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 (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 pfn
+= (1 << PAGE_ALLOC_COSTLY_ORDER
);
321 } while (page
<= end_page
);
327 * This function is called to clear all cached information on pageblocks that
328 * should be skipped for page isolation when the migrate and free page scanner
331 static void __reset_isolation_suitable(struct zone
*zone
)
333 unsigned long migrate_pfn
= zone
->zone_start_pfn
;
334 unsigned long free_pfn
= zone_end_pfn(zone
) - 1;
335 unsigned long reset_migrate
= free_pfn
;
336 unsigned long reset_free
= migrate_pfn
;
337 bool source_set
= false;
338 bool free_set
= false;
340 if (!zone
->compact_blockskip_flush
)
343 zone
->compact_blockskip_flush
= false;
346 * Walk the zone and update pageblock skip information. Source looks
347 * for PageLRU while target looks for PageBuddy. When the scanner
348 * is found, both PageBuddy and PageLRU are checked as the pageblock
349 * is suitable as both source and target.
351 for (; migrate_pfn
< free_pfn
; migrate_pfn
+= pageblock_nr_pages
,
352 free_pfn
-= pageblock_nr_pages
) {
355 /* Update the migrate PFN */
356 if (__reset_isolation_pfn(zone
, migrate_pfn
, true, source_set
) &&
357 migrate_pfn
< reset_migrate
) {
359 reset_migrate
= migrate_pfn
;
360 zone
->compact_init_migrate_pfn
= reset_migrate
;
361 zone
->compact_cached_migrate_pfn
[0] = reset_migrate
;
362 zone
->compact_cached_migrate_pfn
[1] = reset_migrate
;
365 /* Update the free PFN */
366 if (__reset_isolation_pfn(zone
, free_pfn
, free_set
, true) &&
367 free_pfn
> reset_free
) {
369 reset_free
= free_pfn
;
370 zone
->compact_init_free_pfn
= reset_free
;
371 zone
->compact_cached_free_pfn
= reset_free
;
375 /* Leave no distance if no suitable block was reset */
376 if (reset_migrate
>= reset_free
) {
377 zone
->compact_cached_migrate_pfn
[0] = migrate_pfn
;
378 zone
->compact_cached_migrate_pfn
[1] = migrate_pfn
;
379 zone
->compact_cached_free_pfn
= free_pfn
;
383 void reset_isolation_suitable(pg_data_t
*pgdat
)
387 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
388 struct zone
*zone
= &pgdat
->node_zones
[zoneid
];
389 if (!populated_zone(zone
))
392 /* Only flush if a full compaction finished recently */
393 if (zone
->compact_blockskip_flush
)
394 __reset_isolation_suitable(zone
);
399 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
400 * locks are not required for read/writers. Returns true if it was already set.
402 static bool test_and_set_skip(struct compact_control
*cc
, struct page
*page
,
407 /* Do no update if skip hint is being ignored */
408 if (cc
->ignore_skip_hint
)
411 if (!IS_ALIGNED(pfn
, pageblock_nr_pages
))
414 skip
= get_pageblock_skip(page
);
415 if (!skip
&& !cc
->no_set_skip_hint
)
416 set_pageblock_skip(page
);
421 static void update_cached_migrate(struct compact_control
*cc
, unsigned long pfn
)
423 struct zone
*zone
= cc
->zone
;
425 pfn
= pageblock_end_pfn(pfn
);
427 /* Set for isolation rather than compaction */
428 if (cc
->no_set_skip_hint
)
431 if (pfn
> zone
->compact_cached_migrate_pfn
[0])
432 zone
->compact_cached_migrate_pfn
[0] = pfn
;
433 if (cc
->mode
!= MIGRATE_ASYNC
&&
434 pfn
> zone
->compact_cached_migrate_pfn
[1])
435 zone
->compact_cached_migrate_pfn
[1] = pfn
;
439 * If no pages were isolated then mark this pageblock to be skipped in the
440 * future. The information is later cleared by __reset_isolation_suitable().
442 static void update_pageblock_skip(struct compact_control
*cc
,
443 struct page
*page
, unsigned long pfn
)
445 struct zone
*zone
= cc
->zone
;
447 if (cc
->no_set_skip_hint
)
453 set_pageblock_skip(page
);
455 /* Update where async and sync compaction should restart */
456 if (pfn
< zone
->compact_cached_free_pfn
)
457 zone
->compact_cached_free_pfn
= pfn
;
460 static inline bool isolation_suitable(struct compact_control
*cc
,
466 static inline bool pageblock_skip_persistent(struct page
*page
)
471 static inline void update_pageblock_skip(struct compact_control
*cc
,
472 struct page
*page
, unsigned long pfn
)
476 static void update_cached_migrate(struct compact_control
*cc
, unsigned long pfn
)
480 static bool test_and_set_skip(struct compact_control
*cc
, struct page
*page
,
485 #endif /* CONFIG_COMPACTION */
488 * Compaction requires the taking of some coarse locks that are potentially
489 * very heavily contended. For async compaction, trylock and record if the
490 * lock is contended. The lock will still be acquired but compaction will
491 * abort when the current block is finished regardless of success rate.
492 * Sync compaction acquires the lock.
494 * Always returns true which makes it easier to track lock state in callers.
496 static bool compact_lock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
497 struct compact_control
*cc
)
500 /* Track if the lock is contended in async mode */
501 if (cc
->mode
== MIGRATE_ASYNC
&& !cc
->contended
) {
502 if (spin_trylock_irqsave(lock
, *flags
))
505 cc
->contended
= true;
508 spin_lock_irqsave(lock
, *flags
);
513 * Compaction requires the taking of some coarse locks that are potentially
514 * very heavily contended. The lock should be periodically unlocked to avoid
515 * having disabled IRQs for a long time, even when there is nobody waiting on
516 * the lock. It might also be that allowing the IRQs will result in
517 * need_resched() becoming true. If scheduling is needed, async compaction
518 * aborts. Sync compaction schedules.
519 * Either compaction type will also abort if a fatal signal is pending.
520 * In either case if the lock was locked, it is dropped and not regained.
522 * Returns true if compaction should abort due to fatal signal pending, or
523 * async compaction due to need_resched()
524 * Returns false when compaction can continue (sync compaction might have
527 static bool compact_unlock_should_abort(spinlock_t
*lock
,
528 unsigned long flags
, bool *locked
, struct compact_control
*cc
)
531 spin_unlock_irqrestore(lock
, flags
);
535 if (fatal_signal_pending(current
)) {
536 cc
->contended
= true;
546 * Isolate free pages onto a private freelist. If @strict is true, will abort
547 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
548 * (even though it may still end up isolating some pages).
550 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
551 unsigned long *start_pfn
,
552 unsigned long end_pfn
,
553 struct list_head
*freelist
,
557 int nr_scanned
= 0, total_isolated
= 0;
559 unsigned long flags
= 0;
561 unsigned long blockpfn
= *start_pfn
;
564 /* Strict mode is for isolation, speed is secondary */
568 cursor
= pfn_to_page(blockpfn
);
570 /* Isolate free pages. */
571 for (; blockpfn
< end_pfn
; blockpfn
+= stride
, cursor
+= stride
) {
573 struct page
*page
= cursor
;
576 * Periodically drop the lock (if held) regardless of its
577 * contention, to give chance to IRQs. Abort if fatal signal
578 * pending or async compaction detects need_resched()
580 if (!(blockpfn
% SWAP_CLUSTER_MAX
)
581 && compact_unlock_should_abort(&cc
->zone
->lock
, flags
,
588 * For compound pages such as THP and hugetlbfs, we can save
589 * potentially a lot of iterations if we skip them at once.
590 * The check is racy, but we can consider only valid values
591 * and the only danger is skipping too much.
593 if (PageCompound(page
)) {
594 const unsigned int order
= compound_order(page
);
596 if (likely(order
< MAX_ORDER
)) {
597 blockpfn
+= (1UL << order
) - 1;
598 cursor
+= (1UL << order
) - 1;
603 if (!PageBuddy(page
))
607 * If we already hold the lock, we can skip some rechecking.
608 * Note that if we hold the lock now, checked_pageblock was
609 * already set in some previous iteration (or strict is true),
610 * so it is correct to skip the suitable migration target
614 locked
= compact_lock_irqsave(&cc
->zone
->lock
,
617 /* Recheck this is a buddy page under lock */
618 if (!PageBuddy(page
))
622 /* Found a free page, will break it into order-0 pages */
623 order
= buddy_order(page
);
624 isolated
= __isolate_free_page(page
, order
);
627 set_page_private(page
, order
);
629 total_isolated
+= isolated
;
630 cc
->nr_freepages
+= isolated
;
631 list_add_tail(&page
->lru
, freelist
);
633 if (!strict
&& cc
->nr_migratepages
<= cc
->nr_freepages
) {
634 blockpfn
+= isolated
;
637 /* Advance to the end of split page */
638 blockpfn
+= isolated
- 1;
639 cursor
+= isolated
- 1;
651 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
654 * There is a tiny chance that we have read bogus compound_order(),
655 * so be careful to not go outside of the pageblock.
657 if (unlikely(blockpfn
> end_pfn
))
660 trace_mm_compaction_isolate_freepages(*start_pfn
, blockpfn
,
661 nr_scanned
, total_isolated
);
663 /* Record how far we have got within the block */
664 *start_pfn
= blockpfn
;
667 * If strict isolation is requested by CMA then check that all the
668 * pages requested were isolated. If there were any failures, 0 is
669 * returned and CMA will fail.
671 if (strict
&& blockpfn
< end_pfn
)
674 cc
->total_free_scanned
+= nr_scanned
;
676 count_compact_events(COMPACTISOLATED
, total_isolated
);
677 return total_isolated
;
681 * isolate_freepages_range() - isolate free pages.
682 * @cc: Compaction control structure.
683 * @start_pfn: The first PFN to start isolating.
684 * @end_pfn: The one-past-last PFN.
686 * Non-free pages, invalid PFNs, or zone boundaries within the
687 * [start_pfn, end_pfn) range are considered errors, cause function to
688 * undo its actions and return zero.
