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(!PageMovable(page), page);
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.
146 page->mapping = (void *)((unsigned long)page->mapping &
147 PAGE_MAPPING_MOVABLE);
149 EXPORT_SYMBOL(__ClearPageMovable);
151 /* Do not skip compaction more than 64 times */
152 #define COMPACT_MAX_DEFER_SHIFT 6
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
159 static void defer_compaction(struct zone *zone, int order)
161 zone->compact_considered = 0;
162 zone->compact_defer_shift++;
164 if (order < zone->compact_order_failed)
165 zone->compact_order_failed = order;
167 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
168 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
170 trace_mm_compaction_defer_compaction(zone, order);
173 /* Returns true if compaction should be skipped this time */
174 static bool compaction_deferred(struct zone *zone, int order)
176 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
178 if (order < zone->compact_order_failed)
181 /* Avoid possible overflow */
182 if (++zone->compact_considered >= defer_limit) {
183 zone->compact_considered = defer_limit;
187 trace_mm_compaction_deferred(zone, order);
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.
197 void compaction_defer_reset(struct zone *zone, int order,
201 zone->compact_considered = 0;
202 zone->compact_defer_shift = 0;
204 if (order >= zone->compact_order_failed)
205 zone->compact_order_failed = order + 1;
207 trace_mm_compaction_defer_reset(zone, order);
210 /* Returns true if restarting compaction after many failures */
211 static bool compaction_restarting(struct zone *zone, int order)
213 if (order < zone->compact_order_failed)
216 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
217 zone->compact_considered >= 1UL << zone->compact_defer_shift;
220 /* Returns true if the pageblock should be scanned for pages to isolate. */
221 static inline bool isolation_suitable(struct compact_control *cc,
224 if (cc->ignore_skip_hint)
227 return !get_pageblock_skip(page);
230 static void reset_cached_positions(struct zone *zone)
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);
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.
243 static bool pageblock_skip_persistent(struct page *page)
245 if (!PageCompound(page))
248 page = compound_head(page);
250 if (compound_order(page) >= pageblock_order)
257 __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
260 struct page *page = pfn_to_online_page(pfn);
261 struct page *block_page;
262 struct page *end_page;
263 unsigned long block_pfn;
267 if (zone != page_zone(page))
269 if (pageblock_skip_persistent(page))
273 * If skip is already cleared do no further checking once the
274 * restart points have been set.
276 if (check_source && check_target && !get_pageblock_skip(page))
280 * If clearing skip for the target scanner, do not select a
281 * non-movable pageblock as the starting point.
283 if (!check_source && check_target &&
284 get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
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);
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);
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.
309 if (pfn_valid_within(pfn)) {
310 if (check_source && PageLRU(page)) {
311 clear_pageblock_skip(page);
315 if (check_target && PageBuddy(page)) {
316 clear_pageblock_skip(page);
321 page += (1 << PAGE_ALLOC_COSTLY_ORDER);
322 pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
323 } while (page <= end_page);
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
333 static void __reset_isolation_suitable(struct zone *zone)
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;
342 if (!zone->compact_blockskip_flush)
345 zone->compact_blockskip_flush = false;
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.
353 for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
354 free_pfn -= pageblock_nr_pages) {
357 /* Update the migrate PFN */
358 if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
359 migrate_pfn < reset_migrate) {
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;
367 /* Update the free PFN */
368 if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
369 free_pfn > reset_free) {
371 reset_free = free_pfn;
372 zone->compact_init_free_pfn = reset_free;
373 zone->compact_cached_free_pfn = reset_free;
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;
385 void reset_isolation_suitable(pg_data_t *pgdat)
389 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
390 struct zone *zone = &pgdat->node_zones[zoneid];
391 if (!populated_zone(zone))
394 /* Only flush if a full compaction finished recently */
395 if (zone->compact_blockskip_flush)
396 __reset_isolation_suitable(zone);
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.
404 static bool test_and_set_skip(struct compact_control *cc, struct page *page,
409 /* Do no update if skip hint is being ignored */
410 if (cc->ignore_skip_hint)
413 if (!IS_ALIGNED(pfn, pageblock_nr_pages))
416 skip = get_pageblock_skip(page);
417 if (!skip && !cc->no_set_skip_hint)
418 set_pageblock_skip(page);
423 static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
425 struct zone *zone = cc->zone;
427 pfn = pageblock_end_pfn(pfn);
429 /* Set for isolation rather than compaction */
430 if (cc->no_set_skip_hint)
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;
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().
444 static void update_pageblock_skip(struct compact_control *cc,
445 struct page *page, unsigned long pfn)
447 struct zone *zone = cc->zone;
449 if (cc->no_set_skip_hint)
455 set_pageblock_skip(page);
457 /* Update where async and sync compaction should restart */
458 if (pfn < zone->compact_cached_free_pfn)
459 zone->compact_cached_free_pfn = pfn;
462 static inline bool isolation_suitable(struct compact_control *cc,
468 static inline bool pageblock_skip_persistent(struct page *page)
473 static inline void update_pageblock_skip(struct compact_control *cc,
474 struct page *page, unsigned long pfn)
478 static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
482 static bool test_and_set_skip(struct compact_control *cc, struct page *page,
487 #endif /* CONFIG_COMPACTION */
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.
496 * Always returns true which makes it easier to track lock state in callers.
498 static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
499 struct compact_control *cc)
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))
507 cc->contended = true;
510 spin_lock_irqsave(lock, *flags);
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.
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
529 static bool compact_unlock_should_abort(spinlock_t *lock,
530 unsigned long flags, bool *locked, struct compact_control *cc)
533 spin_unlock_irqrestore(lock, flags);
537 if (fatal_signal_pending(current)) {
538 cc->contended = true;
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).
552 static unsigned long isolate_freepages_block(struct compact_control *cc,
553 unsigned long *start_pfn,
554 unsigned long end_pfn,
555 struct list_head *freelist,
559 int nr_scanned = 0, total_isolated = 0;
561 unsigned long flags = 0;
563 unsigned long blockpfn = *start_pfn;
566 /* Strict mode is for isolation, speed is secondary */
570 cursor = pfn_to_page(blockpfn);
572 /* Isolate free pages. */
573 for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
575 struct page *page = cursor;
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()
582 if (!(blockpfn % SWAP_CLUSTER_MAX)
583 && compact_unlock_should_abort(&cc->zone->lock, flags,
588 if (!pfn_valid_within(blockpfn))
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.
597 if (PageCompound(page)) {
598 const unsigned int order = compound_order(page);
600 if (likely(order < MAX_ORDER)) {
601 blockpfn += (1UL << order) - 1;
602 cursor += (1UL << order) - 1;
607 if (!PageBuddy(page))
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
618 locked = compact_lock_irqsave(&cc->zone->lock,
621 /* Recheck this is a buddy page under lock */
622 if (!PageBuddy(page))
626 /* Found a free page, will break it into order-0 pages */
627 order = buddy_order(page);
628 isolated = __isolate_free_page(page, order);
631 set_page_private(page, order);
633 total_isolated += isolated;
634 cc->nr_freepages += isolated;
635 list_add_tail(&page->lru, freelist);
637 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
638 blockpfn += isolated;
641 /* Advance to the end of split page */
642 blockpfn += isolated - 1;
643 cursor += isolated - 1;
655 spin_unlock_irqrestore(&cc->zone->lock, flags);
658 * There is a tiny chance that we have read bogus compound_order(),
659 * so be careful to not go outside of the pageblock.
661 if (unlikely(blockpfn > end_pfn))
664 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
665 nr_scanned, total_isolated);
667 /* Record how far we have got within the block */
668 *start_pfn = blockpfn;
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.
