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
30 * Fragmentation score check interval for proactive compaction purposes.
32 #define HPAGE_FRAG_CHECK_INTERVAL_MSEC (500)
34 static inline void count_compact_event(enum vm_event_item item
)
39 static inline void count_compact_events(enum vm_event_item item
, long delta
)
41 count_vm_events(item
, delta
);
44 #define count_compact_event(item) do { } while (0)
45 #define count_compact_events(item, delta) do { } while (0)
48 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
50 #define CREATE_TRACE_POINTS
51 #include <trace/events/compaction.h>
53 #define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
54 #define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
55 #define pageblock_start_pfn(pfn) block_start_pfn(pfn, pageblock_order)
56 #define pageblock_end_pfn(pfn) block_end_pfn(pfn, pageblock_order)
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 (check_source
&& PageLRU(page
)) {
310 clear_pageblock_skip(page
);
314 if (check_target
&& PageBuddy(page
)) {
315 clear_pageblock_skip(page
);
319 page
+= (1 << PAGE_ALLOC_COSTLY_ORDER
);
320 } while (page
<= end_page
);
326 * This function is called to clear all cached information on pageblocks that
327 * should be skipped for page isolation when the migrate and free page scanner
330 static void __reset_isolation_suitable(struct zone
*zone
)
332 unsigned long migrate_pfn
= zone
->zone_start_pfn
;
333 unsigned long free_pfn
= zone_end_pfn(zone
) - 1;
334 unsigned long reset_migrate
= free_pfn
;
335 unsigned long reset_free
= migrate_pfn
;
336 bool source_set
= false;
337 bool free_set
= false;
339 if (!zone
->compact_blockskip_flush
)
342 zone
->compact_blockskip_flush
= false;
345 * Walk the zone and update pageblock skip information. Source looks
346 * for PageLRU while target looks for PageBuddy. When the scanner
347 * is found, both PageBuddy and PageLRU are checked as the pageblock
348 * is suitable as both source and target.
350 for (; migrate_pfn
< free_pfn
; migrate_pfn
+= pageblock_nr_pages
,
351 free_pfn
-= pageblock_nr_pages
) {
354 /* Update the migrate PFN */
355 if (__reset_isolation_pfn(zone
, migrate_pfn
, true, source_set
) &&
356 migrate_pfn
< reset_migrate
) {
358 reset_migrate
= migrate_pfn
;
359 zone
->compact_init_migrate_pfn
= reset_migrate
;
360 zone
->compact_cached_migrate_pfn
[0] = reset_migrate
;
361 zone
->compact_cached_migrate_pfn
[1] = reset_migrate
;
364 /* Update the free PFN */
365 if (__reset_isolation_pfn(zone
, free_pfn
, free_set
, true) &&
366 free_pfn
> reset_free
) {
368 reset_free
= free_pfn
;
369 zone
->compact_init_free_pfn
= reset_free
;
370 zone
->compact_cached_free_pfn
= reset_free
;
374 /* Leave no distance if no suitable block was reset */
375 if (reset_migrate
>= reset_free
) {
376 zone
->compact_cached_migrate_pfn
[0] = migrate_pfn
;
377 zone
->compact_cached_migrate_pfn
[1] = migrate_pfn
;
378 zone
->compact_cached_free_pfn
= free_pfn
;
382 void reset_isolation_suitable(pg_data_t
*pgdat
)
386 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
387 struct zone
*zone
= &pgdat
->node_zones
[zoneid
];
388 if (!populated_zone(zone
))
391 /* Only flush if a full compaction finished recently */
392 if (zone
->compact_blockskip_flush
)
393 __reset_isolation_suitable(zone
);
398 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
399 * locks are not required for read/writers. Returns true if it was already set.
401 static bool test_and_set_skip(struct compact_control
*cc
, struct page
*page
,
406 /* Do no update if skip hint is being ignored */
407 if (cc
->ignore_skip_hint
)
410 if (!IS_ALIGNED(pfn
, pageblock_nr_pages
))
413 skip
= get_pageblock_skip(page
);
414 if (!skip
&& !cc
->no_set_skip_hint
)
415 set_pageblock_skip(page
);
420 static void update_cached_migrate(struct compact_control
*cc
, unsigned long pfn
)
422 struct zone
*zone
= cc
->zone
;
424 pfn
= pageblock_end_pfn(pfn
);
426 /* Set for isolation rather than compaction */
427 if (cc
->no_set_skip_hint
)
430 if (pfn
> zone
->compact_cached_migrate_pfn
[0])
431 zone
->compact_cached_migrate_pfn
[0] = pfn
;
432 if (cc
->mode
!= MIGRATE_ASYNC
&&
433 pfn
> zone
->compact_cached_migrate_pfn
[1])
434 zone
->compact_cached_migrate_pfn
[1] = pfn
;
438 * If no pages were isolated then mark this pageblock to be skipped in the
439 * future. The information is later cleared by __reset_isolation_suitable().
441 static void update_pageblock_skip(struct compact_control
*cc
,
442 struct page
*page
, unsigned long pfn
)
444 struct zone
*zone
= cc
->zone
;
446 if (cc
->no_set_skip_hint
)
452 set_pageblock_skip(page
);
454 /* Update where async and sync compaction should restart */
455 if (pfn
< zone
->compact_cached_free_pfn
)
456 zone
->compact_cached_free_pfn
= pfn
;
459 static inline bool isolation_suitable(struct compact_control
*cc
,
465 static inline bool pageblock_skip_persistent(struct page
*page
)
470 static inline void update_pageblock_skip(struct compact_control
*cc
,
471 struct page
*page
, unsigned long pfn
)
475 static void update_cached_migrate(struct compact_control
*cc
, unsigned long pfn
)
479 static bool test_and_set_skip(struct compact_control
*cc
, struct page
*page
,
484 #endif /* CONFIG_COMPACTION */
487 * Compaction requires the taking of some coarse locks that are potentially
488 * very heavily contended. For async compaction, trylock and record if the
489 * lock is contended. The lock will still be acquired but compaction will
490 * abort when the current block is finished regardless of success rate.
491 * Sync compaction acquires the lock.
493 * Always returns true which makes it easier to track lock state in callers.
495 static bool compact_lock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
496 struct compact_control
*cc
)
499 /* Track if the lock is contended in async mode */
500 if (cc
->mode
== MIGRATE_ASYNC
&& !cc
->contended
) {
501 if (spin_trylock_irqsave(lock
, *flags
))
504 cc
->contended
= true;
507 spin_lock_irqsave(lock
, *flags
);
512 * Compaction requires the taking of some coarse locks that are potentially
513 * very heavily contended. The lock should be periodically unlocked to avoid
514 * having disabled IRQs for a long time, even when there is nobody waiting on
515 * the lock. It might also be that allowing the IRQs will result in
516 * need_resched() becoming true. If scheduling is needed, compaction schedules.
517 * Either compaction type will also abort if a fatal signal is pending.
518 * In either case if the lock was locked, it is dropped and not regained.
520 * Returns true if compaction should abort due to fatal signal pending.
521 * Returns false when compaction can continue.
523 static bool compact_unlock_should_abort(spinlock_t
*lock
,
524 unsigned long flags
, bool *locked
, struct compact_control
*cc
)
527 spin_unlock_irqrestore(lock
, flags
);
531 if (fatal_signal_pending(current
)) {
532 cc
->contended
= true;
542 * Isolate free pages onto a private freelist. If @strict is true, will abort
543 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
544 * (even though it may still end up isolating some pages).
546 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
547 unsigned long *start_pfn
,
548 unsigned long end_pfn
,
549 struct list_head
*freelist
,
553 int nr_scanned
= 0, total_isolated
= 0;
555 unsigned long flags
= 0;
557 unsigned long blockpfn
= *start_pfn
;
560 /* Strict mode is for isolation, speed is secondary */
564 cursor
= pfn_to_page(blockpfn
);
566 /* Isolate free pages. */
567 for (; blockpfn
< end_pfn
; blockpfn
+= stride
, cursor
+= stride
) {
569 struct page
*page
= cursor
;
572 * Periodically drop the lock (if held) regardless of its
573 * contention, to give chance to IRQs. Abort if fatal signal
576 if (!(blockpfn
% COMPACT_CLUSTER_MAX
)
577 && compact_unlock_should_abort(&cc
->zone
->lock
, flags
,
584 * For compound pages such as THP and hugetlbfs, we can save
585 * potentially a lot of iterations if we skip them at once.
586 * The check is racy, but we can consider only valid values
587 * and the only danger is skipping too much.
589 if (PageCompound(page
)) {
590 const unsigned int order
= compound_order(page
);
592 if (likely(order
< MAX_ORDER
)) {
593 blockpfn
+= (1UL << order
) - 1;
594 cursor
+= (1UL << order
) - 1;
599 if (!PageBuddy(page
))
602 /* If we already hold the lock, we can skip some rechecking. */
604 locked
= compact_lock_irqsave(&cc
->zone
->lock
,
607 /* Recheck this is a buddy page under lock */
608 if (!PageBuddy(page
))
612 /* Found a free page, will break it into order-0 pages */
613 order
= buddy_order(page
);
614 isolated
= __isolate_free_page(page
, order
);
617 set_page_private(page
, order
);
619 total_isolated
+= isolated
;
620 cc
->nr_freepages
+= isolated
;
621 list_add_tail(&page
->lru
, freelist
);
623 if (!strict
&& cc
->nr_migratepages
<= cc
->nr_freepages
) {
624 blockpfn
+= isolated
;
627 /* Advance to the end of split page */
628 blockpfn
+= isolated
- 1;
629 cursor
+= isolated
- 1;
641 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
644 * There is a tiny chance that we have read bogus compound_order(),
645 * so be careful to not go outside of the pageblock.
647 if (unlikely(blockpfn
> end_pfn
))
650 trace_mm_compaction_isolate_freepages(*start_pfn
, blockpfn
,
651 nr_scanned
, total_isolated
);
653 /* Record how far we have got within the block */
654 *start_pfn
= blockpfn
;
657 * If strict isolation is requested by CMA then check that all the
658 * pages requested were isolated. If there were any failures, 0 is
659 * returned and CMA will fail.
661 if (strict
&& blockpfn
< end_pfn
)
664 cc
->total_free_scanned
+= nr_scanned
;
666 count_compact_events(COMPACTISOLATED
, total_isolated
);
667 return total_isolated
;
671 * isolate_freepages_range() - isolate free pages.
672 * @cc: Compaction control structure.
673 * @start_pfn: The first PFN to start isolating.
674 * @end_pfn: The one-past-last PFN.
676 * Non-free pages, invalid PFNs, or zone boundaries within the
677 * [start_pfn, end_pfn) range are considered errors, cause function to
678 * undo its actions and return zero.
