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/file.h>
23 #include <linux/writeback.h>
24 #include <linux/blkdev.h>
25 #include <linux/buffer_head.h> /* for try_to_release_page(),
26 buffer_heads_over_limit */
27 #include <linux/mm_inline.h>
28 #include <linux/pagevec.h>
29 #include <linux/backing-dev.h>
30 #include <linux/rmap.h>
31 #include <linux/topology.h>
32 #include <linux/cpu.h>
33 #include <linux/cpuset.h>
34 #include <linux/notifier.h>
35 #include <linux/rwsem.h>
36 #include <linux/delay.h>
37 #include <linux/kthread.h>
39 #include <asm/tlbflush.h>
40 #include <asm/div64.h>
42 #include <linux/swapops.h>
47 /* Incremented by the number of inactive pages that were scanned */
48 unsigned long nr_scanned
;
50 /* This context's GFP mask */
55 /* Can pages be swapped as part of reclaim? */
58 /* This context's SWAP_CLUSTER_MAX. If freeing memory for
59 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
60 * In this context, it doesn't matter that we scan the
61 * whole list at once. */
68 * The list of shrinker callbacks used by to apply pressure to
73 struct list_head list
;
74 int seeks
; /* seeks to recreate an obj */
75 long nr
; /* objs pending delete */
78 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
80 #ifdef ARCH_HAS_PREFETCH
81 #define prefetch_prev_lru_page(_page, _base, _field) \
83 if ((_page)->lru.prev != _base) { \
86 prev = lru_to_page(&(_page->lru)); \
87 prefetch(&prev->_field); \
91 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
94 #ifdef ARCH_HAS_PREFETCHW
95 #define prefetchw_prev_lru_page(_page, _base, _field) \
97 if ((_page)->lru.prev != _base) { \
100 prev = lru_to_page(&(_page->lru)); \
101 prefetchw(&prev->_field); \
105 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
109 * From 0 .. 100. Higher means more swappy.
111 int vm_swappiness
= 60;
112 long vm_total_pages
; /* The total number of pages which the VM controls */
114 static LIST_HEAD(shrinker_list
);
115 static DECLARE_RWSEM(shrinker_rwsem
);
118 * Add a shrinker callback to be called from the vm
120 struct shrinker
*set_shrinker(int seeks
, shrinker_t theshrinker
)
122 struct shrinker
*shrinker
;
124 shrinker
= kmalloc(sizeof(*shrinker
), GFP_KERNEL
);
126 shrinker
->shrinker
= theshrinker
;
127 shrinker
->seeks
= seeks
;
129 down_write(&shrinker_rwsem
);
130 list_add_tail(&shrinker
->list
, &shrinker_list
);
131 up_write(&shrinker_rwsem
);
135 EXPORT_SYMBOL(set_shrinker
);
140 void remove_shrinker(struct shrinker
*shrinker
)
142 down_write(&shrinker_rwsem
);
143 list_del(&shrinker
->list
);
144 up_write(&shrinker_rwsem
);
147 EXPORT_SYMBOL(remove_shrinker
);
149 #define SHRINK_BATCH 128
151 * Call the shrink functions to age shrinkable caches
153 * Here we assume it costs one seek to replace a lru page and that it also
154 * takes a seek to recreate a cache object. With this in mind we age equal
155 * percentages of the lru and ageable caches. This should balance the seeks
156 * generated by these structures.
158 * If the vm encounted mapped pages on the LRU it increase the pressure on
159 * slab to avoid swapping.
161 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
163 * `lru_pages' represents the number of on-LRU pages in all the zones which
164 * are eligible for the caller's allocation attempt. It is used for balancing
165 * slab reclaim versus page reclaim.
167 * Returns the number of slab objects which we shrunk.
169 unsigned long shrink_slab(unsigned long scanned
, gfp_t gfp_mask
,
170 unsigned long lru_pages
)
172 struct shrinker
*shrinker
;
173 unsigned long ret
= 0;
176 scanned
= SWAP_CLUSTER_MAX
;
178 if (!down_read_trylock(&shrinker_rwsem
))
179 return 1; /* Assume we'll be able to shrink next time */
181 list_for_each_entry(shrinker
, &shrinker_list
, list
) {
182 unsigned long long delta
;
183 unsigned long total_scan
;
184 unsigned long max_pass
= (*shrinker
->shrinker
)(0, gfp_mask
);
186 delta
= (4 * scanned
) / shrinker
->seeks
;
188 do_div(delta
, lru_pages
+ 1);
189 shrinker
->nr
+= delta
;
190 if (shrinker
->nr
< 0) {
191 printk(KERN_ERR
"%s: nr=%ld\n",
192 __FUNCTION__
, shrinker
->nr
);
193 shrinker
->nr
= max_pass
;
197 * Avoid risking looping forever due to too large nr value:
198 * never try to free more than twice the estimate number of
201 if (shrinker
->nr
> max_pass
* 2)
202 shrinker
->nr
= max_pass
* 2;
204 total_scan
= shrinker
->nr
;
207 while (total_scan
>= SHRINK_BATCH
) {
208 long this_scan
= SHRINK_BATCH
;
212 nr_before
= (*shrinker
->shrinker
)(0, gfp_mask
);
213 shrink_ret
= (*shrinker
->shrinker
)(this_scan
, gfp_mask
);
214 if (shrink_ret
== -1)
216 if (shrink_ret
< nr_before
)
217 ret
+= nr_before
- shrink_ret
;
218 mod_page_state(slabs_scanned
, this_scan
);
219 total_scan
-= this_scan
;
224 shrinker
->nr
+= total_scan
;
226 up_read(&shrinker_rwsem
);
230 /* Called without lock on whether page is mapped, so answer is unstable */
231 static inline int page_mapping_inuse(struct page
*page
)
233 struct address_space
*mapping
;
235 /* Page is in somebody's page tables. */
236 if (page_mapped(page
))
239 /* Be more reluctant to reclaim swapcache than pagecache */
240 if (PageSwapCache(page
))
243 mapping
= page_mapping(page
);
247 /* File is mmap'd by somebody? */
248 return mapping_mapped(mapping
);
251 static inline int is_page_cache_freeable(struct page
*page
)
253 return page_count(page
) - !!PagePrivate(page
) == 2;
256 static int may_write_to_queue(struct backing_dev_info
*bdi
)
258 if (current
->flags
& PF_SWAPWRITE
)
260 if (!bdi_write_congested(bdi
))
262 if (bdi
== current
->backing_dev_info
)
268 * We detected a synchronous write error writing a page out. Probably
269 * -ENOSPC. We need to propagate that into the address_space for a subsequent
270 * fsync(), msync() or close().
