Root/mm/vmscan.c

1/*
2 * linux/mm/vmscan.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 *
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.
12 */
13
14#include <linux/mm.h>
15#include <linux/module.h>
16#include <linux/gfp.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/vmstat.h>
23#include <linux/file.h>
24#include <linux/writeback.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/cpuset.h>
35#include <linux/notifier.h>
36#include <linux/rwsem.h>
37#include <linux/delay.h>
38#include <linux/kthread.h>
39#include <linux/freezer.h>
40#include <linux/memcontrol.h>
41#include <linux/delayacct.h>
42#include <linux/sysctl.h>
43
44#include <asm/tlbflush.h>
45#include <asm/div64.h>
46
47#include <linux/swapops.h>
48
49#include "internal.h"
50
51struct scan_control {
52    /* Incremented by the number of inactive pages that were scanned */
53    unsigned long nr_scanned;
54
55    /* Number of pages freed so far during a call to shrink_zones() */
56    unsigned long nr_reclaimed;
57
58    /* How many pages shrink_list() should reclaim */
59    unsigned long nr_to_reclaim;
60
61    unsigned long hibernation_mode;
62
63    /* This context's GFP mask */
64    gfp_t gfp_mask;
65
66    int may_writepage;
67
68    /* Can mapped pages be reclaimed? */
69    int may_unmap;
70
71    /* Can pages be swapped as part of reclaim? */
72    int may_swap;
73
74    int swappiness;
75
76    int order;
77
78    /*
79     * Intend to reclaim enough contenious memory rather than to reclaim
80     * enough amount memory. I.e, it's the mode for high order allocation.
81     */
82    bool lumpy_reclaim_mode;
83
84    /* Which cgroup do we reclaim from */
85    struct mem_cgroup *mem_cgroup;
86
87    /*
88     * Nodemask of nodes allowed by the caller. If NULL, all nodes
89     * are scanned.
90     */
91    nodemask_t *nodemask;
92};
93
94#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
95
96#ifdef ARCH_HAS_PREFETCH
97#define prefetch_prev_lru_page(_page, _base, _field) \
98    do { \
99        if ((_page)->lru.prev != _base) { \
100            struct page *prev; \
101                                    \
102            prev = lru_to_page(&(_page->lru)); \
103            prefetch(&prev->_field); \
104        } \
105    } while (0)
106#else
107#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
108#endif
109
110#ifdef ARCH_HAS_PREFETCHW
111#define prefetchw_prev_lru_page(_page, _base, _field) \
112    do { \
113        if ((_page)->lru.prev != _base) { \
114            struct page *prev; \
115                                    \
116            prev = lru_to_page(&(_page->lru)); \
117            prefetchw(&prev->_field); \
118        } \
119    } while (0)
120#else
121#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
122#endif
123
124/*
125 * From 0 .. 100. Higher means more swappy.
126 */
127int vm_swappiness = 60;
128long vm_total_pages; /* The total number of pages which the VM controls */
129
130static LIST_HEAD(shrinker_list);
131static DECLARE_RWSEM(shrinker_rwsem);
132
133#ifdef CONFIG_CGROUP_MEM_RES_CTLR
134#define scanning_global_lru(sc) (!(sc)->mem_cgroup)
135#else
136#define scanning_global_lru(sc) (1)
137#endif
138
139static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
140                          struct scan_control *sc)
141{
142    if (!scanning_global_lru(sc))
143        return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
144
145    return &zone->reclaim_stat;
146}
147
148static unsigned long zone_nr_lru_pages(struct zone *zone,
149                struct scan_control *sc, enum lru_list lru)
150{
151    if (!scanning_global_lru(sc))
152        return mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, lru);
153
154    return zone_page_state(zone, NR_LRU_BASE + lru);
155}
156
157
158/*
159 * Add a shrinker callback to be called from the vm
160 */
161void register_shrinker(struct shrinker *shrinker)
162{
163    shrinker->nr = 0;
164    down_write(&shrinker_rwsem);
165    list_add_tail(&shrinker->list, &shrinker_list);
166    up_write(&shrinker_rwsem);
167}
168EXPORT_SYMBOL(register_shrinker);
169
170/*
171 * Remove one
172 */
173void unregister_shrinker(struct shrinker *shrinker)
174{
175    down_write(&shrinker_rwsem);
176    list_del(&shrinker->list);
177    up_write(&shrinker_rwsem);
178}
179EXPORT_SYMBOL(unregister_shrinker);
180
181#define SHRINK_BATCH 128
182/*
183 * Call the shrink functions to age shrinkable caches
184 *
185 * Here we assume it costs one seek to replace a lru page and that it also
186 * takes a seek to recreate a cache object. With this in mind we age equal
187 * percentages of the lru and ageable caches. This should balance the seeks
188 * generated by these structures.
189 *
190 * If the vm encountered mapped pages on the LRU it increase the pressure on
191 * slab to avoid swapping.
192 *
193 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
194 *
195 * `lru_pages' represents the number of on-LRU pages in all the zones which
196 * are eligible for the caller's allocation attempt. It is used for balancing
197 * slab reclaim versus page reclaim.
198 *
199 * Returns the number of slab objects which we shrunk.
200 */
201unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
202            unsigned long lru_pages)
203{
204    struct shrinker *shrinker;
205    unsigned long ret = 0;
206
207    if (scanned == 0)
208        scanned = SWAP_CLUSTER_MAX;
209
210    if (!down_read_trylock(&shrinker_rwsem))
211        return 1; /* Assume we'll be able to shrink next time */
212
213    list_for_each_entry(shrinker, &shrinker_list, list) {
214        unsigned long long delta;
215        unsigned long total_scan;
216        unsigned long max_pass;
217
218        max_pass = (*shrinker->shrink)(shrinker, 0, gfp_mask);
219        delta = (4 * scanned) / shrinker->seeks;
220        delta *= max_pass;
221        do_div(delta, lru_pages + 1);
222        shrinker->nr += delta;
223        if (shrinker->nr < 0) {
224            printk(KERN_ERR "shrink_slab: %pF negative objects to "
225                   "delete nr=%ld\n",
226                   shrinker->shrink, shrinker->nr);
227            shrinker->nr = max_pass;
228        }
229
230        /*
231         * Avoid risking looping forever due to too large nr value:
232         * never try to free more than twice the estimate number of
233         * freeable entries.
234         */
235        if (shrinker->nr > max_pass * 2)
236            shrinker->nr = max_pass * 2;
237
238        total_scan = shrinker->nr;
239        shrinker->nr = 0;
240
241        while (total_scan >= SHRINK_BATCH) {
242            long this_scan = SHRINK_BATCH;
243            int shrink_ret;
244            int nr_before;
245
246            nr_before = (*shrinker->shrink)(shrinker, 0, gfp_mask);
247            shrink_ret = (*shrinker->shrink)(shrinker, this_scan,
248                                gfp_mask);
249            if (shrink_ret == -1)
250                break;
251            if (shrink_ret < nr_before)
252                ret += nr_before - shrink_ret;
253            count_vm_events(SLABS_SCANNED, this_scan);
254            total_scan -= this_scan;
255
256            cond_resched();
257        }
258
259        shrinker->nr += total_scan;
260    }
261    up_read(&shrinker_rwsem);
262    return ret;
263}
264
265static inline int is_page_cache_freeable(struct page *page)
266{
267    /*
268     * A freeable page cache page is referenced only by the caller
269     * that isolated the page, the page cache radix tree and
270     * optional buffer heads at page->private.
271     */
272    return page_count(page) - page_has_private(page) == 2;
273}
274
275static int may_write_to_queue(struct backing_dev_info *bdi)
276{
277    if (current->flags & PF_SWAPWRITE)
278        return 1;
279    if (!bdi_write_congested(bdi))
280        return 1;
281    if (bdi == current->backing_dev_info)
282        return 1;
283    return 0;
284}
285
286/*
287 * We detected a synchronous write error writing a page out. Probably
288 * -ENOSPC. We need to propagate that into the address_space for a subsequent
289 * fsync(), msync() or close().
290 *
291 * The tricky part is that after writepage we cannot touch the mapping: nothing
292 * prevents it from being freed up. But we have a ref on the page and once
293 * that page is locked, the mapping is pinned.
294 *
295 * We're allowed to run sleeping lock_page() here because we know the caller has
296 * __GFP_FS.
297 */
298static void handle_write_error(struct address_space *mapping,
299                struct page *page, int error)
300{
301    lock_page_nosync(page);
302    if (page_mapping(page) == mapping)
303        mapping_set_error(mapping, error);
304    unlock_page(page);
305}
306
307/* Request for sync pageout. */
308enum pageout_io {
309    PAGEOUT_IO_ASYNC,
310    PAGEOUT_IO_SYNC,
311};
312
313/* possible outcome of pageout() */
314typedef enum {
315    /* failed to write page out, page is locked */
316    PAGE_KEEP,
317    /* move page to the active list, page is locked */
318    PAGE_ACTIVATE,
319    /* page has been sent to the disk successfully, page is unlocked */
320    PAGE_SUCCESS,
321    /* page is clean and locked */
322    PAGE_CLEAN,
323} pageout_t;
324
325/*
326 * pageout is called by shrink_page_list() for each dirty page.
327 * Calls ->writepage().
328 */
329static pageout_t pageout(struct page *page, struct address_space *mapping,
330                        enum pageout_io sync_writeback)
331{
332    /*
333     * If the page is dirty, only perform writeback if that write
334     * will be non-blocking. To prevent this allocation from being
335     * stalled by pagecache activity. But note that there may be
336     * stalls if we need to run get_block(). We could test
337     * PagePrivate for that.
338     *
339     * If this process is currently in __generic_file_aio_write() against
340     * this page's queue, we can perform writeback even if that
341     * will block.
342     *
343     * If the page is swapcache, write it back even if that would
344     * block, for some throttling. This happens by accident, because
345     * swap_backing_dev_info is bust: it doesn't reflect the
346     * congestion state of the swapdevs. Easy to fix, if needed.
347     */
348    if (!is_page_cache_freeable(page))
349        return PAGE_KEEP;
350    if (!mapping) {
351        /*
352         * Some data journaling orphaned pages can have
353         * page->mapping == NULL while being dirty with clean buffers.
354         */
355        if (page_has_private(page)) {
356            if (try_to_free_buffers(page)) {
357                ClearPageDirty(page);
358                printk("%s: orphaned page\n", __func__);
359                return PAGE_CLEAN;
360            }
361        }
362        return PAGE_KEEP;
363    }
364    if (mapping->a_ops->writepage == NULL)
365        return PAGE_ACTIVATE;
366    if (!may_write_to_queue(mapping->backing_dev_info))
367        return PAGE_KEEP;
368
369    if (clear_page_dirty_for_io(page)) {
370        int res;
371        struct writeback_control wbc = {
372            .sync_mode = WB_SYNC_NONE,
373            .nr_to_write = SWAP_CLUSTER_MAX,
374            .range_start = 0,
375            .range_end = LLONG_MAX,
376            .nonblocking = 1,
377            .for_reclaim = 1,
378        };
379
380        SetPageReclaim(page);
381        res = mapping->a_ops->writepage(page, &wbc);
382        if (res < 0)
383            handle_write_error(mapping, page, res);
384        if (res == AOP_WRITEPAGE_ACTIVATE) {
385            ClearPageReclaim(page);
386            return PAGE_ACTIVATE;
387        }
388
389        /*
390         * Wait on writeback if requested to. This happens when
391         * direct reclaiming a large contiguous area and the
392         * first attempt to free a range of pages fails.
