2 * linux/mm/compaction.c
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
10 #include <linux/swap.h>
11 #include <linux/migrate.h>
12 #include <linux/compaction.h>
13 #include <linux/mm_inline.h>
14 #include <linux/backing-dev.h>
15 #include <linux/sysctl.h>
16 #include <linux/sysfs.h>
17 #include <linux/balloon_compaction.h>
20 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
22 #define CREATE_TRACE_POINTS
23 #include <trace/events/compaction.h>
25 static unsigned long release_freepages(struct list_head
*freelist
)
27 struct page
*page
, *next
;
28 unsigned long count
= 0;
30 list_for_each_entry_safe(page
, next
, freelist
, lru
) {
39 static void map_pages(struct list_head
*list
)
43 list_for_each_entry(page
, list
, lru
) {
44 arch_alloc_page(page
, 0);
45 kernel_map_pages(page
, 1, 1);
49 static inline bool migrate_async_suitable(int migratetype
)
51 return is_migrate_cma(migratetype
) || migratetype
== MIGRATE_MOVABLE
;
54 #ifdef CONFIG_COMPACTION
55 /* Returns true if the pageblock should be scanned for pages to isolate. */
56 static inline bool isolation_suitable(struct compact_control
*cc
,
59 if (cc
->ignore_skip_hint
)
62 return !get_pageblock_skip(page
);
66 * This function is called to clear all cached information on pageblocks that
67 * should be skipped for page isolation when the migrate and free page scanner
70 static void __reset_isolation_suitable(struct zone
*zone
)
72 unsigned long start_pfn
= zone
->zone_start_pfn
;
73 unsigned long end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
76 zone
->compact_cached_migrate_pfn
= start_pfn
;
77 zone
->compact_cached_free_pfn
= end_pfn
;
78 zone
->compact_blockskip_flush
= false;
80 /* Walk the zone and mark every pageblock as suitable for isolation */
81 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= pageblock_nr_pages
) {
89 page
= pfn_to_page(pfn
);
90 if (zone
!= page_zone(page
))
93 clear_pageblock_skip(page
);
97 void reset_isolation_suitable(pg_data_t
*pgdat
)
101 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
102 struct zone
*zone
= &pgdat
->node_zones
[zoneid
];
103 if (!populated_zone(zone
))
106 /* Only flush if a full compaction finished recently */
107 if (zone
->compact_blockskip_flush
)
108 __reset_isolation_suitable(zone
);
113 * If no pages were isolated then mark this pageblock to be skipped in the
114 * future. The information is later cleared by __reset_isolation_suitable().
116 static void update_pageblock_skip(struct compact_control
*cc
,
117 struct page
*page
, unsigned long nr_isolated
,
118 bool migrate_scanner
)
120 struct zone
*zone
= cc
->zone
;
125 unsigned long pfn
= page_to_pfn(page
);
126 set_pageblock_skip(page
);
128 /* Update where compaction should restart */
129 if (migrate_scanner
) {
130 if (!cc
->finished_update_migrate
&&
131 pfn
> zone
->compact_cached_migrate_pfn
)
132 zone
->compact_cached_migrate_pfn
= pfn
;
134 if (!cc
->finished_update_free
&&
135 pfn
< zone
->compact_cached_free_pfn
)
136 zone
->compact_cached_free_pfn
= pfn
;
141 static inline bool isolation_suitable(struct compact_control
*cc
,
147 static void update_pageblock_skip(struct compact_control
*cc
,
148 struct page
*page
, unsigned long nr_isolated
,
149 bool migrate_scanner
)
152 #endif /* CONFIG_COMPACTION */
154 static inline bool should_release_lock(spinlock_t
*lock
)
156 return need_resched() || spin_is_contended(lock
);
160 * Compaction requires the taking of some coarse locks that are potentially
161 * very heavily contended. Check if the process needs to be scheduled or
162 * if the lock is contended. For async compaction, back out in the event
163 * if contention is severe. For sync compaction, schedule.
165 * Returns true if the lock is held.
