4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
6 * Swap reorganised 29.12.95, Stephen Tweedie.
7 * kswapd added: 7.1.96 sct
8 * Removed kswapd_ctl limits, and swap out as many pages as needed
9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11 * Multiqueue VM started 5.8.00, Rik van Riel.
15 #include <linux/module.h>
16 #include <linux/slab.h>
17 #include <linux/kernel_stat.h>
18 #include <linux/swap.h>
19 #include <linux/pagemap.h>
20 #include <linux/init.h>
21 #include <linux/highmem.h>
22 #include <linux/vmstat.h>
23 #include <linux/file.h>
24 #include <linux/writeback.h>
25 #include <linux/blkdev.h>
26 #include <linux/buffer_head.h> /* for try_to_release_page(),
27 buffer_heads_over_limit */
28 #include <linux/mm_inline.h>
29 #include <linux/pagevec.h>
30 #include <linux/backing-dev.h>
31 #include <linux/rmap.h>
32 #include <linux/topology.h>
33 #include <linux/cpu.h>
34 #include <linux/cpuset.h>
35 #include <linux/notifier.h>
36 #include <linux/rwsem.h>
37 #include <linux/delay.h>
38 #include <linux/kthread.h>
39 #include <linux/freezer.h>
40 #include <linux/memcontrol.h>
41 #include <linux/delayacct.h>
43 #include <asm/tlbflush.h>
44 #include <asm/div64.h>
46 #include <linux/swapops.h>
51 /* Incremented by the number of inactive pages that were scanned */
52 unsigned long nr_scanned
;
54 /* This context's GFP mask */
59 /* Can pages be swapped as part of reclaim? */
62 /* This context's SWAP_CLUSTER_MAX. If freeing memory for
63 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
64 * In this context, it doesn't matter that we scan the
65 * whole list at once. */
70 int all_unreclaimable
;
74 /* Which cgroup do we reclaim from */
75 struct mem_cgroup
*mem_cgroup
;
77 /* Pluggable isolate pages callback */
78 unsigned long (*isolate_pages
)(unsigned long nr
, struct list_head
*dst
,
79 unsigned long *scanned
, int order
, int mode
,
80 struct zone
*z
, struct mem_cgroup
*mem_cont
,
84 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
86 #ifdef ARCH_HAS_PREFETCH
87 #define prefetch_prev_lru_page(_page, _base, _field) \
89 if ((_page)->lru.prev != _base) { \
92 prev = lru_to_page(&(_page->lru)); \
93 prefetch(&prev->_field); \
97 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
100 #ifdef ARCH_HAS_PREFETCHW
101 #define prefetchw_prev_lru_page(_page, _base, _field) \
103 if ((_page)->lru.prev != _base) { \
106 prev = lru_to_page(&(_page->lru)); \
107 prefetchw(&prev->_field); \
111 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
115 * From 0 .. 100. Higher means more swappy.
117 int vm_swappiness
= 60;
118 long vm_total_pages
; /* The total number of pages which the VM controls */
120 static LIST_HEAD(shrinker_list
);
121 static DECLARE_RWSEM(shrinker_rwsem
);
123 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
124 #define scan_global_lru(sc) (!(sc)->mem_cgroup)
126 #define scan_global_lru(sc) (1)
130 * Add a shrinker callback to be called from the vm
132 void register_shrinker(struct shrinker
*shrinker
)
135 down_write(&shrinker_rwsem
);
136 list_add_tail(&shrinker
->list
, &shrinker_list
);
137 up_write(&shrinker_rwsem
);
139 EXPORT_SYMBOL(register_shrinker
);
144 void unregister_shrinker(struct shrinker
*shrinker
)
146 down_write(&shrinker_rwsem
);
147 list_del(&shrinker
->list
);
148 up_write(&shrinker_rwsem
);
150 EXPORT_SYMBOL(unregister_shrinker
);
152 #define SHRINK_BATCH 128
154 * Call the shrink functions to age shrinkable caches
156 * Here we assume it costs one seek to replace a lru page and that it also
157 * takes a seek to recreate a cache object. With this in mind we age equal
158 * percentages of the lru and ageable caches. This should balance the seeks
159 * generated by these structures.
161 * If the vm encountered mapped pages on the LRU it increase the pressure on
162 * slab to avoid swapping.
164 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
166 * `lru_pages' represents the number of on-LRU pages in all the zones which
167 * are eligible for the caller's allocation attempt. It is used for balancing
168 * slab reclaim versus page reclaim.
170 * Returns the number of slab objects which we shrunk.
172 unsigned long shrink_slab(unsigned long scanned
, gfp_t gfp_mask
,
173 unsigned long lru_pages
)
175 struct shrinker
*shrinker
;
176 unsigned long ret
= 0;
179 scanned
= SWAP_CLUSTER_MAX
;
181 if (!down_read_trylock(&shrinker_rwsem
))
182 return 1; /* Assume we'll be able to shrink next time */
184 list_for_each_entry(shrinker
, &shrinker_list
, list
) {
185 unsigned long long delta
;
186 unsigned long total_scan
;
187 unsigned long max_pass
= (*shrinker
->shrink
)(0, gfp_mask
);
189 delta
= (4 * scanned
) / shrinker
->seeks
;
191 do_div(delta
, lru_pages
+ 1);
192 shrinker
->nr
+= delta
;
193 if (shrinker
->nr
< 0) {
194 printk(KERN_ERR
"%s: nr=%ld\n",
195 __func__
, shrinker
->nr
);
196 shrinker
->nr
= max_pass
;
200 * Avoid risking looping forever due to too large nr value:
201 * never try to free more than twice the estimate number of
204 if (shrinker
->nr
> max_pass
* 2)
205 shrinker
->nr
= max_pass
* 2;
207 total_scan
= shrinker
->nr
;
210 while (total_scan
>= SHRINK_BATCH
) {
211 long this_scan
= SHRINK_BATCH
;
215 nr_before
= (*shrinker
->shrink
)(0, gfp_mask
);
216 shrink_ret
= (*shrinker
->shrink
)(this_scan
, gfp_mask
);
217 if (shrink_ret
== -1)
219 if (shrink_ret
< nr_before
)
220 ret
+= nr_before
- shrink_ret
;
221 count_vm_events(SLABS_SCANNED
, this_scan
);
222 total_scan
-= this_scan
;
227 shrinker
->nr
+= total_scan
;
229 up_read(&shrinker_rwsem
);
233 /* Called without lock on whether page is mapped, so answer is unstable */
234 static inline int page_mapping_inuse(struct page
*page
)
236 struct address_space
*mapping
;
238 /* Page is in somebody's page tables. */
239 if (page_mapped(page
))
242 /* Be more reluctant to reclaim swapcache than pagecache */
243 if (PageSwapCache(page
))
246 mapping
= page_mapping(page
);
250 /* File is mmap'd by somebody? */
251 return mapping_mapped(mapping
);
254 static inline int is_page_cache_freeable(struct page
*page
)
256 return page_count(page
) - !!PagePrivate(page
) == 2;
259 static int may_write_to_queue(struct backing_dev_info
*bdi
)
261 if (current
->flags
& PF_SWAPWRITE
)
263 if (!bdi_write_congested(bdi
))
265 if (bdi
== current
->backing_dev_info
)
271 * We detected a synchronous write error writing a page out. Probably
272 * -ENOSPC. We need to propagate that into the address_space for a subsequent
273 * fsync(), msync() or close().
275 * The tricky part is that after writepage we cannot touch the mapping: nothing
276 * prevents it from being freed up. But we have a ref on the page and once
277 * that page is locked, the mapping is pinned.
279 * We're allowed to run sleeping lock_page() here because we know the caller has
282 static void handle_write_error(struct address_space
*mapping
,
283 struct page
*page
, int error
)
286 if (page_mapping(page
) == mapping
)
287 mapping_set_error(mapping
, error
);
291 /* Request for sync pageout. */
297 /* possible outcome of pageout() */
299 /* failed to write page out, page is locked */
301 /* move page to the active list, page is locked */
303 /* page has been sent to the disk successfully, page is unlocked */
305 /* page is clean and locked */
310 * pageout is called by shrink_page_list() for each dirty page.