690 * Otherwise, function returns one-past-the-last PFN of isolated page
691 * (which may be greater then end_pfn if end fell in a middle of
695 isolate_freepages_range(struct compact_control
*cc
,
696 unsigned long start_pfn
, unsigned long end_pfn
)
698 unsigned long isolated
, pfn
, block_start_pfn
, block_end_pfn
;
702 block_start_pfn
= pageblock_start_pfn(pfn
);
703 if (block_start_pfn
< cc
->zone
->zone_start_pfn
)
704 block_start_pfn
= cc
->zone
->zone_start_pfn
;
705 block_end_pfn
= pageblock_end_pfn(pfn
);
707 for (; pfn
< end_pfn
; pfn
+= isolated
,
708 block_start_pfn
= block_end_pfn
,
709 block_end_pfn
+= pageblock_nr_pages
) {
710 /* Protect pfn from changing by isolate_freepages_block */
711 unsigned long isolate_start_pfn
= pfn
;
713 block_end_pfn
= min(block_end_pfn
, end_pfn
);
716 * pfn could pass the block_end_pfn if isolated freepage
717 * is more than pageblock order. In this case, we adjust
718 * scanning range to right one.
720 if (pfn
>= block_end_pfn
) {
721 block_start_pfn
= pageblock_start_pfn(pfn
);
722 block_end_pfn
= pageblock_end_pfn(pfn
);
723 block_end_pfn
= min(block_end_pfn
, end_pfn
);
726 if (!pageblock_pfn_to_page(block_start_pfn
,
727 block_end_pfn
, cc
->zone
))
730 isolated
= isolate_freepages_block(cc
, &isolate_start_pfn
,
731 block_end_pfn
, &freelist
, 0, true);
734 * In strict mode, isolate_freepages_block() returns 0 if
735 * there are any holes in the block (ie. invalid PFNs or
742 * If we managed to isolate pages, it is always (1 << n) *
743 * pageblock_nr_pages for some non-negative n. (Max order
744 * page may span two pageblocks).
748 /* __isolate_free_page() does not map the pages */
749 split_map_pages(&freelist
);
752 /* Loop terminated early, cleanup. */
753 release_freepages(&freelist
);
757 /* We don't use freelists for anything. */
761 /* Similar to reclaim, but different enough that they don't share logic */
762 static bool too_many_isolated(pg_data_t
*pgdat
)
764 unsigned long active
, inactive
, isolated
;
766 inactive
= node_page_state(pgdat
, NR_INACTIVE_FILE
) +
767 node_page_state(pgdat
, NR_INACTIVE_ANON
);
768 active
= node_page_state(pgdat
, NR_ACTIVE_FILE
) +
769 node_page_state(pgdat
, NR_ACTIVE_ANON
);
770 isolated
= node_page_state(pgdat
, NR_ISOLATED_FILE
) +
771 node_page_state(pgdat
, NR_ISOLATED_ANON
);
773 return isolated
> (inactive
+ active
) / 2;
777 * isolate_migratepages_block() - isolate all migrate-able pages within
779 * @cc: Compaction control structure.
780 * @low_pfn: The first PFN to isolate
781 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
782 * @isolate_mode: Isolation mode to be used.
784 * Isolate all pages that can be migrated from the range specified by
785 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
786 * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
787 * -ENOMEM in case we could not allocate a page, or 0.
788 * cc->migrate_pfn will contain the next pfn to scan.
790 * The pages are isolated on cc->migratepages list (not required to be empty),
791 * and cc->nr_migratepages is updated accordingly.
794 isolate_migratepages_block(struct compact_control
*cc
, unsigned long low_pfn
,
795 unsigned long end_pfn
, isolate_mode_t isolate_mode
)
797 pg_data_t
*pgdat
= cc
->zone
->zone_pgdat
;
798 unsigned long nr_scanned
= 0, nr_isolated
= 0;
799 struct lruvec
*lruvec
;
800 unsigned long flags
= 0;
801 struct lruvec
*locked
= NULL
;
802 struct page
*page
= NULL
, *valid_page
= NULL
;
803 unsigned long start_pfn
= low_pfn
;
804 bool skip_on_failure
= false;
805 unsigned long next_skip_pfn
= 0;
806 bool skip_updated
= false;
809 cc
->migrate_pfn
= low_pfn
;
812 * Ensure that there are not too many pages isolated from the LRU
813 * list by either parallel reclaimers or compaction. If there are,
814 * delay for some time until fewer pages are isolated
816 while (unlikely(too_many_isolated(pgdat
))) {
817 /* stop isolation if there are still pages not migrated */
818 if (cc
->nr_migratepages
)
821 /* async migration should just abort */
822 if (cc
->mode
== MIGRATE_ASYNC
)
825 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
827 if (fatal_signal_pending(current
))
833 if (cc
->direct_compaction
&& (cc
->mode
== MIGRATE_ASYNC
)) {
834 skip_on_failure
= true;
835 next_skip_pfn
= block_end_pfn(low_pfn
, cc
->order
);
838 /* Time to isolate some pages for migration */
839 for (; low_pfn
< end_pfn
; low_pfn
++) {
841 if (skip_on_failure
&& low_pfn
>= next_skip_pfn
) {
843 * We have isolated all migration candidates in the
844 * previous order-aligned block, and did not skip it due
845 * to failure. We should migrate the pages now and
846 * hopefully succeed compaction.
852 * We failed to isolate in the previous order-aligned
853 * block. Set the new boundary to the end of the
854 * current block. Note we can't simply increase
855 * next_skip_pfn by 1 << order, as low_pfn might have
856 * been incremented by a higher number due to skipping
857 * a compound or a high-order buddy page in the
858 * previous loop iteration.
860 next_skip_pfn
= block_end_pfn(low_pfn
, cc
->order
);
864 * Periodically drop the lock (if held) regardless of its
865 * contention, to give chance to IRQs. Abort completely if
866 * a fatal signal is pending.
868 if (!(low_pfn
% SWAP_CLUSTER_MAX
)) {
870 unlock_page_lruvec_irqrestore(locked
, flags
);
874 if (fatal_signal_pending(current
)) {
875 cc
->contended
= true;
886 page
= pfn_to_page(low_pfn
);
889 * Check if the pageblock has already been marked skipped.
890 * Only the aligned PFN is checked as the caller isolates
891 * COMPACT_CLUSTER_MAX at a time so the second call must
892 * not falsely conclude that the block should be skipped.
894 if (!valid_page
&& IS_ALIGNED(low_pfn
, pageblock_nr_pages
)) {
895 if (!cc
->ignore_skip_hint
&& get_pageblock_skip(page
)) {
903 if (PageHuge(page
) && cc
->alloc_contig
) {
904 ret
= isolate_or_dissolve_huge_page(page
, &cc
->migratepages
);
907 * Fail isolation in case isolate_or_dissolve_huge_page()
908 * reports an error. In case of -ENOMEM, abort right away.
911 /* Do not report -EBUSY down the chain */
914 low_pfn
+= (1UL << compound_order(page
)) - 1;
918 if (PageHuge(page
)) {
920 * Hugepage was successfully isolated and placed
921 * on the cc->migratepages list.
923 low_pfn
+= compound_nr(page
) - 1;
924 goto isolate_success_no_list
;
928 * Ok, the hugepage was dissolved. Now these pages are
929 * Buddy and cannot be re-allocated because they are
930 * isolated. Fall-through as the check below handles
936 * Skip if free. We read page order here without zone lock
937 * which is generally unsafe, but the race window is small and
938 * the worst thing that can happen is that we skip some
939 * potential isolation targets.
941 if (PageBuddy(page
)) {
942 unsigned long freepage_order
= buddy_order_unsafe(page
);
945 * Without lock, we cannot be sure that what we got is
946 * a valid page order. Consider only values in the
947 * valid order range to prevent low_pfn overflow.
949 if (freepage_order
> 0 && freepage_order
< MAX_ORDER
)
950 low_pfn
+= (1UL << freepage_order
) - 1;
955 * Regardless of being on LRU, compound pages such as THP and
956 * hugetlbfs are not to be compacted unless we are attempting
957 * an allocation much larger than the huge page size (eg CMA).
958 * We can potentially save a lot of iterations if we skip them
959 * at once. The check is racy, but we can consider only valid
960 * values and the only danger is skipping too much.
962 if (PageCompound(page
) && !cc
->alloc_contig
) {
963 const unsigned int order
= compound_order(page
);
965 if (likely(order
< MAX_ORDER
))
966 low_pfn
+= (1UL << order
) - 1;
971 * Check may be lockless but that's ok as we recheck later.
972 * It's possible to migrate LRU and non-lru movable pages.
973 * Skip any other type of page
975 if (!PageLRU(page
)) {
977 * __PageMovable can return false positive so we need
978 * to verify it under page_lock.
980 if (unlikely(__PageMovable(page
)) &&
981 !PageIsolated(page
)) {
983 unlock_page_lruvec_irqrestore(locked
, flags
);
987 if (!isolate_movable_page(page
, isolate_mode
))
988 goto isolate_success
;
995 * Migration will fail if an anonymous page is pinned in memory,
996 * so avoid taking lru_lock and isolating it unnecessarily in an
997 * admittedly racy check.
999 if (!page_mapping(page
) &&
1000 page_count(page
) > page_mapcount(page
))
1004 * Only allow to migrate anonymous pages in GFP_NOFS context
1005 * because those do not depend on fs locks.
1007 if (!(cc
->gfp_mask
& __GFP_FS
) && page_mapping(page
))
1011 * Be careful not to clear PageLRU until after we're
1012 * sure the page is not being freed elsewhere -- the
1013 * page release code relies on it.
1015 if (unlikely(!get_page_unless_zero(page
)))
1018 if (!__isolate_lru_page_prepare(page
, isolate_mode
))
1019 goto isolate_fail_put
;
1021 /* Try isolate the page */
1022 if (!TestClearPageLRU(page
))
1023 goto isolate_fail_put
;
1025 lruvec
= mem_cgroup_page_lruvec(page
);
1027 /* If we already hold the lock, we can skip some rechecking */
1028 if (lruvec
!= locked
) {
1030 unlock_page_lruvec_irqrestore(locked
, flags
);
1032 compact_lock_irqsave(&lruvec
->lru_lock
, &flags
, cc
);
1035 lruvec_memcg_debug(lruvec
, page
);
1037 /* Try get exclusive access under lock */
1038 if (!skip_updated
) {
1039 skip_updated
= true;
1040 if (test_and_set_skip(cc
, page
, low_pfn
))
1045 * Page become compound since the non-locked check,
1046 * and it's on LRU. It can only be a THP so the order
1047 * is safe to read and it's 0 for tail pages.