166 * Returns false if the lock is released and compaction should abort
168 static bool compact_checklock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
169 bool locked
, struct compact_control
*cc
)
171 if (should_release_lock(lock
)) {
173 spin_unlock_irqrestore(lock
, *flags
);
177 /* async aborts if taking too long or contended */
179 cc
->contended
= true;
187 spin_lock_irqsave(lock
, *flags
);
191 static inline bool compact_trylock_irqsave(spinlock_t
*lock
,
192 unsigned long *flags
, struct compact_control
*cc
)
194 return compact_checklock_irqsave(lock
, flags
, false, cc
);
197 /* Returns true if the page is within a block suitable for migration to */
198 static bool suitable_migration_target(struct page
*page
)
200 int migratetype
= get_pageblock_migratetype(page
);
202 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
203 if (migratetype
== MIGRATE_ISOLATE
|| migratetype
== MIGRATE_RESERVE
)
206 /* If the page is a large free page, then allow migration */
207 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
210 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
211 if (migrate_async_suitable(migratetype
))
214 /* Otherwise skip the block */
219 * Isolate free pages onto a private freelist. Caller must hold zone->lock.
220 * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
221 * pages inside of the pageblock (even though it may still end up isolating
224 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
225 unsigned long blockpfn
,
226 unsigned long end_pfn
,
227 struct list_head
*freelist
,
230 int nr_scanned
= 0, total_isolated
= 0;
231 struct page
*cursor
, *valid_page
= NULL
;
232 unsigned long nr_strict_required
= end_pfn
- blockpfn
;
236 cursor
= pfn_to_page(blockpfn
);
238 /* Isolate free pages. */
239 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
241 struct page
*page
= cursor
;
244 if (!pfn_valid_within(blockpfn
))
248 if (!PageBuddy(page
))
252 * The zone lock must be held to isolate freepages.
253 * Unfortunately this is a very coarse lock and can be
254 * heavily contended if there are parallel allocations
255 * or parallel compactions. For async compaction do not
256 * spin on the lock and we acquire the lock as late as
259 locked
= compact_checklock_irqsave(&cc
->zone
->lock
, &flags
,
264 /* Recheck this is a suitable migration target under lock */
265 if (!strict
&& !suitable_migration_target(page
))
268 /* Recheck this is a buddy page under lock */
269 if (!PageBuddy(page
))
272 /* Found a free page, break it into order-0 pages */
273 isolated
= split_free_page(page
);
274 if (!isolated
&& strict
)
276 total_isolated
+= isolated
;
277 for (i
= 0; i
< isolated
; i
++) {
278 list_add(&page
->lru
, freelist
);
282 /* If a page was split, advance to the end of it */
284 blockpfn
+= isolated
- 1;
285 cursor
+= isolated
- 1;
289 trace_mm_compaction_isolate_freepages(nr_scanned
, total_isolated
);
292 * If strict isolation is requested by CMA then check that all the
293 * pages requested were isolated. If there were any failures, 0 is
294 * returned and CMA will fail.
296 if (strict
&& nr_strict_required
> total_isolated
)
300 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
302 /* Update the pageblock-skip if the whole pageblock was scanned */
303 if (blockpfn
== end_pfn
)
304 update_pageblock_skip(cc
, valid_page
, total_isolated
, false);
306 return total_isolated
;
310 * isolate_freepages_range() - isolate free pages.
311 * @start_pfn: The first PFN to start isolating.
312 * @end_pfn: The one-past-last PFN.
314 * Non-free pages, invalid PFNs, or zone boundaries within the
315 * [start_pfn, end_pfn) range are considered errors, cause function to
316 * undo its actions and return zero.
318 * Otherwise, function returns one-past-the-last PFN of isolated page
319 * (which may be greater then end_pfn if end fell in a middle of
323 isolate_freepages_range(struct compact_control
*cc
,
324 unsigned long start_pfn
, unsigned long end_pfn
)
326 unsigned long isolated
, pfn
, block_end_pfn
;
329 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= isolated
) {
330 if (!pfn_valid(pfn
) || cc
->zone
!= page_zone(pfn_to_page(pfn
)))
334 * On subsequent iterations ALIGN() is actually not needed,
335 * but we keep it that we not to complicate the code.
337 block_end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
338 block_end_pfn
= min(block_end_pfn
, end_pfn
);
340 isolated
= isolate_freepages_block(cc
, pfn
, block_end_pfn
,
344 * In strict mode, isolate_freepages_block() returns 0 if
345 * there are any holes in the block (ie. invalid PFNs or
352 * If we managed to isolate pages, it is always (1 << n) *
353 * pageblock_nr_pages for some non-negative n. (Max order
354 * page may span two pageblocks).