272 * The tricky part is that after writepage we cannot touch the mapping: nothing
273 * prevents it from being freed up. But we have a ref on the page and once
274 * that page is locked, the mapping is pinned.
276 * We're allowed to run sleeping lock_page() here because we know the caller has
279 static void handle_write_error(struct address_space
*mapping
,
280 struct page
*page
, int error
)
283 if (page_mapping(page
) == mapping
) {
284 if (error
== -ENOSPC
)
285 set_bit(AS_ENOSPC
, &mapping
->flags
);
287 set_bit(AS_EIO
, &mapping
->flags
);
292 /* possible outcome of pageout() */
294 /* failed to write page out, page is locked */
296 /* move page to the active list, page is locked */
298 /* page has been sent to the disk successfully, page is unlocked */
300 /* page is clean and locked */
305 * pageout is called by shrink_page_list() for each dirty page.
306 * Calls ->writepage().
308 static pageout_t
pageout(struct page
*page
, struct address_space
*mapping
)
311 * If the page is dirty, only perform writeback if that write
312 * will be non-blocking. To prevent this allocation from being
313 * stalled by pagecache activity. But note that there may be
314 * stalls if we need to run get_block(). We could test
315 * PagePrivate for that.
317 * If this process is currently in generic_file_write() against
318 * this page's queue, we can perform writeback even if that
321 * If the page is swapcache, write it back even if that would
322 * block, for some throttling. This happens by accident, because
323 * swap_backing_dev_info is bust: it doesn't reflect the
324 * congestion state of the swapdevs. Easy to fix, if needed.
325 * See swapfile.c:page_queue_congested().
327 if (!is_page_cache_freeable(page
))
331 * Some data journaling orphaned pages can have
332 * page->mapping == NULL while being dirty with clean buffers.
334 if (PagePrivate(page
)) {
335 if (try_to_free_buffers(page
)) {
336 ClearPageDirty(page
);
337 printk("%s: orphaned page\n", __FUNCTION__
);
343 if (mapping
->a_ops
->writepage
== NULL
)
344 return PAGE_ACTIVATE
;
345 if (!may_write_to_queue(mapping
->backing_dev_info
))
348 if (clear_page_dirty_for_io(page
)) {
350 struct writeback_control wbc
= {
351 .sync_mode
= WB_SYNC_NONE
,
352 .nr_to_write
= SWAP_CLUSTER_MAX
,
354 .range_end
= LLONG_MAX
,
359 SetPageReclaim(page
);
360 res
= mapping
->a_ops
->writepage(page
, &wbc
);
362 handle_write_error(mapping
, page
, res
);
363 if (res
== AOP_WRITEPAGE_ACTIVATE
) {
364 ClearPageReclaim(page
);
365 return PAGE_ACTIVATE
;
367 if (!PageWriteback(page
)) {
368 /* synchronous write or broken a_ops? */
369 ClearPageReclaim(page
);
378 int remove_mapping(struct address_space
*mapping
, struct page
*page
)
381 return 0; /* truncate got there first */
383 write_lock_irq(&mapping
->tree_lock
);
386 * The non-racy check for busy page. It is critical to check
387 * PageDirty _after_ making sure that the page is freeable and
388 * not in use by anybody. (pagecache + us == 2)
390 if (unlikely(page_count(page
) != 2))
393 if (unlikely(PageDirty(page
)))
396 if (PageSwapCache(page
)) {
397 swp_entry_t swap
= { .val
= page_private(page
) };
398 __delete_from_swap_cache(page
);
399 write_unlock_irq(&mapping
->tree_lock
);
401 __put_page(page
); /* The pagecache ref */
405 __remove_from_page_cache(page
);
406 write_unlock_irq(&mapping
->tree_lock
);
411 write_unlock_irq(&mapping
->tree_lock
);
416 * shrink_page_list() returns the number of reclaimed pages
418 static unsigned long shrink_page_list(struct list_head
*page_list
,
419 struct scan_control
*sc
)
421 LIST_HEAD(ret_pages
);
422 struct pagevec freed_pvec
;
424 unsigned long nr_reclaimed
= 0;
428 pagevec_init(&freed_pvec
, 1);
429 while (!list_empty(page_list
)) {
430 struct address_space
*mapping
;
437 page
= lru_to_page(page_list
);
438 list_del(&page
->lru
);
440 if (TestSetPageLocked(page
))
443 BUG_ON(PageActive(page
));
447 if (!sc
->may_swap
&& page_mapped(page
))
450 /* Double the slab pressure for mapped and swapcache pages */
451 if (page_mapped(page
) || PageSwapCache(page
))
454 if (PageWriteback(page
))
457 referenced
= page_referenced(page
, 1);
458 /* In active use or really unfreeable? Activate it. */
459 if (referenced
&& page_mapping_inuse(page
))
460 goto activate_locked
;
464 * Anonymous process memory has backing store?
465 * Try to allocate it some swap space here.
467 if (PageAnon(page
) && !PageSwapCache(page
))
468 if (!add_to_swap(page
, GFP_ATOMIC
))
469 goto activate_locked
;
470 #endif /* CONFIG_SWAP */
472 mapping
= page_mapping(page
);
473 may_enter_fs
= (sc
->gfp_mask
& __GFP_FS
) ||
474 (PageSwapCache(page
) && (sc
->gfp_mask
& __GFP_IO
));
477 * The page is mapped into the page tables of one or more
478 * processes. Try to unmap it here.
