_cached = false;
2355 last_migrated_pfn = iteration_start_pfn;
2358 err = migrate_pages(&cc->migratepages, compaction_alloc,
2359 compaction_free, (unsigned long)cc, cc->mode,
2362 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
2365 /* All pages were either migrated or will be released */
2366 cc->nr_migratepages = 0;
2368 putback_movable_pages(&cc->migratepages);
2370 * migrate_pages() may return -ENOMEM when scanners meet
2371 * and we want compact_finished() to detect it
2373 if (err == -ENOMEM && !compact_scanners_met(cc)) {
2374 ret = COMPACT_CONTENDED;
2378 * We failed to migrate at least one page in the current
2379 * order-aligned block, so skip the rest of it.
2381 if (cc->direct_compaction &&
2382 (cc->mode == MIGRATE_ASYNC)) {
2383 cc->migrate_pfn = block_end_pfn(
2384 cc->migrate_pfn - 1, cc->order);
2385 /* Draining pcplists is useless in this case */
2386 last_migrated_pfn = 0;
2392 * Has the migration scanner moved away from the previous
2393 * cc->order aligned block where we migrated from? If yes,
2394 * flush the pages that were freed, so that they can merge and
2395 * compact_finished() can detect immediately if allocation
2398 if (cc->order > 0 && last_migrated_pfn) {
2399 unsigned long current_block_start =
2400 block_start_pfn(cc->migrate_pfn, cc->order);
2402 if (last_migrated_pfn < current_block_start) {
2403 lru_add_drain_cpu_zone(cc->zone);
2404 /* No more flushing until we migrate again */
2405 last_migrated_pfn = 0;
2409 /* Stop if a page has been captured */
2410 if (capc && capc->page) {
2411 ret = COMPACT_SUCCESS;
2418 * Release free pages and update where the free scanner should restart,
2419 * so we don't leave any returned pages behind in the next attempt.
2421 if (cc->nr_freepages > 0) {
2422 unsigned long free_pfn = release_freepages(&cc->freepages);
2424 cc->nr_freepages = 0;
2425 VM_BUG_ON(free_pfn == 0);
2426 /* The cached pfn is always the first in a pageblock */
2427 free_pfn = pageblock_start_pfn(free_pfn);
2429 * Only go back, not forward. The cached pfn might have been
2430 * already reset to zone end in compact_finished()
2432 if (free_pfn > cc->zone->compact_cached_free_pfn)
2433 cc->zone->compact_cached_free_pfn = free_pfn;
2436 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2437 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2439 trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
2440 cc->free_pfn, end_pfn, sync, ret);
2445 static enum compact_result compact_zone_order(struct zone *zone, int order,
2446 gfp_t gfp_mask, enum compact_priority prio,
2447 unsigned int alloc_flags, int highest_zoneidx,
2448 struct page **capture)
2450 enum compact_result ret;
2451 struct compact_control cc = {
2453 .search_order = order,
2454 .gfp_mask = gfp_mask,
2456 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2457 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2458 .alloc_flags = alloc_flags,
2459 .highest_zoneidx = highest_zoneidx,
2460 .direct_compaction = true,
2461 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2462 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2463 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2465 struct capture_control capc = {
2471 * Make sure the structs are really initialized before we expose the
2472 * capture control, in case we are interrupted and the interrupt handler
2476 WRITE_ONCE(current->capture_control, &capc);
2478 ret = compact_zone(&cc, &capc);
2480 VM_BUG_ON(!list_empty(&cc.freepages));
2481 VM_BUG_ON(!list_empty(&cc.migratepages));
2484 * Make sure we hide capture control first before we read the captured
2485 * page pointer, otherwise an interrupt could free and capture a page
2486 * and we would leak it.
2488 WRITE_ONCE(current->capture_control, NULL);
2489 *capture = READ_ONCE(capc.page);
2494 int sysctl_extfrag_threshold = 500;
2497 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2498 * @gfp_mask: The GFP mask of the current allocation
2499 * @order: The order of the current allocation
2500 * @alloc_flags: The allocation flags of the current allocation
2501 * @ac: The context of current allocation
2502 * @prio: Determines how hard direct compaction should try to succeed
2503 * @capture: Pointer to free page created by compaction will be stored here
2505 * This is the main entry point for direct page compaction.
