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 /* Account for isolated anon and file pages */
39 unsigned long nr_anon;
40 unsigned long nr_file;
42 unsigned int order; /* order a direct compactor needs */
43 int migratetype; /* MOVABLE, RECLAIMABLE etc */
47 static unsigned long release_freepages(struct list_head *freelist)
49 struct page *page, *next;
50 unsigned long count = 0;
52 list_for_each_entry_safe(page, next, freelist, lru) {
61 /* Isolate free pages onto a private freelist. Must hold zone->lock */
62 static unsigned long isolate_freepages_block(struct zone *zone,
63 unsigned long blockpfn,
64 struct list_head *freelist)
66 unsigned long zone_end_pfn, end_pfn;
67 int nr_scanned = 0, total_isolated = 0;
70 /* Get the last PFN we should scan for free pages at */
71 zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
72 end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
74 /* Find the first usable PFN in the block to initialse page cursor */
75 for (; blockpfn < end_pfn; blockpfn++) {
76 if (pfn_valid_within(blockpfn))
79 cursor = pfn_to_page(blockpfn);
81 /* Isolate free pages. This assumes the block is valid */
82 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
84 struct page *page = cursor;
86 if (!pfn_valid_within(blockpfn))
93 /* Found a free page, break it into order-0 pages */
94 isolated = split_free_page(page);
95 total_isolated += isolated;
96 for (i = 0; i < isolated; i++) {
97 list_add(&page->lru, freelist);
101 /* If a page was split, advance to the end of it */
103 blockpfn += isolated - 1;
104 cursor += isolated - 1;
108 trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
109 return total_isolated;
112 /* Returns true if the page is within a block suitable for migration to */
113 static bool suitable_migration_target(struct page *page)
116 int migratetype = get_pageblock_migratetype(page);
118 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
119 if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
122 /* If the page is a large free page, then allow migration */
123 if (PageBuddy(page) && page_order(page) >= pageblock_order)
126 /* If the block is MIGRATE_MOVABLE, allow migration */
127 if (migratetype == MIGRATE_MOVABLE)
130 /* Otherwise skip the block */
135 * Based on information in the current compact_control, find blocks
136 * suitable for isolating free pages from and then isolate them.
138 static void isolate_freepages(struct zone *zone,
139 struct compact_control *cc)
142 unsigned long high_pfn, low_pfn, pfn;
144 int nr_freepages = cc->nr_freepages;
145 struct list_head *freelist = &cc->freepages;
148 low_pfn = cc->migrate_pfn + pageblock_nr_pages;
152 * Isolate free pages until enough are available to migrate the
153 * pages on cc->migratepages. We stop searching if the migrate
154 * and free page scanners meet or enough free pages are isolated.
156 for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
157 pfn -= pageblock_nr_pages) {
158 unsigned long isolated;
164 * Check for overlapping nodes/zones. It's possible on some
165 * configurations to have a setup like
167 * i.e. it's possible that all pages within a zones range of
168 * pages do not belong to a single zone.
170 page = pfn_to_page(pfn);
171 if (page_zone(page) != zone)
174 /* Check the block is suitable for migration */
175 if (!suitable_migration_target(page))
179 * Found a block suitable for isolating free pages from. Now
180 * we disabled interrupts, double check things are ok and
181 * isolate the pages. This is to minimise the time IRQs
185 spin_lock_irqsave(&zone->lock, flags);
186 if (suitable_migration_target(page)) {
187 isolated = isolate_freepages_block(zone, pfn, freelist);
188 nr_freepages += isolated;
190 spin_unlock_irqrestore(&zone->lock, flags);
193 * Record the highest PFN we isolated pages from. When next
194 * looking for free pages, the search will restart here as
195 * page migration may have returned some pages to the allocator
198 high_pfn = max(high_pfn, pfn);
201 /* split_free_page does not map the pages */
202 list_for_each_entry(page, freelist, lru) {
203 arch_alloc_page(page, 0);
204 kernel_map_pages(page, 1, 1);
207 cc->free_pfn = high_pfn;
208 cc->nr_freepages = nr_freepages;
211 /* Update the number of anon and file isolated pages in the zone */
212 static void acct_isolated(struct zone *zone, struct compact_control *cc)
215 unsigned int count[NR_LRU_LISTS] = { 0, };
217 list_for_each_entry(page, &cc->migratepages, lru) {
218 int lru = page_lru_base_type(page);
222 cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
223 cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
224 __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
225 __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
228 /* Similar to reclaim, but different enough that they don't share logic */
229 static bool too_many_isolated(struct zone *zone)
231 unsigned long active, inactive, isolated;
233 inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
234 zone_page_state(zone, NR_INACTIVE_ANON);
235 active = zone_page_state(zone, NR_ACTIVE_FILE) +
236 zone_page_state(zone, NR_ACTIVE_ANON);
237 isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
238 zone_page_state(zone, NR_ISOLATED_ANON);
240 return isolated > (inactive + active) / 2;
244 * Isolate all pages that can be migrated from the block pointed to by
245 * the migrate scanner within compact_control.
