4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
6 * Swap reorganised 29.12.95, Stephen Tweedie.
7 * kswapd added: 7.1.96 sct
8 * Removed kswapd_ctl limits, and swap out as many pages as needed
9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11 * Multiqueue VM started 5.8.00, Rik van Riel.
15 #include <linux/module.h>
16 #include <linux/slab.h>
17 #include <linux/kernel_stat.h>
18 #include <linux/swap.h>
19 #include <linux/pagemap.h>
20 #include <linux/init.h>
21 #include <linux/highmem.h>
22 #include <linux/file.h>
23 #include <linux/writeback.h>
24 #include <linux/blkdev.h>
25 #include <linux/buffer_head.h> /* for try_to_release_page(),
26 buffer_heads_over_limit */
27 #include <linux/mm_inline.h>
28 #include <linux/pagevec.h>
29 #include <linux/backing-dev.h>
30 #include <linux/rmap.h>
31 #include <linux/topology.h>
32 #include <linux/cpu.h>
33 #include <linux/cpuset.h>
34 #include <linux/notifier.h>
35 #include <linux/rwsem.h>
37 #include <asm/tlbflush.h>
38 #include <asm/div64.h>
40 #include <linux/swapops.h>
42 /* possible outcome of pageout() */
44 /* failed to write page out, page is locked */
46 /* move page to the active list, page is locked */
48 /* page has been sent to the disk successfully, page is unlocked */
50 /* page is clean and locked */
55 /* Incremented by the number of inactive pages that were scanned */
56 unsigned long nr_scanned;
58 /* Incremented by the number of pages reclaimed */
59 unsigned long nr_reclaimed;
61 unsigned long nr_mapped; /* From page_state */
63 /* This context's GFP mask */
68 /* Can pages be swapped as part of reclaim? */
71 /* This context's SWAP_CLUSTER_MAX. If freeing memory for
72 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
73 * In this context, it doesn't matter that we scan the
74 * whole list at once. */
79 * The list of shrinker callbacks used by to apply pressure to
84 struct list_head list;
85 int seeks; /* seeks to recreate an obj */
86 long nr; /* objs pending delete */
89 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
91 #ifdef ARCH_HAS_PREFETCH
92 #define prefetch_prev_lru_page(_page, _base, _field) \
94 if ((_page)->lru.prev != _base) { \
97 prev = lru_to_page(&(_page->lru)); \
98 prefetch(&prev->_field); \
102 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
105 #ifdef ARCH_HAS_PREFETCHW
106 #define prefetchw_prev_lru_page(_page, _base, _field) \
108 if ((_page)->lru.prev != _base) { \
111 prev = lru_to_page(&(_page->lru)); \
112 prefetchw(&prev->_field); \
116 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
120 * From 0 .. 100. Higher means more swappy.
122 int vm_swappiness = 60;
123 static long total_memory;
125 static LIST_HEAD(shrinker_list);
126 static DECLARE_RWSEM(shrinker_rwsem);
129 * Add a shrinker callback to be called from the vm
131 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
133 struct shrinker *shrinker;
135 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
137 shrinker->shrinker = theshrinker;
138 shrinker->seeks = seeks;
140 down_write(&shrinker_rwsem);
141 list_add_tail(&shrinker->list, &shrinker_list);
142 up_write(&shrinker_rwsem);
146 EXPORT_SYMBOL(set_shrinker);
151 void remove_shrinker(struct shrinker *shrinker)
153 down_write(&shrinker_rwsem);
154 list_del(&shrinker->list);
155 up_write(&shrinker_rwsem);
158 EXPORT_SYMBOL(remove_shrinker);
160 #define SHRINK_BATCH 128
162 * Call the shrink functions to age shrinkable caches
164 * Here we assume it costs one seek to replace a lru page and that it also
165 * takes a seek to recreate a cache object. With this in mind we age equal
166 * percentages of the lru and ageable caches. This should balance the seeks
167 * generated by these structures.
169 * If the vm encounted mapped pages on the LRU it increase the pressure on
170 * slab to avoid swapping.
172 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
174 * `lru_pages' represents the number of on-LRU pages in all the zones which
175 * are eligible for the caller's allocation attempt. It is used for balancing
176 * slab reclaim versus page reclaim.
178 * Returns the number of slab objects which we shrunk.
180 int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
182 struct shrinker *shrinker;
186 scanned = SWAP_CLUSTER_MAX;
188 if (!down_read_trylock(&shrinker_rwsem))
189 return 1; /* Assume we'll be able to shrink next time */
191 list_for_each_entry(shrinker, &shrinker_list, list) {
192 unsigned long long delta;
193 unsigned long total_scan;
194 unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
196 delta = (4 * scanned) / shrinker->seeks;
198 do_div(delta, lru_pages + 1);
199 shrinker->nr += delta;
200 if (shrinker->nr < 0) {
201 printk(KERN_ERR "%s: nr=%ld\n",
202 __FUNCTION__, shrinker->nr);
203 shrinker->nr = max_pass;
207 * Avoid risking looping forever due to too large nr value:
208 * never try to free more than twice the estimate number of
211 if (shrinker->nr > max_pass * 2)
212 shrinker->nr = max_pass * 2;
214 total_scan = shrinker->nr;
217 while (total_scan >= SHRINK_BATCH) {
218 long this_scan = SHRINK_BATCH;
222 nr_before = (*shrinker->shrinker)(0, gfp_mask);
223 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
224 if (shrink_ret == -1)
226 if (shrink_ret < nr_before)
227 ret += nr_before - shrink_ret;
228 mod_page_state(slabs_scanned, this_scan);
229 total_scan -= this_scan;
234 shrinker->nr += total_scan;
236 up_read(&shrinker_rwsem);
240 /* Called without lock on whether page is mapped, so answer is unstable */
241 static inline int page_mapping_inuse(struct page *page)
243 struct address_space *mapping;
245 /* Page is in somebody's page tables. */
246 if (page_mapped(page))
249 /* Be more reluctant to reclaim swapcache than pagecache */
250 if (PageSwapCache(page))
253 mapping = page_mapping(page);
257 /* File is mmap'd by somebody? */
258 return mapping_mapped(mapping);
261 static inline int is_page_cache_freeable(struct page *page)
263 return page_count(page) - !!PagePrivate(page) == 2;
266 static int may_write_to_queue(struct backing_dev_info *bdi)
268 if (current->flags & PF_SWAPWRITE)
270 if (!bdi_write_congested(bdi))
272 if (bdi == current->backing_dev_info)
278 * We detected a synchronous write error writing a page out. Probably
279 * -ENOSPC. We need to propagate that into the address_space for a subsequent
280 * fsync(), msync() or close().