393         */
394        if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
395            wait_on_page_writeback(page);
396
397        if (!PageWriteback(page)) {
398            /* synchronous write or broken a_ops? */
399            ClearPageReclaim(page);
400        }
401        inc_zone_page_state(page, NR_VMSCAN_WRITE);
402        return PAGE_SUCCESS;
403    }
404
405    return PAGE_CLEAN;
406}
407
408/*
409 * Same as remove_mapping, but if the page is removed from the mapping, it
410 * gets returned with a refcount of 0.
411 */
412static int __remove_mapping(struct address_space *mapping, struct page *page)
413{
414    BUG_ON(!PageLocked(page));
415    BUG_ON(mapping != page_mapping(page));
416
417    spin_lock_irq(&mapping->tree_lock);
418    /*
419     * The non racy check for a busy page.
420     *
421     * Must be careful with the order of the tests. When someone has
422     * a ref to the page, it may be possible that they dirty it then
423     * drop the reference. So if PageDirty is tested before page_count
424     * here, then the following race may occur:
425     *
426     * get_user_pages(&page);
427     * [user mapping goes away]
428     * write_to(page);
429     * !PageDirty(page) [good]
430     * SetPageDirty(page);
431     * put_page(page);
432     * !page_count(page) [good, discard it]
433     *
434     * [oops, our write_to data is lost]
435     *
436     * Reversing the order of the tests ensures such a situation cannot
437     * escape unnoticed. The smp_rmb is needed to ensure the page->flags
438     * load is not satisfied before that of page->_count.
439     *
440     * Note that if SetPageDirty is always performed via set_page_dirty,
441     * and thus under tree_lock, then this ordering is not required.
442     */
443    if (!page_freeze_refs(page, 2))
444        goto cannot_free;
445    /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
446    if (unlikely(PageDirty(page))) {
447        page_unfreeze_refs(page, 2);
448        goto cannot_free;
449    }
450
451    if (PageSwapCache(page)) {
452        swp_entry_t swap = { .val = page_private(page) };
453        __delete_from_swap_cache(page);
454        spin_unlock_irq(&mapping->tree_lock);
455        swapcache_free(swap, page);
456    } else {
457        __remove_from_page_cache(page);
458        spin_unlock_irq(&mapping->tree_lock);
459        mem_cgroup_uncharge_cache_page(page);
460    }
461
462    return 1;
463
464cannot_free:
465    spin_unlock_irq(&mapping->tree_lock);
466    return 0;
467}
468
469/*
470 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
471 * someone else has a ref on the page, abort and return 0. If it was
472 * successfully detached, return 1. Assumes the caller has a single ref on
473 * this page.
474 */
475int remove_mapping(struct address_space *mapping, struct page *page)
476{
477    if (__remove_mapping(mapping, page)) {
478        /*
479         * Unfreezing the refcount with 1 rather than 2 effectively
480         * drops the pagecache ref for us without requiring another
481         * atomic operation.
482         */
483        page_unfreeze_refs(page, 1);
484        return 1;
485    }
486    return 0;
487}
488
489/**
490 * putback_lru_page - put previously isolated page onto appropriate LRU list
491 * @page: page to be put back to appropriate lru list
492 *
493 * Add previously isolated @page to appropriate LRU list.
494 * Page may still be unevictable for other reasons.
495 *
496 * lru_lock must not be held, interrupts must be enabled.
497 */
498void putback_lru_page(struct page *page)
499{
500    int lru;
501    int active = !!TestClearPageActive(page);
502    int was_unevictable = PageUnevictable(page);
503
504    VM_BUG_ON(PageLRU(page));
505
506redo:
507    ClearPageUnevictable(page);
508
509    if (page_evictable(page, NULL)) {
510        /*
511         * For evictable pages, we can use the cache.
512         * In event of a race, worst case is we end up with an
513         * unevictable page on [in]active list.
514         * We know how to handle that.
515         */
516        lru = active + page_lru_base_type(page);
517        lru_cache_add_lru(page, lru);
518    } else {
519        /*
520         * Put unevictable pages directly on zone's unevictable
521         * list.
522         */
523        lru = LRU_UNEVICTABLE;
524        add_page_to_unevictable_list(page);
525        /*
526         * When racing with an mlock clearing (page is
527         * unlocked), make sure that if the other thread does
528         * not observe our setting of PG_lru and fails
529         * isolation, we see PG_mlocked cleared below and move
530         * the page back to the evictable list.
531         *
532         * The other side is TestClearPageMlocked().
533         */
534        smp_mb();
535    }
536
537    /*
538     * page's status can change while we move it among lru. If an evictable
539     * page is on unevictable list, it never be freed. To avoid that,
540     * check after we added it to the list, again.
541     */
542    if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
543        if (!isolate_lru_page(page)) {
544            put_page(page);
545            goto redo;
546        }
547        /* This means someone else dropped this page from LRU
548         * So, it will be freed or putback to LRU again. There is
549         * nothing to do here.
550         */
551    }
552
553    if (was_unevictable && lru != LRU_UNEVICTABLE)
554        count_vm_event(UNEVICTABLE_PGRESCUED);
555    else if (!was_unevictable && lru == LRU_UNEVICTABLE)
556        count_vm_event(UNEVICTABLE_PGCULLED);
557
558    put_page(page); /* drop ref from isolate */
559}
560
561enum page_references {
562    PAGEREF_RECLAIM,
563    PAGEREF_RECLAIM_CLEAN,
564    PAGEREF_KEEP,
565    PAGEREF_ACTIVATE,
566};
567
568static enum page_references page_check_references(struct page *page,
569                          struct scan_control *sc)
570{
571    int referenced_ptes, referenced_page;
572    unsigned long vm_flags;
573
574    referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
575    referenced_page = TestClearPageReferenced(page);
576
577    /* Lumpy reclaim - ignore references */
578    if (sc->lumpy_reclaim_mode)
579        return PAGEREF_RECLAIM;
580
581    /*
582     * Mlock lost the isolation race with us. Let try_to_unmap()
583     * move the page to the unevictable list.
584     */
585    if (vm_flags & VM_LOCKED)
586        return PAGEREF_RECLAIM;
587
588    if (referenced_ptes) {
589        if (PageAnon(page))
590            return PAGEREF_ACTIVATE;
591        /*
592         * All mapped pages start out with page table
593         * references from the instantiating fault, so we need
594         * to look twice if a mapped file page is used more
595         * than once.
596         *
597         * Mark it and spare it for another trip around the
598         * inactive list. Another page table reference will
599         * lead to its activation.
600         *
601         * Note: the mark is set for activated pages as well
602         * so that recently deactivated but used pages are
603         * quickly recovered.
604         */
605        SetPageReferenced(page);
606
607        if (referenced_page)
608            return PAGEREF_ACTIVATE;
609
610        return PAGEREF_KEEP;
611    }
612
613    /* Reclaim if clean, defer dirty pages to writeback */
614    if (referenced_page)
615        return PAGEREF_RECLAIM_CLEAN;
616
617    return PAGEREF_RECLAIM;
618}
619
620/*
621 * shrink_page_list() returns the number of reclaimed pages
622 */
623static unsigned long shrink_page_list(struct list_head *page_list,
624                    struct scan_control *sc,
625                    enum pageout_io sync_writeback)
626{
627    LIST_HEAD(ret_pages);
628    struct pagevec freed_pvec;
629    int pgactivate = 0;
630    unsigned long nr_reclaimed = 0;
631
632    cond_resched();
633
634    pagevec_init(&freed_pvec, 1);
635    while (!list_empty(page_list)) {
636        enum page_references references;
637        struct address_space *mapping;
638        struct page *page;
639        int may_enter_fs;
640
641        cond_resched();
642
643        page = lru_to_page(page_list);
644        list_del(&page->lru);
645
646        if (!trylock_page(page))
647            goto keep;
648
649        VM_BUG_ON(PageActive(page));
650
651        sc->nr_scanned++;
652
653        if (unlikely(!page_evictable(page, NULL)))
654            goto cull_mlocked;
655
656        if (!sc->may_unmap && page_mapped(page))
657            goto keep_locked;
658
659        /* Double the slab pressure for mapped and swapcache pages */
660        if (page_mapped(page) || PageSwapCache(page))
661            sc->nr_scanned++;
662
663        may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
664            (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
665
666        if (PageWriteback(page)) {
667            /*
668             * Synchronous reclaim is performed in two passes,
669             * first an asynchronous pass over the list to
670             * start parallel writeback, and a second synchronous
671             * pass to wait for the IO to complete. Wait here
672             * for any page for which writeback has already
673             * started.
674             */
675            if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
676                wait_on_page_writeback(page);
677            else
678                goto keep_locked;
679        }
680
681        references = page_check_references(page, sc);
682        switch (references) {
683        case PAGEREF_ACTIVATE:
684            goto activate_locked;
685        case PAGEREF_KEEP:
686            goto keep_locked;
687        case PAGEREF_RECLAIM:
688        case PAGEREF_RECLAIM_CLEAN:
689            ; /* try to reclaim the page below */
690        }
691
692        /*
693         * Anonymous process memory has backing store?
694         * Try to allocate it some swap space here.
695         */
696        if (PageAnon(page) && !PageSwapCache(page)) {
697            if (!(sc->gfp_mask & __GFP_IO))
698                goto keep_locked;
699            if (!add_to_swap(page))
700                goto activate_locked;
701            may_enter_fs = 1;
702        }
703
704        mapping = page_mapping(page);
705
706        /*
707         * The page is mapped into the page tables of one or more
708         * processes. Try to unmap it here.
709         */
710        if (page_mapped(page) && mapping) {
711            switch (try_to_unmap(page, TTU_UNMAP)) {
712            case SWAP_FAIL:
713                goto activate_locked;
714            case SWAP_AGAIN:
715                goto keep_locked;
716            case SWAP_MLOCK:
717                goto cull_mlocked;
718            case SWAP_SUCCESS:
719                ; /* try to free the page below */
720            }
721        }
722
723        if (PageDirty(page)) {
724            if (references == PAGEREF_RECLAIM_CLEAN)
725                goto keep_locked;
726            if (!may_enter_fs)
727                goto keep_locked;
728            if (!sc->may_writepage)
729                goto keep_locked;
730
731            /* Page is dirty, try to write it out here */
732            switch (pageout(page, mapping, sync_writeback)) {
733            case PAGE_KEEP:
734                goto keep_locked;
735            case PAGE_ACTIVATE:
736                goto activate_locked;
737            case PAGE_SUCCESS:
738                if (PageWriteback(page) || PageDirty(page))
739                    goto keep;
740                /*
741                 * A synchronous write - probably a ramdisk. Go
742                 * ahead and try to reclaim the page.
743                 */
744                if (!trylock_page(page))
745                    goto keep;
746                if (PageDirty(page) || PageWriteback(page))
747                    goto keep_locked;
748                mapping = page_mapping(page);
749            case PAGE_CLEAN:
750                ; /* try to free the page below */
751            }
752        }
753
754        /*
755         * If the page has buffers, try to free the buffer mappings
756         * associated with this page. If we succeed we try to free
757         * the page as well.
758         *
759         * We do this even if the page is PageDirty().
760         * try_to_release_page() does not perform I/O, but it is
761         * possible for a page to have PageDirty set, but it is actually
762         * clean (all its buffers are clean). This happens if the
763         * buffers were written out directly, with submit_bh(). ext3
764         * will do this, as well as the blockdev mapping.
765         * try_to_release_page() will discover that cleanness and will
766         * drop the buffers and mark the page clean - it can be freed.