1049 if (unlikely(PageCompound(page
) && !cc
->alloc_contig
)) {
1050 low_pfn
+= compound_nr(page
) - 1;
1052 goto isolate_fail_put
;
1056 /* The whole page is taken off the LRU; skip the tail pages. */
1057 if (PageCompound(page
))
1058 low_pfn
+= compound_nr(page
) - 1;
1060 /* Successfully isolated */
1061 del_page_from_lru_list(page
, lruvec
);
1062 mod_node_page_state(page_pgdat(page
),
1063 NR_ISOLATED_ANON
+ page_is_file_lru(page
),
1064 thp_nr_pages(page
));
1067 list_add(&page
->lru
, &cc
->migratepages
);
1068 isolate_success_no_list
:
1069 cc
->nr_migratepages
+= compound_nr(page
);
1070 nr_isolated
+= compound_nr(page
);
1073 * Avoid isolating too much unless this block is being
1074 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1075 * or a lock is contended. For contention, isolate quickly to
1076 * potentially remove one source of contention.
1078 if (cc
->nr_migratepages
>= COMPACT_CLUSTER_MAX
&&
1079 !cc
->rescan
&& !cc
->contended
) {
1087 /* Avoid potential deadlock in freeing page under lru_lock */
1089 unlock_page_lruvec_irqrestore(locked
, flags
);
1095 if (!skip_on_failure
&& ret
!= -ENOMEM
)
1099 * We have isolated some pages, but then failed. Release them
1100 * instead of migrating, as we cannot form the cc->order buddy
1105 unlock_page_lruvec_irqrestore(locked
, flags
);
1108 putback_movable_pages(&cc
->migratepages
);
1109 cc
->nr_migratepages
= 0;
1113 if (low_pfn
< next_skip_pfn
) {
1114 low_pfn
= next_skip_pfn
- 1;
1116 * The check near the loop beginning would have updated
1117 * next_skip_pfn too, but this is a bit simpler.
1119 next_skip_pfn
+= 1UL << cc
->order
;
1127 * The PageBuddy() check could have potentially brought us outside
1128 * the range to be scanned.
1130 if (unlikely(low_pfn
> end_pfn
))
1137 unlock_page_lruvec_irqrestore(locked
, flags
);
1144 * Updated the cached scanner pfn once the pageblock has been scanned
1145 * Pages will either be migrated in which case there is no point
1146 * scanning in the near future or migration failed in which case the
1147 * failure reason may persist. The block is marked for skipping if
1148 * there were no pages isolated in the block or if the block is
1149 * rescanned twice in a row.
1151 if (low_pfn
== end_pfn
&& (!nr_isolated
|| cc
->rescan
)) {
1152 if (valid_page
&& !skip_updated
)
1153 set_pageblock_skip(valid_page
);
1154 update_cached_migrate(cc
, low_pfn
);
1157 trace_mm_compaction_isolate_migratepages(start_pfn
, low_pfn
,
1158 nr_scanned
, nr_isolated
);
1161 cc
->total_migrate_scanned
+= nr_scanned
;
1163 count_compact_events(COMPACTISOLATED
, nr_isolated
);
1165 cc
->migrate_pfn
= low_pfn
;
1171 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1172 * @cc: Compaction control structure.
1173 * @start_pfn: The first PFN to start isolating.
1174 * @end_pfn: The one-past-last PFN.
1176 * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
1177 * in case we could not allocate a page, or 0.
1180 isolate_migratepages_range(struct compact_control
*cc
, unsigned long start_pfn
,
1181 unsigned long end_pfn
)
1183 unsigned long pfn
, block_start_pfn
, block_end_pfn
;
1186 /* Scan block by block. First and last block may be incomplete */
1188 block_start_pfn
= pageblock_start_pfn(pfn
);
1189 if (block_start_pfn
< cc
->zone
->zone_start_pfn
)
1190 block_start_pfn
= cc
->zone
->zone_start_pfn
;
1191 block_end_pfn
= pageblock_end_pfn(pfn
);
1193 for (; pfn
< end_pfn
; pfn
= block_end_pfn
,
1194 block_start_pfn
= block_end_pfn
,
1195 block_end_pfn
+= pageblock_nr_pages
) {
1197 block_end_pfn
= min(block_end_pfn
, end_pfn
);
1199 if (!pageblock_pfn_to_page(block_start_pfn
,
1200 block_end_pfn
, cc
->zone
))
1203 ret
= isolate_migratepages_block(cc
, pfn
, block_end_pfn
,
1204 ISOLATE_UNEVICTABLE
);
1209 if (cc
->nr_migratepages
>= COMPACT_CLUSTER_MAX
)
1216 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
1217 #ifdef CONFIG_COMPACTION
1219 static bool suitable_migration_source(struct compact_control
*cc
,
1224 if (pageblock_skip_persistent(page
))
1227 if ((cc
->mode
!= MIGRATE_ASYNC
) || !cc
->direct_compaction
)
1230 block_mt
= get_pageblock_migratetype(page
);
1232 if (cc
->migratetype
== MIGRATE_MOVABLE
)
1233 return is_migrate_movable(block_mt
);
1235 return block_mt
== cc
->migratetype
;
1238 /* Returns true if the page is within a block suitable for migration to */
1239 static bool suitable_migration_target(struct compact_control
*cc
,
1242 /* If the page is a large free page, then disallow migration */
1243 if (PageBuddy(page
)) {
1245 * We are checking page_order without zone->lock taken. But
1246 * the only small danger is that we skip a potentially suitable
1247 * pageblock, so it's not worth to check order for valid range.
1249 if (buddy_order_unsafe(page
) >= pageblock_order
)
1253 if (cc
->ignore_block_suitable
)
1256 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1257 if (is_migrate_movable(get_pageblock_migratetype(page
)))
1260 /* Otherwise skip the block */
1264 static inline unsigned int
1265 freelist_scan_limit(struct compact_control
*cc
)
1267 unsigned short shift
= BITS_PER_LONG
- 1;
1269 return (COMPACT_CLUSTER_MAX
>> min(shift
, cc
->fast_search_fail
)) + 1;
1273 * Test whether the free scanner has reached the same or lower pageblock than
1274 * the migration scanner, and compaction should thus terminate.
1276 static inline bool compact_scanners_met(struct compact_control
*cc
)
1278 return (cc
->free_pfn
>> pageblock_order
)
1279 <= (cc
->migrate_pfn
>> pageblock_order
);
1283 * Used when scanning for a suitable migration target which scans freelists
1284 * in reverse. Reorders the list such as the unscanned pages are scanned
1285 * first on the next iteration of the free scanner
1288 move_freelist_head(struct list_head
*freelist
, struct page
*freepage
)
1292 if (!list_is_last(freelist
, &freepage
->lru
)) {
1293 list_cut_before(&sublist
, freelist
, &freepage
->lru
);
1294 list_splice_tail(&sublist
, freelist
);
1299 * Similar to move_freelist_head except used by the migration scanner
1300 * when scanning forward. It's possible for these list operations to
1301 * move against each other if they search the free list exactly in
1305 move_freelist_tail(struct list_head
*freelist
, struct page
*freepage
)
1309 if (!list_is_first(freelist
, &freepage
->lru
)) {
1310 list_cut_position(&sublist
, freelist
, &freepage
->lru
);
1311 list_splice_tail(&sublist
, freelist
);
1316 fast_isolate_around(struct compact_control
*cc
, unsigned long pfn
, unsigned long nr_isolated
)
1318 unsigned long start_pfn
, end_pfn
;
1321 /* Do not search around if there are enough pages already */
1322 if (cc
->nr_freepages
>= cc
->nr_migratepages
)
1325 /* Minimise scanning during async compaction */
1326 if (cc
->direct_compaction
&& cc
->mode
== MIGRATE_ASYNC
)
1329 /* Pageblock boundaries */
1330 start_pfn
= max(pageblock_start_pfn(pfn
), cc
->zone
->zone_start_pfn
);
1331 end_pfn
= min(pageblock_end_pfn(pfn
), zone_end_pfn(cc
->zone
));
1333 page
= pageblock_pfn_to_page(start_pfn
, end_pfn
, cc
->zone
);
1338 if (start_pfn
!= pfn
) {
1339 isolate_freepages_block(cc
, &start_pfn
, pfn
, &cc
->freepages
, 1, false);
1340 if (cc
->nr_freepages
>= cc
->nr_migratepages
)
1345 start_pfn
= pfn
+ nr_isolated
;
1346 if (start_pfn
< end_pfn
)
1347 isolate_freepages_block(cc
, &start_pfn
, end_pfn
, &cc
->freepages
, 1, false);
1349 /* Skip this pageblock in the future as it's full or nearly full */
1350 if (cc
->nr_freepages
< cc
->nr_migratepages
)
1351 set_pageblock_skip(page
);
1354 /* Search orders in round-robin fashion */
1355 static int next_search_order(struct compact_control
*cc
, int order
)
1359 order
= cc
->order
- 1;
1361 /* Search wrapped around? */
1362 if (order
== cc
->search_order
) {
1364 if (cc
->search_order
< 0)
1365 cc
->search_order
= cc
->order
- 1;
1372 static unsigned long
1373 fast_isolate_freepages(struct compact_control
*cc
)
1375 unsigned int limit
= max(1U, freelist_scan_limit(cc
) >> 1);
1376 unsigned int nr_scanned
= 0;
1377 unsigned long low_pfn
, min_pfn
, highest
= 0;
1378 unsigned long nr_isolated
= 0;
1379 unsigned long distance
;
1380 struct page
*page
= NULL
;
1381 bool scan_start
= false;
1384 /* Full compaction passes in a negative order */
1386 return cc
->free_pfn
;
1389 * If starting the scan, use a deeper search and use the highest
1390 * PFN found if a suitable one is not found.
1392 if (cc
->free_pfn
>= cc
->zone
->compact_init_free_pfn
) {
1393 limit
= pageblock_nr_pages
>> 1;
1398 * Preferred point is in the top quarter of the scan space but take
1399 * a pfn from the top half if the search is problematic.