282 * The tricky part is that after writepage we cannot touch the mapping: nothing
283 * prevents it from being freed up. But we have a ref on the page and once
284 * that page is locked, the mapping is pinned.
286 * We're allowed to run sleeping lock_page() here because we know the caller has
289 static void handle_write_error(struct address_space *mapping,
290 struct page *page, int error)
293 if (page_mapping(page) == mapping) {
294 if (error == -ENOSPC)
295 set_bit(AS_ENOSPC, &mapping->flags);
297 set_bit(AS_EIO, &mapping->flags);
303 * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
305 static pageout_t pageout(struct page *page, struct address_space *mapping)
308 * If the page is dirty, only perform writeback if that write
309 * will be non-blocking. To prevent this allocation from being
310 * stalled by pagecache activity. But note that there may be
311 * stalls if we need to run get_block(). We could test
312 * PagePrivate for that.
314 * If this process is currently in generic_file_write() against
315 * this page's queue, we can perform writeback even if that
318 * If the page is swapcache, write it back even if that would
319 * block, for some throttling. This happens by accident, because
320 * swap_backing_dev_info is bust: it doesn't reflect the
321 * congestion state of the swapdevs. Easy to fix, if needed.
322 * See swapfile.c:page_queue_congested().
324 if (!is_page_cache_freeable(page))
328 * Some data journaling orphaned pages can have
329 * page->mapping == NULL while being dirty with clean buffers.
331 if (PagePrivate(page)) {
332 if (try_to_free_buffers(page)) {
333 ClearPageDirty(page);
334 printk("%s: orphaned page\n", __FUNCTION__);
340 if (mapping->a_ops->writepage == NULL)
341 return PAGE_ACTIVATE;
342 if (!may_write_to_queue(mapping->backing_dev_info))
345 if (clear_page_dirty_for_io(page)) {
347 struct writeback_control wbc = {
348 .sync_mode = WB_SYNC_NONE,
349 .nr_to_write = SWAP_CLUSTER_MAX,
354 SetPageReclaim(page);
355 res = mapping->a_ops->writepage(page, &wbc);
357 handle_write_error(mapping, page, res);
358 if (res == AOP_WRITEPAGE_ACTIVATE) {
359 ClearPageReclaim(page);
360 return PAGE_ACTIVATE;
362 if (!PageWriteback(page)) {
363 /* synchronous write or broken a_ops? */
364 ClearPageReclaim(page);
373 static int remove_mapping(struct address_space *mapping, struct page *page)
376 return 0; /* truncate got there first */
378 write_lock_irq(&mapping->tree_lock);
381 * The non-racy check for busy page. It is critical to check
382 * PageDirty _after_ making sure that the page is freeable and
383 * not in use by anybody. (pagecache + us == 2)
385 if (unlikely(page_count(page) != 2))
388 if (unlikely(PageDirty(page)))
391 if (PageSwapCache(page)) {
392 swp_entry_t swap = { .val = page_private(page) };
393 __delete_from_swap_cache(page);
394 write_unlock_irq(&mapping->tree_lock);
396 __put_page(page); /* The pagecache ref */
400 __remove_from_page_cache(page);
401 write_unlock_irq(&mapping->tree_lock);
406 write_unlock_irq(&mapping->tree_lock);
411 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
413 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
415 LIST_HEAD(ret_pages);
416 struct pagevec freed_pvec;
422 pagevec_init(&freed_pvec, 1);
423 while (!list_empty(page_list)) {
424 struct address_space *mapping;
431 page = lru_to_page(page_list);
432 list_del(&page->lru);
434 if (TestSetPageLocked(page))
437 BUG_ON(PageActive(page));
441 if (!sc->may_swap && page_mapped(page))
444 /* Double the slab pressure for mapped and swapcache pages */
445 if (page_mapped(page) || PageSwapCache(page))
448 if (PageWriteback(page))
451 referenced = page_referenced(page, 1);
452 /* In active use or really unfreeable? Activate it. */
453 if (referenced && page_mapping_inuse(page))
454 goto activate_locked;
458 * Anonymous process memory has backing store?
459 * Try to allocate it some swap space here.
461 if (PageAnon(page) && !PageSwapCache(page)) {
464 if (!add_to_swap(page, GFP_ATOMIC))
465 goto activate_locked;
467 #endif /* CONFIG_SWAP */
469 mapping = page_mapping(page);
470 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
471 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
474 * The page is mapped into the page tables of one or more
475 * processes. Try to unmap it here.
477 if (page_mapped(page) && mapping) {
479 * No unmapping if we do not swap
484 switch (try_to_unmap(page, 0)) {
486 goto activate_locked;
490 ; /* try to free the page below */
494 if (PageDirty(page)) {
499 if (!sc->may_writepage)
502 /* Page is dirty, try to write it out here */
503 switch(pageout(page, mapping)) {
507 goto activate_locked;
509 if (PageWriteback(page) || PageDirty(page))
512 * A synchronous write - probably a ramdisk. Go
513 * ahead and try to reclaim the page.
