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/pgalloc.h>
37 #include <asm/tlbflush.h>
38 #include <asm/div64.h>
40 #include <linux/swapops.h>
43 * From 0 .. 100. Higher means more swappy.
45 int vm_swappiness = 60;
46 static long total_memory;
50 void try_to_clip_inodes(void);
53 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
55 #ifdef ARCH_HAS_PREFETCH
56 #define prefetch_prev_lru_page(_page, _base, _field) \
58 if ((_page)->lru.prev != _base) { \
61 prev = lru_to_page(&(_page->lru)); \
62 prefetch(&prev->_field); \
66 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
69 #ifdef ARCH_HAS_PREFETCHW
70 #define prefetchw_prev_lru_page(_page, _base, _field) \
72 if ((_page)->lru.prev != _base) { \
75 prev = lru_to_page(&(_page->lru)); \
76 prefetchw(&prev->_field); \
80 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
84 * The list of shrinker callbacks used by to apply pressure to
89 struct list_head list;
90 int seeks; /* seeks to recreate an obj */
91 long nr; /* objs pending delete */
94 static LIST_HEAD(shrinker_list);
95 static DECLARE_MUTEX(shrinker_sem);
98 * Add a shrinker callback to be called from the vm
100 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
102 struct shrinker *shrinker;
104 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
106 shrinker->shrinker = theshrinker;
107 shrinker->seeks = seeks;
110 list_add(&shrinker->list, &shrinker_list);
116 EXPORT_SYMBOL(set_shrinker);
121 void remove_shrinker(struct shrinker *shrinker)
124 list_del(&shrinker->list);
129 EXPORT_SYMBOL(remove_shrinker);
131 #define SHRINK_BATCH 128
133 * Call the shrink functions to age shrinkable caches
135 * Here we assume it costs one seek to replace a lru page and that it also
136 * takes a seek to recreate a cache object. With this in mind we age equal
137 * percentages of the lru and ageable caches. This should balance the seeks
138 * generated by these structures.
140 * If the vm encounted mapped pages on the LRU it increase the pressure on
141 * slab to avoid swapping.
143 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
145 static int shrink_slab(unsigned long scanned, unsigned int gfp_mask)
147 struct shrinker *shrinker;
150 if (down_trylock(&shrinker_sem))
153 pages = nr_used_zone_pages();
154 list_for_each_entry(shrinker, &shrinker_list, list) {
155 unsigned long long delta;
157 delta = (4 * scanned) / shrinker->seeks;
158 delta *= (*shrinker->shrinker)(0, gfp_mask);
159 do_div(delta, pages + 1);
160 shrinker->nr += delta;
161 if (shrinker->nr < 0)
162 shrinker->nr = LONG_MAX; /* It wrapped! */
164 if (shrinker->nr <= SHRINK_BATCH)
166 while (shrinker->nr) {
167 long this_scan = shrinker->nr;
172 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
173 mod_page_state(slabs_scanned, this_scan);
174 shrinker->nr -= this_scan;
175 if (shrink_ret == -1)
184 /* Must be called with page's rmap lock held. */
185 static inline int page_mapping_inuse(struct page *page)
187 struct address_space *mapping;
189 /* Page is in somebody's page tables. */
190 if (page_mapped(page))
193 /* Be more reluctant to reclaim swapcache than pagecache */
194 if (PageSwapCache(page))
197 mapping = page_mapping(page);
201 /* File is mmap'd by somebody? */
202 return mapping_mapped(mapping);
205 static inline int is_page_cache_freeable(struct page *page)
207 return page_count(page) - !!PagePrivate(page) == 2;
210 static int may_write_to_queue(struct backing_dev_info *bdi)
212 if (current_is_kswapd())
214 if (current_is_pdflush()) /* This is unlikely, but why not... */
216 if (!bdi_write_congested(bdi))
218 if (bdi == current->backing_dev_info)
224 * We detected a synchronous write error writing a page out. Probably
225 * -ENOSPC. We need to propagate that into the address_space for a subsequent
226 * fsync(), msync() or close().