1401 distance
= (cc
->free_pfn
- cc
->migrate_pfn
);
1402 low_pfn
= pageblock_start_pfn(cc
->free_pfn
- (distance
>> 2));
1403 min_pfn
= pageblock_start_pfn(cc
->free_pfn
- (distance
>> 1));
1405 if (WARN_ON_ONCE(min_pfn
> low_pfn
))
1409 * Search starts from the last successful isolation order or the next
1410 * order to search after a previous failure
1412 cc
->search_order
= min_t(unsigned int, cc
->order
- 1, cc
->search_order
);
1414 for (order
= cc
->search_order
;
1415 !page
&& order
>= 0;
1416 order
= next_search_order(cc
, order
)) {
1417 struct free_area
*area
= &cc
->zone
->free_area
[order
];
1418 struct list_head
*freelist
;
1419 struct page
*freepage
;
1420 unsigned long flags
;
1421 unsigned int order_scanned
= 0;
1422 unsigned long high_pfn
= 0;
1427 spin_lock_irqsave(&cc
->zone
->lock
, flags
);
1428 freelist
= &area
->free_list
[MIGRATE_MOVABLE
];
1429 list_for_each_entry_reverse(freepage
, freelist
, lru
) {
1434 pfn
= page_to_pfn(freepage
);
1437 highest
= max(pageblock_start_pfn(pfn
),
1438 cc
->zone
->zone_start_pfn
);
1440 if (pfn
>= low_pfn
) {
1441 cc
->fast_search_fail
= 0;
1442 cc
->search_order
= order
;
1447 if (pfn
>= min_pfn
&& pfn
> high_pfn
) {
1450 /* Shorten the scan if a candidate is found */
1454 if (order_scanned
>= limit
)
1458 /* Use a minimum pfn if a preferred one was not found */
1459 if (!page
&& high_pfn
) {
1460 page
= pfn_to_page(high_pfn
);
1462 /* Update freepage for the list reorder below */
1466 /* Reorder to so a future search skips recent pages */
1467 move_freelist_head(freelist
, freepage
);
1469 /* Isolate the page if available */
1471 if (__isolate_free_page(page
, order
)) {
1472 set_page_private(page
, order
);
1473 nr_isolated
= 1 << order
;
1474 cc
->nr_freepages
+= nr_isolated
;
1475 list_add_tail(&page
->lru
, &cc
->freepages
);
1476 count_compact_events(COMPACTISOLATED
, nr_isolated
);
1478 /* If isolation fails, abort the search */
1479 order
= cc
->search_order
+ 1;
1484 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
1487 * Smaller scan on next order so the total scan is related
1488 * to freelist_scan_limit.
1490 if (order_scanned
>= limit
)
1491 limit
= max(1U, limit
>> 1);
1495 cc
->fast_search_fail
++;
1498 * Use the highest PFN found above min. If one was
1499 * not found, be pessimistic for direct compaction
1500 * and use the min mark.
1503 page
= pfn_to_page(highest
);
1504 cc
->free_pfn
= highest
;
1506 if (cc
->direct_compaction
&& pfn_valid(min_pfn
)) {
1507 page
= pageblock_pfn_to_page(min_pfn
,
1508 min(pageblock_end_pfn(min_pfn
),
1509 zone_end_pfn(cc
->zone
)),
1511 cc
->free_pfn
= min_pfn
;
1517 if (highest
&& highest
>= cc
->zone
->compact_cached_free_pfn
) {
1518 highest
-= pageblock_nr_pages
;
1519 cc
->zone
->compact_cached_free_pfn
= highest
;
1522 cc
->total_free_scanned
+= nr_scanned
;
1524 return cc
->free_pfn
;
1526 low_pfn
= page_to_pfn(page
);
1527 fast_isolate_around(cc
, low_pfn
, nr_isolated
);
1532 * Based on information in the current compact_control, find blocks
1533 * suitable for isolating free pages from and then isolate them.
1535 static void isolate_freepages(struct compact_control
*cc
)
1537 struct zone
*zone
= cc
->zone
;
1539 unsigned long block_start_pfn
; /* start of current pageblock */
1540 unsigned long isolate_start_pfn
; /* exact pfn we start at */
1541 unsigned long block_end_pfn
; /* end of current pageblock */
1542 unsigned long low_pfn
; /* lowest pfn scanner is able to scan */
1543 struct list_head
*freelist
= &cc
->freepages
;
1544 unsigned int stride
;
1546 /* Try a small search of the free lists for a candidate */
1547 isolate_start_pfn
= fast_isolate_freepages(cc
);
1548 if (cc
->nr_freepages
)
1552 * Initialise the free scanner. The starting point is where we last
1553 * successfully isolated from, zone-cached value, or the end of the
1554 * zone when isolating for the first time. For looping we also need
1555 * this pfn aligned down to the pageblock boundary, because we do
1556 * block_start_pfn -= pageblock_nr_pages in the for loop.
1557 * For ending point, take care when isolating in last pageblock of a
1558 * zone which ends in the middle of a pageblock.
1559 * The low boundary is the end of the pageblock the migration scanner
1562 isolate_start_pfn
= cc
->free_pfn
;
1563 block_start_pfn
= pageblock_start_pfn(isolate_start_pfn
);
1564 block_end_pfn
= min(block_start_pfn
+ pageblock_nr_pages
,
1565 zone_end_pfn(zone
));
1566 low_pfn
= pageblock_end_pfn(cc
->migrate_pfn
);
1567 stride
= cc
->mode
== MIGRATE_ASYNC
? COMPACT_CLUSTER_MAX
: 1;
1570 * Isolate free pages until enough are available to migrate the
1571 * pages on cc->migratepages. We stop searching if the migrate
1572 * and free page scanners meet or enough free pages are isolated.
1574 for (; block_start_pfn
>= low_pfn
;
1575 block_end_pfn
= block_start_pfn
,
1576 block_start_pfn
-= pageblock_nr_pages
,
1577 isolate_start_pfn
= block_start_pfn
) {
1578 unsigned long nr_isolated
;
1581 * This can iterate a massively long zone without finding any
1582 * suitable migration targets, so periodically check resched.
1584 if (!(block_start_pfn
% (SWAP_CLUSTER_MAX
* pageblock_nr_pages
)))
1587 page
= pageblock_pfn_to_page(block_start_pfn
, block_end_pfn
,
1592 /* Check the block is suitable for migration */
1593 if (!suitable_migration_target(cc
, page
))
1596 /* If isolation recently failed, do not retry */
1597 if (!isolation_suitable(cc
, page
))
1600 /* Found a block suitable for isolating free pages from. */
1601 nr_isolated
= isolate_freepages_block(cc
, &isolate_start_pfn
,
1602 block_end_pfn
, freelist
, stride
, false);
1604 /* Update the skip hint if the full pageblock was scanned */
1605 if (isolate_start_pfn
== block_end_pfn
)
1606 update_pageblock_skip(cc
, page
, block_start_pfn
);
1608 /* Are enough freepages isolated? */
1609 if (cc
->nr_freepages
>= cc
->nr_migratepages
) {
1610 if (isolate_start_pfn
>= block_end_pfn
) {
1612 * Restart at previous pageblock if more
1613 * freepages can be isolated next time.
1616 block_start_pfn
- pageblock_nr_pages
;
1619 } else if (isolate_start_pfn
< block_end_pfn
) {
1621 * If isolation failed early, do not continue
1627 /* Adjust stride depending on isolation */
1632 stride
= min_t(unsigned int, COMPACT_CLUSTER_MAX
, stride
<< 1);
1636 * Record where the free scanner will restart next time. Either we
1637 * broke from the loop and set isolate_start_pfn based on the last
1638 * call to isolate_freepages_block(), or we met the migration scanner
1639 * and the loop terminated due to isolate_start_pfn < low_pfn
1641 cc
->free_pfn
= isolate_start_pfn
;
1644 /* __isolate_free_page() does not map the pages */
1645 split_map_pages(freelist
);
1649 * This is a migrate-callback that "allocates" freepages by taking pages
1650 * from the isolated freelists in the block we are migrating to.
1652 static struct page
*compaction_alloc(struct page
*migratepage
,
1655 struct compact_control
*cc
= (struct compact_control
*)data
;
1656 struct page
*freepage
;
1658 if (list_empty(&cc
->freepages
)) {
1659 isolate_freepages(cc
);
1661 if (list_empty(&cc
->freepages
))
1665 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
1666 list_del(&freepage
->lru
);
1673 * This is a migrate-callback that "frees" freepages back to the isolated
1674 * freelist. All pages on the freelist are from the same zone, so there is no
1675 * special handling needed for NUMA.
1677 static void compaction_free(struct page
*page
, unsigned long data
)
1679 struct compact_control
*cc
= (struct compact_control
*)data
;
1681 list_add(&page
->lru
, &cc
->freepages
);
1685 /* possible outcome of isolate_migratepages */
1687 ISOLATE_ABORT
, /* Abort compaction now */
1688 ISOLATE_NONE
, /* No pages isolated, continue scanning */
1689 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
1690 } isolate_migrate_t
;
1693 * Allow userspace to control policy on scanning the unevictable LRU for
1694 * compactable pages.
1696 #ifdef CONFIG_PREEMPT_RT
1697 int sysctl_compact_unevictable_allowed __read_mostly
= 0;
1699 int sysctl_compact_unevictable_allowed __read_mostly
= 1;
1703 update_fast_start_pfn(struct compact_control
*cc
, unsigned long pfn
)
1705 if (cc
->fast_start_pfn
== ULONG_MAX
)
1708 if (!cc
->fast_start_pfn
)
1709 cc
->fast_start_pfn
= pfn
;
1711 cc
->fast_start_pfn
= min(cc
->fast_start_pfn
, pfn
);
1714 static inline unsigned long
1715 reinit_migrate_pfn(struct compact_control
*cc
)
1717 if (!cc
->fast_start_pfn
|| cc
->fast_start_pfn
== ULONG_MAX
)
1718 return cc
->migrate_pfn
;
1720 cc
->migrate_pfn
= cc
->fast_start_pfn
;
1721 cc
->fast_start_pfn
= ULONG_MAX
;
1723 return cc
->migrate_pfn
;
1727 * Briefly search the free lists for a migration source that already has
1728 * some free pages to reduce the number of pages that need migration
1729 * before a pageblock is free.
