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>
36 #include <asm/tlbflush.h>
37 #include <asm/div64.h>
39 #include <linux/swapops.h>
42 * From 0 .. 100. Higher means more swappy.
44 int vm_swappiness = 60;
45 static long total_memory;
49 void try_to_clip_inodes(void);
52 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
54 #ifdef ARCH_HAS_PREFETCH
55 #define prefetch_prev_lru_page(_page, _base, _field) \
57 if ((_page)->lru.prev != _base) { \
60 prev = lru_to_page(&(_page->lru)); \
61 prefetch(&prev->_field); \
65 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
68 #ifdef ARCH_HAS_PREFETCHW
69 #define prefetchw_prev_lru_page(_page, _base, _field) \
71 if ((_page)->lru.prev != _base) { \
74 prev = lru_to_page(&(_page->lru)); \
75 prefetchw(&prev->_field); \
79 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
83 * The list of shrinker callbacks used by to apply pressure to
88 struct list_head list;
89 int seeks; /* seeks to recreate an obj */
90 long nr; /* objs pending delete */
93 static LIST_HEAD(shrinker_list);
94 static DECLARE_MUTEX(shrinker_sem);
97 * Add a shrinker callback to be called from the vm
99 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
101 struct shrinker *shrinker;
103 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
105 shrinker->shrinker = theshrinker;
106 shrinker->seeks = seeks;
109 list_add(&shrinker->list, &shrinker_list);
115 EXPORT_SYMBOL(set_shrinker);
120 void remove_shrinker(struct shrinker *shrinker)
123 list_del(&shrinker->list);
128 EXPORT_SYMBOL(remove_shrinker);
130 #define SHRINK_BATCH 128
132 * Call the shrink functions to age shrinkable caches
134 * Here we assume it costs one seek to replace a lru page and that it also
135 * takes a seek to recreate a cache object. With this in mind we age equal
136 * percentages of the lru and ageable caches. This should balance the seeks
137 * generated by these structures.
139 * If the vm encounted mapped pages on the LRU it increase the pressure on
140 * slab to avoid swapping.
142 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
144 static int shrink_slab(unsigned long scanned, unsigned int gfp_mask)
146 struct shrinker *shrinker;
149 if (down_trylock(&shrinker_sem))
152 pages = nr_used_zone_pages();
153 list_for_each_entry(shrinker, &shrinker_list, list) {
154 unsigned long long delta;
156 delta = (4 * scanned) / shrinker->seeks;
157 delta *= (*shrinker->shrinker)(0, gfp_mask);
158 do_div(delta, pages + 1);
159 shrinker->nr += delta;
160 if (shrinker->nr < 0)
161 shrinker->nr = LONG_MAX; /* It wrapped! */
163 if (shrinker->nr <= SHRINK_BATCH)
165 while (shrinker->nr) {
166 long this_scan = shrinker->nr;
171 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
172 mod_page_state(slabs_scanned, this_scan);
173 shrinker->nr -= this_scan;
174 if (shrink_ret == -1)
183 /* Must be called with page's rmap lock held. */
184 static inline int page_mapping_inuse(struct page *page)
186 struct address_space *mapping;
188 /* Page is in somebody's page tables. */
189 if (page_mapped(page))
192 /* Be more reluctant to reclaim swapcache than pagecache */
193 if (PageSwapCache(page))
196 mapping = page_mapping(page);
200 /* File is mmap'd by somebody? */
201 return mapping_mapped(mapping);
204 static inline int is_page_cache_freeable(struct page *page)
206 return page_count(page) - !!PagePrivate(page) == 2;
209 static int may_write_to_queue(struct backing_dev_info *bdi)
211 if (current_is_kswapd())
213 if (current_is_pdflush()) /* This is unlikely, but why not... */
215 if (!bdi_write_congested(bdi))
217 if (bdi == current->backing_dev_info)
223 * We detected a synchronous write error writing a page out. Probably
224 * -ENOSPC. We need to propagate that into the address_space for a subsequent
225 * fsync(), msync() or close().
227 * The tricky part is that after writepage we cannot touch the mapping: nothing
228 * prevents it from being freed up. But we have a ref on the page and once
229 * that page is locked, the mapping is pinned.