311 * Calls ->writepage().
313 static pageout_t
pageout(struct page
*page
, struct address_space
*mapping
,
314 enum pageout_io sync_writeback
)
317 * If the page is dirty, only perform writeback if that write
318 * will be non-blocking. To prevent this allocation from being
319 * stalled by pagecache activity. But note that there may be
320 * stalls if we need to run get_block(). We could test
321 * PagePrivate for that.
323 * If this process is currently in generic_file_write() against
324 * this page's queue, we can perform writeback even if that
327 * If the page is swapcache, write it back even if that would
328 * block, for some throttling. This happens by accident, because
329 * swap_backing_dev_info is bust: it doesn't reflect the
330 * congestion state of the swapdevs. Easy to fix, if needed.
331 * See swapfile.c:page_queue_congested().
333 if (!is_page_cache_freeable(page
))
337 * Some data journaling orphaned pages can have
338 * page->mapping == NULL while being dirty with clean buffers.
340 if (PagePrivate(page
)) {
341 if (try_to_free_buffers(page
)) {
342 ClearPageDirty(page
);
343 printk("%s: orphaned page\n", __func__
);
349 if (mapping
->a_ops
->writepage
== NULL
)
350 return PAGE_ACTIVATE
;
351 if (!may_write_to_queue(mapping
->backing_dev_info
))
354 if (clear_page_dirty_for_io(page
)) {
356 struct writeback_control wbc
= {
357 .sync_mode
= WB_SYNC_NONE
,
358 .nr_to_write
= SWAP_CLUSTER_MAX
,
360 .range_end
= LLONG_MAX
,
365 SetPageReclaim(page
);
366 res
= mapping
->a_ops
->writepage(page
, &wbc
);
368 handle_write_error(mapping
, page
, res
);
369 if (res
== AOP_WRITEPAGE_ACTIVATE
) {
370 ClearPageReclaim(page
);
371 return PAGE_ACTIVATE
;
375 * Wait on writeback if requested to. This happens when
376 * direct reclaiming a large contiguous area and the
377 * first attempt to free a range of pages fails.
379 if (PageWriteback(page
) && sync_writeback
== PAGEOUT_IO_SYNC
)
380 wait_on_page_writeback(page
);
382 if (!PageWriteback(page
)) {
383 /* synchronous write or broken a_ops? */
384 ClearPageReclaim(page
);
386 inc_zone_page_state(page
, NR_VMSCAN_WRITE
);
394 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
395 * someone else has a ref on the page, abort and return 0. If it was
396 * successfully detached, return 1. Assumes the caller has a single ref on
399 int remove_mapping(struct address_space
*mapping
, struct page
*page
)
401 BUG_ON(!PageLocked(page
));
402 BUG_ON(mapping
!= page_mapping(page
));
404 write_lock_irq(&mapping
->tree_lock
);
406 * The non racy check for a busy page.
408 * Must be careful with the order of the tests. When someone has
409 * a ref to the page, it may be possible that they dirty it then
410 * drop the reference. So if PageDirty is tested before page_count
411 * here, then the following race may occur:
413 * get_user_pages(&page);
414 * [user mapping goes away]
416 * !PageDirty(page) [good]
417 * SetPageDirty(page);
419 * !page_count(page) [good, discard it]
421 * [oops, our write_to data is lost]
423 * Reversing the order of the tests ensures such a situation cannot
424 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
425 * load is not satisfied before that of page->_count.
427 * Note that if SetPageDirty is always performed via set_page_dirty,
428 * and thus under tree_lock, then this ordering is not required.
430 if (unlikely(page_count(page
) != 2))
433 if (unlikely(PageDirty(page
)))
436 if (PageSwapCache(page
)) {
437 swp_entry_t swap
= { .val
= page_private(page
) };
438 __delete_from_swap_cache(page
);
439 write_unlock_irq(&mapping
->tree_lock
);
441 __put_page(page
); /* The pagecache ref */
445 __remove_from_page_cache(page
);
446 write_unlock_irq(&mapping
->tree_lock
);
451 write_unlock_irq(&mapping
->tree_lock
);
456 * shrink_page_list() returns the number of reclaimed pages
458 static unsigned long shrink_page_list(struct list_head
*page_list
,
459 struct scan_control
*sc
,
460 enum pageout_io sync_writeback
)
462 LIST_HEAD(ret_pages
);
463 struct pagevec freed_pvec
;
465 unsigned long nr_reclaimed
= 0;
469 pagevec_init(&freed_pvec
, 1);
470 while (!list_empty(page_list
)) {
471 struct address_space
*mapping
;
478 page
= lru_to_page(page_list
);
479 list_del(&page
->lru
);
481 if (TestSetPageLocked(page
))
484 VM_BUG_ON(PageActive(page
));
488 if (!sc
->may_swap
&& page_mapped(page
))
491 /* Double the slab pressure for mapped and swapcache pages */
492 if (page_mapped(page
) || PageSwapCache(page
))
495 may_enter_fs
= (sc
->gfp_mask
& __GFP_FS
) ||
496 (PageSwapCache(page
) && (sc
->gfp_mask
& __GFP_IO
));
498 if (PageWriteback(page
)) {
500 * Synchronous reclaim is performed in two passes,
501 * first an asynchronous pass over the list to
502 * start parallel writeback, and a second synchronous
503 * pass to wait for the IO to complete. Wait here
504 * for any page for which writeback has already
507 if (sync_writeback
== PAGEOUT_IO_SYNC
&& may_enter_fs
)
508 wait_on_page_writeback(page
);
513 referenced
= page_referenced(page
, 1, sc
->mem_cgroup
);
514 /* In active use or really unfreeable? Activate it. */
515 if (sc
->order
<= PAGE_ALLOC_COSTLY_ORDER
&&
516 referenced
&& page_mapping_inuse(page
))
517 goto activate_locked
;
521 * Anonymous process memory has backing store?
522 * Try to allocate it some swap space here.
524 if (PageAnon(page
) && !PageSwapCache(page
))
525 if (!add_to_swap(page
, GFP_ATOMIC
))
526 goto activate_locked
;
527 #endif /* CONFIG_SWAP */
529 mapping
= page_mapping(page
);
532 * The page is mapped into the page tables of one or more
533 * processes. Try to unmap it here.
535 if (page_mapped(page
) && mapping
) {
536 switch (try_to_unmap(page
, 0)) {
538 goto activate_locked
;
542 ; /* try to free the page below */
546 if (PageDirty(page
)) {
547 if (sc
->order
<= PAGE_ALLOC_COSTLY_ORDER
&& referenced
)
551 if (!sc
->may_writepage
)
554 /* Page is dirty, try to write it out here */
555 switch (pageout(page
, mapping
, sync_writeback
)) {
559 goto activate_locked
;
561 if (PageWriteback(page
) || PageDirty(page
))
564 * A synchronous write - probably a ramdisk. Go
565 * ahead and try to reclaim the page.
567 if (TestSetPageLocked(page
))
569 if (PageDirty(page
) || PageWriteback(page
))
571 mapping
= page_mapping(page
);
573 ; /* try to free the page below */
578 * If the page has buffers, try to free the buffer mappings
579 * associated with this page. If we succeed we try to free
582 * We do this even if the page is PageDirty().
583 * try_to_release_page() does not perform I/O, but it is
584 * possible for a page to have PageDirty set, but it is actually
585 * clean (all its buffers are clean). This happens if the
586 * buffers were written out directly, with submit_bh(). ext3
587 * will do this, as well as the blockdev mapping.
588 * try_to_release_page() will discover that cleanness and will
589 * drop the buffers and mark the page clean - it can be freed.
591 * Rarely, pages can have buffers and no ->mapping. These are
592 * the pages which were not successfully invalidated in
593 * truncate_complete_page(). We try to drop those buffers here
594 * and if that worked, and the page is no longer mapped into
595 * process address space (page_count == 1) it can be freed.
