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>
27 #ifdef CONFIG_COMPACTION
28 static inline void count_compact_event(enum vm_event_item item)
33 static inline void count_compact_events(enum vm_event_item item, long delta)
35 count_vm_events(item, delta);
38 #define count_compact_event(item) do { } while (0)
39 #define count_compact_events(item, delta) do { } while (0)
42 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
44 #define CREATE_TRACE_POINTS
45 #include <trace/events/compaction.h>
47 #define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
48 #define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
49 #define pageblock_start_pfn(pfn) block_start_pfn(pfn, pageblock_order)
50 #define pageblock_end_pfn(pfn) block_end_pfn(pfn, pageblock_order)
52 static unsigned long release_freepages(struct list_head *freelist)
54 struct page *page, *next;
55 unsigned long high_pfn = 0;
57 list_for_each_entry_safe(page, next, freelist, lru) {
58 unsigned long pfn = page_to_pfn(page);
68 static void map_pages(struct list_head *list)
70 unsigned int i, order, nr_pages;
71 struct page *page, *next;
74 list_for_each_entry_safe(page, next, list, lru) {
77 order = page_private(page);
78 nr_pages = 1 << order;
80 post_alloc_hook(page, order, __GFP_MOVABLE);
82 split_page(page, order);
84 for (i = 0; i < nr_pages; i++) {
85 list_add(&page->lru, &tmp_list);
90 list_splice(&tmp_list, list);
93 #ifdef CONFIG_COMPACTION
95 int PageMovable(struct page *page)
97 struct address_space *mapping;
99 VM_BUG_ON_PAGE(!PageLocked(page), page);
100 if (!__PageMovable(page))
103 mapping = page_mapping(page);
104 if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
109 EXPORT_SYMBOL(PageMovable);
111 void __SetPageMovable(struct page *page, struct address_space *mapping)
113 VM_BUG_ON_PAGE(!PageLocked(page), page);
114 VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
115 page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
117 EXPORT_SYMBOL(__SetPageMovable);
119 void __ClearPageMovable(struct page *page)
121 VM_BUG_ON_PAGE(!PageLocked(page), page);
122 VM_BUG_ON_PAGE(!PageMovable(page), page);
124 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
125 * flag so that VM can catch up released page by driver after isolation.
126 * With it, VM migration doesn't try to put it back.
128 page->mapping = (void *)((unsigned long)page->mapping &
129 PAGE_MAPPING_MOVABLE);
131 EXPORT_SYMBOL(__ClearPageMovable);
133 /* Do not skip compaction more than 64 times */
134 #define COMPACT_MAX_DEFER_SHIFT 6
137 * Compaction is deferred when compaction fails to result in a page
138 * allocation success. 1 << compact_defer_limit compactions are skipped up
139 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
141 void defer_compaction(struct zone *zone, int order)
143 zone->compact_considered = 0;
144 zone->compact_defer_shift++;
146 if (order < zone->compact_order_failed)
147 zone->compact_order_failed = order;
149 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
150 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
152 trace_mm_compaction_defer_compaction(zone, order);
155 /* Returns true if compaction should be skipped this time */
156 bool compaction_deferred(struct zone *zone, int order)
158 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
160 if (order < zone->compact_order_failed)
163 /* Avoid possible overflow */
164 if (++zone->compact_considered > defer_limit)
165 zone->compact_considered = defer_limit;
167 if (zone->compact_considered >= defer_limit)
170 trace_mm_compaction_deferred(zone, order);
176 * Update defer tracking counters after successful compaction of given order,
177 * which means an allocation either succeeded (alloc_success == true) or is
178 * expected to succeed.
180 void compaction_defer_reset(struct zone *zone, int order,
184 zone->compact_considered = 0;
185 zone->compact_defer_shift = 0;
187 if (order >= zone->compact_order_failed)
188 zone->compact_order_failed = order + 1;
190 trace_mm_compaction_defer_reset(zone, order);
193 /* Returns true if restarting compaction after many failures */
194 bool compaction_restarting(struct zone *zone, int order)
196 if (order < zone->compact_order_failed)
199 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
200 zone->compact_considered >= 1UL << zone->compact_defer_shift;
203 /* Returns true if the pageblock should be scanned for pages to isolate. */
204 static inline bool isolation_suitable(struct compact_control *cc,
207 if (cc->ignore_skip_hint)
210 return !get_pageblock_skip(page);
213 static void reset_cached_positions(struct zone *zone)
215 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
216 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
217 zone->compact_cached_free_pfn =
218 pageblock_start_pfn(zone_end_pfn(zone) - 1);
222 * Compound pages of >= pageblock_order should consistenly be skipped until
223 * released. It is always pointless to compact pages of such order (if they are
224 * migratable), and the pageblocks they occupy cannot contain any free pages.
226 static bool pageblock_skip_persistent(struct page *page)
228 if (!PageCompound(page))
231 page = compound_head(page);
233 if (compound_order(page) >= pageblock_order)
240 * This function is called to clear all cached information on pageblocks that
241 * should be skipped for page isolation when the migrate and free page scanner
244 static void __reset_isolation_suitable(struct zone *zone)
246 unsigned long start_pfn = zone->zone_start_pfn;
247 unsigned long end_pfn = zone_end_pfn(zone);
250 zone->compact_blockskip_flush = false;
252 /* Walk the zone and mark every pageblock as suitable for isolation */
253 for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
258 page = pfn_to_online_page(pfn);
261 if (zone != page_zone(page))
263 if (pageblock_skip_persistent(page))
266 clear_pageblock_skip(page);
269 reset_cached_positions(zone);
272 void reset_isolation_suitable(pg_data_t *pgdat)
276 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
277 struct zone *zone = &pgdat->node_zones[zoneid];
278 if (!populated_zone(zone))
281 /* Only flush if a full compaction finished recently */
282 if (zone->compact_blockskip_flush)
283 __reset_isolation_suitable(zone);
288 * If no pages were isolated then mark this pageblock to be skipped in the
289 * future. The information is later cleared by __reset_isolation_suitable().