228 * The tricky part is that after writepage we cannot touch the mapping: nothing
229 * prevents it from being freed up. But we have a ref on the page and once
230 * that page is locked, the mapping is pinned.
232 * We're allowed to run sleeping lock_page() here because we know the caller has
235 static void handle_write_error(struct address_space *mapping,
236 struct page *page, int error)
239 if (page_mapping(page) == mapping) {
240 if (error == -ENOSPC)
241 set_bit(AS_ENOSPC, &mapping->flags);
243 set_bit(AS_EIO, &mapping->flags);
249 * shrink_list returns the number of reclaimed pages
252 shrink_list(struct list_head *page_list, unsigned int gfp_mask,
253 int *nr_scanned, int do_writepage)
255 LIST_HEAD(ret_pages);
256 struct pagevec freed_pvec;
262 pagevec_init(&freed_pvec, 1);
263 while (!list_empty(page_list)) {
264 struct address_space *mapping;
269 page = lru_to_page(page_list);
270 list_del(&page->lru);
272 if (TestSetPageLocked(page))
275 /* Double the slab pressure for mapped and swapcache pages */
276 if (page_mapped(page) || PageSwapCache(page))
279 BUG_ON(PageActive(page));
281 if (PageWriteback(page))
285 referenced = page_referenced(page);
286 if (referenced && page_mapping_inuse(page)) {
287 /* In active use or really unfreeable. Activate it. */
288 page_map_unlock(page);
289 goto activate_locked;
294 * Anonymous process memory has backing store?
295 * Try to allocate it some swap space here.
297 * XXX: implement swap clustering ?
299 if (PageAnon(page) && !PageSwapCache(page)) {
300 page_map_unlock(page);
301 if (!add_to_swap(page))
302 goto activate_locked;
305 #endif /* CONFIG_SWAP */
307 mapping = page_mapping(page);
308 may_enter_fs = (gfp_mask & __GFP_FS) ||
309 (PageSwapCache(page) && (gfp_mask & __GFP_IO));
312 * The page is mapped into the page tables of one or more
313 * processes. Try to unmap it here.
315 if (page_mapped(page) && mapping) {
316 switch (try_to_unmap(page)) {
318 page_map_unlock(page);
319 goto activate_locked;
321 page_map_unlock(page);
324 ; /* try to free the page below */
327 page_map_unlock(page);
330 * If the page is dirty, only perform writeback if that write
331 * will be non-blocking. To prevent this allocation from being
332 * stalled by pagecache activity. But note that there may be
333 * stalls if we need to run get_block(). We could test
334 * PagePrivate for that.
336 * If this process is currently in generic_file_write() against
337 * this page's queue, we can perform writeback even if that
340 * If the page is swapcache, write it back even if that would
341 * block, for some throttling. This happens by accident, because
342 * swap_backing_dev_info is bust: it doesn't reflect the
343 * congestion state of the swapdevs. Easy to fix, if needed.
344 * See swapfile.c:page_queue_congested().
346 if (PageDirty(page)) {
349 if (!is_page_cache_freeable(page))
353 if (mapping->a_ops->writepage == NULL)
354 goto activate_locked;
357 if (!may_write_to_queue(mapping->backing_dev_info))
359 if (laptop_mode && !do_writepage)
361 if (clear_page_dirty_for_io(page)) {
363 struct writeback_control wbc = {
364 .sync_mode = WB_SYNC_NONE,
365 .nr_to_write = SWAP_CLUSTER_MAX,
370 SetPageReclaim(page);
371 res = mapping->a_ops->writepage(page, &wbc);
373 handle_write_error(mapping, page, res);
374 if (res == WRITEPAGE_ACTIVATE) {
375 ClearPageReclaim(page);
376 goto activate_locked;
378 if (!PageWriteback(page)) {
379 /* synchronous write or broken a_ops? */
380 ClearPageReclaim(page);
387 * If the page has buffers, try to free the buffer mappings
388 * associated with this page. If we succeed we try to free
391 * We do this even if the page is PageDirty().