480 if (page_mapped(page
) && mapping
) {
481 switch (try_to_unmap(page
, 0)) {
483 goto activate_locked
;
487 ; /* try to free the page below */
491 if (PageDirty(page
)) {
496 if (!sc
->may_writepage
)
499 /* Page is dirty, try to write it out here */
500 switch(pageout(page
, mapping
)) {
504 goto activate_locked
;
506 if (PageWriteback(page
) || PageDirty(page
))
509 * A synchronous write - probably a ramdisk. Go
510 * ahead and try to reclaim the page.
512 if (TestSetPageLocked(page
))
514 if (PageDirty(page
) || PageWriteback(page
))
516 mapping
= page_mapping(page
);
518 ; /* try to free the page below */
523 * If the page has buffers, try to free the buffer mappings
524 * associated with this page. If we succeed we try to free
527 * We do this even if the page is PageDirty().
528 * try_to_release_page() does not perform I/O, but it is
529 * possible for a page to have PageDirty set, but it is actually
530 * clean (all its buffers are clean). This happens if the
531 * buffers were written out directly, with submit_bh(). ext3
532 * will do this, as well as the blockdev mapping.
533 * try_to_release_page() will discover that cleanness and will
534 * drop the buffers and mark the page clean - it can be freed.
536 * Rarely, pages can have buffers and no ->mapping. These are
537 * the pages which were not successfully invalidated in
538 * truncate_complete_page(). We try to drop those buffers here
539 * and if that worked, and the page is no longer mapped into
540 * process address space (page_count == 1) it can be freed.
541 * Otherwise, leave the page on the LRU so it is swappable.
543 if (PagePrivate(page
)) {
544 if (!try_to_release_page(page
, sc
->gfp_mask
))
545 goto activate_locked
;
546 if (!mapping
&& page_count(page
) == 1)
550 if (!remove_mapping(mapping
, page
))
556 if (!pagevec_add(&freed_pvec
, page
))
557 __pagevec_release_nonlru(&freed_pvec
);
566 list_add(&page
->lru
, &ret_pages
);
567 BUG_ON(PageLRU(page
));
569 list_splice(&ret_pages
, page_list
);
570 if (pagevec_count(&freed_pvec
))
571 __pagevec_release_nonlru(&freed_pvec
);
572 mod_page_state(pgactivate
, pgactivate
);
577 * zone->lru_lock is heavily contended. Some of the functions that
578 * shrink the lists perform better by taking out a batch of pages
579 * and working on them outside the LRU lock.
581 * For pagecache intensive workloads, this function is the hottest
582 * spot in the kernel (apart from copy_*_user functions).
584 * Appropriate locks must be held before calling this function.
586 * @nr_to_scan: The number of pages to look through on the list.
587 * @src: The LRU list to pull pages off.
588 * @dst: The temp list to put pages on to.
589 * @scanned: The number of pages that were scanned.
591 * returns how many pages were moved onto *@dst.
593 static unsigned long isolate_lru_pages(unsigned long nr_to_scan
,
594 struct list_head
*src
, struct list_head
*dst
,
595 unsigned long *scanned
)
597 unsigned long nr_taken
= 0;
601 for (scan
= 0; scan
< nr_to_scan
&& !list_empty(src
); scan
++) {
602 struct list_head
*target
;
603 page
= lru_to_page(src
);
604 prefetchw_prev_lru_page(page
, src
, flags
);
606 BUG_ON(!PageLRU(page
));
608 list_del(&page
->lru
);
610 if (likely(get_page_unless_zero(page
))) {
612 * Be careful not to clear PageLRU until after we're
613 * sure the page is not being freed elsewhere -- the
614 * page release code relies on it.
619 } /* else it is being freed elsewhere */
621 list_add(&page
->lru
, target
);
629 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
632 static unsigned long shrink_inactive_list(unsigned long max_scan
,
633 struct zone
*zone
, struct scan_control
*sc
)
635 LIST_HEAD(page_list
);
637 unsigned long nr_scanned
= 0;
638 unsigned long nr_reclaimed
= 0;
640 pagevec_init(&pvec
, 1);
643 spin_lock_irq(&zone
->lru_lock
);
646 unsigned long nr_taken
;
647 unsigned long nr_scan
;
648 unsigned long nr_freed
;
650 nr_taken
= isolate_lru_pages(sc
->swap_cluster_max
,
651 &zone
->inactive_list
,
652 &page_list
, &nr_scan
);
653 zone
->nr_inactive
-= nr_taken
;
654 zone
->pages_scanned
+= nr_scan
;
655 spin_unlock_irq(&zone
->lru_lock
);
657 nr_scanned
+= nr_scan
;
658 nr_freed
= shrink_page_list(&page_list
, sc
);
659 nr_reclaimed
+= nr_freed
;
661 if (current_is_kswapd()) {
662 __mod_page_state_zone(zone
, pgscan_kswapd
, nr_scan
);
663 __mod_page_state(kswapd_steal
, nr_freed
);
665 __mod_page_state_zone(zone
, pgscan_direct
, nr_scan
);
666 __mod_page_state_zone(zone
, pgsteal
, nr_freed
);
671 spin_lock(&zone
->lru_lock
);
673 * Put back any unfreeable pages.
675 while (!list_empty(&page_list
)) {
676 page
= lru_to_page(&page_list
);
677 BUG_ON(PageLRU(page
));
679 list_del(&page
->lru
);
680 if (PageActive(page
))
681 add_page_to_active_list(zone
, page
);
683 add_page_to_inactive_list(zone
, page
);
684 if (!pagevec_add(&pvec
, page
)) {
685 spin_unlock_irq(&zone
->lru_lock
);
686 __pagevec_release(&pvec
);
687 spin_lock_irq(&zone
->lru_lock
);
690 } while (nr_scanned
< max_scan
);
691 spin_unlock(&zone
->lru_lock
);
694 pagevec_release(&pvec
);
699 * This moves pages from the active list to the inactive list.
701 * We move them the other way if the page is referenced by one or more
702 * processes, from rmap.
