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 /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
56 unsigned long nr_to_scan;
58 /* Incremented by the number of inactive pages that were scanned */
59 unsigned long nr_scanned;
61 /* Incremented by the number of pages reclaimed */
62 unsigned long nr_reclaimed;
64 unsigned long nr_mapped; /* From page_state */
66 /* Ask shrink_caches, or shrink_zone to scan at this priority */
67 unsigned int priority;
69 /* This context's GFP mask */
74 /* Can pages be swapped as part of reclaim? */
77 /* This context's SWAP_CLUSTER_MAX. If freeing memory for
78 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
79 * In this context, it doesn't matter that we scan the
80 * whole list at once. */
85 * The list of shrinker callbacks used by to apply pressure to
90 struct list_head list;
91 int seeks; /* seeks to recreate an obj */
92 long nr; /* objs pending delete */
95 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
97 #ifdef ARCH_HAS_PREFETCH
98 #define prefetch_prev_lru_page(_page, _base, _field) \
100 if ((_page)->lru.prev != _base) { \
103 prev = lru_to_page(&(_page->lru)); \
104 prefetch(&prev->_field); \
108 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
111 #ifdef ARCH_HAS_PREFETCHW
112 #define prefetchw_prev_lru_page(_page, _base, _field) \
114 if ((_page)->lru.prev != _base) { \
117 prev = lru_to_page(&(_page->lru)); \
118 prefetchw(&prev->_field); \
122 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
126 * From 0 .. 100. Higher means more swappy.
128 int vm_swappiness = 60;
129 static long total_memory;
131 static LIST_HEAD(shrinker_list);
132 static DECLARE_RWSEM(shrinker_rwsem);
135 * Add a shrinker callback to be called from the vm
137 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
139 struct shrinker *shrinker;
141 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
143 shrinker->shrinker = theshrinker;
144 shrinker->seeks = seeks;
146 down_write(&shrinker_rwsem);
147 list_add_tail(&shrinker->list, &shrinker_list);
148 up_write(&shrinker_rwsem);
152 EXPORT_SYMBOL(set_shrinker);
157 void remove_shrinker(struct shrinker *shrinker)
159 down_write(&shrinker_rwsem);
160 list_del(&shrinker->list);
161 up_write(&shrinker_rwsem);
164 EXPORT_SYMBOL(remove_shrinker);
166 #define SHRINK_BATCH 128
168 * Call the shrink functions to age shrinkable caches
170 * Here we assume it costs one seek to replace a lru page and that it also
171 * takes a seek to recreate a cache object. With this in mind we age equal
172 * percentages of the lru and ageable caches. This should balance the seeks
173 * generated by these structures.
175 * If the vm encounted mapped pages on the LRU it increase the pressure on
176 * slab to avoid swapping.
178 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
180 * `lru_pages' represents the number of on-LRU pages in all the zones which
181 * are eligible for the caller's allocation attempt. It is used for balancing
182 * slab reclaim versus page reclaim.
184 * Returns the number of slab objects which we shrunk.
186 int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
188 struct shrinker *shrinker;
192 scanned = SWAP_CLUSTER_MAX;
194 if (!down_read_trylock(&shrinker_rwsem))
195 return 1; /* Assume we'll be able to shrink next time */
197 list_for_each_entry(shrinker, &shrinker_list, list) {
198 unsigned long long delta;
199 unsigned long total_scan;
200 unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
202 delta = (4 * scanned) / shrinker->seeks;
204 do_div(delta, lru_pages + 1);
205 shrinker->nr += delta;
206 if (shrinker->nr < 0) {
207 printk(KERN_ERR "%s: nr=%ld\n",
208 __FUNCTION__, shrinker->nr);
209 shrinker->nr = max_pass;
213 * Avoid risking looping forever due to too large nr value:
214 * never try to free more than twice the estimate number of
217 if (shrinker->nr > max_pass * 2)
218 shrinker->nr = max_pass * 2;
220 total_scan = shrinker->nr;
223 while (total_scan >= SHRINK_BATCH) {
224 long this_scan = SHRINK_BATCH;
228 nr_before = (*shrinker->shrinker)(0, gfp_mask);
229 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
230 if (shrink_ret == -1)
232 if (shrink_ret < nr_before)
233 ret += nr_before - shrink_ret;
234 mod_page_state(slabs_scanned, this_scan);
235 total_scan -= this_scan;
240 shrinker->nr += total_scan;
242 up_read(&shrinker_rwsem);
246 /* Called without lock on whether page is mapped, so answer is unstable */
247 static inline int page_mapping_inuse(struct page *page)
249 struct address_space *mapping;
251 /* Page is in somebody's page tables. */
252 if (page_mapped(page))
255 /* Be more reluctant to reclaim swapcache than pagecache */
256 if (PageSwapCache(page))
259 mapping = page_mapping(page);
263 /* File is mmap'd by somebody? */
264 return mapping_mapped(mapping);
267 static inline int is_page_cache_freeable(struct page *page)
269 return page_count(page) - !!PagePrivate(page) == 2;
272 static int may_write_to_queue(struct backing_dev_info *bdi)
274 if (current->flags & PF_SWAPWRITE)
276 if (!bdi_write_congested(bdi))
278 if (bdi == current->backing_dev_info)
284 * We detected a synchronous write error writing a page out. Probably
285 * -ENOSPC. We need to propagate that into the address_space for a subsequent
286 * fsync(), msync() or close().
288 * The tricky part is that after writepage we cannot touch the mapping: nothing
289 * prevents it from being freed up. But we have a ref on the page and once
290 * that page is locked, the mapping is pinned.
