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/suspend.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/notifier.h>
35 #include <linux/rwsem.h>
37 #include <asm/tlbflush.h>
38 #include <asm/div64.h>
40 #include <linux/swapops.h>
41 #include <linux/vs_cvirt.h>
44 /* possible outcome of pageout() */
46 /* failed to write page out, page is locked */
48 /* move page to the active list, page is locked */
50 /* page has been sent to the disk successfully, page is unlocked */
52 /* page is clean and locked */
57 /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
58 unsigned long nr_to_scan;
60 /* Incremented by the number of inactive pages that were scanned */
61 unsigned long nr_scanned;
63 /* Incremented by the number of pages reclaimed */
64 unsigned long nr_reclaimed;
66 unsigned long nr_mapped; /* From page_state */
68 /* How many pages shrink_cache() should reclaim */
71 /* Ask shrink_caches, or shrink_zone to scan at this priority */
72 unsigned int priority;
74 /* This context's GFP mask */
75 unsigned int gfp_mask;
81 * The list of shrinker callbacks used by to apply pressure to
86 struct list_head list;
87 int seeks; /* seeks to recreate an obj */
88 long nr; /* objs pending delete */
91 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
93 #ifdef ARCH_HAS_PREFETCH
94 #define prefetch_prev_lru_page(_page, _base, _field) \
96 if ((_page)->lru.prev != _base) { \
99 prev = lru_to_page(&(_page->lru)); \
100 prefetch(&prev->_field); \
104 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
107 #ifdef ARCH_HAS_PREFETCHW
108 #define prefetchw_prev_lru_page(_page, _base, _field) \
110 if ((_page)->lru.prev != _base) { \
113 prev = lru_to_page(&(_page->lru)); \
114 prefetchw(&prev->_field); \
118 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
122 * From 0 .. 100. Higher means more swappy.
124 int vm_swappiness = 60;
125 static long total_memory;
127 static LIST_HEAD(shrinker_list);
128 static DECLARE_RWSEM(shrinker_rwsem);
131 * Add a shrinker callback to be called from the vm
133 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
135 struct shrinker *shrinker;
137 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
139 shrinker->shrinker = theshrinker;
140 shrinker->seeks = seeks;
142 down_write(&shrinker_rwsem);
143 list_add(&shrinker->list, &shrinker_list);
144 up_write(&shrinker_rwsem);
148 EXPORT_SYMBOL(set_shrinker);
153 void remove_shrinker(struct shrinker *shrinker)
155 down_write(&shrinker_rwsem);
156 list_del(&shrinker->list);
157 up_write(&shrinker_rwsem);
160 EXPORT_SYMBOL(remove_shrinker);
162 #define SHRINK_BATCH 128
164 * Call the shrink functions to age shrinkable caches
166 * Here we assume it costs one seek to replace a lru page and that it also
167 * takes a seek to recreate a cache object. With this in mind we age equal
168 * percentages of the lru and ageable caches. This should balance the seeks
169 * generated by these structures.
171 * If the vm encounted mapped pages on the LRU it increase the pressure on
172 * slab to avoid swapping.
174 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
176 * `lru_pages' represents the number of on-LRU pages in all the zones which
177 * are eligible for the caller's allocation attempt. It is used for balancing
178 * slab reclaim versus page reclaim.