680 * Otherwise, function returns one-past-the-last PFN of isolated page
681 * (which may be greater then end_pfn if end fell in a middle of
685 isolate_freepages_range(struct compact_control
*cc
,
686 unsigned long start_pfn
, unsigned long end_pfn
)
688 unsigned long isolated
, pfn
, block_start_pfn
, block_end_pfn
;
692 block_start_pfn
= pageblock_start_pfn(pfn
);
693 if (block_start_pfn
< cc
->zone
->zone_start_pfn
)
694 block_start_pfn
= cc
->zone
->zone_start_pfn
;
695 block_end_pfn
= pageblock_end_pfn(pfn
);
697 for (; pfn
< end_pfn
; pfn
+= isolated
,
698 block_start_pfn
= block_end_pfn
,
699 block_end_pfn
+= pageblock_nr_pages
) {
700 /* Protect pfn from changing by isolate_freepages_block */
701 unsigned long isolate_start_pfn
= pfn
;
703 block_end_pfn
= min(block_end_pfn
, end_pfn
);
706 * pfn could pass the block_end_pfn if isolated freepage
707 * is more than pageblock order. In this case, we adjust
708 * scanning range to right one.
710 if (pfn
>= block_end_pfn
) {
711 block_start_pfn
= pageblock_start_pfn(pfn
);
712 block_end_pfn
= pageblock_end_pfn(pfn
);
713 block_end_pfn
= min(block_end_pfn
, end_pfn
);
716 if (!pageblock_pfn_to_page(block_start_pfn
,
717 block_end_pfn
, cc
->zone
))
720 isolated
= isolate_freepages_block(cc
, &isolate_start_pfn
,
721 block_end_pfn
, &freelist
, 0, true);
724 * In strict mode, isolate_freepages_block() returns 0 if
725 * there are any holes in the block (ie. invalid PFNs or
732 * If we managed to isolate pages, it is always (1 << n) *
733 * pageblock_nr_pages for some non-negative n. (Max order
734 * page may span two pageblocks).
738 /* __isolate_free_page() does not map the pages */
739 split_map_pages(&freelist
);
742 /* Loop terminated early, cleanup. */
743 release_freepages(&freelist
);
747 /* We don't use freelists for anything. */
751 /* Similar to reclaim, but different enough that they don't share logic */
752 static bool too_many_isolated(pg_data_t
*pgdat
)
756 unsigned long active
, inactive
, isolated
;
758 inactive
= node_page_state(pgdat
, NR_INACTIVE_FILE
) +
759 node_page_state(pgdat
, NR_INACTIVE_ANON
);
760 active
= node_page_state(pgdat
, NR_ACTIVE_FILE
) +
761 node_page_state(pgdat
, NR_ACTIVE_ANON
);
762 isolated
= node_page_state(pgdat
, NR_ISOLATED_FILE
) +
763 node_page_state(pgdat
, NR_ISOLATED_ANON
);
765 too_many
= isolated
> (inactive
+ active
) / 2;
767 wake_throttle_isolated(pgdat
);
773 * isolate_migratepages_block() - isolate all migrate-able pages within
775 * @cc: Compaction control structure.
776 * @low_pfn: The first PFN to isolate
777 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
778 * @mode: Isolation mode to be used.
780 * Isolate all pages that can be migrated from the range specified by
781 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
782 * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
783 * -ENOMEM in case we could not allocate a page, or 0.
784 * cc->migrate_pfn will contain the next pfn to scan.
786 * The pages are isolated on cc->migratepages list (not required to be empty),
787 * and cc->nr_migratepages is updated accordingly.
790 isolate_migratepages_block(struct compact_control
*cc
, unsigned long low_pfn
,
791 unsigned long end_pfn
, isolate_mode_t mode
)
793 pg_data_t
*pgdat
= cc
->zone
->zone_pgdat
;
794 unsigned long nr_scanned
= 0, nr_isolated
= 0;
795 struct lruvec
*lruvec
;
796 unsigned long flags
= 0;
797 struct lruvec
*locked
= NULL
;
798 struct page
*page
= NULL
, *valid_page
= NULL
;
799 struct address_space
*mapping
;
800 unsigned long start_pfn
= low_pfn
;
801 bool skip_on_failure
= false;
802 unsigned long next_skip_pfn
= 0;
803 bool skip_updated
= false;
806 cc
->migrate_pfn
= low_pfn
;
809 * Ensure that there are not too many pages isolated from the LRU
810 * list by either parallel reclaimers or compaction. If there are,
811 * delay for some time until fewer pages are isolated
813 while (unlikely(too_many_isolated(pgdat
))) {
814 /* stop isolation if there are still pages not migrated */
815 if (cc
->nr_migratepages
)
818 /* async migration should just abort */
819 if (cc
->mode
== MIGRATE_ASYNC
)
822 reclaim_throttle(pgdat
, VMSCAN_THROTTLE_ISOLATED
);
824 if (fatal_signal_pending(current
))
830 if (cc
->direct_compaction
&& (cc
->mode
== MIGRATE_ASYNC
)) {
831 skip_on_failure
= true;
832 next_skip_pfn
= block_end_pfn(low_pfn
, cc
->order
);
835 /* Time to isolate some pages for migration */
836 for (; low_pfn
< end_pfn
; low_pfn
++) {
838 if (skip_on_failure
&& low_pfn
>= next_skip_pfn
) {
840 * We have isolated all migration candidates in the
841 * previous order-aligned block, and did not skip it due
842 * to failure. We should migrate the pages now and
843 * hopefully succeed compaction.
849 * We failed to isolate in the previous order-aligned
850 * block. Set the new boundary to the end of the
851 * current block. Note we can't simply increase
852 * next_skip_pfn by 1 << order, as low_pfn might have
853 * been incremented by a higher number due to skipping
854 * a compound or a high-order buddy page in the
855 * previous loop iteration.
857 next_skip_pfn
= block_end_pfn(low_pfn
, cc
->order
);
861 * Periodically drop the lock (if held) regardless of its
862 * contention, to give chance to IRQs. Abort completely if
863 * a fatal signal is pending.
865 if (!(low_pfn
% COMPACT_CLUSTER_MAX
)) {
867 unlock_page_lruvec_irqrestore(locked
, flags
);
871 if (fatal_signal_pending(current
)) {
872 cc
->contended
= true;
883 page
= pfn_to_page(low_pfn
);
886 * Check if the pageblock has already been marked skipped.
887 * Only the aligned PFN is checked as the caller isolates
888 * COMPACT_CLUSTER_MAX at a time so the second call must
889 * not falsely conclude that the block should be skipped.
891 if (!valid_page
&& IS_ALIGNED(low_pfn
, pageblock_nr_pages
)) {
892 if (!isolation_suitable(cc
, page
)) {
900 if (PageHuge(page
) && cc
->alloc_contig
) {
901 ret
= isolate_or_dissolve_huge_page(page
, &cc
->migratepages
);
904 * Fail isolation in case isolate_or_dissolve_huge_page()
905 * reports an error. In case of -ENOMEM, abort right away.
908 /* Do not report -EBUSY down the chain */
911 low_pfn
+= compound_nr(page
) - 1;
915 if (PageHuge(page
)) {
917 * Hugepage was successfully isolated and placed
918 * on the cc->migratepages list.
920 low_pfn
+= compound_nr(page
) - 1;
921 goto isolate_success_no_list
;
925 * Ok, the hugepage was dissolved. Now these pages are
926 * Buddy and cannot be re-allocated because they are
927 * isolated. Fall-through as the check below handles
933 * Skip if free. We read page order here without zone lock
934 * which is generally unsafe, but the race window is small and
935 * the worst thing that can happen is that we skip some
936 * potential isolation targets.
938 if (PageBuddy(page
)) {
939 unsigned long freepage_order
= buddy_order_unsafe(page
);
942 * Without lock, we cannot be sure that what we got is
943 * a valid page order. Consider only values in the
944 * valid order range to prevent low_pfn overflow.
946 if (freepage_order
> 0 && freepage_order
< MAX_ORDER
)
947 low_pfn
+= (1UL << freepage_order
) - 1;
952 * Regardless of being on LRU, compound pages such as THP and
953 * hugetlbfs are not to be compacted unless we are attempting
954 * an allocation much larger than the huge page size (eg CMA).
955 * We can potentially save a lot of iterations if we skip them
956 * at once. The check is racy, but we can consider only valid
957 * values and the only danger is skipping too much.
959 if (PageCompound(page
) && !cc
->alloc_contig
) {
960 const unsigned int order
= compound_order(page
);
962 if (likely(order
< MAX_ORDER
))
963 low_pfn
+= (1UL << order
) - 1;
968 * Check may be lockless but that's ok as we recheck later.
969 * It's possible to migrate LRU and non-lru movable pages.
970 * Skip any other type of page
972 if (!PageLRU(page
)) {
974 * __PageMovable can return false positive so we need
975 * to verify it under page_lock.
977 if (unlikely(__PageMovable(page
)) &&
978 !PageIsolated(page
)) {
980 unlock_page_lruvec_irqrestore(locked
, flags
);
984 if (!isolate_movable_page(page
, mode
))
985 goto isolate_success
;
992 * Migration will fail if an anonymous page is pinned in memory,
993 * so avoid taking lru_lock and isolating it unnecessarily in an
994 * admittedly racy check.
996 mapping
= page_mapping(page
);
997 if (!mapping
&& page_count(page
) > page_mapcount(page
))
1001 * Only allow to migrate anonymous pages in GFP_NOFS context
1002 * because those do not depend on fs locks.
1004 if (!(cc
->gfp_mask
& __GFP_FS
) && mapping
)
1008 * Be careful not to clear PageLRU until after we're
1009 * sure the page is not being freed elsewhere -- the
1010 * page release code relies on it.
1012 if (unlikely(!get_page_unless_zero(page
)))
1015 /* Only take pages on LRU: a check now makes later tests safe */
1017 goto isolate_fail_put
;
1019 /* Compaction might skip unevictable pages but CMA takes them */
1020 if (!(mode
& ISOLATE_UNEVICTABLE
) && PageUnevictable(page
))
1021 goto isolate_fail_put
;
1024 * To minimise LRU disruption, the caller can indicate with
1025 * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages
1026 * it will be able to migrate without blocking - clean pages
1027 * for the most part. PageWriteback would require blocking.
1029 if ((mode
& ISOLATE_ASYNC_MIGRATE
) && PageWriteback(page
))
1030 goto isolate_fail_put
;
1032 if ((mode
& ISOLATE_ASYNC_MIGRATE
) && PageDirty(page
)) {
1036 * Only pages without mappings or that have a
1037 * ->migratepage callback are possible to migrate
1038 * without blocking. However, we can be racing with
1039 * truncation so it's necessary to lock the page
1040 * to stabilise the mapping as truncation holds
1041 * the page lock until after the page is removed
1042 * from the page cache.
