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 */