515 if (TestSetPageLocked(page))
517 if (PageDirty(page) || PageWriteback(page))
519 mapping = page_mapping(page);
521 ; /* try to free the page below */
526 * If the page has buffers, try to free the buffer mappings
527 * associated with this page. If we succeed we try to free
530 * We do this even if the page is PageDirty().
531 * try_to_release_page() does not perform I/O, but it is
532 * possible for a page to have PageDirty set, but it is actually
533 * clean (all its buffers are clean). This happens if the
534 * buffers were written out directly, with submit_bh(). ext3
535 * will do this, as well as the blockdev mapping.
536 * try_to_release_page() will discover that cleanness and will
537 * drop the buffers and mark the page clean - it can be freed.
539 * Rarely, pages can have buffers and no ->mapping. These are
540 * the pages which were not successfully invalidated in
541 * truncate_complete_page(). We try to drop those buffers here
542 * and if that worked, and the page is no longer mapped into
543 * process address space (page_count == 1) it can be freed.
544 * Otherwise, leave the page on the LRU so it is swappable.
546 if (PagePrivate(page)) {
547 if (!try_to_release_page(page, sc->gfp_mask))
548 goto activate_locked;
549 if (!mapping && page_count(page) == 1)
553 if (!remove_mapping(mapping, page))
559 if (!pagevec_add(&freed_pvec, page))
560 __pagevec_release_nonlru(&freed_pvec);
569 list_add(&page->lru, &ret_pages);
570 BUG_ON(PageLRU(page));
572 list_splice(&ret_pages, page_list);
573 if (pagevec_count(&freed_pvec))
574 __pagevec_release_nonlru(&freed_pvec);
575 mod_page_state(pgactivate, pgactivate);
576 sc->nr_reclaimed += reclaimed;
580 #ifdef CONFIG_MIGRATION
581 static inline void move_to_lru(struct page *page)
583 list_del(&page->lru);
584 if (PageActive(page)) {
586 * lru_cache_add_active checks that
587 * the PG_active bit is off.
589 ClearPageActive(page);
590 lru_cache_add_active(page);
598 * Add isolated pages on the list back to the LRU.
600 * returns the number of pages put back.
602 int putback_lru_pages(struct list_head *l)
608 list_for_each_entry_safe(page, page2, l, lru) {
616 * Non migratable page
618 int fail_migrate_page(struct page *newpage, struct page *page)
622 EXPORT_SYMBOL(fail_migrate_page);
625 * swapout a single page
626 * page is locked upon entry, unlocked on exit
628 static int swap_page(struct page *page)
630 struct address_space *mapping = page_mapping(page);
632 if (page_mapped(page) && mapping)
633 if (try_to_unmap(page, 1) != SWAP_SUCCESS)
636 if (PageDirty(page)) {
637 /* Page is dirty, try to write it out here */
638 switch(pageout(page, mapping)) {
647 ; /* try to free the page below */
651 if (PagePrivate(page)) {
652 if (!try_to_release_page(page, GFP_KERNEL) ||
653 (!mapping && page_count(page) == 1))
657 if (remove_mapping(mapping, page)) {
669 EXPORT_SYMBOL(swap_page);
672 * Page migration was first developed in the context of the memory hotplug
673 * project. The main authors of the migration code are:
675 * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
676 * Hirokazu Takahashi <taka@valinux.co.jp>
677 * Dave Hansen <haveblue@us.ibm.com>
678 * Christoph Lameter <clameter@sgi.com>
682 * Remove references for a page and establish the new page with the correct
683 * basic settings to be able to stop accesses to the page.
685 int migrate_page_remove_references(struct page *newpage,
686 struct page *page, int nr_refs)
688 struct address_space *mapping = page_mapping(page);
689 struct page **radix_pointer;
692 * Avoid doing any of the following work if the page count
693 * indicates that the page is in use or truncate has removed
696 if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
700 * Establish swap ptes for anonymous pages or destroy pte
703 * In order to reestablish file backed mappings the fault handlers
704 * will take the radix tree_lock which may then be used to stop
705 * processses from accessing this page until the new page is ready.
707 * A process accessing via a swap pte (an anonymous page) will take a
708 * page_lock on the old page which will block the process until the
709 * migration attempt is complete. At that time the PageSwapCache bit
710 * will be examined. If the page was migrated then the PageSwapCache
711 * bit will be clear and the operation to retrieve the page will be
712 * retried which will find the new page in the radix tree. Then a new
713 * direct mapping may be generated based on the radix tree contents.
715 * If the page was not migrated then the PageSwapCache bit
716 * is still set and the operation may continue.
718 if (try_to_unmap(page, 1) == SWAP_FAIL)
719 /* A vma has VM_LOCKED set -> Permanent failure */
723 * Give up if we were unable to remove all mappings.
725 if (page_mapcount(page))
728 write_lock_irq(&mapping->tree_lock);
730 radix_pointer = (struct page **)radix_tree_lookup_slot(
734 if (!page_mapping(page) || page_count(page) != nr_refs ||
735 *radix_pointer != page) {
736 write_unlock_irq(&mapping->tree_lock);
741 * Now we know that no one else is looking at the page.
743 * Certain minimal information about a page must be available
744 * in order for other subsystems to properly handle the page if they
745 * find it through the radix tree update before we are finished
749 newpage->index = page->index;
750 newpage->mapping = page->mapping;
751 if (PageSwapCache(page)) {
752 SetPageSwapCache(newpage);
753 set_page_private(newpage, page_private(page));
756 *radix_pointer = newpage;
758 write_unlock_irq(&mapping->tree_lock);
762 EXPORT_SYMBOL(migrate_page_remove_references);
765 * Copy the page to its new location
767 void migrate_page_copy(struct page *newpage, struct page *page)
769 copy_highpage(newpage, page);
772 SetPageError(newpage);
773 if (PageReferenced(page))
774 SetPageReferenced(newpage);
775 if (PageUptodate(page))
776 SetPageUptodate(newpage);
777 if (PageActive(page))
778 SetPageActive(newpage);
779 if (PageChecked(page))
780 SetPageChecked(newpage);
781 if (PageMappedToDisk(page))
782 SetPageMappedToDisk(newpage);
784 if (PageDirty(page)) {
785 clear_page_dirty_for_io(page);
786 set_page_dirty(newpage);
789 ClearPageSwapCache(page);
790 ClearPageActive(page);
791 ClearPagePrivate(page);
792 set_page_private(page, 0);
793 page->mapping = NULL;
796 * If any waiters have accumulated on the new page then
799 if (PageWriteback(newpage))
800 end_page_writeback(newpage);
802 EXPORT_SYMBOL(migrate_page_copy);
805 * Common logic to directly migrate a single page suitable for
806 * pages that do not use PagePrivate.