1731 static unsigned long fast_find_migrateblock(struct compact_control
*cc
)
1733 unsigned int limit
= freelist_scan_limit(cc
);
1734 unsigned int nr_scanned
= 0;
1735 unsigned long distance
;
1736 unsigned long pfn
= cc
->migrate_pfn
;
1737 unsigned long high_pfn
;
1739 bool found_block
= false;
1741 /* Skip hints are relied on to avoid repeats on the fast search */
1742 if (cc
->ignore_skip_hint
)
1746 * If the migrate_pfn is not at the start of a zone or the start
1747 * of a pageblock then assume this is a continuation of a previous
1748 * scan restarted due to COMPACT_CLUSTER_MAX.
1750 if (pfn
!= cc
->zone
->zone_start_pfn
&& pfn
!= pageblock_start_pfn(pfn
))
1754 * For smaller orders, just linearly scan as the number of pages
1755 * to migrate should be relatively small and does not necessarily
1756 * justify freeing up a large block for a small allocation.
1758 if (cc
->order
<= PAGE_ALLOC_COSTLY_ORDER
)
1762 * Only allow kcompactd and direct requests for movable pages to
1763 * quickly clear out a MOVABLE pageblock for allocation. This
1764 * reduces the risk that a large movable pageblock is freed for
1765 * an unmovable/reclaimable small allocation.
1767 if (cc
->direct_compaction
&& cc
->migratetype
!= MIGRATE_MOVABLE
)
1771 * When starting the migration scanner, pick any pageblock within the
1772 * first half of the search space. Otherwise try and pick a pageblock
1773 * within the first eighth to reduce the chances that a migration
1774 * target later becomes a source.
1776 distance
= (cc
->free_pfn
- cc
->migrate_pfn
) >> 1;
1777 if (cc
->migrate_pfn
!= cc
->zone
->zone_start_pfn
)
1779 high_pfn
= pageblock_start_pfn(cc
->migrate_pfn
+ distance
);
1781 for (order
= cc
->order
- 1;
1782 order
>= PAGE_ALLOC_COSTLY_ORDER
&& !found_block
&& nr_scanned
< limit
;
1784 struct free_area
*area
= &cc
->zone
->free_area
[order
];
1785 struct list_head
*freelist
;
1786 unsigned long flags
;
1787 struct page
*freepage
;
1792 spin_lock_irqsave(&cc
->zone
->lock
, flags
);
1793 freelist
= &area
->free_list
[MIGRATE_MOVABLE
];
1794 list_for_each_entry(freepage
, freelist
, lru
) {
1795 unsigned long free_pfn
;
1797 if (nr_scanned
++ >= limit
) {
1798 move_freelist_tail(freelist
, freepage
);
1802 free_pfn
= page_to_pfn(freepage
);
1803 if (free_pfn
< high_pfn
) {
1805 * Avoid if skipped recently. Ideally it would
1806 * move to the tail but even safe iteration of
1807 * the list assumes an entry is deleted, not
1810 if (get_pageblock_skip(freepage
))
1813 /* Reorder to so a future search skips recent pages */
1814 move_freelist_tail(freelist
, freepage
);
1816 update_fast_start_pfn(cc
, free_pfn
);
1817 pfn
= pageblock_start_pfn(free_pfn
);
1818 cc
->fast_search_fail
= 0;
1820 set_pageblock_skip(freepage
);
1824 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
1827 cc
->total_migrate_scanned
+= nr_scanned
;
1830 * If fast scanning failed then use a cached entry for a page block
1831 * that had free pages as the basis for starting a linear scan.
1834 cc
->fast_search_fail
++;
1835 pfn
= reinit_migrate_pfn(cc
);
1841 * Isolate all pages that can be migrated from the first suitable block,
1842 * starting at the block pointed to by the migrate scanner pfn within
1845 static isolate_migrate_t
isolate_migratepages(struct compact_control
*cc
)
1847 unsigned long block_start_pfn
;
1848 unsigned long block_end_pfn
;
1849 unsigned long low_pfn
;
1851 const isolate_mode_t isolate_mode
=
1852 (sysctl_compact_unevictable_allowed
? ISOLATE_UNEVICTABLE
: 0) |
1853 (cc
->mode
!= MIGRATE_SYNC
? ISOLATE_ASYNC_MIGRATE
: 0);
1854 bool fast_find_block
;
1857 * Start at where we last stopped, or beginning of the zone as
1858 * initialized by compact_zone(). The first failure will use
1859 * the lowest PFN as the starting point for linear scanning.
1861 low_pfn
= fast_find_migrateblock(cc
);
1862 block_start_pfn
= pageblock_start_pfn(low_pfn
);
1863 if (block_start_pfn
< cc
->zone
->zone_start_pfn
)
1864 block_start_pfn
= cc
->zone
->zone_start_pfn
;
1867 * fast_find_migrateblock marks a pageblock skipped so to avoid
1868 * the isolation_suitable check below, check whether the fast
1869 * search was successful.
1871 fast_find_block
= low_pfn
!= cc
->migrate_pfn
&& !cc
->fast_search_fail
;
1873 /* Only scan within a pageblock boundary */
1874 block_end_pfn
= pageblock_end_pfn(low_pfn
);
1877 * Iterate over whole pageblocks until we find the first suitable.
1878 * Do not cross the free scanner.
1880 for (; block_end_pfn
<= cc
->free_pfn
;
1881 fast_find_block
= false,
1882 cc
->migrate_pfn
= low_pfn
= block_end_pfn
,
1883 block_start_pfn
= block_end_pfn
,
1884 block_end_pfn
+= pageblock_nr_pages
) {
1887 * This can potentially iterate a massively long zone with
1888 * many pageblocks unsuitable, so periodically check if we
1891 if (!(low_pfn
% (SWAP_CLUSTER_MAX
* pageblock_nr_pages
)))
1894 page
= pageblock_pfn_to_page(block_start_pfn
,
1895 block_end_pfn
, cc
->zone
);
1900 * If isolation recently failed, do not retry. Only check the
1901 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1902 * to be visited multiple times. Assume skip was checked
1903 * before making it "skip" so other compaction instances do
1904 * not scan the same block.
1906 if (IS_ALIGNED(low_pfn
, pageblock_nr_pages
) &&
1907 !fast_find_block
&& !isolation_suitable(cc
, page
))
1911 * For async compaction, also only scan in MOVABLE blocks
1912 * without huge pages. Async compaction is optimistic to see
1913 * if the minimum amount of work satisfies the allocation.
1914 * The cached PFN is updated as it's possible that all
1915 * remaining blocks between source and target are unsuitable
1916 * and the compaction scanners fail to meet.
1918 if (!suitable_migration_source(cc
, page
)) {
1919 update_cached_migrate(cc
, block_end_pfn
);
1923 /* Perform the isolation */
1924 if (isolate_migratepages_block(cc
, low_pfn
, block_end_pfn
,
1926 return ISOLATE_ABORT
;
1929 * Either we isolated something and proceed with migration. Or
1930 * we failed and compact_zone should decide if we should
1936 return cc
->nr_migratepages
? ISOLATE_SUCCESS
: ISOLATE_NONE
;
1940 * order == -1 is expected when compacting via
1941 * /proc/sys/vm/compact_memory
1943 static inline bool is_via_compact_memory(int order
)
1948 static bool kswapd_is_running(pg_data_t
*pgdat
)
1950 return pgdat
->kswapd
&& task_is_running(pgdat
->kswapd
);
1954 * A zone's fragmentation score is the external fragmentation wrt to the
1955 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
1957 static unsigned int fragmentation_score_zone(struct zone
*zone
)
1959 return extfrag_for_order(zone
, COMPACTION_HPAGE_ORDER
);
1963 * A weighted zone's fragmentation score is the external fragmentation
1964 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
1965 * returns a value in the range [0, 100].
1967 * The scaling factor ensures that proactive compaction focuses on larger
1968 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
1969 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
1970 * and thus never exceeds the high threshold for proactive compaction.
1972 static unsigned int fragmentation_score_zone_weighted(struct zone
*zone
)
1974 unsigned long score
;
1976 score
= zone
->present_pages
* fragmentation_score_zone(zone
);
1977 return div64_ul(score
, zone
->zone_pgdat
->node_present_pages
+ 1);
1981 * The per-node proactive (background) compaction process is started by its
1982 * corresponding kcompactd thread when the node's fragmentation score
1983 * exceeds the high threshold. The compaction process remains active till
1984 * the node's score falls below the low threshold, or one of the back-off
1985 * conditions is met.
1987 static unsigned int fragmentation_score_node(pg_data_t
*pgdat
)
1989 unsigned int score
= 0;
1992 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
1995 zone
= &pgdat
->node_zones
[zoneid
];
1996 score
+= fragmentation_score_zone_weighted(zone
);
2002 static unsigned int fragmentation_score_wmark(pg_data_t
*pgdat
, bool low
)
2004 unsigned int wmark_low
;
2007 * Cap the low watermark to avoid excessive compaction
2008 * activity in case a user sets the proactiveness tunable
2009 * close to 100 (maximum).
2011 wmark_low
= max(100U - sysctl_compaction_proactiveness
, 5U);
2012 return low
? wmark_low
: min(wmark_low
+ 10, 100U);
2015 static bool should_proactive_compact_node(pg_data_t
*pgdat
)
2019 if (!sysctl_compaction_proactiveness
|| kswapd_is_running(pgdat
))
2022 wmark_high
= fragmentation_score_wmark(pgdat
, false);
2023 return fragmentation_score_node(pgdat
) > wmark_high
;
2026 static enum compact_result
__compact_finished(struct compact_control
*cc
)
2029 const int migratetype
= cc
->migratetype
;
2032 /* Compaction run completes if the migrate and free scanner meet */
2033 if (compact_scanners_met(cc
)) {
2034 /* Let the next compaction start anew. */
2035 reset_cached_positions(cc
->zone
);
2038 * Mark that the PG_migrate_skip information should be cleared
2039 * by kswapd when it goes to sleep. kcompactd does not set the
2040 * flag itself as the decision to be clear should be directly
2041 * based on an allocation request.