247 static unsigned long isolate_migratepages(struct zone *zone,
248 struct compact_control *cc)
250 unsigned long low_pfn, end_pfn;
251 unsigned long last_pageblock_nr = 0, pageblock_nr;
252 unsigned long nr_scanned = 0, nr_isolated = 0;
253 struct list_head *migratelist = &cc->migratepages;
255 /* Do not scan outside zone boundaries */
256 low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
258 /* Only scan within a pageblock boundary */
259 end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
261 /* Do not cross the free scanner or scan within a memory hole */
262 if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
263 cc->migrate_pfn = end_pfn;
268 * Ensure that there are not too many pages isolated from the LRU
269 * list by either parallel reclaimers or compaction. If there are,
270 * delay for some time until fewer pages are isolated
272 while (unlikely(too_many_isolated(zone))) {
273 congestion_wait(BLK_RW_ASYNC, HZ/10);
275 if (fatal_signal_pending(current))
279 /* Time to isolate some pages for migration */
281 spin_lock_irq(&zone->lru_lock);
282 for (; low_pfn < end_pfn; low_pfn++) {
286 /* give a chance to irqs before checking need_resched() */
287 if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
288 spin_unlock_irq(&zone->lru_lock);
291 if (need_resched() || spin_is_contended(&zone->lru_lock)) {
293 spin_unlock_irq(&zone->lru_lock);
295 spin_lock_irq(&zone->lru_lock);
296 if (fatal_signal_pending(current))
299 spin_lock_irq(&zone->lru_lock);
301 if (!pfn_valid_within(low_pfn))
305 /* Get the page and skip if free */
306 page = pfn_to_page(low_pfn);
311 * For async migration, also only scan in MOVABLE blocks. Async
312 * migration is optimistic to see if the minimum amount of work
313 * satisfies the allocation
315 pageblock_nr = low_pfn >> pageblock_order;
316 if (!cc->sync && last_pageblock_nr != pageblock_nr &&
317 get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
318 low_pfn += pageblock_nr_pages;
319 low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
320 last_pageblock_nr = pageblock_nr;
328 * PageLRU is set, and lru_lock excludes isolation,
329 * splitting and collapsing (collapsing has already
330 * happened if PageLRU is set).
332 if (PageTransHuge(page)) {
333 low_pfn += (1 << compound_order(page)) - 1;
337 /* Try isolate the page */
338 if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
341 VM_BUG_ON(PageTransCompound(page));
343 /* Successfully isolated */
344 del_page_from_lru_list(zone, page, page_lru(page));
345 list_add(&page->lru, migratelist);
346 cc->nr_migratepages++;
349 /* Avoid isolating too much */
350 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
354 acct_isolated(zone, cc);
356 spin_unlock_irq(&zone->lru_lock);
357 cc->migrate_pfn = low_pfn;
359 trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
361 return cc->nr_migratepages;
365 * This is a migrate-callback that "allocates" freepages by taking pages
366 * from the isolated freelists in the block we are migrating to.