292 * We're allowed to run sleeping lock_page() here because we know the caller has
295 static void handle_write_error(struct address_space *mapping,
296 struct page *page, int error)
299 if (page_mapping(page) == mapping) {
300 if (error == -ENOSPC)
301 set_bit(AS_ENOSPC, &mapping->flags);
303 set_bit(AS_EIO, &mapping->flags);
309 * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
311 static pageout_t pageout(struct page *page, struct address_space *mapping)
314 * If the page is dirty, only perform writeback if that write
315 * will be non-blocking. To prevent this allocation from being
316 * stalled by pagecache activity. But note that there may be
317 * stalls if we need to run get_block(). We could test
318 * PagePrivate for that.
320 * If this process is currently in generic_file_write() against
321 * this page's queue, we can perform writeback even if that
324 * If the page is swapcache, write it back even if that would
325 * block, for some throttling. This happens by accident, because
326 * swap_backing_dev_info is bust: it doesn't reflect the
327 * congestion state of the swapdevs. Easy to fix, if needed.
328 * See swapfile.c:page_queue_congested().
330 if (!is_page_cache_freeable(page))
334 * Some data journaling orphaned pages can have
335 * page->mapping == NULL while being dirty with clean buffers.
337 if (PagePrivate(page)) {
338 if (try_to_free_buffers(page)) {
339 ClearPageDirty(page);
340 printk("%s: orphaned page\n", __FUNCTION__);
346 if (mapping->a_ops->writepage == NULL)
347 return PAGE_ACTIVATE;
348 if (!may_write_to_queue(mapping->backing_dev_info))
351 if (clear_page_dirty_for_io(page)) {
353 struct writeback_control wbc = {
354 .sync_mode = WB_SYNC_NONE,
355 .nr_to_write = SWAP_CLUSTER_MAX,
360 SetPageReclaim(page);
361 res = mapping->a_ops->writepage(page, &wbc);
363 handle_write_error(mapping, page, res);
364 if (res == AOP_WRITEPAGE_ACTIVATE) {
365 ClearPageReclaim(page);
366 return PAGE_ACTIVATE;
368 if (!PageWriteback(page)) {
369 /* synchronous write or broken a_ops? */
370 ClearPageReclaim(page);
379 static int remove_mapping(struct address_space *mapping, struct page *page)
382 return 0; /* truncate got there first */
384 write_lock_irq(&mapping->tree_lock);
387 * The non-racy check for busy page. It is critical to check
388 * PageDirty _after_ making sure that the page is freeable and
389 * not in use by anybody. (pagecache + us == 2)
391 if (unlikely(page_count(page) != 2))
394 if (unlikely(PageDirty(page)))
397 if (PageSwapCache(page)) {
398 swp_entry_t swap = { .val = page_private(page) };
399 __delete_from_swap_cache(page);
400 write_unlock_irq(&mapping->tree_lock);
402 __put_page(page); /* The pagecache ref */
406 __remove_from_page_cache(page);
407 write_unlock_irq(&mapping->tree_lock);
412 write_unlock_irq(&mapping->tree_lock);
417 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
419 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
421 LIST_HEAD(ret_pages);
422 struct pagevec freed_pvec;
428 pagevec_init(&freed_pvec, 1);
429 while (!list_empty(page_list)) {
430 struct address_space *mapping;
437 page = lru_to_page(page_list);
438 list_del(&page->lru);
440 if (TestSetPageLocked(page))
443 BUG_ON(PageActive(page));
446 /* Double the slab pressure for mapped and swapcache pages */
447 if (page_mapped(page) || PageSwapCache(page))
450 if (PageWriteback(page))
453 referenced = page_referenced(page, 1);
454 /* In active use or really unfreeable? Activate it. */
455 if (referenced && page_mapping_inuse(page))
456 goto activate_locked;
460 * Anonymous process memory has backing store?
461 * Try to allocate it some swap space here.
463 if (PageAnon(page) && !PageSwapCache(page)) {
466 if (!add_to_swap(page, GFP_ATOMIC))
467 goto activate_locked;
469 #endif /* CONFIG_SWAP */
471 mapping = page_mapping(page);
472 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
473 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
476 * The page is mapped into the page tables of one or more
477 * processes. Try to unmap it here.
479 if (page_mapped(page) && mapping) {
481 * No unmapping if we do not swap
486 switch (try_to_unmap(page, 0)) {
488 goto activate_locked;
492 ; /* try to free the page below */
496 if (PageDirty(page)) {
501 if (!sc->may_writepage)
504 /* Page is dirty, try to write it out here */
505 switch(pageout(page, mapping)) {
509 goto activate_locked;
511 if (PageWriteback(page) || PageDirty(page))
514 * A synchronous write - probably a ramdisk. Go
515 * ahead and try to reclaim the page.
517 if (TestSetPageLocked(page))
519 if (PageDirty(page) || PageWriteback(page))
521 mapping = page_mapping(page);
523 ; /* try to free the page below */
528 * If the page has buffers, try to free the buffer mappings
529 * associated with this page. If we succeed we try to free
532 * We do this even if the page is PageDirty().
533 * try_to_release_page() does not perform I/O, but it is
534 * possible for a page to have PageDirty set, but it is actually
535 * clean (all its buffers are clean). This happens if the
536 * buffers were written out directly, with submit_bh(). ext3
537 * will do this, as well as the blockdev mapping.
538 * try_to_release_page() will discover that cleanness and will
539 * drop the buffers and mark the page clean - it can be freed.