675 if (strict && blockpfn < end_pfn)
678 cc->total_free_scanned += nr_scanned;
680 count_compact_events(COMPACTISOLATED, total_isolated);
681 return total_isolated;
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.
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.
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
699 isolate_freepages_range(struct compact_control *cc,
700 unsigned long start_pfn, unsigned long end_pfn)
702 unsigned long isolated, pfn, block_start_pfn, block_end_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);
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;
717 block_end_pfn = min(block_end_pfn, end_pfn);
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.
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);
730 if (!pageblock_pfn_to_page(block_start_pfn,
731 block_end_pfn, cc->zone))
734 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
735 block_end_pfn, &freelist, 0, true);
738 * In strict mode, isolate_freepages_block() returns 0 if
739 * there are any holes in the block (ie. invalid PFNs or
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).
752 /* __isolate_free_page() does not map the pages */
753 split_map_pages(&freelist);
756 /* Loop terminated early, cleanup. */
757 release_freepages(&freelist);
761 /* We don't use freelists for anything. */
765 /* Similar to reclaim, but different enough that they don't share logic */
766 static bool too_many_isolated(pg_data_t *pgdat)
768 unsigned long active, inactive, isolated;
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);
777 return isolated > (inactive + active) / 2;
781 * isolate_migratepages_block() - isolate all migrate-able pages within
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.
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 zero if there is a fatal signal pending, otherwise PFN of the
791 * first page that was not scanned (which may be both less, equal to or more
794 * The pages are isolated on cc->migratepages list (not required to be empty),
795 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
796 * is neither read nor updated.
799 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
800 unsigned long end_pfn, isolate_mode_t isolate_mode)
802 pg_data_t *pgdat = cc->zone->zone_pgdat;
803 unsigned long nr_scanned = 0, nr_isolated = 0;
804 struct lruvec *lruvec;
805 unsigned long flags = 0;
806 struct lruvec *locked = NULL;
807 struct page *page = NULL, *valid_page = NULL;
808 unsigned long start_pfn = low_pfn;
809 bool skip_on_failure = false;
810 unsigned long next_skip_pfn = 0;
811 bool skip_updated = false;
814 * Ensure that there are not too many pages isolated from the LRU
815 * list by either parallel reclaimers or compaction. If there are,
816 * delay for some time until fewer pages are isolated
818 while (unlikely(too_many_isolated(pgdat))) {
819 /* stop isolation if there are still pages not migrated */
820 if (cc->nr_migratepages)
823 /* async migration should just abort */
824 if (cc->mode == MIGRATE_ASYNC)
827 congestion_wait(BLK_RW_ASYNC, HZ/10);
829 if (fatal_signal_pending(current))
835 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
836 skip_on_failure = true;
837 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
840 /* Time to isolate some pages for migration */
841 for (; low_pfn < end_pfn; low_pfn++) {
843 if (skip_on_failure && low_pfn >= next_skip_pfn) {
845 * We have isolated all migration candidates in the
846 * previous order-aligned block, and did not skip it due
847 * to failure. We should migrate the pages now and
848 * hopefully succeed compaction.
854 * We failed to isolate in the previous order-aligned
855 * block. Set the new boundary to the end of the
856 * current block. Note we can't simply increase
857 * next_skip_pfn by 1 << order, as low_pfn might have
858 * been incremented by a higher number due to skipping
859 * a compound or a high-order buddy page in the
860 * previous loop iteration.
862 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
866 * Periodically drop the lock (if held) regardless of its
867 * contention, to give chance to IRQs. Abort completely if
868 * a fatal signal is pending.
870 if (!(low_pfn % SWAP_CLUSTER_MAX)) {
872 unlock_page_lruvec_irqrestore(locked, flags);
876 if (fatal_signal_pending(current)) {
877 cc->contended = true;
886 if (!pfn_valid_within(low_pfn))
890 page = pfn_to_page(low_pfn);
893 * Check if the pageblock has already been marked skipped.
894 * Only the aligned PFN is checked as the caller isolates
895 * COMPACT_CLUSTER_MAX at a time so the second call must
896 * not falsely conclude that the block should be skipped.
898 if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
899 if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
908 * Skip if free. We read page order here without zone lock
909 * which is generally unsafe, but the race window is small and
910 * the worst thing that can happen is that we skip some
911 * potential isolation targets.
913 if (PageBuddy(page)) {
914 unsigned long freepage_order = buddy_order_unsafe(page);
917 * Without lock, we cannot be sure that what we got is
918 * a valid page order. Consider only values in the
919 * valid order range to prevent low_pfn overflow.
921 if (freepage_order > 0 && freepage_order < MAX_ORDER)
922 low_pfn += (1UL << freepage_order) - 1;
927 * Regardless of being on LRU, compound pages such as THP and
928 * hugetlbfs are not to be compacted unless we are attempting
929 * an allocation much larger than the huge page size (eg CMA).
930 * We can potentially save a lot of iterations if we skip them
931 * at once. The check is racy, but we can consider only valid
932 * values and the only danger is skipping too much.
934 if (PageCompound(page) && !cc->alloc_contig) {
935 const unsigned int order = compound_order(page);
937 if (likely(order < MAX_ORDER))
938 low_pfn += (1UL << order) - 1;
943 * Check may be lockless but that's ok as we recheck later.
944 * It's possible to migrate LRU and non-lru movable pages.
945 * Skip any other type of page
947 if (!PageLRU(page)) {
949 * __PageMovable can return false positive so we need
950 * to verify it under page_lock.
952 if (unlikely(__PageMovable(page)) &&
953 !PageIsolated(page)) {
955 unlock_page_lruvec_irqrestore(locked, flags);
959 if (!isolate_movable_page(page, isolate_mode))
960 goto isolate_success;
967 * Migration will fail if an anonymous page is pinned in memory,
968 * so avoid taking lru_lock and isolating it unnecessarily in an
969 * admittedly racy check.
971 if (!page_mapping(page) &&
972 page_count(page) > page_mapcount(page))
976 * Only allow to migrate anonymous pages in GFP_NOFS context
977 * because those do not depend on fs locks.
979 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
983 * Be careful not to clear PageLRU until after we're
984 * sure the page is not being freed elsewhere -- the
985 * page release code relies on it.
987 if (unlikely(!get_page_unless_zero(page)))
990 if (!__isolate_lru_page_prepare(page, isolate_mode))
991 goto isolate_fail_put;
993 /* Try isolate the page */
994 if (!TestClearPageLRU(page))
995 goto isolate_fail_put;
997 lruvec = mem_cgroup_page_lruvec(page, pgdat);
999 /* If we already hold the lock, we can skip some rechecking */
1000 if (lruvec != locked) {
1002 unlock_page_lruvec_irqrestore(locked, flags);
1004 compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
1007 lruvec_memcg_debug(lruvec, page);
1009 /* Try get exclusive access under lock */
1010 if (!skip_updated) {
1011 skip_updated = true;
1012 if (test_and_set_skip(cc, page, low_pfn))
1017 * Page become compound since the non-locked check,
1018 * and it's on LRU. It can only be a THP so the order
1019 * is safe to read and it's 0 for tail pages.
1021 if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
1022 low_pfn += compound_nr(page) - 1;
1024 goto isolate_fail_put;
1028 /* The whole page is taken off the LRU; skip the tail pages. */
1029 if (PageCompound(page))
1030 low_pfn += compound_nr(page) - 1;
1032 /* Successfully isolated */
1033 del_page_from_lru_list(page, lruvec);
1034 mod_node_page_state(page_pgdat(page),
1035 NR_ISOLATED_ANON + page_is_file_lru(page),
1036 thp_nr_pages(page));
1039 list_add(&page->lru, &cc->migratepages);
1040 cc->nr_migratepages += compound_nr(page);
1041 nr_isolated += compound_nr(page);
1044 * Avoid isolating too much unless this block is being
1045 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1046 * or a lock is contended. For contention, isolate quickly to
1047 * potentially remove one source of contention.