180 static int shrink_slab(unsigned long scanned, unsigned int gfp_mask,
181 unsigned long lru_pages)
183 struct shrinker *shrinker;
186 scanned = SWAP_CLUSTER_MAX;
188 if (!down_read_trylock(&shrinker_rwsem))
191 list_for_each_entry(shrinker, &shrinker_list, list) {
192 unsigned long long delta;
193 unsigned long total_scan;
195 delta = (4 * scanned) / shrinker->seeks;
196 delta *= (*shrinker->shrinker)(0, gfp_mask);
197 do_div(delta, lru_pages + 1);
198 shrinker->nr += delta;
199 if (shrinker->nr < 0)
200 shrinker->nr = LONG_MAX; /* It wrapped! */
202 total_scan = shrinker->nr;
205 while (total_scan >= SHRINK_BATCH) {
206 long this_scan = SHRINK_BATCH;
209 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
210 if (shrink_ret == -1)
212 mod_page_state(slabs_scanned, this_scan);
213 total_scan -= this_scan;
218 shrinker->nr += total_scan;
220 up_read(&shrinker_rwsem);
224 /* Called without lock on whether page is mapped, so answer is unstable */
225 static inline int page_mapping_inuse(struct page *page)
227 struct address_space *mapping;
229 /* Page is in somebody's page tables. */
230 if (page_mapped(page))
233 /* Be more reluctant to reclaim swapcache than pagecache */
234 if (PageSwapCache(page))
237 mapping = page_mapping(page);
241 /* File is mmap'd by somebody? */
242 return mapping_mapped(mapping);
245 static inline int is_page_cache_freeable(struct page *page)
247 return page_count(page) - !!PagePrivate(page) == 2;
250 static int may_write_to_queue(struct backing_dev_info *bdi)
252 if (current_is_kswapd())
254 if (current_is_pdflush()) /* This is unlikely, but why not... */
256 if (!bdi_write_congested(bdi))
258 if (bdi == current->backing_dev_info)
264 * We detected a synchronous write error writing a page out. Probably
265 * -ENOSPC. We need to propagate that into the address_space for a subsequent
266 * fsync(), msync() or close().
268 * The tricky part is that after writepage we cannot touch the mapping: nothing
269 * prevents it from being freed up. But we have a ref on the page and once
270 * that page is locked, the mapping is pinned.
272 * We're allowed to run sleeping lock_page() here because we know the caller has
275 static void handle_write_error(struct address_space *mapping,
276 struct page *page, int error)
279 if (page_mapping(page) == mapping) {
280 if (error == -ENOSPC)
281 set_bit(AS_ENOSPC, &mapping->flags);
283 set_bit(AS_EIO, &mapping->flags);
289 * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
291 static pageout_t pageout(struct page *page, struct address_space *mapping)
294 * If the page is dirty, only perform writeback if that write
295 * will be non-blocking. To prevent this allocation from being
296 * stalled by pagecache activity. But note that there may be
297 * stalls if we need to run get_block(). We could test
298 * PagePrivate for that.
300 * If this process is currently in generic_file_write() against
301 * this page's queue, we can perform writeback even if that
304 * If the page is swapcache, write it back even if that would
305 * block, for some throttling. This happens by accident, because
306 * swap_backing_dev_info is bust: it doesn't reflect the
307 * congestion state of the swapdevs. Easy to fix, if needed.
308 * See swapfile.c:page_queue_congested().
310 if (!is_page_cache_freeable(page))
314 if (mapping->a_ops->writepage == NULL)
315 return PAGE_ACTIVATE;
316 if (!may_write_to_queue(mapping->backing_dev_info))
319 if (clear_page_dirty_for_io(page)) {
321 struct writeback_control wbc = {
322 .sync_mode = WB_SYNC_NONE,
323 .nr_to_write = SWAP_CLUSTER_MAX,
328 SetPageReclaim(page);
329 res = mapping->a_ops->writepage(page, &wbc);
331 handle_write_error(mapping, page, res);
332 if (res == WRITEPAGE_ACTIVATE) {
333 ClearPageReclaim(page);
334 return PAGE_ACTIVATE;
336 if (!PageWriteback(page)) {
337 /* synchronous write or broken a_ops? */
338 ClearPageReclaim(page);
348 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
350 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
352 LIST_HEAD(ret_pages);
353 struct pagevec freed_pvec;
359 pagevec_init(&freed_pvec, 1);
360 while (!list_empty(page_list)) {
361 struct address_space *mapping;
366 page = lru_to_page(page_list);
367 list_del(&page->lru);
369 if (TestSetPageLocked(page))
372 BUG_ON(PageActive(page));
375 /* Double the slab pressure for mapped and swapcache pages */
376 if (page_mapped(page) || PageSwapCache(page))
379 if (PageWriteback(page))
382 referenced = page_referenced(page, 1, sc->priority <= 0);
383 /* In active use or really unfreeable? Activate it. */
384 if (referenced && page_mapping_inuse(page))
385 goto activate_locked;
389 * Anonymous process memory has backing store?