291 static void update_pageblock_skip(struct compact_control *cc,
292 struct page *page, unsigned long nr_isolated,
293 bool migrate_scanner)
295 struct zone *zone = cc->zone;
298 if (cc->ignore_skip_hint)
307 set_pageblock_skip(page);
309 pfn = page_to_pfn(page);
311 /* Update where async and sync compaction should restart */
312 if (migrate_scanner) {
313 if (pfn > zone->compact_cached_migrate_pfn[0])
314 zone->compact_cached_migrate_pfn[0] = pfn;
315 if (cc->mode != MIGRATE_ASYNC &&
316 pfn > zone->compact_cached_migrate_pfn[1])
317 zone->compact_cached_migrate_pfn[1] = pfn;
319 if (pfn < zone->compact_cached_free_pfn)
320 zone->compact_cached_free_pfn = pfn;
324 static inline bool isolation_suitable(struct compact_control *cc,
330 static inline bool pageblock_skip_persistent(struct page *page)
335 static inline void update_pageblock_skip(struct compact_control *cc,
336 struct page *page, unsigned long nr_isolated,
337 bool migrate_scanner)
340 #endif /* CONFIG_COMPACTION */
343 * Compaction requires the taking of some coarse locks that are potentially
344 * very heavily contended. For async compaction, back out if the lock cannot
345 * be taken immediately. For sync compaction, spin on the lock if needed.
347 * Returns true if the lock is held
348 * Returns false if the lock is not held and compaction should abort
350 static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
351 struct compact_control *cc)
353 if (cc->mode == MIGRATE_ASYNC) {
354 if (!spin_trylock_irqsave(lock, *flags)) {
355 cc->contended = true;
359 spin_lock_irqsave(lock, *flags);
366 * Compaction requires the taking of some coarse locks that are potentially
367 * very heavily contended. The lock should be periodically unlocked to avoid
368 * having disabled IRQs for a long time, even when there is nobody waiting on
369 * the lock. It might also be that allowing the IRQs will result in
370 * need_resched() becoming true. If scheduling is needed, async compaction
371 * aborts. Sync compaction schedules.
372 * Either compaction type will also abort if a fatal signal is pending.
373 * In either case if the lock was locked, it is dropped and not regained.
375 * Returns true if compaction should abort due to fatal signal pending, or
376 * async compaction due to need_resched()
377 * Returns false when compaction can continue (sync compaction might have
380 static bool compact_unlock_should_abort(spinlock_t *lock,
381 unsigned long flags, bool *locked, struct compact_control *cc)
384 spin_unlock_irqrestore(lock, flags);
388 if (fatal_signal_pending(current)) {
389 cc->contended = true;
393 if (need_resched()) {
394 if (cc->mode == MIGRATE_ASYNC) {
395 cc->contended = true;
405 * Aside from avoiding lock contention, compaction also periodically checks
406 * need_resched() and either schedules in sync compaction or aborts async
407 * compaction. This is similar to what compact_unlock_should_abort() does, but
408 * is used where no lock is concerned.
410 * Returns false when no scheduling was needed, or sync compaction scheduled.
411 * Returns true when async compaction should abort.
413 static inline bool compact_should_abort(struct compact_control *cc)
415 /* async compaction aborts if contended */
416 if (need_resched()) {
417 if (cc->mode == MIGRATE_ASYNC) {
418 cc->contended = true;
429 * Isolate free pages onto a private freelist. If @strict is true, will abort
430 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
431 * (even though it may still end up isolating some pages).
433 static unsigned long isolate_freepages_block(struct compact_control *cc,
434 unsigned long *start_pfn,
435 unsigned long end_pfn,
436 struct list_head *freelist,
439 int nr_scanned = 0, total_isolated = 0;
440 struct page *cursor, *valid_page = NULL;
441 unsigned long flags = 0;
443 unsigned long blockpfn = *start_pfn;
446 cursor = pfn_to_page(blockpfn);
448 /* Isolate free pages. */
449 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
451 struct page *page = cursor;
454 * Periodically drop the lock (if held) regardless of its
455 * contention, to give chance to IRQs. Abort if fatal signal
456 * pending or async compaction detects need_resched()
458 if (!(blockpfn % SWAP_CLUSTER_MAX)
459 && compact_unlock_should_abort(&cc->zone->lock, flags,
464 if (!pfn_valid_within(blockpfn))
471 * For compound pages such as THP and hugetlbfs, we can save
472 * potentially a lot of iterations if we skip them at once.
473 * The check is racy, but we can consider only valid values
474 * and the only danger is skipping too much.
476 if (PageCompound(page)) {
477 const unsigned int order = compound_order(page);
479 if (pageblock_skip_persistent(page, order)) {
480 set_pageblock_skip(page);
482 } else if (likely(order < MAX_ORDER)) {
483 blockpfn += (1UL << order) - 1;
484 cursor += (1UL << order) - 1;
489 if (!PageBuddy(page))
493 * If we already hold the lock, we can skip some rechecking.
494 * Note that if we hold the lock now, checked_pageblock was
495 * already set in some previous iteration (or strict is true),
496 * so it is correct to skip the suitable migration target
501 * The zone lock must be held to isolate freepages.
502 * Unfortunately this is a very coarse lock and can be
503 * heavily contended if there are parallel allocations
504 * or parallel compactions. For async compaction do not
505 * spin on the lock and we acquire the lock as late as
508 locked = compact_trylock_irqsave(&cc->zone->lock,
513 /* Recheck this is a buddy page under lock */
514 if (!PageBuddy(page))
518 /* Found a free page, will break it into order-0 pages */
519 order = page_order(page);
520 isolated = __isolate_free_page(page, order);
523 set_page_private(page, order);
525 total_isolated += isolated;
526 cc->nr_freepages += isolated;
527 list_add_tail(&page->lru, freelist);
529 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
530 blockpfn += isolated;
533 /* Advance to the end of split page */
534 blockpfn += isolated - 1;
535 cursor += isolated - 1;
547 spin_unlock_irqrestore(&cc->zone->lock, flags);
550 * There is a tiny chance that we have read bogus compound_order(),
551 * so be careful to not go outside of the pageblock.
553 if (unlikely(blockpfn > end_pfn))
556 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
557 nr_scanned, total_isolated);
559 /* Record how far we have got within the block */
560 *start_pfn = blockpfn;
563 * If strict isolation is requested by CMA then check that all the
564 * pages requested were isolated. If there were any failures, 0 is
565 * returned and CMA will fail.
567 if (strict && blockpfn < end_pfn)
570 /* Update the pageblock-skip if the whole pageblock was scanned */
571 if (blockpfn == end_pfn)
572 update_pageblock_skip(cc, valid_page, total_isolated, false);
574 cc->total_free_scanned += nr_scanned;
576 count_compact_events(COMPACTISOLATED, total_isolated);
577 return total_isolated;
581 * isolate_freepages_range() - isolate free pages.
582 * @start_pfn: The first PFN to start isolating.
583 * @end_pfn: The one-past-last PFN.
585 * Non-free pages, invalid PFNs, or zone boundaries within the
586 * [start_pfn, end_pfn) range are considered errors, cause function to
587 * undo its actions and return zero.