704 * If the pages are mostly unmapped, the processing is fast and it is
705 * appropriate to hold zone->lru_lock across the whole operation. But if
706 * the pages are mapped, the processing is slow (page_referenced()) so we
707 * should drop zone->lru_lock around each page. It's impossible to balance
708 * this, so instead we remove the pages from the LRU while processing them.
709 * It is safe to rely on PG_active against the non-LRU pages in here because
710 * nobody will play with that bit on a non-LRU page.
712 * The downside is that we have to touch page->_count against each page.
713 * But we had to alter page->flags anyway.
715 static void shrink_active_list(unsigned long nr_pages
, struct zone
*zone
,
716 struct scan_control
*sc
)
718 unsigned long pgmoved
;
719 int pgdeactivate
= 0;
720 unsigned long pgscanned
;
721 LIST_HEAD(l_hold
); /* The pages which were snipped off */
722 LIST_HEAD(l_inactive
); /* Pages to go onto the inactive_list */
723 LIST_HEAD(l_active
); /* Pages to go onto the active_list */
726 int reclaim_mapped
= 0;
734 * `distress' is a measure of how much trouble we're having
735 * reclaiming pages. 0 -> no problems. 100 -> great trouble.
737 distress
= 100 >> zone
->prev_priority
;
740 * The point of this algorithm is to decide when to start
741 * reclaiming mapped memory instead of just pagecache. Work out
745 mapped_ratio
= ((global_page_state(NR_FILE_MAPPED
) +
746 global_page_state(NR_ANON_PAGES
)) * 100) /
750 * Now decide how much we really want to unmap some pages. The
751 * mapped ratio is downgraded - just because there's a lot of
752 * mapped memory doesn't necessarily mean that page reclaim
755 * The distress ratio is important - we don't want to start
758 * A 100% value of vm_swappiness overrides this algorithm
761 swap_tendency
= mapped_ratio
/ 2 + distress
+ sc
->swappiness
;
764 * Now use this metric to decide whether to start moving mapped
765 * memory onto the inactive list.
767 if (swap_tendency
>= 100)
772 spin_lock_irq(&zone
->lru_lock
);
773 pgmoved
= isolate_lru_pages(nr_pages
, &zone
->active_list
,
774 &l_hold
, &pgscanned
);
775 zone
->pages_scanned
+= pgscanned
;
776 zone
->nr_active
-= pgmoved
;
777 spin_unlock_irq(&zone
->lru_lock
);
779 while (!list_empty(&l_hold
)) {
781 page
= lru_to_page(&l_hold
);
782 list_del(&page
->lru
);
783 if (page_mapped(page
)) {
784 if (!reclaim_mapped
||
785 (total_swap_pages
== 0 && PageAnon(page
)) ||
786 page_referenced(page
, 0)) {
787 list_add(&page
->lru
, &l_active
);
791 list_add(&page
->lru
, &l_inactive
);
794 pagevec_init(&pvec
, 1);
796 spin_lock_irq(&zone
->lru_lock
);
797 while (!list_empty(&l_inactive
)) {
798 page
= lru_to_page(&l_inactive
);
799 prefetchw_prev_lru_page(page
, &l_inactive
, flags
);
800 BUG_ON(PageLRU(page
));
802 BUG_ON(!PageActive(page
));
803 ClearPageActive(page
);
805 list_move(&page
->lru
, &zone
->inactive_list
);
807 if (!pagevec_add(&pvec
, page
)) {
808 zone
->nr_inactive
+= pgmoved
;
809 spin_unlock_irq(&zone
->lru_lock
);
810 pgdeactivate
+= pgmoved
;
812 if (buffer_heads_over_limit
)
813 pagevec_strip(&pvec
);
814 __pagevec_release(&pvec
);
815 spin_lock_irq(&zone
->lru_lock
);
818 zone
->nr_inactive
+= pgmoved
;
819 pgdeactivate
+= pgmoved
;
820 if (buffer_heads_over_limit
) {
821 spin_unlock_irq(&zone
->lru_lock
);
822 pagevec_strip(&pvec
);
823 spin_lock_irq(&zone
->lru_lock
);
827 while (!list_empty(&l_active
)) {
828 page
= lru_to_page(&l_active
);
829 prefetchw_prev_lru_page(page
, &l_active
, flags
);
830 BUG_ON(PageLRU(page
));
832 BUG_ON(!PageActive(page
));
833 list_move(&page
->lru
, &zone
->active_list
);
835 if (!pagevec_add(&pvec
, page
)) {
836 zone
->nr_active
+= pgmoved
;
838 spin_unlock_irq(&zone
->lru_lock
);
839 __pagevec_release(&pvec
);
840 spin_lock_irq(&zone
->lru_lock
);
843 zone
->nr_active
+= pgmoved
;
844 spin_unlock(&zone
->lru_lock
);
846 __mod_page_state_zone(zone
, pgrefill
, pgscanned
);
847 __mod_page_state(pgdeactivate
, pgdeactivate
);
850 pagevec_release(&pvec
);
854 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
856 static unsigned long shrink_zone(int priority
, struct zone
*zone
,
857 struct scan_control
*sc
)
859 unsigned long nr_active
;
860 unsigned long nr_inactive
;
861 unsigned long nr_to_scan
;
862 unsigned long nr_reclaimed
= 0;
864 atomic_inc(&zone
->reclaim_in_progress
);
867 * Add one to `nr_to_scan' just to make sure that the kernel will
868 * slowly sift through the active list.