231 * We're allowed to run sleeping lock_page() here because we know the caller has
234 static void handle_write_error(struct address_space *mapping,
235 struct page *page, int error)
238 if (page_mapping(page) == mapping) {
239 if (error == -ENOSPC)
240 set_bit(AS_ENOSPC, &mapping->flags);
242 set_bit(AS_EIO, &mapping->flags);
247 /* possible outcome of pageout() */
249 /* failed to write page out, page is locked */
251 /* move page to the active list, page is locked */
253 /* page has been sent to the disk successfully, page is unlocked */
255 /* page is clean and locked */
260 * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
262 static pageout_t pageout(struct page *page, struct address_space *mapping)
265 * If the page is dirty, only perform writeback if that write
266 * will be non-blocking. To prevent this allocation from being
267 * stalled by pagecache activity. But note that there may be
268 * stalls if we need to run get_block(). We could test
269 * PagePrivate for that.
271 * If this process is currently in generic_file_write() against
272 * this page's queue, we can perform writeback even if that
275 * If the page is swapcache, write it back even if that would
276 * block, for some throttling. This happens by accident, because
277 * swap_backing_dev_info is bust: it doesn't reflect the
278 * congestion state of the swapdevs. Easy to fix, if needed.
279 * See swapfile.c:page_queue_congested().
281 if (!is_page_cache_freeable(page))
285 if (mapping->a_ops->writepage == NULL)
286 return PAGE_ACTIVATE;
287 if (!may_write_to_queue(mapping->backing_dev_info))
290 if (clear_page_dirty_for_io(page)) {
292 struct writeback_control wbc = {
293 .sync_mode = WB_SYNC_NONE,
294 .nr_to_write = SWAP_CLUSTER_MAX,
299 SetPageReclaim(page);
300 res = mapping->a_ops->writepage(page, &wbc);
302 handle_write_error(mapping, page, res);
303 if (res == WRITEPAGE_ACTIVATE) {
304 ClearPageReclaim(page);
305 return PAGE_ACTIVATE;
307 if (!PageWriteback(page)) {
308 /* synchronous write or broken a_ops? */
309 ClearPageReclaim(page);
318 struct scan_control {
319 /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
320 unsigned long nr_to_scan;
322 /* Incremented by the number of inactive pages that were scanned */
323 unsigned long nr_scanned;
325 /* Incremented by the number of pages reclaimed */
326 unsigned long nr_reclaimed;
328 unsigned long nr_mapped; /* From page_state */
330 /* Ask shrink_caches, or shrink_zone to scan at this priority */
331 unsigned int priority;
333 /* This context's GFP mask */
334 unsigned int gfp_mask;
340 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
342 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
344 LIST_HEAD(ret_pages);
345 struct pagevec freed_pvec;
351 pagevec_init(&freed_pvec, 1);
352 while (!list_empty(page_list)) {
353 struct address_space *mapping;
358 page = lru_to_page(page_list);
359 list_del(&page->lru);
361 if (TestSetPageLocked(page))
364 BUG_ON(PageActive(page));
366 if (PageWriteback(page))
370 /* Double the slab pressure for mapped and swapcache pages */
371 if (page_mapped(page) || PageSwapCache(page))
375 referenced = page_referenced(page);
376 if (referenced && page_mapping_inuse(page)) {
377 /* In active use or really unfreeable. Activate it. */
378 page_map_unlock(page);
379 goto activate_locked;
384 * Anonymous process memory has backing store?
385 * Try to allocate it some swap space here.
387 * XXX: implement swap clustering ?
389 if (PageAnon(page) && !PageSwapCache(page)) {
390 page_map_unlock(page);
391 if (!add_to_swap(page))
392 goto activate_locked;
395 #endif /* CONFIG_SWAP */
397 mapping = page_mapping(page);
398 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
399 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
402 * The page is mapped into the page tables of one or more
403 * processes. Try to unmap it here.
405 if (page_mapped(page) && mapping) {
406 switch (try_to_unmap(page)) {
408 page_map_unlock(page);
409 goto activate_locked;
411 page_map_unlock(page);
414 ; /* try to free the page below */
417 page_map_unlock(page);
419 if (PageDirty(page)) {
424 if (laptop_mode && !sc->may_writepage)
427 /* Page is dirty, try to write it out here */
428 switch(pageout(page, mapping)) {
432 goto activate_locked;
434 if (PageWriteback(page) || PageDirty(page))
437 * A synchronous write - probably a ramdisk. Go
438 * ahead and try to reclaim the page.