589 * Otherwise, function returns one-past-the-last PFN of isolated page
590 * (which may be greater then end_pfn if end fell in a middle of
594 isolate_freepages_range(struct compact_control *cc,
595 unsigned long start_pfn, unsigned long end_pfn)
597 unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
601 block_start_pfn = pageblock_start_pfn(pfn);
602 if (block_start_pfn < cc->zone->zone_start_pfn)
603 block_start_pfn = cc->zone->zone_start_pfn;
604 block_end_pfn = pageblock_end_pfn(pfn);
606 for (; pfn < end_pfn; pfn += isolated,
607 block_start_pfn = block_end_pfn,
608 block_end_pfn += pageblock_nr_pages) {
609 /* Protect pfn from changing by isolate_freepages_block */
610 unsigned long isolate_start_pfn = pfn;
612 block_end_pfn = min(block_end_pfn, end_pfn);
615 * pfn could pass the block_end_pfn if isolated freepage
616 * is more than pageblock order. In this case, we adjust
617 * scanning range to right one.
619 if (pfn >= block_end_pfn) {
620 block_start_pfn = pageblock_start_pfn(pfn);
621 block_end_pfn = pageblock_end_pfn(pfn);
622 block_end_pfn = min(block_end_pfn, end_pfn);
625 if (!pageblock_pfn_to_page(block_start_pfn,
626 block_end_pfn, cc->zone))
629 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
630 block_end_pfn, &freelist, true);
633 * In strict mode, isolate_freepages_block() returns 0 if
634 * there are any holes in the block (ie. invalid PFNs or
641 * If we managed to isolate pages, it is always (1 << n) *
642 * pageblock_nr_pages for some non-negative n. (Max order
643 * page may span two pageblocks).
647 /* __isolate_free_page() does not map the pages */
648 map_pages(&freelist);
651 /* Loop terminated early, cleanup. */
652 release_freepages(&freelist);
656 /* We don't use freelists for anything. */
660 /* Similar to reclaim, but different enough that they don't share logic */
661 static bool too_many_isolated(struct zone *zone)
663 unsigned long active, inactive, isolated;
665 inactive = node_page_state(zone->zone_pgdat, NR_INACTIVE_FILE) +
666 node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
667 active = node_page_state(zone->zone_pgdat, NR_ACTIVE_FILE) +
668 node_page_state(zone->zone_pgdat, NR_ACTIVE_ANON);
669 isolated = node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE) +
670 node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON);
672 return isolated > (inactive + active) / 2;
676 * isolate_migratepages_block() - isolate all migrate-able pages within
678 * @cc: Compaction control structure.
679 * @low_pfn: The first PFN to isolate
680 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
681 * @isolate_mode: Isolation mode to be used.
683 * Isolate all pages that can be migrated from the range specified by
684 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
685 * Returns zero if there is a fatal signal pending, otherwise PFN of the
686 * first page that was not scanned (which may be both less, equal to or more
689 * The pages are isolated on cc->migratepages list (not required to be empty),
690 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
691 * is neither read nor updated.
694 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
695 unsigned long end_pfn, isolate_mode_t isolate_mode)
697 struct zone *zone = cc->zone;
698 unsigned long nr_scanned = 0, nr_isolated = 0;
699 struct lruvec *lruvec;
700 unsigned long flags = 0;
702 struct page *page = NULL, *valid_page = NULL;
703 unsigned long start_pfn = low_pfn;
704 bool skip_on_failure = false;
705 unsigned long next_skip_pfn = 0;
708 * Ensure that there are not too many pages isolated from the LRU
709 * list by either parallel reclaimers or compaction. If there are,
710 * delay for some time until fewer pages are isolated
712 while (unlikely(too_many_isolated(zone))) {
713 /* async migration should just abort */
714 if (cc->mode == MIGRATE_ASYNC)
717 congestion_wait(BLK_RW_ASYNC, HZ/10);
719 if (fatal_signal_pending(current))
723 if (compact_should_abort(cc))
726 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
727 skip_on_failure = true;
728 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
731 /* Time to isolate some pages for migration */
732 for (; low_pfn < end_pfn; low_pfn++) {
734 if (skip_on_failure && low_pfn >= next_skip_pfn) {
736 * We have isolated all migration candidates in the
737 * previous order-aligned block, and did not skip it due
738 * to failure. We should migrate the pages now and
739 * hopefully succeed compaction.
745 * We failed to isolate in the previous order-aligned
746 * block. Set the new boundary to the end of the
747 * current block. Note we can't simply increase
748 * next_skip_pfn by 1 << order, as low_pfn might have
749 * been incremented by a higher number due to skipping
750 * a compound or a high-order buddy page in the
751 * previous loop iteration.
753 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
757 * Periodically drop the lock (if held) regardless of its
758 * contention, to give chance to IRQs. Abort async compaction
761 if (!(low_pfn % SWAP_CLUSTER_MAX)
762 && compact_unlock_should_abort(zone_lru_lock(zone), flags,
766 if (!pfn_valid_within(low_pfn))
770 page = pfn_to_page(low_pfn);
776 * Skip if free. We read page order here without zone lock
777 * which is generally unsafe, but the race window is small and
778 * the worst thing that can happen is that we skip some
779 * potential isolation targets.
781 if (PageBuddy(page)) {
782 unsigned long freepage_order = page_order_unsafe(page);
785 * Without lock, we cannot be sure that what we got is
786 * a valid page order. Consider only values in the
787 * valid order range to prevent low_pfn overflow.
789 if (freepage_order > 0 && freepage_order < MAX_ORDER)
790 low_pfn += (1UL << freepage_order) - 1;
795 * Regardless of being on LRU, compound pages such as THP and
796 * hugetlbfs are not to be compacted. We can potentially save
797 * a lot of iterations if we skip them at once. The check is
798 * racy, but we can consider only valid values and the only
799 * danger is skipping too much.
801 if (PageCompound(page)) {
802 const unsigned int order = compound_order(page);
804 if (pageblock_skip_persistent(page, order)) {
805 set_pageblock_skip(page);
807 } else if (likely(order < MAX_ORDER))
808 low_pfn += (1UL << order) - 1;
813 * Check may be lockless but that's ok as we recheck later.
814 * It's possible to migrate LRU and non-lru movable pages.
815 * Skip any other type of page
817 if (!PageLRU(page)) {
819 * __PageMovable can return false positive so we need
820 * to verify it under page_lock.
822 if (unlikely(__PageMovable(page)) &&
823 !PageIsolated(page)) {
825 spin_unlock_irqrestore(zone_lru_lock(zone),
830 if (!isolate_movable_page(page, isolate_mode))
831 goto isolate_success;
838 * Migration will fail if an anonymous page is pinned in memory,
839 * so avoid taking lru_lock and isolating it unnecessarily in an
840 * admittedly racy check.