767         *
768         * Rarely, pages can have buffers and no ->mapping. These are
769         * the pages which were not successfully invalidated in
770         * truncate_complete_page(). We try to drop those buffers here
771         * and if that worked, and the page is no longer mapped into
772         * process address space (page_count == 1) it can be freed.
773         * Otherwise, leave the page on the LRU so it is swappable.
774         */
775        if (page_has_private(page)) {
776            if (!try_to_release_page(page, sc->gfp_mask))
777                goto activate_locked;
778            if (!mapping && page_count(page) == 1) {
779                unlock_page(page);
780                if (put_page_testzero(page))
781                    goto free_it;
782                else {
783                    /*
784                     * rare race with speculative reference.
785                     * the speculative reference will free
786                     * this page shortly, so we may
787                     * increment nr_reclaimed here (and
788                     * leave it off the LRU).
789                     */
790                    nr_reclaimed++;
791                    continue;
792                }
793            }
794        }
795
796        if (!mapping || !__remove_mapping(mapping, page))
797            goto keep_locked;
798
799        /*
800         * At this point, we have no other references and there is
801         * no way to pick any more up (removed from LRU, removed
802         * from pagecache). Can use non-atomic bitops now (and
803         * we obviously don't have to worry about waking up a process
804         * waiting on the page lock, because there are no references.
805         */
806        __clear_page_locked(page);
807free_it:
808        nr_reclaimed++;
809        if (!pagevec_add(&freed_pvec, page)) {
810            __pagevec_free(&freed_pvec);
811            pagevec_reinit(&freed_pvec);
812        }
813        continue;
814
815cull_mlocked:
816        if (PageSwapCache(page))
817            try_to_free_swap(page);
818        unlock_page(page);
819        putback_lru_page(page);
820        continue;
821
822activate_locked:
823        /* Not a candidate for swapping, so reclaim swap space. */
824        if (PageSwapCache(page) && vm_swap_full())
825            try_to_free_swap(page);
826        VM_BUG_ON(PageActive(page));
827        SetPageActive(page);
828        pgactivate++;
829keep_locked:
830        unlock_page(page);
831keep:
832        list_add(&page->lru, &ret_pages);
833        VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
834    }
835    list_splice(&ret_pages, page_list);
836    if (pagevec_count(&freed_pvec))
837        __pagevec_free(&freed_pvec);
838    count_vm_events(PGACTIVATE, pgactivate);
839    return nr_reclaimed;
840}
841
842/*
843 * Attempt to remove the specified page from its LRU. Only take this page
844 * if it is of the appropriate PageActive status. Pages which are being
845 * freed elsewhere are also ignored.
846 *
847 * page: page to consider
848 * mode: one of the LRU isolation modes defined above
849 *
850 * returns 0 on success, -ve errno on failure.
851 */
852int __isolate_lru_page(struct page *page, int mode, int file)
853{
854    int ret = -EINVAL;
855
856    /* Only take pages on the LRU. */
857    if (!PageLRU(page))
858        return ret;
859
860    /*
861     * When checking the active state, we need to be sure we are
862     * dealing with comparible boolean values. Take the logical not
863     * of each.
864     */
865    if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
866        return ret;
867
868    if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
869        return ret;
870
871    /*
872     * When this function is being called for lumpy reclaim, we
873     * initially look into all LRU pages, active, inactive and
874     * unevictable; only give shrink_page_list evictable pages.
875     */
876    if (PageUnevictable(page))
877        return ret;
878
879    ret = -EBUSY;
880
881    if (likely(get_page_unless_zero(page))) {
882        /*
883         * Be careful not to clear PageLRU until after we're
884         * sure the page is not being freed elsewhere -- the
885         * page release code relies on it.
886         */
887        ClearPageLRU(page);
888        ret = 0;
889    }
890
891    return ret;
892}
893
894/*
895 * zone->lru_lock is heavily contended. Some of the functions that
896 * shrink the lists perform better by taking out a batch of pages
897 * and working on them outside the LRU lock.
898 *
899 * For pagecache intensive workloads, this function is the hottest
900 * spot in the kernel (apart from copy_*_user functions).
901 *
902 * Appropriate locks must be held before calling this function.
903 *
904 * @nr_to_scan: The number of pages to look through on the list.
905 * @src: The LRU list to pull pages off.
906 * @dst: The temp list to put pages on to.
907 * @scanned: The number of pages that were scanned.
908 * @order: The caller's attempted allocation order
909 * @mode: One of the LRU isolation modes
910 * @file: True [1] if isolating file [!anon] pages
911 *
912 * returns how many pages were moved onto *@dst.
913 */
914static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
915        struct list_head *src, struct list_head *dst,
916        unsigned long *scanned, int order, int mode, int file)
917{
918    unsigned long nr_taken = 0;
919    unsigned long scan;
920
921    for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
922        struct page *page;
923        unsigned long pfn;
924        unsigned long end_pfn;
925        unsigned long page_pfn;
926        int zone_id;
927
928        page = lru_to_page(src);
929        prefetchw_prev_lru_page(page, src, flags);
930
931        VM_BUG_ON(!PageLRU(page));
932
933        switch (__isolate_lru_page(page, mode, file)) {
934        case 0:
935            list_move(&page->lru, dst);
936            mem_cgroup_del_lru(page);
937            nr_taken++;
938            break;
939
940        case -EBUSY:
941            /* else it is being freed elsewhere */
942            list_move(&page->lru, src);
943            mem_cgroup_rotate_lru_list(page, page_lru(page));
944            continue;
945
946        default:
947            BUG();
948        }
949
950        if (!order)
951            continue;
952
953        /*
954         * Attempt to take all pages in the order aligned region
955         * surrounding the tag page. Only take those pages of
956         * the same active state as that tag page. We may safely
957         * round the target page pfn down to the requested order
958         * as the mem_map is guarenteed valid out to MAX_ORDER,
959         * where that page is in a different zone we will detect
960         * it from its zone id and abort this block scan.
961         */
962        zone_id = page_zone_id(page);
963        page_pfn = page_to_pfn(page);
964        pfn = page_pfn & ~((1 << order) - 1);
965        end_pfn = pfn + (1 << order);
966        for (; pfn < end_pfn; pfn++) {
967            struct page *cursor_page;
968
969            /* The target page is in the block, ignore it. */
970            if (unlikely(pfn == page_pfn))
971                continue;
972
973            /* Avoid holes within the zone. */
974            if (unlikely(!pfn_valid_within(pfn)))
975                break;
976
977            cursor_page = pfn_to_page(pfn);
978
979            /* Check that we have not crossed a zone boundary. */
980            if (unlikely(page_zone_id(cursor_page) != zone_id))
981                continue;
982
983            /*
984             * If we don't have enough swap space, reclaiming of
985             * anon page which don't already have a swap slot is
986             * pointless.
987             */
988            if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
989                    !PageSwapCache(cursor_page))
990                continue;
991
992            if (__isolate_lru_page(cursor_page, mode, file) == 0) {
993                list_move(&cursor_page->lru, dst);
994                mem_cgroup_del_lru(cursor_page);
995                nr_taken++;
996                scan++;
997            }
998        }
999    }
1000
1001    *scanned = scan;
1002    return nr_taken;
1003}
1004
1005static unsigned long isolate_pages_global(unsigned long nr,
1006                    struct list_head *dst,
1007                    unsigned long *scanned, int order,
1008                    int mode, struct zone *z,
1009                    int active, int file)
1010{
1011    int lru = LRU_BASE;
1012    if (active)
1013        lru += LRU_ACTIVE;
1014    if (file)
1015        lru += LRU_FILE;
1016    return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
1017                                mode, file);
1018}
1019
1020/*
1021 * clear_active_flags() is a helper for shrink_active_list(), clearing
1022 * any active bits from the pages in the list.
1023 */
1024static unsigned long clear_active_flags(struct list_head *page_list,
1025                    unsigned int *count)
1026{
1027    int nr_active = 0;
1028    int lru;
1029    struct page *page;
1030
1031    list_for_each_entry(page, page_list, lru) {
1032        lru = page_lru_base_type(page);
1033        if (PageActive(page)) {
1034            lru += LRU_ACTIVE;
1035            ClearPageActive(page);
1036            nr_active++;
1037        }
1038        count[lru]++;
1039    }
1040
1041    return nr_active;
1042}
1043
1044/**
1045 * isolate_lru_page - tries to isolate a page from its LRU list
1046 * @page: page to isolate from its LRU list
1047 *
1048 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1049 * vmstat statistic corresponding to whatever LRU list the page was on.
1050 *
1051 * Returns 0 if the page was removed from an LRU list.
1052 * Returns -EBUSY if the page was not on an LRU list.
1053 *
1054 * The returned page will have PageLRU() cleared. If it was found on
1055 * the active list, it will have PageActive set. If it was found on
1056 * the unevictable list, it will have the PageUnevictable bit set. That flag
1057 * may need to be cleared by the caller before letting the page go.
1058 *
1059 * The vmstat statistic corresponding to the list on which the page was
1060 * found will be decremented.
1061 *
1062 * Restrictions:
1063 * (1) Must be called with an elevated refcount on the page. This is a
1064 * fundamentnal difference from isolate_lru_pages (which is called
1065 * without a stable reference).
1066 * (2) the lru_lock must not be held.
1067 * (3) interrupts must be enabled.
1068 */
1069int isolate_lru_page(struct page *page)
1070{
1071    int ret = -EBUSY;
1072
1073    if (PageLRU(page)) {
1074        struct zone *zone = page_zone(page);
1075
1076        spin_lock_irq(&zone->lru_lock);
1077        if (PageLRU(page) && get_page_unless_zero(page)) {
1078            int lru = page_lru(page);
1079            ret = 0;
1080            ClearPageLRU(page);
1081
1082            del_page_from_lru_list(zone, page, lru);
1083        }
1084        spin_unlock_irq(&zone->lru_lock);
1085    }
1086    return ret;
1087}
1088
1089/*
1090 * Are there way too many processes in the direct reclaim path already?
1091 */
1092static int too_many_isolated(struct zone *zone, int file,
1093        struct scan_control *sc)
1094{
1095    unsigned long inactive, isolated;
1096
1097    if (current_is_kswapd())
1098        return 0;
1099
1100    if (!scanning_global_lru(sc))
1101        return 0;
1102
1103    if (file) {
1104        inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1105        isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1106    } else {
1107        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1108        isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1109    }
1110
1111    return isolated > inactive;
1112}
1113
1114/*
1115 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1116 * of reclaimed pages
1117 */
1118static unsigned long shrink_inactive_list(unsigned long max_scan,
1119            struct zone *zone, struct scan_control *sc,
1120            int priority, int file)
1121{
1122    LIST_HEAD(page_list);
1123    struct pagevec pvec;
1124    unsigned long nr_scanned = 0;
1125    unsigned long nr_reclaimed = 0;
1126    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1127
1128    while (unlikely(too_many_isolated(zone, file, sc))) {
1129        congestion_wait(BLK_RW_ASYNC, HZ/10);
1130
1131        /* We are about to die and free our memory. Return now. */
1132        if (fatal_signal_pending(current))
1133            return SWAP_CLUSTER_MAX;
1134    }
1135
1136
1137    pagevec_init(&pvec, 1);
1138
1139    lru_add_drain();
1140    spin_lock_irq(&zone->lru_lock);
1141    do {
1142        struct page *page;
1143        unsigned long nr_taken;
1144        unsigned long nr_scan;
1145        unsigned long nr_freed;
1146        unsigned long nr_active;
1147        unsigned int count[NR_LRU_LISTS] = { 0, };
1148        int mode = sc->lumpy_reclaim_mode ? ISOLATE_BOTH : ISOLATE_INACTIVE;
1149        unsigned long nr_anon;
1150        unsigned long nr_file;
1151
1152        if (scanning_global_lru(sc)) {
1153            nr_taken = isolate_pages_global(SWAP_CLUSTER_MAX,
1154                            &page_list, &nr_scan,
1155                            sc->order, mode,
1156                            zone, 0, file);
1157            zone->pages_scanned += nr_scan;
1158            if (current_is_kswapd())
1159                __count_zone_vm_events(PGSCAN_KSWAPD, zone,
1160                               nr_scan);
1161            else
1162                __count_zone_vm_events(PGSCAN_DIRECT, zone,
1163                               nr_scan);
1164        } else {
1165            nr_taken = mem_cgroup_isolate_pages(SWAP_CLUSTER_MAX,
1166                            &page_list, &nr_scan,
1167                            sc->order, mode,
1168                            zone, sc->mem_cgroup,
1169                            0, file);
1170            /*
1171             * mem_cgroup_isolate_pages() keeps track of
1172             * scanned pages on its own.