2043 if (cc
->direct_compaction
)
2044 cc
->zone
->compact_blockskip_flush
= true;
2047 return COMPACT_COMPLETE
;
2049 return COMPACT_PARTIAL_SKIPPED
;
2052 if (cc
->proactive_compaction
) {
2053 int score
, wmark_low
;
2056 pgdat
= cc
->zone
->zone_pgdat
;
2057 if (kswapd_is_running(pgdat
))
2058 return COMPACT_PARTIAL_SKIPPED
;
2060 score
= fragmentation_score_zone(cc
->zone
);
2061 wmark_low
= fragmentation_score_wmark(pgdat
, true);
2063 if (score
> wmark_low
)
2064 ret
= COMPACT_CONTINUE
;
2066 ret
= COMPACT_SUCCESS
;
2071 if (is_via_compact_memory(cc
->order
))
2072 return COMPACT_CONTINUE
;
2075 * Always finish scanning a pageblock to reduce the possibility of
2076 * fallbacks in the future. This is particularly important when
2077 * migration source is unmovable/reclaimable but it's not worth
2080 if (!IS_ALIGNED(cc
->migrate_pfn
, pageblock_nr_pages
))
2081 return COMPACT_CONTINUE
;
2083 /* Direct compactor: Is a suitable page free? */
2084 ret
= COMPACT_NO_SUITABLE_PAGE
;
2085 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
2086 struct free_area
*area
= &cc
->zone
->free_area
[order
];
2089 /* Job done if page is free of the right migratetype */
2090 if (!free_area_empty(area
, migratetype
))
2091 return COMPACT_SUCCESS
;
2094 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2095 if (migratetype
== MIGRATE_MOVABLE
&&
2096 !free_area_empty(area
, MIGRATE_CMA
))
2097 return COMPACT_SUCCESS
;
2100 * Job done if allocation would steal freepages from
2101 * other migratetype buddy lists.
2103 if (find_suitable_fallback(area
, order
, migratetype
,
2104 true, &can_steal
) != -1) {
2106 /* movable pages are OK in any pageblock */
2107 if (migratetype
== MIGRATE_MOVABLE
)
2108 return COMPACT_SUCCESS
;
2111 * We are stealing for a non-movable allocation. Make
2112 * sure we finish compacting the current pageblock
2113 * first so it is as free as possible and we won't
2114 * have to steal another one soon. This only applies
2115 * to sync compaction, as async compaction operates
2116 * on pageblocks of the same migratetype.
2118 if (cc
->mode
== MIGRATE_ASYNC
||
2119 IS_ALIGNED(cc
->migrate_pfn
,
2120 pageblock_nr_pages
)) {
2121 return COMPACT_SUCCESS
;
2124 ret
= COMPACT_CONTINUE
;
2130 if (cc
->contended
|| fatal_signal_pending(current
))
2131 ret
= COMPACT_CONTENDED
;
2136 static enum compact_result
compact_finished(struct compact_control
*cc
)
2140 ret
= __compact_finished(cc
);
2141 trace_mm_compaction_finished(cc
->zone
, cc
->order
, ret
);
2142 if (ret
== COMPACT_NO_SUITABLE_PAGE
)
2143 ret
= COMPACT_CONTINUE
;
2148 static enum compact_result
__compaction_suitable(struct zone
*zone
, int order
,
2149 unsigned int alloc_flags
,
2150 int highest_zoneidx
,
2151 unsigned long wmark_target
)
2153 unsigned long watermark
;
2155 if (is_via_compact_memory(order
))
2156 return COMPACT_CONTINUE
;
2158 watermark
= wmark_pages(zone
, alloc_flags
& ALLOC_WMARK_MASK
);
2160 * If watermarks for high-order allocation are already met, there
2161 * should be no need for compaction at all.
2163 if (zone_watermark_ok(zone
, order
, watermark
, highest_zoneidx
,
2165 return COMPACT_SUCCESS
;
2168 * Watermarks for order-0 must be met for compaction to be able to
2169 * isolate free pages for migration targets. This means that the
2170 * watermark and alloc_flags have to match, or be more pessimistic than
2171 * the check in __isolate_free_page(). We don't use the direct
2172 * compactor's alloc_flags, as they are not relevant for freepage
2173 * isolation. We however do use the direct compactor's highest_zoneidx
2174 * to skip over zones where lowmem reserves would prevent allocation
2175 * even if compaction succeeds.
2176 * For costly orders, we require low watermark instead of min for
2177 * compaction to proceed to increase its chances.
2178 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2179 * suitable migration targets
2181 watermark
= (order
> PAGE_ALLOC_COSTLY_ORDER
) ?
2182 low_wmark_pages(zone
) : min_wmark_pages(zone
);
2183 watermark
+= compact_gap(order
);
2184 if (!__zone_watermark_ok(zone
, 0, watermark
, highest_zoneidx
,
2185 ALLOC_CMA
, wmark_target
))
2186 return COMPACT_SKIPPED
;
2188 return COMPACT_CONTINUE
;
2192 * compaction_suitable: Is this suitable to run compaction on this zone now?
2194 * COMPACT_SKIPPED - If there are too few free pages for compaction
2195 * COMPACT_SUCCESS - If the allocation would succeed without compaction
2196 * COMPACT_CONTINUE - If compaction should run now
2198 enum compact_result
compaction_suitable(struct zone
*zone
, int order
,
2199 unsigned int alloc_flags
,
2200 int highest_zoneidx
)
2202 enum compact_result ret
;
2205 ret
= __compaction_suitable(zone
, order
, alloc_flags
, highest_zoneidx
,
2206 zone_page_state(zone
, NR_FREE_PAGES
));
2208 * fragmentation index determines if allocation failures are due to
2209 * low memory or external fragmentation
2211 * index of -1000 would imply allocations might succeed depending on
2212 * watermarks, but we already failed the high-order watermark check
2213 * index towards 0 implies failure is due to lack of memory
2214 * index towards 1000 implies failure is due to fragmentation
2216 * Only compact if a failure would be due to fragmentation. Also
2217 * ignore fragindex for non-costly orders where the alternative to
2218 * a successful reclaim/compaction is OOM. Fragindex and the
2219 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2220 * excessive compaction for costly orders, but it should not be at the
2221 * expense of system stability.
2223 if (ret
== COMPACT_CONTINUE
&& (order
> PAGE_ALLOC_COSTLY_ORDER
)) {
2224 fragindex
= fragmentation_index(zone
, order
);
2225 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
2226 ret
= COMPACT_NOT_SUITABLE_ZONE
;
2229 trace_mm_compaction_suitable(zone
, order
, ret
);
2230 if (ret
== COMPACT_NOT_SUITABLE_ZONE
)
2231 ret
= COMPACT_SKIPPED
;
2236 bool compaction_zonelist_suitable(struct alloc_context
*ac
, int order
,
2243 * Make sure at least one zone would pass __compaction_suitable if we continue
2244 * retrying the reclaim.
2246 for_each_zone_zonelist_nodemask(zone
, z
, ac
->zonelist
,
2247 ac
->highest_zoneidx
, ac
->nodemask
) {
2248 unsigned long available
;
2249 enum compact_result compact_result
;
2252 * Do not consider all the reclaimable memory because we do not
2253 * want to trash just for a single high order allocation which
2254 * is even not guaranteed to appear even if __compaction_suitable
2255 * is happy about the watermark check.
2257 available
= zone_reclaimable_pages(zone
) / order
;
2258 available
+= zone_page_state_snapshot(zone
, NR_FREE_PAGES
);
2259 compact_result
= __compaction_suitable(zone
, order
, alloc_flags
,
2260 ac
->highest_zoneidx
, available
);
2261 if (compact_result
!= COMPACT_SKIPPED
)
2268 static enum compact_result
2269 compact_zone(struct compact_control
*cc
, struct capture_control
*capc
)
2271 enum compact_result ret
;
2272 unsigned long start_pfn
= cc
->zone
->zone_start_pfn
;
2273 unsigned long end_pfn
= zone_end_pfn(cc
->zone
);
2274 unsigned long last_migrated_pfn
;
2275 const bool sync
= cc
->mode
!= MIGRATE_ASYNC
;
2279 * These counters track activities during zone compaction. Initialize
2280 * them before compacting a new zone.
2282 cc
->total_migrate_scanned
= 0;
2283 cc
->total_free_scanned
= 0;
2284 cc
->nr_migratepages
= 0;
2285 cc
->nr_freepages
= 0;
2286 INIT_LIST_HEAD(&cc
->freepages
);
2287 INIT_LIST_HEAD(&cc
->migratepages
);
2289 cc
->migratetype
= gfp_migratetype(cc
->gfp_mask
);
2290 ret
= compaction_suitable(cc
->zone
, cc
->order
, cc
->alloc_flags
,
2291 cc
->highest_zoneidx
);
2292 /* Compaction is likely to fail */
2293 if (ret
== COMPACT_SUCCESS
|| ret
== COMPACT_SKIPPED
)
2296 /* huh, compaction_suitable is returning something unexpected */
2297 VM_BUG_ON(ret
!= COMPACT_CONTINUE
);
2300 * Clear pageblock skip if there were failures recently and compaction
2301 * is about to be retried after being deferred.
2303 if (compaction_restarting(cc
->zone
, cc
->order
))
2304 __reset_isolation_suitable(cc
->zone
);
2307 * Setup to move all movable pages to the end of the zone. Used cached
2308 * information on where the scanners should start (unless we explicitly
2309 * want to compact the whole zone), but check that it is initialised
2310 * by ensuring the values are within zone boundaries.
2312 cc
->fast_start_pfn
= 0;
2313 if (cc
->whole_zone
) {
2314 cc
->migrate_pfn
= start_pfn
;
2315 cc
->free_pfn
= pageblock_start_pfn(end_pfn
- 1);
2317 cc
->migrate_pfn
= cc
->zone
->compact_cached_migrate_pfn
[sync
];
2318 cc
->free_pfn
= cc
->zone
->compact_cached_free_pfn
;
2319 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
>= end_pfn
) {
2320 cc
->free_pfn
= pageblock_start_pfn(end_pfn
- 1);
2321 cc
->zone
->compact_cached_free_pfn
= cc
->free_pfn
;
2323 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
>= end_pfn
) {
2324 cc
->migrate_pfn
= start_pfn
;
2325 cc
->zone
->compact_cached_migrate_pfn
[0] = cc
->migrate_pfn
;
2326 cc
->zone
->compact_cached_migrate_pfn
[1] = cc
->migrate_pfn
;
2329 if (cc
->migrate_pfn
<= cc
->zone
->compact_init_migrate_pfn
)
2330 cc
->whole_zone
= true;
2333 last_migrated_pfn
= 0;
2336 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2337 * the basis that some migrations will fail in ASYNC mode. However,
2338 * if the cached PFNs match and pageblocks are skipped due to having
2339 * no isolation candidates, then the sync state does not matter.