842 if (!page_mapping(page) &&
843 page_count(page) > page_mapcount(page))
847 * Only allow to migrate anonymous pages in GFP_NOFS context
848 * because those do not depend on fs locks.
850 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
853 /* If we already hold the lock, we can skip some rechecking */
855 locked = compact_trylock_irqsave(zone_lru_lock(zone),
860 /* Recheck PageLRU and PageCompound under lock */
865 * Page become compound since the non-locked check,
866 * and it's on LRU. It can only be a THP so the order
867 * is safe to read and it's 0 for tail pages.
869 if (unlikely(PageCompound(page))) {
870 const unsigned int order = compound_order(page);
872 if (pageblock_skip_persistent(page, order)) {
873 set_pageblock_skip(page);
876 low_pfn += (1UL << order) - 1;
881 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
883 /* Try isolate the page */
884 if (__isolate_lru_page(page, isolate_mode) != 0)
887 VM_BUG_ON_PAGE(PageCompound(page), page);
889 /* Successfully isolated */
890 del_page_from_lru_list(page, lruvec, page_lru(page));
891 inc_node_page_state(page,
892 NR_ISOLATED_ANON + page_is_file_cache(page));
895 list_add(&page->lru, &cc->migratepages);
896 cc->nr_migratepages++;
900 * Record where we could have freed pages by migration and not
901 * yet flushed them to buddy allocator.
902 * - this is the lowest page that was isolated and likely be
903 * then freed by migration.
905 if (!cc->last_migrated_pfn)
906 cc->last_migrated_pfn = low_pfn;
908 /* Avoid isolating too much */
909 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
916 if (!skip_on_failure)
920 * We have isolated some pages, but then failed. Release them
921 * instead of migrating, as we cannot form the cc->order buddy
926 spin_unlock_irqrestore(zone_lru_lock(zone), flags);
929 putback_movable_pages(&cc->migratepages);
930 cc->nr_migratepages = 0;
931 cc->last_migrated_pfn = 0;
935 if (low_pfn < next_skip_pfn) {
936 low_pfn = next_skip_pfn - 1;
938 * The check near the loop beginning would have updated
939 * next_skip_pfn too, but this is a bit simpler.
941 next_skip_pfn += 1UL << cc->order;
946 * The PageBuddy() check could have potentially brought us outside
947 * the range to be scanned.
949 if (unlikely(low_pfn > end_pfn))
953 spin_unlock_irqrestore(zone_lru_lock(zone), flags);
956 * Update the pageblock-skip information and cached scanner pfn,
957 * if the whole pageblock was scanned without isolating any page.
959 if (low_pfn == end_pfn)
960 update_pageblock_skip(cc, valid_page, nr_isolated, true);
962 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
963 nr_scanned, nr_isolated);
965 cc->total_migrate_scanned += nr_scanned;
967 count_compact_events(COMPACTISOLATED, nr_isolated);
973 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
974 * @cc: Compaction control structure.
975 * @start_pfn: The first PFN to start isolating.
976 * @end_pfn: The one-past-last PFN.
978 * Returns zero if isolation fails fatally due to e.g. pending signal.
979 * Otherwise, function returns one-past-the-last PFN of isolated page
980 * (which may be greater than end_pfn if end fell in a middle of a THP page).
983 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
984 unsigned long end_pfn)
986 unsigned long pfn, block_start_pfn, block_end_pfn;
988 /* Scan block by block. First and last block may be incomplete */
990 block_start_pfn = pageblock_start_pfn(pfn);
991 if (block_start_pfn < cc->zone->zone_start_pfn)
992 block_start_pfn = cc->zone->zone_start_pfn;
993 block_end_pfn = pageblock_end_pfn(pfn);
995 for (; pfn < end_pfn; pfn = block_end_pfn,
996 block_start_pfn = block_end_pfn,
997 block_end_pfn += pageblock_nr_pages) {
999 block_end_pfn = min(block_end_pfn, end_pfn);
1001 if (!pageblock_pfn_to_page(block_start_pfn,
1002 block_end_pfn, cc->zone))
1005 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
1006 ISOLATE_UNEVICTABLE);
1011 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
1018 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
1019 #ifdef CONFIG_COMPACTION
1021 static bool suitable_migration_source(struct compact_control *cc,
1026 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1029 block_mt = get_pageblock_migratetype(page);
1031 if (cc->migratetype == MIGRATE_MOVABLE)
1032 return is_migrate_movable(block_mt);
1034 return block_mt == cc->migratetype;
1037 /* Returns true if the page is within a block suitable for migration to */
1038 static bool suitable_migration_target(struct compact_control *cc,
1041 /* If the page is a large free page, then disallow migration */
1042 if (PageBuddy(page)) {
1044 * We are checking page_order without zone->lock taken. But
1045 * the only small danger is that we skip a potentially suitable
1046 * pageblock, so it's not worth to check order for valid range.
1048 if (page_order_unsafe(page) >= pageblock_order)
1052 if (cc->ignore_block_suitable)
1055 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1056 if (is_migrate_movable(get_pageblock_migratetype(page)))
1059 /* Otherwise skip the block */
1064 * Test whether the free scanner has reached the same or lower pageblock than
1065 * the migration scanner, and compaction should thus terminate.
1067 static inline bool compact_scanners_met(struct compact_control *cc)
1069 return (cc->free_pfn >> pageblock_order)
1070 <= (cc->migrate_pfn >> pageblock_order);
1074 * Based on information in the current compact_control, find blocks
1075 * suitable for isolating free pages from and then isolate them.
1077 static void isolate_freepages(struct compact_control *cc)
1079 struct zone *zone = cc->zone;
1081 unsigned long block_start_pfn; /* start of current pageblock */
1082 unsigned long isolate_start_pfn; /* exact pfn we start at */
1083 unsigned long block_end_pfn; /* end of current pageblock */
1084 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1085 struct list_head *freelist = &cc->freepages;
1088 * Initialise the free scanner. The starting point is where we last
1089 * successfully isolated from, zone-cached value, or the end of the
1090 * zone when isolating for the first time. For looping we also need
1091 * this pfn aligned down to the pageblock boundary, because we do
1092 * block_start_pfn -= pageblock_nr_pages in the for loop.
1093 * For ending point, take care when isolating in last pageblock of a
1094 * a zone which ends in the middle of a pageblock.
1095 * The low boundary is the end of the pageblock the migration scanner
1098 isolate_start_pfn = cc->free_pfn;
1099 block_start_pfn = pageblock_start_pfn(cc->free_pfn);
1100 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1101 zone_end_pfn(zone));
1102 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1105 * Isolate free pages until enough are available to migrate the
1106 * pages on cc->migratepages. We stop searching if the migrate
1107 * and free page scanners meet or enough free pages are isolated.