358 /* split_free_page does not map the pages */
359 map_pages(&freelist
);
362 /* Loop terminated early, cleanup. */
363 release_freepages(&freelist
);
367 /* We don't use freelists for anything. */
371 /* Update the number of anon and file isolated pages in the zone */
372 static void acct_isolated(struct zone
*zone
, bool locked
, struct compact_control
*cc
)
375 unsigned int count
[2] = { 0, };
377 list_for_each_entry(page
, &cc
->migratepages
, lru
)
378 count
[!!page_is_file_cache(page
)]++;
380 /* If locked we can use the interrupt unsafe versions */
382 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
383 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
385 mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
386 mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
390 /* Similar to reclaim, but different enough that they don't share logic */
391 static bool too_many_isolated(struct zone
*zone
)
393 unsigned long active
, inactive
, isolated
;
395 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
396 zone_page_state(zone
, NR_INACTIVE_ANON
);
397 active
= zone_page_state(zone
, NR_ACTIVE_FILE
) +
398 zone_page_state(zone
, NR_ACTIVE_ANON
);
399 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
400 zone_page_state(zone
, NR_ISOLATED_ANON
);
402 return isolated
> (inactive
+ active
) / 2;
406 * isolate_migratepages_range() - isolate all migrate-able pages in range.
407 * @zone: Zone pages are in.
408 * @cc: Compaction control structure.
409 * @low_pfn: The first PFN of the range.
410 * @end_pfn: The one-past-the-last PFN of the range.
411 * @unevictable: true if it allows to isolate unevictable pages
413 * Isolate all pages that can be migrated from the range specified by
414 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
415 * pending), otherwise PFN of the first page that was not scanned
416 * (which may be both less, equal to or more then end_pfn).
418 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
421 * Apart from cc->migratepages and cc->nr_migratetypes this function
422 * does not modify any cc's fields, in particular it does not modify
423 * (or read for that matter) cc->migrate_pfn.
426 isolate_migratepages_range(struct zone
*zone
, struct compact_control
*cc
,
427 unsigned long low_pfn
, unsigned long end_pfn
, bool unevictable
)
429 unsigned long last_pageblock_nr
= 0, pageblock_nr
;
430 unsigned long nr_scanned
= 0, nr_isolated
= 0;
431 struct list_head
*migratelist
= &cc
->migratepages
;
432 isolate_mode_t mode
= 0;
433 struct lruvec
*lruvec
;
436 struct page
*page
= NULL
, *valid_page
= NULL
;
439 * Ensure that there are not too many pages isolated from the LRU
440 * list by either parallel reclaimers or compaction. If there are,
441 * delay for some time until fewer pages are isolated
443 while (unlikely(too_many_isolated(zone
))) {
444 /* async migration should just abort */
448 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
450 if (fatal_signal_pending(current
))
454 /* Time to isolate some pages for migration */
456 for (; low_pfn
< end_pfn
; low_pfn
++) {
457 /* give a chance to irqs before checking need_resched() */
458 if (locked
&& !((low_pfn
+1) % SWAP_CLUSTER_MAX
)) {
459 if (should_release_lock(&zone
->lru_lock
)) {
460 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
466 * migrate_pfn does not necessarily start aligned to a
467 * pageblock. Ensure that pfn_valid is called when moving
468 * into a new MAX_ORDER_NR_PAGES range in case of large
469 * memory holes within the zone
471 if ((low_pfn
& (MAX_ORDER_NR_PAGES
- 1)) == 0) {
472 if (!pfn_valid(low_pfn
)) {
473 low_pfn
+= MAX_ORDER_NR_PAGES
- 1;
478 if (!pfn_valid_within(low_pfn
))
483 * Get the page and ensure the page is within the same zone.
484 * See the comment in isolate_freepages about overlapping
485 * nodes. It is deliberate that the new zone lock is not taken
486 * as memory compaction should not move pages between nodes.