1173             */
1174        }
1175
1176        if (nr_taken == 0)
1177            goto done;
1178
1179        nr_active = clear_active_flags(&page_list, count);
1180        __count_vm_events(PGDEACTIVATE, nr_active);
1181
1182        __mod_zone_page_state(zone, NR_ACTIVE_FILE,
1183                        -count[LRU_ACTIVE_FILE]);
1184        __mod_zone_page_state(zone, NR_INACTIVE_FILE,
1185                        -count[LRU_INACTIVE_FILE]);
1186        __mod_zone_page_state(zone, NR_ACTIVE_ANON,
1187                        -count[LRU_ACTIVE_ANON]);
1188        __mod_zone_page_state(zone, NR_INACTIVE_ANON,
1189                        -count[LRU_INACTIVE_ANON]);
1190
1191        nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1192        nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1193        __mod_zone_page_state(zone, NR_ISOLATED_ANON, nr_anon);
1194        __mod_zone_page_state(zone, NR_ISOLATED_FILE, nr_file);
1195
1196        reclaim_stat->recent_scanned[0] += nr_anon;
1197        reclaim_stat->recent_scanned[1] += nr_file;
1198
1199        spin_unlock_irq(&zone->lru_lock);
1200
1201        nr_scanned += nr_scan;
1202        nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
1203
1204        /*
1205         * If we are direct reclaiming for contiguous pages and we do
1206         * not reclaim everything in the list, try again and wait
1207         * for IO to complete. This will stall high-order allocations
1208         * but that should be acceptable to the caller
1209         */
1210        if (nr_freed < nr_taken && !current_is_kswapd() &&
1211            sc->lumpy_reclaim_mode) {
1212            congestion_wait(BLK_RW_ASYNC, HZ/10);
1213
1214            /*
1215             * The attempt at page out may have made some
1216             * of the pages active, mark them inactive again.
1217             */
1218            nr_active = clear_active_flags(&page_list, count);
1219            count_vm_events(PGDEACTIVATE, nr_active);
1220
1221            nr_freed += shrink_page_list(&page_list, sc,
1222                            PAGEOUT_IO_SYNC);
1223        }
1224
1225        nr_reclaimed += nr_freed;
1226
1227        local_irq_disable();
1228        if (current_is_kswapd())
1229            __count_vm_events(KSWAPD_STEAL, nr_freed);
1230        __count_zone_vm_events(PGSTEAL, zone, nr_freed);
1231
1232        spin_lock(&zone->lru_lock);
1233        /*
1234         * Put back any unfreeable pages.
1235         */
1236        while (!list_empty(&page_list)) {
1237            int lru;
1238            page = lru_to_page(&page_list);
1239            VM_BUG_ON(PageLRU(page));
1240            list_del(&page->lru);
1241            if (unlikely(!page_evictable(page, NULL))) {
1242                spin_unlock_irq(&zone->lru_lock);
1243                putback_lru_page(page);
1244                spin_lock_irq(&zone->lru_lock);
1245                continue;
1246            }
1247            SetPageLRU(page);
1248            lru = page_lru(page);
1249            add_page_to_lru_list(zone, page, lru);
1250            if (is_active_lru(lru)) {
1251                int file = is_file_lru(lru);
1252                reclaim_stat->recent_rotated[file]++;
1253            }
1254            if (!pagevec_add(&pvec, page)) {
1255                spin_unlock_irq(&zone->lru_lock);
1256                __pagevec_release(&pvec);
1257                spin_lock_irq(&zone->lru_lock);
1258            }
1259        }
1260        __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1261        __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1262
1263      } while (nr_scanned < max_scan);
1264
1265done:
1266    spin_unlock_irq(&zone->lru_lock);
1267    pagevec_release(&pvec);
1268    return nr_reclaimed;
1269}
1270
1271/*
1272 * We are about to scan this zone at a certain priority level. If that priority
1273 * level is smaller (ie: more urgent) than the previous priority, then note
1274 * that priority level within the zone. This is done so that when the next
1275 * process comes in to scan this zone, it will immediately start out at this
1276 * priority level rather than having to build up its own scanning priority.
1277 * Here, this priority affects only the reclaim-mapped threshold.
1278 */
1279static inline void note_zone_scanning_priority(struct zone *zone, int priority)
1280{
1281    if (priority < zone->prev_priority)
1282        zone->prev_priority = priority;
1283}
1284
1285/*
1286 * This moves pages from the active list to the inactive list.
1287 *
1288 * We move them the other way if the page is referenced by one or more
1289 * processes, from rmap.
1290 *
1291 * If the pages are mostly unmapped, the processing is fast and it is
1292 * appropriate to hold zone->lru_lock across the whole operation. But if
1293 * the pages are mapped, the processing is slow (page_referenced()) so we
1294 * should drop zone->lru_lock around each page. It's impossible to balance
1295 * this, so instead we remove the pages from the LRU while processing them.
1296 * It is safe to rely on PG_active against the non-LRU pages in here because
1297 * nobody will play with that bit on a non-LRU page.
1298 *
1299 * The downside is that we have to touch page->_count against each page.
1300 * But we had to alter page->flags anyway.
1301 */
1302
1303static void move_active_pages_to_lru(struct zone *zone,
1304                     struct list_head *list,
1305                     enum lru_list lru)
1306{
1307    unsigned long pgmoved = 0;
1308    struct pagevec pvec;
1309    struct page *page;
1310
1311    pagevec_init(&pvec, 1);
1312
1313    while (!list_empty(list)) {
1314        page = lru_to_page(list);
1315
1316        VM_BUG_ON(PageLRU(page));
1317        SetPageLRU(page);
1318
1319        list_move(&page->lru, &zone->lru[lru].list);
1320        mem_cgroup_add_lru_list(page, lru);
1321        pgmoved++;
1322
1323        if (!pagevec_add(&pvec, page) || list_empty(list)) {
1324            spin_unlock_irq(&zone->lru_lock);
1325            if (buffer_heads_over_limit)
1326                pagevec_strip(&pvec);
1327            __pagevec_release(&pvec);
1328            spin_lock_irq(&zone->lru_lock);
1329        }
1330    }
1331    __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1332    if (!is_active_lru(lru))
1333        __count_vm_events(PGDEACTIVATE, pgmoved);
1334}
1335
1336static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1337            struct scan_control *sc, int priority, int file)
1338{
1339    unsigned long nr_taken;
1340    unsigned long pgscanned;
1341    unsigned long vm_flags;
1342    LIST_HEAD(l_hold); /* The pages which were snipped off */
1343    LIST_HEAD(l_active);
1344    LIST_HEAD(l_inactive);
1345    struct page *page;
1346    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1347    unsigned long nr_rotated = 0;
1348
1349    lru_add_drain();
1350    spin_lock_irq(&zone->lru_lock);
1351    if (scanning_global_lru(sc)) {
1352        nr_taken = isolate_pages_global(nr_pages, &l_hold,
1353                        &pgscanned, sc->order,
1354                        ISOLATE_ACTIVE, zone,
1355                        1, file);
1356        zone->pages_scanned += pgscanned;
1357    } else {
1358        nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
1359                        &pgscanned, sc->order,
1360                        ISOLATE_ACTIVE, zone,
1361                        sc->mem_cgroup, 1, file);
1362        /*
1363         * mem_cgroup_isolate_pages() keeps track of
1364         * scanned pages on its own.
1365         */
1366    }
1367
1368    reclaim_stat->recent_scanned[file] += nr_taken;
1369
1370    __count_zone_vm_events(PGREFILL, zone, pgscanned);
1371    if (file)
1372        __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1373    else
1374        __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1375    __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1376    spin_unlock_irq(&zone->lru_lock);
1377
1378    while (!list_empty(&l_hold)) {
1379        cond_resched();
1380        page = lru_to_page(&l_hold);
1381        list_del(&page->lru);
1382
1383        if (unlikely(!page_evictable(page, NULL))) {
1384            putback_lru_page(page);
1385            continue;
1386        }
1387
1388        if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1389            nr_rotated++;
1390            /*
1391             * Identify referenced, file-backed active pages and
1392             * give them one more trip around the active list. So
1393             * that executable code get better chances to stay in
1394             * memory under moderate memory pressure. Anon pages
1395             * are not likely to be evicted by use-once streaming
1396             * IO, plus JVM can create lots of anon VM_EXEC pages,
1397             * so we ignore them here.
1398             */
1399            if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1400                list_add(&page->lru, &l_active);
1401                continue;
1402            }
1403        }
1404
1405        ClearPageActive(page); /* we are de-activating */
1406        list_add(&page->lru, &l_inactive);
1407    }
1408
1409    /*
1410     * Move pages back to the lru list.
1411     */
1412    spin_lock_irq(&zone->lru_lock);
1413    /*
1414     * Count referenced pages from currently used mappings as rotated,
1415     * even though only some of them are actually re-activated. This
1416     * helps balance scan pressure between file and anonymous pages in
1417     * get_scan_ratio.
1418     */
1419    reclaim_stat->recent_rotated[file] += nr_rotated;
1420
1421    move_active_pages_to_lru(zone, &l_active,
1422                        LRU_ACTIVE + file * LRU_FILE);
1423    move_active_pages_to_lru(zone, &l_inactive,
1424                        LRU_BASE + file * LRU_FILE);
1425    __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1426    spin_unlock_irq(&zone->lru_lock);
1427}
1428
1429static int inactive_anon_is_low_global(struct zone *zone)
1430{
1431    unsigned long active, inactive;
1432
1433    active = zone_page_state(zone, NR_ACTIVE_ANON);
1434    inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1435
1436    if (inactive * zone->inactive_ratio < active)
1437        return 1;
1438
1439    return 0;
1440}
1441
1442/**
1443 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1444 * @zone: zone to check
1445 * @sc: scan control of this context
1446 *
1447 * Returns true if the zone does not have enough inactive anon pages,
1448 * meaning some active anon pages need to be deactivated.
1449 */
1450static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1451{
1452    int low;
1453
1454    if (scanning_global_lru(sc))
1455        low = inactive_anon_is_low_global(zone);
1456    else
1457        low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1458    return low;
1459}
1460
1461static int inactive_file_is_low_global(struct zone *zone)
1462{
1463    unsigned long active, inactive;
1464
1465    active = zone_page_state(zone, NR_ACTIVE_FILE);
1466    inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1467
1468    return (active > inactive);
1469}
1470
1471/**
1472 * inactive_file_is_low - check if file pages need to be deactivated
1473 * @zone: zone to check
1474 * @sc: scan control of this context
1475 *
1476 * When the system is doing streaming IO, memory pressure here
1477 * ensures that active file pages get deactivated, until more
1478 * than half of the file pages are on the inactive list.