440 if (TestSetPageLocked(page))
442 if (PageDirty(page) || PageWriteback(page))
444 mapping = page_mapping(page);
446 ; /* try to free the page below */
451 * If the page has buffers, try to free the buffer mappings
452 * associated with this page. If we succeed we try to free
455 * We do this even if the page is PageDirty().
456 * try_to_release_page() does not perform I/O, but it is
457 * possible for a page to have PageDirty set, but it is actually
458 * clean (all its buffers are clean). This happens if the
459 * buffers were written out directly, with submit_bh(). ext3
460 * will do this, as well as the blockdev mapping.
461 * try_to_release_page() will discover that cleanness and will
462 * drop the buffers and mark the page clean - it can be freed.
464 * Rarely, pages can have buffers and no ->mapping. These are
465 * the pages which were not successfully invalidated in
466 * truncate_complete_page(). We try to drop those buffers here
467 * and if that worked, and the page is no longer mapped into
468 * process address space (page_count == 1) it can be freed.
469 * Otherwise, leave the page on the LRU so it is swappable.
471 if (PagePrivate(page)) {
472 if (!try_to_release_page(page, sc->gfp_mask))
473 goto activate_locked;
474 if (!mapping && page_count(page) == 1)
479 goto keep_locked; /* truncate got there first */
481 spin_lock_irq(&mapping->tree_lock);
484 * The non-racy check for busy page. It is critical to check
485 * PageDirty _after_ making sure that the page is freeable and
486 * not in use by anybody. (pagecache + us == 2)
488 if (page_count(page) != 2 || PageDirty(page)) {
489 spin_unlock_irq(&mapping->tree_lock);
494 if (PageSwapCache(page)) {
495 swp_entry_t swap = { .val = page->private };
496 __delete_from_swap_cache(page);
497 spin_unlock_irq(&mapping->tree_lock);
499 __put_page(page); /* The pagecache ref */
502 #endif /* CONFIG_SWAP */
504 __remove_from_page_cache(page);
505 spin_unlock_irq(&mapping->tree_lock);
511 if (!pagevec_add(&freed_pvec, page))
512 __pagevec_release_nonlru(&freed_pvec);
521 list_add(&page->lru, &ret_pages);
522 BUG_ON(PageLRU(page));
524 list_splice(&ret_pages, page_list);
525 if (pagevec_count(&freed_pvec))
526 __pagevec_release_nonlru(&freed_pvec);
527 mod_page_state(pgactivate, pgactivate);
528 sc->nr_reclaimed += reclaimed;
533 * zone->lru_lock is heavily contented. We relieve it by quickly privatising
534 * a batch of pages and working on them outside the lock. Any pages which were
535 * not freed will be added back to the LRU.
537 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
539 * For pagecache intensive workloads, the first loop here is the hottest spot
540 * in the kernel (apart from the copy_*_user functions).
542 static void shrink_cache(struct zone *zone, struct scan_control *sc)
544 LIST_HEAD(page_list);
546 int max_scan = sc->nr_to_scan;
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(&zone->inactive_list)) {
560 page = lru_to_page(&zone->inactive_list);
562 prefetchw_prev_lru_page(page,
563 &zone->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, &zone->inactive_list);
577 list_add(&page->lru, &page_list);
580 zone->nr_inactive -= nr_taken;
581 zone->pages_scanned += nr_taken;
582 spin_unlock_irq(&zone->lru_lock);
588 if (current_is_kswapd())
589 mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
591 mod_page_state_zone(zone, pgscan_direct, nr_scan);
592 nr_freed = shrink_list(&page_list, sc);
593 if (current_is_kswapd())
594 mod_page_state(kswapd_steal, nr_freed);
595 mod_page_state_zone(zone, pgsteal, 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))
607 add_page_to_active_list(zone, page);
609 add_page_to_inactive_list(zone, page);
610 if (!pagevec_add(&pvec, page)) {
611 spin_unlock_irq(&zone->lru_lock);
612 __pagevec_release(&pvec);
613 spin_lock_irq(&zone->lru_lock);
617 spin_unlock_irq(&zone->lru_lock);
619 pagevec_release(&pvec);
623 * This moves pages from the active list to the inactive list.
625 * We move them the other way if the page is referenced by one or more
626 * processes, from rmap.
628 * If the pages are mostly unmapped, the processing is fast and it is
629 * appropriate to hold zone->lru_lock across the whole operation. But if
630 * the pages are mapped, the processing is slow (page_referenced()) so we
631 * should drop zone->lru_lock around each page. It's impossible to balance
632 * this, so instead we remove the pages from the LRU while processing them.