808 * Pages are locked upon entry and exit.
810 int migrate_page(struct page *newpage, struct page *page)
814 BUG_ON(PageWriteback(page)); /* Writeback must be complete */
816 rc = migrate_page_remove_references(newpage, page, 2);
821 migrate_page_copy(newpage, page);
824 * Remove auxiliary swap entries and replace
825 * them with real ptes.
827 * Note that a real pte entry will allow processes that are not
828 * waiting on the page lock to use the new page via the page tables
829 * before the new page is unlocked.
831 remove_from_swap(newpage);
834 EXPORT_SYMBOL(migrate_page);
839 * Two lists are passed to this function. The first list
840 * contains the pages isolated from the LRU to be migrated.
841 * The second list contains new pages that the pages isolated
842 * can be moved to. If the second list is NULL then all
843 * pages are swapped out.
845 * The function returns after 10 attempts or if no pages
846 * are movable anymore because to has become empty
847 * or no retryable pages exist anymore.
849 * Return: Number of pages not migrated when "to" ran empty.
851 int migrate_pages(struct list_head *from, struct list_head *to,
852 struct list_head *moved, struct list_head *failed)
859 int swapwrite = current->flags & PF_SWAPWRITE;
863 current->flags |= PF_SWAPWRITE;
868 list_for_each_entry_safe(page, page2, from, lru) {
869 struct page *newpage = NULL;
870 struct address_space *mapping;
875 if (page_count(page) == 1)
876 /* page was freed from under us. So we are done. */
879 if (to && list_empty(to))
883 * Skip locked pages during the first two passes to give the
884 * functions holding the lock time to release the page. Later we
885 * use lock_page() to have a higher chance of acquiring the
892 if (TestSetPageLocked(page))
896 * Only wait on writeback if we have already done a pass where
897 * we we may have triggered writeouts for lots of pages.
900 wait_on_page_writeback(page);
902 if (PageWriteback(page))
907 * Anonymous pages must have swap cache references otherwise
908 * the information contained in the page maps cannot be
911 if (PageAnon(page) && !PageSwapCache(page)) {
912 if (!add_to_swap(page, GFP_KERNEL)) {
919 rc = swap_page(page);
923 newpage = lru_to_page(to);
927 * Pages are properly locked and writeback is complete.
928 * Try to migrate the page.
930 mapping = page_mapping(page);
934 if (mapping->a_ops->migratepage) {
936 * Most pages have a mapping and most filesystems
937 * should provide a migration function. Anonymous
938 * pages are part of swap space which also has its
939 * own migration function. This is the most common
940 * path for page migration.
942 rc = mapping->a_ops->migratepage(newpage, page);
947 * Default handling if a filesystem does not provide
948 * a migration function. We can only migrate clean
949 * pages so try to write out any dirty pages first.
951 if (PageDirty(page)) {
952 switch (pageout(page, mapping)) {
958 unlock_page(newpage);
962 ; /* try to migrate the page below */
967 * Buffers are managed in a filesystem specific way.
968 * We must have no buffers or drop them.
970 if (!page_has_buffers(page) ||
971 try_to_release_page(page, GFP_KERNEL)) {
972 rc = migrate_page(newpage, page);
977 * On early passes with mapped pages simply
978 * retry. There may be a lock held for some
979 * buffers that may go away. Later
984 * Persistently unable to drop buffers..... As a
985 * measure of last resort we fall back to
988 unlock_page(newpage);
990 rc = swap_page(page);
995 unlock_page(newpage);
1001 if (rc == -EAGAIN) {
1004 /* Permanent failure */
1005 list_move(&page->lru, failed);
1009 /* Successful migration. Return page to LRU */
1010 move_to_lru(newpage);
1012 list_move(&page->lru, moved);
1015 if (retry && pass++ < 10)
1019 current->flags &= ~PF_SWAPWRITE;
1021 return nr_failed + retry;
1025 * Isolate one page from the LRU lists and put it on the
1026 * indicated list with elevated refcount.
1029 * 0 = page not on LRU list
1030 * 1 = page removed from LRU list and added to the specified list.
1032 int isolate_lru_page(struct page *page)
1036 if (PageLRU(page)) {
1037 struct zone *zone = page_zone(page);
1038 spin_lock_irq(&zone->lru_lock);
1039 if (PageLRU(page)) {
1043 if (PageActive(page))
1044 del_page_from_active_list(zone, page);
1046 del_page_from_inactive_list(zone, page);
1048 spin_unlock_irq(&zone->lru_lock);
1056 * zone->lru_lock is heavily contended. Some of the functions that
1057 * shrink the lists perform better by taking out a batch of pages
1058 * and working on them outside the LRU lock.
1060 * For pagecache intensive workloads, this function is the hottest
1061 * spot in the kernel (apart from copy_*_user functions).
1063 * Appropriate locks must be held before calling this function.
1065 * @nr_to_scan: The number of pages to look through on the list.
1066 * @src: The LRU list to pull pages off.
1067 * @dst: The temp list to put pages on to.
1068 * @scanned: The number of pages that were scanned.
1070 * returns how many pages were moved onto *@dst.