1049 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
1050 !cc->rescan && !cc->contended) {
1058 /* Avoid potential deadlock in freeing page under lru_lock */
1060 unlock_page_lruvec_irqrestore(locked, flags);
1066 if (!skip_on_failure)
1070 * We have isolated some pages, but then failed. Release them
1071 * instead of migrating, as we cannot form the cc->order buddy
1076 unlock_page_lruvec_irqrestore(locked, flags);
1079 putback_movable_pages(&cc->migratepages);
1080 cc->nr_migratepages = 0;
1084 if (low_pfn < next_skip_pfn) {
1085 low_pfn = next_skip_pfn - 1;
1087 * The check near the loop beginning would have updated
1088 * next_skip_pfn too, but this is a bit simpler.
1090 next_skip_pfn += 1UL << cc->order;
1095 * The PageBuddy() check could have potentially brought us outside
1096 * the range to be scanned.
1098 if (unlikely(low_pfn > end_pfn))
1105 unlock_page_lruvec_irqrestore(locked, flags);
1112 * Updated the cached scanner pfn once the pageblock has been scanned
1113 * Pages will either be migrated in which case there is no point
1114 * scanning in the near future or migration failed in which case the
1115 * failure reason may persist. The block is marked for skipping if
1116 * there were no pages isolated in the block or if the block is
1117 * rescanned twice in a row.
1119 if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
1120 if (valid_page && !skip_updated)
1121 set_pageblock_skip(valid_page);
1122 update_cached_migrate(cc, low_pfn);
1125 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1126 nr_scanned, nr_isolated);
1129 cc->total_migrate_scanned += nr_scanned;
1131 count_compact_events(COMPACTISOLATED, nr_isolated);
1137 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1138 * @cc: Compaction control structure.
1139 * @start_pfn: The first PFN to start isolating.
1140 * @end_pfn: The one-past-last PFN.
1142 * Returns zero if isolation fails fatally due to e.g. pending signal.
1143 * Otherwise, function returns one-past-the-last PFN of isolated page
1144 * (which may be greater than end_pfn if end fell in a middle of a THP page).
1147 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1148 unsigned long end_pfn)
1150 unsigned long pfn, block_start_pfn, block_end_pfn;
1152 /* Scan block by block. First and last block may be incomplete */
1154 block_start_pfn = pageblock_start_pfn(pfn);
1155 if (block_start_pfn < cc->zone->zone_start_pfn)
1156 block_start_pfn = cc->zone->zone_start_pfn;
1157 block_end_pfn = pageblock_end_pfn(pfn);
1159 for (; pfn < end_pfn; pfn = block_end_pfn,
1160 block_start_pfn = block_end_pfn,
1161 block_end_pfn += pageblock_nr_pages) {
1163 block_end_pfn = min(block_end_pfn, end_pfn);
1165 if (!pageblock_pfn_to_page(block_start_pfn,
1166 block_end_pfn, cc->zone))
1169 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
1170 ISOLATE_UNEVICTABLE);
1175 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
1182 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
1183 #ifdef CONFIG_COMPACTION
1185 static bool suitable_migration_source(struct compact_control *cc,
1190 if (pageblock_skip_persistent(page))
1193 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1196 block_mt = get_pageblock_migratetype(page);
1198 if (cc->migratetype == MIGRATE_MOVABLE)
1199 return is_migrate_movable(block_mt);
1201 return block_mt == cc->migratetype;
1204 /* Returns true if the page is within a block suitable for migration to */
1205 static bool suitable_migration_target(struct compact_control *cc,
1208 /* If the page is a large free page, then disallow migration */
1209 if (PageBuddy(page)) {
1211 * We are checking page_order without zone->lock taken. But
1212 * the only small danger is that we skip a potentially suitable
1213 * pageblock, so it's not worth to check order for valid range.
1215 if (buddy_order_unsafe(page) >= pageblock_order)
1219 if (cc->ignore_block_suitable)
1222 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1223 if (is_migrate_movable(get_pageblock_migratetype(page)))
1226 /* Otherwise skip the block */
1230 static inline unsigned int
1231 freelist_scan_limit(struct compact_control *cc)
1233 unsigned short shift = BITS_PER_LONG - 1;
1235 return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1239 * Test whether the free scanner has reached the same or lower pageblock than
1240 * the migration scanner, and compaction should thus terminate.
1242 static inline bool compact_scanners_met(struct compact_control *cc)
1244 return (cc->free_pfn >> pageblock_order)
1245 <= (cc->migrate_pfn >> pageblock_order);
1249 * Used when scanning for a suitable migration target which scans freelists
1250 * in reverse. Reorders the list such as the unscanned pages are scanned
1251 * first on the next iteration of the free scanner
1254 move_freelist_head(struct list_head *freelist, struct page *freepage)
1258 if (!list_is_last(freelist, &freepage->lru)) {
1259 list_cut_before(&sublist, freelist, &freepage->lru);
1260 if (!list_empty(&sublist))
1261 list_splice_tail(&sublist, freelist);
1266 * Similar to move_freelist_head except used by the migration scanner
1267 * when scanning forward. It's possible for these list operations to
1268 * move against each other if they search the free list exactly in
1272 move_freelist_tail(struct list_head *freelist, struct page *freepage)
1276 if (!list_is_first(freelist, &freepage->lru)) {
1277 list_cut_position(&sublist, freelist, &freepage->lru);
1278 if (!list_empty(&sublist))
1279 list_splice_tail(&sublist, freelist);
1284 fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
1286 unsigned long start_pfn, end_pfn;
1289 /* Do not search around if there are enough pages already */
1290 if (cc->nr_freepages >= cc->nr_migratepages)
1293 /* Minimise scanning during async compaction */
1294 if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1297 /* Pageblock boundaries */
1298 start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
1299 end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
1301 page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
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 = max(pageblock_start_pfn(pfn),
1406 cc->zone->zone_start_pfn);
1408 if (pfn >= low_pfn) {
1409 cc->fast_search_fail = 0;
1410 cc->search_order = order;
1415 if (pfn >= min_pfn && pfn > high_pfn) {
1418 /* Shorten the scan if a candidate is found */
1422 if (order_scanned >= limit)
1426 /* Use a minimum pfn if a preferred one was not found */
1427 if (!page && high_pfn) {
1428 page = pfn_to_page(high_pfn);
1430 /* Update freepage for the list reorder below */
1434 /* Reorder to so a future search skips recent pages */
1435 move_freelist_head(freelist, freepage);
1437 /* Isolate the page if available */
1439 if (__isolate_free_page(page, order)) {
1440 set_page_private(page, order);
1441 nr_isolated = 1 << order;
1442 cc->nr_freepages += nr_isolated;
1443 list_add_tail(&page->lru, &cc->freepages);
1444 count_compact_events(COMPACTISOLATED, nr_isolated);
1446 /* If isolation fails, abort the search */
1447 order = cc->search_order + 1;
1452 spin_unlock_irqrestore(&cc->zone->lock, flags);
1455 * Smaller scan on next order so the total scan ig related
1456 * to freelist_scan_limit.
1458 if (order_scanned >= limit)
1459 limit = min(1U, limit >> 1);
1463 cc->fast_search_fail++;
1466 * Use the highest PFN found above min. If one was
1467 * not found, be pessimistic for direct compaction
1468 * and use the min mark.