390 * Try to allocate it some swap space here.
392 if (PageAnon(page) && !PageSwapCache(page)) {
393 if (!add_to_swap(page))
394 goto activate_locked;
396 #endif /* CONFIG_SWAP */
398 mapping = page_mapping(page);
399 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
400 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
403 * The page is mapped into the page tables of one or more
404 * processes. Try to unmap it here.
406 if (page_mapped(page) && mapping) {
407 switch (try_to_unmap(page)) {
409 goto activate_locked;
413 ; /* try to free the page below */
417 if (PageDirty(page)) {
422 if (laptop_mode && !sc->may_writepage)
425 /* Page is dirty, try to write it out here */
426 switch(pageout(page, mapping)) {
430 goto activate_locked;
432 if (PageWriteback(page) || PageDirty(page))
435 * A synchronous write - probably a ramdisk. Go
436 * ahead and try to reclaim the page.
438 if (TestSetPageLocked(page))
440 if (PageDirty(page) || PageWriteback(page))
442 mapping = page_mapping(page);
444 ; /* try to free the page below */
449 * If the page has buffers, try to free the buffer mappings
450 * associated with this page. If we succeed we try to free
453 * We do this even if the page is PageDirty().
454 * try_to_release_page() does not perform I/O, but it is
455 * possible for a page to have PageDirty set, but it is actually
456 * clean (all its buffers are clean). This happens if the
457 * buffers were written out directly, with submit_bh(). ext3
458 * will do this, as well as the blockdev mapping.
459 * try_to_release_page() will discover that cleanness and will
460 * drop the buffers and mark the page clean - it can be freed.
462 * Rarely, pages can have buffers and no ->mapping. These are
463 * the pages which were not successfully invalidated in
464 * truncate_complete_page(). We try to drop those buffers here
465 * and if that worked, and the page is no longer mapped into
466 * process address space (page_count == 1) it can be freed.
467 * Otherwise, leave the page on the LRU so it is swappable.
469 if (PagePrivate(page)) {
470 if (!try_to_release_page(page, sc->gfp_mask))
471 goto activate_locked;
472 if (!mapping && page_count(page) == 1)
477 goto keep_locked; /* truncate got there first */
479 spin_lock_irq(&mapping->tree_lock);
482 * The non-racy check for busy page. It is critical to check
483 * PageDirty _after_ making sure that the page is freeable and
484 * not in use by anybody. (pagecache + us == 2)
486 if (page_count(page) != 2 || PageDirty(page)) {
487 spin_unlock_irq(&mapping->tree_lock);
492 if (PageSwapCache(page)) {
493 swp_entry_t swap = { .val = page->private };
494 __delete_from_swap_cache(page);
495 spin_unlock_irq(&mapping->tree_lock);
497 __put_page(page); /* The pagecache ref */
500 #endif /* CONFIG_SWAP */
502 __remove_from_page_cache(page);
503 spin_unlock_irq(&mapping->tree_lock);
509 if (!pagevec_add(&freed_pvec, page))
510 __pagevec_release_nonlru(&freed_pvec);
519 list_add(&page->lru, &ret_pages);
520 BUG_ON(PageLRU(page));
522 list_splice(&ret_pages, page_list);
523 if (pagevec_count(&freed_pvec))
524 __pagevec_release_nonlru(&freed_pvec);
525 mod_page_state(pgactivate, pgactivate);
526 sc->nr_reclaimed += reclaimed;
531 * zone->lru_lock is heavily contented. We relieve it by quickly privatising
532 * a batch of pages and working on them outside the lock. Any pages which were
533 * not freed will be added back to the LRU.
535 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
537 * For pagecache intensive workloads, the first loop here is the hottest spot
538 * in the kernel (apart from the copy_*_user functions).