596 * Otherwise, leave the page on the LRU so it is swappable.
598 if (PagePrivate(page
)) {
599 if (!try_to_release_page(page
, sc
->gfp_mask
))
600 goto activate_locked
;
601 if (!mapping
&& page_count(page
) == 1)
605 if (!mapping
|| !remove_mapping(mapping
, page
))
611 if (!pagevec_add(&freed_pvec
, page
))
612 __pagevec_release_nonlru(&freed_pvec
);
621 list_add(&page
->lru
, &ret_pages
);
622 VM_BUG_ON(PageLRU(page
));
624 list_splice(&ret_pages
, page_list
);
625 if (pagevec_count(&freed_pvec
))
626 __pagevec_release_nonlru(&freed_pvec
);
627 count_vm_events(PGACTIVATE
, pgactivate
);
631 /* LRU Isolation modes. */
632 #define ISOLATE_INACTIVE 0 /* Isolate inactive pages. */
633 #define ISOLATE_ACTIVE 1 /* Isolate active pages. */
634 #define ISOLATE_BOTH 2 /* Isolate both active and inactive pages. */
637 * Attempt to remove the specified page from its LRU. Only take this page
638 * if it is of the appropriate PageActive status. Pages which are being
639 * freed elsewhere are also ignored.
641 * page: page to consider
642 * mode: one of the LRU isolation modes defined above
644 * returns 0 on success, -ve errno on failure.
646 int __isolate_lru_page(struct page
*page
, int mode
)
650 /* Only take pages on the LRU. */
655 * When checking the active state, we need to be sure we are
656 * dealing with comparible boolean values. Take the logical not
659 if (mode
!= ISOLATE_BOTH
&& (!PageActive(page
) != !mode
))
663 if (likely(get_page_unless_zero(page
))) {
665 * Be careful not to clear PageLRU until after we're
666 * sure the page is not being freed elsewhere -- the
667 * page release code relies on it.
677 * zone->lru_lock is heavily contended. Some of the functions that
678 * shrink the lists perform better by taking out a batch of pages
679 * and working on them outside the LRU lock.
681 * For pagecache intensive workloads, this function is the hottest
682 * spot in the kernel (apart from copy_*_user functions).
684 * Appropriate locks must be held before calling this function.
686 * @nr_to_scan: The number of pages to look through on the list.
687 * @src: The LRU list to pull pages off.
688 * @dst: The temp list to put pages on to.
689 * @scanned: The number of pages that were scanned.
690 * @order: The caller's attempted allocation order
691 * @mode: One of the LRU isolation modes
693 * returns how many pages were moved onto *@dst.
695 static unsigned long isolate_lru_pages(unsigned long nr_to_scan
,
696 struct list_head
*src
, struct list_head
*dst
,
697 unsigned long *scanned
, int order
, int mode
)
699 unsigned long nr_taken
= 0;
702 for (scan
= 0; scan
< nr_to_scan
&& !list_empty(src
); scan
++) {
705 unsigned long end_pfn
;
706 unsigned long page_pfn
;
709 page
= lru_to_page(src
);
710 prefetchw_prev_lru_page(page
, src
, flags
);
712 VM_BUG_ON(!PageLRU(page
));
714 switch (__isolate_lru_page(page
, mode
)) {
716 list_move(&page
->lru
, dst
);
721 /* else it is being freed elsewhere */
722 list_move(&page
->lru
, src
);
733 * Attempt to take all pages in the order aligned region
734 * surrounding the tag page. Only take those pages of
735 * the same active state as that tag page. We may safely
736 * round the target page pfn down to the requested order
737 * as the mem_map is guarenteed valid out to MAX_ORDER,
738 * where that page is in a different zone we will detect
739 * it from its zone id and abort this block scan.
741 zone_id
= page_zone_id(page
);
742 page_pfn
= page_to_pfn(page
);
743 pfn
= page_pfn
& ~((1 << order
) - 1);
744 end_pfn
= pfn
+ (1 << order
);
745 for (; pfn
< end_pfn
; pfn
++) {
746 struct page
*cursor_page
;
748 /* The target page is in the block, ignore it. */
749 if (unlikely(pfn
== page_pfn
))
752 /* Avoid holes within the zone. */
753 if (unlikely(!pfn_valid_within(pfn
)))
756 cursor_page
= pfn_to_page(pfn
);
757 /* Check that we have not crossed a zone boundary. */
758 if (unlikely(page_zone_id(cursor_page
) != zone_id
))
760 switch (__isolate_lru_page(cursor_page
, mode
)) {
762 list_move(&cursor_page
->lru
, dst
);
768 /* else it is being freed elsewhere */
769 list_move(&cursor_page
->lru
, src
);
780 static unsigned long isolate_pages_global(unsigned long nr
,
781 struct list_head
*dst
,
782 unsigned long *scanned
, int order
,
783 int mode
, struct zone
*z
,
784 struct mem_cgroup
*mem_cont
,
788 return isolate_lru_pages(nr
, &z
->active_list
, dst
,
789 scanned
, order
, mode
);
791 return isolate_lru_pages(nr
, &z
->inactive_list
, dst
,
792 scanned
, order
, mode
);
796 * clear_active_flags() is a helper for shrink_active_list(), clearing
797 * any active bits from the pages in the list.
799 static unsigned long clear_active_flags(struct list_head
*page_list
)
804 list_for_each_entry(page
, page_list
, lru
)
805 if (PageActive(page
)) {
806 ClearPageActive(page
);
814 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
817 static unsigned long shrink_inactive_list(unsigned long max_scan
,
818 struct zone
*zone
, struct scan_control
*sc
)
820 LIST_HEAD(page_list
);
822 unsigned long nr_scanned
= 0;
823 unsigned long nr_reclaimed
= 0;
825 pagevec_init(&pvec
, 1);
828 spin_lock_irq(&zone
->lru_lock
);
831 unsigned long nr_taken
;
832 unsigned long nr_scan
;
833 unsigned long nr_freed
;
834 unsigned long nr_active
;
836 nr_taken
= sc
->isolate_pages(sc
->swap_cluster_max
,
837 &page_list
, &nr_scan
, sc
->order
,
838 (sc
->order
> PAGE_ALLOC_COSTLY_ORDER
)?
839 ISOLATE_BOTH
: ISOLATE_INACTIVE
,
840 zone
, sc
->mem_cgroup
, 0);
841 nr_active
= clear_active_flags(&page_list
);
842 __count_vm_events(PGDEACTIVATE
, nr_active
);
844 __mod_zone_page_state(zone
, NR_ACTIVE
, -nr_active
);
845 __mod_zone_page_state(zone
, NR_INACTIVE
,
846 -(nr_taken
- nr_active
));
847 if (scan_global_lru(sc
))
848 zone
->pages_scanned
+= nr_scan
;
849 spin_unlock_irq(&zone
->lru_lock
);
851 nr_scanned
+= nr_scan
;
852 nr_freed
= shrink_page_list(&page_list
, sc
, PAGEOUT_IO_ASYNC
);
855 * If we are direct reclaiming for contiguous pages and we do
856 * not reclaim everything in the list, try again and wait
857 * for IO to complete. This will stall high-order allocations
858 * but that should be acceptable to the caller
860 if (nr_freed
< nr_taken
&& !current_is_kswapd() &&
861 sc
->order
> PAGE_ALLOC_COSTLY_ORDER
) {
862 congestion_wait(WRITE
, HZ
/10);
865 * The attempt at page out may have made some
866 * of the pages active, mark them inactive again.
868 nr_active
= clear_active_flags(&page_list
);
869 count_vm_events(PGDEACTIVATE
, nr_active
);
871 nr_freed
+= shrink_page_list(&page_list
, sc
,
875 nr_reclaimed
+= nr_freed
;
877 if (current_is_kswapd()) {
878 __count_zone_vm_events(PGSCAN_KSWAPD
, zone
, nr_scan
);
879 __count_vm_events(KSWAPD_STEAL
, nr_freed
);
880 } else if (scan_global_lru(sc
))
881 __count_zone_vm_events(PGSCAN_DIRECT
, zone
, nr_scan
);
883 __count_zone_vm_events(PGSTEAL
, zone
, nr_freed
);
888 spin_lock(&zone
->lru_lock
);
890 * Put back any unfreeable pages.
