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>
19 * compact_control is used to track pages being migrated and the free pages
20 * they are being migrated to during memory compaction. The free_pfn starts
21 * at the end of a zone and migrate_pfn begins at the start. Movable pages
22 * are moved to the end of a zone during a compaction run and the run
23 * completes when free_pfn <= migrate_pfn
25 struct compact_control
{
26 struct list_head freepages
; /* List of free pages to migrate to */
27 struct list_head migratepages
; /* List of pages being migrated */
28 unsigned long nr_freepages
; /* Number of isolated free pages */
29 unsigned long nr_migratepages
; /* Number of pages to migrate */
30 unsigned long free_pfn
; /* isolate_freepages search base */
31 unsigned long migrate_pfn
; /* isolate_migratepages search base */
33 /* Account for isolated anon and file pages */
34 unsigned long nr_anon
;
35 unsigned long nr_file
;
40 static unsigned long release_freepages(struct list_head
*freelist
)
42 struct page
*page
, *next
;
43 unsigned long count
= 0;
45 list_for_each_entry_safe(page
, next
, freelist
, lru
) {
54 /* Isolate free pages onto a private freelist. Must hold zone->lock */
55 static unsigned long isolate_freepages_block(struct zone
*zone
,
56 unsigned long blockpfn
,
57 struct list_head
*freelist
)
59 unsigned long zone_end_pfn
, end_pfn
;
60 int total_isolated
= 0;
63 /* Get the last PFN we should scan for free pages at */
64 zone_end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
65 end_pfn
= min(blockpfn
+ pageblock_nr_pages
, zone_end_pfn
);
67 /* Find the first usable PFN in the block to initialse page cursor */
68 for (; blockpfn
< end_pfn
; blockpfn
++) {
69 if (pfn_valid_within(blockpfn
))
72 cursor
= pfn_to_page(blockpfn
);
74 /* Isolate free pages. This assumes the block is valid */
75 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
77 struct page
*page
= cursor
;
79 if (!pfn_valid_within(blockpfn
))
85 /* Found a free page, break it into order-0 pages */
86 isolated
= split_free_page(page
);
87 total_isolated
+= isolated
;
88 for (i
= 0; i
< isolated
; i
++) {
89 list_add(&page
->lru
, freelist
);
93 /* If a page was split, advance to the end of it */
95 blockpfn
+= isolated
- 1;
96 cursor
+= isolated
- 1;
100 return total_isolated
;
103 /* Returns true if the page is within a block suitable for migration to */
104 static bool suitable_migration_target(struct page
*page
)
107 int migratetype
= get_pageblock_migratetype(page
);
109 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
110 if (migratetype
== MIGRATE_ISOLATE
|| migratetype
== MIGRATE_RESERVE
)
113 /* If the page is a large free page, then allow migration */
114 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
117 /* If the block is MIGRATE_MOVABLE, allow migration */
118 if (migratetype
== MIGRATE_MOVABLE
)
121 /* Otherwise skip the block */
126 * Based on information in the current compact_control, find blocks
127 * suitable for isolating free pages from and then isolate them.
129 static void isolate_freepages(struct zone
*zone
,
130 struct compact_control
*cc
)
133 unsigned long high_pfn
, low_pfn
, pfn
;
135 int nr_freepages
= cc
->nr_freepages
;
136 struct list_head
*freelist
= &cc
->freepages
;
139 low_pfn
= cc
->migrate_pfn
+ pageblock_nr_pages
;
143 * Isolate free pages until enough are available to migrate the
144 * pages on cc->migratepages. We stop searching if the migrate
145 * and free page scanners meet or enough free pages are isolated.
147 spin_lock_irqsave(&zone
->lock
, flags
);
148 for (; pfn
> low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
149 pfn
-= pageblock_nr_pages
) {
150 unsigned long isolated
;
156 * Check for overlapping nodes/zones. It's possible on some
157 * configurations to have a setup like
159 * i.e. it's possible that all pages within a zones range of
160 * pages do not belong to a single zone.
