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
51#define CREATE_TRACE_POINTS
52#include <trace/events/vmscan.h>
53
54struct scan_control {
55    /* Incremented by the number of inactive pages that were scanned */
56    unsigned long nr_scanned;
57
58    /* Number of pages freed so far during a call to shrink_zones() */
59    unsigned long nr_reclaimed;
60
61    /* How many pages shrink_list() should reclaim */
62    unsigned long nr_to_reclaim;
63
64    unsigned long hibernation_mode;
65
66    /* This context's GFP mask */
67    gfp_t gfp_mask;
68
69    int may_writepage;
70
71    /* Can mapped pages be reclaimed? */
72    int may_unmap;
73
74    /* Can pages be swapped as part of reclaim? */
75    int may_swap;
76
77    int swappiness;
78
79    int order;
80
81    /*
82     * Intend to reclaim enough contenious memory rather than to reclaim
83     * enough amount memory. I.e, it's the mode for high order allocation.
84     */
85    bool lumpy_reclaim_mode;
86
87    /* Which cgroup do we reclaim from */
88    struct mem_cgroup *mem_cgroup;
89
90    /*
91     * Nodemask of nodes allowed by the caller. If NULL, all nodes
92     * are scanned.
93     */
94    nodemask_t *nodemask;
95};
96
97#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
98
99#ifdef ARCH_HAS_PREFETCH
100#define prefetch_prev_lru_page(_page, _base, _field) \
101    do { \
102        if ((_page)->lru.prev != _base) { \
103            struct page *prev; \
104                                    \
105            prev = lru_to_page(&(_page->lru)); \
106            prefetch(&prev->_field); \
107        } \
108    } while (0)
109#else
110#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
111#endif
112
113#ifdef ARCH_HAS_PREFETCHW
114#define prefetchw_prev_lru_page(_page, _base, _field) \
115    do { \
116        if ((_page)->lru.prev != _base) { \
117            struct page *prev; \
118                                    \
119            prev = lru_to_page(&(_page->lru)); \
120            prefetchw(&prev->_field); \
121        } \
122    } while (0)
123#else
124#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
125#endif
126
127/*
128 * From 0 .. 100. Higher means more swappy.
129 */
130int vm_swappiness = 60;
131long vm_total_pages; /* The total number of pages which the VM controls */
132
133static LIST_HEAD(shrinker_list);
134static DECLARE_RWSEM(shrinker_rwsem);
135
136#ifdef CONFIG_CGROUP_MEM_RES_CTLR
137#define scanning_global_lru(sc) (!(sc)->mem_cgroup)
138#else
139#define scanning_global_lru(sc) (1)
140#endif
141
142static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
143                          struct scan_control *sc)
144{
145    if (!scanning_global_lru(sc))
146        return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
147
148    return &zone->reclaim_stat;
149}
150
151static unsigned long zone_nr_lru_pages(struct zone *zone,
152                struct scan_control *sc, enum lru_list lru)
153{
154    if (!scanning_global_lru(sc))
155        return mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, lru);
156
157    return zone_page_state(zone, NR_LRU_BASE + lru);
158}
159
160
161/*
162 * Add a shrinker callback to be called from the vm
163 */
164void register_shrinker(struct shrinker *shrinker)
165{
166    shrinker->nr = 0;
167    down_write(&shrinker_rwsem);
168    list_add_tail(&shrinker->list, &shrinker_list);
169    up_write(&shrinker_rwsem);
170}
171EXPORT_SYMBOL(register_shrinker);
172
173/*
174 * Remove one
175 */
176void unregister_shrinker(struct shrinker *shrinker)
177{
178    down_write(&shrinker_rwsem);
179    list_del(&shrinker->list);
180    up_write(&shrinker_rwsem);
181}
182EXPORT_SYMBOL(unregister_shrinker);
183
184#define SHRINK_BATCH 128
185/*
186 * Call the shrink functions to age shrinkable caches
187 *
188 * Here we assume it costs one seek to replace a lru page and that it also
189 * takes a seek to recreate a cache object. With this in mind we age equal
190 * percentages of the lru and ageable caches. This should balance the seeks
191 * generated by these structures.
192 *
193 * If the vm encountered mapped pages on the LRU it increase the pressure on
194 * slab to avoid swapping.
195 *
196 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
197 *
198 * `lru_pages' represents the number of on-LRU pages in all the zones which
199 * are eligible for the caller's allocation attempt. It is used for balancing
200 * slab reclaim versus page reclaim.