368 static struct page *compaction_alloc(struct page *migratepage,
372 struct compact_control *cc = (struct compact_control *)data;
373 struct page *freepage;
375 /* Isolate free pages if necessary */
376 if (list_empty(&cc->freepages)) {
377 isolate_freepages(cc->zone, cc);
379 if (list_empty(&cc->freepages))
383 freepage = list_entry(cc->freepages.next, struct page, lru);
384 list_del(&freepage->lru);
391 * We cannot control nr_migratepages and nr_freepages fully when migration is
392 * running as migrate_pages() has no knowledge of compact_control. When
393 * migration is complete, we count the number of pages on the lists by hand.
395 static void update_nr_listpages(struct compact_control *cc)
397 int nr_migratepages = 0;
398 int nr_freepages = 0;
401 list_for_each_entry(page, &cc->migratepages, lru)
403 list_for_each_entry(page, &cc->freepages, lru)
406 cc->nr_migratepages = nr_migratepages;
407 cc->nr_freepages = nr_freepages;
410 static int compact_finished(struct zone *zone,
411 struct compact_control *cc)
414 unsigned long watermark;
416 if (fatal_signal_pending(current))
417 return COMPACT_PARTIAL;
419 /* Compaction run completes if the migrate and free scanner meet */
420 if (cc->free_pfn <= cc->migrate_pfn)
421 return COMPACT_COMPLETE;
424 * order == -1 is expected when compacting via
425 * /proc/sys/vm/compact_memory
428 return COMPACT_CONTINUE;
430 /* Compaction run is not finished if the watermark is not met */
431 watermark = low_wmark_pages(zone);
432 watermark += (1 << cc->order);
434 if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
435 return COMPACT_CONTINUE;
437 /* Direct compactor: Is a suitable page free? */
438 for (order = cc->order; order < MAX_ORDER; order++) {
439 /* Job done if page is free of the right migratetype */
440 if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
441 return COMPACT_PARTIAL;
443 /* Job done if allocation would set block type */
444 if (order >= pageblock_order && zone->free_area[order].nr_free)
445 return COMPACT_PARTIAL;
448 return COMPACT_CONTINUE;
452 * compaction_suitable: Is this suitable to run compaction on this zone now?
454 * COMPACT_SKIPPED - If there are too few free pages for compaction
455 * COMPACT_PARTIAL - If the allocation would succeed without compaction
456 * COMPACT_CONTINUE - If compaction should run now
458 unsigned long compaction_suitable(struct zone *zone, int order)
461 unsigned long watermark;
464 * order == -1 is expected when compacting via
465 * /proc/sys/vm/compact_memory
468 return COMPACT_CONTINUE;
471 * Watermarks for order-0 must be met for compaction. Note the 2UL.
472 * This is because during migration, copies of pages need to be
473 * allocated and for a short time, the footprint is higher
475 watermark = low_wmark_pages(zone) + (2UL << order);
476 if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
477 return COMPACT_SKIPPED;
480 * fragmentation index determines if allocation failures are due to
481 * low memory or external fragmentation
483 * index of -1 implies allocations might succeed dependingon watermarks
484 * index towards 0 implies failure is due to lack of memory
485 * index towards 1000 implies failure is due to fragmentation
487 * Only compact if a failure would be due to fragmentation.