633 * It is safe to rely on PG_active against the non-LRU pages in here because
634 * nobody will play with that bit on a non-LRU page.
636 * The downside is that we have to touch page->_count against each page.
637 * But we had to alter page->flags anyway.
640 refill_inactive_zone(struct zone *zone, struct scan_control *sc)
643 int pgdeactivate = 0;
645 int nr_pages = sc->nr_to_scan;
646 LIST_HEAD(l_hold); /* The pages which were snipped off */
647 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
648 LIST_HEAD(l_active); /* Pages to go onto the active_list */
651 int reclaim_mapped = 0;
658 spin_lock_irq(&zone->lru_lock);
659 while (pgscanned < nr_pages && !list_empty(&zone->active_list)) {
660 page = lru_to_page(&zone->active_list);
661 prefetchw_prev_lru_page(page, &zone->active_list, flags);
662 if (!TestClearPageLRU(page))
664 list_del(&page->lru);
665 if (get_page_testone(page)) {
667 * It was already free! release_pages() or put_page()
668 * are about to remove it from the LRU and free it. So
669 * put the refcount back and put the page back on the
674 list_add(&page->lru, &zone->active_list);
676 list_add(&page->lru, &l_hold);
681 zone->nr_active -= pgmoved;
682 spin_unlock_irq(&zone->lru_lock);
685 * `distress' is a measure of how much trouble we're having reclaiming
686 * pages. 0 -> no problems. 100 -> great trouble.
688 distress = 100 >> zone->prev_priority;
691 * The point of this algorithm is to decide when to start reclaiming
692 * mapped memory instead of just pagecache. Work out how much memory
695 mapped_ratio = (sc->nr_mapped * 100) / total_memory;
698 * Now decide how much we really want to unmap some pages. The mapped
699 * ratio is downgraded - just because there's a lot of mapped memory
700 * doesn't necessarily mean that page reclaim isn't succeeding.
702 * The distress ratio is important - we don't want to start going oom.
704 * A 100% value of vm_swappiness overrides this algorithm altogether.
706 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
709 * Now use this metric to decide whether to start moving mapped memory
710 * onto the inactive list.
712 if (swap_tendency >= 100)
715 while (!list_empty(&l_hold)) {
716 page = lru_to_page(&l_hold);
717 list_del(&page->lru);
718 if (page_mapped(page)) {
719 if (!reclaim_mapped) {
720 list_add(&page->lru, &l_active);
724 if (page_referenced(page)) {
725 page_map_unlock(page);
726 list_add(&page->lru, &l_active);
729 page_map_unlock(page);
732 * FIXME: need to consider page_count(page) here if/when we
733 * reap orphaned pages via the LRU (Daniel's locking stuff)
735 if (total_swap_pages == 0 && PageAnon(page)) {
736 list_add(&page->lru, &l_active);
739 list_add(&page->lru, &l_inactive);
742 pagevec_init(&pvec, 1);
744 spin_lock_irq(&zone->lru_lock);
745 while (!list_empty(&l_inactive)) {
746 page = lru_to_page(&l_inactive);
747 prefetchw_prev_lru_page(page, &l_inactive, flags);
748 if (TestSetPageLRU(page))
750 if (!TestClearPageActive(page))
752 list_move(&page->lru, &zone->inactive_list);
754 if (!pagevec_add(&pvec, page)) {
755 zone->nr_inactive += pgmoved;
756 spin_unlock_irq(&zone->lru_lock);
757 pgdeactivate += pgmoved;
759 if (buffer_heads_over_limit)
760 pagevec_strip(&pvec);
761 __pagevec_release(&pvec);
762 spin_lock_irq(&zone->lru_lock);
765 zone->nr_inactive += pgmoved;
766 pgdeactivate += pgmoved;
767 if (buffer_heads_over_limit) {
768 spin_unlock_irq(&zone->lru_lock);
769 pagevec_strip(&pvec);
770 spin_lock_irq(&zone->lru_lock);
774 while (!list_empty(&l_active)) {
775 page = lru_to_page(&l_active);
776 prefetchw_prev_lru_page(page, &l_active, flags);
777 if (TestSetPageLRU(page))
779 BUG_ON(!PageActive(page));
780 list_move(&page->lru, &zone->active_list);
782 if (!pagevec_add(&pvec, page)) {
783 zone->nr_active += pgmoved;
785 spin_unlock_irq(&zone->lru_lock);
786 __pagevec_release(&pvec);
787 spin_lock_irq(&zone->lru_lock);
790 zone->nr_active += pgmoved;
791 spin_unlock_irq(&zone->lru_lock);
792 pagevec_release(&pvec);
794 mod_page_state_zone(zone, pgrefill, pgscanned);
795 mod_page_state(pgdeactivate, pgdeactivate);
799 * Scan `nr_pages' from this zone. Returns the number of reclaimed pages.