488 page
= pfn_to_page(low_pfn
);
489 if (page_zone(page
) != zone
)
495 /* If isolation recently failed, do not retry */
496 pageblock_nr
= low_pfn
>> pageblock_order
;
497 if (!isolation_suitable(cc
, page
))
505 * For async migration, also only scan in MOVABLE blocks. Async
506 * migration is optimistic to see if the minimum amount of work
507 * satisfies the allocation
509 if (!cc
->sync
&& last_pageblock_nr
!= pageblock_nr
&&
510 !migrate_async_suitable(get_pageblock_migratetype(page
))) {
511 cc
->finished_update_migrate
= true;
516 * Check may be lockless but that's ok as we recheck later.
517 * It's possible to migrate LRU pages and balloon pages
518 * Skip any other type of page
520 if (!PageLRU(page
)) {
521 if (unlikely(balloon_page_movable(page
))) {
522 if (locked
&& balloon_page_isolate(page
)) {
523 /* Successfully isolated */
524 cc
->finished_update_migrate
= true;
525 list_add(&page
->lru
, migratelist
);
526 cc
->nr_migratepages
++;
528 goto check_compact_cluster
;
535 * PageLRU is set. lru_lock normally excludes isolation
536 * splitting and collapsing (collapsing has already happened
537 * if PageLRU is set) but the lock is not necessarily taken
538 * here and it is wasteful to take it just to check transhuge.
539 * Check TransHuge without lock and skip the whole pageblock if
540 * it's either a transhuge or hugetlbfs page, as calling
541 * compound_order() without preventing THP from splitting the
542 * page underneath us may return surprising results.
544 if (PageTransHuge(page
)) {
547 low_pfn
+= (1 << compound_order(page
)) - 1;
551 /* Check if it is ok to still hold the lock */
552 locked
= compact_checklock_irqsave(&zone
->lru_lock
, &flags
,
554 if (!locked
|| fatal_signal_pending(current
))
557 /* Recheck PageLRU and PageTransHuge under lock */
560 if (PageTransHuge(page
)) {
561 low_pfn
+= (1 << compound_order(page
)) - 1;
566 mode
|= ISOLATE_ASYNC_MIGRATE
;
569 mode
|= ISOLATE_UNEVICTABLE
;
571 lruvec
= mem_cgroup_page_lruvec(page
, zone
);
573 /* Try isolate the page */
574 if (__isolate_lru_page(page
, mode
) != 0)
577 VM_BUG_ON(PageTransCompound(page
));
579 /* Successfully isolated */
580 cc
->finished_update_migrate
= true;
581 del_page_from_lru_list(page
, lruvec
, page_lru(page
));
582 list_add(&page
->lru
, migratelist
);
583 cc
->nr_migratepages
++;
586 check_compact_cluster
:
587 /* Avoid isolating too much */
588 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
) {
596 low_pfn
+= pageblock_nr_pages
;
597 low_pfn
= ALIGN(low_pfn
, pageblock_nr_pages
) - 1;
598 last_pageblock_nr
= pageblock_nr
;
601 acct_isolated(zone
, locked
, cc
);
604 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
606 /* Update the pageblock-skip if the whole pageblock was scanned */
607 if (low_pfn
== end_pfn
)
608 update_pageblock_skip(cc
, valid_page
, nr_isolated
, true);
610 trace_mm_compaction_isolate_migratepages(nr_scanned
, nr_isolated
);
615 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
616 #ifdef CONFIG_COMPACTION
618 * Based on information in the current compact_control, find blocks
619 * suitable for isolating free pages from and then isolate them.
621 static void isolate_freepages(struct zone
*zone
,
622 struct compact_control
*cc
)
625 unsigned long high_pfn
, low_pfn
, pfn
, zone_end_pfn
, end_pfn
;
626 int nr_freepages
= cc
->nr_freepages
;
627 struct list_head
*freelist
= &cc
->freepages
;
630 * Initialise the free scanner. The starting point is where we last
631 * scanned from (or the end of the zone if starting). The low point
632 * is the end of the pageblock the migration scanner is using.
635 low_pfn
= cc
->migrate_pfn
+ pageblock_nr_pages
;
638 * Take care that if the migration scanner is at the end of the zone
639 * that the free scanner does not accidentally move to the next zone
640 * in the next isolation cycle.
642 high_pfn
= min(low_pfn
, pfn
);
644 zone_end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
647 * Isolate free pages until enough are available to migrate the
648 * pages on cc->migratepages. We stop searching if the migrate
649 * and free page scanners meet or enough free pages are isolated.