1072 static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
1073 struct list_head *dst, int *scanned)
1079 while (scan++ < nr_to_scan && !list_empty(src)) {
1080 struct list_head *target;
1081 page = lru_to_page(src);
1082 prefetchw_prev_lru_page(page, src, flags);
1084 BUG_ON(!PageLRU(page));
1086 list_del(&page->lru);
1088 if (likely(get_page_unless_zero(page))) {
1090 * Be careful not to clear PageLRU until after we're
1091 * sure the page is not being freed elsewhere -- the
1092 * page release code relies on it.
1097 } /* else it is being freed elsewhere */
1099 list_add(&page->lru, target);
1107 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
1109 static void shrink_cache(int max_scan, struct zone *zone, struct scan_control *sc)
1111 LIST_HEAD(page_list);
1112 struct pagevec pvec;
1114 pagevec_init(&pvec, 1);
1117 spin_lock_irq(&zone->lru_lock);
1118 while (max_scan > 0) {
1124 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
1125 &zone->inactive_list,
1126 &page_list, &nr_scan);
1127 zone->nr_inactive -= nr_taken;
1128 zone->pages_scanned += nr_scan;
1129 spin_unlock_irq(&zone->lru_lock);
1134 max_scan -= nr_scan;
1135 nr_freed = shrink_list(&page_list, sc);
1137 local_irq_disable();
1138 if (current_is_kswapd()) {
1139 __mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
1140 __mod_page_state(kswapd_steal, nr_freed);
1142 __mod_page_state_zone(zone, pgscan_direct, nr_scan);
1143 __mod_page_state_zone(zone, pgsteal, nr_freed);
1145 spin_lock(&zone->lru_lock);
1147 * Put back any unfreeable pages.
1149 while (!list_empty(&page_list)) {
1150 page = lru_to_page(&page_list);
1151 BUG_ON(PageLRU(page));
1153 list_del(&page->lru);
1154 if (PageActive(page))
1155 add_page_to_active_list(zone, page);
1157 add_page_to_inactive_list(zone, page);
1158 if (!pagevec_add(&pvec, page)) {
1159 spin_unlock_irq(&zone->lru_lock);
1160 __pagevec_release(&pvec);
1161 spin_lock_irq(&zone->lru_lock);
1165 spin_unlock_irq(&zone->lru_lock);
1167 pagevec_release(&pvec);
1171 * This moves pages from the active list to the inactive list.
1173 * We move them the other way if the page is referenced by one or more
1174 * processes, from rmap.
1176 * If the pages are mostly unmapped, the processing is fast and it is
1177 * appropriate to hold zone->lru_lock across the whole operation. But if
1178 * the pages are mapped, the processing is slow (page_referenced()) so we
1179 * should drop zone->lru_lock around each page. It's impossible to balance
1180 * this, so instead we remove the pages from the LRU while processing them.
1181 * It is safe to rely on PG_active against the non-LRU pages in here because
1182 * nobody will play with that bit on a non-LRU page.
1184 * The downside is that we have to touch page->_count against each page.
1185 * But we had to alter page->flags anyway.
1188 refill_inactive_zone(int nr_pages, struct zone *zone, struct scan_control *sc)
1191 int pgdeactivate = 0;
1193 LIST_HEAD(l_hold); /* The pages which were snipped off */
1194 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
1195 LIST_HEAD(l_active); /* Pages to go onto the active_list */
1197 struct pagevec pvec;
1198 int reclaim_mapped = 0;
1200 if (unlikely(sc->may_swap)) {
1206 * `distress' is a measure of how much trouble we're having
1207 * reclaiming pages. 0 -> no problems. 100 -> great trouble.
1209 distress = 100 >> zone->prev_priority;
1212 * The point of this algorithm is to decide when to start
1213 * reclaiming mapped memory instead of just pagecache. Work out
1217 mapped_ratio = (sc->nr_mapped * 100) / total_memory;
1220 * Now decide how much we really want to unmap some pages. The
1221 * mapped ratio is downgraded - just because there's a lot of
1222 * mapped memory doesn't necessarily mean that page reclaim
1225 * The distress ratio is important - we don't want to start
1228 * A 100% value of vm_swappiness overrides this algorithm
1231 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
1234 * Now use this metric to decide whether to start moving mapped
1235 * memory onto the inactive list.
1237 if (swap_tendency >= 100)
1242 spin_lock_irq(&zone->lru_lock);
1243 pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
1244 &l_hold, &pgscanned);
1245 zone->pages_scanned += pgscanned;
1246 zone->nr_active -= pgmoved;
1247 spin_unlock_irq(&zone->lru_lock);
1249 while (!list_empty(&l_hold)) {
1251 page = lru_to_page(&l_hold);
1252 list_del(&page->lru);
1253 if (page_mapped(page)) {
1254 if (!reclaim_mapped ||
1255 (total_swap_pages == 0 && PageAnon(page)) ||
1256 page_referenced(page, 0)) {
1257 list_add(&page->lru, &l_active);
1261 list_add(&page->lru, &l_inactive);
1264 pagevec_init(&pvec, 1);
1266 spin_lock_irq(&zone->lru_lock);
1267 while (!list_empty(&l_inactive)) {
1268 page = lru_to_page(&l_inactive);
1269 prefetchw_prev_lru_page(page, &l_inactive, flags);
1270 BUG_ON(PageLRU(page));
1272 BUG_ON(!PageActive(page));
1273 ClearPageActive(page);
1275 list_move(&page->lru, &zone->inactive_list);
1277 if (!pagevec_add(&pvec, page)) {
1278 zone->nr_inactive += pgmoved;
1279 spin_unlock_irq(&zone->lru_lock);
1280 pgdeactivate += pgmoved;
1282 if (buffer_heads_over_limit)
1283 pagevec_strip(&pvec);
1284 __pagevec_release(&pvec);
1285 spin_lock_irq(&zone->lru_lock);
1288 zone->nr_inactive += pgmoved;
1289 pgdeactivate += pgmoved;
1290 if (buffer_heads_over_limit) {
1291 spin_unlock_irq(&zone->lru_lock);
1292 pagevec_strip(&pvec);
1293 spin_lock_irq(&zone->lru_lock);
1297 while (!list_empty(&l_active)) {
1298 page = lru_to_page(&l_active);
1299 prefetchw_prev_lru_page(page, &l_active, flags);
1300 BUG_ON(PageLRU(page));
1302 BUG_ON(!PageActive(page));
1303 list_move(&page->lru, &zone->active_list);
1305 if (!pagevec_add(&pvec, page)) {
1306 zone->nr_active += pgmoved;
1308 spin_unlock_irq(&zone->lru_lock);
1309 __pagevec_release(&pvec);
1310 spin_lock_irq(&zone->lru_lock);
1313 zone->nr_active += pgmoved;
1314 spin_unlock(&zone->lru_lock);
1316 __mod_page_state_zone(zone, pgrefill, pgscanned);
1317 __mod_page_state(pgdeactivate, pgdeactivate);
1320 pagevec_release(&pvec);
1324 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1327 shrink_zone(int priority, struct zone *zone, struct scan_control *sc)
1329 unsigned long nr_active;
1330 unsigned long nr_inactive;
1331 unsigned long nr_to_scan;
1333 atomic_inc(&zone->reclaim_in_progress);
1336 * Add one to `nr_to_scan' just to make sure that the kernel will
1337 * slowly sift through the active list.