870 zone
->nr_scan_active
+= (zone
->nr_active
>> priority
) + 1;
871 nr_active
= zone
->nr_scan_active
;
872 if (nr_active
>= sc
->swap_cluster_max
)
873 zone
->nr_scan_active
= 0;
877 zone
->nr_scan_inactive
+= (zone
->nr_inactive
>> priority
) + 1;
878 nr_inactive
= zone
->nr_scan_inactive
;
879 if (nr_inactive
>= sc
->swap_cluster_max
)
880 zone
->nr_scan_inactive
= 0;
884 while (nr_active
|| nr_inactive
) {
886 nr_to_scan
= min(nr_active
,
887 (unsigned long)sc
->swap_cluster_max
);
888 nr_active
-= nr_to_scan
;
889 shrink_active_list(nr_to_scan
, zone
, sc
);
893 nr_to_scan
= min(nr_inactive
,
894 (unsigned long)sc
->swap_cluster_max
);
895 nr_inactive
-= nr_to_scan
;
896 nr_reclaimed
+= shrink_inactive_list(nr_to_scan
, zone
,
901 throttle_vm_writeout();
903 atomic_dec(&zone
->reclaim_in_progress
);
908 * This is the direct reclaim path, for page-allocating processes. We only
909 * try to reclaim pages from zones which will satisfy the caller's allocation
912 * We reclaim from a zone even if that zone is over pages_high. Because:
913 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
915 * b) The zones may be over pages_high but they must go *over* pages_high to
916 * satisfy the `incremental min' zone defense algorithm.
918 * Returns the number of reclaimed pages.
920 * If a zone is deemed to be full of pinned pages then just give it a light
921 * scan then give up on it.
923 static unsigned long shrink_zones(int priority
, struct zone
**zones
,
924 struct scan_control
*sc
)
926 unsigned long nr_reclaimed
= 0;
929 for (i
= 0; zones
[i
] != NULL
; i
++) {
930 struct zone
*zone
= zones
[i
];
932 if (!populated_zone(zone
))
935 if (!cpuset_zone_allowed(zone
, __GFP_HARDWALL
))
938 zone
->temp_priority
= priority
;
939 if (zone
->prev_priority
> priority
)
940 zone
->prev_priority
= priority
;
942 if (zone
->all_unreclaimable
&& priority
!= DEF_PRIORITY
)
943 continue; /* Let kswapd poll it */
945 nr_reclaimed
+= shrink_zone(priority
, zone
, sc
);
951 * This is the main entry point to direct page reclaim.
953 * If a full scan of the inactive list fails to free enough memory then we
954 * are "out of memory" and something needs to be killed.
956 * If the caller is !__GFP_FS then the probability of a failure is reasonably
957 * high - the zone may be full of dirty or under-writeback pages, which this
958 * caller can't do much about. We kick pdflush and take explicit naps in the
959 * hope that some of these pages can be written. But if the allocating task
960 * holds filesystem locks which prevent writeout this might not work, and the
961 * allocation attempt will fail.
963 unsigned long try_to_free_pages(struct zone
**zones
, gfp_t gfp_mask
)
967 unsigned long total_scanned
= 0;
968 unsigned long nr_reclaimed
= 0;
969 struct reclaim_state
*reclaim_state
= current
->reclaim_state
;
970 unsigned long lru_pages
= 0;
972 struct scan_control sc
= {
973 .gfp_mask
= gfp_mask
,
974 .may_writepage
= !laptop_mode
,
975 .swap_cluster_max
= SWAP_CLUSTER_MAX
,
977 .swappiness
= vm_swappiness
,
980 inc_page_state(allocstall
);
982 for (i
= 0; zones
[i
] != NULL
; i
++) {
983 struct zone
*zone
= zones
[i
];
985 if (!cpuset_zone_allowed(zone
, __GFP_HARDWALL
))
988 zone
->temp_priority
= DEF_PRIORITY
;
989 lru_pages
+= zone
->nr_active
+ zone
->nr_inactive
;
992 for (priority
= DEF_PRIORITY
; priority
>= 0; priority
--) {
995 disable_swap_token();
996 nr_reclaimed
+= shrink_zones(priority
, zones
, &sc
);
997 shrink_slab(sc
.nr_scanned
, gfp_mask
, lru_pages
);
999 nr_reclaimed
+= reclaim_state
->reclaimed_slab
;
1000 reclaim_state
->reclaimed_slab
= 0;
1002 total_scanned
+= sc
.nr_scanned
;
1003 if (nr_reclaimed
>= sc
.swap_cluster_max
) {
1009 * Try to write back as many pages as we just scanned. This
1010 * tends to cause slow streaming writers to write data to the
1011 * disk smoothly, at the dirtying rate, which is nice. But
1012 * that's undesirable in laptop mode, where we *want* lumpy
1013 * writeout. So in laptop mode, write out the whole world.
1015 if (total_scanned
> sc
.swap_cluster_max
+
1016 sc
.swap_cluster_max
/ 2) {
1017 wakeup_pdflush(laptop_mode
? 0 : total_scanned
);
1018 sc
.may_writepage
= 1;
1021 /* Take a nap, wait for some writeback to complete */
1022 if (sc
.nr_scanned
&& priority
< DEF_PRIORITY
- 2)
1023 blk_congestion_wait(WRITE
, HZ
/10);
1026 for (i
= 0; zones
[i
] != 0; i
++) {
1027 struct zone
*zone
= zones
[i
];
1029 if (!cpuset_zone_allowed(zone
, __GFP_HARDWALL
))
1032 zone
->prev_priority
= zone
->temp_priority
;
1038 * For kswapd, balance_pgdat() will work across all this node's zones until
1039 * they are all at pages_high.
1041 * Returns the number of pages which were actually freed.
1043 * There is special handling here for zones which are full of pinned pages.
1044 * This can happen if the pages are all mlocked, or if they are all used by
1045 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
1046 * What we do is to detect the case where all pages in the zone have been
1047 * scanned twice and there has been zero successful reclaim. Mark the zone as
1048 * dead and from now on, only perform a short scan. Basically we're polling
1049 * the zone for when the problem goes away.