651 for (; pfn
> low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
652 pfn
-= pageblock_nr_pages
) {
653 unsigned long isolated
;
659 * Check for overlapping nodes/zones. It's possible on some
660 * configurations to have a setup like
662 * i.e. it's possible that all pages within a zones range of
663 * pages do not belong to a single zone.
665 page
= pfn_to_page(pfn
);
666 if (page_zone(page
) != zone
)
669 /* Check the block is suitable for migration */
670 if (!suitable_migration_target(page
))
673 /* If isolation recently failed, do not retry */
674 if (!isolation_suitable(cc
, page
))
677 /* Found a block suitable for isolating free pages from */
681 * As pfn may not start aligned, pfn+pageblock_nr_page
682 * may cross a MAX_ORDER_NR_PAGES boundary and miss
683 * a pfn_valid check. Ensure isolate_freepages_block()
684 * only scans within a pageblock
686 end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
687 end_pfn
= min(end_pfn
, zone_end_pfn
);
688 isolated
= isolate_freepages_block(cc
, pfn
, end_pfn
,
690 nr_freepages
+= isolated
;
693 * Record the highest PFN we isolated pages from. When next
694 * looking for free pages, the search will restart here as
695 * page migration may have returned some pages to the allocator
698 cc
->finished_update_free
= true;
699 high_pfn
= max(high_pfn
, pfn
);
703 /* split_free_page does not map the pages */
706 cc
->free_pfn
= high_pfn
;
707 cc
->nr_freepages
= nr_freepages
;
711 * This is a migrate-callback that "allocates" freepages by taking pages
712 * from the isolated freelists in the block we are migrating to.
714 static struct page
*compaction_alloc(struct page
*migratepage
,
718 struct compact_control
*cc
= (struct compact_control
*)data
;
719 struct page
*freepage
;
721 /* Isolate free pages if necessary */
722 if (list_empty(&cc
->freepages
)) {
723 isolate_freepages(cc
->zone
, cc
);
725 if (list_empty(&cc
->freepages
))
729 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
730 list_del(&freepage
->lru
);
737 * We cannot control nr_migratepages and nr_freepages fully when migration is
738 * running as migrate_pages() has no knowledge of compact_control. When
739 * migration is complete, we count the number of pages on the lists by hand.
741 static void update_nr_listpages(struct compact_control
*cc
)
743 int nr_migratepages
= 0;
744 int nr_freepages
= 0;
747 list_for_each_entry(page
, &cc
->migratepages
, lru
)
749 list_for_each_entry(page
, &cc
->freepages
, lru
)
752 cc
->nr_migratepages
= nr_migratepages
;
753 cc
->nr_freepages
= nr_freepages
;
756 /* possible outcome of isolate_migratepages */
758 ISOLATE_ABORT
, /* Abort compaction now */
759 ISOLATE_NONE
, /* No pages isolated, continue scanning */
760 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
764 * Isolate all pages that can be migrated from the block pointed to by
765 * the migrate scanner within compact_control.
767 static isolate_migrate_t
isolate_migratepages(struct zone
*zone
,
768 struct compact_control
*cc
)
770 unsigned long low_pfn
, end_pfn
;
772 /* Do not scan outside zone boundaries */
773 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
775 /* Only scan within a pageblock boundary */
776 end_pfn
= ALIGN(low_pfn
+ pageblock_nr_pages
, pageblock_nr_pages
);
778 /* Do not cross the free scanner or scan within a memory hole */
779 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
780 cc
->migrate_pfn
= end_pfn
;
784 /* Perform the isolation */
785 low_pfn
= isolate_migratepages_range(zone
, cc
, low_pfn
, end_pfn
, false);
786 if (!low_pfn
|| cc
->contended
)
787 return ISOLATE_ABORT
;
789 cc
->migrate_pfn
= low_pfn
;
791 return ISOLATE_SUCCESS
;
794 static int compact_finished(struct zone
*zone
,
795 struct compact_control
*cc
)
797 unsigned long watermark
;
799 if (fatal_signal_pending(current
))
800 return COMPACT_PARTIAL
;
802 /* Compaction run completes if the migrate and free scanner meet */
803 if (cc
->free_pfn
<= cc
->migrate_pfn
) {
805 * Mark that the PG_migrate_skip information should be cleared
806 * by kswapd when it goes to sleep. kswapd does not set the
807 * flag itself as the decision to be clear should be directly
808 * based on an allocation request.