1044 if (!trylock_page(page
))
1045 goto isolate_fail_put
;
1047 mapping
= page_mapping(page
);
1048 migrate_dirty
= !mapping
|| mapping
->a_ops
->migratepage
;
1051 goto isolate_fail_put
;
1054 /* Try isolate the page */
1055 if (!TestClearPageLRU(page
))
1056 goto isolate_fail_put
;
1058 lruvec
= folio_lruvec(page_folio(page
));
1060 /* If we already hold the lock, we can skip some rechecking */
1061 if (lruvec
!= locked
) {
1063 unlock_page_lruvec_irqrestore(locked
, flags
);
1065 compact_lock_irqsave(&lruvec
->lru_lock
, &flags
, cc
);
1068 lruvec_memcg_debug(lruvec
, page_folio(page
));
1070 /* Try get exclusive access under lock */
1071 if (!skip_updated
) {
1072 skip_updated
= true;
1073 if (test_and_set_skip(cc
, page
, low_pfn
))
1078 * Page become compound since the non-locked check,
1079 * and it's on LRU. It can only be a THP so the order
1080 * is safe to read and it's 0 for tail pages.
1082 if (unlikely(PageCompound(page
) && !cc
->alloc_contig
)) {
1083 low_pfn
+= compound_nr(page
) - 1;
1085 goto isolate_fail_put
;
1089 /* The whole page is taken off the LRU; skip the tail pages. */
1090 if (PageCompound(page
))
1091 low_pfn
+= compound_nr(page
) - 1;
1093 /* Successfully isolated */
1094 del_page_from_lru_list(page
, lruvec
);
1095 mod_node_page_state(page_pgdat(page
),
1096 NR_ISOLATED_ANON
+ page_is_file_lru(page
),
1097 thp_nr_pages(page
));
1100 list_add(&page
->lru
, &cc
->migratepages
);
1101 isolate_success_no_list
:
1102 cc
->nr_migratepages
+= compound_nr(page
);
1103 nr_isolated
+= compound_nr(page
);
1106 * Avoid isolating too much unless this block is being
1107 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1108 * or a lock is contended. For contention, isolate quickly to
1109 * potentially remove one source of contention.
1111 if (cc
->nr_migratepages
>= COMPACT_CLUSTER_MAX
&&
1112 !cc
->rescan
&& !cc
->contended
) {
1120 /* Avoid potential deadlock in freeing page under lru_lock */
1122 unlock_page_lruvec_irqrestore(locked
, flags
);
1128 if (!skip_on_failure
&& ret
!= -ENOMEM
)
1132 * We have isolated some pages, but then failed. Release them
1133 * instead of migrating, as we cannot form the cc->order buddy
1138 unlock_page_lruvec_irqrestore(locked
, flags
);
1141 putback_movable_pages(&cc
->migratepages
);
1142 cc
->nr_migratepages
= 0;
1146 if (low_pfn
< next_skip_pfn
) {
1147 low_pfn
= next_skip_pfn
- 1;
1149 * The check near the loop beginning would have updated
1150 * next_skip_pfn too, but this is a bit simpler.
1152 next_skip_pfn
+= 1UL << cc
->order
;
1160 * The PageBuddy() check could have potentially brought us outside
1161 * the range to be scanned.
1163 if (unlikely(low_pfn
> end_pfn
))
1170 unlock_page_lruvec_irqrestore(locked
, flags
);
1177 * Updated the cached scanner pfn once the pageblock has been scanned
1178 * Pages will either be migrated in which case there is no point
1179 * scanning in the near future or migration failed in which case the
1180 * failure reason may persist. The block is marked for skipping if
1181 * there were no pages isolated in the block or if the block is
1182 * rescanned twice in a row.
1184 if (low_pfn
== end_pfn
&& (!nr_isolated
|| cc
->rescan
)) {
1185 if (valid_page
&& !skip_updated
)
1186 set_pageblock_skip(valid_page
);
1187 update_cached_migrate(cc
, low_pfn
);
1190 trace_mm_compaction_isolate_migratepages(start_pfn
, low_pfn
,
1191 nr_scanned
, nr_isolated
);
1194 cc
->total_migrate_scanned
+= nr_scanned
;
1196 count_compact_events(COMPACTISOLATED
, nr_isolated
);
1198 cc
->migrate_pfn
= low_pfn
;
1204 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1205 * @cc: Compaction control structure.
1206 * @start_pfn: The first PFN to start isolating.
1207 * @end_pfn: The one-past-last PFN.
1209 * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
1210 * in case we could not allocate a page, or 0.
1213 isolate_migratepages_range(struct compact_control
*cc
, unsigned long start_pfn
,
1214 unsigned long end_pfn
)
1216 unsigned long pfn
, block_start_pfn
, block_end_pfn
;
1219 /* Scan block by block. First and last block may be incomplete */
1221 block_start_pfn
= pageblock_start_pfn(pfn
);
1222 if (block_start_pfn
< cc
->zone
->zone_start_pfn
)
1223 block_start_pfn
= cc
->zone
->zone_start_pfn
;
1224 block_end_pfn
= pageblock_end_pfn(pfn
);
1226 for (; pfn
< end_pfn
; pfn
= block_end_pfn
,
1227 block_start_pfn
= block_end_pfn
,
1228 block_end_pfn
+= pageblock_nr_pages
) {
1230 block_end_pfn
= min(block_end_pfn
, end_pfn
);
1232 if (!pageblock_pfn_to_page(block_start_pfn
,
1233 block_end_pfn
, cc
->zone
))
1236 ret
= isolate_migratepages_block(cc
, pfn
, block_end_pfn
,
1237 ISOLATE_UNEVICTABLE
);
1242 if (cc
->nr_migratepages
>= COMPACT_CLUSTER_MAX
)
1249 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
1250 #ifdef CONFIG_COMPACTION
1252 static bool suitable_migration_source(struct compact_control
*cc
,
1257 if (pageblock_skip_persistent(page
))
1260 if ((cc
->mode
!= MIGRATE_ASYNC
) || !cc
->direct_compaction
)
1263 block_mt
= get_pageblock_migratetype(page
);
1265 if (cc
->migratetype
== MIGRATE_MOVABLE
)
1266 return is_migrate_movable(block_mt
);
1268 return block_mt
== cc
->migratetype
;
1271 /* Returns true if the page is within a block suitable for migration to */
1272 static bool suitable_migration_target(struct compact_control
*cc
,
1275 /* If the page is a large free page, then disallow migration */
1276 if (PageBuddy(page
)) {
1278 * We are checking page_order without zone->lock taken. But
1279 * the only small danger is that we skip a potentially suitable
1280 * pageblock, so it's not worth to check order for valid range.
1282 if (buddy_order_unsafe(page
) >= pageblock_order
)
1286 if (cc
->ignore_block_suitable
)
1289 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1290 if (is_migrate_movable(get_pageblock_migratetype(page
)))
1293 /* Otherwise skip the block */
1297 static inline unsigned int
1298 freelist_scan_limit(struct compact_control
*cc
)
1300 unsigned short shift
= BITS_PER_LONG
- 1;
1302 return (COMPACT_CLUSTER_MAX
>> min(shift
, cc
->fast_search_fail
)) + 1;
1306 * Test whether the free scanner has reached the same or lower pageblock than
1307 * the migration scanner, and compaction should thus terminate.
1309 static inline bool compact_scanners_met(struct compact_control
*cc
)
1311 return (cc
->free_pfn
>> pageblock_order
)
1312 <= (cc
->migrate_pfn
>> pageblock_order
);
1316 * Used when scanning for a suitable migration target which scans freelists
1317 * in reverse. Reorders the list such as the unscanned pages are scanned
1318 * first on the next iteration of the free scanner
1321 move_freelist_head(struct list_head
*freelist
, struct page
*freepage
)
1325 if (!list_is_last(freelist
, &freepage
->lru
)) {
1326 list_cut_before(&sublist
, freelist
, &freepage
->lru
);
1327 list_splice_tail(&sublist
, freelist
);
1332 * Similar to move_freelist_head except used by the migration scanner
1333 * when scanning forward. It's possible for these list operations to
1334 * move against each other if they search the free list exactly in
1338 move_freelist_tail(struct list_head
*freelist
, struct page
*freepage
)
1342 if (!list_is_first(freelist
, &freepage
->lru
)) {
1343 list_cut_position(&sublist
, freelist
, &freepage
->lru
);
1344 list_splice_tail(&sublist
, freelist
);
1349 fast_isolate_around(struct compact_control
*cc
, unsigned long pfn
, unsigned long nr_isolated
)
1351 unsigned long start_pfn
, end_pfn
;
1354 /* Do not search around if there are enough pages already */
1355 if (cc
->nr_freepages
>= cc
->nr_migratepages
)
1358 /* Minimise scanning during async compaction */
1359 if (cc
->direct_compaction
&& cc
->mode
== MIGRATE_ASYNC
)
1362 /* Pageblock boundaries */
1363 start_pfn
= max(pageblock_start_pfn(pfn
), cc
->zone
->zone_start_pfn
);
1364 end_pfn
= min(pageblock_end_pfn(pfn
), zone_end_pfn(cc
->zone
));
1366 page
= pageblock_pfn_to_page(start_pfn
, end_pfn
, cc
->zone
);
1371 if (start_pfn
!= pfn
) {
1372 isolate_freepages_block(cc
, &start_pfn
, pfn
, &cc
->freepages
, 1, false);
1373 if (cc
->nr_freepages
>= cc
->nr_migratepages
)
1378 start_pfn
= pfn
+ nr_isolated
;
1379 if (start_pfn
< end_pfn
)
1380 isolate_freepages_block(cc
, &start_pfn
, end_pfn
, &cc
->freepages
, 1, false);
1382 /* Skip this pageblock in the future as it's full or nearly full */
1383 if (cc
->nr_freepages
< cc
->nr_migratepages
)
1384 set_pageblock_skip(page
);
1387 /* Search orders in round-robin fashion */
1388 static int next_search_order(struct compact_control
*cc
, int order
)
1392 order
= cc
->order
- 1;
1394 /* Search wrapped around? */
1395 if (order
== cc
->search_order
) {
1397 if (cc
->search_order
< 0)
1398 cc
->search_order
= cc
->order
- 1;
1405 static unsigned long
1406 fast_isolate_freepages(struct compact_control
*cc
)
1408 unsigned int limit
= max(1U, freelist_scan_limit(cc
) >> 1);
1409 unsigned int nr_scanned
= 0;
1410 unsigned long low_pfn
, min_pfn
, highest
= 0;
1411 unsigned long nr_isolated
= 0;
1412 unsigned long distance
;
1413 struct page
*page
= NULL
;
1414 bool scan_start
= false;
1417 /* Full compaction passes in a negative order */
1419 return cc
->free_pfn
;
1422 * If starting the scan, use a deeper search and use the highest
1423 * PFN found if a suitable one is not found.