1109 for (; block_start_pfn >= low_pfn;
1110 block_end_pfn = block_start_pfn,
1111 block_start_pfn -= pageblock_nr_pages,
1112 isolate_start_pfn = block_start_pfn) {
1114 * This can iterate a massively long zone without finding any
1115 * suitable migration targets, so periodically check if we need
1116 * to schedule, or even abort async compaction.
1118 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1119 && compact_should_abort(cc))
1122 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1127 /* Check the block is suitable for migration */
1128 if (!suitable_migration_target(cc, page))
1131 /* If isolation recently failed, do not retry */
1132 if (!isolation_suitable(cc, page))
1135 /* Found a block suitable for isolating free pages from. */
1136 isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn,
1140 * If we isolated enough freepages, or aborted due to lock
1141 * contention, terminate.
1143 if ((cc->nr_freepages >= cc->nr_migratepages)
1145 if (isolate_start_pfn >= block_end_pfn) {
1147 * Restart at previous pageblock if more
1148 * freepages can be isolated next time.
1151 block_start_pfn - pageblock_nr_pages;
1154 } else if (isolate_start_pfn < block_end_pfn) {
1156 * If isolation failed early, do not continue
1163 /* __isolate_free_page() does not map the pages */
1164 map_pages(freelist);
1167 * Record where the free scanner will restart next time. Either we
1168 * broke from the loop and set isolate_start_pfn based on the last
1169 * call to isolate_freepages_block(), or we met the migration scanner
1170 * and the loop terminated due to isolate_start_pfn < low_pfn
1172 cc->free_pfn = isolate_start_pfn;
1176 * This is a migrate-callback that "allocates" freepages by taking pages
1177 * from the isolated freelists in the block we are migrating to.
1179 static struct page *compaction_alloc(struct page *migratepage,
1183 struct compact_control *cc = (struct compact_control *)data;
1184 struct page *freepage;
1187 * Isolate free pages if necessary, and if we are not aborting due to
1190 if (list_empty(&cc->freepages)) {
1192 isolate_freepages(cc);
1194 if (list_empty(&cc->freepages))
1198 freepage = list_entry(cc->freepages.next, struct page, lru);
1199 list_del(&freepage->lru);
1206 * This is a migrate-callback that "frees" freepages back to the isolated
1207 * freelist. All pages on the freelist are from the same zone, so there is no
1208 * special handling needed for NUMA.
1210 static void compaction_free(struct page *page, unsigned long data)
1212 struct compact_control *cc = (struct compact_control *)data;
1214 list_add(&page->lru, &cc->freepages);
1218 /* possible outcome of isolate_migratepages */
1220 ISOLATE_ABORT, /* Abort compaction now */
1221 ISOLATE_NONE, /* No pages isolated, continue scanning */
1222 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1223 } isolate_migrate_t;
1226 * Allow userspace to control policy on scanning the unevictable LRU for
1227 * compactable pages.
1229 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1232 * Isolate all pages that can be migrated from the first suitable block,
1233 * starting at the block pointed to by the migrate scanner pfn within
1236 static isolate_migrate_t isolate_migratepages(struct zone *zone,
1237 struct compact_control *cc)
1239 unsigned long block_start_pfn;
1240 unsigned long block_end_pfn;
1241 unsigned long low_pfn;
1243 const isolate_mode_t isolate_mode =
1244 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1245 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1248 * Start at where we last stopped, or beginning of the zone as
1249 * initialized by compact_zone()
1251 low_pfn = cc->migrate_pfn;
1252 block_start_pfn = pageblock_start_pfn(low_pfn);
1253 if (block_start_pfn < zone->zone_start_pfn)
1254 block_start_pfn = zone->zone_start_pfn;
1256 /* Only scan within a pageblock boundary */
1257 block_end_pfn = pageblock_end_pfn(low_pfn);
1260 * Iterate over whole pageblocks until we find the first suitable.
1261 * Do not cross the free scanner.
1263 for (; block_end_pfn <= cc->free_pfn;
1264 low_pfn = block_end_pfn,
1265 block_start_pfn = block_end_pfn,
1266 block_end_pfn += pageblock_nr_pages) {
1269 * This can potentially iterate a massively long zone with
1270 * many pageblocks unsuitable, so periodically check if we
1271 * need to schedule, or even abort async compaction.
1273 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1274 && compact_should_abort(cc))
1277 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1282 /* If isolation recently failed, do not retry */
1283 if (!isolation_suitable(cc, page))
1287 * For async compaction, also only scan in MOVABLE blocks.
1288 * Async compaction is optimistic to see if the minimum amount
1289 * of work satisfies the allocation.
1291 if (!suitable_migration_source(cc, page))
1294 /* Perform the isolation */
1295 low_pfn = isolate_migratepages_block(cc, low_pfn,
1296 block_end_pfn, isolate_mode);
1298 if (!low_pfn || cc->contended)
1299 return ISOLATE_ABORT;
1302 * Either we isolated something and proceed with migration. Or
1303 * we failed and compact_zone should decide if we should
1309 /* Record where migration scanner will be restarted. */
1310 cc->migrate_pfn = low_pfn;
1312 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1316 * order == -1 is expected when compacting via
1317 * /proc/sys/vm/compact_memory
1319 static inline bool is_via_compact_memory(int order)
1324 static enum compact_result __compact_finished(struct zone *zone,
1325 struct compact_control *cc)
1328 const int migratetype = cc->migratetype;
1330 if (cc->contended || fatal_signal_pending(current))
1331 return COMPACT_CONTENDED;
1333 /* Compaction run completes if the migrate and free scanner meet */
1334 if (compact_scanners_met(cc)) {
1335 /* Let the next compaction start anew. */
1336 reset_cached_positions(zone);
1339 * Mark that the PG_migrate_skip information should be cleared
1340 * by kswapd when it goes to sleep. kcompactd does not set the
1341 * flag itself as the decision to be clear should be directly
1342 * based on an allocation request.
1344 if (cc->direct_compaction)
1345 zone->compact_blockskip_flush = true;
1348 return COMPACT_COMPLETE;
1350 return COMPACT_PARTIAL_SKIPPED;
1353 if (is_via_compact_memory(cc->order))
1354 return COMPACT_CONTINUE;
1356 if (cc->finishing_block) {
1358 * We have finished the pageblock, but better check again that
1359 * we really succeeded.