892 while (!list_empty(&page_list
)) {
893 page
= lru_to_page(&page_list
);
894 VM_BUG_ON(PageLRU(page
));
896 list_del(&page
->lru
);
897 if (PageActive(page
))
898 add_page_to_active_list(zone
, page
);
900 add_page_to_inactive_list(zone
, page
);
901 if (!pagevec_add(&pvec
, page
)) {
902 spin_unlock_irq(&zone
->lru_lock
);
903 __pagevec_release(&pvec
);
904 spin_lock_irq(&zone
->lru_lock
);
907 } while (nr_scanned
< max_scan
);
908 spin_unlock(&zone
->lru_lock
);
911 pagevec_release(&pvec
);
916 * We are about to scan this zone at a certain priority level. If that priority
917 * level is smaller (ie: more urgent) than the previous priority, then note
918 * that priority level within the zone. This is done so that when the next
919 * process comes in to scan this zone, it will immediately start out at this
920 * priority level rather than having to build up its own scanning priority.
921 * Here, this priority affects only the reclaim-mapped threshold.
923 static inline void note_zone_scanning_priority(struct zone
*zone
, int priority
)
925 if (priority
< zone
->prev_priority
)
926 zone
->prev_priority
= priority
;
929 static inline int zone_is_near_oom(struct zone
*zone
)
931 return zone
->pages_scanned
>= (zone_page_state(zone
, NR_ACTIVE
)
932 + zone_page_state(zone
, NR_INACTIVE
))*3;
936 * Determine we should try to reclaim mapped pages.
937 * This is called only when sc->mem_cgroup is NULL.
939 static int calc_reclaim_mapped(struct scan_control
*sc
, struct zone
*zone
,
946 int reclaim_mapped
= 0;
949 if (scan_global_lru(sc
) && zone_is_near_oom(zone
))
952 * `distress' is a measure of how much trouble we're having
953 * reclaiming pages. 0 -> no problems. 100 -> great trouble.
955 if (scan_global_lru(sc
))
956 prev_priority
= zone
->prev_priority
;
958 prev_priority
= mem_cgroup_get_reclaim_priority(sc
->mem_cgroup
);
960 distress
= 100 >> min(prev_priority
, priority
);
963 * The point of this algorithm is to decide when to start
964 * reclaiming mapped memory instead of just pagecache. Work out
968 if (scan_global_lru(sc
))
969 mapped_ratio
= ((global_page_state(NR_FILE_MAPPED
) +
970 global_page_state(NR_ANON_PAGES
)) * 100) /
973 mapped_ratio
= mem_cgroup_calc_mapped_ratio(sc
->mem_cgroup
);
976 * Now decide how much we really want to unmap some pages. The
977 * mapped ratio is downgraded - just because there's a lot of
978 * mapped memory doesn't necessarily mean that page reclaim
981 * The distress ratio is important - we don't want to start
984 * A 100% value of vm_swappiness overrides this algorithm
987 swap_tendency
= mapped_ratio
/ 2 + distress
+ sc
->swappiness
;
990 * If there's huge imbalance between active and inactive
991 * (think active 100 times larger than inactive) we should
992 * become more permissive, or the system will take too much
993 * cpu before it start swapping during memory pressure.
994 * Distress is about avoiding early-oom, this is about
995 * making swappiness graceful despite setting it to low
998 * Avoid div by zero with nr_inactive+1, and max resulting
999 * value is vm_total_pages.
1001 if (scan_global_lru(sc
)) {
1002 imbalance
= zone_page_state(zone
, NR_ACTIVE
);
1003 imbalance
/= zone_page_state(zone
, NR_INACTIVE
) + 1;
1005 imbalance
= mem_cgroup_reclaim_imbalance(sc
->mem_cgroup
);
1008 * Reduce the effect of imbalance if swappiness is low,
1009 * this means for a swappiness very low, the imbalance
1010 * must be much higher than 100 for this logic to make
1013 * Max temporary value is vm_total_pages*100.
1015 imbalance
*= (vm_swappiness
+ 1);
1019 * If not much of the ram is mapped, makes the imbalance
1020 * less relevant, it's high priority we refill the inactive
1021 * list with mapped pages only in presence of high ratio of
1024 * Max temporary value is vm_total_pages*100.
1026 imbalance
*= mapped_ratio
;
1029 /* apply imbalance feedback to swap_tendency */
1030 swap_tendency
+= imbalance
;
1033 * Now use this metric to decide whether to start moving mapped
1034 * memory onto the inactive list.
1036 if (swap_tendency
>= 100)
1039 return reclaim_mapped
;
1043 * This moves pages from the active list to the inactive list.
1045 * We move them the other way if the page is referenced by one or more
1046 * processes, from rmap.
1048 * If the pages are mostly unmapped, the processing is fast and it is
1049 * appropriate to hold zone->lru_lock across the whole operation. But if
1050 * the pages are mapped, the processing is slow (page_referenced()) so we
1051 * should drop zone->lru_lock around each page. It's impossible to balance
1052 * this, so instead we remove the pages from the LRU while processing them.
1053 * It is safe to rely on PG_active against the non-LRU pages in here because
1054 * nobody will play with that bit on a non-LRU page.
1056 * The downside is that we have to touch page->_count against each page.
1057 * But we had to alter page->flags anyway.
1061 static void shrink_active_list(unsigned long nr_pages
, struct zone
*zone
,
1062 struct scan_control
*sc
, int priority
)
1064 unsigned long pgmoved
;
1065 int pgdeactivate
= 0;
1066 unsigned long pgscanned
;
1067 LIST_HEAD(l_hold
); /* The pages which were snipped off */
1068 LIST_HEAD(l_inactive
); /* Pages to go onto the inactive_list */
1069 LIST_HEAD(l_active
); /* Pages to go onto the active_list */
1071 struct pagevec pvec
;
1072 int reclaim_mapped
= 0;
1075 reclaim_mapped
= calc_reclaim_mapped(sc
, zone
, priority
);
1078 spin_lock_irq(&zone
->lru_lock
);
1079 pgmoved
= sc
->isolate_pages(nr_pages
, &l_hold
, &pgscanned
, sc
->order
,
1080 ISOLATE_ACTIVE
, zone
,
1083 * zone->pages_scanned is used for detect zone's oom
1084 * mem_cgroup remembers nr_scan by itself.