1339 zone->nr_scan_active += (zone->nr_active >> priority) + 1;
1340 nr_active = zone->nr_scan_active;
1341 if (nr_active >= sc->swap_cluster_max)
1342 zone->nr_scan_active = 0;
1346 zone->nr_scan_inactive += (zone->nr_inactive >> priority) + 1;
1347 nr_inactive = zone->nr_scan_inactive;
1348 if (nr_inactive >= sc->swap_cluster_max)
1349 zone->nr_scan_inactive = 0;
1353 while (nr_active || nr_inactive) {
1355 nr_to_scan = min(nr_active,
1356 (unsigned long)sc->swap_cluster_max);
1357 nr_active -= nr_to_scan;
1358 refill_inactive_zone(nr_to_scan, zone, sc);
1362 nr_to_scan = min(nr_inactive,
1363 (unsigned long)sc->swap_cluster_max);
1364 nr_inactive -= nr_to_scan;
1365 shrink_cache(nr_to_scan, zone, sc);
1369 throttle_vm_writeout();
1371 atomic_dec(&zone->reclaim_in_progress);
1375 * This is the direct reclaim path, for page-allocating processes. We only
1376 * try to reclaim pages from zones which will satisfy the caller's allocation
1379 * We reclaim from a zone even if that zone is over pages_high. Because:
1380 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1382 * b) The zones may be over pages_high but they must go *over* pages_high to
1383 * satisfy the `incremental min' zone defense algorithm.
1385 * Returns the number of reclaimed pages.
1387 * If a zone is deemed to be full of pinned pages then just give it a light
1388 * scan then give up on it.
1391 shrink_caches(int priority, struct zone **zones, struct scan_control *sc)
1395 for (i = 0; zones[i] != NULL; i++) {
1396 struct zone *zone = zones[i];
1398 if (!populated_zone(zone))
1401 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1404 zone->temp_priority = priority;
1405 if (zone->prev_priority > priority)
1406 zone->prev_priority = priority;
1408 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1409 continue; /* Let kswapd poll it */
1411 shrink_zone(priority, zone, sc);
1416 * This is the main entry point to direct page reclaim.
1418 * If a full scan of the inactive list fails to free enough memory then we
1419 * are "out of memory" and something needs to be killed.
1421 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1422 * high - the zone may be full of dirty or under-writeback pages, which this
1423 * caller can't do much about. We kick pdflush and take explicit naps in the
1424 * hope that some of these pages can be written. But if the allocating task
1425 * holds filesystem locks which prevent writeout this might not work, and the
1426 * allocation attempt will fail.
1428 int try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
1432 int total_scanned = 0, total_reclaimed = 0;
1433 struct reclaim_state *reclaim_state = current->reclaim_state;
1434 struct scan_control sc;
1435 unsigned long lru_pages = 0;
1438 sc.gfp_mask = gfp_mask;
1439 sc.may_writepage = !laptop_mode;
1442 inc_page_state(allocstall);
1444 for (i = 0; zones[i] != NULL; i++) {
1445 struct zone *zone = zones[i];
1447 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1450 zone->temp_priority = DEF_PRIORITY;
1451 lru_pages += zone->nr_active + zone->nr_inactive;
1454 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1455 sc.nr_mapped = read_page_state(nr_mapped);
1457 sc.nr_reclaimed = 0;
1458 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1460 disable_swap_token();
1461 shrink_caches(priority, zones, &sc);
1462 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
1463 if (reclaim_state) {
1464 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1465 reclaim_state->reclaimed_slab = 0;
1467 total_scanned += sc.nr_scanned;
1468 total_reclaimed += sc.nr_reclaimed;
1469 if (total_reclaimed >= sc.swap_cluster_max) {
1475 * Try to write back as many pages as we just scanned. This
1476 * tends to cause slow streaming writers to write data to the
1477 * disk smoothly, at the dirtying rate, which is nice. But
1478 * that's undesirable in laptop mode, where we *want* lumpy
1479 * writeout. So in laptop mode, write out the whole world.
1481 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
1482 wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1483 sc.may_writepage = 1;
1486 /* Take a nap, wait for some writeback to complete */
1487 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1488 blk_congestion_wait(WRITE, HZ/10);
1491 for (i = 0; zones[i] != 0; i++) {
1492 struct zone *zone = zones[i];
1494 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1497 zone->prev_priority = zone->temp_priority;
1503 * For kswapd, balance_pgdat() will work across all this node's zones until
1504 * they are all at pages_high.