1361 if (IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
1362 cc->finishing_block = false;
1364 return COMPACT_CONTINUE;
1367 /* Direct compactor: Is a suitable page free? */
1368 for (order = cc->order; order < MAX_ORDER; order++) {
1369 struct free_area *area = &zone->free_area[order];
1372 /* Job done if page is free of the right migratetype */
1373 if (!list_empty(&area->free_list[migratetype]))
1374 return COMPACT_SUCCESS;
1377 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1378 if (migratetype == MIGRATE_MOVABLE &&
1379 !list_empty(&area->free_list[MIGRATE_CMA]))
1380 return COMPACT_SUCCESS;
1383 * Job done if allocation would steal freepages from
1384 * other migratetype buddy lists.
1386 if (find_suitable_fallback(area, order, migratetype,
1387 true, &can_steal) != -1) {
1389 /* movable pages are OK in any pageblock */
1390 if (migratetype == MIGRATE_MOVABLE)
1391 return COMPACT_SUCCESS;
1394 * We are stealing for a non-movable allocation. Make
1395 * sure we finish compacting the current pageblock
1396 * first so it is as free as possible and we won't
1397 * have to steal another one soon. This only applies
1398 * to sync compaction, as async compaction operates
1399 * on pageblocks of the same migratetype.
1401 if (cc->mode == MIGRATE_ASYNC ||
1402 IS_ALIGNED(cc->migrate_pfn,
1403 pageblock_nr_pages)) {
1404 return COMPACT_SUCCESS;
1407 cc->finishing_block = true;
1408 return COMPACT_CONTINUE;
1412 return COMPACT_NO_SUITABLE_PAGE;
1415 static enum compact_result compact_finished(struct zone *zone,
1416 struct compact_control *cc)
1420 ret = __compact_finished(zone, cc);
1421 trace_mm_compaction_finished(zone, cc->order, ret);
1422 if (ret == COMPACT_NO_SUITABLE_PAGE)
1423 ret = COMPACT_CONTINUE;
1429 * compaction_suitable: Is this suitable to run compaction on this zone now?
1431 * COMPACT_SKIPPED - If there are too few free pages for compaction
1432 * COMPACT_SUCCESS - If the allocation would succeed without compaction
1433 * COMPACT_CONTINUE - If compaction should run now
1435 static enum compact_result __compaction_suitable(struct zone *zone, int order,
1436 unsigned int alloc_flags,
1438 unsigned long wmark_target)
1440 unsigned long watermark;
1442 if (is_via_compact_memory(order))
1443 return COMPACT_CONTINUE;
1445 watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
1447 * If watermarks for high-order allocation are already met, there
1448 * should be no need for compaction at all.
1450 if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1452 return COMPACT_SUCCESS;
1455 * Watermarks for order-0 must be met for compaction to be able to
1456 * isolate free pages for migration targets. This means that the
1457 * watermark and alloc_flags have to match, or be more pessimistic than
1458 * the check in __isolate_free_page(). We don't use the direct
1459 * compactor's alloc_flags, as they are not relevant for freepage
1460 * isolation. We however do use the direct compactor's classzone_idx to
1461 * skip over zones where lowmem reserves would prevent allocation even
1462 * if compaction succeeds.
1463 * For costly orders, we require low watermark instead of min for
1464 * compaction to proceed to increase its chances.
1465 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
1466 * suitable migration targets
1468 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
1469 low_wmark_pages(zone) : min_wmark_pages(zone);
1470 watermark += compact_gap(order);
1471 if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
1472 ALLOC_CMA, wmark_target))
1473 return COMPACT_SKIPPED;
1475 return COMPACT_CONTINUE;
1478 enum compact_result compaction_suitable(struct zone *zone, int order,
1479 unsigned int alloc_flags,
1482 enum compact_result ret;
1485 ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
1486 zone_page_state(zone, NR_FREE_PAGES));
1488 * fragmentation index determines if allocation failures are due to
1489 * low memory or external fragmentation
1491 * index of -1000 would imply allocations might succeed depending on
1492 * watermarks, but we already failed the high-order watermark check
1493 * index towards 0 implies failure is due to lack of memory
1494 * index towards 1000 implies failure is due to fragmentation
1496 * Only compact if a failure would be due to fragmentation. Also
1497 * ignore fragindex for non-costly orders where the alternative to
1498 * a successful reclaim/compaction is OOM. Fragindex and the
1499 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
1500 * excessive compaction for costly orders, but it should not be at the
1501 * expense of system stability.
1503 if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
1504 fragindex = fragmentation_index(zone, order);
1505 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
1506 ret = COMPACT_NOT_SUITABLE_ZONE;
1509 trace_mm_compaction_suitable(zone, order, ret);
1510 if (ret == COMPACT_NOT_SUITABLE_ZONE)
1511 ret = COMPACT_SKIPPED;
1516 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
1523 * Make sure at least one zone would pass __compaction_suitable if we continue
1524 * retrying the reclaim.
1526 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1528 unsigned long available;
1529 enum compact_result compact_result;
1532 * Do not consider all the reclaimable memory because we do not
1533 * want to trash just for a single high order allocation which
1534 * is even not guaranteed to appear even if __compaction_suitable
1535 * is happy about the watermark check.
1537 available = zone_reclaimable_pages(zone) / order;
1538 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
1539 compact_result = __compaction_suitable(zone, order, alloc_flags,
1540 ac_classzone_idx(ac), available);
1541 if (compact_result != COMPACT_SKIPPED)
1548 static enum compact_result compact_zone(struct zone *zone, struct compact_control *cc)
1550 enum compact_result ret;
1551 unsigned long start_pfn = zone->zone_start_pfn;
1552 unsigned long end_pfn = zone_end_pfn(zone);
1553 const bool sync = cc->mode != MIGRATE_ASYNC;
1555 cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
1556 ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
1558 /* Compaction is likely to fail */
1559 if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
1562 /* huh, compaction_suitable is returning something unexpected */
1563 VM_BUG_ON(ret != COMPACT_CONTINUE);
1566 * Clear pageblock skip if there were failures recently and compaction
1567 * is about to be retried after being deferred.
1569 if (compaction_restarting(zone, cc->order))
1570 __reset_isolation_suitable(zone);
1573 * Setup to move all movable pages to the end of the zone. Used cached
1574 * information on where the scanners should start (unless we explicitly
1575 * want to compact the whole zone), but check that it is initialised
1576 * by ensuring the values are within zone boundaries.
1578 if (cc->whole_zone) {
1579 cc->migrate_pfn = start_pfn;
1580 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1582 cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1583 cc->free_pfn = zone->compact_cached_free_pfn;
1584 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
1585 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1586 zone->compact_cached_free_pfn = cc->free_pfn;
1588 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
1589 cc->migrate_pfn = start_pfn;
1590 zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1591 zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1594 if (cc->migrate_pfn == start_pfn)
1595 cc->whole_zone = true;
1598 cc->last_migrated_pfn = 0;
1600 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
1601 cc->free_pfn, end_pfn, sync);
1603 migrate_prep_local();
1605 while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
1608 switch (isolate_migratepages(zone, cc)) {
1610 ret = COMPACT_CONTENDED;
1611 putback_movable_pages(&cc->migratepages);
1612 cc->nr_migratepages = 0;
1616 * We haven't isolated and migrated anything, but
1617 * there might still be unflushed migrations from
1618 * previous cc->order aligned block.