201 *
202 * Returns the number of slab objects which we shrunk.
203 */
204unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
205            unsigned long lru_pages)
206{
207    struct shrinker *shrinker;
208    unsigned long ret = 0;
209
210    if (scanned == 0)
211        scanned = SWAP_CLUSTER_MAX;
212
213    if (!down_read_trylock(&shrinker_rwsem))
214        return 1; /* Assume we'll be able to shrink next time */
215
216    list_for_each_entry(shrinker, &shrinker_list, list) {
217        unsigned long long delta;
218        unsigned long total_scan;
219        unsigned long max_pass;
220
221        max_pass = (*shrinker->shrink)(shrinker, 0, gfp_mask);
222        delta = (4 * scanned) / shrinker->seeks;
223        delta *= max_pass;
224        do_div(delta, lru_pages + 1);
225        shrinker->nr += delta;
226        if (shrinker->nr < 0) {
227            printk(KERN_ERR "shrink_slab: %pF negative objects to "
228                   "delete nr=%ld\n",
229                   shrinker->shrink, shrinker->nr);
230            shrinker->nr = max_pass;
231        }
232
233        /*
234         * Avoid risking looping forever due to too large nr value:
235         * never try to free more than twice the estimate number of
236         * freeable entries.
237         */
238        if (shrinker->nr > max_pass * 2)
239            shrinker->nr = max_pass * 2;
240
241        total_scan = shrinker->nr;
242        shrinker->nr = 0;
243
244        while (total_scan >= SHRINK_BATCH) {
245            long this_scan = SHRINK_BATCH;
246            int shrink_ret;
247            int nr_before;
248
249            nr_before = (*shrinker->shrink)(shrinker, 0, gfp_mask);
250            shrink_ret = (*shrinker->shrink)(shrinker, this_scan,
251                                gfp_mask);
252            if (shrink_ret == -1)
253                break;
254            if (shrink_ret < nr_before)
255                ret += nr_before - shrink_ret;
256            count_vm_events(SLABS_SCANNED, this_scan);
257            total_scan -= this_scan;
258
259            cond_resched();
260        }
261
262        shrinker->nr += total_scan;
263    }
264    up_read(&shrinker_rwsem);
265    return ret;
266}
267
268static inline int is_page_cache_freeable(struct page *page)
269{
270    /*
271     * A freeable page cache page is referenced only by the caller
272     * that isolated the page, the page cache radix tree and
273     * optional buffer heads at page->private.
274     */
275    return page_count(page) - page_has_private(page) == 2;
276}
277
278static int may_write_to_queue(struct backing_dev_info *bdi)
279{
280    if (current->flags & PF_SWAPWRITE)
281        return 1;
282    if (!bdi_write_congested(bdi))
283        return 1;
284    if (bdi == current->backing_dev_info)
285        return 1;
286    return 0;
287}
288
289/*
290 * We detected a synchronous write error writing a page out. Probably
291 * -ENOSPC. We need to propagate that into the address_space for a subsequent
292 * fsync(), msync() or close().
293 *
294 * The tricky part is that after writepage we cannot touch the mapping: nothing
295 * prevents it from being freed up. But we have a ref on the page and once
296 * that page is locked, the mapping is pinned.
297 *
298 * We're allowed to run sleeping lock_page() here because we know the caller has
299 * __GFP_FS.
300 */
301static void handle_write_error(struct address_space *mapping,
302                struct page *page, int error)
303{
304    lock_page_nosync(page);
305    if (page_mapping(page) == mapping)
306        mapping_set_error(mapping, error);
307    unlock_page(page);
308}
309
310/* Request for sync pageout. */
311enum pageout_io {
312    PAGEOUT_IO_ASYNC,
313    PAGEOUT_IO_SYNC,
314};
315
316/* possible outcome of pageout() */
317typedef enum {
318    /* failed to write page out, page is locked */
319    PAGE_KEEP,
320    /* move page to the active list, page is locked */
321    PAGE_ACTIVATE,
322    /* page has been sent to the disk successfully, page is unlocked */
323    PAGE_SUCCESS,
324    /* page is clean and locked */
325    PAGE_CLEAN,
326} pageout_t;
327
328/*
329 * pageout is called by shrink_page_list() for each dirty page.
330 * Calls ->writepage().