810 if (!current_is_kswapd())
811 zone
->compact_blockskip_flush
= true;
813 return COMPACT_COMPLETE
;
817 * order == -1 is expected when compacting via
818 * /proc/sys/vm/compact_memory
821 return COMPACT_CONTINUE
;
823 /* Compaction run is not finished if the watermark is not met */
824 watermark
= low_wmark_pages(zone
);
825 watermark
+= (1 << cc
->order
);
827 if (!zone_watermark_ok(zone
, cc
->order
, watermark
, 0, 0))
828 return COMPACT_CONTINUE
;
830 /* Direct compactor: Is a suitable page free? */
832 /* Was a suitable page captured? */
834 return COMPACT_PARTIAL
;
837 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
838 struct free_area
*area
= &zone
->free_area
[cc
->order
];
839 /* Job done if page is free of the right migratetype */
840 if (!list_empty(&area
->free_list
[cc
->migratetype
]))
841 return COMPACT_PARTIAL
;
843 /* Job done if allocation would set block type */
844 if (cc
->order
>= pageblock_order
&& area
->nr_free
)
845 return COMPACT_PARTIAL
;
849 return COMPACT_CONTINUE
;
853 * compaction_suitable: Is this suitable to run compaction on this zone now?
855 * COMPACT_SKIPPED - If there are too few free pages for compaction
856 * COMPACT_PARTIAL - If the allocation would succeed without compaction
857 * COMPACT_CONTINUE - If compaction should run now
859 unsigned long compaction_suitable(struct zone
*zone
, int order
)
862 unsigned long watermark
;
865 * order == -1 is expected when compacting via
866 * /proc/sys/vm/compact_memory
869 return COMPACT_CONTINUE
;
872 * Watermarks for order-0 must be met for compaction. Note the 2UL.
873 * This is because during migration, copies of pages need to be
874 * allocated and for a short time, the footprint is higher
876 watermark
= low_wmark_pages(zone
) + (2UL << order
);
877 if (!zone_watermark_ok(zone
, 0, watermark
, 0, 0))
878 return COMPACT_SKIPPED
;
881 * fragmentation index determines if allocation failures are due to
882 * low memory or external fragmentation
884 * index of -1000 implies allocations might succeed depending on
886 * index towards 0 implies failure is due to lack of memory
887 * index towards 1000 implies failure is due to fragmentation
889 * Only compact if a failure would be due to fragmentation.
891 fragindex
= fragmentation_index(zone
, order
);
892 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
893 return COMPACT_SKIPPED
;
895 if (fragindex
== -1000 && zone_watermark_ok(zone
, order
, watermark
,
897 return COMPACT_PARTIAL
;
899 return COMPACT_CONTINUE
;
902 static void compact_capture_page(struct compact_control
*cc
)
905 int mtype
, mtype_low
, mtype_high
;
907 if (!cc
->page
|| *cc
->page
)
911 * For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
912 * regardless of the migratetype of the freelist is is captured from.
913 * This is fine because the order for a high-order MIGRATE_MOVABLE
914 * allocation is typically at least a pageblock size and overall
915 * fragmentation is not impaired. Other allocation types must
916 * capture pages from their own migratelist because otherwise they
917 * could pollute other pageblocks like MIGRATE_MOVABLE with
918 * difficult to move pages and making fragmentation worse overall.
920 if (cc
->migratetype
== MIGRATE_MOVABLE
) {
922 mtype_high
= MIGRATE_PCPTYPES
;
924 mtype_low
= cc
->migratetype
;
925 mtype_high
= cc
->migratetype
+ 1;
928 /* Speculatively examine the free lists without zone lock */
929 for (mtype
= mtype_low
; mtype
< mtype_high
; mtype
++) {
931 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
933 struct free_area
*area
;
934 area
= &(cc
->zone
->free_area
[order
]);
935 if (list_empty(&area
->free_list
[mtype
]))
938 /* Take the lock and attempt capture of the page */
939 if (!compact_trylock_irqsave(&cc
->zone
->lock
, &flags
, cc
))
941 if (!list_empty(&area
->free_list
[mtype
])) {
942 page
= list_entry(area
->free_list
[mtype
].next
,
944 if (capture_free_page(page
, cc
->order
, mtype
)) {
945 spin_unlock_irqrestore(&cc
->zone
->lock
,
951 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
956 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
959 unsigned long start_pfn
= zone
->zone_start_pfn
;
960 unsigned long end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
962 ret
= compaction_suitable(zone
, cc
->order
);
964 case COMPACT_PARTIAL
:
965 case COMPACT_SKIPPED
:
966 /* Compaction is likely to fail */
968 case COMPACT_CONTINUE
:
969 /* Fall through to compaction */
974 * Setup to move all movable pages to the end of the zone. Used cached
975 * information on where the scanners should start but check that it
976 * is initialised by ensuring the values are within zone boundaries.