1425 if (cc
->free_pfn
>= cc
->zone
->compact_init_free_pfn
) {
1426 limit
= pageblock_nr_pages
>> 1;
1431 * Preferred point is in the top quarter of the scan space but take
1432 * a pfn from the top half if the search is problematic.
1434 distance
= (cc
->free_pfn
- cc
->migrate_pfn
);
1435 low_pfn
= pageblock_start_pfn(cc
->free_pfn
- (distance
>> 2));
1436 min_pfn
= pageblock_start_pfn(cc
->free_pfn
- (distance
>> 1));
1438 if (WARN_ON_ONCE(min_pfn
> low_pfn
))
1442 * Search starts from the last successful isolation order or the next
1443 * order to search after a previous failure
1445 cc
->search_order
= min_t(unsigned int, cc
->order
- 1, cc
->search_order
);
1447 for (order
= cc
->search_order
;
1448 !page
&& order
>= 0;
1449 order
= next_search_order(cc
, order
)) {
1450 struct free_area
*area
= &cc
->zone
->free_area
[order
];
1451 struct list_head
*freelist
;
1452 struct page
*freepage
;
1453 unsigned long flags
;
1454 unsigned int order_scanned
= 0;
1455 unsigned long high_pfn
= 0;
1460 spin_lock_irqsave(&cc
->zone
->lock
, flags
);
1461 freelist
= &area
->free_list
[MIGRATE_MOVABLE
];
1462 list_for_each_entry_reverse(freepage
, freelist
, lru
) {
1467 pfn
= page_to_pfn(freepage
);
1470 highest
= max(pageblock_start_pfn(pfn
),
1471 cc
->zone
->zone_start_pfn
);
1473 if (pfn
>= low_pfn
) {
1474 cc
->fast_search_fail
= 0;
1475 cc
->search_order
= order
;
1480 if (pfn
>= min_pfn
&& pfn
> high_pfn
) {
1483 /* Shorten the scan if a candidate is found */
1487 if (order_scanned
>= limit
)
1491 /* Use a minimum pfn if a preferred one was not found */
1492 if (!page
&& high_pfn
) {
1493 page
= pfn_to_page(high_pfn
);
1495 /* Update freepage for the list reorder below */
1499 /* Reorder to so a future search skips recent pages */
1500 move_freelist_head(freelist
, freepage
);
1502 /* Isolate the page if available */
1504 if (__isolate_free_page(page
, order
)) {
1505 set_page_private(page
, order
);
1506 nr_isolated
= 1 << order
;
1507 cc
->nr_freepages
+= nr_isolated
;
1508 list_add_tail(&page
->lru
, &cc
->freepages
);
1509 count_compact_events(COMPACTISOLATED
, nr_isolated
);
1511 /* If isolation fails, abort the search */
1512 order
= cc
->search_order
+ 1;
1517 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
1520 * Smaller scan on next order so the total scan is related
1521 * to freelist_scan_limit.
1523 if (order_scanned
>= limit
)
1524 limit
= max(1U, limit
>> 1);
1528 cc
->fast_search_fail
++;
1531 * Use the highest PFN found above min. If one was
1532 * not found, be pessimistic for direct compaction
1533 * and use the min mark.
1535 if (highest
>= min_pfn
) {
1536 page
= pfn_to_page(highest
);
1537 cc
->free_pfn
= highest
;
1539 if (cc
->direct_compaction
&& pfn_valid(min_pfn
)) {
1540 page
= pageblock_pfn_to_page(min_pfn
,
1541 min(pageblock_end_pfn(min_pfn
),
1542 zone_end_pfn(cc
->zone
)),
1544 cc
->free_pfn
= min_pfn
;
1550 if (highest
&& highest
>= cc
->zone
->compact_cached_free_pfn
) {
1551 highest
-= pageblock_nr_pages
;
1552 cc
->zone
->compact_cached_free_pfn
= highest
;
1555 cc
->total_free_scanned
+= nr_scanned
;
1557 return cc
->free_pfn
;
1559 low_pfn
= page_to_pfn(page
);
1560 fast_isolate_around(cc
, low_pfn
, nr_isolated
);
1565 * Based on information in the current compact_control, find blocks
1566 * suitable for isolating free pages from and then isolate them.
1568 static void isolate_freepages(struct compact_control
*cc
)
1570 struct zone
*zone
= cc
->zone
;
1572 unsigned long block_start_pfn
; /* start of current pageblock */
1573 unsigned long isolate_start_pfn
; /* exact pfn we start at */
1574 unsigned long block_end_pfn
; /* end of current pageblock */
1575 unsigned long low_pfn
; /* lowest pfn scanner is able to scan */
1576 struct list_head
*freelist
= &cc
->freepages
;
1577 unsigned int stride
;
1579 /* Try a small search of the free lists for a candidate */
1580 fast_isolate_freepages(cc
);
1581 if (cc
->nr_freepages
)
1585 * Initialise the free scanner. The starting point is where we last
1586 * successfully isolated from, zone-cached value, or the end of the
1587 * zone when isolating for the first time. For looping we also need
1588 * this pfn aligned down to the pageblock boundary, because we do
1589 * block_start_pfn -= pageblock_nr_pages in the for loop.
1590 * For ending point, take care when isolating in last pageblock of a
1591 * zone which ends in the middle of a pageblock.
1592 * The low boundary is the end of the pageblock the migration scanner
1595 isolate_start_pfn
= cc
->free_pfn
;
1596 block_start_pfn
= pageblock_start_pfn(isolate_start_pfn
);
1597 block_end_pfn
= min(block_start_pfn
+ pageblock_nr_pages
,
1598 zone_end_pfn(zone
));
1599 low_pfn
= pageblock_end_pfn(cc
->migrate_pfn
);
1600 stride
= cc
->mode
== MIGRATE_ASYNC
? COMPACT_CLUSTER_MAX
: 1;
1603 * Isolate free pages until enough are available to migrate the
1604 * pages on cc->migratepages. We stop searching if the migrate
1605 * and free page scanners meet or enough free pages are isolated.
1607 for (; block_start_pfn
>= low_pfn
;
1608 block_end_pfn
= block_start_pfn
,
1609 block_start_pfn
-= pageblock_nr_pages
,
1610 isolate_start_pfn
= block_start_pfn
) {
1611 unsigned long nr_isolated
;
1614 * This can iterate a massively long zone without finding any
1615 * suitable migration targets, so periodically check resched.
1617 if (!(block_start_pfn
% (COMPACT_CLUSTER_MAX
* pageblock_nr_pages
)))
1620 page
= pageblock_pfn_to_page(block_start_pfn
, block_end_pfn
,
1625 /* Check the block is suitable for migration */
1626 if (!suitable_migration_target(cc
, page
))
1629 /* If isolation recently failed, do not retry */
1630 if (!isolation_suitable(cc
, page
))
1633 /* Found a block suitable for isolating free pages from. */
1634 nr_isolated
= isolate_freepages_block(cc
, &isolate_start_pfn
,
1635 block_end_pfn
, freelist
, stride
, false);
1637 /* Update the skip hint if the full pageblock was scanned */
1638 if (isolate_start_pfn
== block_end_pfn
)
1639 update_pageblock_skip(cc
, page
, block_start_pfn
);
1641 /* Are enough freepages isolated? */
1642 if (cc
->nr_freepages
>= cc
->nr_migratepages
) {
1643 if (isolate_start_pfn
>= block_end_pfn
) {
1645 * Restart at previous pageblock if more
1646 * freepages can be isolated next time.
1649 block_start_pfn
- pageblock_nr_pages
;
1652 } else if (isolate_start_pfn
< block_end_pfn
) {
1654 * If isolation failed early, do not continue
1660 /* Adjust stride depending on isolation */
1665 stride
= min_t(unsigned int, COMPACT_CLUSTER_MAX
, stride
<< 1);
1669 * Record where the free scanner will restart next time. Either we
1670 * broke from the loop and set isolate_start_pfn based on the last
1671 * call to isolate_freepages_block(), or we met the migration scanner
1672 * and the loop terminated due to isolate_start_pfn < low_pfn
1674 cc
->free_pfn
= isolate_start_pfn
;
1677 /* __isolate_free_page() does not map the pages */
1678 split_map_pages(freelist
);
1682 * This is a migrate-callback that "allocates" freepages by taking pages
1683 * from the isolated freelists in the block we are migrating to.
1685 static struct page
*compaction_alloc(struct page
*migratepage
,
1688 struct compact_control
*cc
= (struct compact_control
*)data
;
1689 struct page
*freepage
;
1691 if (list_empty(&cc
->freepages
)) {
1692 isolate_freepages(cc
);
1694 if (list_empty(&cc
->freepages
))
1698 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
1699 list_del(&freepage
->lru
);
1706 * This is a migrate-callback that "frees" freepages back to the isolated
1707 * freelist. All pages on the freelist are from the same zone, so there is no
1708 * special handling needed for NUMA.
1710 static void compaction_free(struct page
*page
, unsigned long data
)
1712 struct compact_control
*cc
= (struct compact_control
*)data
;
1714 list_add(&page
->lru
, &cc
->freepages
);
1718 /* possible outcome of isolate_migratepages */
1720 ISOLATE_ABORT
, /* Abort compaction now */
1721 ISOLATE_NONE
, /* No pages isolated, continue scanning */
1722 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
1723 } isolate_migrate_t
;
1726 * Allow userspace to control policy on scanning the unevictable LRU for
1727 * compactable pages.
1729 #ifdef CONFIG_PREEMPT_RT
1730 int sysctl_compact_unevictable_allowed __read_mostly
= 0;
1732 int sysctl_compact_unevictable_allowed __read_mostly
= 1;
1736 update_fast_start_pfn(struct compact_control
*cc
, unsigned long pfn
)
1738 if (cc
->fast_start_pfn
== ULONG_MAX
)
1741 if (!cc
->fast_start_pfn
)
1742 cc
->fast_start_pfn
= pfn
;
1744 cc
->fast_start_pfn
= min(cc
->fast_start_pfn
, pfn
);
1747 static inline unsigned long
1748 reinit_migrate_pfn(struct compact_control
*cc
)
1750 if (!cc
->fast_start_pfn
|| cc
->fast_start_pfn
== ULONG_MAX
)
1751 return cc
->migrate_pfn
;
1753 cc
->migrate_pfn
= cc
->fast_start_pfn
;
1754 cc
->fast_start_pfn
= ULONG_MAX
;
1756 return cc
->migrate_pfn
;
1760 * Briefly search the free lists for a migration source that already has
1761 * some free pages to reduce the number of pages that need migration
1762 * before a pageblock is free.