331 */
332static pageout_t pageout(struct page *page, struct address_space *mapping,
333                        enum pageout_io sync_writeback)
334{
335    /*
336     * If the page is dirty, only perform writeback if that write
337     * will be non-blocking. To prevent this allocation from being
338     * stalled by pagecache activity. But note that there may be
339     * stalls if we need to run get_block(). We could test
340     * PagePrivate for that.
341     *
342     * If this process is currently in __generic_file_aio_write() against
343     * this page's queue, we can perform writeback even if that
344     * will block.
345     *
346     * If the page is swapcache, write it back even if that would
347     * block, for some throttling. This happens by accident, because
348     * swap_backing_dev_info is bust: it doesn't reflect the
349     * congestion state of the swapdevs. Easy to fix, if needed.
350     */
351    if (!is_page_cache_freeable(page))
352        return PAGE_KEEP;
353    if (!mapping) {
354        /*
355         * Some data journaling orphaned pages can have
356         * page->mapping == NULL while being dirty with clean buffers.
357         */
358        if (page_has_private(page)) {
359            if (try_to_free_buffers(page)) {
360                ClearPageDirty(page);
361                printk("%s: orphaned page\n", __func__);
362                return PAGE_CLEAN;
363            }
364        }
365        return PAGE_KEEP;
366    }
367    if (mapping->a_ops->writepage == NULL)
368        return PAGE_ACTIVATE;
369    if (!may_write_to_queue(mapping->backing_dev_info))
370        return PAGE_KEEP;
371
372    if (clear_page_dirty_for_io(page)) {
373        int res;
374        struct writeback_control wbc = {
375            .sync_mode = WB_SYNC_NONE,
376            .nr_to_write = SWAP_CLUSTER_MAX,
377            .range_start = 0,
378            .range_end = LLONG_MAX,
379            .nonblocking = 1,
380            .for_reclaim = 1,
381        };
382
383        SetPageReclaim(page);
384        res = mapping->a_ops->writepage(page, &wbc);
385        if (res < 0)
386            handle_write_error(mapping, page, res);
387        if (res == AOP_WRITEPAGE_ACTIVATE) {
388            ClearPageReclaim(page);
389            return PAGE_ACTIVATE;
390        }
391
392        /*
393         * Wait on writeback if requested to. This happens when
394         * direct reclaiming a large contiguous area and the
395         * first attempt to free a range of pages fails.
396         */
397        if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
398            wait_on_page_writeback(page);
399
400        if (!PageWriteback(page)) {
401            /* synchronous write or broken a_ops? */
402            ClearPageReclaim(page);
403        }
404        trace_mm_vmscan_writepage(page,
405            trace_reclaim_flags(page, sync_writeback));
406        inc_zone_page_state(page, NR_VMSCAN_WRITE);
407        return PAGE_SUCCESS;
408    }
409
410    return PAGE_CLEAN;
411}
412
413/*
414 * Same as remove_mapping, but if the page is removed from the mapping, it
415 * gets returned with a refcount of 0.
416 */
417static int __remove_mapping(struct address_space *mapping, struct page *page)
418{
419    BUG_ON(!PageLocked(page));
420    BUG_ON(mapping != page_mapping(page));
421
422    spin_lock_irq(&mapping->tree_lock);
423    /*
424     * The non racy check for a busy page.
425     *
426     * Must be careful with the order of the tests. When someone has
427     * a ref to the page, it may be possible that they dirty it then
428     * drop the reference. So if PageDirty is tested before page_count
429     * here, then the following race may occur:
430     *
431     * get_user_pages(&page);
432     * [user mapping goes away]
433     * write_to(page);
434     * !PageDirty(page) [good]
435     * SetPageDirty(page);
436     * put_page(page);
437     * !page_count(page) [good, discard it]
438     *
439     * [oops, our write_to data is lost]
440     *
441     * Reversing the order of the tests ensures such a situation cannot
442     * escape unnoticed. The smp_rmb is needed to ensure the page->flags
443     * load is not satisfied before that of page->_count.
444     *
445     * Note that if SetPageDirty is always performed via set_page_dirty,
446     * and thus under tree_lock, then this ordering is not required.
