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>
19 #define CREATE_TRACE_POINTS
20 #include <trace/events/compaction.h>
23 * compact_control is used to track pages being migrated and the free pages
24 * they are being migrated to during memory compaction. The free_pfn starts
25 * at the end of a zone and migrate_pfn begins at the start. Movable pages
26 * are moved to the end of a zone during a compaction run and the run
27 * completes when free_pfn <= migrate_pfn
29 struct compact_control
{
30 struct list_head freepages
; /* List of free pages to migrate to */
31 struct list_head migratepages
; /* List of pages being migrated */
32 unsigned long nr_freepages
; /* Number of isolated free pages */
33 unsigned long nr_migratepages
; /* Number of pages to migrate */
34 unsigned long free_pfn
; /* isolate_freepages search base */
35 unsigned long migrate_pfn
; /* isolate_migratepages search base */
36 bool sync
; /* Synchronous migration */
38 int order
; /* order a direct compactor needs */
39 int migratetype
; /* MOVABLE, RECLAIMABLE etc */
43 static unsigned long release_freepages(struct list_head
*freelist
)
45 struct page
*page
, *next
;
46 unsigned long count
= 0;
48 list_for_each_entry_safe(page
, next
, freelist
, lru
) {
57 /* Isolate free pages onto a private freelist. Must hold zone->lock */
58 static unsigned long isolate_freepages_block(struct zone
*zone
,
59 unsigned long blockpfn
,
60 struct list_head
*freelist
)
62 unsigned long zone_end_pfn
, end_pfn
;
63 int nr_scanned
= 0, total_isolated
= 0;
66 /* Get the last PFN we should scan for free pages at */
67 zone_end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
68 end_pfn
= min(blockpfn
+ pageblock_nr_pages
, zone_end_pfn
);
70 /* Find the first usable PFN in the block to initialse page cursor */
71 for (; blockpfn
< end_pfn
; blockpfn
++) {
72 if (pfn_valid_within(blockpfn
))
75 cursor
= pfn_to_page(blockpfn
);
77 /* Isolate free pages. This assumes the block is valid */
78 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
80 struct page
*page
= cursor
;
82 if (!pfn_valid_within(blockpfn
))
89 /* Found a free page, break it into order-0 pages */
90 isolated
= split_free_page(page
);
91 total_isolated
+= isolated
;
92 for (i
= 0; i
< isolated
; i
++) {
93 list_add(&page
->lru
, freelist
);
97 /* If a page was split, advance to the end of it */
99 blockpfn
+= isolated
- 1;
100 cursor
+= isolated
- 1;
104 trace_mm_compaction_isolate_freepages(nr_scanned
, total_isolated
);
105 return total_isolated
;
108 /* Returns true if the page is within a block suitable for migration to */
109 static bool suitable_migration_target(struct page
*page
)
112 int migratetype
= get_pageblock_migratetype(page
);
114 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
115 if (migratetype
== MIGRATE_ISOLATE
|| migratetype
== MIGRATE_RESERVE
)
118 /* If the page is a large free page, then allow migration */
119 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
122 /* If the block is MIGRATE_MOVABLE, allow migration */
123 if (migratetype
== MIGRATE_MOVABLE
)
126 /* Otherwise skip the block */
131 * Based on information in the current compact_control, find blocks
132 * suitable for isolating free pages from and then isolate them.
134 static void isolate_freepages(struct zone
*zone
,
135 struct compact_control
*cc
)
138 unsigned long high_pfn
, low_pfn
, pfn
;
140 int nr_freepages
= cc
->nr_freepages
;
141 struct list_head
*freelist
= &cc
->freepages
;
144 * Initialise the free scanner. The starting point is where we last
145 * scanned from (or the end of the zone if starting). The low point
146 * is the end of the pageblock the migration scanner is using.
149 low_pfn
= cc
->migrate_pfn
+ pageblock_nr_pages
;
152 * Take care that if the migration scanner is at the end of the zone
153 * that the free scanner does not accidentally move to the next zone
154 * in the next isolation cycle.
156 high_pfn
= min(low_pfn
, pfn
);
159 * Isolate free pages until enough are available to migrate the
160 * pages on cc->migratepages. We stop searching if the migrate
161 * and free page scanners meet or enough free pages are isolated.