1479 *
1480 * Once we get to that situation, protect the system's working
1481 * set from being evicted by disabling active file page aging.
1482 *
1483 * This uses a different ratio than the anonymous pages, because
1484 * the page cache uses a use-once replacement algorithm.
1485 */
1486static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1487{
1488    int low;
1489
1490    if (scanning_global_lru(sc))
1491        low = inactive_file_is_low_global(zone);
1492    else
1493        low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1494    return low;
1495}
1496
1497static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1498                int file)
1499{
1500    if (file)
1501        return inactive_file_is_low(zone, sc);
1502    else
1503        return inactive_anon_is_low(zone, sc);
1504}
1505
1506static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1507    struct zone *zone, struct scan_control *sc, int priority)
1508{
1509    int file = is_file_lru(lru);
1510
1511    if (is_active_lru(lru)) {
1512        if (inactive_list_is_low(zone, sc, file))
1513            shrink_active_list(nr_to_scan, zone, sc, priority, file);
1514        return 0;
1515    }
1516
1517    return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1518}
1519
1520/*
1521 * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
1522 * until we collected @swap_cluster_max pages to scan.
1523 */
1524static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
1525                       unsigned long *nr_saved_scan)
1526{
1527    unsigned long nr;
1528
1529    *nr_saved_scan += nr_to_scan;
1530    nr = *nr_saved_scan;
1531
1532    if (nr >= SWAP_CLUSTER_MAX)
1533        *nr_saved_scan = 0;
1534    else
1535        nr = 0;
1536
1537    return nr;
1538}
1539
1540/*
1541 * Determine how aggressively the anon and file LRU lists should be
1542 * scanned. The relative value of each set of LRU lists is determined
1543 * by looking at the fraction of the pages scanned we did rotate back
1544 * onto the active list instead of evict.
1545 *
1546 * nr[0] = anon pages to scan; nr[1] = file pages to scan
1547 */
1548static void get_scan_count(struct zone *zone, struct scan_control *sc,
1549                    unsigned long *nr, int priority)
1550{
1551    unsigned long anon, file, free;
1552    unsigned long anon_prio, file_prio;
1553    unsigned long ap, fp;
1554    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1555    u64 fraction[2], denominator;
1556    enum lru_list l;
1557    int noswap = 0;
1558
1559    /* If we have no swap space, do not bother scanning anon pages. */
1560    if (!sc->may_swap || (nr_swap_pages <= 0)) {
1561        noswap = 1;
1562        fraction[0] = 0;
1563        fraction[1] = 1;
1564        denominator = 1;
1565        goto out;
1566    }
1567
1568    anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1569        zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1570    file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1571        zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1572
1573    if (scanning_global_lru(sc)) {
1574        free = zone_page_state(zone, NR_FREE_PAGES);
1575        /* If we have very few page cache pages,
1576           force-scan anon pages. */
1577        if (unlikely(file + free <= high_wmark_pages(zone))) {
1578            fraction[0] = 1;
1579            fraction[1] = 0;
1580            denominator = 1;
1581            goto out;
1582        }
1583    }
1584
1585    /*
1586     * OK, so we have swap space and a fair amount of page cache
1587     * pages. We use the recently rotated / recently scanned
1588     * ratios to determine how valuable each cache is.
1589     *
1590     * Because workloads change over time (and to avoid overflow)
1591     * we keep these statistics as a floating average, which ends
1592     * up weighing recent references more than old ones.
1593     *
1594     * anon in [0], file in [1]
1595     */
1596    if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1597        spin_lock_irq(&zone->lru_lock);
1598        reclaim_stat->recent_scanned[0] /= 2;
1599        reclaim_stat->recent_rotated[0] /= 2;
1600        spin_unlock_irq(&zone->lru_lock);
1601    }
1602
1603    if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1604        spin_lock_irq(&zone->lru_lock);
1605        reclaim_stat->recent_scanned[1] /= 2;
1606        reclaim_stat->recent_rotated[1] /= 2;
1607        spin_unlock_irq(&zone->lru_lock);
1608    }
1609
1610    /*
1611     * With swappiness at 100, anonymous and file have the same priority.
1612     * This scanning priority is essentially the inverse of IO cost.
1613     */
1614    anon_prio = sc->swappiness;
1615    file_prio = 200 - sc->swappiness;
1616
1617    /*
1618     * The amount of pressure on anon vs file pages is inversely
1619     * proportional to the fraction of recently scanned pages on
1620     * each list that were recently referenced and in active use.
1621     */
1622    ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1623    ap /= reclaim_stat->recent_rotated[0] + 1;
1624
1625    fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1626    fp /= reclaim_stat->recent_rotated[1] + 1;
1627
1628    fraction[0] = ap;
1629    fraction[1] = fp;
1630    denominator = ap + fp + 1;
1631out:
1632    for_each_evictable_lru(l) {
1633        int file = is_file_lru(l);
1634        unsigned long scan;
1635
1636        scan = zone_nr_lru_pages(zone, sc, l);
1637        if (priority || noswap) {
1638            scan >>= priority;
1639            scan = div64_u64(scan * fraction[file], denominator);
1640        }
1641        nr[l] = nr_scan_try_batch(scan,
1642                      &reclaim_stat->nr_saved_scan[l]);
1643    }
1644}
1645
1646static void set_lumpy_reclaim_mode(int priority, struct scan_control *sc)
1647{
1648    /*
1649     * If we need a large contiguous chunk of memory, or have
1650     * trouble getting a small set of contiguous pages, we
1651     * will reclaim both active and inactive pages.
1652     */
1653    if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1654        sc->lumpy_reclaim_mode = 1;
1655    else if (sc->order && priority < DEF_PRIORITY - 2)
1656        sc->lumpy_reclaim_mode = 1;
1657    else
1658        sc->lumpy_reclaim_mode = 0;
1659}
1660
1661/*
1662 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1663 */
1664static void shrink_zone(int priority, struct zone *zone,
1665                struct scan_control *sc)
1666{
1667    unsigned long nr[NR_LRU_LISTS];
1668    unsigned long nr_to_scan;
1669    enum lru_list l;
1670    unsigned long nr_reclaimed = sc->nr_reclaimed;
1671    unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1672
1673    get_scan_count(zone, sc, nr, priority);
1674
1675    set_lumpy_reclaim_mode(priority, sc);
1676
1677    while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1678                    nr[LRU_INACTIVE_FILE]) {
1679        for_each_evictable_lru(l) {
1680            if (nr[l]) {
1681                nr_to_scan = min_t(unsigned long,
1682                           nr[l], SWAP_CLUSTER_MAX);
1683                nr[l] -= nr_to_scan;
1684
1685                nr_reclaimed += shrink_list(l, nr_to_scan,
1686                                zone, sc, priority);
1687            }
1688        }
1689        /*
1690         * On large memory systems, scan >> priority can become
1691         * really large. This is fine for the starting priority;
1692         * we want to put equal scanning pressure on each zone.
1693         * However, if the VM has a harder time of freeing pages,
1694         * with multiple processes reclaiming pages, the total
1695         * freeing target can get unreasonably large.
1696         */
1697        if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
1698            break;
1699    }
1700
1701    sc->nr_reclaimed = nr_reclaimed;
1702
1703    /*
1704     * Even if we did not try to evict anon pages at all, we want to
1705     * rebalance the anon lru active/inactive ratio.
1706     */
1707    if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)
1708        shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
1709
1710    throttle_vm_writeout(sc->gfp_mask);
1711}
1712
1713/*
1714 * This is the direct reclaim path, for page-allocating processes. We only
1715 * try to reclaim pages from zones which will satisfy the caller's allocation
1716 * request.
1717 *
1718 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1719 * Because:
1720 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1721 * allocation or
1722 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1723 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1724 * zone defense algorithm.
1725 *
1726 * If a zone is deemed to be full of pinned pages then just give it a light
1727 * scan then give up on it.
1728 */
1729static bool shrink_zones(int priority, struct zonelist *zonelist,
1730                    struct scan_control *sc)
1731{
1732    enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1733    struct zoneref *z;
1734    struct zone *zone;
1735    bool all_unreclaimable = true;
1736
1737    for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
1738                    sc->nodemask) {
1739        if (!populated_zone(zone))
1740            continue;
1741        /*
1742         * Take care memory controller reclaiming has small influence
1743         * to global LRU.
1744         */
1745        if (scanning_global_lru(sc)) {
1746            if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1747                continue;
1748            note_zone_scanning_priority(zone, priority);
1749
1750            if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1751                continue; /* Let kswapd poll it */
1752        } else {
1753            /*
1754             * Ignore cpuset limitation here. We just want to reduce
1755             * # of used pages by us regardless of memory shortage.
1756             */
1757            mem_cgroup_note_reclaim_priority(sc->mem_cgroup,
1758                            priority);
1759        }
1760
1761        shrink_zone(priority, zone, sc);
1762        all_unreclaimable = false;
1763    }
1764    return all_unreclaimable;
1765}
1766
1767/*
1768 * This is the main entry point to direct page reclaim.
1769 *
1770 * If a full scan of the inactive list fails to free enough memory then we
1771 * are "out of memory" and something needs to be killed.
1772 *
1773 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1774 * high - the zone may be full of dirty or under-writeback pages, which this
1775 * caller can't do much about. We kick the writeback threads and take explicit
1776 * naps in the hope that some of these pages can be written. But if the
1777 * allocating task holds filesystem locks which prevent writeout this might not
1778 * work, and the allocation attempt will fail.
1779 *
1780 * returns: 0, if no pages reclaimed
1781 * else, the number of pages reclaimed
1782 */
1783static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
1784                    struct scan_control *sc)
1785{
1786    int priority;
1787    bool all_unreclaimable;
1788    unsigned long total_scanned = 0;
1789    struct reclaim_state *reclaim_state = current->reclaim_state;
1790    unsigned long lru_pages = 0;
1791    struct zoneref *z;
1792    struct zone *zone;
1793    enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1794    unsigned long writeback_threshold;
1795
1796    get_mems_allowed();
1797    delayacct_freepages_start();
1798
1799    if (scanning_global_lru(sc))
1800        count_vm_event(ALLOCSTALL);
1801    /*
1802     * mem_cgroup will not do shrink_slab.
1803     */
1804    if (scanning_global_lru(sc)) {
1805        for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1806
1807            if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1808                continue;
1809
1810            lru_pages += zone_reclaimable_pages(zone);
1811        }
1812    }
1813
1814    for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1815        sc->nr_scanned = 0;
1816        if (!priority)
1817            disable_swap_token();
1818        all_unreclaimable = shrink_zones(priority, zonelist, sc);
1819        /*
1820         * Don't shrink slabs when reclaiming memory from
1821         * over limit cgroups
1822         */
1823        if (scanning_global_lru(sc)) {
1824            shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
1825            if (reclaim_state) {
1826                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
1827                reclaim_state->reclaimed_slab = 0;
1828            }
1829        }
1830        total_scanned += sc->nr_scanned;
1831        if (sc->nr_reclaimed >= sc->nr_to_reclaim)
1832            goto out;
1833
1834        /*
1835         * Try to write back as many pages as we just scanned. This
1836         * tends to cause slow streaming writers to write data to the
1837         * disk smoothly, at the dirtying rate, which is nice. But
1838         * that's undesirable in laptop mode, where we *want* lumpy
1839         * writeout. So in laptop mode, write out the whole world.