1506 * If `nr_pages' is non-zero then it is the number of pages which are to be
1507 * reclaimed, regardless of the zone occupancies. This is a software suspend
1510 * Returns the number of pages which were actually freed.
1512 * There is special handling here for zones which are full of pinned pages.
1513 * This can happen if the pages are all mlocked, or if they are all used by
1514 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
1515 * What we do is to detect the case where all pages in the zone have been
1516 * scanned twice and there has been zero successful reclaim. Mark the zone as
1517 * dead and from now on, only perform a short scan. Basically we're polling
1518 * the zone for when the problem goes away.
1520 * kswapd scans the zones in the highmem->normal->dma direction. It skips
1521 * zones which have free_pages > pages_high, but once a zone is found to have
1522 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1523 * of the number of free pages in the lower zones. This interoperates with
1524 * the page allocator fallback scheme to ensure that aging of pages is balanced
1527 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
1529 int to_free = nr_pages;
1533 int total_scanned, total_reclaimed;
1534 struct reclaim_state *reclaim_state = current->reclaim_state;
1535 struct scan_control sc;
1539 total_reclaimed = 0;
1540 sc.gfp_mask = GFP_KERNEL;
1541 sc.may_writepage = !laptop_mode;
1543 sc.nr_mapped = read_page_state(nr_mapped);
1545 inc_page_state(pageoutrun);
1547 for (i = 0; i < pgdat->nr_zones; i++) {
1548 struct zone *zone = pgdat->node_zones + i;
1550 zone->temp_priority = DEF_PRIORITY;
1553 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1554 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
1555 unsigned long lru_pages = 0;
1557 /* The swap token gets in the way of swapout... */
1559 disable_swap_token();
1563 if (nr_pages == 0) {
1565 * Scan in the highmem->dma direction for the highest
1566 * zone which needs scanning
1568 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1569 struct zone *zone = pgdat->node_zones + i;
1571 if (!populated_zone(zone))
1574 if (zone->all_unreclaimable &&
1575 priority != DEF_PRIORITY)
1578 if (!zone_watermark_ok(zone, order,
1579 zone->pages_high, 0, 0)) {
1586 end_zone = pgdat->nr_zones - 1;
1589 for (i = 0; i <= end_zone; i++) {
1590 struct zone *zone = pgdat->node_zones + i;
1592 lru_pages += zone->nr_active + zone->nr_inactive;
1596 * Now scan the zone in the dma->highmem direction, stopping
1597 * at the last zone which needs scanning.
1599 * We do this because the page allocator works in the opposite
1600 * direction. This prevents the page allocator from allocating
1601 * pages behind kswapd's direction of progress, which would
1602 * cause too much scanning of the lower zones.
1604 for (i = 0; i <= end_zone; i++) {
1605 struct zone *zone = pgdat->node_zones + i;
1608 if (!populated_zone(zone))
1611 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1614 if (nr_pages == 0) { /* Not software suspend */
1615 if (!zone_watermark_ok(zone, order,
1616 zone->pages_high, end_zone, 0))
1619 zone->temp_priority = priority;
1620 if (zone->prev_priority > priority)
1621 zone->prev_priority = priority;
1623 sc.nr_reclaimed = 0;
1624 sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
1625 shrink_zone(priority, zone, &sc);
1626 reclaim_state->reclaimed_slab = 0;
1627 nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1629 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1630 total_reclaimed += sc.nr_reclaimed;
1631 total_scanned += sc.nr_scanned;
1632 if (zone->all_unreclaimable)
1634 if (nr_slab == 0 && zone->pages_scanned >=
1635 (zone->nr_active + zone->nr_inactive) * 4)
1636 zone->all_unreclaimable = 1;
1638 * If we've done a decent amount of scanning and
1639 * the reclaim ratio is low, start doing writepage
1640 * even in laptop mode
1642 if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1643 total_scanned > total_reclaimed+total_reclaimed/2)
1644 sc.may_writepage = 1;
1646 if (nr_pages && to_free > total_reclaimed)
1647 continue; /* swsusp: need to do more work */
1649 break; /* kswapd: all done */
1651 * OK, kswapd is getting into trouble. Take a nap, then take
1652 * another pass across the zones.
1654 if (total_scanned && priority < DEF_PRIORITY - 2)
1655 blk_congestion_wait(WRITE, HZ/10);
1658 * We do this so kswapd doesn't build up large priorities for
1659 * example when it is freeing in parallel with allocators. It
1660 * matches the direct reclaim path behaviour in terms of impact
1661 * on zone->*_priority.
1663 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
1667 for (i = 0; i < pgdat->nr_zones; i++) {
1668 struct zone *zone = pgdat->node_zones + i;
1670 zone->prev_priority = zone->temp_priority;
1672 if (!all_zones_ok) {
1677 return total_reclaimed;
1681 * The background pageout daemon, started as a kernel thread
1682 * from the init process.
1684 * This basically trickles out pages so that we have _some_
1685 * free memory available even if there is no other activity
1686 * that frees anything up. This is needed for things like routing
1687 * etc, where we otherwise might have all activity going on in
1688 * asynchronous contexts that cannot page things out.
1690 * If there are applications that are active memory-allocators
1691 * (most normal use), this basically shouldn't matter.
1693 static int kswapd(void *p)
1695 unsigned long order;
1696 pg_data_t *pgdat = (pg_data_t*)p;
1697 struct task_struct *tsk = current;
1699 struct reclaim_state reclaim_state = {
1700 .reclaimed_slab = 0,
1704 daemonize("kswapd%d", pgdat->node_id);
1705 cpumask = node_to_cpumask(pgdat->node_id);
1706 if (!cpus_empty(cpumask))
1707 set_cpus_allowed(tsk, cpumask);
1708 current->reclaim_state = &reclaim_state;
1711 * Tell the memory management that we're a "memory allocator",
1712 * and that if we need more memory we should get access to it
1713 * regardless (see "__alloc_pages()"). "kswapd" should
1714 * never get caught in the normal page freeing logic.