1051 * kswapd scans the zones in the highmem->normal->dma direction. It skips
1052 * zones which have free_pages > pages_high, but once a zone is found to have
1053 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1054 * of the number of free pages in the lower zones. This interoperates with
1055 * the page allocator fallback scheme to ensure that aging of pages is balanced
1058 static unsigned long balance_pgdat(pg_data_t
*pgdat
, int order
)
1063 unsigned long total_scanned
;
1064 unsigned long nr_reclaimed
;
1065 struct reclaim_state
*reclaim_state
= current
->reclaim_state
;
1066 struct scan_control sc
= {
1067 .gfp_mask
= GFP_KERNEL
,
1069 .swap_cluster_max
= SWAP_CLUSTER_MAX
,
1070 .swappiness
= vm_swappiness
,
1076 sc
.may_writepage
= !laptop_mode
;
1077 inc_page_state(pageoutrun
);
1079 for (i
= 0; i
< pgdat
->nr_zones
; i
++) {
1080 struct zone
*zone
= pgdat
->node_zones
+ i
;
1082 zone
->temp_priority
= DEF_PRIORITY
;
1085 for (priority
= DEF_PRIORITY
; priority
>= 0; priority
--) {
1086 int end_zone
= 0; /* Inclusive. 0 = ZONE_DMA */
1087 unsigned long lru_pages
= 0;
1089 /* The swap token gets in the way of swapout... */
1091 disable_swap_token();
1096 * Scan in the highmem->dma direction for the highest
1097 * zone which needs scanning
1099 for (i
= pgdat
->nr_zones
- 1; i
>= 0; i
--) {
1100 struct zone
*zone
= pgdat
->node_zones
+ i
;
1102 if (!populated_zone(zone
))
1105 if (zone
->all_unreclaimable
&& priority
!= DEF_PRIORITY
)
1108 if (!zone_watermark_ok(zone
, order
, zone
->pages_high
,
1116 for (i
= 0; i
<= end_zone
; i
++) {
1117 struct zone
*zone
= pgdat
->node_zones
+ i
;
1119 lru_pages
+= zone
->nr_active
+ zone
->nr_inactive
;
1123 * Now scan the zone in the dma->highmem direction, stopping
1124 * at the last zone which needs scanning.
1126 * We do this because the page allocator works in the opposite
1127 * direction. This prevents the page allocator from allocating
1128 * pages behind kswapd's direction of progress, which would
1129 * cause too much scanning of the lower zones.
1131 for (i
= 0; i
<= end_zone
; i
++) {
1132 struct zone
*zone
= pgdat
->node_zones
+ i
;
1135 if (!populated_zone(zone
))
1138 if (zone
->all_unreclaimable
&& priority
!= DEF_PRIORITY
)
1141 if (!zone_watermark_ok(zone
, order
, zone
->pages_high
,
1144 zone
->temp_priority
= priority
;
1145 if (zone
->prev_priority
> priority
)
1146 zone
->prev_priority
= priority
;
1148 nr_reclaimed
+= shrink_zone(priority
, zone
, &sc
);
1149 reclaim_state
->reclaimed_slab
= 0;
1150 nr_slab
= shrink_slab(sc
.nr_scanned
, GFP_KERNEL
,
1152 nr_reclaimed
+= reclaim_state
->reclaimed_slab
;
1153 total_scanned
+= sc
.nr_scanned
;
1154 if (zone
->all_unreclaimable
)
1156 if (nr_slab
== 0 && zone
->pages_scanned
>=
1157 (zone
->nr_active
+ zone
->nr_inactive
) * 4)
1158 zone
->all_unreclaimable
= 1;
1160 * If we've done a decent amount of scanning and
1161 * the reclaim ratio is low, start doing writepage
1162 * even in laptop mode
1164 if (total_scanned
> SWAP_CLUSTER_MAX
* 2 &&
1165 total_scanned
> nr_reclaimed
+ nr_reclaimed
/ 2)
1166 sc
.may_writepage
= 1;
1169 break; /* kswapd: all done */
1171 * OK, kswapd is getting into trouble. Take a nap, then take
1172 * another pass across the zones.
1174 if (total_scanned
&& priority
< DEF_PRIORITY
- 2)
1175 blk_congestion_wait(WRITE
, HZ
/10);
1178 * We do this so kswapd doesn't build up large priorities for
1179 * example when it is freeing in parallel with allocators. It
1180 * matches the direct reclaim path behaviour in terms of impact
1181 * on zone->*_priority.
1183 if (nr_reclaimed
>= SWAP_CLUSTER_MAX
)
1187 for (i
= 0; i
< pgdat
->nr_zones
; i
++) {
1188 struct zone
*zone
= pgdat
->node_zones
+ i
;
1190 zone
->prev_priority
= zone
->temp_priority
;
1192 if (!all_zones_ok
) {
1197 return nr_reclaimed
;
1201 * The background pageout daemon, started as a kernel thread
1202 * from the init process.
1204 * This basically trickles out pages so that we have _some_
1205 * free memory available even if there is no other activity
1206 * that frees anything up. This is needed for things like routing
1207 * etc, where we otherwise might have all activity going on in
1208 * asynchronous contexts that cannot page things out.
1210 * If there are applications that are active memory-allocators
1211 * (most normal use), this basically shouldn't matter.
1213 static int kswapd(void *p
)
1215 unsigned long order
;
1216 pg_data_t
*pgdat
= (pg_data_t
*)p
;
1217 struct task_struct
*tsk
= current
;
1219 struct reclaim_state reclaim_state
= {
1220 .reclaimed_slab
= 0,
1224 cpumask
= node_to_cpumask(pgdat
->node_id
);
1225 if (!cpus_empty(cpumask
))
1226 set_cpus_allowed(tsk
, cpumask
);
1227 current
->reclaim_state
= &reclaim_state
;
1230 * Tell the memory management that we're a "memory allocator",
1231 * and that if we need more memory we should get access to it
1232 * regardless (see "__alloc_pages()"). "kswapd" should
1233 * never get caught in the normal page freeing logic.
1235 * (Kswapd normally doesn't need memory anyway, but sometimes
1236 * you need a small amount of memory in order to be able to
1237 * page out something else, and this flag essentially protects
1238 * us from recursively trying to free more memory as we're
1239 * trying to free the first piece of memory in the first place).
