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>
20 * compact_control is used to track pages being migrated and the free pages
21 * they are being migrated to during memory compaction. The free_pfn starts
22 * at the end of a zone and migrate_pfn begins at the start. Movable pages
23 * are moved to the end of a zone during a compaction run and the run
24 * completes when free_pfn <= migrate_pfn
26 struct compact_control {
27 struct list_head freepages; /* List of free pages to migrate to */
28 struct list_head migratepages; /* List of pages being migrated */
29 unsigned long nr_freepages; /* Number of isolated free pages */
30 unsigned long nr_migratepages; /* Number of pages to migrate */
31 unsigned long free_pfn; /* isolate_freepages search base */
32 unsigned long migrate_pfn; /* isolate_migratepages search base */
34 /* Account for isolated anon and file pages */
35 unsigned long nr_anon;
36 unsigned long nr_file;
41 static unsigned long release_freepages(struct list_head *freelist)
43 struct page *page, *next;
44 unsigned long count = 0;
46 list_for_each_entry_safe(page, next, freelist, lru) {
55 /* Isolate free pages onto a private freelist. Must hold zone->lock */
56 static unsigned long isolate_freepages_block(struct zone *zone,
57 unsigned long blockpfn,
58 struct list_head *freelist)
60 unsigned long zone_end_pfn, end_pfn;
61 int total_isolated = 0;
64 /* Get the last PFN we should scan for free pages at */
65 zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
66 end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
68 /* Find the first usable PFN in the block to initialse page cursor */
69 for (; blockpfn < end_pfn; blockpfn++) {
70 if (pfn_valid_within(blockpfn))
73 cursor = pfn_to_page(blockpfn);
75 /* Isolate free pages. This assumes the block is valid */
76 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
78 struct page *page = cursor;
80 if (!pfn_valid_within(blockpfn))
86 /* Found a free page, break it into order-0 pages */
87 isolated = split_free_page(page);
88 total_isolated += isolated;
89 for (i = 0; i < isolated; i++) {
90 list_add(&page->lru, freelist);
94 /* If a page was split, advance to the end of it */
96 blockpfn += isolated - 1;
97 cursor += isolated - 1;
101 return total_isolated;
104 /* Returns true if the page is within a block suitable for migration to */
105 static bool suitable_migration_target(struct page *page)
108 int migratetype = get_pageblock_migratetype(page);
110 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
111 if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
114 /* If the page is a large free page, then allow migration */
115 if (PageBuddy(page) && page_order(page) >= pageblock_order)
118 /* If the block is MIGRATE_MOVABLE, allow migration */
119 if (migratetype == MIGRATE_MOVABLE)
122 /* Otherwise skip the block */
127 * Based on information in the current compact_control, find blocks
128 * suitable for isolating free pages from and then isolate them.
130 static void isolate_freepages(struct zone *zone,
131 struct compact_control *cc)
134 unsigned long high_pfn, low_pfn, pfn;
136 int nr_freepages = cc->nr_freepages;
137 struct list_head *freelist = &cc->freepages;
140 low_pfn = cc->migrate_pfn + pageblock_nr_pages;
144 * Isolate free pages until enough are available to migrate the
145 * pages on cc->migratepages. We stop searching if the migrate
146 * and free page scanners meet or enough free pages are isolated.
148 spin_lock_irqsave(&zone->lock, flags);
149 for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
150 pfn -= pageblock_nr_pages) {
151 unsigned long isolated;
157 * Check for overlapping nodes/zones. It's possible on some
158 * configurations to have a setup like
160 * i.e. it's possible that all pages within a zones range of
161 * pages do not belong to a single zone.
163 page = pfn_to_page(pfn);
164 if (page_zone(page) != zone)
167 /* Check the block is suitable for migration */
168 if (!suitable_migration_target(page))
171 /* Found a block suitable for isolating free pages from */
172 isolated = isolate_freepages_block(zone, pfn, freelist);
173 nr_freepages += isolated;
176 * Record the highest PFN we isolated pages from. When next
177 * looking for free pages, the search will restart here as
178 * page migration may have returned some pages to the allocator
181 high_pfn = max(high_pfn, pfn);
183 spin_unlock_irqrestore(&zone->lock, flags);
185 /* split_free_page does not map the pages */
186 list_for_each_entry(page, freelist, lru) {
187 arch_alloc_page(page, 0);
188 kernel_map_pages(page, 1, 1);
191 cc->free_pfn = high_pfn;
192 cc->nr_freepages = nr_freepages;
195 /* Update the number of anon and file isolated pages in the zone */
196 static void acct_isolated(struct zone *zone, struct compact_control *cc)
199 unsigned int count[NR_LRU_LISTS] = { 0, };
201 list_for_each_entry(page, &cc->migratepages, lru) {
202 int lru = page_lru_base_type(page);
206 cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
207 cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
208 __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
209 __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
212 /* Similar to reclaim, but different enough that they don't share logic */
213 static bool too_many_isolated(struct zone *zone)
216 unsigned long inactive, isolated;
218 inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
219 zone_page_state(zone, NR_INACTIVE_ANON);
220 isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
221 zone_page_state(zone, NR_ISOLATED_ANON);
223 return isolated > inactive;
227 * Isolate all pages that can be migrated from the block pointed to by
228 * the migrate scanner within compact_control.