541 * Rarely, pages can have buffers and no ->mapping. These are
542 * the pages which were not successfully invalidated in
543 * truncate_complete_page(). We try to drop those buffers here
544 * and if that worked, and the page is no longer mapped into
545 * process address space (page_count == 1) it can be freed.
546 * Otherwise, leave the page on the LRU so it is swappable.
548 if (PagePrivate(page)) {
549 if (!try_to_release_page(page, sc->gfp_mask))
550 goto activate_locked;
551 if (!mapping && page_count(page) == 1)
555 if (!remove_mapping(mapping, page))
561 if (!pagevec_add(&freed_pvec, page))
562 __pagevec_release_nonlru(&freed_pvec);
571 list_add(&page->lru, &ret_pages);
572 BUG_ON(PageLRU(page));
574 list_splice(&ret_pages, page_list);
575 if (pagevec_count(&freed_pvec))
576 __pagevec_release_nonlru(&freed_pvec);
577 mod_page_state(pgactivate, pgactivate);
578 sc->nr_reclaimed += reclaimed;
582 #ifdef CONFIG_MIGRATION
583 static inline void move_to_lru(struct page *page)
585 list_del(&page->lru);
586 if (PageActive(page)) {
588 * lru_cache_add_active checks that
589 * the PG_active bit is off.
591 ClearPageActive(page);
592 lru_cache_add_active(page);
600 * Add isolated pages on the list back to the LRU.
602 * returns the number of pages put back.
604 int putback_lru_pages(struct list_head *l)
610 list_for_each_entry_safe(page, page2, l, lru) {
618 * swapout a single page
619 * page is locked upon entry, unlocked on exit
621 static int swap_page(struct page *page)
623 struct address_space *mapping = page_mapping(page);
625 if (page_mapped(page) && mapping)
626 if (try_to_unmap(page, 0) != SWAP_SUCCESS)
629 if (PageDirty(page)) {
630 /* Page is dirty, try to write it out here */
631 switch(pageout(page, mapping)) {
640 ; /* try to free the page below */
644 if (PagePrivate(page)) {
645 if (!try_to_release_page(page, GFP_KERNEL) ||
646 (!mapping && page_count(page) == 1))
650 if (remove_mapping(mapping, page)) {
664 * Page migration was first developed in the context of the memory hotplug
665 * project. The main authors of the migration code are:
667 * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
668 * Hirokazu Takahashi <taka@valinux.co.jp>
669 * Dave Hansen <haveblue@us.ibm.com>
670 * Christoph Lameter <clameter@sgi.com>
674 * Remove references for a page and establish the new page with the correct
675 * basic settings to be able to stop accesses to the page.
677 static int migrate_page_remove_references(struct page *newpage,
678 struct page *page, int nr_refs)
680 struct address_space *mapping = page_mapping(page);
681 struct page **radix_pointer;
684 * Avoid doing any of the following work if the page count
685 * indicates that the page is in use or truncate has removed
688 if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
692 * Establish swap ptes for anonymous pages or destroy pte
695 * In order to reestablish file backed mappings the fault handlers
696 * will take the radix tree_lock which may then be used to stop
697 * processses from accessing this page until the new page is ready.
699 * A process accessing via a swap pte (an anonymous page) will take a
700 * page_lock on the old page which will block the process until the
701 * migration attempt is complete. At that time the PageSwapCache bit
702 * will be examined. If the page was migrated then the PageSwapCache
703 * bit will be clear and the operation to retrieve the page will be
704 * retried which will find the new page in the radix tree. Then a new
705 * direct mapping may be generated based on the radix tree contents.
707 * If the page was not migrated then the PageSwapCache bit
708 * is still set and the operation may continue.
710 try_to_unmap(page, 1);
713 * Give up if we were unable to remove all mappings.
715 if (page_mapcount(page))
718 write_lock_irq(&mapping->tree_lock);
720 radix_pointer = (struct page **)radix_tree_lookup_slot(
724 if (!page_mapping(page) || page_count(page) != nr_refs ||
725 *radix_pointer != page) {
726 write_unlock_irq(&mapping->tree_lock);
731 * Now we know that no one else is looking at the page.
733 * Certain minimal information about a page must be available
734 * in order for other subsystems to properly handle the page if they
735 * find it through the radix tree update before we are finished
739 newpage->index = page->index;
740 newpage->mapping = page->mapping;
741 if (PageSwapCache(page)) {
742 SetPageSwapCache(newpage);
743 set_page_private(newpage, page_private(page));
746 *radix_pointer = newpage;
748 write_unlock_irq(&mapping->tree_lock);
754 * Copy the page to its new location
756 void migrate_page_copy(struct page *newpage, struct page *page)
758 copy_highpage(newpage, page);
761 SetPageError(newpage);
762 if (PageReferenced(page))
763 SetPageReferenced(newpage);
764 if (PageUptodate(page))
765 SetPageUptodate(newpage);
766 if (PageActive(page))
767 SetPageActive(newpage);
768 if (PageChecked(page))
769 SetPageChecked(newpage);
770 if (PageMappedToDisk(page))
771 SetPageMappedToDisk(newpage);
773 if (PageDirty(page)) {
774 clear_page_dirty_for_io(page);
775 set_page_dirty(newpage);
778 ClearPageSwapCache(page);
779 ClearPageActive(page);
780 ClearPagePrivate(page);
781 set_page_private(page, 0);
782 page->mapping = NULL;
785 * If any waiters have accumulated on the new page then
788 if (PageWriteback(newpage))
789 end_page_writeback(newpage);
793 * Common logic to directly migrate a single page suitable for
794 * pages that do not use PagePrivate.