1086 if (scan_global_lru(sc
))
1087 zone
->pages_scanned
+= pgscanned
;
1089 __mod_zone_page_state(zone
, NR_ACTIVE
, -pgmoved
);
1090 spin_unlock_irq(&zone
->lru_lock
);
1092 while (!list_empty(&l_hold
)) {
1094 page
= lru_to_page(&l_hold
);
1095 list_del(&page
->lru
);
1096 if (page_mapped(page
)) {
1097 if (!reclaim_mapped
||
1098 (total_swap_pages
== 0 && PageAnon(page
)) ||
1099 page_referenced(page
, 0, sc
->mem_cgroup
)) {
1100 list_add(&page
->lru
, &l_active
);
1104 list_add(&page
->lru
, &l_inactive
);
1107 pagevec_init(&pvec
, 1);
1109 spin_lock_irq(&zone
->lru_lock
);
1110 while (!list_empty(&l_inactive
)) {
1111 page
= lru_to_page(&l_inactive
);
1112 prefetchw_prev_lru_page(page
, &l_inactive
, flags
);
1113 VM_BUG_ON(PageLRU(page
));
1115 VM_BUG_ON(!PageActive(page
));
1116 ClearPageActive(page
);
1118 list_move(&page
->lru
, &zone
->inactive_list
);
1119 mem_cgroup_move_lists(page
, false);
1121 if (!pagevec_add(&pvec
, page
)) {
1122 __mod_zone_page_state(zone
, NR_INACTIVE
, pgmoved
);
1123 spin_unlock_irq(&zone
->lru_lock
);
1124 pgdeactivate
+= pgmoved
;
1126 if (buffer_heads_over_limit
)
1127 pagevec_strip(&pvec
);
1128 __pagevec_release(&pvec
);
1129 spin_lock_irq(&zone
->lru_lock
);
1132 __mod_zone_page_state(zone
, NR_INACTIVE
, pgmoved
);
1133 pgdeactivate
+= pgmoved
;
1134 if (buffer_heads_over_limit
) {
1135 spin_unlock_irq(&zone
->lru_lock
);
1136 pagevec_strip(&pvec
);
1137 spin_lock_irq(&zone
->lru_lock
);
1141 while (!list_empty(&l_active
)) {
1142 page
= lru_to_page(&l_active
);
1143 prefetchw_prev_lru_page(page
, &l_active
, flags
);
1144 VM_BUG_ON(PageLRU(page
));
1146 VM_BUG_ON(!PageActive(page
));
1148 list_move(&page
->lru
, &zone
->active_list
);
1149 mem_cgroup_move_lists(page
, true);
1151 if (!pagevec_add(&pvec
, page
)) {
1152 __mod_zone_page_state(zone
, NR_ACTIVE
, pgmoved
);
1154 spin_unlock_irq(&zone
->lru_lock
);
1155 __pagevec_release(&pvec
);
1156 spin_lock_irq(&zone
->lru_lock
);
1159 __mod_zone_page_state(zone
, NR_ACTIVE
, pgmoved
);
1161 __count_zone_vm_events(PGREFILL
, zone
, pgscanned
);
1162 __count_vm_events(PGDEACTIVATE
, pgdeactivate
);
1163 spin_unlock_irq(&zone
->lru_lock
);
1165 pagevec_release(&pvec
);
1169 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1171 static unsigned long shrink_zone(int priority
, struct zone
*zone
,
1172 struct scan_control
*sc
)
1174 unsigned long nr_active
;
1175 unsigned long nr_inactive
;
1176 unsigned long nr_to_scan
;
1177 unsigned long nr_reclaimed
= 0;
1179 if (scan_global_lru(sc
)) {
1181 * Add one to nr_to_scan just to make sure that the kernel
1182 * will slowly sift through the active list.
1184 zone
->nr_scan_active
+=
1185 (zone_page_state(zone
, NR_ACTIVE
) >> priority
) + 1;
1186 nr_active
= zone
->nr_scan_active
;
1187 zone
->nr_scan_inactive
+=
1188 (zone_page_state(zone
, NR_INACTIVE
) >> priority
) + 1;
1189 nr_inactive
= zone
->nr_scan_inactive
;
1190 if (nr_inactive
>= sc
->swap_cluster_max
)
1191 zone
->nr_scan_inactive
= 0;
1195 if (nr_active
>= sc
->swap_cluster_max
)
1196 zone
->nr_scan_active
= 0;
1201 * This reclaim occurs not because zone memory shortage but
1202 * because memory controller hits its limit.
1203 * Then, don't modify zone reclaim related data.
1205 nr_active
= mem_cgroup_calc_reclaim_active(sc
->mem_cgroup
,
1208 nr_inactive
= mem_cgroup_calc_reclaim_inactive(sc
->mem_cgroup
,
1213 while (nr_active
|| nr_inactive
) {
1215 nr_to_scan
= min(nr_active
,
1216 (unsigned long)sc
->swap_cluster_max
);
1217 nr_active
-= nr_to_scan
;
1218 shrink_active_list(nr_to_scan
, zone
, sc
, priority
);
1222 nr_to_scan
= min(nr_inactive
,
1223 (unsigned long)sc
->swap_cluster_max
);
1224 nr_inactive
-= nr_to_scan
;
1225 nr_reclaimed
+= shrink_inactive_list(nr_to_scan
, zone
,
1230 throttle_vm_writeout(sc
->gfp_mask
);
1231 return nr_reclaimed
;
1235 * This is the direct reclaim path, for page-allocating processes. We only
1236 * try to reclaim pages from zones which will satisfy the caller's allocation
1239 * We reclaim from a zone even if that zone is over pages_high. Because:
1240 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1242 * b) The zones may be over pages_high but they must go *over* pages_high to
1243 * satisfy the `incremental min' zone defense algorithm.
1245 * Returns the number of reclaimed pages.
1247 * If a zone is deemed to be full of pinned pages then just give it a light
1248 * scan then give up on it.
1250 static unsigned long shrink_zones(int priority
, struct zonelist
*zonelist
,
1251 struct scan_control
*sc
)
1253 enum zone_type high_zoneidx
= gfp_zone(sc
->gfp_mask
);
1254 unsigned long nr_reclaimed
= 0;
1258 sc
->all_unreclaimable
= 1;
1259 for_each_zone_zonelist(zone
, z
, zonelist
, high_zoneidx
) {
1260 if (!populated_zone(zone
))
1263 * Take care memory controller reclaiming has small influence
1266 if (scan_global_lru(sc
)) {
1267 if (!cpuset_zone_allowed_hardwall(zone
, GFP_KERNEL
))
1269 note_zone_scanning_priority(zone
, priority
);
1271 if (zone_is_all_unreclaimable(zone
) &&
1272 priority
!= DEF_PRIORITY
)
1273 continue; /* Let kswapd poll it */
1274 sc
->all_unreclaimable
= 0;
1277 * Ignore cpuset limitation here. We just want to reduce
1278 * # of used pages by us regardless of memory shortage.
1280 sc
->all_unreclaimable
= 0;
1281 mem_cgroup_note_reclaim_priority(sc
->mem_cgroup
,
1285 nr_reclaimed
+= shrink_zone(priority
, zone
, sc
);
1288 return nr_reclaimed
;
1292 * This is the main entry point to direct page reclaim.
1294 * If a full scan of the inactive list fails to free enough memory then we
1295 * are "out of memory" and something needs to be killed.
1297 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1298 * high - the zone may be full of dirty or under-writeback pages, which this
1299 * caller can't do much about. We kick pdflush and take explicit naps in the
1300 * hope that some of these pages can be written. But if the allocating task
1301 * holds filesystem locks which prevent writeout this might not work, and the
1302 * allocation attempt will fail.
1304 * returns: 0, if no pages reclaimed
1305 * else, the number of pages reclaimed
1307 static unsigned long do_try_to_free_pages(struct zonelist
*zonelist
,
1308 struct scan_control
*sc
)
1311 unsigned long ret
= 0;
1312 unsigned long total_scanned
= 0;
1313 unsigned long nr_reclaimed
= 0;
1314 struct reclaim_state
*reclaim_state
= current
->reclaim_state
;
1315 unsigned long lru_pages
= 0;
1318 enum zone_type high_zoneidx
= gfp_zone(sc
->gfp_mask
);
1320 delayacct_freepages_start();
1322 if (scan_global_lru(sc
))
1323 count_vm_event(ALLOCSTALL
);
1325 * mem_cgroup will not do shrink_slab.
1327 if (scan_global_lru(sc
)) {
1328 for_each_zone_zonelist(zone
, z
, zonelist
, high_zoneidx
) {
1330 if (!cpuset_zone_allowed_hardwall(zone
, GFP_KERNEL
))
1333 lru_pages
+= zone_page_state(zone
, NR_ACTIVE
)
1334 + zone_page_state(zone
, NR_INACTIVE
);
1338 for (priority
= DEF_PRIORITY
; priority
>= 0; priority
--) {
1341 disable_swap_token();
1342 nr_reclaimed
+= shrink_zones(priority
, zonelist
, sc
);
1344 * Don't shrink slabs when reclaiming memory from
1345 * over limit cgroups
1347 if (scan_global_lru(sc
)) {
1348 shrink_slab(sc
->nr_scanned
, sc
->gfp_mask
, lru_pages
);
1349 if (reclaim_state
) {
1350 nr_reclaimed
+= reclaim_state
->reclaimed_slab
;
1351 reclaim_state
->reclaimed_slab
= 0;
1354 total_scanned
+= sc
->nr_scanned
;
1355 if (nr_reclaimed
>= sc
->swap_cluster_max
) {
1361 * Try to write back as many pages as we just scanned. This
1362 * tends to cause slow streaming writers to write data to the
1363 * disk smoothly, at the dirtying rate, which is nice. But
1364 * that's undesirable in laptop mode, where we *want* lumpy
1365 * writeout. So in laptop mode, write out the whole world.