1716 * (Kswapd normally doesn't need memory anyway, but sometimes
1717 * you need a small amount of memory in order to be able to
1718 * page out something else, and this flag essentially protects
1719 * us from recursively trying to free more memory as we're
1720 * trying to free the first piece of memory in the first place).
1722 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1726 unsigned long new_order;
1730 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1731 new_order = pgdat->kswapd_max_order;
1732 pgdat->kswapd_max_order = 0;
1733 if (order < new_order) {
1735 * Don't sleep if someone wants a larger 'order'
1741 order = pgdat->kswapd_max_order;
1743 finish_wait(&pgdat->kswapd_wait, &wait);
1745 balance_pgdat(pgdat, 0, order);
1751 * A zone is low on free memory, so wake its kswapd task to service it.
1753 void wakeup_kswapd(struct zone *zone, int order)
1757 if (!populated_zone(zone))
1760 pgdat = zone->zone_pgdat;
1761 if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1763 if (pgdat->kswapd_max_order < order)
1764 pgdat->kswapd_max_order = order;
1765 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1767 if (!waitqueue_active(&pgdat->kswapd_wait))
1769 wake_up_interruptible(&pgdat->kswapd_wait);
1774 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed
1777 int shrink_all_memory(int nr_pages)
1780 int nr_to_free = nr_pages;
1782 struct reclaim_state reclaim_state = {
1783 .reclaimed_slab = 0,
1786 current->reclaim_state = &reclaim_state;
1787 for_each_pgdat(pgdat) {
1789 freed = balance_pgdat(pgdat, nr_to_free, 0);
1791 nr_to_free -= freed;
1792 if (nr_to_free <= 0)
1795 current->reclaim_state = NULL;
1800 #ifdef CONFIG_HOTPLUG_CPU
1801 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1802 not required for correctness. So if the last cpu in a node goes
1803 away, we get changed to run anywhere: as the first one comes back,
1804 restore their cpu bindings. */
1805 static int __devinit cpu_callback(struct notifier_block *nfb,
1806 unsigned long action,
1812 if (action == CPU_ONLINE) {
1813 for_each_pgdat(pgdat) {
1814 mask = node_to_cpumask(pgdat->node_id);
1815 if (any_online_cpu(mask) != NR_CPUS)
1816 /* One of our CPUs online: restore mask */
1817 set_cpus_allowed(pgdat->kswapd, mask);
1822 #endif /* CONFIG_HOTPLUG_CPU */
1824 static int __init kswapd_init(void)
1828 for_each_pgdat(pgdat)
1830 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1831 total_memory = nr_free_pagecache_pages();
1832 hotcpu_notifier(cpu_callback, 0);
1836 module_init(kswapd_init)
1842 * If non-zero call zone_reclaim when the number of free pages falls below
1845 * In the future we may add flags to the mode. However, the page allocator
1846 * should only have to check that zone_reclaim_mode != 0 before calling
1849 int zone_reclaim_mode __read_mostly;
1851 #define RECLAIM_OFF 0
1852 #define RECLAIM_ZONE (1<<0) /* Run shrink_cache on the zone */
1853 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
1854 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
1855 #define RECLAIM_SLAB (1<<3) /* Do a global slab shrink if the zone is out of memory */
1858 * Mininum time between zone reclaim scans
1860 int zone_reclaim_interval __read_mostly = 30*HZ;
1863 * Priority for ZONE_RECLAIM. This determines the fraction of pages
1864 * of a node considered for each zone_reclaim. 4 scans 1/16th of
1867 #define ZONE_RECLAIM_PRIORITY 4
1870 * Try to free up some pages from this zone through reclaim.
1872 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1875 struct task_struct *p = current;
1876 struct reclaim_state reclaim_state;
1877 struct scan_control sc;
1882 if (time_before(jiffies,
1883 zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval))
1886 if (!(gfp_mask & __GFP_WAIT) ||
1887 zone->all_unreclaimable ||
1888 atomic_read(&zone->reclaim_in_progress) > 0 ||
1889 (p->flags & PF_MEMALLOC))
1892 node_id = zone->zone_pgdat->node_id;
1893 mask = node_to_cpumask(node_id);
1894 if (!cpus_empty(mask) && node_id != numa_node_id())
1897 sc.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE);
1898 sc.may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP);
1900 sc.nr_reclaimed = 0;
1901 sc.nr_mapped = read_page_state(nr_mapped);
1902 sc.gfp_mask = gfp_mask;
1904 disable_swap_token();
1906 nr_pages = 1 << order;
1907 if (nr_pages > SWAP_CLUSTER_MAX)
1908 sc.swap_cluster_max = nr_pages;
1910 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1914 * We need to be able to allocate from the reserves for RECLAIM_SWAP
1915 * and we also need to be able to write out pages for RECLAIM_WRITE
1918 p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
1919 reclaim_state.reclaimed_slab = 0;
1920 p->reclaim_state = &reclaim_state;
1923 * Free memory by calling shrink zone with increasing priorities
1924 * until we have enough memory freed.
1926 priority = ZONE_RECLAIM_PRIORITY;
1928 shrink_zone(priority, zone, &sc);
1930 } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
1932 if (sc.nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) {
1934 * shrink_slab does not currently allow us to determine
1935 * how many pages were freed in the zone. So we just
1936 * shake the slab and then go offnode for a single allocation.
1938 * shrink_slab will free memory on all zones and may take
1941 shrink_slab(sc.nr_scanned, gfp_mask, order);
1944 p->reclaim_state = NULL;
1945 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
1947 if (sc.nr_reclaimed == 0)
1948 zone->last_unsuccessful_zone_reclaim = jiffies;
1950 return sc.nr_reclaimed >= nr_pages;