1241 tsk
->flags
|= PF_MEMALLOC
| PF_SWAPWRITE
| PF_KSWAPD
;
1245 unsigned long new_order
;
1249 prepare_to_wait(&pgdat
->kswapd_wait
, &wait
, TASK_INTERRUPTIBLE
);
1250 new_order
= pgdat
->kswapd_max_order
;
1251 pgdat
->kswapd_max_order
= 0;
1252 if (order
< new_order
) {
1254 * Don't sleep if someone wants a larger 'order'
1260 order
= pgdat
->kswapd_max_order
;
1262 finish_wait(&pgdat
->kswapd_wait
, &wait
);
1264 balance_pgdat(pgdat
, order
);
1270 * A zone is low on free memory, so wake its kswapd task to service it.
1272 void wakeup_kswapd(struct zone
*zone
, int order
)
1276 if (!populated_zone(zone
))
1279 pgdat
= zone
->zone_pgdat
;
1280 if (zone_watermark_ok(zone
, order
, zone
->pages_low
, 0, 0))
1282 if (pgdat
->kswapd_max_order
< order
)
1283 pgdat
->kswapd_max_order
= order
;
1284 if (!cpuset_zone_allowed(zone
, __GFP_HARDWALL
))
1286 if (!waitqueue_active(&pgdat
->kswapd_wait
))
1288 wake_up_interruptible(&pgdat
->kswapd_wait
);
1293 * Helper function for shrink_all_memory(). Tries to reclaim 'nr_pages' pages
1294 * from LRU lists system-wide, for given pass and priority, and returns the
1295 * number of reclaimed pages
1297 * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1299 static unsigned long shrink_all_zones(unsigned long nr_pages
, int pass
,
1300 int prio
, struct scan_control
*sc
)
1303 unsigned long nr_to_scan
, ret
= 0;
1305 for_each_zone(zone
) {
1307 if (!populated_zone(zone
))
1310 if (zone
->all_unreclaimable
&& prio
!= DEF_PRIORITY
)
1313 /* For pass = 0 we don't shrink the active list */
1315 zone
->nr_scan_active
+= (zone
->nr_active
>> prio
) + 1;
1316 if (zone
->nr_scan_active
>= nr_pages
|| pass
> 3) {
1317 zone
->nr_scan_active
= 0;
1318 nr_to_scan
= min(nr_pages
, zone
->nr_active
);
1319 shrink_active_list(nr_to_scan
, zone
, sc
);
1323 zone
->nr_scan_inactive
+= (zone
->nr_inactive
>> prio
) + 1;
1324 if (zone
->nr_scan_inactive
>= nr_pages
|| pass
> 3) {
1325 zone
->nr_scan_inactive
= 0;
1326 nr_to_scan
= min(nr_pages
, zone
->nr_inactive
);
1327 ret
+= shrink_inactive_list(nr_to_scan
, zone
, sc
);
1328 if (ret
>= nr_pages
)
1337 * Try to free `nr_pages' of memory, system-wide, and return the number of
1340 * Rather than trying to age LRUs the aim is to preserve the overall
1341 * LRU order by reclaiming preferentially
1342 * inactive > active > active referenced > active mapped
1344 unsigned long shrink_all_memory(unsigned long nr_pages
)
1346 unsigned long lru_pages
, nr_slab
;
1347 unsigned long ret
= 0;
1349 struct reclaim_state reclaim_state
;
1351 struct scan_control sc
= {
1352 .gfp_mask
= GFP_KERNEL
,
1354 .swap_cluster_max
= nr_pages
,
1356 .swappiness
= vm_swappiness
,
1359 current
->reclaim_state
= &reclaim_state
;
1363 lru_pages
+= zone
->nr_active
+ zone
->nr_inactive
;
1365 nr_slab
= global_page_state(NR_SLAB
);
1366 /* If slab caches are huge, it's better to hit them first */
1367 while (nr_slab
>= lru_pages
) {
1368 reclaim_state
.reclaimed_slab
= 0;
1369 shrink_slab(nr_pages
, sc
.gfp_mask
, lru_pages
);
1370 if (!reclaim_state
.reclaimed_slab
)
1373 ret
+= reclaim_state
.reclaimed_slab
;
1374 if (ret
>= nr_pages
)
1377 nr_slab
-= reclaim_state
.reclaimed_slab
;
1381 * We try to shrink LRUs in 5 passes:
1382 * 0 = Reclaim from inactive_list only
1383 * 1 = Reclaim from active list but don't reclaim mapped
1384 * 2 = 2nd pass of type 1
1385 * 3 = Reclaim mapped (normal reclaim)
1386 * 4 = 2nd pass of type 3
1388 for (pass
= 0; pass
< 5; pass
++) {
1391 /* Needed for shrinking slab caches later on */
1393 for_each_zone(zone
) {
1394 lru_pages
+= zone
->nr_active
;
1395 lru_pages
+= zone
->nr_inactive
;
1398 /* Force reclaiming mapped pages in the passes #3 and #4 */
1401 sc
.swappiness
= 100;
1404 for (prio
= DEF_PRIORITY
; prio
>= 0; prio
--) {
1405 unsigned long nr_to_scan
= nr_pages
- ret
;
1408 ret
+= shrink_all_zones(nr_to_scan
, prio
, pass
, &sc
);
1409 if (ret
>= nr_pages
)
1412 reclaim_state
.reclaimed_slab
= 0;
1413 shrink_slab(sc
.nr_scanned
, sc
.gfp_mask
, lru_pages
);
1414 ret
+= reclaim_state
.reclaimed_slab
;
1415 if (ret
>= nr_pages
)
1418 if (sc
.nr_scanned
&& prio
< DEF_PRIORITY
- 2)
1419 blk_congestion_wait(WRITE
, HZ
/ 10);
1426 * If ret = 0, we could not shrink LRUs, but there may be something
1431 reclaim_state
.reclaimed_slab
= 0;
1432 shrink_slab(nr_pages
, sc
.gfp_mask
, lru_pages
);
1433 ret
+= reclaim_state
.reclaimed_slab
;
1434 } while (ret
< nr_pages
&& reclaim_state
.reclaimed_slab
> 0);
1437 current
->reclaim_state
= NULL
;
1443 #ifdef CONFIG_HOTPLUG_CPU
1444 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1445 not required for correctness. So if the last cpu in a node goes
1446 away, we get changed to run anywhere: as the first one comes back,
1447 restore their cpu bindings. */
1448 static int __devinit
cpu_callback(struct notifier_block
*nfb
,
1449 unsigned long action
, void *hcpu
)
1454 if (action
== CPU_ONLINE
) {
1455 for_each_online_pgdat(pgdat
) {
1456 mask
= node_to_cpumask(pgdat
->node_id
);
1457 if (any_online_cpu(mask
) != NR_CPUS
)
1458 /* One of our CPUs online: restore mask */
1459 set_cpus_allowed(pgdat
->kswapd
, mask
);
1464 #endif /* CONFIG_HOTPLUG_CPU */
1467 * This kswapd start function will be called by init and node-hot-add.