1367 if (total_scanned
> sc
->swap_cluster_max
+
1368 sc
->swap_cluster_max
/ 2) {
1369 wakeup_pdflush(laptop_mode
? 0 : total_scanned
);
1370 sc
->may_writepage
= 1;
1373 /* Take a nap, wait for some writeback to complete */
1374 if (sc
->nr_scanned
&& priority
< DEF_PRIORITY
- 2)
1375 congestion_wait(WRITE
, HZ
/10);
1377 /* top priority shrink_caches still had more to do? don't OOM, then */
1378 if (!sc
->all_unreclaimable
&& scan_global_lru(sc
))
1382 * Now that we've scanned all the zones at this priority level, note
1383 * that level within the zone so that the next thread which performs
1384 * scanning of this zone will immediately start out at this priority
1385 * level. This affects only the decision whether or not to bring
1386 * mapped pages onto the inactive list.
1391 if (scan_global_lru(sc
)) {
1392 for_each_zone_zonelist(zone
, z
, zonelist
, high_zoneidx
) {
1394 if (!cpuset_zone_allowed_hardwall(zone
, GFP_KERNEL
))
1397 zone
->prev_priority
= priority
;
1400 mem_cgroup_record_reclaim_priority(sc
->mem_cgroup
, priority
);
1402 delayacct_freepages_end();
1407 unsigned long try_to_free_pages(struct zonelist
*zonelist
, int order
,
1410 struct scan_control sc
= {
1411 .gfp_mask
= gfp_mask
,
1412 .may_writepage
= !laptop_mode
,
1413 .swap_cluster_max
= SWAP_CLUSTER_MAX
,
1415 .swappiness
= vm_swappiness
,
1418 .isolate_pages
= isolate_pages_global
,
1421 return do_try_to_free_pages(zonelist
, &sc
);
1424 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1426 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup
*mem_cont
,
1429 struct scan_control sc
= {
1430 .may_writepage
= !laptop_mode
,
1432 .swap_cluster_max
= SWAP_CLUSTER_MAX
,
1433 .swappiness
= vm_swappiness
,
1435 .mem_cgroup
= mem_cont
,
1436 .isolate_pages
= mem_cgroup_isolate_pages
,
1438 struct zonelist
*zonelist
;
1440 sc
.gfp_mask
= (gfp_mask
& GFP_RECLAIM_MASK
) |
1441 (GFP_HIGHUSER_MOVABLE
& ~GFP_RECLAIM_MASK
);
1442 zonelist
= NODE_DATA(numa_node_id())->node_zonelists
;
1443 return do_try_to_free_pages(zonelist
, &sc
);
1448 * For kswapd, balance_pgdat() will work across all this node's zones until
1449 * they are all at pages_high.
1451 * Returns the number of pages which were actually freed.
1453 * There is special handling here for zones which are full of pinned pages.
1454 * This can happen if the pages are all mlocked, or if they are all used by
1455 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
1456 * What we do is to detect the case where all pages in the zone have been
1457 * scanned twice and there has been zero successful reclaim. Mark the zone as
1458 * dead and from now on, only perform a short scan. Basically we're polling
1459 * the zone for when the problem goes away.
1461 * kswapd scans the zones in the highmem->normal->dma direction. It skips
1462 * zones which have free_pages > pages_high, but once a zone is found to have
1463 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1464 * of the number of free pages in the lower zones. This interoperates with
1465 * the page allocator fallback scheme to ensure that aging of pages is balanced
1468 static unsigned long balance_pgdat(pg_data_t
*pgdat
, int order
)
1473 unsigned long total_scanned
;
1474 unsigned long nr_reclaimed
;
1475 struct reclaim_state
*reclaim_state
= current
->reclaim_state
;
1476 struct scan_control sc
= {
1477 .gfp_mask
= GFP_KERNEL
,
1479 .swap_cluster_max
= SWAP_CLUSTER_MAX
,
1480 .swappiness
= vm_swappiness
,
1483 .isolate_pages
= isolate_pages_global
,
1486 * temp_priority is used to remember the scanning priority at which
1487 * this zone was successfully refilled to free_pages == pages_high.
1489 int temp_priority
[MAX_NR_ZONES
];
1494 sc
.may_writepage
= !laptop_mode
;
1495 count_vm_event(PAGEOUTRUN
);
1497 for (i
= 0; i
< pgdat
->nr_zones
; i
++)
1498 temp_priority
[i
] = DEF_PRIORITY
;
1500 for (priority
= DEF_PRIORITY
; priority
>= 0; priority
--) {
1501 int end_zone
= 0; /* Inclusive. 0 = ZONE_DMA */
1502 unsigned long lru_pages
= 0;
1504 /* The swap token gets in the way of swapout... */
1506 disable_swap_token();
1511 * Scan in the highmem->dma direction for the highest
1512 * zone which needs scanning
1514 for (i
= pgdat
->nr_zones
- 1; i
>= 0; i
--) {
1515 struct zone
*zone
= pgdat
->node_zones
+ i
;
1517 if (!populated_zone(zone
))
1520 if (zone_is_all_unreclaimable(zone
) &&
1521 priority
!= DEF_PRIORITY
)
1524 if (!zone_watermark_ok(zone
, order
, zone
->pages_high
,
1533 for (i
= 0; i
<= end_zone
; i
++) {
1534 struct zone
*zone
= pgdat
->node_zones
+ i
;
1536 lru_pages
+= zone_page_state(zone
, NR_ACTIVE
)
1537 + zone_page_state(zone
, NR_INACTIVE
);
1541 * Now scan the zone in the dma->highmem direction, stopping
1542 * at the last zone which needs scanning.
1544 * We do this because the page allocator works in the opposite
1545 * direction. This prevents the page allocator from allocating
1546 * pages behind kswapd's direction of progress, which would
1547 * cause too much scanning of the lower zones.
1549 for (i
= 0; i
<= end_zone
; i
++) {
1550 struct zone
*zone
= pgdat
->node_zones
+ i
;
1553 if (!populated_zone(zone
))
1556 if (zone_is_all_unreclaimable(zone
) &&
1557 priority
!= DEF_PRIORITY
)
1560 if (!zone_watermark_ok(zone
, order
, zone
->pages_high
,
1563 temp_priority
[i
] = priority
;
1565 note_zone_scanning_priority(zone
, priority
);
1567 * We put equal pressure on every zone, unless one
1568 * zone has way too many pages free already.
1570 if (!zone_watermark_ok(zone
, order
, 8*zone
->pages_high
,
1572 nr_reclaimed
+= shrink_zone(priority
, zone
, &sc
);
1573 reclaim_state
->reclaimed_slab
= 0;
1574 nr_slab
= shrink_slab(sc
.nr_scanned
, GFP_KERNEL
,
1576 nr_reclaimed
+= reclaim_state
->reclaimed_slab
;
1577 total_scanned
+= sc
.nr_scanned
;
1578 if (zone_is_all_unreclaimable(zone
))
1580 if (nr_slab
== 0 && zone
->pages_scanned
>=
1581 (zone_page_state(zone
, NR_ACTIVE
)
1582 + zone_page_state(zone
, NR_INACTIVE
)) * 6)
1584 ZONE_ALL_UNRECLAIMABLE
);
1586 * If we've done a decent amount of scanning and
1587 * the reclaim ratio is low, start doing writepage
1588 * even in laptop mode
1590 if (total_scanned
> SWAP_CLUSTER_MAX
* 2 &&
1591 total_scanned
> nr_reclaimed
+ nr_reclaimed
/ 2)
1592 sc
.may_writepage
= 1;
1595 break; /* kswapd: all done */
1597 * OK, kswapd is getting into trouble. Take a nap, then take
1598 * another pass across the zones.