392 * try_to_release_page() does not perform I/O, but it is
393 * possible for a page to have PageDirty set, but it is actually
394 * clean (all its buffers are clean). This happens if the
395 * buffers were written out directly, with submit_bh(). ext3
396 * will do this, as well as the blockdev mapping.
397 * try_to_release_page() will discover that cleanness and will
398 * drop the buffers and mark the page clean - it can be freed.
400 * Rarely, pages can have buffers and no ->mapping. These are
401 * the pages which were not successfully invalidated in
402 * truncate_complete_page(). We try to drop those buffers here
403 * and if that worked, and the page is no longer mapped into
404 * process address space (page_count == 0) it can be freed.
405 * Otherwise, leave the page on the LRU so it is swappable.
407 if (PagePrivate(page)) {
408 if (!try_to_release_page(page, gfp_mask))
409 goto activate_locked;
410 if (!mapping && page_count(page) == 1)
415 goto keep_locked; /* truncate got there first */
417 spin_lock_irq(&mapping->tree_lock);
420 * The non-racy check for busy page. It is critical to check
421 * PageDirty _after_ making sure that the page is freeable and
422 * not in use by anybody. (pagecache + us == 2)
424 if (page_count(page) != 2 || PageDirty(page)) {
425 spin_unlock_irq(&mapping->tree_lock);
430 if (PageSwapCache(page)) {
431 swp_entry_t swap = { .val = page->private };
432 __delete_from_swap_cache(page);
433 spin_unlock_irq(&mapping->tree_lock);
435 __put_page(page); /* The pagecache ref */
438 #endif /* CONFIG_SWAP */
440 __remove_from_page_cache(page);
441 spin_unlock_irq(&mapping->tree_lock);
447 if (!pagevec_add(&freed_pvec, page))
448 __pagevec_release_nonlru(&freed_pvec);
457 list_add(&page->lru, &ret_pages);
458 BUG_ON(PageLRU(page));
460 list_splice(&ret_pages, page_list);
461 if (pagevec_count(&freed_pvec))
462 __pagevec_release_nonlru(&freed_pvec);
463 mod_page_state(pgactivate, pgactivate);
468 * zone->lru_lock is heavily contented. We relieve it by quickly privatising
469 * a batch of pages and working on them outside the lock. Any pages which were
470 * not freed will be added back to the LRU.
472 * shrink_cache() is passed the number of pages to scan and returns the number
473 * of pages which were reclaimed.
475 * For pagecache intensive workloads, the first loop here is the hottest spot
476 * in the kernel (apart from the copy_*_user functions).
479 shrink_cache(struct zone *zone, unsigned int gfp_mask,
480 int max_scan, int *total_scanned, int do_writepage)
482 LIST_HEAD(page_list);
486 pagevec_init(&pvec, 1);
489 spin_lock_irq(&zone->lru_lock);
490 while (max_scan > 0) {
496 while (nr_scan++ < SWAP_CLUSTER_MAX &&
497 !list_empty(&zone->inactive_list)) {
498 page = lru_to_page(&zone->inactive_list);
500 prefetchw_prev_lru_page(page,
501 &zone->inactive_list, flags);
503 if (!TestClearPageLRU(page))
505 list_del(&page->lru);
506 if (get_page_testone(page)) {
508 * It is being freed elsewhere
512 list_add(&page->lru, &zone->inactive_list);
515 list_add(&page->lru, &page_list);
518 zone->nr_inactive -= nr_taken;
519 zone->pages_scanned += nr_taken;
520 spin_unlock_irq(&zone->lru_lock);
526 if (current_is_kswapd())
527 mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
529 mod_page_state_zone(zone, pgscan_direct, nr_scan);
530 nr_freed = shrink_list(&page_list, gfp_mask,
531 total_scanned, do_writepage);
532 *total_scanned += nr_taken;
533 if (current_is_kswapd())
534 mod_page_state(kswapd_steal, nr_freed);
535 mod_page_state_zone(zone, pgsteal, nr_freed);
538 if (nr_freed <= 0 && list_empty(&page_list))
541 spin_lock_irq(&zone->lru_lock);
543 * Put back any unfreeable pages.