800 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
803 shrink_zone(struct zone *zone, struct scan_control *sc)
805 unsigned long scan_active, scan_inactive;
808 scan_inactive = (zone->nr_active + zone->nr_inactive) >> sc->priority;
811 * Try to keep the active list 2/3 of the size of the cache. And
812 * make sure that refill_inactive is given a decent number of pages.
814 * The "scan_active + 1" here is important. With pagecache-intensive
815 * workloads the inactive list is huge, and `ratio' evaluates to zero
816 * all the time. Which pins the active list memory. So we add one to
817 * `scan_active' just to make sure that the kernel will slowly sift
818 * through the active list.
820 if (zone->nr_active >= 4*(zone->nr_inactive*2 + 1)) {
821 /* Don't scan more than 4 times the inactive list scan size */
822 scan_active = 4*scan_inactive;
824 unsigned long long tmp;
826 /* Cast to long long so the multiply doesn't overflow */
828 tmp = (unsigned long long)scan_inactive * zone->nr_active;
829 do_div(tmp, zone->nr_inactive*2 + 1);
830 scan_active = (unsigned long)tmp;
833 atomic_add(scan_active + 1, &zone->nr_scan_active);
834 count = atomic_read(&zone->nr_scan_active);
835 if (count >= SWAP_CLUSTER_MAX) {
836 atomic_set(&zone->nr_scan_active, 0);
837 sc->nr_to_scan = count;
838 refill_inactive_zone(zone, sc);
841 atomic_add(scan_inactive, &zone->nr_scan_inactive);
842 count = atomic_read(&zone->nr_scan_inactive);
843 if (count >= SWAP_CLUSTER_MAX) {
844 atomic_set(&zone->nr_scan_inactive, 0);
845 sc->nr_to_scan = count;
846 shrink_cache(zone, sc);
851 * This is the direct reclaim path, for page-allocating processes. We only
852 * try to reclaim pages from zones which will satisfy the caller's allocation
855 * We reclaim from a zone even if that zone is over pages_high. Because:
856 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
858 * b) The zones may be over pages_high but they must go *over* pages_high to
859 * satisfy the `incremental min' zone defense algorithm.
861 * Returns the number of reclaimed pages.
863 * If a zone is deemed to be full of pinned pages then just give it a light
864 * scan then give up on it.
867 shrink_caches(struct zone **zones, struct scan_control *sc)
871 for (i = 0; zones[i] != NULL; i++) {
872 struct zone *zone = zones[i];
874 zone->temp_priority = sc->priority;
875 if (zone->prev_priority > sc->priority)
876 zone->prev_priority = sc->priority;
878 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
879 continue; /* Let kswapd poll it */
881 shrink_zone(zone, sc);
886 * This is the main entry point to direct page reclaim.
888 * If a full scan of the inactive list fails to free enough memory then we
889 * are "out of memory" and something needs to be killed.
891 * If the caller is !__GFP_FS then the probability of a failure is reasonably
892 * high - the zone may be full of dirty or under-writeback pages, which this
893 * caller can't do much about. We kick pdflush and take explicit naps in the
894 * hope that some of these pages can be written. But if the allocating task
895 * holds filesystem locks which prevent writeout this might not work, and the
896 * allocation attempt will fail.