230 static unsigned long isolate_migratepages(struct zone *zone,
231 struct compact_control *cc)
233 unsigned long low_pfn, end_pfn;
234 struct list_head *migratelist = &cc->migratepages;
236 /* Do not scan outside zone boundaries */
237 low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
239 /* Only scan within a pageblock boundary */
240 end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
242 /* Do not cross the free scanner or scan within a memory hole */
243 if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
244 cc->migrate_pfn = end_pfn;
249 * Ensure that there are not too many pages isolated from the LRU
250 * list by either parallel reclaimers or compaction. If there are,
251 * delay for some time until fewer pages are isolated
253 while (unlikely(too_many_isolated(zone))) {
254 congestion_wait(BLK_RW_ASYNC, HZ/10);
256 if (fatal_signal_pending(current))
260 /* Time to isolate some pages for migration */
261 spin_lock_irq(&zone->lru_lock);
262 for (; low_pfn < end_pfn; low_pfn++) {
264 if (!pfn_valid_within(low_pfn))
267 /* Get the page and skip if free */
268 page = pfn_to_page(low_pfn);
272 /* Try isolate the page */
273 if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
276 /* Successfully isolated */
277 del_page_from_lru_list(zone, page, page_lru(page));
278 list_add(&page->lru, migratelist);
279 mem_cgroup_del_lru(page);
280 cc->nr_migratepages++;
282 /* Avoid isolating too much */
283 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
287 acct_isolated(zone, cc);
289 spin_unlock_irq(&zone->lru_lock);
290 cc->migrate_pfn = low_pfn;
292 return cc->nr_migratepages;
296 * This is a migrate-callback that "allocates" freepages by taking pages
297 * from the isolated freelists in the block we are migrating to.
299 static struct page *compaction_alloc(struct page *migratepage,
303 struct compact_control *cc = (struct compact_control *)data;
304 struct page *freepage;
306 /* Isolate free pages if necessary */
307 if (list_empty(&cc->freepages)) {
308 isolate_freepages(cc->zone, cc);
310 if (list_empty(&cc->freepages))
314 freepage = list_entry(cc->freepages.next, struct page, lru);
315 list_del(&freepage->lru);
322 * We cannot control nr_migratepages and nr_freepages fully when migration is
323 * running as migrate_pages() has no knowledge of compact_control. When
324 * migration is complete, we count the number of pages on the lists by hand.
326 static void update_nr_listpages(struct compact_control *cc)
328 int nr_migratepages = 0;
329 int nr_freepages = 0;
332 list_for_each_entry(page, &cc->migratepages, lru)
334 list_for_each_entry(page, &cc->freepages, lru)
337 cc->nr_migratepages = nr_migratepages;
338 cc->nr_freepages = nr_freepages;
341 static int compact_finished(struct zone *zone,
342 struct compact_control *cc)
344 if (fatal_signal_pending(current))
345 return COMPACT_PARTIAL;
347 /* Compaction run completes if the migrate and free scanner meet */
348 if (cc->free_pfn <= cc->migrate_pfn)
349 return COMPACT_COMPLETE;
351 return COMPACT_CONTINUE;
354 static int compact_zone(struct zone *zone, struct compact_control *cc)
358 /* Setup to move all movable pages to the end of the zone */
359 cc->migrate_pfn = zone->zone_start_pfn;
360 cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
361 cc->free_pfn &= ~(pageblock_nr_pages-1);
363 migrate_prep_local();
365 while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
366 unsigned long nr_migrate, nr_remaining;
368 if (!isolate_migratepages(zone, cc))
371 nr_migrate = cc->nr_migratepages;
372 migrate_pages(&cc->migratepages, compaction_alloc,
373 (unsigned long)cc, 0);
374 update_nr_listpages(cc);
375 nr_remaining = cc->nr_migratepages;
377 count_vm_event(COMPACTBLOCKS);
378 count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
380 count_vm_events(COMPACTPAGEFAILED, nr_remaining);
382 /* Release LRU pages not migrated */
383 if (!list_empty(&cc->migratepages)) {
384 putback_lru_pages(&cc->migratepages);
385 cc->nr_migratepages = 0;
390 /* Release free pages and check accounting */
391 cc->nr_freepages -= release_freepages(&cc->freepages);
392 VM_BUG_ON(cc->nr_freepages != 0);
397 /* Compact all zones within a node */
398 static int compact_node(int nid)
404 if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
406 pgdat = NODE_DATA(nid);
408 /* Flush pending updates to the LRU lists */
411 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
412 struct compact_control cc = {
414 .nr_migratepages = 0,
417 zone = &pgdat->node_zones[zoneid];
418 if (!populated_zone(zone))
422 INIT_LIST_HEAD(&cc.freepages);
423 INIT_LIST_HEAD(&cc.migratepages);
425 compact_zone(zone, &cc);
427 VM_BUG_ON(!list_empty(&cc.freepages));
428 VM_BUG_ON(!list_empty(&cc.migratepages));
434 /* Compact all nodes in the system */
435 static int compact_nodes(void)
439 for_each_online_node(nid)
442 return COMPACT_COMPLETE;
445 /* The written value is actually unused, all memory is compacted */
446 int sysctl_compact_memory;
448 /* This is the entry point for compacting all nodes via /proc/sys/vm */
449 int sysctl_compaction_handler(struct ctl_table *table, int write,
450 void __user *buffer, size_t *length, loff_t *ppos)
453 return compact_nodes();
458 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
459 ssize_t sysfs_compact_node(struct sys_device *dev,
460 struct sysdev_attribute *attr,
461 const char *buf, size_t count)
463 compact_node(dev->id);
467 static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
469 int compaction_register_node(struct node *node)
471 return sysdev_create_file(&node->sysdev, &attr_compact);
474 void compaction_unregister_node(struct node *node)
476 return sysdev_remove_file(&node->sysdev, &attr_compact);
478 #endif /* CONFIG_SYSFS && CONFIG_NUMA */