1600 if (total_scanned
&& priority
< DEF_PRIORITY
- 2)
1601 congestion_wait(WRITE
, HZ
/10);
1604 * We do this so kswapd doesn't build up large priorities for
1605 * example when it is freeing in parallel with allocators. It
1606 * matches the direct reclaim path behaviour in terms of impact
1607 * on zone->*_priority.
1609 if (nr_reclaimed
>= SWAP_CLUSTER_MAX
)
1614 * Note within each zone the priority level at which this zone was
1615 * brought into a happy state. So that the next thread which scans this
1616 * zone will start out at that priority level.
1618 for (i
= 0; i
< pgdat
->nr_zones
; i
++) {
1619 struct zone
*zone
= pgdat
->node_zones
+ i
;
1621 zone
->prev_priority
= temp_priority
[i
];
1623 if (!all_zones_ok
) {
1631 return nr_reclaimed
;
1635 * The background pageout daemon, started as a kernel thread
1636 * from the init process.
1638 * This basically trickles out pages so that we have _some_
1639 * free memory available even if there is no other activity
1640 * that frees anything up. This is needed for things like routing
1641 * etc, where we otherwise might have all activity going on in
1642 * asynchronous contexts that cannot page things out.
1644 * If there are applications that are active memory-allocators
1645 * (most normal use), this basically shouldn't matter.
1647 static int kswapd(void *p
)
1649 unsigned long order
;
1650 pg_data_t
*pgdat
= (pg_data_t
*)p
;
1651 struct task_struct
*tsk
= current
;
1653 struct reclaim_state reclaim_state
= {
1654 .reclaimed_slab
= 0,
1656 node_to_cpumask_ptr(cpumask
, pgdat
->node_id
);
1658 if (!cpus_empty(*cpumask
))
1659 set_cpus_allowed_ptr(tsk
, cpumask
);
1660 current
->reclaim_state
= &reclaim_state
;
1663 * Tell the memory management that we're a "memory allocator",
1664 * and that if we need more memory we should get access to it
1665 * regardless (see "__alloc_pages()"). "kswapd" should
1666 * never get caught in the normal page freeing logic.
1668 * (Kswapd normally doesn't need memory anyway, but sometimes
1669 * you need a small amount of memory in order to be able to
1670 * page out something else, and this flag essentially protects
1671 * us from recursively trying to free more memory as we're
1672 * trying to free the first piece of memory in the first place).
1674 tsk
->flags
|= PF_MEMALLOC
| PF_SWAPWRITE
| PF_KSWAPD
;
1679 unsigned long new_order
;
1681 prepare_to_wait(&pgdat
->kswapd_wait
, &wait
, TASK_INTERRUPTIBLE
);
1682 new_order
= pgdat
->kswapd_max_order
;
1683 pgdat
->kswapd_max_order
= 0;
1684 if (order
< new_order
) {
1686 * Don't sleep if someone wants a larger 'order'
1691 if (!freezing(current
))
1694 order
= pgdat
->kswapd_max_order
;
1696 finish_wait(&pgdat
->kswapd_wait
, &wait
);
1698 if (!try_to_freeze()) {
1699 /* We can speed up thawing tasks if we don't call
1700 * balance_pgdat after returning from the refrigerator
1702 balance_pgdat(pgdat
, order
);
1709 * A zone is low on free memory, so wake its kswapd task to service it.
1711 void wakeup_kswapd(struct zone
*zone
, int order
)
1715 if (!populated_zone(zone
))
1718 pgdat
= zone
->zone_pgdat
;
1719 if (zone_watermark_ok(zone
, order
, zone
->pages_low
, 0, 0))
1721 if (pgdat
->kswapd_max_order
< order
)
1722 pgdat
->kswapd_max_order
= order
;
1723 if (!cpuset_zone_allowed_hardwall(zone
, GFP_KERNEL
))
1725 if (!waitqueue_active(&pgdat
->kswapd_wait
))
1727 wake_up_interruptible(&pgdat
->kswapd_wait
);
1732 * Helper function for shrink_all_memory(). Tries to reclaim 'nr_pages' pages
1733 * from LRU lists system-wide, for given pass and priority, and returns the
1734 * number of reclaimed pages
1736 * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1738 static unsigned long shrink_all_zones(unsigned long nr_pages
, int prio
,
1739 int pass
, struct scan_control
*sc
)
1742 unsigned long nr_to_scan
, ret
= 0;
1744 for_each_zone(zone
) {
1746 if (!populated_zone(zone
))
1749 if (zone_is_all_unreclaimable(zone
) && prio
!= DEF_PRIORITY
)
1752 /* For pass = 0 we don't shrink the active list */
1754 zone
->nr_scan_active
+=
1755 (zone_page_state(zone
, NR_ACTIVE
) >> prio
) + 1;
1756 if (zone
->nr_scan_active
>= nr_pages
|| pass
> 3) {
1757 zone
->nr_scan_active
= 0;
1758 nr_to_scan
= min(nr_pages
,
1759 zone_page_state(zone
, NR_ACTIVE
));
1760 shrink_active_list(nr_to_scan
, zone
, sc
, prio
);
1764 zone
->nr_scan_inactive
+=
1765 (zone_page_state(zone
, NR_INACTIVE
) >> prio
) + 1;
1766 if (zone
->nr_scan_inactive
>= nr_pages
|| pass
> 3) {
1767 zone
->nr_scan_inactive
= 0;
1768 nr_to_scan
= min(nr_pages
,
1769 zone_page_state(zone
, NR_INACTIVE
));
1770 ret
+= shrink_inactive_list(nr_to_scan
, zone
, sc
);
1771 if (ret
>= nr_pages
)
1779 static unsigned long count_lru_pages(void)
1781 return global_page_state(NR_ACTIVE
) + global_page_state(NR_INACTIVE
);
1785 * Try to free `nr_pages' of memory, system-wide, and return the number of
1788 * Rather than trying to age LRUs the aim is to preserve the overall
1789 * LRU order by reclaiming preferentially
1790 * inactive > active > active referenced > active mapped
1792 unsigned long shrink_all_memory(unsigned long nr_pages
)
1794 unsigned long lru_pages
, nr_slab
;
1795 unsigned long ret
= 0;
1797 struct reclaim_state reclaim_state
;
1798 struct scan_control sc
= {
1799 .gfp_mask
= GFP_KERNEL
,
1801 .swap_cluster_max
= nr_pages
,
1803 .swappiness
= vm_swappiness
,
1804 .isolate_pages
= isolate_pages_global
,
1807 current
->reclaim_state
= &reclaim_state
;
1809 lru_pages
= count_lru_pages();
1810 nr_slab
= global_page_state(NR_SLAB_RECLAIMABLE
);
1811 /* If slab caches are huge, it's better to hit them first */
1812 while (nr_slab
>= lru_pages
) {
1813 reclaim_state
.reclaimed_slab
= 0;
1814 shrink_slab(nr_pages
, sc
.gfp_mask
, lru_pages
);
1815 if (!reclaim_state
.reclaimed_slab
)
1818 ret
+= reclaim_state
.reclaimed_slab
;
1819 if (ret
>= nr_pages
)
1822 nr_slab
-= reclaim_state
.reclaimed_slab
;
1826 * We try to shrink LRUs in 5 passes:
1827 * 0 = Reclaim from inactive_list only
1828 * 1 = Reclaim from active list but don't reclaim mapped
1829 * 2 = 2nd pass of type 1
1830 * 3 = Reclaim mapped (normal reclaim)
1831 * 4 = 2nd pass of type 3
1833 for (pass
= 0; pass
< 5; pass
++) {
1836 /* Force reclaiming mapped pages in the passes #3 and #4 */
1839 sc
.swappiness
= 100;
1842 for (prio
= DEF_PRIORITY
; prio
>= 0; prio
--) {
1843 unsigned long nr_to_scan
= nr_pages
- ret
;
1846 ret
+= shrink_all_zones(nr_to_scan
, prio
, pass
, &sc
);
1847 if (ret
>= nr_pages
)
1850 reclaim_state
.reclaimed_slab
= 0;
1851 shrink_slab(sc
.nr_scanned
, sc
.gfp_mask
,
1853 ret
+= reclaim_state
.reclaimed_slab
;
1854 if (ret
>= nr_pages
)
1857 if (sc
.nr_scanned
&& prio
< DEF_PRIORITY
- 2)
1858 congestion_wait(WRITE
, HZ
/ 10);
1863 * If ret = 0, we could not shrink LRUs, but there may be something
1868 reclaim_state
.reclaimed_slab
= 0;
1869 shrink_slab(nr_pages
, sc
.gfp_mask
, count_lru_pages());
1870 ret
+= reclaim_state
.reclaimed_slab
;
1871 } while (ret
< nr_pages
&& reclaim_state
.reclaimed_slab
> 0);
1875 current
->reclaim_state
= NULL
;
1881 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1882 not required for correctness. So if the last cpu in a node goes
1883 away, we get changed to run anywhere: as the first one comes back,
1884 restore their cpu bindings. */
1885 static int __devinit
cpu_callback(struct notifier_block
*nfb
,
1886 unsigned long action
, void *hcpu
)
1890 if (action
== CPU_ONLINE
|| action
== CPU_ONLINE_FROZEN
) {
1891 for_each_node_state(nid
, N_HIGH_MEMORY
) {
1892 pg_data_t
*pgdat
= NODE_DATA(nid
);
1893 node_to_cpumask_ptr(mask
, pgdat
->node_id
);
1895 if (any_online_cpu(*mask
) < nr_cpu_ids
)
1896 /* One of our CPUs online: restore mask */
1897 set_cpus_allowed_ptr(pgdat
->kswapd
, mask
);
1904 * This kswapd start function will be called by init and node-hot-add.