545 while (!list_empty(&page_list)) {
546 page = lru_to_page(&page_list);
547 if (TestSetPageLRU(page))
549 list_del(&page->lru);
550 if (PageActive(page))
551 add_page_to_active_list(zone, page);
553 add_page_to_inactive_list(zone, page);
554 if (!pagevec_add(&pvec, page)) {
555 spin_unlock_irq(&zone->lru_lock);
556 __pagevec_release(&pvec);
557 spin_lock_irq(&zone->lru_lock);
561 spin_unlock_irq(&zone->lru_lock);
563 pagevec_release(&pvec);
568 * This moves pages from the active list to the inactive list.
570 * We move them the other way if the page is referenced by one or more
571 * processes, from rmap.
573 * If the pages are mostly unmapped, the processing is fast and it is
574 * appropriate to hold zone->lru_lock across the whole operation. But if
575 * the pages are mapped, the processing is slow (page_referenced()) so we
576 * should drop zone->lru_lock around each page. It's impossible to balance
577 * this, so instead we remove the pages from the LRU while processing them.
578 * It is safe to rely on PG_active against the non-LRU pages in here because
579 * nobody will play with that bit on a non-LRU page.
581 * The downside is that we have to touch page->_count against each page.
582 * But we had to alter page->flags anyway.
585 refill_inactive_zone(struct zone *zone, const int nr_pages_in,
586 struct page_state *ps)
589 int pgdeactivate = 0;
590 int nr_pages = nr_pages_in;
591 LIST_HEAD(l_hold); /* The pages which were snipped off */
592 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
593 LIST_HEAD(l_active); /* Pages to go onto the active_list */
596 int reclaim_mapped = 0;
603 spin_lock_irq(&zone->lru_lock);
604 while (nr_pages && !list_empty(&zone->active_list)) {
605 page = lru_to_page(&zone->active_list);
606 prefetchw_prev_lru_page(page, &zone->active_list, flags);
607 if (!TestClearPageLRU(page))
609 list_del(&page->lru);
610 if (get_page_testone(page)) {
612 * It was already free! release_pages() or put_page()
613 * are about to remove it from the LRU and free it. So
614 * put the refcount back and put the page back on the
619 list_add(&page->lru, &zone->active_list);
621 list_add(&page->lru, &l_hold);
626 zone->nr_active -= pgmoved;
627 spin_unlock_irq(&zone->lru_lock);
630 * `distress' is a measure of how much trouble we're having reclaiming
631 * pages. 0 -> no problems. 100 -> great trouble.
633 distress = 100 >> zone->prev_priority;
636 * The point of this algorithm is to decide when to start reclaiming
637 * mapped memory instead of just pagecache. Work out how much memory
640 mapped_ratio = (ps->nr_mapped * 100) / total_memory;
643 * Now decide how much we really want to unmap some pages. The mapped
644 * ratio is downgraded - just because there's a lot of mapped memory
645 * doesn't necessarily mean that page reclaim isn't succeeding.
647 * The distress ratio is important - we don't want to start going oom.
649 * A 100% value of vm_swappiness overrides this algorithm altogether.
651 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
654 * Now use this metric to decide whether to start moving mapped memory
655 * onto the inactive list.