540 static void shrink_cache(struct zone *zone, struct scan_control *sc)
542 LIST_HEAD(page_list);
544 int max_scan = sc->nr_to_scan;
545 struct list_head *inactive_list = &zone->inactive_list;
546 struct list_head *active_list = &zone->active_list;
548 pagevec_init(&pvec, 1);
551 spin_lock_irq(&zone->lru_lock);
552 while (max_scan > 0) {
558 while (nr_scan++ < SWAP_CLUSTER_MAX &&
559 !list_empty(inactive_list)) {
560 page = lru_to_page(inactive_list);
562 prefetchw_prev_lru_page(page,
563 inactive_list, flags);
565 if (!TestClearPageLRU(page))
567 list_del(&page->lru);
568 if (get_page_testone(page)) {
570 * It is being freed elsewhere
574 list_add(&page->lru, inactive_list);
577 list_add(&page->lru, &page_list);
580 zone->nr_inactive -= nr_taken;
581 spin_unlock_irq(&zone->lru_lock);
587 if (current_is_kswapd())
588 mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
590 mod_page_state_zone(zone, pgscan_direct, nr_scan);
591 nr_freed = shrink_list(&page_list, sc);
592 if (current_is_kswapd())
593 mod_page_state(kswapd_steal, nr_freed);
594 mod_page_state_zone(zone, pgsteal, nr_freed);
595 sc->nr_to_reclaim -= nr_freed;
597 spin_lock_irq(&zone->lru_lock);
599 * Put back any unfreeable pages.
601 while (!list_empty(&page_list)) {
602 page = lru_to_page(&page_list);
603 if (TestSetPageLRU(page))
605 list_del(&page->lru);
606 if (PageActive(page)) {
608 list_add(&page->lru, active_list);
611 list_add(&page->lru, inactive_list);
613 if (!pagevec_add(&pvec, page)) {
614 spin_unlock_irq(&zone->lru_lock);
615 __pagevec_release(&pvec);
616 spin_lock_irq(&zone->lru_lock);
620 spin_unlock_irq(&zone->lru_lock);
622 pagevec_release(&pvec);
626 * This moves pages from the active list to the inactive list.
628 * We move them the other way if the page is referenced by one or more
629 * processes, from rmap.
631 * If the pages are mostly unmapped, the processing is fast and it is
632 * appropriate to hold zone->lru_lock across the whole operation. But if
633 * the pages are mapped, the processing is slow (page_referenced()) so we
634 * should drop zone->lru_lock around each page. It's impossible to balance
635 * this, so instead we remove the pages from the LRU while processing them.
636 * It is safe to rely on PG_active against the non-LRU pages in here because
637 * nobody will play with that bit on a non-LRU page.
639 * The downside is that we have to touch page->_count against each page.
640 * But we had to alter page->flags anyway.
643 refill_inactive_zone(struct zone *zone, struct scan_control *sc)
646 int pgdeactivate = 0;
648 int nr_pages = sc->nr_to_scan;
649 LIST_HEAD(l_hold); /* The pages which were snipped off */
650 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
651 LIST_HEAD(l_active); /* Pages to go onto the active_list */
654 int reclaim_mapped = 0;
658 struct list_head *active_list = &zone->active_list;
659 struct list_head *inactive_list = &zone->inactive_list;
663 spin_lock_irq(&zone->lru_lock);
664 while (pgscanned < nr_pages && !list_empty(active_list)) {
665 page = lru_to_page(active_list);
666 prefetchw_prev_lru_page(page, active_list, flags);
667 if (!TestClearPageLRU(page))
669 list_del(&page->lru);
670 if (get_page_testone(page)) {
672 * It was already free! release_pages() or put_page()
673 * are about to remove it from the LRU and free it. So
674 * put the refcount back and put the page back on the
679 list_add(&page->lru, active_list);
681 list_add(&page->lru, &l_hold);
686 zone->pages_scanned += pgscanned;
687 zone->nr_active -= pgmoved;
688 spin_unlock_irq(&zone->lru_lock);
691 * `distress' is a measure of how much trouble we're having reclaiming
692 * pages. 0 -> no problems. 100 -> great trouble.