898 int try_to_free_pages(struct zone **zones,
899 unsigned int gfp_mask, unsigned int order)
903 int total_scanned = 0, total_reclaimed = 0;
904 struct reclaim_state *reclaim_state = current->reclaim_state;
905 struct scan_control sc;
908 sc.gfp_mask = gfp_mask;
909 sc.may_writepage = 0;
911 inc_page_state(allocstall);
913 for (i = 0; zones[i] != 0; i++)
914 zones[i]->temp_priority = DEF_PRIORITY;
916 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
917 sc.nr_mapped = read_page_state(nr_mapped);
920 sc.priority = priority;
921 shrink_caches(zones, &sc);
922 shrink_slab(sc.nr_scanned, gfp_mask);
924 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
925 reclaim_state->reclaimed_slab = 0;
927 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) {
931 total_scanned += sc.nr_scanned;
932 total_reclaimed += sc.nr_reclaimed;
935 * Try to write back as many pages as we just scanned. This
936 * tends to cause slow streaming writers to write data to the
937 * disk smoothly, at the dirtying rate, which is nice. But
938 * that's undesirable in laptop mode, where we *want* lumpy
939 * writeout. So in laptop mode, write out the whole world.
941 if (total_scanned > SWAP_CLUSTER_MAX + SWAP_CLUSTER_MAX/2) {
942 wakeup_bdflush(laptop_mode ? 0 : total_scanned);
943 sc.may_writepage = 1;
946 /* Take a nap, wait for some writeback to complete */
947 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
948 blk_congestion_wait(WRITE, HZ/10);
950 if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
953 for (i = 0; zones[i] != 0; i++)
954 zones[i]->prev_priority = zones[i]->temp_priority;
959 * For kswapd, balance_pgdat() will work across all this node's zones until
960 * they are all at pages_high.
962 * If `nr_pages' is non-zero then it is the number of pages which are to be
963 * reclaimed, regardless of the zone occupancies. This is a software suspend
966 * Returns the number of pages which were actually freed.
968 * There is special handling here for zones which are full of pinned pages.
969 * This can happen if the pages are all mlocked, or if they are all used by
970 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
971 * What we do is to detect the case where all pages in the zone have been
972 * scanned twice and there has been zero successful reclaim. Mark the zone as
973 * dead and from now on, only perform a short scan. Basically we're polling
974 * the zone for when the problem goes away.
976 * kswapd scans the zones in the highmem->normal->dma direction. It skips
977 * zones which have free_pages > pages_high, but once a zone is found to have
978 * free_pages <= pages_high, we scan that zone and the lower zones regardless
979 * of the number of free pages in the lower zones. This interoperates with
980 * the page allocator fallback scheme to ensure that aging of pages is balanced
983 static int balance_pgdat(pg_data_t *pgdat, int nr_pages)
985 int to_free = nr_pages;
988 int total_scanned = 0, total_reclaimed = 0;
989 struct reclaim_state *reclaim_state = current->reclaim_state;
990 struct scan_control sc;
992 sc.gfp_mask = GFP_KERNEL;
993 sc.may_writepage = 0;
994 sc.nr_mapped = read_page_state(nr_mapped);
996 inc_page_state(pageoutrun);
998 for (i = 0; i < pgdat->nr_zones; i++) {
999 struct zone *zone = pgdat->node_zones + i;
1001 zone->temp_priority = DEF_PRIORITY;
1004 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1005 int all_zones_ok = 1;
1006 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
1009 if (nr_pages == 0) {
1011 * Scan in the highmem->dma direction for the highest
1012 * zone which needs scanning
1014 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1015 struct zone *zone = pgdat->node_zones + i;
1017 if (zone->all_unreclaimable &&
1018 priority != DEF_PRIORITY)
1021 if (zone->free_pages <= zone->pages_high) {
1028 end_zone = pgdat->nr_zones - 1;
1032 * Now scan the zone in the dma->highmem direction, stopping
1033 * at the last zone which needs scanning.
1035 * We do this because the page allocator works in the opposite
1036 * direction. This prevents the page allocator from allocating
1037 * pages behind kswapd's direction of progress, which would
1038 * cause too much scanning of the lower zones.
1040 for (i = 0; i <= end_zone; i++) {
1041 struct zone *zone = pgdat->node_zones + i;
1043 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1046 if (nr_pages == 0) { /* Not software suspend */
1047 if (zone->free_pages <= zone->pages_high)
1050 zone->temp_priority = priority;
1051 if (zone->prev_priority > priority)
1052 zone->prev_priority = priority;
1054 sc.nr_reclaimed = 0;
1055 sc.priority = priority;
1056 shrink_zone(zone, &sc);
1057 reclaim_state->reclaimed_slab = 0;
1058 shrink_slab(sc.nr_scanned, GFP_KERNEL);
1059 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1060 total_reclaimed += sc.nr_reclaimed;
1061 if (zone->all_unreclaimable)
1063 if (zone->pages_scanned > zone->present_pages * 2)
1064 zone->all_unreclaimable = 1;
1066 * If we've done a decent amount of scanning and
1067 * the reclaim ratio is low, start doing writepage
1068 * even in laptop mode
1070 if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1071 total_scanned > total_reclaimed+total_reclaimed/2)
1072 sc.may_writepage = 1;
1074 if (nr_pages && to_free > total_reclaimed)
1075 continue; /* swsusp: need to do more work */
1077 break; /* kswapd: all done */
1079 * OK, kswapd is getting into trouble. Take a nap, then take
1080 * another pass across the zones.