657 if (swap_tendency >= 100)
660 while (!list_empty(&l_hold)) {
661 page = lru_to_page(&l_hold);
662 list_del(&page->lru);
663 if (page_mapped(page)) {
664 if (!reclaim_mapped) {
665 list_add(&page->lru, &l_active);
669 if (page_referenced(page)) {
670 page_map_unlock(page);
671 list_add(&page->lru, &l_active);
674 page_map_unlock(page);
677 * FIXME: need to consider page_count(page) here if/when we
678 * reap orphaned pages via the LRU (Daniel's locking stuff)
680 if (total_swap_pages == 0 && PageAnon(page)) {
681 list_add(&page->lru, &l_active);
684 list_add(&page->lru, &l_inactive);
687 pagevec_init(&pvec, 1);
689 spin_lock_irq(&zone->lru_lock);
690 while (!list_empty(&l_inactive)) {
691 page = lru_to_page(&l_inactive);
692 prefetchw_prev_lru_page(page, &l_inactive, flags);
693 if (TestSetPageLRU(page))
695 if (!TestClearPageActive(page))
697 list_move(&page->lru, &zone->inactive_list);
699 if (!pagevec_add(&pvec, page)) {
700 zone->nr_inactive += pgmoved;
701 spin_unlock_irq(&zone->lru_lock);
702 pgdeactivate += pgmoved;
704 if (buffer_heads_over_limit)
705 pagevec_strip(&pvec);
706 __pagevec_release(&pvec);
707 spin_lock_irq(&zone->lru_lock);
710 zone->nr_inactive += pgmoved;
711 pgdeactivate += pgmoved;
712 if (buffer_heads_over_limit) {
713 spin_unlock_irq(&zone->lru_lock);
714 pagevec_strip(&pvec);
715 spin_lock_irq(&zone->lru_lock);
719 while (!list_empty(&l_active)) {
720 page = lru_to_page(&l_active);
721 prefetchw_prev_lru_page(page, &l_active, flags);
722 if (TestSetPageLRU(page))
724 BUG_ON(!PageActive(page));
725 list_move(&page->lru, &zone->active_list);
727 if (!pagevec_add(&pvec, page)) {
728 zone->nr_active += pgmoved;
730 spin_unlock_irq(&zone->lru_lock);
731 __pagevec_release(&pvec);
732 spin_lock_irq(&zone->lru_lock);
735 zone->nr_active += pgmoved;
736 spin_unlock_irq(&zone->lru_lock);
737 pagevec_release(&pvec);
739 mod_page_state_zone(zone, pgrefill, nr_pages_in - nr_pages);
740 mod_page_state(pgdeactivate, pgdeactivate);
744 * Scan `nr_pages' from this zone. Returns the number of reclaimed pages.
745 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
748 shrink_zone(struct zone *zone, int max_scan, unsigned int gfp_mask,
749 int *total_scanned, struct page_state *ps, int do_writepage)
751 unsigned long scan_active;
755 * Try to keep the active list 2/3 of the size of the cache. And
756 * make sure that refill_inactive is given a decent number of pages.
758 * The "scan_active + 1" here is important. With pagecache-intensive
759 * workloads the inactive list is huge, and `ratio' evaluates to zero
760 * all the time. Which pins the active list memory. So we add one to
761 * `scan_active' just to make sure that the kernel will slowly sift
762 * through the active list.