1471 page = pfn_to_page(highest);
1472 cc->free_pfn = highest;
1474 if (cc->direct_compaction && pfn_valid(min_pfn)) {
1475 page = pageblock_pfn_to_page(min_pfn,
1476 min(pageblock_end_pfn(min_pfn),
1477 zone_end_pfn(cc->zone)),
1479 cc->free_pfn = min_pfn;
1485 if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1486 highest -= pageblock_nr_pages;
1487 cc->zone->compact_cached_free_pfn = highest;
1490 cc->total_free_scanned += nr_scanned;
1492 return cc->free_pfn;
1494 low_pfn = page_to_pfn(page);
1495 fast_isolate_around(cc, low_pfn, nr_isolated);
1500 * Based on information in the current compact_control, find blocks
1501 * suitable for isolating free pages from and then isolate them.
1503 static void isolate_freepages(struct compact_control *cc)
1505 struct zone *zone = cc->zone;
1507 unsigned long block_start_pfn; /* start of current pageblock */
1508 unsigned long isolate_start_pfn; /* exact pfn we start at */
1509 unsigned long block_end_pfn; /* end of current pageblock */
1510 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1511 struct list_head *freelist = &cc->freepages;
1512 unsigned int stride;
1514 /* Try a small search of the free lists for a candidate */
1515 isolate_start_pfn = fast_isolate_freepages(cc);
1516 if (cc->nr_freepages)
1520 * Initialise the free scanner. The starting point is where we last
1521 * successfully isolated from, zone-cached value, or the end of the
1522 * zone when isolating for the first time. For looping we also need
1523 * this pfn aligned down to the pageblock boundary, because we do
1524 * block_start_pfn -= pageblock_nr_pages in the for loop.
1525 * For ending point, take care when isolating in last pageblock of a
1526 * zone which ends in the middle of a pageblock.
1527 * The low boundary is the end of the pageblock the migration scanner
1530 isolate_start_pfn = cc->free_pfn;
1531 block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1532 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1533 zone_end_pfn(zone));
1534 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1535 stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1538 * Isolate free pages until enough are available to migrate the
1539 * pages on cc->migratepages. We stop searching if the migrate
1540 * and free page scanners meet or enough free pages are isolated.
1542 for (; block_start_pfn >= low_pfn;
1543 block_end_pfn = block_start_pfn,
1544 block_start_pfn -= pageblock_nr_pages,
1545 isolate_start_pfn = block_start_pfn) {
1546 unsigned long nr_isolated;
1549 * This can iterate a massively long zone without finding any
1550 * suitable migration targets, so periodically check resched.
1552 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1555 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1560 /* Check the block is suitable for migration */
1561 if (!suitable_migration_target(cc, page))
1564 /* If isolation recently failed, do not retry */
1565 if (!isolation_suitable(cc, page))
1568 /* Found a block suitable for isolating free pages from. */
1569 nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1570 block_end_pfn, freelist, stride, false);
1572 /* Update the skip hint if the full pageblock was scanned */
1573 if (isolate_start_pfn == block_end_pfn)
1574 update_pageblock_skip(cc, page, block_start_pfn);
1576 /* Are enough freepages isolated? */
1577 if (cc->nr_freepages >= cc->nr_migratepages) {
1578 if (isolate_start_pfn >= block_end_pfn) {
1580 * Restart at previous pageblock if more
1581 * freepages can be isolated next time.
1584 block_start_pfn - pageblock_nr_pages;
1587 } else if (isolate_start_pfn < block_end_pfn) {
1589 * If isolation failed early, do not continue
1595 /* Adjust stride depending on isolation */
1600 stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1604 * Record where the free scanner will restart next time. Either we
1605 * broke from the loop and set isolate_start_pfn based on the last
1606 * call to isolate_freepages_block(), or we met the migration scanner
1607 * and the loop terminated due to isolate_start_pfn < low_pfn
1609 cc->free_pfn = isolate_start_pfn;
1612 /* __isolate_free_page() does not map the pages */
1613 split_map_pages(freelist);
1617 * This is a migrate-callback that "allocates" freepages by taking pages
1618 * from the isolated freelists in the block we are migrating to.
1620 static struct page *compaction_alloc(struct page *migratepage,
1623 struct compact_control *cc = (struct compact_control *)data;
1624 struct page *freepage;
1626 if (list_empty(&cc->freepages)) {
1627 isolate_freepages(cc);
1629 if (list_empty(&cc->freepages))
1633 freepage = list_entry(cc->freepages.next, struct page, lru);
1634 list_del(&freepage->lru);
1641 * This is a migrate-callback that "frees" freepages back to the isolated
1642 * freelist. All pages on the freelist are from the same zone, so there is no
1643 * special handling needed for NUMA.
1645 static void compaction_free(struct page *page, unsigned long data)
1647 struct compact_control *cc = (struct compact_control *)data;
1649 list_add(&page->lru, &cc->freepages);
1653 /* possible outcome of isolate_migratepages */
1655 ISOLATE_ABORT, /* Abort compaction now */
1656 ISOLATE_NONE, /* No pages isolated, continue scanning */
1657 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1658 } isolate_migrate_t;
1661 * Allow userspace to control policy on scanning the unevictable LRU for
1662 * compactable pages.
1664 #ifdef CONFIG_PREEMPT_RT
1665 int sysctl_compact_unevictable_allowed __read_mostly = 0;
1667 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1671 update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1673 if (cc->fast_start_pfn == ULONG_MAX)
1676 if (!cc->fast_start_pfn)
1677 cc->fast_start_pfn = pfn;
1679 cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1682 static inline unsigned long
1683 reinit_migrate_pfn(struct compact_control *cc)
1685 if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1686 return cc->migrate_pfn;
1688 cc->migrate_pfn = cc->fast_start_pfn;
1689 cc->fast_start_pfn = ULONG_MAX;
1691 return cc->migrate_pfn;
1695 * Briefly search the free lists for a migration source that already has
1696 * some free pages to reduce the number of pages that need migration
1697 * before a pageblock is free.
1699 static unsigned long fast_find_migrateblock(struct compact_control *cc)
1701 unsigned int limit = freelist_scan_limit(cc);
1702 unsigned int nr_scanned = 0;
1703 unsigned long distance;
1704 unsigned long pfn = cc->migrate_pfn;
1705 unsigned long high_pfn;
1707 bool found_block = false;
1709 /* Skip hints are relied on to avoid repeats on the fast search */
1710 if (cc->ignore_skip_hint)
1714 * If the migrate_pfn is not at the start of a zone or the start
1715 * of a pageblock then assume this is a continuation of a previous
1716 * scan restarted due to COMPACT_CLUSTER_MAX.
1718 if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1722 * For smaller orders, just linearly scan as the number of pages
1723 * to migrate should be relatively small and does not necessarily
1724 * justify freeing up a large block for a small allocation.
1726 if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1730 * Only allow kcompactd and direct requests for movable pages to
1731 * quickly clear out a MOVABLE pageblock for allocation. This
1732 * reduces the risk that a large movable pageblock is freed for
1733 * an unmovable/reclaimable small allocation.
1735 if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1739 * When starting the migration scanner, pick any pageblock within the
1740 * first half of the search space. Otherwise try and pick a pageblock
1741 * within the first eighth to reduce the chances that a migration
1742 * target later becomes a source.