694 distress = 100 >> zone->prev_priority;
697 * The point of this algorithm is to decide when to start reclaiming
698 * mapped memory instead of just pagecache. Work out how much memory
701 mapped_ratio = (sc->nr_mapped * 100) / total_memory;
704 * Now decide how much we really want to unmap some pages. The mapped
705 * ratio is downgraded - just because there's a lot of mapped memory
706 * doesn't necessarily mean that page reclaim isn't succeeding.
708 * The distress ratio is important - we don't want to start going oom.
710 * A 100% value of vm_swappiness overrides this algorithm altogether.
712 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
715 * Now use this metric to decide whether to start moving mapped memory
716 * onto the inactive list.
718 if (swap_tendency >= 100)
721 while (!list_empty(&l_hold)) {
722 page = lru_to_page(&l_hold);
723 list_del(&page->lru);
724 if (page_mapped(page)) {
725 if (!reclaim_mapped ||
726 (total_swap_pages == 0 && PageAnon(page)) ||
727 page_referenced(page, 0, sc->priority <= 0)) {
728 list_add(&page->lru, &l_active);
732 list_add(&page->lru, &l_inactive);
735 pagevec_init(&pvec, 1);
737 spin_lock_irq(&zone->lru_lock);
738 while (!list_empty(&l_inactive)) {
739 page = lru_to_page(&l_inactive);
740 prefetchw_prev_lru_page(page, &l_inactive, flags);
741 if (TestSetPageLRU(page))
743 if (!TestClearPageActive(page))
745 list_move(&page->lru, inactive_list);
747 if (!pagevec_add(&pvec, page)) {
748 zone->nr_inactive += pgmoved;
749 spin_unlock_irq(&zone->lru_lock);
750 pgdeactivate += pgmoved;
752 if (buffer_heads_over_limit)
753 pagevec_strip(&pvec);
754 __pagevec_release(&pvec);
755 spin_lock_irq(&zone->lru_lock);
758 zone->nr_inactive += pgmoved;
759 pgdeactivate += pgmoved;
760 if (buffer_heads_over_limit) {
761 spin_unlock_irq(&zone->lru_lock);
762 pagevec_strip(&pvec);
763 spin_lock_irq(&zone->lru_lock);
767 while (!list_empty(&l_active)) {
768 page = lru_to_page(&l_active);
769 prefetchw_prev_lru_page(page, &l_active, flags);
770 if (TestSetPageLRU(page))
772 BUG_ON(!PageActive(page));
773 list_move(&page->lru, active_list);
775 if (!pagevec_add(&pvec, page)) {
776 zone->nr_active += pgmoved;
778 spin_unlock_irq(&zone->lru_lock);
779 __pagevec_release(&pvec);
780 spin_lock_irq(&zone->lru_lock);
783 zone->nr_active += pgmoved;
784 spin_unlock_irq(&zone->lru_lock);
785 pagevec_release(&pvec);
787 mod_page_state_zone(zone, pgrefill, pgscanned);
788 mod_page_state(pgdeactivate, pgdeactivate);
792 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
795 shrink_zone(struct zone *zone, struct scan_control *sc)
797 unsigned long nr_active;
798 unsigned long nr_inactive;
801 * Add one to `nr_to_scan' just to make sure that the kernel will
802 * slowly sift through the active list.