2340 * Until a pageblock with isolation candidates is found, keep the
2341 * cached PFNs in sync to avoid revisiting the same blocks.
2343 update_cached
= !sync
&&
2344 cc
->zone
->compact_cached_migrate_pfn
[0] == cc
->zone
->compact_cached_migrate_pfn
[1];
2346 trace_mm_compaction_begin(start_pfn
, cc
->migrate_pfn
,
2347 cc
->free_pfn
, end_pfn
, sync
);
2349 /* lru_add_drain_all could be expensive with involving other CPUs */
2352 while ((ret
= compact_finished(cc
)) == COMPACT_CONTINUE
) {
2354 unsigned long iteration_start_pfn
= cc
->migrate_pfn
;
2357 * Avoid multiple rescans which can happen if a page cannot be
2358 * isolated (dirty/writeback in async mode) or if the migrated
2359 * pages are being allocated before the pageblock is cleared.
2360 * The first rescan will capture the entire pageblock for
2361 * migration. If it fails, it'll be marked skip and scanning
2362 * will proceed as normal.
2365 if (pageblock_start_pfn(last_migrated_pfn
) ==
2366 pageblock_start_pfn(iteration_start_pfn
)) {
2370 switch (isolate_migratepages(cc
)) {
2372 ret
= COMPACT_CONTENDED
;
2373 putback_movable_pages(&cc
->migratepages
);
2374 cc
->nr_migratepages
= 0;
2377 if (update_cached
) {
2378 cc
->zone
->compact_cached_migrate_pfn
[1] =
2379 cc
->zone
->compact_cached_migrate_pfn
[0];
2383 * We haven't isolated and migrated anything, but
2384 * there might still be unflushed migrations from
2385 * previous cc->order aligned block.
2388 case ISOLATE_SUCCESS
:
2389 update_cached
= false;
2390 last_migrated_pfn
= iteration_start_pfn
;
2393 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
2394 compaction_free
, (unsigned long)cc
, cc
->mode
,
2397 trace_mm_compaction_migratepages(cc
->nr_migratepages
, err
,
2400 /* All pages were either migrated or will be released */
2401 cc
->nr_migratepages
= 0;
2403 putback_movable_pages(&cc
->migratepages
);
2405 * migrate_pages() may return -ENOMEM when scanners meet
2406 * and we want compact_finished() to detect it
2408 if (err
== -ENOMEM
&& !compact_scanners_met(cc
)) {
2409 ret
= COMPACT_CONTENDED
;
2413 * We failed to migrate at least one page in the current
2414 * order-aligned block, so skip the rest of it.
2416 if (cc
->direct_compaction
&&
2417 (cc
->mode
== MIGRATE_ASYNC
)) {
2418 cc
->migrate_pfn
= block_end_pfn(
2419 cc
->migrate_pfn
- 1, cc
->order
);
2420 /* Draining pcplists is useless in this case */
2421 last_migrated_pfn
= 0;
2427 * Has the migration scanner moved away from the previous
2428 * cc->order aligned block where we migrated from? If yes,
2429 * flush the pages that were freed, so that they can merge and
2430 * compact_finished() can detect immediately if allocation
2433 if (cc
->order
> 0 && last_migrated_pfn
) {
2434 unsigned long current_block_start
=
2435 block_start_pfn(cc
->migrate_pfn
, cc
->order
);
2437 if (last_migrated_pfn
< current_block_start
) {
2438 lru_add_drain_cpu_zone(cc
->zone
);
2439 /* No more flushing until we migrate again */
2440 last_migrated_pfn
= 0;
2444 /* Stop if a page has been captured */
2445 if (capc
&& capc
->page
) {
2446 ret
= COMPACT_SUCCESS
;
2453 * Release free pages and update where the free scanner should restart,
2454 * so we don't leave any returned pages behind in the next attempt.
2456 if (cc
->nr_freepages
> 0) {
2457 unsigned long free_pfn
= release_freepages(&cc
->freepages
);
2459 cc
->nr_freepages
= 0;
2460 VM_BUG_ON(free_pfn
== 0);
2461 /* The cached pfn is always the first in a pageblock */
2462 free_pfn
= pageblock_start_pfn(free_pfn
);
2464 * Only go back, not forward. The cached pfn might have been
2465 * already reset to zone end in compact_finished()
2467 if (free_pfn
> cc
->zone
->compact_cached_free_pfn
)
2468 cc
->zone
->compact_cached_free_pfn
= free_pfn
;
2471 count_compact_events(COMPACTMIGRATE_SCANNED
, cc
->total_migrate_scanned
);
2472 count_compact_events(COMPACTFREE_SCANNED
, cc
->total_free_scanned
);
2474 trace_mm_compaction_end(start_pfn
, cc
->migrate_pfn
,
2475 cc
->free_pfn
, end_pfn
, sync
, ret
);
2480 static enum compact_result
compact_zone_order(struct zone
*zone
, int order
,
2481 gfp_t gfp_mask
, enum compact_priority prio
,
2482 unsigned int alloc_flags
, int highest_zoneidx
,
2483 struct page
**capture
)
2485 enum compact_result ret
;
2486 struct compact_control cc
= {
2488 .search_order
= order
,
2489 .gfp_mask
= gfp_mask
,
2491 .mode
= (prio
== COMPACT_PRIO_ASYNC
) ?
2492 MIGRATE_ASYNC
: MIGRATE_SYNC_LIGHT
,
2493 .alloc_flags
= alloc_flags
,
2494 .highest_zoneidx
= highest_zoneidx
,
2495 .direct_compaction
= true,
2496 .whole_zone
= (prio
== MIN_COMPACT_PRIORITY
),
2497 .ignore_skip_hint
= (prio
== MIN_COMPACT_PRIORITY
),
2498 .ignore_block_suitable
= (prio
== MIN_COMPACT_PRIORITY
)
2500 struct capture_control capc
= {
2506 * Make sure the structs are really initialized before we expose the
2507 * capture control, in case we are interrupted and the interrupt handler
2511 WRITE_ONCE(current
->capture_control
, &capc
);
2513 ret
= compact_zone(&cc
, &capc
);
2515 VM_BUG_ON(!list_empty(&cc
.freepages
));
2516 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2519 * Make sure we hide capture control first before we read the captured
2520 * page pointer, otherwise an interrupt could free and capture a page
2521 * and we would leak it.
2523 WRITE_ONCE(current
->capture_control
, NULL
);
2524 *capture
= READ_ONCE(capc
.page
);
2526 * Technically, it is also possible that compaction is skipped but
2527 * the page is still captured out of luck(IRQ came and freed the page).
2528 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
2529 * the COMPACT[STALL|FAIL] when compaction is skipped.
2532 ret
= COMPACT_SUCCESS
;
2537 int sysctl_extfrag_threshold
= 500;
2540 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2541 * @gfp_mask: The GFP mask of the current allocation
2542 * @order: The order of the current allocation
2543 * @alloc_flags: The allocation flags of the current allocation
2544 * @ac: The context of current allocation
2545 * @prio: Determines how hard direct compaction should try to succeed
2546 * @capture: Pointer to free page created by compaction will be stored here
2548 * This is the main entry point for direct page compaction.
2550 enum compact_result
try_to_compact_pages(gfp_t gfp_mask
, unsigned int order
,
2551 unsigned int alloc_flags
, const struct alloc_context
*ac
,
2552 enum compact_priority prio
, struct page
**capture
)
2554 int may_perform_io
= gfp_mask
& __GFP_IO
;
2557 enum compact_result rc
= COMPACT_SKIPPED
;
2560 * Check if the GFP flags allow compaction - GFP_NOIO is really
2561 * tricky context because the migration might require IO
2563 if (!may_perform_io
)
2564 return COMPACT_SKIPPED
;
2566 trace_mm_compaction_try_to_compact_pages(order
, gfp_mask
, prio
);
2568 /* Compact each zone in the list */
2569 for_each_zone_zonelist_nodemask(zone
, z
, ac
->zonelist
,
2570 ac
->highest_zoneidx
, ac
->nodemask
) {
2571 enum compact_result status
;
2573 if (prio
> MIN_COMPACT_PRIORITY
2574 && compaction_deferred(zone
, order
)) {
2575 rc
= max_t(enum compact_result
, COMPACT_DEFERRED
, rc
);
2579 status
= compact_zone_order(zone
, order
, gfp_mask
, prio
,
2580 alloc_flags
, ac
->highest_zoneidx
, capture
);
2581 rc
= max(status
, rc
);
2583 /* The allocation should succeed, stop compacting */
2584 if (status
== COMPACT_SUCCESS
) {
2586 * We think the allocation will succeed in this zone,
2587 * but it is not certain, hence the false. The caller
2588 * will repeat this with true if allocation indeed
2589 * succeeds in this zone.
2591 compaction_defer_reset(zone
, order
, false);
2596 if (prio
!= COMPACT_PRIO_ASYNC
&& (status
== COMPACT_COMPLETE
||
2597 status
== COMPACT_PARTIAL_SKIPPED
))
2599 * We think that allocation won't succeed in this zone
2600 * so we defer compaction there. If it ends up
2601 * succeeding after all, it will be reset.
2603 defer_compaction(zone
, order
);
2606 * We might have stopped compacting due to need_resched() in
2607 * async compaction, or due to a fatal signal detected. In that
2608 * case do not try further zones
2610 if ((prio
== COMPACT_PRIO_ASYNC
&& need_resched())
2611 || fatal_signal_pending(current
))
2619 * Compact all zones within a node till each zone's fragmentation score
2620 * reaches within proactive compaction thresholds (as determined by the
2621 * proactiveness tunable).