796 * Pages are locked upon entry and exit.
798 int migrate_page(struct page *newpage, struct page *page)
800 BUG_ON(PageWriteback(page)); /* Writeback must be complete */
802 if (migrate_page_remove_references(newpage, page, 2))
805 migrate_page_copy(newpage, page);
813 * Two lists are passed to this function. The first list
814 * contains the pages isolated from the LRU to be migrated.
815 * The second list contains new pages that the pages isolated
816 * can be moved to. If the second list is NULL then all
817 * pages are swapped out.
819 * The function returns after 10 attempts or if no pages
820 * are movable anymore because t has become empty
821 * or no retryable pages exist anymore.
823 * Return: Number of pages not migrated when "to" ran empty.
825 int migrate_pages(struct list_head *from, struct list_head *to,
826 struct list_head *moved, struct list_head *failed)
833 int swapwrite = current->flags & PF_SWAPWRITE;
837 current->flags |= PF_SWAPWRITE;
842 list_for_each_entry_safe(page, page2, from, lru) {
843 struct page *newpage = NULL;
844 struct address_space *mapping;
849 if (page_count(page) == 1)
850 /* page was freed from under us. So we are done. */
853 if (to && list_empty(to))
857 * Skip locked pages during the first two passes to give the
858 * functions holding the lock time to release the page. Later we
859 * use lock_page() to have a higher chance of acquiring the
866 if (TestSetPageLocked(page))
870 * Only wait on writeback if we have already done a pass where
871 * we we may have triggered writeouts for lots of pages.
874 wait_on_page_writeback(page);
876 if (PageWriteback(page))
881 * Anonymous pages must have swap cache references otherwise
882 * the information contained in the page maps cannot be
885 if (PageAnon(page) && !PageSwapCache(page)) {
886 if (!add_to_swap(page, GFP_KERNEL)) {
893 rc = swap_page(page);
897 newpage = lru_to_page(to);
901 * Pages are properly locked and writeback is complete.
902 * Try to migrate the page.
904 mapping = page_mapping(page);
909 * Trigger writeout if page is dirty
911 if (PageDirty(page)) {
912 switch (pageout(page, mapping)) {
918 unlock_page(newpage);
922 ; /* try to migrate the page below */
926 * If we have no buffer or can release the buffer
927 * then do a simple migration.
929 if (!page_has_buffers(page) ||
930 try_to_release_page(page, GFP_KERNEL)) {
931 rc = migrate_page(newpage, page);
936 * On early passes with mapped pages simply
937 * retry. There may be a lock held for some
938 * buffers that may go away. Later
942 unlock_page(newpage);
944 rc = swap_page(page);
949 unlock_page(newpage);
958 /* Permanent failure */
959 list_move(&page->lru, failed);
963 /* Successful migration. Return page to LRU */
964 move_to_lru(newpage);
966 list_move(&page->lru, moved);
969 if (retry && pass++ < 10)
973 current->flags &= ~PF_SWAPWRITE;
975 return nr_failed + retry;
979 * Isolate one page from the LRU lists and put it on the
980 * indicated list with elevated refcount.
983 * 0 = page not on LRU list
984 * 1 = page removed from LRU list and added to the specified list.
986 int isolate_lru_page(struct page *page)
991 struct zone *zone = page_zone(page);
992 spin_lock_irq(&zone->lru_lock);
993 if (TestClearPageLRU(page)) {
996 if (PageActive(page))
997 del_page_from_active_list(zone, page);
999 del_page_from_inactive_list(zone, page);
1001 spin_unlock_irq(&zone->lru_lock);
1009 * zone->lru_lock is heavily contended. Some of the functions that
1010 * shrink the lists perform better by taking out a batch of pages
1011 * and working on them outside the LRU lock.
1013 * For pagecache intensive workloads, this function is the hottest
1014 * spot in the kernel (apart from copy_*_user functions).
1016 * Appropriate locks must be held before calling this function.
1018 * @nr_to_scan: The number of pages to look through on the list.
1019 * @src: The LRU list to pull pages off.
1020 * @dst: The temp list to put pages on to.
1021 * @scanned: The number of pages that were scanned.
1023 * returns how many pages were moved onto *@dst.
1025 static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
1026 struct list_head *dst, int *scanned)
1032 while (scan++ < nr_to_scan && !list_empty(src)) {
1033 page = lru_to_page(src);
1034 prefetchw_prev_lru_page(page, src, flags);
1036 if (!TestClearPageLRU(page))
1038 list_del(&page->lru);
1039 if (get_page_testone(page)) {
1041 * It is being freed elsewhere
1045 list_add(&page->lru, src);
1048 list_add(&page->lru, dst);
1058 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
1060 static void shrink_cache(struct zone *zone, struct scan_control *sc)
1062 LIST_HEAD(page_list);
1063 struct pagevec pvec;
1064 int max_scan = sc->nr_to_scan;
1066 pagevec_init(&pvec, 1);
1069 spin_lock_irq(&zone->lru_lock);
1070 while (max_scan > 0) {
1076 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
1077 &zone->inactive_list,
1078 &page_list, &nr_scan);
1079 zone->nr_inactive -= nr_taken;
1080 zone->pages_scanned += nr_scan;
1081 spin_unlock_irq(&zone->lru_lock);
1086 max_scan -= nr_scan;
1087 nr_freed = shrink_list(&page_list, sc);
1089 local_irq_disable();
1090 if (current_is_kswapd()) {
1091 __mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
1092 __mod_page_state(kswapd_steal, nr_freed);
1094 __mod_page_state_zone(zone, pgscan_direct, nr_scan);
1095 __mod_page_state_zone(zone, pgsteal, nr_freed);
1097 spin_lock(&zone->lru_lock);
1099 * Put back any unfreeable pages.