804 zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
805 nr_active = zone->nr_scan_active;
806 if (nr_active >= SWAP_CLUSTER_MAX)
807 zone->nr_scan_active = 0;
811 zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
812 nr_inactive = zone->nr_scan_inactive;
813 if (nr_inactive >= SWAP_CLUSTER_MAX)
814 zone->nr_scan_inactive = 0;
818 sc->nr_to_reclaim = SWAP_CLUSTER_MAX;
820 while (nr_active || nr_inactive) {
822 sc->nr_to_scan = min(nr_active,
823 (unsigned long)SWAP_CLUSTER_MAX);
824 nr_active -= sc->nr_to_scan;
825 refill_inactive_zone(zone, sc);
829 sc->nr_to_scan = min(nr_inactive,
830 (unsigned long)SWAP_CLUSTER_MAX);
831 nr_inactive -= sc->nr_to_scan;
832 shrink_cache(zone, sc);
833 if (sc->nr_to_reclaim <= 0)
840 * This is the direct reclaim path, for page-allocating processes. We only
841 * try to reclaim pages from zones which will satisfy the caller's allocation
844 * We reclaim from a zone even if that zone is over pages_high. Because:
845 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
847 * b) The zones may be over pages_high but they must go *over* pages_high to
848 * satisfy the `incremental min' zone defense algorithm.
850 * Returns the number of reclaimed pages.
852 * If a zone is deemed to be full of pinned pages then just give it a light
853 * scan then give up on it.
856 shrink_caches(struct zone **zones, struct scan_control *sc)
860 for (i = 0; zones[i] != NULL; i++) {
861 struct zone *zone = zones[i];
863 if (zone->present_pages == 0)
866 zone->temp_priority = sc->priority;
867 if (zone->prev_priority > sc->priority)
868 zone->prev_priority = sc->priority;
870 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
871 continue; /* Let kswapd poll it */
873 shrink_zone(zone, sc);
878 * This is the main entry point to direct page reclaim.
880 * If a full scan of the inactive list fails to free enough memory then we
881 * are "out of memory" and something needs to be killed.
883 * If the caller is !__GFP_FS then the probability of a failure is reasonably
884 * high - the zone may be full of dirty or under-writeback pages, which this
885 * caller can't do much about. We kick pdflush and take explicit naps in the
886 * hope that some of these pages can be written. But if the allocating task
887 * holds filesystem locks which prevent writeout this might not work, and the
888 * allocation attempt will fail.
890 int try_to_free_pages(struct zone **zones,
891 unsigned int gfp_mask, unsigned int order)
895 int total_scanned = 0, total_reclaimed = 0;
896 struct reclaim_state *reclaim_state = current->reclaim_state;
897 struct scan_control sc;
898 unsigned long lru_pages = 0;
901 sc.gfp_mask = gfp_mask;
902 sc.may_writepage = 0;
904 inc_page_state(allocstall);
906 for (i = 0; zones[i] != NULL; i++) {
907 struct zone *zone = zones[i];
909 zone->temp_priority = DEF_PRIORITY;
910 lru_pages += zone->nr_active + zone->nr_inactive;
913 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
914 sc.nr_mapped = read_page_state(nr_mapped);
917 sc.priority = priority;
918 shrink_caches(zones, &sc);
919 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
921 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
922 reclaim_state->reclaimed_slab = 0;
924 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) {
928 total_scanned += sc.nr_scanned;
929 total_reclaimed += sc.nr_reclaimed;
932 * Try to write back as many pages as we just scanned. This
933 * tends to cause slow streaming writers to write data to the
934 * disk smoothly, at the dirtying rate, which is nice. But
935 * that's undesirable in laptop mode, where we *want* lumpy
936 * writeout. So in laptop mode, write out the whole world.
938 if (total_scanned > SWAP_CLUSTER_MAX + SWAP_CLUSTER_MAX/2) {
939 wakeup_bdflush(laptop_mode ? 0 : total_scanned);
940 sc.may_writepage = 1;
943 /* Take a nap, wait for some writeback to complete */
944 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
945 blk_congestion_wait(WRITE, HZ/10);
947 if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
948 out_of_memory(gfp_mask);
950 for (i = 0; zones[i] != 0; i++)
951 zones[i]->prev_priority = zones[i]->temp_priority;
956 * For kswapd, balance_pgdat() will work across all this node's zones until
957 * they are all at pages_high.
959 * If `nr_pages' is non-zero then it is the number of pages which are to be
960 * reclaimed, regardless of the zone occupancies. This is a software suspend
963 * Returns the number of pages which were actually freed.