1744 distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1745 if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1747 high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1749 for (order = cc->order - 1;
1750 order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
1752 struct free_area *area = &cc->zone->free_area[order];
1753 struct list_head *freelist;
1754 unsigned long flags;
1755 struct page *freepage;
1760 spin_lock_irqsave(&cc->zone->lock, flags);
1761 freelist = &area->free_list[MIGRATE_MOVABLE];
1762 list_for_each_entry(freepage, freelist, lru) {
1763 unsigned long free_pfn;
1765 if (nr_scanned++ >= limit) {
1766 move_freelist_tail(freelist, freepage);
1770 free_pfn = page_to_pfn(freepage);
1771 if (free_pfn < high_pfn) {
1773 * Avoid if skipped recently. Ideally it would
1774 * move to the tail but even safe iteration of
1775 * the list assumes an entry is deleted, not
1778 if (get_pageblock_skip(freepage))
1781 /* Reorder to so a future search skips recent pages */
1782 move_freelist_tail(freelist, freepage);
1784 update_fast_start_pfn(cc, free_pfn);
1785 pfn = pageblock_start_pfn(free_pfn);
1786 cc->fast_search_fail = 0;
1788 set_pageblock_skip(freepage);
1792 spin_unlock_irqrestore(&cc->zone->lock, flags);
1795 cc->total_migrate_scanned += nr_scanned;
1798 * If fast scanning failed then use a cached entry for a page block
1799 * that had free pages as the basis for starting a linear scan.
1802 cc->fast_search_fail++;
1803 pfn = reinit_migrate_pfn(cc);
1809 * Isolate all pages that can be migrated from the first suitable block,
1810 * starting at the block pointed to by the migrate scanner pfn within
1813 static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1815 unsigned long block_start_pfn;
1816 unsigned long block_end_pfn;
1817 unsigned long low_pfn;
1819 const isolate_mode_t isolate_mode =
1820 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1821 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1822 bool fast_find_block;
1825 * Start at where we last stopped, or beginning of the zone as
1826 * initialized by compact_zone(). The first failure will use
1827 * the lowest PFN as the starting point for linear scanning.
1829 low_pfn = fast_find_migrateblock(cc);
1830 block_start_pfn = pageblock_start_pfn(low_pfn);
1831 if (block_start_pfn < cc->zone->zone_start_pfn)
1832 block_start_pfn = cc->zone->zone_start_pfn;
1835 * fast_find_migrateblock marks a pageblock skipped so to avoid
1836 * the isolation_suitable check below, check whether the fast
1837 * search was successful.
1839 fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
1841 /* Only scan within a pageblock boundary */
1842 block_end_pfn = pageblock_end_pfn(low_pfn);
1845 * Iterate over whole pageblocks until we find the first suitable.
1846 * Do not cross the free scanner.
1848 for (; block_end_pfn <= cc->free_pfn;
1849 fast_find_block = false,
1850 low_pfn = block_end_pfn,
1851 block_start_pfn = block_end_pfn,
1852 block_end_pfn += pageblock_nr_pages) {
1855 * This can potentially iterate a massively long zone with
1856 * many pageblocks unsuitable, so periodically check if we
1859 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1862 page = pageblock_pfn_to_page(block_start_pfn,
1863 block_end_pfn, cc->zone);
1868 * If isolation recently failed, do not retry. Only check the
1869 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1870 * to be visited multiple times. Assume skip was checked
1871 * before making it "skip" so other compaction instances do
1872 * not scan the same block.
1874 if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
1875 !fast_find_block && !isolation_suitable(cc, page))
1879 * For async compaction, also only scan in MOVABLE blocks
1880 * without huge pages. Async compaction is optimistic to see
1881 * if the minimum amount of work satisfies the allocation.
1882 * The cached PFN is updated as it's possible that all
1883 * remaining blocks between source and target are unsuitable
1884 * and the compaction scanners fail to meet.
1886 if (!suitable_migration_source(cc, page)) {
1887 update_cached_migrate(cc, block_end_pfn);
1891 /* Perform the isolation */
1892 low_pfn = isolate_migratepages_block(cc, low_pfn,
1893 block_end_pfn, isolate_mode);
1896 return ISOLATE_ABORT;
1899 * Either we isolated something and proceed with migration. Or
1900 * we failed and compact_zone should decide if we should
1906 /* Record where migration scanner will be restarted. */
1907 cc->migrate_pfn = low_pfn;
1909 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1913 * order == -1 is expected when compacting via
1914 * /proc/sys/vm/compact_memory
1916 static inline bool is_via_compact_memory(int order)
1921 static bool kswapd_is_running(pg_data_t *pgdat)
1923 return pgdat->kswapd && (pgdat->kswapd->state == TASK_RUNNING);
1927 * A zone's fragmentation score is the external fragmentation wrt to the
1928 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
1930 static unsigned int fragmentation_score_zone(struct zone *zone)
1932 return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
1936 * A weighted zone's fragmentation score is the external fragmentation
1937 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
1938 * returns a value in the range [0, 100].
1940 * The scaling factor ensures that proactive compaction focuses on larger
1941 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
1942 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
1943 * and thus never exceeds the high threshold for proactive compaction.
1945 static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
1947 unsigned long score;
1949 score = zone->present_pages * fragmentation_score_zone(zone);
1950 return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
1954 * The per-node proactive (background) compaction process is started by its
1955 * corresponding kcompactd thread when the node's fragmentation score
1956 * exceeds the high threshold. The compaction process remains active till
1957 * the node's score falls below the low threshold, or one of the back-off
1958 * conditions is met.
1960 static unsigned int fragmentation_score_node(pg_data_t *pgdat)
1962 unsigned int score = 0;
1965 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1968 zone = &pgdat->node_zones[zoneid];
1969 score += fragmentation_score_zone_weighted(zone);
1975 static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
1977 unsigned int wmark_low;
1980 * Cap the low watermak to avoid excessive compaction
1981 * activity in case a user sets the proactivess tunable
1982 * close to 100 (maximum).
1984 wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
1985 return low ? wmark_low : min(wmark_low + 10, 100U);
1988 static bool should_proactive_compact_node(pg_data_t *pgdat)
1992 if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
1995 wmark_high = fragmentation_score_wmark(pgdat, false);
1996 return fragmentation_score_node(pgdat) > wmark_high;
1999 static enum compact_result __compact_finished(struct compact_control *cc)
2002 const int migratetype = cc->migratetype;
2005 /* Compaction run completes if the migrate and free scanner meet */
2006 if (compact_scanners_met(cc)) {
2007 /* Let the next compaction start anew. */
2008 reset_cached_positions(cc->zone);
2011 * Mark that the PG_migrate_skip information should be cleared
2012 * by kswapd when it goes to sleep. kcompactd does not set the
2013 * flag itself as the decision to be clear should be directly
2014 * based on an allocation request.
2016 if (cc->direct_compaction)
2017 cc->zone->compact_blockskip_flush = true;
2020 return COMPACT_COMPLETE;
2022 return COMPACT_PARTIAL_SKIPPED;
2025 if (cc->proactive_compaction) {
2026 int score, wmark_low;
2029 pgdat = cc->zone->zone_pgdat;
2030 if (kswapd_is_running(pgdat))
2031 return COMPACT_PARTIAL_SKIPPED;
2033 score = fragmentation_score_zone(cc->zone);
2034 wmark_low = fragmentation_score_wmark(pgdat, true);
2036 if (score > wmark_low)
2037 ret = COMPACT_CONTINUE;
2039 ret = COMPACT_SUCCESS;
2044 if (is_via_compact_memory(cc->order))
2045 return COMPACT_CONTINUE;
2048 * Always finish scanning a pageblock to reduce the possibility of
2049 * fallbacks in the future. This is particularly important when
2050 * migration source is unmovable/reclaimable but it's not worth
2053 if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
2054 return COMPACT_CONTINUE;
2056 /* Direct compactor: Is a suitable page free? */
2057 ret = COMPACT_NO_SUITABLE_PAGE;
2058 for (order = cc->order; order < MAX_ORDER; order++) {
2059 struct free_area *area = &cc->zone->free_area[order];
2062 /* Job done if page is free of the right migratetype */
2063 if (!free_area_empty(area, migratetype))
2064 return COMPACT_SUCCESS;
2067 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2068 if (migratetype == MIGRATE_MOVABLE &&
2069 !free_area_empty(area, MIGRATE_CMA))
2070 return COMPACT_SUCCESS;
2073 * Job done if allocation would steal freepages from
2074 * other migratetype buddy lists.