1101 while (!list_empty(&page_list)) {
1102 page = lru_to_page(&page_list);
1103 if (TestSetPageLRU(page))
1105 list_del(&page->lru);
1106 if (PageActive(page))
1107 add_page_to_active_list(zone, page);
1109 add_page_to_inactive_list(zone, page);
1110 if (!pagevec_add(&pvec, page)) {
1111 spin_unlock_irq(&zone->lru_lock);
1112 __pagevec_release(&pvec);
1113 spin_lock_irq(&zone->lru_lock);
1117 spin_unlock_irq(&zone->lru_lock);
1119 pagevec_release(&pvec);
1123 * This moves pages from the active list to the inactive list.
1125 * We move them the other way if the page is referenced by one or more
1126 * processes, from rmap.
1128 * If the pages are mostly unmapped, the processing is fast and it is
1129 * appropriate to hold zone->lru_lock across the whole operation. But if
1130 * the pages are mapped, the processing is slow (page_referenced()) so we
1131 * should drop zone->lru_lock around each page. It's impossible to balance
1132 * this, so instead we remove the pages from the LRU while processing them.
1133 * It is safe to rely on PG_active against the non-LRU pages in here because
1134 * nobody will play with that bit on a non-LRU page.
1136 * The downside is that we have to touch page->_count against each page.
1137 * But we had to alter page->flags anyway.
1140 refill_inactive_zone(struct zone *zone, struct scan_control *sc)
1143 int pgdeactivate = 0;
1145 int nr_pages = sc->nr_to_scan;
1146 LIST_HEAD(l_hold); /* The pages which were snipped off */
1147 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
1148 LIST_HEAD(l_active); /* Pages to go onto the active_list */
1150 struct pagevec pvec;
1151 int reclaim_mapped = 0;
1157 spin_lock_irq(&zone->lru_lock);
1158 pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
1159 &l_hold, &pgscanned);
1160 zone->pages_scanned += pgscanned;
1161 zone->nr_active -= pgmoved;
1162 spin_unlock_irq(&zone->lru_lock);
1165 * `distress' is a measure of how much trouble we're having reclaiming
1166 * pages. 0 -> no problems. 100 -> great trouble.
1168 distress = 100 >> zone->prev_priority;
1171 * The point of this algorithm is to decide when to start reclaiming
1172 * mapped memory instead of just pagecache. Work out how much memory
1175 mapped_ratio = (sc->nr_mapped * 100) / total_memory;
1178 * Now decide how much we really want to unmap some pages. The mapped
1179 * ratio is downgraded - just because there's a lot of mapped memory
1180 * doesn't necessarily mean that page reclaim isn't succeeding.
1182 * The distress ratio is important - we don't want to start going oom.
1184 * A 100% value of vm_swappiness overrides this algorithm altogether.
1186 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
1189 * Now use this metric to decide whether to start moving mapped memory
1190 * onto the inactive list.
1192 if (swap_tendency >= 100)
1195 while (!list_empty(&l_hold)) {
1197 page = lru_to_page(&l_hold);
1198 list_del(&page->lru);
1199 if (page_mapped(page)) {
1200 if (!reclaim_mapped ||
1201 (total_swap_pages == 0 && PageAnon(page)) ||
1202 page_referenced(page, 0)) {
1203 list_add(&page->lru, &l_active);
1207 list_add(&page->lru, &l_inactive);
1210 pagevec_init(&pvec, 1);
1212 spin_lock_irq(&zone->lru_lock);
1213 while (!list_empty(&l_inactive)) {
1214 page = lru_to_page(&l_inactive);
1215 prefetchw_prev_lru_page(page, &l_inactive, flags);
1216 if (TestSetPageLRU(page))
1218 if (!TestClearPageActive(page))
1220 list_move(&page->lru, &zone->inactive_list);
1222 if (!pagevec_add(&pvec, page)) {
1223 zone->nr_inactive += pgmoved;
1224 spin_unlock_irq(&zone->lru_lock);
1225 pgdeactivate += pgmoved;
1227 if (buffer_heads_over_limit)
1228 pagevec_strip(&pvec);
1229 __pagevec_release(&pvec);
1230 spin_lock_irq(&zone->lru_lock);
1233 zone->nr_inactive += pgmoved;
1234 pgdeactivate += pgmoved;
1235 if (buffer_heads_over_limit) {
1236 spin_unlock_irq(&zone->lru_lock);
1237 pagevec_strip(&pvec);
1238 spin_lock_irq(&zone->lru_lock);
1242 while (!list_empty(&l_active)) {
1243 page = lru_to_page(&l_active);
1244 prefetchw_prev_lru_page(page, &l_active, flags);
1245 if (TestSetPageLRU(page))
1247 BUG_ON(!PageActive(page));
1248 list_move(&page->lru, &zone->active_list);
1250 if (!pagevec_add(&pvec, page)) {
1251 zone->nr_active += pgmoved;
1253 spin_unlock_irq(&zone->lru_lock);
1254 __pagevec_release(&pvec);
1255 spin_lock_irq(&zone->lru_lock);
1258 zone->nr_active += pgmoved;
1259 spin_unlock(&zone->lru_lock);
1261 __mod_page_state_zone(zone, pgrefill, pgscanned);
1262 __mod_page_state(pgdeactivate, pgdeactivate);
1265 pagevec_release(&pvec);
1269 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1272 shrink_zone(struct zone *zone, struct scan_control *sc)
1274 unsigned long nr_active;
1275 unsigned long nr_inactive;
1277 atomic_inc(&zone->reclaim_in_progress);
1280 * Add one to `nr_to_scan' just to make sure that the kernel will
1281 * slowly sift through the active list.