1468 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
1470 int kswapd_run(int nid
)
1472 pg_data_t
*pgdat
= NODE_DATA(nid
);
1478 pgdat
->kswapd
= kthread_run(kswapd
, pgdat
, "kswapd%d", nid
);
1479 if (IS_ERR(pgdat
->kswapd
)) {
1480 /* failure at boot is fatal */
1481 BUG_ON(system_state
== SYSTEM_BOOTING
);
1482 printk("Failed to start kswapd on node %d\n",nid
);
1488 static int __init
kswapd_init(void)
1493 for_each_online_node(nid
)
1495 hotcpu_notifier(cpu_callback
, 0);
1499 module_init(kswapd_init
)
1505 * If non-zero call zone_reclaim when the number of free pages falls below
1508 * In the future we may add flags to the mode. However, the page allocator
1509 * should only have to check that zone_reclaim_mode != 0 before calling
1512 int zone_reclaim_mode __read_mostly
;
1514 #define RECLAIM_OFF 0
1515 #define RECLAIM_ZONE (1<<0) /* Run shrink_cache on the zone */
1516 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
1517 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
1518 #define RECLAIM_SLAB (1<<3) /* Do a global slab shrink if the zone is out of memory */
1521 * Priority for ZONE_RECLAIM. This determines the fraction of pages
1522 * of a node considered for each zone_reclaim. 4 scans 1/16th of
1525 #define ZONE_RECLAIM_PRIORITY 4
1528 * Try to free up some pages from this zone through reclaim.
1530 static int __zone_reclaim(struct zone
*zone
, gfp_t gfp_mask
, unsigned int order
)
1532 /* Minimum pages needed in order to stay on node */
1533 const unsigned long nr_pages
= 1 << order
;
1534 struct task_struct
*p
= current
;
1535 struct reclaim_state reclaim_state
;
1537 unsigned long nr_reclaimed
= 0;
1538 struct scan_control sc
= {
1539 .may_writepage
= !!(zone_reclaim_mode
& RECLAIM_WRITE
),
1540 .may_swap
= !!(zone_reclaim_mode
& RECLAIM_SWAP
),
1541 .swap_cluster_max
= max_t(unsigned long, nr_pages
,
1543 .gfp_mask
= gfp_mask
,
1544 .swappiness
= vm_swappiness
,
1547 disable_swap_token();
1550 * We need to be able to allocate from the reserves for RECLAIM_SWAP
1551 * and we also need to be able to write out pages for RECLAIM_WRITE
1554 p
->flags
|= PF_MEMALLOC
| PF_SWAPWRITE
;
1555 reclaim_state
.reclaimed_slab
= 0;
1556 p
->reclaim_state
= &reclaim_state
;
1559 * Free memory by calling shrink zone with increasing priorities
1560 * until we have enough memory freed.
1562 priority
= ZONE_RECLAIM_PRIORITY
;
1564 nr_reclaimed
+= shrink_zone(priority
, zone
, &sc
);
1566 } while (priority
>= 0 && nr_reclaimed
< nr_pages
);
1568 if (nr_reclaimed
< nr_pages
&& (zone_reclaim_mode
& RECLAIM_SLAB
)) {
1570 * shrink_slab() does not currently allow us to determine how
1571 * many pages were freed in this zone. So we just shake the slab
1572 * a bit and then go off node for this particular allocation
1573 * despite possibly having freed enough memory to allocate in
1574 * this zone. If we freed local memory then the next
1575 * allocations will be local again.
1577 * shrink_slab will free memory on all zones and may take
1580 shrink_slab(sc
.nr_scanned
, gfp_mask
, order
);
1583 p
->reclaim_state
= NULL
;
1584 current
->flags
&= ~(PF_MEMALLOC
| PF_SWAPWRITE
);
1585 return nr_reclaimed
>= nr_pages
;
1588 int zone_reclaim(struct zone
*zone
, gfp_t gfp_mask
, unsigned int order
)
1594 * Do not reclaim if there are not enough reclaimable pages in this
1595 * zone that would satify this allocations.
1597 * All unmapped pagecache pages are reclaimable.
1599 * Both counters may be temporarily off a bit so we use
1600 * SWAP_CLUSTER_MAX as the boundary. It may also be good to
1601 * leave a few frequently used unmapped pagecache pages around.
1603 if (zone_page_state(zone
, NR_FILE_PAGES
) -
1604 zone_page_state(zone
, NR_FILE_MAPPED
) < SWAP_CLUSTER_MAX
)
1608 * Avoid concurrent zone reclaims, do not reclaim in a zone that does
1609 * not have reclaimable pages and if we should not delay the allocation
1612 if (!(gfp_mask
& __GFP_WAIT
) ||
1613 zone
->all_unreclaimable
||
1614 atomic_read(&zone
->reclaim_in_progress
) > 0 ||
1615 (current
->flags
& PF_MEMALLOC
))
1619 * Only run zone reclaim on the local zone or on zones that do not
1620 * have associated processors. This will favor the local processor
1621 * over remote processors and spread off node memory allocations
1622 * as wide as possible.
1624 node_id
= zone
->zone_pgdat
->node_id
;
1625 mask
= node_to_cpumask(node_id
);
1626 if (!cpus_empty(mask
) && node_id
!= numa_node_id())
1628 return __zone_reclaim(zone
, gfp_mask
, order
);