163 for (; pfn
> low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
164 pfn
-= pageblock_nr_pages
) {
165 unsigned long isolated
;
171 * Check for overlapping nodes/zones. It's possible on some
172 * configurations to have a setup like
174 * i.e. it's possible that all pages within a zones range of
175 * pages do not belong to a single zone.
177 page
= pfn_to_page(pfn
);
178 if (page_zone(page
) != zone
)
181 /* Check the block is suitable for migration */
182 if (!suitable_migration_target(page
))
186 * Found a block suitable for isolating free pages from. Now
187 * we disabled interrupts, double check things are ok and
188 * isolate the pages. This is to minimise the time IRQs
192 spin_lock_irqsave(&zone
->lock
, flags
);
193 if (suitable_migration_target(page
)) {
194 isolated
= isolate_freepages_block(zone
, pfn
, freelist
);
195 nr_freepages
+= isolated
;
197 spin_unlock_irqrestore(&zone
->lock
, flags
);
200 * Record the highest PFN we isolated pages from. When next
201 * looking for free pages, the search will restart here as
202 * page migration may have returned some pages to the allocator
205 high_pfn
= max(high_pfn
, pfn
);
208 /* split_free_page does not map the pages */
209 list_for_each_entry(page
, freelist
, lru
) {
210 arch_alloc_page(page
, 0);
211 kernel_map_pages(page
, 1, 1);
214 cc
->free_pfn
= high_pfn
;
215 cc
->nr_freepages
= nr_freepages
;
218 /* Update the number of anon and file isolated pages in the zone */
219 static void acct_isolated(struct zone
*zone
, struct compact_control
*cc
)
222 unsigned int count
[2] = { 0, };
224 list_for_each_entry(page
, &cc
->migratepages
, lru
)
225 count
[!!page_is_file_cache(page
)]++;
227 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
228 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
231 /* Similar to reclaim, but different enough that they don't share logic */
232 static bool too_many_isolated(struct zone
*zone
)
234 unsigned long active
, inactive
, isolated
;
236 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
237 zone_page_state(zone
, NR_INACTIVE_ANON
);
238 active
= zone_page_state(zone
, NR_ACTIVE_FILE
) +
239 zone_page_state(zone
, NR_ACTIVE_ANON
);
240 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
241 zone_page_state(zone
, NR_ISOLATED_ANON
);
243 return isolated
> (inactive
+ active
) / 2;
246 /* possible outcome of isolate_migratepages */
248 ISOLATE_ABORT
, /* Abort compaction now */
249 ISOLATE_NONE
, /* No pages isolated, continue scanning */
250 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
254 * Isolate all pages that can be migrated from the block pointed to by
255 * the migrate scanner within compact_control.
257 static isolate_migrate_t
isolate_migratepages(struct zone
*zone
,
258 struct compact_control
*cc
)
260 unsigned long low_pfn
, end_pfn
;
261 unsigned long last_pageblock_nr
= 0, pageblock_nr
;
262 unsigned long nr_scanned
= 0, nr_isolated
= 0;
263 struct list_head
*migratelist
= &cc
->migratepages
;
264 isolate_mode_t mode
= ISOLATE_ACTIVE
|ISOLATE_INACTIVE
;
266 /* Do not scan outside zone boundaries */
267 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
269 /* Only scan within a pageblock boundary */
270 end_pfn
= ALIGN(low_pfn
+ pageblock_nr_pages
, pageblock_nr_pages
);
272 /* Do not cross the free scanner or scan within a memory hole */
273 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
274 cc
->migrate_pfn
= end_pfn
;
279 * Ensure that there are not too many pages isolated from the LRU
280 * list by either parallel reclaimers or compaction. If there are,
281 * delay for some time until fewer pages are isolated
283 while (unlikely(too_many_isolated(zone
))) {
284 /* async migration should just abort */
286 return ISOLATE_ABORT
;
288 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
290 if (fatal_signal_pending(current
))
291 return ISOLATE_ABORT
;
294 /* Time to isolate some pages for migration */
296 spin_lock_irq(&zone
->lru_lock
);
297 for (; low_pfn
< end_pfn
; low_pfn
++) {
301 /* give a chance to irqs before checking need_resched() */
302 if (!((low_pfn
+1) % SWAP_CLUSTER_MAX
)) {
303 spin_unlock_irq(&zone
->lru_lock
);
306 if (need_resched() || spin_is_contended(&zone
->lru_lock
)) {
308 spin_unlock_irq(&zone
->lru_lock
);
310 spin_lock_irq(&zone
->lru_lock
);
311 if (fatal_signal_pending(current
))
314 spin_lock_irq(&zone
->lru_lock
);
317 * migrate_pfn does not necessarily start aligned to a
318 * pageblock. Ensure that pfn_valid is called when moving
319 * into a new MAX_ORDER_NR_PAGES range in case of large
320 * memory holes within the zone
322 if ((low_pfn
& (MAX_ORDER_NR_PAGES
- 1)) == 0) {
323 if (!pfn_valid(low_pfn
)) {
324 low_pfn
+= MAX_ORDER_NR_PAGES
- 1;
329 if (!pfn_valid_within(low_pfn
))
334 * Get the page and ensure the page is within the same zone.