764 if (zone->nr_active >= 4*(zone->nr_inactive*2 + 1)) {
765 /* Don't scan more than 4 times the inactive list scan size */
766 scan_active = 4*max_scan;
768 unsigned long long tmp;
770 /* Cast to long long so the multiply doesn't overflow */
772 tmp = (unsigned long long)max_scan * zone->nr_active;
773 do_div(tmp, zone->nr_inactive*2 + 1);
774 scan_active = (unsigned long)tmp;
777 atomic_add(scan_active + 1, &zone->nr_scan_active);
778 count = atomic_read(&zone->nr_scan_active);
779 if (count >= SWAP_CLUSTER_MAX) {
780 atomic_set(&zone->nr_scan_active, 0);
781 refill_inactive_zone(zone, count, ps);
784 atomic_add(max_scan, &zone->nr_scan_inactive);
785 count = atomic_read(&zone->nr_scan_inactive);
786 if (count >= SWAP_CLUSTER_MAX) {
787 atomic_set(&zone->nr_scan_inactive, 0);
788 return shrink_cache(zone, gfp_mask, count,
789 total_scanned, do_writepage);
795 * This is the direct reclaim path, for page-allocating processes. We only
796 * try to reclaim pages from zones which will satisfy the caller's allocation
799 * We reclaim from a zone even if that zone is over pages_high. Because:
800 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
802 * b) The zones may be over pages_high but they must go *over* pages_high to
803 * satisfy the `incremental min' zone defense algorithm.
805 * Returns the number of reclaimed pages.
807 * If a zone is deemed to be full of pinned pages then just give it a light
808 * scan then give up on it.
811 shrink_caches(struct zone **zones, int priority, int *total_scanned,
812 int gfp_mask, struct page_state *ps, int do_writepage)
817 for (i = 0; zones[i] != NULL; i++) {
818 struct zone *zone = zones[i];
821 if (zone->free_pages < zone->pages_high)
822 zone->temp_priority = priority;
824 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
825 continue; /* Let kswapd poll it */
827 max_scan = (zone->nr_active + zone->nr_inactive) >> priority;
828 ret += shrink_zone(zone, max_scan, gfp_mask,
829 total_scanned, ps, do_writepage);
835 * This is the main entry point to direct page reclaim.
837 * If a full scan of the inactive list fails to free enough memory then we
838 * are "out of memory" and something needs to be killed.
840 * If the caller is !__GFP_FS then the probability of a failure is reasonably
841 * high - the zone may be full of dirty or under-writeback pages, which this
842 * caller can't do much about. So for !__GFP_FS callers, we just perform a
843 * small LRU walk and if that didn't work out, fail the allocation back to the
844 * caller. GFP_NOFS allocators need to know how to deal with it. Kicking
845 * bdflush, waiting and retrying will work.
847 * This is a fairly lame algorithm - it can result in excessive CPU burning and
848 * excessive rotation of the inactive list, which is _supposed_ to be an LRU,
851 int try_to_free_pages(struct zone **zones,
852 unsigned int gfp_mask, unsigned int order)
856 int nr_reclaimed = 0;
857 struct reclaim_state *reclaim_state = current->reclaim_state;
859 unsigned long total_scanned = 0;
860 int do_writepage = 0;
862 inc_page_state(allocstall);
864 for (i = 0; zones[i] != 0; i++)
865 zones[i]->temp_priority = DEF_PRIORITY;
867 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
869 struct page_state ps;
872 nr_reclaimed += shrink_caches(zones, priority, &scanned,
873 gfp_mask, &ps, do_writepage);
874 shrink_slab(scanned, gfp_mask);
876 nr_reclaimed += reclaim_state->reclaimed_slab;
877 reclaim_state->reclaimed_slab = 0;
879 if (nr_reclaimed >= SWAP_CLUSTER_MAX) {
883 if (!(gfp_mask & __GFP_FS))
884 break; /* Let the caller handle it */
886 * Try to write back as many pages as we just scanned. This
887 * tends to cause slow streaming writers to write data to the
888 * disk smoothly, at the dirtying rate, which is nice. But
889 * that's undesirable in laptop mode, where we *want* lumpy
890 * writeout. So in laptop mode, write out the whole world.
892 total_scanned += scanned;
893 if (total_scanned > SWAP_CLUSTER_MAX + SWAP_CLUSTER_MAX/2) {
894 wakeup_bdflush(laptop_mode ? 0 : total_scanned);
898 /* Take a nap, wait for some writeback to complete */
899 if (scanned && priority < DEF_PRIORITY - 2)
900 blk_congestion_wait(WRITE, HZ/10);
902 if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
905 for (i = 0; zones[i] != 0; i++)
906 zones[i]->prev_priority = zones[i]->temp_priority;
911 * For kswapd, balance_pgdat() will work across all this node's zones until
912 * they are all at pages_high.