1621 case ISOLATE_SUCCESS:
1625 err = migrate_pages(&cc->migratepages, compaction_alloc,
1626 compaction_free, (unsigned long)cc, cc->mode,
1629 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
1632 /* All pages were either migrated or will be released */
1633 cc->nr_migratepages = 0;
1635 putback_movable_pages(&cc->migratepages);
1637 * migrate_pages() may return -ENOMEM when scanners meet
1638 * and we want compact_finished() to detect it
1640 if (err == -ENOMEM && !compact_scanners_met(cc)) {
1641 ret = COMPACT_CONTENDED;
1645 * We failed to migrate at least one page in the current
1646 * order-aligned block, so skip the rest of it.
1648 if (cc->direct_compaction &&
1649 (cc->mode == MIGRATE_ASYNC)) {
1650 cc->migrate_pfn = block_end_pfn(
1651 cc->migrate_pfn - 1, cc->order);
1652 /* Draining pcplists is useless in this case */
1653 cc->last_migrated_pfn = 0;
1660 * Has the migration scanner moved away from the previous
1661 * cc->order aligned block where we migrated from? If yes,
1662 * flush the pages that were freed, so that they can merge and
1663 * compact_finished() can detect immediately if allocation
1666 if (cc->order > 0 && cc->last_migrated_pfn) {
1668 unsigned long current_block_start =
1669 block_start_pfn(cc->migrate_pfn, cc->order);
1671 if (cc->last_migrated_pfn < current_block_start) {
1673 lru_add_drain_cpu(cpu);
1674 drain_local_pages(zone);
1676 /* No more flushing until we migrate again */
1677 cc->last_migrated_pfn = 0;
1685 * Release free pages and update where the free scanner should restart,
1686 * so we don't leave any returned pages behind in the next attempt.
1688 if (cc->nr_freepages > 0) {
1689 unsigned long free_pfn = release_freepages(&cc->freepages);
1691 cc->nr_freepages = 0;
1692 VM_BUG_ON(free_pfn == 0);
1693 /* The cached pfn is always the first in a pageblock */
1694 free_pfn = pageblock_start_pfn(free_pfn);
1696 * Only go back, not forward. The cached pfn might have been
1697 * already reset to zone end in compact_finished()
1699 if (free_pfn > zone->compact_cached_free_pfn)
1700 zone->compact_cached_free_pfn = free_pfn;
1703 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
1704 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
1706 trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
1707 cc->free_pfn, end_pfn, sync, ret);
1712 static enum compact_result compact_zone_order(struct zone *zone, int order,
1713 gfp_t gfp_mask, enum compact_priority prio,
1714 unsigned int alloc_flags, int classzone_idx)
1716 enum compact_result ret;
1717 struct compact_control cc = {
1719 .nr_migratepages = 0,
1720 .total_migrate_scanned = 0,
1721 .total_free_scanned = 0,
1723 .gfp_mask = gfp_mask,
1725 .mode = (prio == COMPACT_PRIO_ASYNC) ?
1726 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
1727 .alloc_flags = alloc_flags,
1728 .classzone_idx = classzone_idx,
1729 .direct_compaction = true,
1730 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
1731 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
1732 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
1734 INIT_LIST_HEAD(&cc.freepages);
1735 INIT_LIST_HEAD(&cc.migratepages);
1737 ret = compact_zone(zone, &cc);
1739 VM_BUG_ON(!list_empty(&cc.freepages));
1740 VM_BUG_ON(!list_empty(&cc.migratepages));
1745 int sysctl_extfrag_threshold = 500;
1748 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1749 * @gfp_mask: The GFP mask of the current allocation
1750 * @order: The order of the current allocation
1751 * @alloc_flags: The allocation flags of the current allocation
1752 * @ac: The context of current allocation
1753 * @mode: The migration mode for async, sync light, or sync migration
1755 * This is the main entry point for direct page compaction.
1757 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
1758 unsigned int alloc_flags, const struct alloc_context *ac,
1759 enum compact_priority prio)
1761 int may_perform_io = gfp_mask & __GFP_IO;
1764 enum compact_result rc = COMPACT_SKIPPED;
1767 * Check if the GFP flags allow compaction - GFP_NOIO is really
1768 * tricky context because the migration might require IO
1770 if (!may_perform_io)
1771 return COMPACT_SKIPPED;
1773 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
1775 /* Compact each zone in the list */
1776 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1778 enum compact_result status;
1780 if (prio > MIN_COMPACT_PRIORITY
1781 && compaction_deferred(zone, order)) {
1782 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
1786 status = compact_zone_order(zone, order, gfp_mask, prio,
1787 alloc_flags, ac_classzone_idx(ac));
1788 rc = max(status, rc);
1790 /* The allocation should succeed, stop compacting */
1791 if (status == COMPACT_SUCCESS) {
1793 * We think the allocation will succeed in this zone,
1794 * but it is not certain, hence the false. The caller
1795 * will repeat this with true if allocation indeed
1796 * succeeds in this zone.
1798 compaction_defer_reset(zone, order, false);
1803 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
1804 status == COMPACT_PARTIAL_SKIPPED))
1806 * We think that allocation won't succeed in this zone
1807 * so we defer compaction there. If it ends up
1808 * succeeding after all, it will be reset.