2507 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2508 unsigned int alloc_flags, const struct alloc_context *ac,
2509 enum compact_priority prio, struct page **capture)
2511 int may_perform_io = gfp_mask & __GFP_IO;
2514 enum compact_result rc = COMPACT_SKIPPED;
2517 * Check if the GFP flags allow compaction - GFP_NOIO is really
2518 * tricky context because the migration might require IO
2520 if (!may_perform_io)
2521 return COMPACT_SKIPPED;
2523 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2525 /* Compact each zone in the list */
2526 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2527 ac->highest_zoneidx, ac->nodemask) {
2528 enum compact_result status;
2530 if (prio > MIN_COMPACT_PRIORITY
2531 && compaction_deferred(zone, order)) {
2532 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2536 status = compact_zone_order(zone, order, gfp_mask, prio,
2537 alloc_flags, ac->highest_zoneidx, capture);
2538 rc = max(status, rc);
2540 /* The allocation should succeed, stop compacting */
2541 if (status == COMPACT_SUCCESS) {
2543 * We think the allocation will succeed in this zone,
2544 * but it is not certain, hence the false. The caller
2545 * will repeat this with true if allocation indeed
2546 * succeeds in this zone.
2548 compaction_defer_reset(zone, order, false);
2553 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2554 status == COMPACT_PARTIAL_SKIPPED))
2556 * We think that allocation won't succeed in this zone
2557 * so we defer compaction there. If it ends up
2558 * succeeding after all, it will be reset.
2560 defer_compaction(zone, order);
2563 * We might have stopped compacting due to need_resched() in
2564 * async compaction, or due to a fatal signal detected. In that
2565 * case do not try further zones
2567 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2568 || fatal_signal_pending(current))
2576 * Compact all zones within a node till each zone's fragmentation score
2577 * reaches within proactive compaction thresholds (as determined by the
2578 * proactiveness tunable).
2580 * It is possible that the function returns before reaching score targets
2581 * due to various back-off conditions, such as, contention on per-node or
2584 static void proactive_compact_node(pg_data_t *pgdat)
2588 struct compact_control cc = {
2590 .mode = MIGRATE_SYNC_LIGHT,
2591 .ignore_skip_hint = true,
2593 .gfp_mask = GFP_KERNEL,
2594 .proactive_compaction = true,
2597 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2598 zone = &pgdat->node_zones[zoneid];
2599 if (!populated_zone(zone))
2604 compact_zone(&cc, NULL);
2606 VM_BUG_ON(!list_empty(&cc.freepages));
2607 VM_BUG_ON(!list_empty(&cc.migratepages));
2611 /* Compact all zones within a node */
2612 static void compact_node(int nid)
2614 pg_data_t *pgdat = NODE_DATA(nid);
2617 struct compact_control cc = {
2619 .mode = MIGRATE_SYNC,
2620 .ignore_skip_hint = true,
2622 .gfp_mask = GFP_KERNEL,
2626 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2628 zone = &pgdat->node_zones[zoneid];
2629 if (!populated_zone(zone))
2634 compact_zone(&cc, NULL);
2636 VM_BUG_ON(!list_empty(&cc.freepages));
2637 VM_BUG_ON(!list_empty(&cc.migratepages));
2641 /* Compact all nodes in the system */
2642 static void compact_nodes(void)
2646 /* Flush pending updates to the LRU lists */
2647 lru_add_drain_all();
2649 for_each_online_node(nid)
2653 /* The written value is actually unused, all memory is compacted */
2654 int sysctl_compact_memory;
2657 * Tunable for proactive compaction. It determines how
2658 * aggressively the kernel should compact memory in the
2659 * background. It takes values in the range [0, 100].
2661 unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
2664 * This is the entry point for compacting all nodes via
2665 * /proc/sys/vm/compact_memory
2667 int sysctl_compaction_handler(struct ctl_table *table, int write,
2668 void *buffer, size_t *length, loff_t *ppos)
2676 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2677 static ssize_t sysfs_compact_node(struct device *dev,
2678 struct device_attribute *attr,
2679 const char *buf, size_t count)
2683 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2684 /* Flush pending updates to the LRU lists */
2685 lru_add_drain_all();
2692 static DEVICE_ATTR(compact, 0200, NULL, sysfs_compact_node);
2694 int compaction_register_node(struct node *node)
2696 return device_create_file(&node->dev, &dev_attr_compact);
2699 void compaction_unregister_node(struct node *node)
2701 return device_remove_file(&node->dev, &dev_attr_compact);
2703 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
2705 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2707 return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
2710 static bool kcompactd_node_suitable(pg_data_t *pgdat)
2714 enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
2716 for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
2717 zone = &pgdat->node_zones[zoneid];
2719 if (!populated_zone(zone))
2722 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
2723 highest_zoneidx) == COMPACT_CONTINUE)
2730 static void kcompactd_do_work(pg_data_t *pgdat)
2733 * With no special task, compact all zones so that a page of requested
2734 * order is allocatable.