2076 if (find_suitable_fallback(area, order, migratetype,
2077 true, &can_steal) != -1) {
2079 /* movable pages are OK in any pageblock */
2080 if (migratetype == MIGRATE_MOVABLE)
2081 return COMPACT_SUCCESS;
2084 * We are stealing for a non-movable allocation. Make
2085 * sure we finish compacting the current pageblock
2086 * first so it is as free as possible and we won't
2087 * have to steal another one soon. This only applies
2088 * to sync compaction, as async compaction operates
2089 * on pageblocks of the same migratetype.
2091 if (cc->mode == MIGRATE_ASYNC ||
2092 IS_ALIGNED(cc->migrate_pfn,
2093 pageblock_nr_pages)) {
2094 return COMPACT_SUCCESS;
2097 ret = COMPACT_CONTINUE;
2103 if (cc->contended || fatal_signal_pending(current))
2104 ret = COMPACT_CONTENDED;
2109 static enum compact_result compact_finished(struct compact_control *cc)
2113 ret = __compact_finished(cc);
2114 trace_mm_compaction_finished(cc->zone, cc->order, ret);
2115 if (ret == COMPACT_NO_SUITABLE_PAGE)
2116 ret = COMPACT_CONTINUE;
2121 static enum compact_result __compaction_suitable(struct zone *zone, int order,
2122 unsigned int alloc_flags,
2123 int highest_zoneidx,
2124 unsigned long wmark_target)
2126 unsigned long watermark;
2128 if (is_via_compact_memory(order))
2129 return COMPACT_CONTINUE;
2131 watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2133 * If watermarks for high-order allocation are already met, there
2134 * should be no need for compaction at all.
2136 if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2138 return COMPACT_SUCCESS;
2141 * Watermarks for order-0 must be met for compaction to be able to
2142 * isolate free pages for migration targets. This means that the
2143 * watermark and alloc_flags have to match, or be more pessimistic than
2144 * the check in __isolate_free_page(). We don't use the direct
2145 * compactor's alloc_flags, as they are not relevant for freepage
2146 * isolation. We however do use the direct compactor's highest_zoneidx
2147 * to skip over zones where lowmem reserves would prevent allocation
2148 * even if compaction succeeds.
2149 * For costly orders, we require low watermark instead of min for
2150 * compaction to proceed to increase its chances.
2151 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2152 * suitable migration targets
2154 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2155 low_wmark_pages(zone) : min_wmark_pages(zone);
2156 watermark += compact_gap(order);
2157 if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2158 ALLOC_CMA, wmark_target))
2159 return COMPACT_SKIPPED;
2161 return COMPACT_CONTINUE;
2165 * compaction_suitable: Is this suitable to run compaction on this zone now?
2167 * COMPACT_SKIPPED - If there are too few free pages for compaction
2168 * COMPACT_SUCCESS - If the allocation would succeed without compaction
2169 * COMPACT_CONTINUE - If compaction should run now
2171 enum compact_result compaction_suitable(struct zone *zone, int order,
2172 unsigned int alloc_flags,
2173 int highest_zoneidx)
2175 enum compact_result ret;
2178 ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
2179 zone_page_state(zone, NR_FREE_PAGES));
2181 * fragmentation index determines if allocation failures are due to
2182 * low memory or external fragmentation
2184 * index of -1000 would imply allocations might succeed depending on
2185 * watermarks, but we already failed the high-order watermark check
2186 * index towards 0 implies failure is due to lack of memory
2187 * index towards 1000 implies failure is due to fragmentation
2189 * Only compact if a failure would be due to fragmentation. Also
2190 * ignore fragindex for non-costly orders where the alternative to
2191 * a successful reclaim/compaction is OOM. Fragindex and the
2192 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2193 * excessive compaction for costly orders, but it should not be at the
2194 * expense of system stability.
2196 if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
2197 fragindex = fragmentation_index(zone, order);
2198 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
2199 ret = COMPACT_NOT_SUITABLE_ZONE;
2202 trace_mm_compaction_suitable(zone, order, ret);
2203 if (ret == COMPACT_NOT_SUITABLE_ZONE)
2204 ret = COMPACT_SKIPPED;
2209 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2216 * Make sure at least one zone would pass __compaction_suitable if we continue
2217 * retrying the reclaim.
2219 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2220 ac->highest_zoneidx, ac->nodemask) {
2221 unsigned long available;
2222 enum compact_result compact_result;
2225 * Do not consider all the reclaimable memory because we do not
2226 * want to trash just for a single high order allocation which
2227 * is even not guaranteed to appear even if __compaction_suitable
2228 * is happy about the watermark check.
2230 available = zone_reclaimable_pages(zone) / order;
2231 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2232 compact_result = __compaction_suitable(zone, order, alloc_flags,
2233 ac->highest_zoneidx, available);
2234 if (compact_result != COMPACT_SKIPPED)
2241 static enum compact_result
2242 compact_zone(struct compact_control *cc, struct capture_control *capc)
2244 enum compact_result ret;
2245 unsigned long start_pfn = cc->zone->zone_start_pfn;
2246 unsigned long end_pfn = zone_end_pfn(cc->zone);
2247 unsigned long last_migrated_pfn;
2248 const bool sync = cc->mode != MIGRATE_ASYNC;
2252 * These counters track activities during zone compaction. Initialize
2253 * them before compacting a new zone.
2255 cc->total_migrate_scanned = 0;
2256 cc->total_free_scanned = 0;
2257 cc->nr_migratepages = 0;
2258 cc->nr_freepages = 0;
2259 INIT_LIST_HEAD(&cc->freepages);
2260 INIT_LIST_HEAD(&cc->migratepages);
2262 cc->migratetype = gfp_migratetype(cc->gfp_mask);
2263 ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
2264 cc->highest_zoneidx);
2265 /* Compaction is likely to fail */
2266 if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
2269 /* huh, compaction_suitable is returning something unexpected */
2270 VM_BUG_ON(ret != COMPACT_CONTINUE);
2273 * Clear pageblock skip if there were failures recently and compaction
2274 * is about to be retried after being deferred.
2276 if (compaction_restarting(cc->zone, cc->order))
2277 __reset_isolation_suitable(cc->zone);
2280 * Setup to move all movable pages to the end of the zone. Used cached
2281 * information on where the scanners should start (unless we explicitly
2282 * want to compact the whole zone), but check that it is initialised
2283 * by ensuring the values are within zone boundaries.
2285 cc->fast_start_pfn = 0;
2286 if (cc->whole_zone) {
2287 cc->migrate_pfn = start_pfn;
2288 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2290 cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2291 cc->free_pfn = cc->zone->compact_cached_free_pfn;
2292 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2293 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2294 cc->zone->compact_cached_free_pfn = cc->free_pfn;
2296 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2297 cc->migrate_pfn = start_pfn;
2298 cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2299 cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2302 if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2303 cc->whole_zone = true;
2306 last_migrated_pfn = 0;
2309 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2310 * the basis that some migrations will fail in ASYNC mode. However,
2311 * if the cached PFNs match and pageblocks are skipped due to having
2312 * no isolation candidates, then the sync state does not matter.
2313 * Until a pageblock with isolation candidates is found, keep the
2314 * cached PFNs in sync to avoid revisiting the same blocks.