335 * See the comment in isolate_freepages about overlapping
336 * nodes. It is deliberate that the new zone lock is not taken
337 * as memory compaction should not move pages between nodes.
339 page
= pfn_to_page(low_pfn
);
340 if (page_zone(page
) != zone
)
348 * For async migration, also only scan in MOVABLE blocks. Async
349 * migration is optimistic to see if the minimum amount of work
350 * satisfies the allocation
352 pageblock_nr
= low_pfn
>> pageblock_order
;
353 if (!cc
->sync
&& last_pageblock_nr
!= pageblock_nr
&&
354 get_pageblock_migratetype(page
) != MIGRATE_MOVABLE
) {
355 low_pfn
+= pageblock_nr_pages
;
356 low_pfn
= ALIGN(low_pfn
, pageblock_nr_pages
) - 1;
357 last_pageblock_nr
= pageblock_nr
;
365 * PageLRU is set, and lru_lock excludes isolation,
366 * splitting and collapsing (collapsing has already
367 * happened if PageLRU is set).
369 if (PageTransHuge(page
)) {
370 low_pfn
+= (1 << compound_order(page
)) - 1;
375 mode
|= ISOLATE_ASYNC_MIGRATE
;
377 /* Try isolate the page */
378 if (__isolate_lru_page(page
, mode
, 0) != 0)
381 VM_BUG_ON(PageTransCompound(page
));
383 /* Successfully isolated */
384 del_page_from_lru_list(zone
, page
, page_lru(page
));
385 list_add(&page
->lru
, migratelist
);
386 cc
->nr_migratepages
++;
389 /* Avoid isolating too much */
390 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
) {
396 acct_isolated(zone
, cc
);
398 spin_unlock_irq(&zone
->lru_lock
);
399 cc
->migrate_pfn
= low_pfn
;
401 trace_mm_compaction_isolate_migratepages(nr_scanned
, nr_isolated
);
403 return ISOLATE_SUCCESS
;
407 * This is a migrate-callback that "allocates" freepages by taking pages
408 * from the isolated freelists in the block we are migrating to.
410 static struct page
*compaction_alloc(struct page
*migratepage
,
414 struct compact_control
*cc
= (struct compact_control
*)data
;
415 struct page
*freepage
;
417 /* Isolate free pages if necessary */
418 if (list_empty(&cc
->freepages
)) {
419 isolate_freepages(cc
->zone
, cc
);
421 if (list_empty(&cc
->freepages
))
425 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
426 list_del(&freepage
->lru
);
433 * We cannot control nr_migratepages and nr_freepages fully when migration is
434 * running as migrate_pages() has no knowledge of compact_control. When
435 * migration is complete, we count the number of pages on the lists by hand.
437 static void update_nr_listpages(struct compact_control
*cc
)
439 int nr_migratepages
= 0;
440 int nr_freepages
= 0;
443 list_for_each_entry(page
, &cc
->migratepages
, lru
)
445 list_for_each_entry(page
, &cc
->freepages
, lru
)
448 cc
->nr_migratepages
= nr_migratepages
;
449 cc
->nr_freepages
= nr_freepages
;
452 static int compact_finished(struct zone
*zone
,
453 struct compact_control
*cc
)
456 unsigned long watermark
;
458 if (fatal_signal_pending(current
))
459 return COMPACT_PARTIAL
;
461 /* Compaction run completes if the migrate and free scanner meet */
462 if (cc
->free_pfn
<= cc
->migrate_pfn
)
463 return COMPACT_COMPLETE
;
466 * order == -1 is expected when compacting via
467 * /proc/sys/vm/compact_memory
470 return COMPACT_CONTINUE
;
472 /* Compaction run is not finished if the watermark is not met */
473 watermark
= low_wmark_pages(zone
);
474 watermark
+= (1 << cc
->order
);
476 if (!zone_watermark_ok(zone
, cc
->order
, watermark
, 0, 0))
477 return COMPACT_CONTINUE
;
479 /* Direct compactor: Is a suitable page free? */
480 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
481 /* Job done if page is free of the right migratetype */
482 if (!list_empty(&zone
->free_area
[order
].free_list
[cc
->migratetype
]))
483 return COMPACT_PARTIAL
;
485 /* Job done if allocation would set block type */
486 if (order
>= pageblock_order
&& zone
->free_area
[order
].nr_free
)
487 return COMPACT_PARTIAL
;
490 return COMPACT_CONTINUE
;
494 * compaction_suitable: Is this suitable to run compaction on this zone now?