162 page
= pfn_to_page(pfn
);
163 if (page_zone(page
) != zone
)
166 /* Check the block is suitable for migration */
167 if (!suitable_migration_target(page
))
170 /* Found a block suitable for isolating free pages from */
171 isolated
= isolate_freepages_block(zone
, pfn
, freelist
);
172 nr_freepages
+= isolated
;
175 * Record the highest PFN we isolated pages from. When next
176 * looking for free pages, the search will restart here as
177 * page migration may have returned some pages to the allocator
180 high_pfn
= max(high_pfn
, pfn
);
182 spin_unlock_irqrestore(&zone
->lock
, flags
);
184 /* split_free_page does not map the pages */
185 list_for_each_entry(page
, freelist
, lru
) {
186 arch_alloc_page(page
, 0);
187 kernel_map_pages(page
, 1, 1);
190 cc
->free_pfn
= high_pfn
;
191 cc
->nr_freepages
= nr_freepages
;
194 /* Update the number of anon and file isolated pages in the zone */
195 static void acct_isolated(struct zone
*zone
, struct compact_control
*cc
)
198 unsigned int count
[NR_LRU_LISTS
] = { 0, };
200 list_for_each_entry(page
, &cc
->migratepages
, lru
) {
201 int lru
= page_lru_base_type(page
);
205 cc
->nr_anon
= count
[LRU_ACTIVE_ANON
] + count
[LRU_INACTIVE_ANON
];
206 cc
->nr_file
= count
[LRU_ACTIVE_FILE
] + count
[LRU_INACTIVE_FILE
];
207 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, cc
->nr_anon
);
208 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, cc
->nr_file
);
211 /* Similar to reclaim, but different enough that they don't share logic */
212 static bool too_many_isolated(struct zone
*zone
)
215 unsigned long inactive
, isolated
;
217 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
218 zone_page_state(zone
, NR_INACTIVE_ANON
);
219 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
220 zone_page_state(zone
, NR_ISOLATED_ANON
);
222 return isolated
> inactive
;
226 * Isolate all pages that can be migrated from the block pointed to by
227 * the migrate scanner within compact_control.
229 static unsigned long isolate_migratepages(struct zone
*zone
,
230 struct compact_control
*cc
)
232 unsigned long low_pfn
, end_pfn
;
233 struct list_head
*migratelist
= &cc
->migratepages
;
235 /* Do not scan outside zone boundaries */
236 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
238 /* Only scan within a pageblock boundary */
239 end_pfn
= ALIGN(low_pfn
+ pageblock_nr_pages
, pageblock_nr_pages
);
241 /* Do not cross the free scanner or scan within a memory hole */
242 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
243 cc
->migrate_pfn
= end_pfn
;
248 * Ensure that there are not too many pages isolated from the LRU
249 * list by either parallel reclaimers or compaction. If there are,
250 * delay for some time until fewer pages are isolated
252 while (unlikely(too_many_isolated(zone
))) {
253 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
255 if (fatal_signal_pending(current
))
259 /* Time to isolate some pages for migration */
260 spin_lock_irq(&zone
->lru_lock
);
261 for (; low_pfn
< end_pfn
; low_pfn
++) {
263 if (!pfn_valid_within(low_pfn
))
266 /* Get the page and skip if free */
267 page
= pfn_to_page(low_pfn
);
271 /* Try isolate the page */
272 if (__isolate_lru_page(page
, ISOLATE_BOTH
, 0) != 0)
275 /* Successfully isolated */
276 del_page_from_lru_list(zone
, page
, page_lru(page
));
277 list_add(&page
->lru
, migratelist
);
278 mem_cgroup_del_lru(page
);
279 cc
->nr_migratepages
++;
281 /* Avoid isolating too much */
282 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
)
286 acct_isolated(zone
, cc
);
288 spin_unlock_irq(&zone
->lru_lock
);
289 cc
->migrate_pfn
= low_pfn
;
291 return cc
->nr_migratepages
;
295 * This is a migrate-callback that "allocates" freepages by taking pages
296 * from the isolated freelists in the block we are migrating to.