965 * There is special handling here for zones which are full of pinned pages.
966 * This can happen if the pages are all mlocked, or if they are all used by
967 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
968 * What we do is to detect the case where all pages in the zone have been
969 * scanned twice and there has been zero successful reclaim. Mark the zone as
970 * dead and from now on, only perform a short scan. Basically we're polling
971 * the zone for when the problem goes away.
973 * kswapd scans the zones in the highmem->normal->dma direction. It skips
974 * zones which have free_pages > pages_high, but once a zone is found to have
975 * free_pages <= pages_high, we scan that zone and the lower zones regardless
976 * of the number of free pages in the lower zones. This interoperates with
977 * the page allocator fallback scheme to ensure that aging of pages is balanced
980 static int balance_pgdat(pg_data_t *pgdat, int nr_pages)
982 int to_free = nr_pages;
986 int total_scanned, total_reclaimed;
987 struct reclaim_state *reclaim_state = current->reclaim_state;
988 struct scan_control sc;
993 sc.gfp_mask = GFP_KERNEL;
994 sc.may_writepage = 0;
995 sc.nr_mapped = read_page_state(nr_mapped);
997 inc_page_state(pageoutrun);
999 for (i = 0; i < pgdat->nr_zones; i++) {
1000 struct zone *zone = pgdat->node_zones + i;
1002 zone->temp_priority = DEF_PRIORITY;
1005 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1006 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
1007 unsigned long lru_pages = 0;
1011 if (nr_pages == 0) {
1013 * Scan in the highmem->dma direction for the highest
1014 * zone which needs scanning
1016 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1017 struct zone *zone = pgdat->node_zones + i;
1019 if (zone->present_pages == 0)
1022 if (zone->all_unreclaimable &&
1023 priority != DEF_PRIORITY)
1026 if (zone->free_pages <= zone->pages_high) {
1033 end_zone = pgdat->nr_zones - 1;
1036 for (i = 0; i <= end_zone; i++) {
1037 struct zone *zone = pgdat->node_zones + i;
1039 lru_pages += zone->nr_active + zone->nr_inactive;
1043 * Now scan the zone in the dma->highmem direction, stopping
1044 * at the last zone which needs scanning.
1046 * We do this because the page allocator works in the opposite
1047 * direction. This prevents the page allocator from allocating
1048 * pages behind kswapd's direction of progress, which would
1049 * cause too much scanning of the lower zones.
1051 for (i = 0; i <= end_zone; i++) {
1052 struct zone *zone = pgdat->node_zones + i;
1054 if (zone->present_pages == 0)
1057 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1060 if (nr_pages == 0) { /* Not software suspend */
1061 if (zone->free_pages <= zone->pages_high)
1064 zone->temp_priority = priority;
1065 if (zone->prev_priority > priority)
1066 zone->prev_priority = priority;
1068 sc.nr_reclaimed = 0;
1069 sc.priority = priority;
1070 shrink_zone(zone, &sc);
1071 reclaim_state->reclaimed_slab = 0;
1072 shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
1073 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1074 total_reclaimed += sc.nr_reclaimed;
1075 total_scanned += sc.nr_scanned;
1076 if (zone->all_unreclaimable)
1078 if (zone->pages_scanned >= (zone->nr_active +
1079 zone->nr_inactive) * 4)
1080 zone->all_unreclaimable = 1;
1082 * If we've done a decent amount of scanning and
1083 * the reclaim ratio is low, start doing writepage
1084 * even in laptop mode
1086 if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1087 total_scanned > total_reclaimed+total_reclaimed/2)
1088 sc.may_writepage = 1;
1090 if (nr_pages && to_free > total_reclaimed)
1091 continue; /* swsusp: need to do more work */
1093 break; /* kswapd: all done */
1095 * OK, kswapd is getting into trouble. Take a nap, then take
1096 * another pass across the zones.