496 * COMPACT_SKIPPED - If there are too few free pages for compaction
497 * COMPACT_PARTIAL - If the allocation would succeed without compaction
498 * COMPACT_CONTINUE - If compaction should run now
500 unsigned long compaction_suitable(struct zone
*zone
, int order
)
503 unsigned long watermark
;
506 * order == -1 is expected when compacting via
507 * /proc/sys/vm/compact_memory
510 return COMPACT_CONTINUE
;
513 * Watermarks for order-0 must be met for compaction. Note the 2UL.
514 * This is because during migration, copies of pages need to be
515 * allocated and for a short time, the footprint is higher
517 watermark
= low_wmark_pages(zone
) + (2UL << order
);
518 if (!zone_watermark_ok(zone
, 0, watermark
, 0, 0))
519 return COMPACT_SKIPPED
;
522 * fragmentation index determines if allocation failures are due to
523 * low memory or external fragmentation
525 * index of -1000 implies allocations might succeed depending on
527 * index towards 0 implies failure is due to lack of memory
528 * index towards 1000 implies failure is due to fragmentation
530 * Only compact if a failure would be due to fragmentation.
532 fragindex
= fragmentation_index(zone
, order
);
533 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
534 return COMPACT_SKIPPED
;
536 if (fragindex
== -1000 && zone_watermark_ok(zone
, order
, watermark
,
538 return COMPACT_PARTIAL
;
540 return COMPACT_CONTINUE
;
543 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
547 ret
= compaction_suitable(zone
, cc
->order
);
549 case COMPACT_PARTIAL
:
550 case COMPACT_SKIPPED
:
551 /* Compaction is likely to fail */
553 case COMPACT_CONTINUE
:
554 /* Fall through to compaction */
558 /* Setup to move all movable pages to the end of the zone */
559 cc
->migrate_pfn
= zone
->zone_start_pfn
;
560 cc
->free_pfn
= cc
->migrate_pfn
+ zone
->spanned_pages
;
561 cc
->free_pfn
&= ~(pageblock_nr_pages
-1);
563 migrate_prep_local();
565 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
566 unsigned long nr_migrate
, nr_remaining
;
569 switch (isolate_migratepages(zone
, cc
)) {
571 ret
= COMPACT_PARTIAL
;
575 case ISOLATE_SUCCESS
:
579 nr_migrate
= cc
->nr_migratepages
;
580 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
581 (unsigned long)cc
, false,
582 cc
->sync
? MIGRATE_SYNC_LIGHT
: MIGRATE_ASYNC
);
583 update_nr_listpages(cc
);
584 nr_remaining
= cc
->nr_migratepages
;
586 count_vm_event(COMPACTBLOCKS
);
587 count_vm_events(COMPACTPAGES
, nr_migrate
- nr_remaining
);
589 count_vm_events(COMPACTPAGEFAILED
, nr_remaining
);
590 trace_mm_compaction_migratepages(nr_migrate
- nr_remaining
,
593 /* Release LRU pages not migrated */
595 putback_lru_pages(&cc
->migratepages
);
596 cc
->nr_migratepages
= 0;
602 /* Release free pages and check accounting */
603 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
604 VM_BUG_ON(cc
->nr_freepages
!= 0);
609 static unsigned long compact_zone_order(struct zone
*zone
,
610 int order
, gfp_t gfp_mask
,
613 struct compact_control cc
= {
615 .nr_migratepages
= 0,
617 .migratetype
= allocflags_to_migratetype(gfp_mask
),
621 INIT_LIST_HEAD(&cc
.freepages
);
622 INIT_LIST_HEAD(&cc
.migratepages
);
624 return compact_zone(zone
, &cc
);
627 int sysctl_extfrag_threshold
= 500;
630 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
631 * @zonelist: The zonelist used for the current allocation
632 * @order: The order of the current allocation
633 * @gfp_mask: The GFP mask of the current allocation
634 * @nodemask: The allowed nodes to allocate from
635 * @sync: Whether migration is synchronous or not
637 * This is the main entry point for direct page compaction.