2316 update_cached = !sync &&
2317 cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2319 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
2320 cc->free_pfn, end_pfn, sync);
2322 migrate_prep_local();
2324 while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2326 unsigned long iteration_start_pfn = cc->migrate_pfn;
2329 * Avoid multiple rescans which can happen if a page cannot be
2330 * isolated (dirty/writeback in async mode) or if the migrated
2331 * pages are being allocated before the pageblock is cleared.
2332 * The first rescan will capture the entire pageblock for
2333 * migration. If it fails, it'll be marked skip and scanning
2334 * will proceed as normal.
2337 if (pageblock_start_pfn(last_migrated_pfn) ==
2338 pageblock_start_pfn(iteration_start_pfn)) {
2342 switch (isolate_migratepages(cc)) {
2344 ret = COMPACT_CONTENDED;
2345 putback_movable_pages(&cc->migratepages);
2346 cc->nr_migratepages = 0;
2349 if (update_cached) {
2350 cc->zone->compact_cached_migrate_pfn[1] =
2351 cc->zone->compact_cached_migrate_pfn[0];
2355 * We haven't isolated and migrated anything, but
2356 * there might still be unflushed migrations from
2357 * previous cc->order aligned block.
2360 case ISOLATE_SUCCESS:
2361 update_cached = false;
2362 last_migrated_pfn = iteration_start_pfn;
2365 err = migrate_pages(&cc->migratepages, compaction_alloc,
2366 compaction_free, (unsigned long)cc, cc->mode,
2369 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
2372 /* All pages were either migrated or will be released */
2373 cc->nr_migratepages = 0;
2375 putback_movable_pages(&cc->migratepages);
2377 * migrate_pages() may return -ENOMEM when scanners meet
2378 * and we want compact_finished() to detect it
2380 if (err == -ENOMEM && !compact_scanners_met(cc)) {
2381 ret = COMPACT_CONTENDED;
2385 * We failed to migrate at least one page in the current
2386 * order-aligned block, so skip the rest of it.
2388 if (cc->direct_compaction &&
2389 (cc->mode == MIGRATE_ASYNC)) {
2390 cc->migrate_pfn = block_end_pfn(
2391 cc->migrate_pfn - 1, cc->order);
2392 /* Draining pcplists is useless in this case */
2393 last_migrated_pfn = 0;
2399 * Has the migration scanner moved away from the previous
2400 * cc->order aligned block where we migrated from? If yes,
2401 * flush the pages that were freed, so that they can merge and
2402 * compact_finished() can detect immediately if allocation
2405 if (cc->order > 0 && last_migrated_pfn) {
2406 unsigned long current_block_start =
2407 block_start_pfn(cc->migrate_pfn, cc->order);
2409 if (last_migrated_pfn < current_block_start) {
2410 lru_add_drain_cpu_zone(cc->zone);
2411 /* No more flushing until we migrate again */
2412 last_migrated_pfn = 0;
2416 /* Stop if a page has been captured */
2417 if (capc && capc->page) {
2418 ret = COMPACT_SUCCESS;
2425 * Release free pages and update where the free scanner should restart,
2426 * so we don't leave any returned pages behind in the next attempt.
2428 if (cc->nr_freepages > 0) {
2429 unsigned long free_pfn = release_freepages(&cc->freepages);
2431 cc->nr_freepages = 0;
2432 VM_BUG_ON(free_pfn == 0);
2433 /* The cached pfn is always the first in a pageblock */
2434 free_pfn = pageblock_start_pfn(free_pfn);
2436 * Only go back, not forward. The cached pfn might have been
2437 * already reset to zone end in compact_finished()
2439 if (free_pfn > cc->zone->compact_cached_free_pfn)
2440 cc->zone->compact_cached_free_pfn = free_pfn;
2443 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2444 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2446 trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
2447 cc->free_pfn, end_pfn, sync, ret);
2452 static enum compact_result compact_zone_order(struct zone *zone, int order,
2453 gfp_t gfp_mask, enum compact_priority prio,
2454 unsigned int alloc_flags, int highest_zoneidx,
2455 struct page **capture)
2457 enum compact_result ret;
2458 struct compact_control cc = {
2460 .search_order = order,
2461 .gfp_mask = gfp_mask,
2463 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2464 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2465 .alloc_flags = alloc_flags,
2466 .highest_zoneidx = highest_zoneidx,
2467 .direct_compaction = true,
2468 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2469 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2470 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2472 struct capture_control capc = {
2478 * Make sure the structs are really initialized before we expose the
2479 * capture control, in case we are interrupted and the interrupt handler
2483 WRITE_ONCE(current->capture_control, &capc);
2485 ret = compact_zone(&cc, &capc);
2487 VM_BUG_ON(!list_empty(&cc.freepages));
2488 VM_BUG_ON(!list_empty(&cc.migratepages));
2491 * Make sure we hide capture control first before we read the captured
2492 * page pointer, otherwise an interrupt could free and capture a page
2493 * and we would leak it.
2495 WRITE_ONCE(current->capture_control, NULL);
2496 *capture = READ_ONCE(capc.page);
2501 int sysctl_extfrag_threshold = 500;
2504 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2505 * @gfp_mask: The GFP mask of the current allocation
2506 * @order: The order of the current allocation
2507 * @alloc_flags: The allocation flags of the current allocation
2508 * @ac: The context of current allocation
2509 * @prio: Determines how hard direct compaction should try to succeed
2510 * @capture: Pointer to free page created by compaction will be stored here
2512 * This is the main entry point for direct page compaction.
2514 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2515 unsigned int alloc_flags, const struct alloc_context *ac,
2516 enum compact_priority prio, struct page **capture)
2518 int may_perform_io = gfp_mask & __GFP_IO;
2521 enum compact_result rc = COMPACT_SKIPPED;
2524 * Check if the GFP flags allow compaction - GFP_NOIO is really
2525 * tricky context because the migration might require IO
2527 if (!may_perform_io)
2528 return COMPACT_SKIPPED;
2530 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2532 /* Compact each zone in the list */
2533 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2534 ac->highest_zoneidx, ac->nodemask) {
2535 enum compact_result status;
2537 if (prio > MIN_COMPACT_PRIORITY
2538 && compaction_deferred(zone, order)) {
2539 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2543 status = compact_zone_order(zone, order, gfp_mask, prio,
2544 alloc_flags, ac->highest_zoneidx, capture);
2545 rc = max(status, rc);
2547 /* The allocation should succeed, stop compacting */
2548 if (status == COMPACT_SUCCESS) {
2550 * We think the allocation will succeed in this zone,
2551 * but it is not certain, hence the false. The caller
2552 * will repeat this with true if allocation indeed
2553 * succeeds in this zone.
2555 compaction_defer_reset(zone, order, false);
2560 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2561 status == COMPACT_PARTIAL_SKIPPED))
2563 * We think that allocation won't succeed in this zone
2564 * so we defer compaction there. If it ends up
2565 * succeeding after all, it will be reset.
2567 defer_compaction(zone, order);
2570 * We might have stopped compacting due to need_resched() in
2571 * async compaction, or due to a fatal signal detected. In that
2572 * case do not try further zones
2574 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2575 || fatal_signal_pending(current))
2583 * Compact all zones within a node till each zone's fragmentation score
2584 * reaches within proactive compaction thresholds (as determined by the
2585 * proactiveness tunable).