978 cc
->migrate_pfn
= zone
->compact_cached_migrate_pfn
;
979 cc
->free_pfn
= zone
->compact_cached_free_pfn
;
980 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
> end_pfn
) {
981 cc
->free_pfn
= end_pfn
& ~(pageblock_nr_pages
-1);
982 zone
->compact_cached_free_pfn
= cc
->free_pfn
;
984 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
> end_pfn
) {
985 cc
->migrate_pfn
= start_pfn
;
986 zone
->compact_cached_migrate_pfn
= cc
->migrate_pfn
;
990 * Clear pageblock skip if there were failures recently and compaction
991 * is about to be retried after being deferred. kswapd does not do
992 * this reset as it'll reset the cached information when going to sleep.
994 if (compaction_restarting(zone
, cc
->order
) && !current_is_kswapd())
995 __reset_isolation_suitable(zone
);
997 migrate_prep_local();
999 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
1000 unsigned long nr_migrate
, nr_remaining
;
1003 switch (isolate_migratepages(zone
, cc
)) {
1005 ret
= COMPACT_PARTIAL
;
1006 putback_movable_pages(&cc
->migratepages
);
1007 cc
->nr_migratepages
= 0;
1011 case ISOLATE_SUCCESS
:
1015 nr_migrate
= cc
->nr_migratepages
;
1016 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
1017 (unsigned long)cc
, false,
1018 cc
->sync
? MIGRATE_SYNC_LIGHT
: MIGRATE_ASYNC
);
1019 update_nr_listpages(cc
);
1020 nr_remaining
= cc
->nr_migratepages
;
1022 count_vm_event(COMPACTBLOCKS
);
1023 count_vm_events(COMPACTPAGES
, nr_migrate
- nr_remaining
);
1025 count_vm_events(COMPACTPAGEFAILED
, nr_remaining
);
1026 trace_mm_compaction_migratepages(nr_migrate
- nr_remaining
,
1029 /* Release isolated pages not migrated */
1031 putback_movable_pages(&cc
->migratepages
);
1032 cc
->nr_migratepages
= 0;
1033 if (err
== -ENOMEM
) {
1034 ret
= COMPACT_PARTIAL
;
1039 /* Capture a page now if it is a suitable size */
1040 compact_capture_page(cc
);
1044 /* Release free pages and check accounting */
1045 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
1046 VM_BUG_ON(cc
->nr_freepages
!= 0);
1051 static unsigned long compact_zone_order(struct zone
*zone
,
1052 int order
, gfp_t gfp_mask
,
1053 bool sync
, bool *contended
,
1057 struct compact_control cc
= {
1059 .nr_migratepages
= 0,
1061 .migratetype
= allocflags_to_migratetype(gfp_mask
),
1066 INIT_LIST_HEAD(&cc
.freepages
);
1067 INIT_LIST_HEAD(&cc
.migratepages
);
1069 ret
= compact_zone(zone
, &cc
);
1071 VM_BUG_ON(!list_empty(&cc
.freepages
));
1072 VM_BUG_ON(!list_empty(&cc
.migratepages
));
1074 *contended
= cc
.contended
;
1078 int sysctl_extfrag_threshold
= 500;
1081 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1082 * @zonelist: The zonelist used for the current allocation
1083 * @order: The order of the current allocation
1084 * @gfp_mask: The GFP mask of the current allocation
1085 * @nodemask: The allowed nodes to allocate from
1086 * @sync: Whether migration is synchronous or not
1087 * @contended: Return value that is true if compaction was aborted due to lock contention
1088 * @page: Optionally capture a free page of the requested order during compaction
1090 * This is the main entry point for direct page compaction.