1764 static unsigned long fast_find_migrateblock(struct compact_control
*cc
)
1766 unsigned int limit
= freelist_scan_limit(cc
);
1767 unsigned int nr_scanned
= 0;
1768 unsigned long distance
;
1769 unsigned long pfn
= cc
->migrate_pfn
;
1770 unsigned long high_pfn
;
1772 bool found_block
= false;
1774 /* Skip hints are relied on to avoid repeats on the fast search */
1775 if (cc
->ignore_skip_hint
)
1779 * If the migrate_pfn is not at the start of a zone or the start
1780 * of a pageblock then assume this is a continuation of a previous
1781 * scan restarted due to COMPACT_CLUSTER_MAX.
1783 if (pfn
!= cc
->zone
->zone_start_pfn
&& pfn
!= pageblock_start_pfn(pfn
))
1787 * For smaller orders, just linearly scan as the number of pages
1788 * to migrate should be relatively small and does not necessarily
1789 * justify freeing up a large block for a small allocation.
1791 if (cc
->order
<= PAGE_ALLOC_COSTLY_ORDER
)
1795 * Only allow kcompactd and direct requests for movable pages to
1796 * quickly clear out a MOVABLE pageblock for allocation. This
1797 * reduces the risk that a large movable pageblock is freed for
1798 * an unmovable/reclaimable small allocation.
1800 if (cc
->direct_compaction
&& cc
->migratetype
!= MIGRATE_MOVABLE
)
1804 * When starting the migration scanner, pick any pageblock within the
1805 * first half of the search space. Otherwise try and pick a pageblock
1806 * within the first eighth to reduce the chances that a migration
1807 * target later becomes a source.
1809 distance
= (cc
->free_pfn
- cc
->migrate_pfn
) >> 1;
1810 if (cc
->migrate_pfn
!= cc
->zone
->zone_start_pfn
)
1812 high_pfn
= pageblock_start_pfn(cc
->migrate_pfn
+ distance
);
1814 for (order
= cc
->order
- 1;
1815 order
>= PAGE_ALLOC_COSTLY_ORDER
&& !found_block
&& nr_scanned
< limit
;
1817 struct free_area
*area
= &cc
->zone
->free_area
[order
];
1818 struct list_head
*freelist
;
1819 unsigned long flags
;
1820 struct page
*freepage
;
1825 spin_lock_irqsave(&cc
->zone
->lock
, flags
);
1826 freelist
= &area
->free_list
[MIGRATE_MOVABLE
];
1827 list_for_each_entry(freepage
, freelist
, lru
) {
1828 unsigned long free_pfn
;
1830 if (nr_scanned
++ >= limit
) {
1831 move_freelist_tail(freelist
, freepage
);
1835 free_pfn
= page_to_pfn(freepage
);
1836 if (free_pfn
< high_pfn
) {
1838 * Avoid if skipped recently. Ideally it would
1839 * move to the tail but even safe iteration of
1840 * the list assumes an entry is deleted, not
1843 if (get_pageblock_skip(freepage
))
1846 /* Reorder to so a future search skips recent pages */
1847 move_freelist_tail(freelist
, freepage
);
1849 update_fast_start_pfn(cc
, free_pfn
);
1850 pfn
= pageblock_start_pfn(free_pfn
);
1851 if (pfn
< cc
->zone
->zone_start_pfn
)
1852 pfn
= cc
->zone
->zone_start_pfn
;
1853 cc
->fast_search_fail
= 0;
1855 set_pageblock_skip(freepage
);
1859 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
1862 cc
->total_migrate_scanned
+= nr_scanned
;
1865 * If fast scanning failed then use a cached entry for a page block
1866 * that had free pages as the basis for starting a linear scan.
1869 cc
->fast_search_fail
++;
1870 pfn
= reinit_migrate_pfn(cc
);
1876 * Isolate all pages that can be migrated from the first suitable block,
1877 * starting at the block pointed to by the migrate scanner pfn within
1880 static isolate_migrate_t
isolate_migratepages(struct compact_control
*cc
)
1882 unsigned long block_start_pfn
;
1883 unsigned long block_end_pfn
;
1884 unsigned long low_pfn
;
1886 const isolate_mode_t isolate_mode
=
1887 (sysctl_compact_unevictable_allowed
? ISOLATE_UNEVICTABLE
: 0) |
1888 (cc
->mode
!= MIGRATE_SYNC
? ISOLATE_ASYNC_MIGRATE
: 0);
1889 bool fast_find_block
;
1892 * Start at where we last stopped, or beginning of the zone as
1893 * initialized by compact_zone(). The first failure will use
1894 * the lowest PFN as the starting point for linear scanning.
1896 low_pfn
= fast_find_migrateblock(cc
);
1897 block_start_pfn
= pageblock_start_pfn(low_pfn
);
1898 if (block_start_pfn
< cc
->zone
->zone_start_pfn
)
1899 block_start_pfn
= cc
->zone
->zone_start_pfn
;
1902 * fast_find_migrateblock marks a pageblock skipped so to avoid
1903 * the isolation_suitable check below, check whether the fast
1904 * search was successful.
1906 fast_find_block
= low_pfn
!= cc
->migrate_pfn
&& !cc
->fast_search_fail
;
1908 /* Only scan within a pageblock boundary */
1909 block_end_pfn
= pageblock_end_pfn(low_pfn
);
1912 * Iterate over whole pageblocks until we find the first suitable.
1913 * Do not cross the free scanner.
1915 for (; block_end_pfn
<= cc
->free_pfn
;
1916 fast_find_block
= false,
1917 cc
->migrate_pfn
= low_pfn
= block_end_pfn
,
1918 block_start_pfn
= block_end_pfn
,
1919 block_end_pfn
+= pageblock_nr_pages
) {
1922 * This can potentially iterate a massively long zone with
1923 * many pageblocks unsuitable, so periodically check if we
1926 if (!(low_pfn
% (COMPACT_CLUSTER_MAX
* pageblock_nr_pages
)))
1929 page
= pageblock_pfn_to_page(block_start_pfn
,
1930 block_end_pfn
, cc
->zone
);
1935 * If isolation recently failed, do not retry. Only check the
1936 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1937 * to be visited multiple times. Assume skip was checked
1938 * before making it "skip" so other compaction instances do
1939 * not scan the same block.
1941 if (IS_ALIGNED(low_pfn
, pageblock_nr_pages
) &&
1942 !fast_find_block
&& !isolation_suitable(cc
, page
))
1946 * For async direct compaction, only scan the pageblocks of the
1947 * same migratetype without huge pages. Async direct compaction
1948 * is optimistic to see if the minimum amount of work satisfies
1949 * the allocation. The cached PFN is updated as it's possible
1950 * that all remaining blocks between source and target are
1951 * unsuitable and the compaction scanners fail to meet.
1953 if (!suitable_migration_source(cc
, page
)) {
1954 update_cached_migrate(cc
, block_end_pfn
);
1958 /* Perform the isolation */
1959 if (isolate_migratepages_block(cc
, low_pfn
, block_end_pfn
,
1961 return ISOLATE_ABORT
;
1964 * Either we isolated something and proceed with migration. Or
1965 * we failed and compact_zone should decide if we should
1971 return cc
->nr_migratepages
? ISOLATE_SUCCESS
: ISOLATE_NONE
;
1975 * order == -1 is expected when compacting via
1976 * /proc/sys/vm/compact_memory
1978 static inline bool is_via_compact_memory(int order
)
1983 static bool kswapd_is_running(pg_data_t
*pgdat
)
1985 return pgdat
->kswapd
&& task_is_running(pgdat
->kswapd
);
1989 * A zone's fragmentation score is the external fragmentation wrt to the
1990 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
1992 static unsigned int fragmentation_score_zone(struct zone
*zone
)
1994 return extfrag_for_order(zone
, COMPACTION_HPAGE_ORDER
);
1998 * A weighted zone's fragmentation score is the external fragmentation
1999 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
2000 * returns a value in the range [0, 100].
2002 * The scaling factor ensures that proactive compaction focuses on larger
2003 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
2004 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
2005 * and thus never exceeds the high threshold for proactive compaction.
2007 static unsigned int fragmentation_score_zone_weighted(struct zone
*zone
)
2009 unsigned long score
;
2011 score
= zone
->present_pages
* fragmentation_score_zone(zone
);
2012 return div64_ul(score
, zone
->zone_pgdat
->node_present_pages
+ 1);
2016 * The per-node proactive (background) compaction process is started by its
2017 * corresponding kcompactd thread when the node's fragmentation score
2018 * exceeds the high threshold. The compaction process remains active till
2019 * the node's score falls below the low threshold, or one of the back-off
2020 * conditions is met.
2022 static unsigned int fragmentation_score_node(pg_data_t
*pgdat
)
2024 unsigned int score
= 0;
2027 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
2030 zone
= &pgdat
->node_zones
[zoneid
];
2031 score
+= fragmentation_score_zone_weighted(zone
);
2037 static unsigned int fragmentation_score_wmark(pg_data_t
*pgdat
, bool low
)
2039 unsigned int wmark_low
;
2042 * Cap the low watermark to avoid excessive compaction
2043 * activity in case a user sets the proactiveness tunable
2044 * close to 100 (maximum).
2046 wmark_low
= max(100U - sysctl_compaction_proactiveness
, 5U);
2047 return low
? wmark_low
: min(wmark_low
+ 10, 100U);
2050 static bool should_proactive_compact_node(pg_data_t
*pgdat
)
2054 if (!sysctl_compaction_proactiveness
|| kswapd_is_running(pgdat
))
2057 wmark_high
= fragmentation_score_wmark(pgdat
, false);
2058 return fragmentation_score_node(pgdat
) > wmark_high
;
2061 static enum compact_result
__compact_finished(struct compact_control
*cc
)
2064 const int migratetype
= cc
->migratetype
;
2067 /* Compaction run completes if the migrate and free scanner meet */
2068 if (compact_scanners_met(cc
)) {
2069 /* Let the next compaction start anew. */
2070 reset_cached_positions(cc
->zone
);
2073 * Mark that the PG_migrate_skip information should be cleared
2074 * by kswapd when it goes to sleep. kcompactd does not set the
2075 * flag itself as the decision to be clear should be directly
2076 * based on an allocation request.