2587 * It is possible that the function returns before reaching score targets
2588 * due to various back-off conditions, such as, contention on per-node or
2591 static void proactive_compact_node(pg_data_t *pgdat)
2595 struct compact_control cc = {
2597 .mode = MIGRATE_SYNC_LIGHT,
2598 .ignore_skip_hint = true,
2600 .gfp_mask = GFP_KERNEL,
2601 .proactive_compaction = true,
2604 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2605 zone = &pgdat->node_zones[zoneid];
2606 if (!populated_zone(zone))
2611 compact_zone(&cc, NULL);
2613 VM_BUG_ON(!list_empty(&cc.freepages));
2614 VM_BUG_ON(!list_empty(&cc.migratepages));
2618 /* Compact all zones within a node */
2619 static void compact_node(int nid)
2621 pg_data_t *pgdat = NODE_DATA(nid);
2624 struct compact_control cc = {
2626 .mode = MIGRATE_SYNC,
2627 .ignore_skip_hint = true,
2629 .gfp_mask = GFP_KERNEL,
2633 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2635 zone = &pgdat->node_zones[zoneid];
2636 if (!populated_zone(zone))
2641 compact_zone(&cc, NULL);
2643 VM_BUG_ON(!list_empty(&cc.freepages));
2644 VM_BUG_ON(!list_empty(&cc.migratepages));
2648 /* Compact all nodes in the system */
2649 static void compact_nodes(void)
2653 /* Flush pending updates to the LRU lists */
2654 lru_add_drain_all();
2656 for_each_online_node(nid)
2660 /* The written value is actually unused, all memory is compacted */
2661 int sysctl_compact_memory;
2664 * Tunable for proactive compaction. It determines how
2665 * aggressively the kernel should compact memory in the
2666 * background. It takes values in the range [0, 100].
2668 unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
2671 * This is the entry point for compacting all nodes via
2672 * /proc/sys/vm/compact_memory
2674 int sysctl_compaction_handler(struct ctl_table *table, int write,
2675 void *buffer, size_t *length, loff_t *ppos)
2683 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2684 static ssize_t sysfs_compact_node(struct device *dev,
2685 struct device_attribute *attr,
2686 const char *buf, size_t count)
2690 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2691 /* Flush pending updates to the LRU lists */
2692 lru_add_drain_all();
2699 static DEVICE_ATTR(compact, 0200, NULL, sysfs_compact_node);
2701 int compaction_register_node(struct node *node)
2703 return device_create_file(&node->dev, &dev_attr_compact);
2706 void compaction_unregister_node(struct node *node)
2708 return device_remove_file(&node->dev, &dev_attr_compact);
2710 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
2712 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2714 return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
2717 static bool kcompactd_node_suitable(pg_data_t *pgdat)
2721 enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
2723 for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
2724 zone = &pgdat->node_zones[zoneid];
2726 if (!populated_zone(zone))
2729 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
2730 highest_zoneidx) == COMPACT_CONTINUE)
2737 static void kcompactd_do_work(pg_data_t *pgdat)
2740 * With no special task, compact all zones so that a page of requested
2741 * order is allocatable.
2745 struct compact_control cc = {
2746 .order = pgdat->kcompactd_max_order,
2747 .search_order = pgdat->kcompactd_max_order,
2748 .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
2749 .mode = MIGRATE_SYNC_LIGHT,
2750 .ignore_skip_hint = false,
2751 .gfp_mask = GFP_KERNEL,
2753 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2754 cc.highest_zoneidx);
2755 count_compact_event(KCOMPACTD_WAKE);
2757 for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
2760 zone = &pgdat->node_zones[zoneid];
2761 if (!populated_zone(zone))
2764 if (compaction_deferred(zone, cc.order))
2767 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
2771 if (kthread_should_stop())
2775 status = compact_zone(&cc, NULL);
2777 if (status == COMPACT_SUCCESS) {
2778 compaction_defer_reset(zone, cc.order, false);
2779 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2781 * Buddy pages may become stranded on pcps that could
2782 * otherwise coalesce on the zone's free area for
2783 * order >= cc.order. This is ratelimited by the
2784 * upcoming deferral.
2786 drain_all_pages(zone);
2789 * We use sync migration mode here, so we defer like
2790 * sync direct compaction does.
2792 defer_compaction(zone, cc.order);
2795 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2796 cc.total_migrate_scanned);
2797 count_compact_events(KCOMPACTD_FREE_SCANNED,
2798 cc.total_free_scanned);
2800 VM_BUG_ON(!list_empty(&cc.freepages));
2801 VM_BUG_ON(!list_empty(&cc.migratepages));
2805 * Regardless of success, we are done until woken up next. But remember
2806 * the requested order/highest_zoneidx in case it was higher/tighter
2807 * than our current ones
2809 if (pgdat->kcompactd_max_order <= cc.order)
2810 pgdat->kcompactd_max_order = 0;
2811 if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
2812 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2815 void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
2820 if (pgdat->kcompactd_max_order < order)
2821 pgdat->kcompactd_max_order = order;
2823 if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
2824 pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
2827 * Pairs with implicit barrier in wait_event_freezable()
2828 * such that wakeups are not missed.
2830 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2833 if (!kcompactd_node_suitable(pgdat))
2836 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2838 wake_up_interruptible(&pgdat->kcompactd_wait);
2842 * The background compaction daemon, started as a kernel thread
2843 * from the init process.
2845 static int kcompactd(void *p)
2847 pg_data_t *pgdat = (pg_data_t*)p;
2848 struct task_struct *tsk = current;
2849 unsigned int proactive_defer = 0;
2851 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2853 if (!cpumask_empty(cpumask))
2854 set_cpus_allowed_ptr(tsk, cpumask);
2858 pgdat->kcompactd_max_order = 0;
2859 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2861 while (!kthread_should_stop()) {
2862 unsigned long pflags;
2864 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2865 if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
2866 kcompactd_work_requested(pgdat),
2867 msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
2869 psi_memstall_enter(&pflags);
2870 kcompactd_do_work(pgdat);
2871 psi_memstall_leave(&pflags);
2875 /* kcompactd wait timeout */
2876 if (should_proactive_compact_node(pgdat)) {
2877 unsigned int prev_score, score;
2879 if (proactive_defer) {
2883 prev_score = fragmentation_score_node(pgdat);
2884 proactive_compact_node(pgdat);
2885 score = fragmentation_score_node(pgdat);
2887 * Defer proactive compaction if the fragmentation
2888 * score did not go down i.e. no progress made.
2890 proactive_defer = score < prev_score ?
2891 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
2899 * This kcompactd start function will be called by init and node-hot-add.
2900 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2902 int kcompactd_run(int nid)
2904 pg_data_t *pgdat = NODE_DATA(nid);
2907 if (pgdat->kcompactd)
2910 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2911 if (IS_ERR(pgdat->kcompactd)) {
2912 pr_err("Failed to start kcompactd on node %d\n", nid);
2913 ret = PTR_ERR(pgdat->kcompactd);
2914 pgdat->kcompactd = NULL;
2920 * Called by memory hotplug when all memory in a node is offlined. Caller must
2921 * hold mem_hotplug_begin/end().
2923 void kcompactd_stop(int nid)
2925 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2928 kthread_stop(kcompactd);
2929 NODE_DATA(nid)->kcompactd = NULL;
2934 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2935 * not required for correctness. So if the last cpu in a node goes
2936 * away, we get changed to run anywhere: as the first one comes back,
2937 * restore their cpu bindings.
2939 static int kcompactd_cpu_online(unsigned int cpu)
2943 for_each_node_state(nid, N_MEMORY) {
2944 pg_data_t *pgdat = NODE_DATA(nid);
2945 const struct cpumask *mask;
2947 mask = cpumask_of_node(pgdat->node_id);
2949 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2950 /* One of our CPUs online: restore mask */
2951 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2956 static int __init kcompactd_init(void)
2961 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2962 "mm/compaction:online",
2963 kcompactd_cpu_online, NULL);
2965 pr_err("kcompactd: failed to register hotplug callbacks.\n");
2969 for_each_node_state(nid, N_MEMORY)
2973 subsys_initcall(kcompactd_init)
2975 #endif /* CONFIG_COMPACTION */