1840         */
1841        writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
1842        if (total_scanned > writeback_threshold) {
1843            wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
1844            sc->may_writepage = 1;
1845        }
1846
1847        /* Take a nap, wait for some writeback to complete */
1848        if (!sc->hibernation_mode && sc->nr_scanned &&
1849            priority < DEF_PRIORITY - 2)
1850            congestion_wait(BLK_RW_ASYNC, HZ/10);
1851    }
1852
1853out:
1854    /*
1855     * Now that we've scanned all the zones at this priority level, note
1856     * that level within the zone so that the next thread which performs
1857     * scanning of this zone will immediately start out at this priority
1858     * level. This affects only the decision whether or not to bring
1859     * mapped pages onto the inactive list.
1860     */
1861    if (priority < 0)
1862        priority = 0;
1863
1864    if (scanning_global_lru(sc)) {
1865        for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1866
1867            if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1868                continue;
1869
1870            zone->prev_priority = priority;
1871        }
1872    } else
1873        mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority);
1874
1875    delayacct_freepages_end();
1876    put_mems_allowed();
1877
1878    if (sc->nr_reclaimed)
1879        return sc->nr_reclaimed;
1880
1881    /* top priority shrink_zones still had more to do? don't OOM, then */
1882    if (scanning_global_lru(sc) && !all_unreclaimable)
1883        return 1;
1884
1885    return 0;
1886}
1887
1888unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
1889                gfp_t gfp_mask, nodemask_t *nodemask)
1890{
1891    struct scan_control sc = {
1892        .gfp_mask = gfp_mask,
1893        .may_writepage = !laptop_mode,
1894        .nr_to_reclaim = SWAP_CLUSTER_MAX,
1895        .may_unmap = 1,
1896        .may_swap = 1,
1897        .swappiness = vm_swappiness,
1898        .order = order,
1899        .mem_cgroup = NULL,
1900        .nodemask = nodemask,
1901    };
1902
1903    return do_try_to_free_pages(zonelist, &sc);
1904}
1905
1906#ifdef CONFIG_CGROUP_MEM_RES_CTLR
1907
1908unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
1909                        gfp_t gfp_mask, bool noswap,
1910                        unsigned int swappiness,
1911                        struct zone *zone, int nid)
1912{
1913    struct scan_control sc = {
1914        .may_writepage = !laptop_mode,
1915        .may_unmap = 1,
1916        .may_swap = !noswap,
1917        .swappiness = swappiness,
1918        .order = 0,
1919        .mem_cgroup = mem,
1920    };
1921    nodemask_t nm = nodemask_of_node(nid);
1922
1923    sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
1924            (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
1925    sc.nodemask = &nm;
1926    sc.nr_reclaimed = 0;
1927    sc.nr_scanned = 0;
1928    /*
1929     * NOTE: Although we can get the priority field, using it
1930     * here is not a good idea, since it limits the pages we can scan.
1931     * if we don't reclaim here, the shrink_zone from balance_pgdat
1932     * will pick up pages from other mem cgroup's as well. We hack
1933     * the priority and make it zero.
1934     */
1935    shrink_zone(0, zone, &sc);
1936    return sc.nr_reclaimed;
1937}
1938
1939unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
1940                       gfp_t gfp_mask,
1941                       bool noswap,
1942                       unsigned int swappiness)
1943{
1944    struct zonelist *zonelist;
1945    struct scan_control sc = {
1946        .may_writepage = !laptop_mode,
1947        .may_unmap = 1,
1948        .may_swap = !noswap,
1949        .nr_to_reclaim = SWAP_CLUSTER_MAX,
1950        .swappiness = swappiness,
1951        .order = 0,
1952        .mem_cgroup = mem_cont,
1953        .nodemask = NULL, /* we don't care the placement */
1954    };
1955
1956    sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
1957            (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
1958    zonelist = NODE_DATA(numa_node_id())->node_zonelists;
1959    return do_try_to_free_pages(zonelist, &sc);
1960}
1961#endif
1962
1963/* is kswapd sleeping prematurely? */
1964static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
1965{
1966    int i;
1967
1968    /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
1969    if (remaining)
1970        return 1;
1971
1972    /* If after HZ/10, a zone is below the high mark, it's premature */
1973    for (i = 0; i < pgdat->nr_zones; i++) {
1974        struct zone *zone = pgdat->node_zones + i;
1975
1976        if (!populated_zone(zone))
1977            continue;
1978
1979        if (zone->all_unreclaimable)
1980            continue;
1981
1982        if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
1983                                0, 0))
1984            return 1;
1985    }
1986
1987    return 0;
1988}
1989
1990/*
1991 * For kswapd, balance_pgdat() will work across all this node's zones until
1992 * they are all at high_wmark_pages(zone).
1993 *
1994 * Returns the number of pages which were actually freed.
1995 *
1996 * There is special handling here for zones which are full of pinned pages.
1997 * This can happen if the pages are all mlocked, or if they are all used by
1998 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
1999 * What we do is to detect the case where all pages in the zone have been
2000 * scanned twice and there has been zero successful reclaim. Mark the zone as
2001 * dead and from now on, only perform a short scan. Basically we're polling
2002 * the zone for when the problem goes away.
2003 *
2004 * kswapd scans the zones in the highmem->normal->dma direction. It skips
2005 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2006 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2007 * lower zones regardless of the number of free pages in the lower zones. This
2008 * interoperates with the page allocator fallback scheme to ensure that aging
2009 * of pages is balanced across the zones.
2010 */
2011static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
2012{
2013    int all_zones_ok;
2014    int priority;
2015    int i;
2016    unsigned long total_scanned;
2017    struct reclaim_state *reclaim_state = current->reclaim_state;
2018    struct scan_control sc = {
2019        .gfp_mask = GFP_KERNEL,
2020        .may_unmap = 1,
2021        .may_swap = 1,
2022        /*
2023         * kswapd doesn't want to be bailed out while reclaim. because
2024         * we want to put equal scanning pressure on each zone.
2025         */
2026        .nr_to_reclaim = ULONG_MAX,
2027        .swappiness = vm_swappiness,
2028        .order = order,
2029        .mem_cgroup = NULL,
2030    };
2031    /*
2032     * temp_priority is used to remember the scanning priority at which
2033     * this zone was successfully refilled to
2034     * free_pages == high_wmark_pages(zone).
2035     */
2036    int temp_priority[MAX_NR_ZONES];
2037
2038loop_again:
2039    total_scanned = 0;
2040    sc.nr_reclaimed = 0;
2041    sc.may_writepage = !laptop_mode;
2042    count_vm_event(PAGEOUTRUN);
2043
2044    for (i = 0; i < pgdat->nr_zones; i++)
2045        temp_priority[i] = DEF_PRIORITY;
2046
2047    for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2048        int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2049        unsigned long lru_pages = 0;
2050        int has_under_min_watermark_zone = 0;
2051
2052        /* The swap token gets in the way of swapout... */
2053        if (!priority)
2054            disable_swap_token();
2055
2056        all_zones_ok = 1;
2057
2058        /*
2059         * Scan in the highmem->dma direction for the highest
2060         * zone which needs scanning
2061         */
2062        for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2063            struct zone *zone = pgdat->node_zones + i;
2064
2065            if (!populated_zone(zone))
2066                continue;
2067
2068            if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2069                continue;
2070
2071            /*
2072             * Do some background aging of the anon list, to give
2073             * pages a chance to be referenced before reclaiming.
2074             */
2075            if (inactive_anon_is_low(zone, &sc))
2076                shrink_active_list(SWAP_CLUSTER_MAX, zone,
2077                            &sc, priority, 0);
2078
2079            if (!zone_watermark_ok(zone, order,
2080                    high_wmark_pages(zone), 0, 0)) {
2081                end_zone = i;
2082                break;
2083            }
2084        }
2085        if (i < 0)
2086            goto out;
2087
2088        for (i = 0; i <= end_zone; i++) {
2089            struct zone *zone = pgdat->node_zones + i;
2090
2091            lru_pages += zone_reclaimable_pages(zone);
2092        }
2093
2094        /*
2095         * Now scan the zone in the dma->highmem direction, stopping
2096         * at the last zone which needs scanning.
2097         *
2098         * We do this because the page allocator works in the opposite
2099         * direction. This prevents the page allocator from allocating
2100         * pages behind kswapd's direction of progress, which would
2101         * cause too much scanning of the lower zones.
2102         */
2103        for (i = 0; i <= end_zone; i++) {
2104            struct zone *zone = pgdat->node_zones + i;
2105            int nr_slab;
2106            int nid, zid;
2107
2108            if (!populated_zone(zone))
2109                continue;
2110
2111            if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2112                continue;
2113
2114            temp_priority[i] = priority;
2115            sc.nr_scanned = 0;
2116            note_zone_scanning_priority(zone, priority);
2117
2118            nid = pgdat->node_id;
2119            zid = zone_idx(zone);
2120            /*
2121             * Call soft limit reclaim before calling shrink_zone.
2122             * For now we ignore the return value
2123             */
2124            mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask,
2125                            nid, zid);
2126            /*
2127             * We put equal pressure on every zone, unless one
2128             * zone has way too many pages free already.
2129             */
2130            if (!zone_watermark_ok(zone, order,
2131                    8*high_wmark_pages(zone), end_zone, 0))
2132                shrink_zone(priority, zone, &sc);
2133            reclaim_state->reclaimed_slab = 0;
2134            nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
2135                        lru_pages);
2136            sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2137            total_scanned += sc.nr_scanned;
2138            if (zone->all_unreclaimable)
2139                continue;
2140            if (nr_slab == 0 &&
2141                zone->pages_scanned >= (zone_reclaimable_pages(zone) * 6))
2142                zone->all_unreclaimable = 1;
2143            /*
2144             * If we've done a decent amount of scanning and
2145             * the reclaim ratio is low, start doing writepage
2146             * even in laptop mode
2147             */
2148            if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2149                total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2150                sc.may_writepage = 1;
2151
2152            if (!zone_watermark_ok(zone, order,
2153                    high_wmark_pages(zone), end_zone, 0)) {
2154                all_zones_ok = 0;
2155                /*
2156                 * We are still under min water mark. This
2157                 * means that we have a GFP_ATOMIC allocation
2158                 * failure risk. Hurry up!
2159                 */
2160                if (!zone_watermark_ok(zone, order,
2161                        min_wmark_pages(zone), end_zone, 0))
2162                    has_under_min_watermark_zone = 1;
2163            }
2164
2165        }
2166        if (all_zones_ok)
2167            break; /* kswapd: all done */
2168        /*
2169         * OK, kswapd is getting into trouble. Take a nap, then take
2170         * another pass across the zones.
2171         */
2172        if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2173            if (has_under_min_watermark_zone)
2174                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2175            else
2176                congestion_wait(BLK_RW_ASYNC, HZ/10);
2177        }
2178
2179        /*
2180         * We do this so kswapd doesn't build up large priorities for
2181         * example when it is freeing in parallel with allocators. It
2182         * matches the direct reclaim path behaviour in terms of impact
2183         * on zone->*_priority.
2184         */
2185        if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2186            break;
2187    }
2188out:
2189    /*
2190     * Note within each zone the priority level at which this zone was
2191     * brought into a happy state. So that the next thread which scans this
2192     * zone will start out at that priority level.
2193     */
2194    for (i = 0; i < pgdat->nr_zones; i++) {
2195        struct zone *zone = pgdat->node_zones + i;
2196
2197        zone->prev_priority = temp_priority[i];
2198    }
2199    if (!all_zones_ok) {
2200        cond_resched();
2201
2202        try_to_freeze();
2203
2204        /*
2205         * Fragmentation may mean that the system cannot be
2206         * rebalanced for high-order allocations in all zones.