1082 if (total_scanned && priority < DEF_PRIORITY - 2)
1083 blk_congestion_wait(WRITE, HZ/10);
1086 for (i = 0; i < pgdat->nr_zones; i++) {
1087 struct zone *zone = pgdat->node_zones + i;
1089 zone->prev_priority = zone->temp_priority;
1091 return total_reclaimed;
1095 * The background pageout daemon, started as a kernel thread
1096 * from the init process.
1098 * This basically trickles out pages so that we have _some_
1099 * free memory available even if there is no other activity
1100 * that frees anything up. This is needed for things like routing
1101 * etc, where we otherwise might have all activity going on in
1102 * asynchronous contexts that cannot page things out.
1104 * If there are applications that are active memory-allocators
1105 * (most normal use), this basically shouldn't matter.
1109 pg_data_t *pgdat = (pg_data_t*)p;
1110 struct task_struct *tsk = current;
1112 struct reclaim_state reclaim_state = {
1113 .reclaimed_slab = 0,
1117 daemonize("kswapd%d", pgdat->node_id);
1118 cpumask = node_to_cpumask(pgdat->node_id);
1119 if (!cpus_empty(cpumask))
1120 set_cpus_allowed(tsk, cpumask);
1121 current->reclaim_state = &reclaim_state;
1124 * Tell the memory management that we're a "memory allocator",
1125 * and that if we need more memory we should get access to it
1126 * regardless (see "__alloc_pages()"). "kswapd" should
1127 * never get caught in the normal page freeing logic.
1129 * (Kswapd normally doesn't need memory anyway, but sometimes
1130 * you need a small amount of memory in order to be able to
1131 * page out something else, and this flag essentially protects
1132 * us from recursively trying to free more memory as we're
1133 * trying to free the first piece of memory in the first place).
1135 tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
1138 if (current->flags & PF_FREEZE)
1139 refrigerator(PF_FREEZE);
1140 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1142 finish_wait(&pgdat->kswapd_wait, &wait);
1143 try_to_clip_inodes();
1145 balance_pgdat(pgdat, 0);
1150 * A zone is low on free memory, so wake its kswapd task to service it.
1152 void wakeup_kswapd(struct zone *zone)
1154 if (zone->free_pages > zone->pages_low)
1156 if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
1158 wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
1163 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed
1166 int shrink_all_memory(int nr_pages)
1169 int nr_to_free = nr_pages;
1171 struct reclaim_state reclaim_state = {
1172 .reclaimed_slab = 0,
1175 current->reclaim_state = &reclaim_state;
1176 for_each_pgdat(pgdat) {
1178 freed = balance_pgdat(pgdat, nr_to_free);
1180 nr_to_free -= freed;
1181 if (nr_to_free <= 0)
1184 current->reclaim_state = NULL;
1189 #ifdef CONFIG_HOTPLUG_CPU
1190 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1191 not required for correctness. So if the last cpu in a node goes
1192 away, we get changed to run anywhere: as the first one comes back,
1193 restore their cpu bindings. */
1194 static int __devinit cpu_callback(struct notifier_block *nfb,
1195 unsigned long action,
1201 if (action == CPU_ONLINE) {
1202 for_each_pgdat(pgdat) {
1203 mask = node_to_cpumask(pgdat->node_id);
1204 if (any_online_cpu(mask) != NR_CPUS)
1205 /* One of our CPUs online: restore mask */
1206 set_cpus_allowed(pgdat->kswapd, mask);
1211 #endif /* CONFIG_HOTPLUG_CPU */
1213 static int __init kswapd_init(void)
1217 for_each_pgdat(pgdat)
1219 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1220 total_memory = nr_free_pagecache_pages();
1221 hotcpu_notifier(cpu_callback, 0);
1225 module_init(kswapd_init)