1905 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
1907 int kswapd_run(int nid
)
1909 pg_data_t
*pgdat
= NODE_DATA(nid
);
1915 pgdat
->kswapd
= kthread_run(kswapd
, pgdat
, "kswapd%d", nid
);
1916 if (IS_ERR(pgdat
->kswapd
)) {
1917 /* failure at boot is fatal */
1918 BUG_ON(system_state
== SYSTEM_BOOTING
);
1919 printk("Failed to start kswapd on node %d\n",nid
);
1925 static int __init
kswapd_init(void)
1930 for_each_node_state(nid
, N_HIGH_MEMORY
)
1932 hotcpu_notifier(cpu_callback
, 0);
1936 module_init(kswapd_init
)
1942 * If non-zero call zone_reclaim when the number of free pages falls below
1945 int zone_reclaim_mode __read_mostly
;
1947 #define RECLAIM_OFF 0
1948 #define RECLAIM_ZONE (1<<0) /* Run shrink_cache on the zone */
1949 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
1950 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
1953 * Priority for ZONE_RECLAIM. This determines the fraction of pages
1954 * of a node considered for each zone_reclaim. 4 scans 1/16th of
1957 #define ZONE_RECLAIM_PRIORITY 4
1960 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
1963 int sysctl_min_unmapped_ratio
= 1;
1966 * If the number of slab pages in a zone grows beyond this percentage then
1967 * slab reclaim needs to occur.
1969 int sysctl_min_slab_ratio
= 5;
1972 * Try to free up some pages from this zone through reclaim.
1974 static int __zone_reclaim(struct zone
*zone
, gfp_t gfp_mask
, unsigned int order
)
1976 /* Minimum pages needed in order to stay on node */
1977 const unsigned long nr_pages
= 1 << order
;
1978 struct task_struct
*p
= current
;
1979 struct reclaim_state reclaim_state
;
1981 unsigned long nr_reclaimed
= 0;
1982 struct scan_control sc
= {
1983 .may_writepage
= !!(zone_reclaim_mode
& RECLAIM_WRITE
),
1984 .may_swap
= !!(zone_reclaim_mode
& RECLAIM_SWAP
),
1985 .swap_cluster_max
= max_t(unsigned long, nr_pages
,
1987 .gfp_mask
= gfp_mask
,
1988 .swappiness
= vm_swappiness
,
1989 .isolate_pages
= isolate_pages_global
,
1991 unsigned long slab_reclaimable
;
1993 disable_swap_token();
1996 * We need to be able to allocate from the reserves for RECLAIM_SWAP
1997 * and we also need to be able to write out pages for RECLAIM_WRITE
2000 p
->flags
|= PF_MEMALLOC
| PF_SWAPWRITE
;
2001 reclaim_state
.reclaimed_slab
= 0;
2002 p
->reclaim_state
= &reclaim_state
;
2004 if (zone_page_state(zone
, NR_FILE_PAGES
) -
2005 zone_page_state(zone
, NR_FILE_MAPPED
) >
2006 zone
->min_unmapped_pages
) {
2008 * Free memory by calling shrink zone with increasing
2009 * priorities until we have enough memory freed.
2011 priority
= ZONE_RECLAIM_PRIORITY
;
2013 note_zone_scanning_priority(zone
, priority
);
2014 nr_reclaimed
+= shrink_zone(priority
, zone
, &sc
);
2016 } while (priority
>= 0 && nr_reclaimed
< nr_pages
);
2019 slab_reclaimable
= zone_page_state(zone
, NR_SLAB_RECLAIMABLE
);
2020 if (slab_reclaimable
> zone
->min_slab_pages
) {
2022 * shrink_slab() does not currently allow us to determine how
2023 * many pages were freed in this zone. So we take the current
2024 * number of slab pages and shake the slab until it is reduced
2025 * by the same nr_pages that we used for reclaiming unmapped
2028 * Note that shrink_slab will free memory on all zones and may
2031 while (shrink_slab(sc
.nr_scanned
, gfp_mask
, order
) &&
2032 zone_page_state(zone
, NR_SLAB_RECLAIMABLE
) >
2033 slab_reclaimable
- nr_pages
)
2037 * Update nr_reclaimed by the number of slab pages we
2038 * reclaimed from this zone.
2040 nr_reclaimed
+= slab_reclaimable
-
2041 zone_page_state(zone
, NR_SLAB_RECLAIMABLE
);
2044 p
->reclaim_state
= NULL
;
2045 current
->flags
&= ~(PF_MEMALLOC
| PF_SWAPWRITE
);
2046 return nr_reclaimed
>= nr_pages
;
2049 int zone_reclaim(struct zone
*zone
, gfp_t gfp_mask
, unsigned int order
)
2055 * Zone reclaim reclaims unmapped file backed pages and
2056 * slab pages if we are over the defined limits.
2058 * A small portion of unmapped file backed pages is needed for
2059 * file I/O otherwise pages read by file I/O will be immediately
2060 * thrown out if the zone is overallocated. So we do not reclaim
2061 * if less than a specified percentage of the zone is used by
2062 * unmapped file backed pages.
2064 if (zone_page_state(zone
, NR_FILE_PAGES
) -
2065 zone_page_state(zone
, NR_FILE_MAPPED
) <= zone
->min_unmapped_pages
2066 && zone_page_state(zone
, NR_SLAB_RECLAIMABLE
)
2067 <= zone
->min_slab_pages
)
2070 if (zone_is_all_unreclaimable(zone
))
2074 * Do not scan if the allocation should not be delayed.
2076 if (!(gfp_mask
& __GFP_WAIT
) || (current
->flags
& PF_MEMALLOC
))
2080 * Only run zone reclaim on the local zone or on zones that do not
2081 * have associated processors. This will favor the local processor
2082 * over remote processors and spread off node memory allocations
2083 * as wide as possible.
2085 node_id
= zone_to_nid(zone
);
2086 if (node_state(node_id
, N_CPU
) && node_id
!= numa_node_id())
2089 if (zone_test_and_set_flag(zone
, ZONE_RECLAIM_LOCKED
))
2091 ret
= __zone_reclaim(zone
, gfp_mask
, order
);
2092 zone_clear_flag(zone
, ZONE_RECLAIM_LOCKED
);