2078 if (cc
->direct_compaction
)
2079 cc
->zone
->compact_blockskip_flush
= true;
2082 return COMPACT_COMPLETE
;
2084 return COMPACT_PARTIAL_SKIPPED
;
2087 if (cc
->proactive_compaction
) {
2088 int score
, wmark_low
;
2091 pgdat
= cc
->zone
->zone_pgdat
;
2092 if (kswapd_is_running(pgdat
))
2093 return COMPACT_PARTIAL_SKIPPED
;
2095 score
= fragmentation_score_zone(cc
->zone
);
2096 wmark_low
= fragmentation_score_wmark(pgdat
, true);
2098 if (score
> wmark_low
)
2099 ret
= COMPACT_CONTINUE
;
2101 ret
= COMPACT_SUCCESS
;
2106 if (is_via_compact_memory(cc
->order
))
2107 return COMPACT_CONTINUE
;
2110 * Always finish scanning a pageblock to reduce the possibility of
2111 * fallbacks in the future. This is particularly important when
2112 * migration source is unmovable/reclaimable but it's not worth
2115 if (!IS_ALIGNED(cc
->migrate_pfn
, pageblock_nr_pages
))
2116 return COMPACT_CONTINUE
;
2118 /* Direct compactor: Is a suitable page free? */
2119 ret
= COMPACT_NO_SUITABLE_PAGE
;
2120 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
2121 struct free_area
*area
= &cc
->zone
->free_area
[order
];
2124 /* Job done if page is free of the right migratetype */
2125 if (!free_area_empty(area
, migratetype
))
2126 return COMPACT_SUCCESS
;
2129 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2130 if (migratetype
== MIGRATE_MOVABLE
&&
2131 !free_area_empty(area
, MIGRATE_CMA
))
2132 return COMPACT_SUCCESS
;
2135 * Job done if allocation would steal freepages from
2136 * other migratetype buddy lists.
2138 if (find_suitable_fallback(area
, order
, migratetype
,
2139 true, &can_steal
) != -1)
2141 * Movable pages are OK in any pageblock. If we are
2142 * stealing for a non-movable allocation, make sure
2143 * we finish compacting the current pageblock first
2144 * (which is assured by the above migrate_pfn align
2145 * check) so it is as free as possible and we won't
2146 * have to steal another one soon.
2148 return COMPACT_SUCCESS
;
2152 if (cc
->contended
|| fatal_signal_pending(current
))
2153 ret
= COMPACT_CONTENDED
;
2158 static enum compact_result
compact_finished(struct compact_control
*cc
)
2162 ret
= __compact_finished(cc
);
2163 trace_mm_compaction_finished(cc
->zone
, cc
->order
, ret
);
2164 if (ret
== COMPACT_NO_SUITABLE_PAGE
)
2165 ret
= COMPACT_CONTINUE
;
2170 static enum compact_result
__compaction_suitable(struct zone
*zone
, int order
,
2171 unsigned int alloc_flags
,
2172 int highest_zoneidx
,
2173 unsigned long wmark_target
)
2175 unsigned long watermark
;
2177 if (is_via_compact_memory(order
))
2178 return COMPACT_CONTINUE
;
2180 watermark
= wmark_pages(zone
, alloc_flags
& ALLOC_WMARK_MASK
);
2182 * If watermarks for high-order allocation are already met, there
2183 * should be no need for compaction at all.
2185 if (zone_watermark_ok(zone
, order
, watermark
, highest_zoneidx
,
2187 return COMPACT_SUCCESS
;
2190 * Watermarks for order-0 must be met for compaction to be able to
2191 * isolate free pages for migration targets. This means that the
2192 * watermark and alloc_flags have to match, or be more pessimistic than
2193 * the check in __isolate_free_page(). We don't use the direct
2194 * compactor's alloc_flags, as they are not relevant for freepage
2195 * isolation. We however do use the direct compactor's highest_zoneidx
2196 * to skip over zones where lowmem reserves would prevent allocation
2197 * even if compaction succeeds.
2198 * For costly orders, we require low watermark instead of min for
2199 * compaction to proceed to increase its chances.
2200 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2201 * suitable migration targets
2203 watermark
= (order
> PAGE_ALLOC_COSTLY_ORDER
) ?
2204 low_wmark_pages(zone
) : min_wmark_pages(zone
);
2205 watermark
+= compact_gap(order
);
2206 if (!__zone_watermark_ok(zone
, 0, watermark
, highest_zoneidx
,
2207 ALLOC_CMA
, wmark_target
))
2208 return COMPACT_SKIPPED
;
2210 return COMPACT_CONTINUE
;
2214 * compaction_suitable: Is this suitable to run compaction on this zone now?
2216 * COMPACT_SKIPPED - If there are too few free pages for compaction
2217 * COMPACT_SUCCESS - If the allocation would succeed without compaction
2218 * COMPACT_CONTINUE - If compaction should run now
2220 enum compact_result
compaction_suitable(struct zone
*zone
, int order
,
2221 unsigned int alloc_flags
,
2222 int highest_zoneidx
)
2224 enum compact_result ret
;
2227 ret
= __compaction_suitable(zone
, order
, alloc_flags
, highest_zoneidx
,
2228 zone_page_state(zone
, NR_FREE_PAGES
));
2230 * fragmentation index determines if allocation failures are due to
2231 * low memory or external fragmentation
2233 * index of -1000 would imply allocations might succeed depending on
2234 * watermarks, but we already failed the high-order watermark check
2235 * index towards 0 implies failure is due to lack of memory
2236 * index towards 1000 implies failure is due to fragmentation
2238 * Only compact if a failure would be due to fragmentation. Also
2239 * ignore fragindex for non-costly orders where the alternative to
2240 * a successful reclaim/compaction is OOM. Fragindex and the
2241 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2242 * excessive compaction for costly orders, but it should not be at the
2243 * expense of system stability.
2245 if (ret
== COMPACT_CONTINUE
&& (order
> PAGE_ALLOC_COSTLY_ORDER
)) {
2246 fragindex
= fragmentation_index(zone
, order
);
2247 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
2248 ret
= COMPACT_NOT_SUITABLE_ZONE
;
2251 trace_mm_compaction_suitable(zone
, order
, ret
);
2252 if (ret
== COMPACT_NOT_SUITABLE_ZONE
)
2253 ret
= COMPACT_SKIPPED
;
2258 bool compaction_zonelist_suitable(struct alloc_context
*ac
, int order
,
2265 * Make sure at least one zone would pass __compaction_suitable if we continue
2266 * retrying the reclaim.
2268 for_each_zone_zonelist_nodemask(zone
, z
, ac
->zonelist
,
2269 ac
->highest_zoneidx
, ac
->nodemask
) {
2270 unsigned long available
;
2271 enum compact_result compact_result
;
2274 * Do not consider all the reclaimable memory because we do not
2275 * want to trash just for a single high order allocation which
2276 * is even not guaranteed to appear even if __compaction_suitable
2277 * is happy about the watermark check.
2279 available
= zone_reclaimable_pages(zone
) / order
;
2280 available
+= zone_page_state_snapshot(zone
, NR_FREE_PAGES
);
2281 compact_result
= __compaction_suitable(zone
, order
, alloc_flags
,
2282 ac
->highest_zoneidx
, available
);
2283 if (compact_result
== COMPACT_CONTINUE
)
2290 static enum compact_result
2291 compact_zone(struct compact_control
*cc
, struct capture_control
*capc
)
2293 enum compact_result ret
;
2294 unsigned long start_pfn
= cc
->zone
->zone_start_pfn
;
2295 unsigned long end_pfn
= zone_end_pfn(cc
->zone
);
2296 unsigned long last_migrated_pfn
;
2297 const bool sync
= cc
->mode
!= MIGRATE_ASYNC
;
2299 unsigned int nr_succeeded
= 0;
2302 * These counters track activities during zone compaction. Initialize
2303 * them before compacting a new zone.
2305 cc
->total_migrate_scanned
= 0;
2306 cc
->total_free_scanned
= 0;
2307 cc
->nr_migratepages
= 0;
2308 cc
->nr_freepages
= 0;
2309 INIT_LIST_HEAD(&cc
->freepages
);
2310 INIT_LIST_HEAD(&cc
->migratepages
);
2312 cc
->migratetype
= gfp_migratetype(cc
->gfp_mask
);
2313 ret
= compaction_suitable(cc
->zone
, cc
->order
, cc
->alloc_flags
,
2314 cc
->highest_zoneidx
);
2315 /* Compaction is likely to fail */
2316 if (ret
== COMPACT_SUCCESS
|| ret
== COMPACT_SKIPPED
)
2319 /* huh, compaction_suitable is returning something unexpected */
2320 VM_BUG_ON(ret
!= COMPACT_CONTINUE
);
2323 * Clear pageblock skip if there were failures recently and compaction
2324 * is about to be retried after being deferred.
2326 if (compaction_restarting(cc
->zone
, cc
->order
))
2327 __reset_isolation_suitable(cc
->zone
);
2330 * Setup to move all movable pages to the end of the zone. Used cached
2331 * information on where the scanners should start (unless we explicitly
2332 * want to compact the whole zone), but check that it is initialised
2333 * by ensuring the values are within zone boundaries.
2335 cc
->fast_start_pfn
= 0;
2336 if (cc
->whole_zone
) {
2337 cc
->migrate_pfn
= start_pfn
;
2338 cc
->free_pfn
= pageblock_start_pfn(end_pfn
- 1);
2340 cc
->migrate_pfn
= cc
->zone
->compact_cached_migrate_pfn
[sync
];
2341 cc
->free_pfn
= cc
->zone
->compact_cached_free_pfn
;
2342 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
>= end_pfn
) {
2343 cc
->free_pfn
= pageblock_start_pfn(end_pfn
- 1);
2344 cc
->zone
->compact_cached_free_pfn
= cc
->free_pfn
;
2346 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
>= end_pfn
) {
2347 cc
->migrate_pfn
= start_pfn
;
2348 cc
->zone
->compact_cached_migrate_pfn
[0] = cc
->migrate_pfn
;
2349 cc
->zone
->compact_cached_migrate_pfn
[1] = cc
->migrate_pfn
;
2352 if (cc
->migrate_pfn
<= cc
->zone
->compact_init_migrate_pfn
)
2353 cc
->whole_zone
= true;
2356 last_migrated_pfn
= 0;
2359 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2360 * the basis that some migrations will fail in ASYNC mode. However,
2361 * if the cached PFNs match and pageblocks are skipped due to having
2362 * no isolation candidates, then the sync state does not matter.
2363 * Until a pageblock with isolation candidates is found, keep the
2364 * cached PFNs in sync to avoid revisiting the same blocks.