914 * If `nr_pages' is non-zero then it is the number of pages which are to be
915 * reclaimed, regardless of the zone occupancies. This is a software suspend
918 * Returns the number of pages which were actually freed.
920 * There is special handling here for zones which are full of pinned pages.
921 * This can happen if the pages are all mlocked, or if they are all used by
922 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
923 * What we do is to detect the case where all pages in the zone have been
924 * scanned twice and there has been zero successful reclaim. Mark the zone as
925 * dead and from now on, only perform a short scan. Basically we're polling
926 * the zone for when the problem goes away.
928 * kswapd scans the zones in the highmem->normal->dma direction. It skips
929 * zones which have free_pages > pages_high, but once a zone is found to have
930 * free_pages <= pages_high, we scan that zone and the lower zones regardless
931 * of the number of free pages in the lower zones. This interoperates with
932 * the page allocator fallback scheme to ensure that aging of pages is balanced
935 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, struct page_state *ps)
937 int to_free = nr_pages;
940 struct reclaim_state *reclaim_state = current->reclaim_state;
941 unsigned long total_scanned = 0;
942 unsigned long total_reclaimed = 0;
943 int do_writepage = 0;
945 inc_page_state(pageoutrun);
947 for (i = 0; i < pgdat->nr_zones; i++) {
948 struct zone *zone = pgdat->node_zones + i;
950 zone->temp_priority = DEF_PRIORITY;
953 for (priority = DEF_PRIORITY; priority; priority--) {
954 int all_zones_ok = 1;
955 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
960 * Scan in the highmem->dma direction for the highest
961 * zone which needs scanning
963 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
964 struct zone *zone = pgdat->node_zones + i;
966 if (zone->all_unreclaimable &&
967 priority != DEF_PRIORITY)
970 if (zone->free_pages <= zone->pages_high) {
977 end_zone = pgdat->nr_zones - 1;
981 * Now scan the zone in the dma->highmem direction, stopping
982 * at the last zone which needs scanning.
984 * We do this because the page allocator works in the opposite
985 * direction. This prevents the page allocator from allocating
986 * pages behind kswapd's direction of progress, which would
987 * cause too much scanning of the lower zones.
989 for (i = 0; i <= end_zone; i++) {
990 struct zone *zone = pgdat->node_zones + i;
995 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
998 if (nr_pages == 0) { /* Not software suspend */
999 if (zone->free_pages <= zone->pages_high)
1002 zone->temp_priority = priority;
1003 max_scan = (zone->nr_active + zone->nr_inactive)
1005 reclaimed = shrink_zone(zone, max_scan, GFP_KERNEL,
1006 &scanned, ps, do_writepage);
1007 total_scanned += scanned;
1008 reclaim_state->reclaimed_slab = 0;
1009 shrink_slab(scanned, GFP_KERNEL);
1010 reclaimed += reclaim_state->reclaimed_slab;
1011 total_reclaimed += reclaimed;
1012 to_free -= reclaimed;
1013 if (zone->all_unreclaimable)
1015 if (zone->pages_scanned > zone->present_pages * 2)
1016 zone->all_unreclaimable = 1;
1018 * If we've done a decent amount of scanning and
1019 * the reclaim ratio is low, start doing writepage
1020 * even in laptop mode
1022 if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1023 total_scanned > total_reclaimed+total_reclaimed/2)
1026 if (nr_pages && to_free > 0)
1027 continue; /* swsusp: need to do more work */
1029 break; /* kswapd: all done */
1031 * OK, kswapd is getting into trouble. Take a nap, then take
1032 * another pass across the zones.