1810 defer_compaction(zone, order);
1813 * We might have stopped compacting due to need_resched() in
1814 * async compaction, or due to a fatal signal detected. In that
1815 * case do not try further zones
1817 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
1818 || fatal_signal_pending(current))
1826 /* Compact all zones within a node */
1827 static void compact_node(int nid)
1829 pg_data_t *pgdat = NODE_DATA(nid);
1832 struct compact_control cc = {
1834 .total_migrate_scanned = 0,
1835 .total_free_scanned = 0,
1836 .mode = MIGRATE_SYNC,
1837 .ignore_skip_hint = true,
1839 .gfp_mask = GFP_KERNEL,
1843 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1845 zone = &pgdat->node_zones[zoneid];
1846 if (!populated_zone(zone))
1849 cc.nr_freepages = 0;
1850 cc.nr_migratepages = 0;
1852 INIT_LIST_HEAD(&cc.freepages);
1853 INIT_LIST_HEAD(&cc.migratepages);
1855 compact_zone(zone, &cc);
1857 VM_BUG_ON(!list_empty(&cc.freepages));
1858 VM_BUG_ON(!list_empty(&cc.migratepages));
1862 /* Compact all nodes in the system */
1863 static void compact_nodes(void)
1867 /* Flush pending updates to the LRU lists */
1868 lru_add_drain_all();
1870 for_each_online_node(nid)
1874 /* The written value is actually unused, all memory is compacted */
1875 int sysctl_compact_memory;
1878 * This is the entry point for compacting all nodes via
1879 * /proc/sys/vm/compact_memory
1881 int sysctl_compaction_handler(struct ctl_table *table, int write,
1882 void __user *buffer, size_t *length, loff_t *ppos)
1890 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1891 void __user *buffer, size_t *length, loff_t *ppos)
1893 proc_dointvec_minmax(table, write, buffer, length, ppos);
1898 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1899 static ssize_t sysfs_compact_node(struct device *dev,
1900 struct device_attribute *attr,
1901 const char *buf, size_t count)
1905 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1906 /* Flush pending updates to the LRU lists */
1907 lru_add_drain_all();
1914 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1916 int compaction_register_node(struct node *node)
1918 return device_create_file(&node->dev, &dev_attr_compact);
1921 void compaction_unregister_node(struct node *node)
1923 return device_remove_file(&node->dev, &dev_attr_compact);
1925 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1927 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
1929 return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
1932 static bool kcompactd_node_suitable(pg_data_t *pgdat)
1936 enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx;
1938 for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
1939 zone = &pgdat->node_zones[zoneid];
1941 if (!populated_zone(zone))
1944 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
1945 classzone_idx) == COMPACT_CONTINUE)
1952 static void kcompactd_do_work(pg_data_t *pgdat)
1955 * With no special task, compact all zones so that a page of requested
1956 * order is allocatable.
1960 struct compact_control cc = {
1961 .order = pgdat->kcompactd_max_order,
1962 .total_migrate_scanned = 0,
1963 .total_free_scanned = 0,
1964 .classzone_idx = pgdat->kcompactd_classzone_idx,
1965 .mode = MIGRATE_SYNC_LIGHT,
1966 .ignore_skip_hint = false,
1967 .gfp_mask = GFP_KERNEL,
1969 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
1971 count_compact_event(KCOMPACTD_WAKE);
1973 for (zoneid = 0; zoneid <= cc.classzone_idx; zoneid++) {
1976 zone = &pgdat->node_zones[zoneid];
1977 if (!populated_zone(zone))
1980 if (compaction_deferred(zone, cc.order))
1983 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
1987 cc.nr_freepages = 0;
1988 cc.nr_migratepages = 0;
1989 cc.total_migrate_scanned = 0;
1990 cc.total_free_scanned = 0;
1992 INIT_LIST_HEAD(&cc.freepages);
1993 INIT_LIST_HEAD(&cc.migratepages);
1995 if (kthread_should_stop())
1997 status = compact_zone(zone, &cc);
1999 if (status == COMPACT_SUCCESS) {
2000 compaction_defer_reset(zone, cc.order, false);
2001 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2003 * We use sync migration mode here, so we defer like
2004 * sync direct compaction does.
2006 defer_compaction(zone, cc.order);
2009 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2010 cc.total_migrate_scanned);
2011 count_compact_events(KCOMPACTD_FREE_SCANNED,
2012 cc.total_free_scanned);
2014 VM_BUG_ON(!list_empty(&cc.freepages));
2015 VM_BUG_ON(!list_empty(&cc.migratepages));
2019 * Regardless of success, we are done until woken up next. But remember
2020 * the requested order/classzone_idx in case it was higher/tighter than
2023 if (pgdat->kcompactd_max_order <= cc.order)
2024 pgdat->kcompactd_max_order = 0;
2025 if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx)
2026 pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2029 void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
2034 if (pgdat->kcompactd_max_order < order)
2035 pgdat->kcompactd_max_order = order;
2037 if (pgdat->kcompactd_classzone_idx > classzone_idx)
2038 pgdat->kcompactd_classzone_idx = classzone_idx;
2041 * Pairs with implicit barrier in wait_event_freezable()
2042 * such that wakeups are not missed.
2044 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2047 if (!kcompactd_node_suitable(pgdat))
2050 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2052 wake_up_interruptible(&pgdat->kcompactd_wait);
2056 * The background compaction daemon, started as a kernel thread
2057 * from the init process.
2059 static int kcompactd(void *p)
2061 pg_data_t *pgdat = (pg_data_t*)p;
2062 struct task_struct *tsk = current;
2064 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2066 if (!cpumask_empty(cpumask))
2067 set_cpus_allowed_ptr(tsk, cpumask);
2071 pgdat->kcompactd_max_order = 0;
2072 pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2074 while (!kthread_should_stop()) {
2075 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2076 wait_event_freezable(pgdat->kcompactd_wait,
2077 kcompactd_work_requested(pgdat));
2079 kcompactd_do_work(pgdat);
2086 * This kcompactd start function will be called by init and node-hot-add.
2087 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2089 int kcompactd_run(int nid)
2091 pg_data_t *pgdat = NODE_DATA(nid);
2094 if (pgdat->kcompactd)
2097 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2098 if (IS_ERR(pgdat->kcompactd)) {
2099 pr_err("Failed to start kcompactd on node %d\n", nid);
2100 ret = PTR_ERR(pgdat->kcompactd);
2101 pgdat->kcompactd = NULL;
2107 * Called by memory hotplug when all memory in a node is offlined. Caller must
2108 * hold mem_hotplug_begin/end().
2110 void kcompactd_stop(int nid)
2112 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2115 kthread_stop(kcompactd);
2116 NODE_DATA(nid)->kcompactd = NULL;
2121 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2122 * not required for correctness. So if the last cpu in a node goes
2123 * away, we get changed to run anywhere: as the first one comes back,
2124 * restore their cpu bindings.
2126 static int kcompactd_cpu_online(unsigned int cpu)
2130 for_each_node_state(nid, N_MEMORY) {
2131 pg_data_t *pgdat = NODE_DATA(nid);
2132 const struct cpumask *mask;
2134 mask = cpumask_of_node(pgdat->node_id);
2136 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2137 /* One of our CPUs online: restore mask */
2138 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2143 static int __init kcompactd_init(void)
2148 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2149 "mm/compaction:online",
2150 kcompactd_cpu_online, NULL);
2152 pr_err("kcompactd: failed to register hotplug callbacks.\n");
2156 for_each_node_state(nid, N_MEMORY)
2160 subsys_initcall(kcompactd_init)
2162 #endif /* CONFIG_COMPACTION */