2366 update_cached
= !sync
&&
2367 cc
->zone
->compact_cached_migrate_pfn
[0] == cc
->zone
->compact_cached_migrate_pfn
[1];
2369 trace_mm_compaction_begin(cc
, start_pfn
, end_pfn
, sync
);
2371 /* lru_add_drain_all could be expensive with involving other CPUs */
2374 while ((ret
= compact_finished(cc
)) == COMPACT_CONTINUE
) {
2376 unsigned long iteration_start_pfn
= cc
->migrate_pfn
;
2379 * Avoid multiple rescans which can happen if a page cannot be
2380 * isolated (dirty/writeback in async mode) or if the migrated
2381 * pages are being allocated before the pageblock is cleared.
2382 * The first rescan will capture the entire pageblock for
2383 * migration. If it fails, it'll be marked skip and scanning
2384 * will proceed as normal.
2387 if (pageblock_start_pfn(last_migrated_pfn
) ==
2388 pageblock_start_pfn(iteration_start_pfn
)) {
2392 switch (isolate_migratepages(cc
)) {
2394 ret
= COMPACT_CONTENDED
;
2395 putback_movable_pages(&cc
->migratepages
);
2396 cc
->nr_migratepages
= 0;
2399 if (update_cached
) {
2400 cc
->zone
->compact_cached_migrate_pfn
[1] =
2401 cc
->zone
->compact_cached_migrate_pfn
[0];
2405 * We haven't isolated and migrated anything, but
2406 * there might still be unflushed migrations from
2407 * previous cc->order aligned block.
2410 case ISOLATE_SUCCESS
:
2411 update_cached
= false;
2412 last_migrated_pfn
= iteration_start_pfn
;
2415 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
2416 compaction_free
, (unsigned long)cc
, cc
->mode
,
2417 MR_COMPACTION
, &nr_succeeded
);
2419 trace_mm_compaction_migratepages(cc
, nr_succeeded
);
2421 /* All pages were either migrated or will be released */
2422 cc
->nr_migratepages
= 0;
2424 putback_movable_pages(&cc
->migratepages
);
2426 * migrate_pages() may return -ENOMEM when scanners meet
2427 * and we want compact_finished() to detect it
2429 if (err
== -ENOMEM
&& !compact_scanners_met(cc
)) {
2430 ret
= COMPACT_CONTENDED
;
2434 * We failed to migrate at least one page in the current
2435 * order-aligned block, so skip the rest of it.
2437 if (cc
->direct_compaction
&&
2438 (cc
->mode
== MIGRATE_ASYNC
)) {
2439 cc
->migrate_pfn
= block_end_pfn(
2440 cc
->migrate_pfn
- 1, cc
->order
);
2441 /* Draining pcplists is useless in this case */
2442 last_migrated_pfn
= 0;
2448 * Has the migration scanner moved away from the previous
2449 * cc->order aligned block where we migrated from? If yes,
2450 * flush the pages that were freed, so that they can merge and
2451 * compact_finished() can detect immediately if allocation
2454 if (cc
->order
> 0 && last_migrated_pfn
) {
2455 unsigned long current_block_start
=
2456 block_start_pfn(cc
->migrate_pfn
, cc
->order
);
2458 if (last_migrated_pfn
< current_block_start
) {
2459 lru_add_drain_cpu_zone(cc
->zone
);
2460 /* No more flushing until we migrate again */
2461 last_migrated_pfn
= 0;
2465 /* Stop if a page has been captured */
2466 if (capc
&& capc
->page
) {
2467 ret
= COMPACT_SUCCESS
;
2474 * Release free pages and update where the free scanner should restart,
2475 * so we don't leave any returned pages behind in the next attempt.
2477 if (cc
->nr_freepages
> 0) {
2478 unsigned long free_pfn
= release_freepages(&cc
->freepages
);
2480 cc
->nr_freepages
= 0;
2481 VM_BUG_ON(free_pfn
== 0);
2482 /* The cached pfn is always the first in a pageblock */
2483 free_pfn
= pageblock_start_pfn(free_pfn
);
2485 * Only go back, not forward. The cached pfn might have been
2486 * already reset to zone end in compact_finished()
2488 if (free_pfn
> cc
->zone
->compact_cached_free_pfn
)
2489 cc
->zone
->compact_cached_free_pfn
= free_pfn
;
2492 count_compact_events(COMPACTMIGRATE_SCANNED
, cc
->total_migrate_scanned
);
2493 count_compact_events(COMPACTFREE_SCANNED
, cc
->total_free_scanned
);
2495 trace_mm_compaction_end(cc
, start_pfn
, end_pfn
, sync
, ret
);
2500 static enum compact_result
compact_zone_order(struct zone
*zone
, int order
,
2501 gfp_t gfp_mask
, enum compact_priority prio
,
2502 unsigned int alloc_flags
, int highest_zoneidx
,
2503 struct page
**capture
)
2505 enum compact_result ret
;
2506 struct compact_control cc
= {
2508 .search_order
= order
,
2509 .gfp_mask
= gfp_mask
,
2511 .mode
= (prio
== COMPACT_PRIO_ASYNC
) ?
2512 MIGRATE_ASYNC
: MIGRATE_SYNC_LIGHT
,
2513 .alloc_flags
= alloc_flags
,
2514 .highest_zoneidx
= highest_zoneidx
,
2515 .direct_compaction
= true,
2516 .whole_zone
= (prio
== MIN_COMPACT_PRIORITY
),
2517 .ignore_skip_hint
= (prio
== MIN_COMPACT_PRIORITY
),
2518 .ignore_block_suitable
= (prio
== MIN_COMPACT_PRIORITY
)
2520 struct capture_control capc
= {
2526 * Make sure the structs are really initialized before we expose the
2527 * capture control, in case we are interrupted and the interrupt handler
2531 WRITE_ONCE(current
->capture_control
, &capc
);
2533 ret
= compact_zone(&cc
, &capc
);
2535 VM_BUG_ON(!list_empty(&cc
.freepages
));
2536 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2539 * Make sure we hide capture control first before we read the captured
2540 * page pointer, otherwise an interrupt could free and capture a page
2541 * and we would leak it.
2543 WRITE_ONCE(current
->capture_control
, NULL
);
2544 *capture
= READ_ONCE(capc
.page
);
2546 * Technically, it is also possible that compaction is skipped but
2547 * the page is still captured out of luck(IRQ came and freed the page).
2548 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
2549 * the COMPACT[STALL|FAIL] when compaction is skipped.
2552 ret
= COMPACT_SUCCESS
;
2557 int sysctl_extfrag_threshold
= 500;
2560 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2561 * @gfp_mask: The GFP mask of the current allocation
2562 * @order: The order of the current allocation
2563 * @alloc_flags: The allocation flags of the current allocation
2564 * @ac: The context of current allocation
2565 * @prio: Determines how hard direct compaction should try to succeed
2566 * @capture: Pointer to free page created by compaction will be stored here
2568 * This is the main entry point for direct page compaction.
2570 enum compact_result
try_to_compact_pages(gfp_t gfp_mask
, unsigned int order
,
2571 unsigned int alloc_flags
, const struct alloc_context
*ac
,
2572 enum compact_priority prio
, struct page
**capture
)
2574 int may_perform_io
= (__force
int)(gfp_mask
& __GFP_IO
);
2577 enum compact_result rc
= COMPACT_SKIPPED
;
2580 * Check if the GFP flags allow compaction - GFP_NOIO is really
2581 * tricky context because the migration might require IO
2583 if (!may_perform_io
)
2584 return COMPACT_SKIPPED
;
2586 trace_mm_compaction_try_to_compact_pages(order
, gfp_mask
, prio
);
2588 /* Compact each zone in the list */
2589 for_each_zone_zonelist_nodemask(zone
, z
, ac
->zonelist
,
2590 ac
->highest_zoneidx
, ac
->nodemask
) {
2591 enum compact_result status
;
2593 if (prio
> MIN_COMPACT_PRIORITY
2594 && compaction_deferred(zone
, order
)) {
2595 rc
= max_t(enum compact_result
, COMPACT_DEFERRED
, rc
);
2599 status
= compact_zone_order(zone
, order
, gfp_mask
, prio
,
2600 alloc_flags
, ac
->highest_zoneidx
, capture
);
2601 rc
= max(status
, rc
);
2603 /* The allocation should succeed, stop compacting */
2604 if (status
== COMPACT_SUCCESS
) {
2606 * We think the allocation will succeed in this zone,
2607 * but it is not certain, hence the false. The caller
2608 * will repeat this with true if allocation indeed
2609 * succeeds in this zone.
2611 compaction_defer_reset(zone
, order
, false);
2616 if (prio
!= COMPACT_PRIO_ASYNC
&& (status
== COMPACT_COMPLETE
||
2617 status
== COMPACT_PARTIAL_SKIPPED
))
2619 * We think that allocation won't succeed in this zone
2620 * so we defer compaction there. If it ends up
2621 * succeeding after all, it will be reset.
2623 defer_compaction(zone
, order
);
2626 * We might have stopped compacting due to need_resched() in
2627 * async compaction, or due to a fatal signal detected. In that
2628 * case do not try further zones
2630 if ((prio
== COMPACT_PRIO_ASYNC
&& need_resched())
2631 || fatal_signal_pending(current
))
2639 * Compact all zones within a node till each zone's fragmentation score
2640 * reaches within proactive compaction thresholds (as determined by the
2641 * proactiveness tunable).
2643 * It is possible that the function returns before reaching score targets
2644 * due to various back-off conditions, such as, contention on per-node or
2647 static void proactive_compact_node(pg_data_t
*pgdat
)
2651 struct compact_control cc
= {
2653 .mode
= MIGRATE_SYNC_LIGHT
,
2654 .ignore_skip_hint
= true,
2656 .gfp_mask
= GFP_KERNEL
,
2657 .proactive_compaction
= true,
2660 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
2661 zone
= &pgdat
->node_zones
[zoneid
];
2662 if (!populated_zone(zone
))
2667 compact_zone(&cc
, NULL
);
2669 VM_BUG_ON(!list_empty(&cc
.freepages
));
2670 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2674 /* Compact all zones within a node */
2675 static void compact_node(int nid
)
2677 pg_data_t
*pgdat
= NODE_DATA(nid
);
2680 struct compact_control cc
= {
2682 .mode
= MIGRATE_SYNC
,
2683 .ignore_skip_hint
= true,
2685 .gfp_mask
= GFP_KERNEL
,
2689 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
2691 zone
= &pgdat
->node_zones
[zoneid
];
2692 if (!populated_zone(zone
))
2697 compact_zone(&cc
, NULL
);
2699 VM_BUG_ON(!list_empty(&cc
.freepages
));
2700 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2704 /* Compact all nodes in the system */
2705 static void compact_nodes(void)
2709 /* Flush pending updates to the LRU lists */
2710 lru_add_drain_all();
2712 for_each_online_node(nid
)
2717 * Tunable for proactive compaction. It determines how
2718 * aggressively the kernel should compact memory in the
2719 * background. It takes values in the range [0, 100].