639 unsigned long try_to_compact_pages(struct zonelist
*zonelist
,
640 int order
, gfp_t gfp_mask
, nodemask_t
*nodemask
,
643 enum zone_type high_zoneidx
= gfp_zone(gfp_mask
);
644 int may_enter_fs
= gfp_mask
& __GFP_FS
;
645 int may_perform_io
= gfp_mask
& __GFP_IO
;
648 int rc
= COMPACT_SKIPPED
;
651 * Check whether it is worth even starting compaction. The order check is
652 * made because an assumption is made that the page allocator can satisfy
653 * the "cheaper" orders without taking special steps
655 if (!order
|| !may_enter_fs
|| !may_perform_io
)
658 count_vm_event(COMPACTSTALL
);
660 /* Compact each zone in the list */
661 for_each_zone_zonelist_nodemask(zone
, z
, zonelist
, high_zoneidx
,
665 status
= compact_zone_order(zone
, order
, gfp_mask
, sync
);
666 rc
= max(status
, rc
);
668 /* If a normal allocation would succeed, stop compacting */
669 if (zone_watermark_ok(zone
, order
, low_wmark_pages(zone
), 0, 0))
677 /* Compact all zones within a node */
678 static int __compact_pgdat(pg_data_t
*pgdat
, struct compact_control
*cc
)
683 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
685 zone
= &pgdat
->node_zones
[zoneid
];
686 if (!populated_zone(zone
))
689 cc
->nr_freepages
= 0;
690 cc
->nr_migratepages
= 0;
692 INIT_LIST_HEAD(&cc
->freepages
);
693 INIT_LIST_HEAD(&cc
->migratepages
);
695 if (cc
->order
== -1 || !compaction_deferred(zone
, cc
->order
))
696 compact_zone(zone
, cc
);
699 int ok
= zone_watermark_ok(zone
, cc
->order
,
700 low_wmark_pages(zone
), 0, 0);
701 if (ok
&& cc
->order
> zone
->compact_order_failed
)
702 zone
->compact_order_failed
= cc
->order
+ 1;
703 /* Currently async compaction is never deferred. */
704 else if (!ok
&& cc
->sync
)
705 defer_compaction(zone
, cc
->order
);
708 VM_BUG_ON(!list_empty(&cc
->freepages
));
709 VM_BUG_ON(!list_empty(&cc
->migratepages
));
715 int compact_pgdat(pg_data_t
*pgdat
, int order
)
717 struct compact_control cc
= {
722 return __compact_pgdat(pgdat
, &cc
);
725 static int compact_node(int nid
)
727 struct compact_control cc
= {
732 return __compact_pgdat(NODE_DATA(nid
), &cc
);
735 /* Compact all nodes in the system */
736 static int compact_nodes(void)
740 /* Flush pending updates to the LRU lists */
743 for_each_online_node(nid
)
746 return COMPACT_COMPLETE
;
749 /* The written value is actually unused, all memory is compacted */
750 int sysctl_compact_memory
;
752 /* This is the entry point for compacting all nodes via /proc/sys/vm */
753 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
754 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
757 return compact_nodes();
762 int sysctl_extfrag_handler(struct ctl_table
*table
, int write
,
763 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
765 proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
770 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
771 ssize_t
sysfs_compact_node(struct device
*dev
,
772 struct device_attribute
*attr
,
773 const char *buf
, size_t count
)
777 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
778 /* Flush pending updates to the LRU lists */
786 static DEVICE_ATTR(compact
, S_IWUSR
, NULL
, sysfs_compact_node
);
788 int compaction_register_node(struct node
*node
)
790 return device_create_file(&node
->dev
, &dev_attr_compact
);
793 void compaction_unregister_node(struct node
*node
)
795 return device_remove_file(&node
->dev
, &dev_attr_compact
);
797 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
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