1034 if (total_scanned && priority < DEF_PRIORITY - 2)
1035 blk_congestion_wait(WRITE, HZ/10);
1038 for (i = 0; i < pgdat->nr_zones; i++) {
1039 struct zone *zone = pgdat->node_zones + i;
1041 zone->prev_priority = zone->temp_priority;
1043 return total_reclaimed;
1047 * The background pageout daemon, started as a kernel thread
1048 * from the init process.
1050 * This basically trickles out pages so that we have _some_
1051 * free memory available even if there is no other activity
1052 * that frees anything up. This is needed for things like routing
1053 * etc, where we otherwise might have all activity going on in
1054 * asynchronous contexts that cannot page things out.
1056 * If there are applications that are active memory-allocators
1057 * (most normal use), this basically shouldn't matter.
1061 pg_data_t *pgdat = (pg_data_t*)p;
1062 struct task_struct *tsk = current;
1064 struct reclaim_state reclaim_state = {
1065 .reclaimed_slab = 0,
1069 daemonize("kswapd%d", pgdat->node_id);
1070 cpumask = node_to_cpumask(pgdat->node_id);
1071 if (!cpus_empty(cpumask))
1072 set_cpus_allowed(tsk, cpumask);
1073 current->reclaim_state = &reclaim_state;
1076 * Tell the memory management that we're a "memory allocator",
1077 * and that if we need more memory we should get access to it
1078 * regardless (see "__alloc_pages()"). "kswapd" should
1079 * never get caught in the normal page freeing logic.
1081 * (Kswapd normally doesn't need memory anyway, but sometimes
1082 * you need a small amount of memory in order to be able to
1083 * page out something else, and this flag essentially protects
1084 * us from recursively trying to free more memory as we're
1085 * trying to free the first piece of memory in the first place).
1087 tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
1090 struct page_state ps;
1092 if (current->flags & PF_FREEZE)
1093 refrigerator(PF_FREEZE);
1094 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1096 finish_wait(&pgdat->kswapd_wait, &wait);
1097 try_to_clip_inodes();
1098 get_page_state(&ps);
1099 balance_pgdat(pgdat, 0, &ps);
1104 * A zone is low on free memory, so wake its kswapd task to service it.
1106 void wakeup_kswapd(struct zone *zone)
1108 if (zone->free_pages > zone->pages_low)
1110 if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
1112 wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
1117 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed
1120 int shrink_all_memory(int nr_pages)
1123 int nr_to_free = nr_pages;
1125 struct reclaim_state reclaim_state = {
1126 .reclaimed_slab = 0,
1129 current->reclaim_state = &reclaim_state;
1130 for_each_pgdat(pgdat) {
1132 struct page_state ps;
1134 get_page_state(&ps);
1135 freed = balance_pgdat(pgdat, nr_to_free, &ps);
1137 nr_to_free -= freed;
1138 if (nr_to_free <= 0)
1141 current->reclaim_state = NULL;
1146 #ifdef CONFIG_HOTPLUG_CPU
1147 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1148 not required for correctness. So if the last cpu in a node goes
1149 away, we get changed to run anywhere: as the first one comes back,
1150 restore their cpu bindings. */
1151 static int __devinit cpu_callback(struct notifier_block *nfb,
1152 unsigned long action,
1158 if (action == CPU_ONLINE) {
1159 for_each_pgdat(pgdat) {
1160 mask = node_to_cpumask(pgdat->node_id);
1161 if (any_online_cpu(mask) != NR_CPUS)
1162 /* One of our CPUs online: restore mask */
1163 set_cpus_allowed(pgdat->kswapd, mask);
1168 #endif /* CONFIG_HOTPLUG_CPU */
1170 static int __init kswapd_init(void)
1174 for_each_pgdat(pgdat)
1176 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1177 total_memory = nr_free_pagecache_pages();
1178 hotcpu_notifier(cpu_callback, 0);
1182 module_init(kswapd_init)