2721 unsigned int __read_mostly sysctl_compaction_proactiveness
= 20;
2723 int compaction_proactiveness_sysctl_handler(struct ctl_table
*table
, int write
,
2724 void *buffer
, size_t *length
, loff_t
*ppos
)
2728 rc
= proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
2732 if (write
&& sysctl_compaction_proactiveness
) {
2733 for_each_online_node(nid
) {
2734 pg_data_t
*pgdat
= NODE_DATA(nid
);
2736 if (pgdat
->proactive_compact_trigger
)
2739 pgdat
->proactive_compact_trigger
= true;
2740 wake_up_interruptible(&pgdat
->kcompactd_wait
);
2748 * This is the entry point for compacting all nodes via
2749 * /proc/sys/vm/compact_memory
2751 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
2752 void *buffer
, size_t *length
, loff_t
*ppos
)
2760 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2761 static ssize_t
compact_store(struct device
*dev
,
2762 struct device_attribute
*attr
,
2763 const char *buf
, size_t count
)
2767 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
2768 /* Flush pending updates to the LRU lists */
2769 lru_add_drain_all();
2776 static DEVICE_ATTR_WO(compact
);
2778 int compaction_register_node(struct node
*node
)
2780 return device_create_file(&node
->dev
, &dev_attr_compact
);
2783 void compaction_unregister_node(struct node
*node
)
2785 return device_remove_file(&node
->dev
, &dev_attr_compact
);
2787 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
2789 static inline bool kcompactd_work_requested(pg_data_t
*pgdat
)
2791 return pgdat
->kcompactd_max_order
> 0 || kthread_should_stop() ||
2792 pgdat
->proactive_compact_trigger
;
2795 static bool kcompactd_node_suitable(pg_data_t
*pgdat
)
2799 enum zone_type highest_zoneidx
= pgdat
->kcompactd_highest_zoneidx
;
2801 for (zoneid
= 0; zoneid
<= highest_zoneidx
; zoneid
++) {
2802 zone
= &pgdat
->node_zones
[zoneid
];
2804 if (!populated_zone(zone
))
2807 if (compaction_suitable(zone
, pgdat
->kcompactd_max_order
, 0,
2808 highest_zoneidx
) == COMPACT_CONTINUE
)
2815 static void kcompactd_do_work(pg_data_t
*pgdat
)
2818 * With no special task, compact all zones so that a page of requested
2819 * order is allocatable.
2823 struct compact_control cc
= {
2824 .order
= pgdat
->kcompactd_max_order
,
2825 .search_order
= pgdat
->kcompactd_max_order
,
2826 .highest_zoneidx
= pgdat
->kcompactd_highest_zoneidx
,
2827 .mode
= MIGRATE_SYNC_LIGHT
,
2828 .ignore_skip_hint
= false,
2829 .gfp_mask
= GFP_KERNEL
,
2831 trace_mm_compaction_kcompactd_wake(pgdat
->node_id
, cc
.order
,
2832 cc
.highest_zoneidx
);
2833 count_compact_event(KCOMPACTD_WAKE
);
2835 for (zoneid
= 0; zoneid
<= cc
.highest_zoneidx
; zoneid
++) {
2838 zone
= &pgdat
->node_zones
[zoneid
];
2839 if (!populated_zone(zone
))
2842 if (compaction_deferred(zone
, cc
.order
))
2845 if (compaction_suitable(zone
, cc
.order
, 0, zoneid
) !=
2849 if (kthread_should_stop())
2853 status
= compact_zone(&cc
, NULL
);
2855 if (status
== COMPACT_SUCCESS
) {
2856 compaction_defer_reset(zone
, cc
.order
, false);
2857 } else if (status
== COMPACT_PARTIAL_SKIPPED
|| status
== COMPACT_COMPLETE
) {
2859 * Buddy pages may become stranded on pcps that could
2860 * otherwise coalesce on the zone's free area for
2861 * order >= cc.order. This is ratelimited by the
2862 * upcoming deferral.
2864 drain_all_pages(zone
);
2867 * We use sync migration mode here, so we defer like
2868 * sync direct compaction does.
2870 defer_compaction(zone
, cc
.order
);
2873 count_compact_events(KCOMPACTD_MIGRATE_SCANNED
,
2874 cc
.total_migrate_scanned
);
2875 count_compact_events(KCOMPACTD_FREE_SCANNED
,
2876 cc
.total_free_scanned
);
2878 VM_BUG_ON(!list_empty(&cc
.freepages
));
2879 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2883 * Regardless of success, we are done until woken up next. But remember
2884 * the requested order/highest_zoneidx in case it was higher/tighter
2885 * than our current ones
2887 if (pgdat
->kcompactd_max_order
<= cc
.order
)
2888 pgdat
->kcompactd_max_order
= 0;
2889 if (pgdat
->kcompactd_highest_zoneidx
>= cc
.highest_zoneidx
)
2890 pgdat
->kcompactd_highest_zoneidx
= pgdat
->nr_zones
- 1;
2893 void wakeup_kcompactd(pg_data_t
*pgdat
, int order
, int highest_zoneidx
)
2898 if (pgdat
->kcompactd_max_order
< order
)
2899 pgdat
->kcompactd_max_order
= order
;
2901 if (pgdat
->kcompactd_highest_zoneidx
> highest_zoneidx
)
2902 pgdat
->kcompactd_highest_zoneidx
= highest_zoneidx
;
2905 * Pairs with implicit barrier in wait_event_freezable()
2906 * such that wakeups are not missed.
2908 if (!wq_has_sleeper(&pgdat
->kcompactd_wait
))
2911 if (!kcompactd_node_suitable(pgdat
))
2914 trace_mm_compaction_wakeup_kcompactd(pgdat
->node_id
, order
,
2916 wake_up_interruptible(&pgdat
->kcompactd_wait
);
2920 * The background compaction daemon, started as a kernel thread
2921 * from the init process.
2923 static int kcompactd(void *p
)
2925 pg_data_t
*pgdat
= (pg_data_t
*)p
;
2926 struct task_struct
*tsk
= current
;
2927 long default_timeout
= msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC
);
2928 long timeout
= default_timeout
;
2930 const struct cpumask
*cpumask
= cpumask_of_node(pgdat
->node_id
);
2932 if (!cpumask_empty(cpumask
))
2933 set_cpus_allowed_ptr(tsk
, cpumask
);
2937 pgdat
->kcompactd_max_order
= 0;
2938 pgdat
->kcompactd_highest_zoneidx
= pgdat
->nr_zones
- 1;
2940 while (!kthread_should_stop()) {
2941 unsigned long pflags
;
2944 * Avoid the unnecessary wakeup for proactive compaction
2945 * when it is disabled.
2947 if (!sysctl_compaction_proactiveness
)
2948 timeout
= MAX_SCHEDULE_TIMEOUT
;
2949 trace_mm_compaction_kcompactd_sleep(pgdat
->node_id
);
2950 if (wait_event_freezable_timeout(pgdat
->kcompactd_wait
,
2951 kcompactd_work_requested(pgdat
), timeout
) &&
2952 !pgdat
->proactive_compact_trigger
) {
2954 psi_memstall_enter(&pflags
);
2955 kcompactd_do_work(pgdat
);
2956 psi_memstall_leave(&pflags
);
2958 * Reset the timeout value. The defer timeout from
2959 * proactive compaction is lost here but that is fine
2960 * as the condition of the zone changing substantionally
2961 * then carrying on with the previous defer interval is
2964 timeout
= default_timeout
;
2969 * Start the proactive work with default timeout. Based
2970 * on the fragmentation score, this timeout is updated.
2972 timeout
= default_timeout
;
2973 if (should_proactive_compact_node(pgdat
)) {
2974 unsigned int prev_score
, score
;
2976 prev_score
= fragmentation_score_node(pgdat
);
2977 proactive_compact_node(pgdat
);
2978 score
= fragmentation_score_node(pgdat
);
2980 * Defer proactive compaction if the fragmentation
2981 * score did not go down i.e. no progress made.
2983 if (unlikely(score
>= prev_score
))
2985 default_timeout
<< COMPACT_MAX_DEFER_SHIFT
;
2987 if (unlikely(pgdat
->proactive_compact_trigger
))
2988 pgdat
->proactive_compact_trigger
= false;
2995 * This kcompactd start function will be called by init and node-hot-add.
2996 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2998 void kcompactd_run(int nid
)
3000 pg_data_t
*pgdat
= NODE_DATA(nid
);
3002 if (pgdat
->kcompactd
)
3005 pgdat
->kcompactd
= kthread_run(kcompactd
, pgdat
, "kcompactd%d", nid
);
3006 if (IS_ERR(pgdat
->kcompactd
)) {
3007 pr_err("Failed to start kcompactd on node %d\n", nid
);
3008 pgdat
->kcompactd
= NULL
;
3013 * Called by memory hotplug when all memory in a node is offlined. Caller must
3014 * hold mem_hotplug_begin/end().
3016 void kcompactd_stop(int nid
)
3018 struct task_struct
*kcompactd
= NODE_DATA(nid
)->kcompactd
;
3021 kthread_stop(kcompactd
);
3022 NODE_DATA(nid
)->kcompactd
= NULL
;
3027 * It's optimal to keep kcompactd on the same CPUs as their memory, but
3028 * not required for correctness. So if the last cpu in a node goes
3029 * away, we get changed to run anywhere: as the first one comes back,
3030 * restore their cpu bindings.
3032 static int kcompactd_cpu_online(unsigned int cpu
)
3036 for_each_node_state(nid
, N_MEMORY
) {
3037 pg_data_t
*pgdat
= NODE_DATA(nid
);
3038 const struct cpumask
*mask
;
3040 mask
= cpumask_of_node(pgdat
->node_id
);
3042 if (cpumask_any_and(cpu_online_mask
, mask
) < nr_cpu_ids
)
3043 /* One of our CPUs online: restore mask */
3044 if (pgdat
->kcompactd
)
3045 set_cpus_allowed_ptr(pgdat
->kcompactd
, mask
);
3050 static int __init
kcompactd_init(void)
3055 ret
= cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN
,
3056 "mm/compaction:online",
3057 kcompactd_cpu_online
, NULL
);
3059 pr_err("kcompactd: failed to register hotplug callbacks.\n");
3063 for_each_node_state(nid
, N_MEMORY
)
3067 subsys_initcall(kcompactd_init
)
3069 #endif /* CONFIG_COMPACTION */