1092 unsigned long try_to_compact_pages(struct zonelist
*zonelist
,
1093 int order
, gfp_t gfp_mask
, nodemask_t
*nodemask
,
1094 bool sync
, bool *contended
, struct page
**page
)
1096 enum zone_type high_zoneidx
= gfp_zone(gfp_mask
);
1097 int may_enter_fs
= gfp_mask
& __GFP_FS
;
1098 int may_perform_io
= gfp_mask
& __GFP_IO
;
1101 int rc
= COMPACT_SKIPPED
;
1102 int alloc_flags
= 0;
1104 /* Check if the GFP flags allow compaction */
1105 if (!order
|| !may_enter_fs
|| !may_perform_io
)
1108 count_vm_event(COMPACTSTALL
);
1111 if (allocflags_to_migratetype(gfp_mask
) == MIGRATE_MOVABLE
)
1112 alloc_flags
|= ALLOC_CMA
;
1114 /* Compact each zone in the list */
1115 for_each_zone_zonelist_nodemask(zone
, z
, zonelist
, high_zoneidx
,
1119 status
= compact_zone_order(zone
, order
, gfp_mask
, sync
,
1121 rc
= max(status
, rc
);
1123 /* If a normal allocation would succeed, stop compacting */
1124 if (zone_watermark_ok(zone
, order
, low_wmark_pages(zone
), 0,
1133 /* Compact all zones within a node */
1134 static int __compact_pgdat(pg_data_t
*pgdat
, struct compact_control
*cc
)
1139 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
1141 zone
= &pgdat
->node_zones
[zoneid
];
1142 if (!populated_zone(zone
))
1145 cc
->nr_freepages
= 0;
1146 cc
->nr_migratepages
= 0;
1148 INIT_LIST_HEAD(&cc
->freepages
);
1149 INIT_LIST_HEAD(&cc
->migratepages
);
1151 if (cc
->order
== -1 || !compaction_deferred(zone
, cc
->order
))
1152 compact_zone(zone
, cc
);
1154 if (cc
->order
> 0) {
1155 int ok
= zone_watermark_ok(zone
, cc
->order
,
1156 low_wmark_pages(zone
), 0, 0);
1157 if (ok
&& cc
->order
>= zone
->compact_order_failed
)
1158 zone
->compact_order_failed
= cc
->order
+ 1;
1159 /* Currently async compaction is never deferred. */
1160 else if (!ok
&& cc
->sync
)
1161 defer_compaction(zone
, cc
->order
);
1164 VM_BUG_ON(!list_empty(&cc
->freepages
));
1165 VM_BUG_ON(!list_empty(&cc
->migratepages
));
1171 int compact_pgdat(pg_data_t
*pgdat
, int order
)
1173 struct compact_control cc
= {
1179 return __compact_pgdat(pgdat
, &cc
);
1182 static int compact_node(int nid
)
1184 struct compact_control cc
= {
1190 return __compact_pgdat(NODE_DATA(nid
), &cc
);
1193 /* Compact all nodes in the system */
1194 static int compact_nodes(void)
1198 /* Flush pending updates to the LRU lists */
1199 lru_add_drain_all();
1201 for_each_online_node(nid
)
1204 return COMPACT_COMPLETE
;
1207 /* The written value is actually unused, all memory is compacted */
1208 int sysctl_compact_memory
;
1210 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1211 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
1212 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1215 return compact_nodes();
1220 int sysctl_extfrag_handler(struct ctl_table
*table
, int write
,
1221 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1223 proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
1228 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1229 ssize_t
sysfs_compact_node(struct device
*dev
,
1230 struct device_attribute
*attr
,
1231 const char *buf
, size_t count
)
1235 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
1236 /* Flush pending updates to the LRU lists */
1237 lru_add_drain_all();
1244 static DEVICE_ATTR(compact
, S_IWUSR
, NULL
, sysfs_compact_node
);
1246 int compaction_register_node(struct node
*node
)
1248 return device_create_file(&node
->dev
, &dev_attr_compact
);
1251 void compaction_unregister_node(struct node
*node
)
1253 return device_remove_file(&node
->dev
, &dev_attr_compact
);
1255 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1257 #endif /* CONFIG_COMPACTION */