1098 if (total_scanned && priority < DEF_PRIORITY - 2)
1099 blk_congestion_wait(WRITE, HZ/10);
1102 * We do this so kswapd doesn't build up large priorities for
1103 * example when it is freeing in parallel with allocators. It
1104 * matches the direct reclaim path behaviour in terms of impact
1105 * on zone->*_priority.
1107 if (total_reclaimed >= SWAP_CLUSTER_MAX)
1111 for (i = 0; i < pgdat->nr_zones; i++) {
1112 struct zone *zone = pgdat->node_zones + i;
1114 zone->prev_priority = zone->temp_priority;
1116 if (!all_zones_ok) {
1121 return total_reclaimed;
1125 * The background pageout daemon, started as a kernel thread
1126 * from the init process.
1128 * This basically trickles out pages so that we have _some_
1129 * free memory available even if there is no other activity
1130 * that frees anything up. This is needed for things like routing
1131 * etc, where we otherwise might have all activity going on in
1132 * asynchronous contexts that cannot page things out.
1134 * If there are applications that are active memory-allocators
1135 * (most normal use), this basically shouldn't matter.
1137 static int kswapd(void *p)
1139 pg_data_t *pgdat = (pg_data_t*)p;
1140 struct task_struct *tsk = current;
1142 struct reclaim_state reclaim_state = {
1143 .reclaimed_slab = 0,
1147 daemonize("kswapd%d", pgdat->node_id);
1148 cpumask = node_to_cpumask(pgdat->node_id);
1149 if (!cpus_empty(cpumask))
1150 set_cpus_allowed(tsk, cpumask);
1151 current->reclaim_state = &reclaim_state;
1154 * Tell the memory management that we're a "memory allocator",
1155 * and that if we need more memory we should get access to it
1156 * regardless (see "__alloc_pages()"). "kswapd" should
1157 * never get caught in the normal page freeing logic.
1159 * (Kswapd normally doesn't need memory anyway, but sometimes
1160 * you need a small amount of memory in order to be able to
1161 * page out something else, and this flag essentially protects
1162 * us from recursively trying to free more memory as we're
1163 * trying to free the first piece of memory in the first place).
1165 tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
1168 if (current->flags & PF_FREEZE)
1169 refrigerator(PF_FREEZE);
1170 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1172 finish_wait(&pgdat->kswapd_wait, &wait);
1173 balance_pgdat(pgdat, 0);
1179 * A zone is low on free memory, so wake its kswapd task to service it.
1181 void wakeup_kswapd(struct zone *zone)
1183 if (zone->present_pages == 0)
1185 if (zone->free_pages > zone->pages_low)
1187 if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
1189 wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
1194 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed
1197 int shrink_all_memory(int nr_pages)
1200 int nr_to_free = nr_pages;
1202 struct reclaim_state reclaim_state = {
1203 .reclaimed_slab = 0,
1206 current->reclaim_state = &reclaim_state;
1207 for_each_pgdat(pgdat) {
1209 freed = balance_pgdat(pgdat, nr_to_free);
1211 nr_to_free -= freed;
1212 if (nr_to_free <= 0)
1215 current->reclaim_state = NULL;
1220 #ifdef CONFIG_HOTPLUG_CPU
1221 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1222 not required for correctness. So if the last cpu in a node goes
1223 away, we get changed to run anywhere: as the first one comes back,
1224 restore their cpu bindings. */
1225 static int __devinit cpu_callback(struct notifier_block *nfb,
1226 unsigned long action,
1232 if (action == CPU_ONLINE) {
1233 for_each_pgdat(pgdat) {
1234 mask = node_to_cpumask(pgdat->node_id);
1235 if (any_online_cpu(mask) != NR_CPUS)
1236 /* One of our CPUs online: restore mask */
1237 set_cpus_allowed(pgdat->kswapd, mask);
1242 #endif /* CONFIG_HOTPLUG_CPU */
1244 static int __init kswapd_init(void)
1248 for_each_pgdat(pgdat)
1250 = find_task_by_real_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1251 total_memory = nr_free_pagecache_pages();
1252 hotcpu_notifier(cpu_callback, 0);
1256 module_init(kswapd_init)