1283 zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
1284 nr_active = zone->nr_scan_active;
1285 if (nr_active >= sc->swap_cluster_max)
1286 zone->nr_scan_active = 0;
1290 zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
1291 nr_inactive = zone->nr_scan_inactive;
1292 if (nr_inactive >= sc->swap_cluster_max)
1293 zone->nr_scan_inactive = 0;
1297 while (nr_active || nr_inactive) {
1299 sc->nr_to_scan = min(nr_active,
1300 (unsigned long)sc->swap_cluster_max);
1301 nr_active -= sc->nr_to_scan;
1302 refill_inactive_zone(zone, sc);
1306 sc->nr_to_scan = min(nr_inactive,
1307 (unsigned long)sc->swap_cluster_max);
1308 nr_inactive -= sc->nr_to_scan;
1309 shrink_cache(zone, sc);
1313 throttle_vm_writeout();
1315 atomic_dec(&zone->reclaim_in_progress);
1319 * This is the direct reclaim path, for page-allocating processes. We only
1320 * try to reclaim pages from zones which will satisfy the caller's allocation
1323 * We reclaim from a zone even if that zone is over pages_high. Because:
1324 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1326 * b) The zones may be over pages_high but they must go *over* pages_high to
1327 * satisfy the `incremental min' zone defense algorithm.
1329 * Returns the number of reclaimed pages.
1331 * If a zone is deemed to be full of pinned pages then just give it a light
1332 * scan then give up on it.
1335 shrink_caches(struct zone **zones, struct scan_control *sc)
1339 for (i = 0; zones[i] != NULL; i++) {
1340 struct zone *zone = zones[i];
1342 if (!populated_zone(zone))
1345 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1348 zone->temp_priority = sc->priority;
1349 if (zone->prev_priority > sc->priority)
1350 zone->prev_priority = sc->priority;
1352 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
1353 continue; /* Let kswapd poll it */
1355 shrink_zone(zone, sc);
1360 * This is the main entry point to direct page reclaim.
1362 * If a full scan of the inactive list fails to free enough memory then we
1363 * are "out of memory" and something needs to be killed.
1365 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1366 * high - the zone may be full of dirty or under-writeback pages, which this
1367 * caller can't do much about. We kick pdflush and take explicit naps in the
1368 * hope that some of these pages can be written. But if the allocating task
1369 * holds filesystem locks which prevent writeout this might not work, and the
1370 * allocation attempt will fail.
1372 int try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
1376 int total_scanned = 0, total_reclaimed = 0;
1377 struct reclaim_state *reclaim_state = current->reclaim_state;
1378 struct scan_control sc;
1379 unsigned long lru_pages = 0;
1382 sc.gfp_mask = gfp_mask;
1383 sc.may_writepage = !laptop_mode;
1386 inc_page_state(allocstall);
1388 for (i = 0; zones[i] != NULL; i++) {
1389 struct zone *zone = zones[i];
1391 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1394 zone->temp_priority = DEF_PRIORITY;
1395 lru_pages += zone->nr_active + zone->nr_inactive;
1398 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1399 sc.nr_mapped = read_page_state(nr_mapped);
1401 sc.nr_reclaimed = 0;
1402 sc.priority = priority;
1403 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1405 disable_swap_token();
1406 shrink_caches(zones, &sc);
1407 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
1408 if (reclaim_state) {
1409 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1410 reclaim_state->reclaimed_slab = 0;
1412 total_scanned += sc.nr_scanned;
1413 total_reclaimed += sc.nr_reclaimed;
1414 if (total_reclaimed >= sc.swap_cluster_max) {
1420 * Try to write back as many pages as we just scanned. This
1421 * tends to cause slow streaming writers to write data to the
1422 * disk smoothly, at the dirtying rate, which is nice. But
1423 * that's undesirable in laptop mode, where we *want* lumpy
1424 * writeout. So in laptop mode, write out the whole world.
1426 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
1427 wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1428 sc.may_writepage = 1;
1431 /* Take a nap, wait for some writeback to complete */
1432 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1433 blk_congestion_wait(WRITE, HZ/10);
1436 for (i = 0; zones[i] != 0; i++) {
1437 struct zone *zone = zones[i];
1439 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1442 zone->prev_priority = zone->temp_priority;
1448 * For kswapd, balance_pgdat() will work across all this node's zones until
1449 * they are all at pages_high.
1451 * If `nr_pages' is non-zero then it is the number of pages which are to be
1452 * reclaimed, regardless of the zone occupancies. This is a software suspend
1455 * Returns the number of pages which were actually freed.
1457 * There is special handling here for zones which are full of pinned pages.
1458 * This can happen if the pages are all mlocked, or if they are all used by
1459 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
1460 * What we do is to detect the case where all pages in the zone have been
1461 * scanned twice and there has been zero successful reclaim. Mark the zone as
1462 * dead and from now on, only perform a short scan. Basically we're polling
1463 * the zone for when the problem goes away.