2738 struct compact_control cc = {
2739 .order = pgdat->kcompactd_max_order,
2740 .search_order = pgdat->kcompactd_max_order,
2741 .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
2742 .mode = MIGRATE_SYNC_LIGHT,
2743 .ignore_skip_hint = false,
2744 .gfp_mask = GFP_KERNEL,
2746 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2747 cc.highest_zoneidx);
2748 count_compact_event(KCOMPACTD_WAKE);
2750 for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
2753 zone = &pgdat->node_zones[zoneid];
2754 if (!populated_zone(zone))
2757 if (compaction_deferred(zone, cc.order))
2760 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
2764 if (kthread_should_stop())
2768 status = compact_zone(&cc, NULL);
2770 if (status == COMPACT_SUCCESS) {
2771 compaction_defer_reset(zone, cc.order, false);
2772 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2774 * Buddy pages may become stranded on pcps that could
2775 * otherwise coalesce on the zone's free area for
2776 * order >= cc.order. This is ratelimited by the
2777 * upcoming deferral.
2779 drain_all_pages(zone);
2782 * We use sync migration mode here, so we defer like
2783 * sync direct compaction does.
2785 defer_compaction(zone, cc.order);
2788 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2789 cc.total_migrate_scanned);
2790 count_compact_events(KCOMPACTD_FREE_SCANNED,
2791 cc.total_free_scanned);
2793 VM_BUG_ON(!list_empty(&cc.freepages));
2794 VM_BUG_ON(!list_empty(&cc.migratepages));
2798 * Regardless of success, we are done until woken up next. But remember
2799 * the requested order/highest_zoneidx in case it was higher/tighter
2800 * than our current ones
2802 if (pgdat->kcompactd_max_order <= cc.order)
2803 pgdat->kcompactd_max_order = 0;
2804 if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
2805 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2808 void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
2813 if (pgdat->kcompactd_max_order < order)
2814 pgdat->kcompactd_max_order = order;
2816 if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
2817 pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
2820 * Pairs with implicit barrier in wait_event_freezable()
2821 * such that wakeups are not missed.
2823 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2826 if (!kcompactd_node_suitable(pgdat))
2829 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2831 wake_up_interruptible(&pgdat->kcompactd_wait);
2835 * The background compaction daemon, started as a kernel thread
2836 * from the init process.
2838 static int kcompactd(void *p)
2840 pg_data_t *pgdat = (pg_data_t*)p;
2841 struct task_struct *tsk = current;
2842 unsigned int proactive_defer = 0;
2844 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2846 if (!cpumask_empty(cpumask))
2847 set_cpus_allowed_ptr(tsk, cpumask);
2851 pgdat->kcompactd_max_order = 0;
2852 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2854 while (!kthread_should_stop()) {
2855 unsigned long pflags;
2857 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2858 if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
2859 kcompactd_work_requested(pgdat),
2860 msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
2862 psi_memstall_enter(&pflags);
2863 kcompactd_do_work(pgdat);
2864 psi_memstall_leave(&pflags);
2868 /* kcompactd wait timeout */
2869 if (should_proactive_compact_node(pgdat)) {
2870 unsigned int prev_score, score;
2872 if (proactive_defer) {
2876 prev_score = fragmentation_score_node(pgdat);
2877 proactive_compact_node(pgdat);
2878 score = fragmentation_score_node(pgdat);
2880 * Defer proactive compaction if the fragmentation
2881 * score did not go down i.e. no progress made.
2883 proactive_defer = score < prev_score ?
2884 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
2892 * This kcompactd start function will be called by init and node-hot-add.
2893 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2895 int kcompactd_run(int nid)
2897 pg_data_t *pgdat = NODE_DATA(nid);
2900 if (pgdat->kcompactd)
2903 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2904 if (IS_ERR(pgdat->kcompactd)) {
2905 pr_err("Failed to start kcompactd on node %d\n", nid);
2906 ret = PTR_ERR(pgdat->kcompactd);
2907 pgdat->kcompactd = NULL;
2913 * Called by memory hotplug when all memory in a node is offlined. Caller must
2914 * hold mem_hotplug_begin/end().
2916 void kcompactd_stop(int nid)
2918 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2921 kthread_stop(kcompactd);
2922 NODE_DATA(nid)->kcompactd = NULL;
2927 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2928 * not required for correctness. So if the last cpu in a node goes
2929 * away, we get changed to run anywhere: as the first one comes back,
2930 * restore their cpu bindings.
2932 static int kcompactd_cpu_online(unsigned int cpu)
2936 for_each_node_state(nid, N_MEMORY) {
2937 pg_data_t *pgdat = NODE_DATA(nid);
2938 const struct cpumask *mask;
2940 mask = cpumask_of_node(pgdat->node_id);
2942 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2943 /* One of our CPUs online: restore mask */
2944 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2949 static int __init kcompactd_init(void)
2954 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2955 "mm/compaction:online",
2956 kcompactd_cpu_online, NULL);
2958 pr_err("kcompactd: failed to register hotplug callbacks.\n");
2962 for_each_node_state(nid, N_MEMORY)
2966 subsys_initcall(kcompactd_init)
2968 #endif /* CONFIG_COMPACTION */