2207         * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2208         * it means the zones have been fully scanned and are still
2209         * not balanced. For high-order allocations, there is
2210         * little point trying all over again as kswapd may
2211         * infinite loop.
2212         *
2213         * Instead, recheck all watermarks at order-0 as they
2214         * are the most important. If watermarks are ok, kswapd will go
2215         * back to sleep. High-order users can still perform direct
2216         * reclaim if they wish.
2217         */
2218        if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2219            order = sc.order = 0;
2220
2221        goto loop_again;
2222    }
2223
2224    return sc.nr_reclaimed;
2225}
2226
2227/*
2228 * The background pageout daemon, started as a kernel thread
2229 * from the init process.
2230 *
2231 * This basically trickles out pages so that we have _some_
2232 * free memory available even if there is no other activity
2233 * that frees anything up. This is needed for things like routing
2234 * etc, where we otherwise might have all activity going on in
2235 * asynchronous contexts that cannot page things out.
2236 *
2237 * If there are applications that are active memory-allocators
2238 * (most normal use), this basically shouldn't matter.
2239 */
2240static int kswapd(void *p)
2241{
2242    unsigned long order;
2243    pg_data_t *pgdat = (pg_data_t*)p;
2244    struct task_struct *tsk = current;
2245    DEFINE_WAIT(wait);
2246    struct reclaim_state reclaim_state = {
2247        .reclaimed_slab = 0,
2248    };
2249    const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2250
2251    lockdep_set_current_reclaim_state(GFP_KERNEL);
2252
2253    if (!cpumask_empty(cpumask))
2254        set_cpus_allowed_ptr(tsk, cpumask);
2255    current->reclaim_state = &reclaim_state;
2256
2257    /*
2258     * Tell the memory management that we're a "memory allocator",
2259     * and that if we need more memory we should get access to it
2260     * regardless (see "__alloc_pages()"). "kswapd" should
2261     * never get caught in the normal page freeing logic.
2262     *
2263     * (Kswapd normally doesn't need memory anyway, but sometimes
2264     * you need a small amount of memory in order to be able to
2265     * page out something else, and this flag essentially protects
2266     * us from recursively trying to free more memory as we're
2267     * trying to free the first piece of memory in the first place).
2268     */
2269    tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2270    set_freezable();
2271
2272    order = 0;
2273    for ( ; ; ) {
2274        unsigned long new_order;
2275        int ret;
2276
2277        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2278        new_order = pgdat->kswapd_max_order;
2279        pgdat->kswapd_max_order = 0;
2280        if (order < new_order) {
2281            /*
2282             * Don't sleep if someone wants a larger 'order'
2283             * allocation
2284             */
2285            order = new_order;
2286        } else {
2287            if (!freezing(current) && !kthread_should_stop()) {
2288                long remaining = 0;
2289
2290                /* Try to sleep for a short interval */
2291                if (!sleeping_prematurely(pgdat, order, remaining)) {
2292                    remaining = schedule_timeout(HZ/10);
2293                    finish_wait(&pgdat->kswapd_wait, &wait);
2294                    prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2295                }
2296
2297                /*
2298                 * After a short sleep, check if it was a
2299                 * premature sleep. If not, then go fully
2300                 * to sleep until explicitly woken up
2301                 */
2302                if (!sleeping_prematurely(pgdat, order, remaining))
2303                    schedule();
2304                else {
2305                    if (remaining)
2306                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2307                    else
2308                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2309                }
2310            }
2311
2312            order = pgdat->kswapd_max_order;
2313        }
2314        finish_wait(&pgdat->kswapd_wait, &wait);
2315
2316        ret = try_to_freeze();
2317        if (kthread_should_stop())
2318            break;
2319
2320        /*
2321         * We can speed up thawing tasks if we don't call balance_pgdat
2322         * after returning from the refrigerator
2323         */
2324        if (!ret)
2325            balance_pgdat(pgdat, order);
2326    }
2327    return 0;
2328}
2329
2330/*
2331 * A zone is low on free memory, so wake its kswapd task to service it.
2332 */
2333void wakeup_kswapd(struct zone *zone, int order)
2334{
2335    pg_data_t *pgdat;
2336
2337    if (!populated_zone(zone))
2338        return;
2339
2340    pgdat = zone->zone_pgdat;
2341    if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
2342        return;
2343    if (pgdat->kswapd_max_order < order)
2344        pgdat->kswapd_max_order = order;
2345    if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2346        return;
2347    if (!waitqueue_active(&pgdat->kswapd_wait))
2348        return;
2349    wake_up_interruptible(&pgdat->kswapd_wait);
2350}
2351
2352/*
2353 * The reclaimable count would be mostly accurate.
2354 * The less reclaimable pages may be
2355 * - mlocked pages, which will be moved to unevictable list when encountered
2356 * - mapped pages, which may require several travels to be reclaimed
2357 * - dirty pages, which is not "instantly" reclaimable
2358 */
2359unsigned long global_reclaimable_pages(void)
2360{
2361    int nr;
2362
2363    nr = global_page_state(NR_ACTIVE_FILE) +
2364         global_page_state(NR_INACTIVE_FILE);
2365
2366    if (nr_swap_pages > 0)
2367        nr += global_page_state(NR_ACTIVE_ANON) +
2368              global_page_state(NR_INACTIVE_ANON);
2369
2370    return nr;
2371}
2372
2373unsigned long zone_reclaimable_pages(struct zone *zone)
2374{
2375    int nr;
2376
2377    nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2378         zone_page_state(zone, NR_INACTIVE_FILE);
2379
2380    if (nr_swap_pages > 0)
2381        nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2382              zone_page_state(zone, NR_INACTIVE_ANON);
2383
2384    return nr;
2385}
2386
2387#ifdef CONFIG_HIBERNATION
2388/*
2389 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2390 * freed pages.
2391 *
2392 * Rather than trying to age LRUs the aim is to preserve the overall
2393 * LRU order by reclaiming preferentially
2394 * inactive > active > active referenced > active mapped
2395 */
2396unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2397{
2398    struct reclaim_state reclaim_state;
2399    struct scan_control sc = {
2400        .gfp_mask = GFP_HIGHUSER_MOVABLE,
2401        .may_swap = 1,
2402        .may_unmap = 1,
2403        .may_writepage = 1,
2404        .nr_to_reclaim = nr_to_reclaim,
2405        .hibernation_mode = 1,
2406        .swappiness = vm_swappiness,
2407        .order = 0,
2408    };
2409    struct zonelist * zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2410    struct task_struct *p = current;
2411    unsigned long nr_reclaimed;
2412
2413    p->flags |= PF_MEMALLOC;
2414    lockdep_set_current_reclaim_state(sc.gfp_mask);
2415    reclaim_state.reclaimed_slab = 0;
2416    p->reclaim_state = &reclaim_state;
2417
2418    nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2419
2420    p->reclaim_state = NULL;
2421    lockdep_clear_current_reclaim_state();
2422    p->flags &= ~PF_MEMALLOC;
2423
2424    return nr_reclaimed;
2425}
2426#endif /* CONFIG_HIBERNATION */
2427
2428/* It's optimal to keep kswapds on the same CPUs as their memory, but
2429   not required for correctness. So if the last cpu in a node goes
2430   away, we get changed to run anywhere: as the first one comes back,
2431   restore their cpu bindings. */
2432static int __devinit cpu_callback(struct notifier_block *nfb,
2433                  unsigned long action, void *hcpu)
2434{
2435    int nid;
2436
2437    if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2438        for_each_node_state(nid, N_HIGH_MEMORY) {
2439            pg_data_t *pgdat = NODE_DATA(nid);
2440            const struct cpumask *mask;
2441
2442            mask = cpumask_of_node(pgdat->node_id);
2443
2444            if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2445                /* One of our CPUs online: restore mask */
2446                set_cpus_allowed_ptr(pgdat->kswapd, mask);
2447        }
2448    }
2449    return NOTIFY_OK;
2450}
2451
2452/*
2453 * This kswapd start function will be called by init and node-hot-add.
2454 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2455 */
2456int kswapd_run(int nid)
2457{
2458    pg_data_t *pgdat = NODE_DATA(nid);
2459    int ret = 0;
2460
2461    if (pgdat->kswapd)
2462        return 0;
2463
2464    pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2465    if (IS_ERR(pgdat->kswapd)) {
2466        /* failure at boot is fatal */
2467        BUG_ON(system_state == SYSTEM_BOOTING);
2468        printk("Failed to start kswapd on node %d\n",nid);
2469        ret = -1;
2470    }
2471    return ret;
2472}
2473
2474/*
2475 * Called by memory hotplug when all memory in a node is offlined.
2476 */
2477void kswapd_stop(int nid)
2478{
2479    struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2480
2481    if (kswapd)
2482        kthread_stop(kswapd);
2483}
2484
2485static int __init kswapd_init(void)
2486{
2487    int nid;
2488
2489    swap_setup();
2490    for_each_node_state(nid, N_HIGH_MEMORY)
2491         kswapd_run(nid);
2492    hotcpu_notifier(cpu_callback, 0);
2493    return 0;
2494}
2495
2496module_init(kswapd_init)
2497
2498#ifdef CONFIG_NUMA
2499/*
2500 * Zone reclaim mode
2501 *
2502 * If non-zero call zone_reclaim when the number of free pages falls below
2503 * the watermarks.
2504 */
2505int zone_reclaim_mode __read_mostly;
2506
2507#define RECLAIM_OFF 0
2508#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
2509#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
2510#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
2511
2512/*
2513 * Priority for ZONE_RECLAIM. This determines the fraction of pages
2514 * of a node considered for each zone_reclaim. 4 scans 1/16th of
2515 * a zone.
2516 */
2517#define ZONE_RECLAIM_PRIORITY 4
2518
2519/*
2520 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
2521 * occur.
2522 */
2523int sysctl_min_unmapped_ratio = 1;
2524
2525/*
2526 * If the number of slab pages in a zone grows beyond this percentage then
2527 * slab reclaim needs to occur.
2528 */
2529int sysctl_min_slab_ratio = 5;
2530
2531static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
2532{
2533    unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
2534    unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
2535        zone_page_state(zone, NR_ACTIVE_FILE);
2536
2537    /*
2538     * It's possible for there to be more file mapped pages than
2539     * accounted for by the pages on the file LRU lists because
2540     * tmpfs pages accounted for as ANON can also be FILE_MAPPED
2541     */
2542    return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
2543}
2544
2545/* Work out how many page cache pages we can reclaim in this reclaim_mode */
2546static long zone_pagecache_reclaimable(struct zone *zone)
2547{
2548    long nr_pagecache_reclaimable;
2549    long delta = 0;
2550
2551    /*
2552     * If RECLAIM_SWAP is set, then all file pages are considered
2553     * potentially reclaimable. Otherwise, we have to worry about
2554     * pages like swapcache and zone_unmapped_file_pages() provides
2555     * a better estimate
2556     */
2557    if (zone_reclaim_mode & RECLAIM_SWAP)
2558        nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
2559    else
2560        nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
2561
2562    /* If we can't clean pages, remove dirty pages from consideration */
2563    if (!(zone_reclaim_mode & RECLAIM_WRITE))
2564        delta += zone_page_state(zone, NR_FILE_DIRTY);
2565
2566    /* Watch for any possible underflows due to delta */
2567    if (unlikely(delta > nr_pagecache_reclaimable))
2568        delta = nr_pagecache_reclaimable;
2569
2570    return nr_pagecache_reclaimable - delta;
2571}
2572
2573/*
2574 * Try to free up some pages from this zone through reclaim.