489 fragindex = fragmentation_index(zone, order);
490 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
491 return COMPACT_SKIPPED;
493 if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
494 return COMPACT_PARTIAL;
496 return COMPACT_CONTINUE;
499 static int compact_zone(struct zone *zone, struct compact_control *cc)
503 ret = compaction_suitable(zone, cc->order);
505 case COMPACT_PARTIAL:
506 case COMPACT_SKIPPED:
507 /* Compaction is likely to fail */
509 case COMPACT_CONTINUE:
510 /* Fall through to compaction */
514 /* Setup to move all movable pages to the end of the zone */
515 cc->migrate_pfn = zone->zone_start_pfn;
516 cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
517 cc->free_pfn &= ~(pageblock_nr_pages-1);
519 migrate_prep_local();
521 while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
522 unsigned long nr_migrate, nr_remaining;
525 if (!isolate_migratepages(zone, cc))
528 nr_migrate = cc->nr_migratepages;
529 err = migrate_pages(&cc->migratepages, compaction_alloc,
530 (unsigned long)cc, false,
532 update_nr_listpages(cc);
533 nr_remaining = cc->nr_migratepages;
535 count_vm_event(COMPACTBLOCKS);
536 count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
538 count_vm_events(COMPACTPAGEFAILED, nr_remaining);
539 trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
542 /* Release LRU pages not migrated */
544 putback_lru_pages(&cc->migratepages);
545 cc->nr_migratepages = 0;
550 /* Release free pages and check accounting */
551 cc->nr_freepages -= release_freepages(&cc->freepages);
552 VM_BUG_ON(cc->nr_freepages != 0);
557 unsigned long compact_zone_order(struct zone *zone,
558 int order, gfp_t gfp_mask,
561 struct compact_control cc = {
563 .nr_migratepages = 0,
565 .migratetype = allocflags_to_migratetype(gfp_mask),
569 INIT_LIST_HEAD(&cc.freepages);
570 INIT_LIST_HEAD(&cc.migratepages);
572 return compact_zone(zone, &cc);
575 int sysctl_extfrag_threshold = 500;
578 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
579 * @zonelist: The zonelist used for the current allocation
580 * @order: The order of the current allocation
581 * @gfp_mask: The GFP mask of the current allocation
582 * @nodemask: The allowed nodes to allocate from
583 * @sync: Whether migration is synchronous or not
585 * This is the main entry point for direct page compaction.
587 unsigned long try_to_compact_pages(struct zonelist *zonelist,
588 int order, gfp_t gfp_mask, nodemask_t *nodemask,
591 enum zone_type high_zoneidx = gfp_zone(gfp_mask);
592 int may_enter_fs = gfp_mask & __GFP_FS;
593 int may_perform_io = gfp_mask & __GFP_IO;
596 int rc = COMPACT_SKIPPED;
599 * Check whether it is worth even starting compaction. The order check is
600 * made because an assumption is made that the page allocator can satisfy
601 * the "cheaper" orders without taking special steps
603 if (!order || !may_enter_fs || !may_perform_io)
606 count_vm_event(COMPACTSTALL);
608 /* Compact each zone in the list */
609 for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
613 status = compact_zone_order(zone, order, gfp_mask, sync);
614 rc = max(status, rc);
616 /* If a normal allocation would succeed, stop compacting */
617 if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
625 /* Compact all zones within a node */
626 static int compact_node(int nid)
632 if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
634 pgdat = NODE_DATA(nid);
636 /* Flush pending updates to the LRU lists */
639 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
640 struct compact_control cc = {
642 .nr_migratepages = 0,
646 zone = &pgdat->node_zones[zoneid];
647 if (!populated_zone(zone))
651 INIT_LIST_HEAD(&cc.freepages);
652 INIT_LIST_HEAD(&cc.migratepages);
654 compact_zone(zone, &cc);
656 VM_BUG_ON(!list_empty(&cc.freepages));
657 VM_BUG_ON(!list_empty(&cc.migratepages));
663 /* Compact all nodes in the system */
664 static int compact_nodes(void)
668 for_each_online_node(nid)
671 return COMPACT_COMPLETE;
674 /* The written value is actually unused, all memory is compacted */
675 int sysctl_compact_memory;
677 /* This is the entry point for compacting all nodes via /proc/sys/vm */
678 int sysctl_compaction_handler(struct ctl_table *table, int write,
679 void __user *buffer, size_t *length, loff_t *ppos)
682 return compact_nodes();
687 int sysctl_extfrag_handler(struct ctl_table *table, int write,
688 void __user *buffer, size_t *length, loff_t *ppos)
690 proc_dointvec_minmax(table, write, buffer, length, ppos);
695 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
696 ssize_t sysfs_compact_node(struct sys_device *dev,
697 struct sysdev_attribute *attr,
698 const char *buf, size_t count)
700 compact_node(dev->id);
704 static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
706 int compaction_register_node(struct node *node)
708 return sysdev_create_file(&node->sysdev, &attr_compact);
711 void compaction_unregister_node(struct node *node)
713 return sysdev_remove_file(&node->sysdev, &attr_compact);
715 #endif /* CONFIG_SYSFS && CONFIG_NUMA */