298 static struct page
*compaction_alloc(struct page
*migratepage
,
302 struct compact_control
*cc
= (struct compact_control
*)data
;
303 struct page
*freepage
;
305 /* Isolate free pages if necessary */
306 if (list_empty(&cc
->freepages
)) {
307 isolate_freepages(cc
->zone
, cc
);
309 if (list_empty(&cc
->freepages
))
313 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
314 list_del(&freepage
->lru
);
321 * We cannot control nr_migratepages and nr_freepages fully when migration is
322 * running as migrate_pages() has no knowledge of compact_control. When
323 * migration is complete, we count the number of pages on the lists by hand.
325 static void update_nr_listpages(struct compact_control
*cc
)
327 int nr_migratepages
= 0;
328 int nr_freepages
= 0;
331 list_for_each_entry(page
, &cc
->migratepages
, lru
)
333 list_for_each_entry(page
, &cc
->freepages
, lru
)
336 cc
->nr_migratepages
= nr_migratepages
;
337 cc
->nr_freepages
= nr_freepages
;
340 static int compact_finished(struct zone
*zone
,
341 struct compact_control
*cc
)
343 if (fatal_signal_pending(current
))
344 return COMPACT_PARTIAL
;
346 /* Compaction run completes if the migrate and free scanner meet */
347 if (cc
->free_pfn
<= cc
->migrate_pfn
)
348 return COMPACT_COMPLETE
;
350 return COMPACT_CONTINUE
;
353 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
357 /* Setup to move all movable pages to the end of the zone */
358 cc
->migrate_pfn
= zone
->zone_start_pfn
;
359 cc
->free_pfn
= cc
->migrate_pfn
+ zone
->spanned_pages
;
360 cc
->free_pfn
&= ~(pageblock_nr_pages
-1);
362 migrate_prep_local();
364 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
365 unsigned long nr_migrate
, nr_remaining
;
367 if (!isolate_migratepages(zone
, cc
))
370 nr_migrate
= cc
->nr_migratepages
;
371 migrate_pages(&cc
->migratepages
, compaction_alloc
,
372 (unsigned long)cc
, 0);
373 update_nr_listpages(cc
);
374 nr_remaining
= cc
->nr_migratepages
;
376 count_vm_event(COMPACTBLOCKS
);
377 count_vm_events(COMPACTPAGES
, nr_migrate
- nr_remaining
);
379 count_vm_events(COMPACTPAGEFAILED
, nr_remaining
);
381 /* Release LRU pages not migrated */
382 if (!list_empty(&cc
->migratepages
)) {
383 putback_lru_pages(&cc
->migratepages
);
384 cc
->nr_migratepages
= 0;
389 /* Release free pages and check accounting */
390 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
391 VM_BUG_ON(cc
->nr_freepages
!= 0);
396 /* Compact all zones within a node */
397 static int compact_node(int nid
)
403 if (nid
< 0 || nid
>= nr_node_ids
|| !node_online(nid
))
405 pgdat
= NODE_DATA(nid
);
407 /* Flush pending updates to the LRU lists */
410 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
411 struct compact_control cc
= {
413 .nr_migratepages
= 0,
416 zone
= &pgdat
->node_zones
[zoneid
];
417 if (!populated_zone(zone
))
421 INIT_LIST_HEAD(&cc
.freepages
);
422 INIT_LIST_HEAD(&cc
.migratepages
);
424 compact_zone(zone
, &cc
);
426 VM_BUG_ON(!list_empty(&cc
.freepages
));
427 VM_BUG_ON(!list_empty(&cc
.migratepages
));
433 /* Compact all nodes in the system */
434 static int compact_nodes(void)
438 for_each_online_node(nid
)
441 return COMPACT_COMPLETE
;
444 /* The written value is actually unused, all memory is compacted */
445 int sysctl_compact_memory
;
447 /* This is the entry point for compacting all nodes via /proc/sys/vm */
448 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
449 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
452 return compact_nodes();
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