2575 */
2576static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2577{
2578    /* Minimum pages needed in order to stay on node */
2579    const unsigned long nr_pages = 1 << order;
2580    struct task_struct *p = current;
2581    struct reclaim_state reclaim_state;
2582    int priority;
2583    struct scan_control sc = {
2584        .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
2585        .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
2586        .may_swap = 1,
2587        .nr_to_reclaim = max_t(unsigned long, nr_pages,
2588                       SWAP_CLUSTER_MAX),
2589        .gfp_mask = gfp_mask,
2590        .swappiness = vm_swappiness,
2591        .order = order,
2592    };
2593    unsigned long slab_reclaimable;
2594
2595    disable_swap_token();
2596    cond_resched();
2597    /*
2598     * We need to be able to allocate from the reserves for RECLAIM_SWAP
2599     * and we also need to be able to write out pages for RECLAIM_WRITE
2600     * and RECLAIM_SWAP.
2601     */
2602    p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
2603    lockdep_set_current_reclaim_state(gfp_mask);
2604    reclaim_state.reclaimed_slab = 0;
2605    p->reclaim_state = &reclaim_state;
2606
2607    if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
2608        /*
2609         * Free memory by calling shrink zone with increasing
2610         * priorities until we have enough memory freed.
2611         */
2612        priority = ZONE_RECLAIM_PRIORITY;
2613        do {
2614            note_zone_scanning_priority(zone, priority);
2615            shrink_zone(priority, zone, &sc);
2616            priority--;
2617        } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
2618    }
2619
2620    slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2621    if (slab_reclaimable > zone->min_slab_pages) {
2622        /*
2623         * shrink_slab() does not currently allow us to determine how
2624         * many pages were freed in this zone. So we take the current
2625         * number of slab pages and shake the slab until it is reduced
2626         * by the same nr_pages that we used for reclaiming unmapped
2627         * pages.
2628         *
2629         * Note that shrink_slab will free memory on all zones and may
2630         * take a long time.
2631         */
2632        while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
2633            zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
2634                slab_reclaimable - nr_pages)
2635            ;
2636
2637        /*
2638         * Update nr_reclaimed by the number of slab pages we
2639         * reclaimed from this zone.
2640         */
2641        sc.nr_reclaimed += slab_reclaimable -
2642            zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2643    }
2644
2645    p->reclaim_state = NULL;
2646    current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
2647    lockdep_clear_current_reclaim_state();
2648    return sc.nr_reclaimed >= nr_pages;
2649}
2650
2651int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2652{
2653    int node_id;
2654    int ret;
2655
2656    /*
2657     * Zone reclaim reclaims unmapped file backed pages and
2658     * slab pages if we are over the defined limits.
2659     *
2660     * A small portion of unmapped file backed pages is needed for
2661     * file I/O otherwise pages read by file I/O will be immediately
2662     * thrown out if the zone is overallocated. So we do not reclaim
2663     * if less than a specified percentage of the zone is used by
2664     * unmapped file backed pages.
2665     */
2666    if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
2667        zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
2668        return ZONE_RECLAIM_FULL;
2669
2670    if (zone->all_unreclaimable)
2671        return ZONE_RECLAIM_FULL;
2672
2673    /*
2674     * Do not scan if the allocation should not be delayed.
2675     */
2676    if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
2677        return ZONE_RECLAIM_NOSCAN;
2678
2679    /*
2680     * Only run zone reclaim on the local zone or on zones that do not
2681     * have associated processors. This will favor the local processor
2682     * over remote processors and spread off node memory allocations
2683     * as wide as possible.
2684     */
2685    node_id = zone_to_nid(zone);
2686    if (node_state(node_id, N_CPU) && node_id != numa_node_id())
2687        return ZONE_RECLAIM_NOSCAN;
2688
2689    if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
2690        return ZONE_RECLAIM_NOSCAN;
2691
2692    ret = __zone_reclaim(zone, gfp_mask, order);
2693    zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
2694
2695    if (!ret)
2696        count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
2697
2698    return ret;
2699}
2700#endif
2701
2702/*
2703 * page_evictable - test whether a page is evictable
2704 * @page: the page to test
2705 * @vma: the VMA in which the page is or will be mapped, may be NULL
2706 *
2707 * Test whether page is evictable--i.e., should be placed on active/inactive
2708 * lists vs unevictable list. The vma argument is !NULL when called from the
2709 * fault path to determine how to instantate a new page.
2710 *
2711 * Reasons page might not be evictable:
2712 * (1) page's mapping marked unevictable
2713 * (2) page is part of an mlocked VMA
2714 *
2715 */
2716int page_evictable(struct page *page, struct vm_area_struct *vma)
2717{
2718
2719    if (mapping_unevictable(page_mapping(page)))
2720        return 0;
2721
2722    if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
2723        return 0;
2724
2725    return 1;
2726}
2727
2728/**
2729 * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
2730 * @page: page to check evictability and move to appropriate lru list
2731 * @zone: zone page is in
2732 *
2733 * Checks a page for evictability and moves the page to the appropriate
2734 * zone lru list.
2735 *
2736 * Restrictions: zone->lru_lock must be held, page must be on LRU and must
2737 * have PageUnevictable set.
2738 */
2739static void check_move_unevictable_page(struct page *page, struct zone *zone)
2740{
2741    VM_BUG_ON(PageActive(page));
2742
2743retry:
2744    ClearPageUnevictable(page);
2745    if (page_evictable(page, NULL)) {
2746        enum lru_list l = page_lru_base_type(page);
2747
2748        __dec_zone_state(zone, NR_UNEVICTABLE);
2749        list_move(&page->lru, &zone->lru[l].list);
2750        mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
2751        __inc_zone_state(zone, NR_INACTIVE_ANON + l);
2752        __count_vm_event(UNEVICTABLE_PGRESCUED);
2753    } else {
2754        /*
2755         * rotate unevictable list
2756         */
2757        SetPageUnevictable(page);
2758        list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
2759        mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
2760        if (page_evictable(page, NULL))
2761            goto retry;
2762    }
2763}
2764
2765/**
2766 * scan_mapping_unevictable_pages - scan an address space for evictable pages
2767 * @mapping: struct address_space to scan for evictable pages
2768 *
2769 * Scan all pages in mapping. Check unevictable pages for
2770 * evictability and move them to the appropriate zone lru list.
2771 */
2772void scan_mapping_unevictable_pages(struct address_space *mapping)
2773{
2774    pgoff_t next = 0;
2775    pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
2776             PAGE_CACHE_SHIFT;
2777    struct zone *zone;
2778    struct pagevec pvec;
2779
2780    if (mapping->nrpages == 0)
2781        return;
2782
2783    pagevec_init(&pvec, 0);
2784    while (next < end &&
2785        pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
2786        int i;
2787        int pg_scanned = 0;
2788
2789        zone = NULL;
2790
2791        for (i = 0; i < pagevec_count(&pvec); i++) {
2792            struct page *page = pvec.pages[i];
2793            pgoff_t page_index = page->index;
2794            struct zone *pagezone = page_zone(page);
2795
2796            pg_scanned++;
2797            if (page_index > next)
2798                next = page_index;
2799            next++;
2800
2801            if (pagezone != zone) {
2802                if (zone)
2803                    spin_unlock_irq(&zone->lru_lock);
2804                zone = pagezone;
2805                spin_lock_irq(&zone->lru_lock);
2806            }
2807
2808            if (PageLRU(page) && PageUnevictable(page))
2809                check_move_unevictable_page(page, zone);
2810        }
2811        if (zone)
2812            spin_unlock_irq(&zone->lru_lock);
2813        pagevec_release(&pvec);
2814
2815        count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
2816    }
2817
2818}
2819
2820/**
2821 * scan_zone_unevictable_pages - check unevictable list for evictable pages
2822 * @zone - zone of which to scan the unevictable list
2823 *
2824 * Scan @zone's unevictable LRU lists to check for pages that have become
2825 * evictable. Move those that have to @zone's inactive list where they
2826 * become candidates for reclaim, unless shrink_inactive_zone() decides
2827 * to reactivate them. Pages that are still unevictable are rotated
2828 * back onto @zone's unevictable list.
2829 */
2830#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
2831static void scan_zone_unevictable_pages(struct zone *zone)
2832{
2833    struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
2834    unsigned long scan;
2835    unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
2836
2837    while (nr_to_scan > 0) {
2838        unsigned long batch_size = min(nr_to_scan,
2839                        SCAN_UNEVICTABLE_BATCH_SIZE);
2840
2841        spin_lock_irq(&zone->lru_lock);
2842        for (scan = 0; scan < batch_size; scan++) {
2843            struct page *page = lru_to_page(l_unevictable);
2844
2845            if (!trylock_page(page))
2846                continue;
2847
2848            prefetchw_prev_lru_page(page, l_unevictable, flags);
2849
2850            if (likely(PageLRU(page) && PageUnevictable(page)))
2851                check_move_unevictable_page(page, zone);
2852
2853            unlock_page(page);
2854        }
2855        spin_unlock_irq(&zone->lru_lock);
2856
2857        nr_to_scan -= batch_size;
2858    }
2859}
2860
2861
2862/**
2863 * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
2864 *
2865 * A really big hammer: scan all zones' unevictable LRU lists to check for
2866 * pages that have become evictable. Move those back to the zones'
2867 * inactive list where they become candidates for reclaim.
2868 * This occurs when, e.g., we have unswappable pages on the unevictable lists,
2869 * and we add swap to the system. As such, it runs in the context of a task
2870 * that has possibly/probably made some previously unevictable pages
2871 * evictable.
2872 */
2873static void scan_all_zones_unevictable_pages(void)
2874{
2875    struct zone *zone;
2876
2877    for_each_zone(zone) {
2878        scan_zone_unevictable_pages(zone);
2879    }
2880}
2881
2882/*
2883 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
2884 * all nodes' unevictable lists for evictable pages
2885 */
2886unsigned long scan_unevictable_pages;
2887
2888int scan_unevictable_handler(struct ctl_table *table, int write,
2889               void __user *buffer,
2890               size_t *length, loff_t *ppos)
2891{
2892    proc_doulongvec_minmax(table, write, buffer, length, ppos);
2893
2894    if (write && *(unsigned long *)table->data)
2895        scan_all_zones_unevictable_pages();
2896
2897    scan_unevictable_pages = 0;
2898    return 0;
2899}
2900
2901/*
2902 * per node 'scan_unevictable_pages' attribute. On demand re-scan of
2903 * a specified node's per zone unevictable lists for evictable pages.
2904 */
2905
2906static ssize_t read_scan_unevictable_node(struct sys_device *dev,
2907                      struct sysdev_attribute *attr,
2908                      char *buf)
2909{
2910    return sprintf(buf, "0\n"); /* always zero; should fit... */
2911}
2912
2913static ssize_t write_scan_unevictable_node(struct sys_device *dev,
2914                       struct sysdev_attribute *attr,
2915                    const char *buf, size_t count)
2916{
2917    struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
2918    struct zone *zone;
2919    unsigned long res;
2920    unsigned long req = strict_strtoul(buf, 10, &res);
2921
2922    if (!req)
2923        return 1; /* zero is no-op */
2924
2925    for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
2926        if (!populated_zone(zone))
2927            continue;
2928        scan_zone_unevictable_pages(zone);
2929    }
2930    return 1;
2931}
2932
2933
2934static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
2935            read_scan_unevictable_node,
2936            write_scan_unevictable_node);
2937
2938int scan_unevictable_register_node(struct node *node)
2939{
2940    return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
2941}
2942
2943void scan_unevictable_unregister_node(struct node *node)
2944{
2945    sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
2946}
2947
2948

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