1465 * kswapd scans the zones in the highmem->normal->dma direction. It skips
1466 * zones which have free_pages > pages_high, but once a zone is found to have
1467 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1468 * of the number of free pages in the lower zones. This interoperates with
1469 * the page allocator fallback scheme to ensure that aging of pages is balanced
1472 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
1474 int to_free = nr_pages;
1478 int total_scanned, total_reclaimed;
1479 struct reclaim_state *reclaim_state = current->reclaim_state;
1480 struct scan_control sc;
1484 total_reclaimed = 0;
1485 sc.gfp_mask = GFP_KERNEL;
1486 sc.may_writepage = !laptop_mode;
1488 sc.nr_mapped = read_page_state(nr_mapped);
1490 inc_page_state(pageoutrun);
1492 for (i = 0; i < pgdat->nr_zones; i++) {
1493 struct zone *zone = pgdat->node_zones + i;
1495 zone->temp_priority = DEF_PRIORITY;
1498 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1499 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
1500 unsigned long lru_pages = 0;
1502 /* The swap token gets in the way of swapout... */
1504 disable_swap_token();
1508 if (nr_pages == 0) {
1510 * Scan in the highmem->dma direction for the highest
1511 * zone which needs scanning
1513 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1514 struct zone *zone = pgdat->node_zones + i;
1516 if (!populated_zone(zone))
1519 if (zone->all_unreclaimable &&
1520 priority != DEF_PRIORITY)
1523 if (!zone_watermark_ok(zone, order,
1524 zone->pages_high, 0, 0)) {
1531 end_zone = pgdat->nr_zones - 1;
1534 for (i = 0; i <= end_zone; i++) {
1535 struct zone *zone = pgdat->node_zones + i;
1537 lru_pages += zone->nr_active + zone->nr_inactive;
1541 * Now scan the zone in the dma->highmem direction, stopping
1542 * at the last zone which needs scanning.
1544 * We do this because the page allocator works in the opposite
1545 * direction. This prevents the page allocator from allocating
1546 * pages behind kswapd's direction of progress, which would
1547 * cause too much scanning of the lower zones.
1549 for (i = 0; i <= end_zone; i++) {
1550 struct zone *zone = pgdat->node_zones + i;
1553 if (!populated_zone(zone))
1556 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1559 if (nr_pages == 0) { /* Not software suspend */
1560 if (!zone_watermark_ok(zone, order,
1561 zone->pages_high, end_zone, 0))
1564 zone->temp_priority = priority;
1565 if (zone->prev_priority > priority)
1566 zone->prev_priority = priority;
1568 sc.nr_reclaimed = 0;
1569 sc.priority = priority;
1570 sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
1571 atomic_inc(&zone->reclaim_in_progress);
1572 shrink_zone(zone, &sc);
1573 atomic_dec(&zone->reclaim_in_progress);
1574 reclaim_state->reclaimed_slab = 0;
1575 nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1577 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1578 total_reclaimed += sc.nr_reclaimed;
1579 total_scanned += sc.nr_scanned;
1580 if (zone->all_unreclaimable)
1582 if (nr_slab == 0 && zone->pages_scanned >=
1583 (zone->nr_active + zone->nr_inactive) * 4)
1584 zone->all_unreclaimable = 1;
1586 * If we've done a decent amount of scanning and
1587 * the reclaim ratio is low, start doing writepage
1588 * even in laptop mode
1590 if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1591 total_scanned > total_reclaimed+total_reclaimed/2)
1592 sc.may_writepage = 1;
1594 if (nr_pages && to_free > total_reclaimed)
1595 continue; /* swsusp: need to do more work */
1597 break; /* kswapd: all done */
1599 * OK, kswapd is getting into trouble. Take a nap, then take
1600 * another pass across the zones.
1602 if (total_scanned && priority < DEF_PRIORITY - 2)
1603 blk_congestion_wait(WRITE, HZ/10);
1606 * We do this so kswapd doesn't build up large priorities for
1607 * example when it is freeing in parallel with allocators. It
1608 * matches the direct reclaim path behaviour in terms of impact
1609 * on zone->*_priority.
1611 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
1615 for (i = 0; i < pgdat->nr_zones; i++) {
1616 struct zone *zone = pgdat->node_zones + i;
1618 zone->prev_priority = zone->temp_priority;
1620 if (!all_zones_ok) {
1625 return total_reclaimed;
1629 * The background pageout daemon, started as a kernel thread
1630 * from the init process.
1632 * This basically trickles out pages so that we have _some_
1633 * free memory available even if there is no other activity
1634 * that frees anything up. This is needed for things like routing
1635 * etc, where we otherwise might have all activity going on in
1636 * asynchronous contexts that cannot page things out.
1638 * If there are applications that are active memory-allocators
1639 * (most normal use), this basically shouldn't matter.
1641 static int kswapd(void *p)
1643 unsigned long order;
1644 pg_data_t *pgdat = (pg_data_t*)p;
1645 struct task_struct *tsk = current;
1647 struct reclaim_state reclaim_state = {
1648 .reclaimed_slab = 0,
1652 daemonize("kswapd%d", pgdat->node_id);
1653 cpumask = node_to_cpumask(pgdat->node_id);
1654 if (!cpus_empty(cpumask))
1655 set_cpus_allowed(tsk, cpumask);
1656 current->reclaim_state = &reclaim_state;
1659 * Tell the memory management that we're a "memory allocator",
1660 * and that if we need more memory we should get access to it
1661 * regardless (see "__alloc_pages()"). "kswapd" should
1662 * never get caught in the normal page freeing logic.
1664 * (Kswapd normally doesn't need memory anyway, but sometimes
1665 * you need a small amount of memory in order to be able to
1666 * page out something else, and this flag essentially protects
1667 * us from recursively trying to free more memory as we're
1668 * trying to free the first piece of memory in the first place).