2623 * It is possible that the function returns before reaching score targets
2624 * due to various back-off conditions, such as, contention on per-node or
2627 static void proactive_compact_node(pg_data_t
*pgdat
)
2631 struct compact_control cc
= {
2633 .mode
= MIGRATE_SYNC_LIGHT
,
2634 .ignore_skip_hint
= true,
2636 .gfp_mask
= GFP_KERNEL
,
2637 .proactive_compaction
= true,
2640 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
2641 zone
= &pgdat
->node_zones
[zoneid
];
2642 if (!populated_zone(zone
))
2647 compact_zone(&cc
, NULL
);
2649 VM_BUG_ON(!list_empty(&cc
.freepages
));
2650 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2654 /* Compact all zones within a node */
2655 static void compact_node(int nid
)
2657 pg_data_t
*pgdat
= NODE_DATA(nid
);
2660 struct compact_control cc
= {
2662 .mode
= MIGRATE_SYNC
,
2663 .ignore_skip_hint
= true,
2665 .gfp_mask
= GFP_KERNEL
,
2669 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
2671 zone
= &pgdat
->node_zones
[zoneid
];
2672 if (!populated_zone(zone
))
2677 compact_zone(&cc
, NULL
);
2679 VM_BUG_ON(!list_empty(&cc
.freepages
));
2680 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2684 /* Compact all nodes in the system */
2685 static void compact_nodes(void)
2689 /* Flush pending updates to the LRU lists */
2690 lru_add_drain_all();
2692 for_each_online_node(nid
)
2697 * Tunable for proactive compaction. It determines how
2698 * aggressively the kernel should compact memory in the
2699 * background. It takes values in the range [0, 100].
2701 unsigned int __read_mostly sysctl_compaction_proactiveness
= 20;
2704 * This is the entry point for compacting all nodes via
2705 * /proc/sys/vm/compact_memory
2707 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
2708 void *buffer
, size_t *length
, loff_t
*ppos
)
2716 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2717 static ssize_t
compact_store(struct device
*dev
,
2718 struct device_attribute
*attr
,
2719 const char *buf
, size_t count
)
2723 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
2724 /* Flush pending updates to the LRU lists */
2725 lru_add_drain_all();
2732 static DEVICE_ATTR_WO(compact
);
2734 int compaction_register_node(struct node
*node
)
2736 return device_create_file(&node
->dev
, &dev_attr_compact
);
2739 void compaction_unregister_node(struct node
*node
)
2741 return device_remove_file(&node
->dev
, &dev_attr_compact
);
2743 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
2745 static inline bool kcompactd_work_requested(pg_data_t
*pgdat
)
2747 return pgdat
->kcompactd_max_order
> 0 || kthread_should_stop();
2750 static bool kcompactd_node_suitable(pg_data_t
*pgdat
)
2754 enum zone_type highest_zoneidx
= pgdat
->kcompactd_highest_zoneidx
;
2756 for (zoneid
= 0; zoneid
<= highest_zoneidx
; zoneid
++) {
2757 zone
= &pgdat
->node_zones
[zoneid
];
2759 if (!populated_zone(zone
))
2762 if (compaction_suitable(zone
, pgdat
->kcompactd_max_order
, 0,
2763 highest_zoneidx
) == COMPACT_CONTINUE
)
2770 static void kcompactd_do_work(pg_data_t
*pgdat
)
2773 * With no special task, compact all zones so that a page of requested
2774 * order is allocatable.
2778 struct compact_control cc
= {
2779 .order
= pgdat
->kcompactd_max_order
,
2780 .search_order
= pgdat
->kcompactd_max_order
,
2781 .highest_zoneidx
= pgdat
->kcompactd_highest_zoneidx
,
2782 .mode
= MIGRATE_SYNC_LIGHT
,
2783 .ignore_skip_hint
= false,
2784 .gfp_mask
= GFP_KERNEL
,
2786 trace_mm_compaction_kcompactd_wake(pgdat
->node_id
, cc
.order
,
2787 cc
.highest_zoneidx
);
2788 count_compact_event(KCOMPACTD_WAKE
);
2790 for (zoneid
= 0; zoneid
<= cc
.highest_zoneidx
; zoneid
++) {
2793 zone
= &pgdat
->node_zones
[zoneid
];
2794 if (!populated_zone(zone
))
2797 if (compaction_deferred(zone
, cc
.order
))
2800 if (compaction_suitable(zone
, cc
.order
, 0, zoneid
) !=
2804 if (kthread_should_stop())
2808 status
= compact_zone(&cc
, NULL
);
2810 if (status
== COMPACT_SUCCESS
) {
2811 compaction_defer_reset(zone
, cc
.order
, false);
2812 } else if (status
== COMPACT_PARTIAL_SKIPPED
|| status
== COMPACT_COMPLETE
) {
2814 * Buddy pages may become stranded on pcps that could
2815 * otherwise coalesce on the zone's free area for
2816 * order >= cc.order. This is ratelimited by the
2817 * upcoming deferral.
2819 drain_all_pages(zone
);
2822 * We use sync migration mode here, so we defer like
2823 * sync direct compaction does.
2825 defer_compaction(zone
, cc
.order
);
2828 count_compact_events(KCOMPACTD_MIGRATE_SCANNED
,
2829 cc
.total_migrate_scanned
);
2830 count_compact_events(KCOMPACTD_FREE_SCANNED
,
2831 cc
.total_free_scanned
);
2833 VM_BUG_ON(!list_empty(&cc
.freepages
));
2834 VM_BUG_ON(!list_empty(&cc
.migratepages
));
2838 * Regardless of success, we are done until woken up next. But remember
2839 * the requested order/highest_zoneidx in case it was higher/tighter
2840 * than our current ones
2842 if (pgdat
->kcompactd_max_order
<= cc
.order
)
2843 pgdat
->kcompactd_max_order
= 0;
2844 if (pgdat
->kcompactd_highest_zoneidx
>= cc
.highest_zoneidx
)
2845 pgdat
->kcompactd_highest_zoneidx
= pgdat
->nr_zones
- 1;
2848 void wakeup_kcompactd(pg_data_t
*pgdat
, int order
, int highest_zoneidx
)
2853 if (pgdat
->kcompactd_max_order
< order
)
2854 pgdat
->kcompactd_max_order
= order
;
2856 if (pgdat
->kcompactd_highest_zoneidx
> highest_zoneidx
)
2857 pgdat
->kcompactd_highest_zoneidx
= highest_zoneidx
;
2860 * Pairs with implicit barrier in wait_event_freezable()
2861 * such that wakeups are not missed.
2863 if (!wq_has_sleeper(&pgdat
->kcompactd_wait
))
2866 if (!kcompactd_node_suitable(pgdat
))
2869 trace_mm_compaction_wakeup_kcompactd(pgdat
->node_id
, order
,
2871 wake_up_interruptible(&pgdat
->kcompactd_wait
);
2875 * The background compaction daemon, started as a kernel thread
2876 * from the init process.
2878 static int kcompactd(void *p
)
2880 pg_data_t
*pgdat
= (pg_data_t
*)p
;
2881 struct task_struct
*tsk
= current
;
2882 unsigned int proactive_defer
= 0;
2884 const struct cpumask
*cpumask
= cpumask_of_node(pgdat
->node_id
);
2886 if (!cpumask_empty(cpumask
))
2887 set_cpus_allowed_ptr(tsk
, cpumask
);
2891 pgdat
->kcompactd_max_order
= 0;
2892 pgdat
->kcompactd_highest_zoneidx
= pgdat
->nr_zones
- 1;
2894 while (!kthread_should_stop()) {
2895 unsigned long pflags
;
2897 trace_mm_compaction_kcompactd_sleep(pgdat
->node_id
);
2898 if (wait_event_freezable_timeout(pgdat
->kcompactd_wait
,
2899 kcompactd_work_requested(pgdat
),
2900 msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC
))) {
2902 psi_memstall_enter(&pflags
);
2903 kcompactd_do_work(pgdat
);
2904 psi_memstall_leave(&pflags
);
2908 /* kcompactd wait timeout */
2909 if (should_proactive_compact_node(pgdat
)) {
2910 unsigned int prev_score
, score
;
2912 if (proactive_defer
) {
2916 prev_score
= fragmentation_score_node(pgdat
);
2917 proactive_compact_node(pgdat
);
2918 score
= fragmentation_score_node(pgdat
);
2920 * Defer proactive compaction if the fragmentation
2921 * score did not go down i.e. no progress made.
2923 proactive_defer
= score
< prev_score
?
2924 0 : 1 << COMPACT_MAX_DEFER_SHIFT
;
2932 * This kcompactd start function will be called by init and node-hot-add.
2933 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2935 int kcompactd_run(int nid
)
2937 pg_data_t
*pgdat
= NODE_DATA(nid
);
2940 if (pgdat
->kcompactd
)
2943 pgdat
->kcompactd
= kthread_run(kcompactd
, pgdat
, "kcompactd%d", nid
);
2944 if (IS_ERR(pgdat
->kcompactd
)) {
2945 pr_err("Failed to start kcompactd on node %d\n", nid
);
2946 ret
= PTR_ERR(pgdat
->kcompactd
);
2947 pgdat
->kcompactd
= NULL
;
2953 * Called by memory hotplug when all memory in a node is offlined. Caller must
2954 * hold mem_hotplug_begin/end().
2956 void kcompactd_stop(int nid
)
2958 struct task_struct
*kcompactd
= NODE_DATA(nid
)->kcompactd
;
2961 kthread_stop(kcompactd
);
2962 NODE_DATA(nid
)->kcompactd
= NULL
;
2967 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2968 * not required for correctness. So if the last cpu in a node goes
2969 * away, we get changed to run anywhere: as the first one comes back,
2970 * restore their cpu bindings.
2972 static int kcompactd_cpu_online(unsigned int cpu
)
2976 for_each_node_state(nid
, N_MEMORY
) {
2977 pg_data_t
*pgdat
= NODE_DATA(nid
);
2978 const struct cpumask
*mask
;
2980 mask
= cpumask_of_node(pgdat
->node_id
);
2982 if (cpumask_any_and(cpu_online_mask
, mask
) < nr_cpu_ids
)
2983 /* One of our CPUs online: restore mask */
2984 set_cpus_allowed_ptr(pgdat
->kcompactd
, mask
);
2989 static int __init
kcompactd_init(void)
2994 ret
= cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN
,
2995 "mm/compaction:online",
2996 kcompactd_cpu_online
, NULL
);
2998 pr_err("kcompactd: failed to register hotplug callbacks.\n");
3002 for_each_node_state(nid
, N_MEMORY
)
3006 subsys_initcall(kcompactd_init
)
3008 #endif /* CONFIG_COMPACTION */