1670 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1674 unsigned long new_order;
1678 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1679 new_order = pgdat->kswapd_max_order;
1680 pgdat->kswapd_max_order = 0;
1681 if (order < new_order) {
1683 * Don't sleep if someone wants a larger 'order'
1689 order = pgdat->kswapd_max_order;
1691 finish_wait(&pgdat->kswapd_wait, &wait);
1693 balance_pgdat(pgdat, 0, order);
1699 * A zone is low on free memory, so wake its kswapd task to service it.
1701 void wakeup_kswapd(struct zone *zone, int order)
1705 if (!populated_zone(zone))
1708 pgdat = zone->zone_pgdat;
1709 if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1711 if (pgdat->kswapd_max_order < order)
1712 pgdat->kswapd_max_order = order;
1713 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1715 if (!waitqueue_active(&pgdat->kswapd_wait))
1717 wake_up_interruptible(&pgdat->kswapd_wait);
1722 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed
1725 int shrink_all_memory(int nr_pages)
1728 int nr_to_free = nr_pages;
1730 struct reclaim_state reclaim_state = {
1731 .reclaimed_slab = 0,
1734 current->reclaim_state = &reclaim_state;
1735 for_each_pgdat(pgdat) {
1737 freed = balance_pgdat(pgdat, nr_to_free, 0);
1739 nr_to_free -= freed;
1740 if (nr_to_free <= 0)
1743 current->reclaim_state = NULL;
1748 #ifdef CONFIG_HOTPLUG_CPU
1749 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1750 not required for correctness. So if the last cpu in a node goes
1751 away, we get changed to run anywhere: as the first one comes back,
1752 restore their cpu bindings. */
1753 static int __devinit cpu_callback(struct notifier_block *nfb,
1754 unsigned long action,
1760 if (action == CPU_ONLINE) {
1761 for_each_pgdat(pgdat) {
1762 mask = node_to_cpumask(pgdat->node_id);
1763 if (any_online_cpu(mask) != NR_CPUS)
1764 /* One of our CPUs online: restore mask */
1765 set_cpus_allowed(pgdat->kswapd, mask);
1770 #endif /* CONFIG_HOTPLUG_CPU */
1772 static int __init kswapd_init(void)
1776 for_each_pgdat(pgdat)
1778 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1779 total_memory = nr_free_pagecache_pages();
1780 hotcpu_notifier(cpu_callback, 0);
1784 module_init(kswapd_init)
1790 * If non-zero call zone_reclaim when the number of free pages falls below
1793 * In the future we may add flags to the mode. However, the page allocator
1794 * should only have to check that zone_reclaim_mode != 0 before calling
1797 int zone_reclaim_mode __read_mostly;
1799 #define RECLAIM_OFF 0
1800 #define RECLAIM_ZONE (1<<0) /* Run shrink_cache on the zone */
1801 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
1802 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
1803 #define RECLAIM_SLAB (1<<3) /* Do a global slab shrink if the zone is out of memory */
1806 * Mininum time between zone reclaim scans
1808 int zone_reclaim_interval __read_mostly = 30*HZ;
1811 * Priority for ZONE_RECLAIM. This determines the fraction of pages
1812 * of a node considered for each zone_reclaim. 4 scans 1/16th of
1815 #define ZONE_RECLAIM_PRIORITY 4
1818 * Try to free up some pages from this zone through reclaim.
1820 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1823 struct task_struct *p = current;
1824 struct reclaim_state reclaim_state;
1825 struct scan_control sc;
1829 if (time_before(jiffies,
1830 zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval))
1833 if (!(gfp_mask & __GFP_WAIT) ||
1834 zone->all_unreclaimable ||
1835 atomic_read(&zone->reclaim_in_progress) > 0)
1838 node_id = zone->zone_pgdat->node_id;
1839 mask = node_to_cpumask(node_id);
1840 if (!cpus_empty(mask) && node_id != numa_node_id())
1843 sc.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE);
1844 sc.may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP);
1846 sc.nr_reclaimed = 0;
1847 sc.priority = ZONE_RECLAIM_PRIORITY + 1;
1848 sc.nr_mapped = read_page_state(nr_mapped);
1849 sc.gfp_mask = gfp_mask;
1851 disable_swap_token();
1853 nr_pages = 1 << order;
1854 if (nr_pages > SWAP_CLUSTER_MAX)
1855 sc.swap_cluster_max = nr_pages;
1857 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1860 p->flags |= PF_MEMALLOC;
1861 reclaim_state.reclaimed_slab = 0;
1862 p->reclaim_state = &reclaim_state;
1865 * Free memory by calling shrink zone with increasing priorities
1866 * until we have enough memory freed.
1870 shrink_zone(zone, &sc);
1872 } while (sc.nr_reclaimed < nr_pages && sc.priority > 0);
1874 if (sc.nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) {
1876 * shrink_slab does not currently allow us to determine
1877 * how many pages were freed in the zone. So we just
1878 * shake the slab and then go offnode for a single allocation.
1880 * shrink_slab will free memory on all zones and may take
1883 shrink_slab(sc.nr_scanned, gfp_mask, order);
1884 sc.nr_reclaimed = 1; /* Avoid getting the off node timeout */
1887 p->reclaim_state = NULL;
1888 current->flags &= ~PF_MEMALLOC;
1890 if (sc.nr_reclaimed == 0)
1891 zone->last_unsuccessful_zone_reclaim = jiffies;
1893 return sc.nr_reclaimed >= nr_pages;