447     */
448    if (!page_freeze_refs(page, 2))
449        goto cannot_free;
450    /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
451    if (unlikely(PageDirty(page))) {
452        page_unfreeze_refs(page, 2);
453        goto cannot_free;
454    }
455
456    if (PageSwapCache(page)) {
457        swp_entry_t swap = { .val = page_private(page) };
458        __delete_from_swap_cache(page);
459        spin_unlock_irq(&mapping->tree_lock);
460        swapcache_free(swap, page);
461    } else {
462        __remove_from_page_cache(page);
463        spin_unlock_irq(&mapping->tree_lock);
464        mem_cgroup_uncharge_cache_page(page);
465    }
466
467    return 1;
468
469cannot_free:
470    spin_unlock_irq(&mapping->tree_lock);
471    return 0;
472}
473
474/*
475 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
476 * someone else has a ref on the page, abort and return 0. If it was
477 * successfully detached, return 1. Assumes the caller has a single ref on
478 * this page.
479 */
480int remove_mapping(struct address_space *mapping, struct page *page)
481{
482    if (__remove_mapping(mapping, page)) {
483        /*
484         * Unfreezing the refcount with 1 rather than 2 effectively
485         * drops the pagecache ref for us without requiring another
486         * atomic operation.
487         */
488        page_unfreeze_refs(page, 1);
489        return 1;
490    }
491    return 0;
492}
493
494/**
495 * putback_lru_page - put previously isolated page onto appropriate LRU list
496 * @page: page to be put back to appropriate lru list
497 *
498 * Add previously isolated @page to appropriate LRU list.
499 * Page may still be unevictable for other reasons.
500 *
501 * lru_lock must not be held, interrupts must be enabled.
502 */
503void putback_lru_page(struct page *page)
504{
505    int lru;
506    int active = !!TestClearPageActive(page);
507    int was_unevictable = PageUnevictable(page);
508
509    VM_BUG_ON(PageLRU(page));
510
511redo:
512    ClearPageUnevictable(page);
513
514    if (page_evictable(page, NULL)) {
515        /*
516         * For evictable pages, we can use the cache.
517         * In event of a race, worst case is we end up with an
518         * unevictable page on [in]active list.
519         * We know how to handle that.
520         */
521        lru = active + page_lru_base_type(page);
522        lru_cache_add_lru(page, lru);
523    } else {
524        /*
525         * Put unevictable pages directly on zone's unevictable
526         * list.
527         */
528        lru = LRU_UNEVICTABLE;
529        add_page_to_unevictable_list(page);
530        /*
531         * When racing with an mlock clearing (page is
532         * unlocked), make sure that if the other thread does
533         * not observe our setting of PG_lru and fails
534         * isolation, we see PG_mlocked cleared below and move
535         * the page back to the evictable list.
536         *
537         * The other side is TestClearPageMlocked().
538         */
539        smp_mb();
540    }
541
542    /*
543     * page's status can change while we move it among lru. If an evictable
544     * page is on unevictable list, it never be freed. To avoid that,
545     * check after we added it to the list, again.
546     */
547    if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
548        if (!isolate_lru_page(page)) {
549            put_page(page);
550            goto redo;
551        }
552        /* This means someone else dropped this page from LRU
553         * So, it will be freed or putback to LRU again. There is
554         * nothing to do here.
555         */
556    }
557
558    if (was_unevictable && lru != LRU_UNEVICTABLE)
559        count_vm_event(UNEVICTABLE_PGRESCUED);
560    else if (!was_unevictable && lru == LRU_UNEVICTABLE)
561        count_vm_event(UNEVICTABLE_PGCULLED);
562
563    put_page(page); /* drop ref from isolate */
564}
565
566enum page_references {
567    PAGEREF_RECLAIM,
568    PAGEREF_RECLAIM_CLEAN,
569    PAGEREF_KEEP,
570    PAGEREF_ACTIVATE,
571};
572
573static enum page_references page_check_references(struct page *page,
574                          struct scan_control *sc)
575{
576    int referenced_ptes, referenced_page;
577    unsigned long vm_flags;
578
579    referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
580    referenced_page = TestClearPageReferenced(page);
581
582    /* Lumpy reclaim - ignore references */
583    if (sc->lumpy_reclaim_mode)
584        return PAGEREF_RECLAIM;
585
586    /*
587     * Mlock lost the isolation race with us. Let try_to_unmap()
588     * move the page to the unevictable list.
589     */
590    if (vm_flags & VM_LOCKED)
591        return PAGEREF_RECLAIM;
592
593    if (referenced_ptes) {
594        if (PageAnon(page))
595            return PAGEREF_ACTIVATE;
596        /*
597         * All mapped pages start out with page table
598         * references from the instantiating fault, so we need
599         * to look twice if a mapped file page is used more
600         * than once.
601         *
602         * Mark it and spare it for another trip around the
603         * inactive list. Another page table reference will
604         * lead to its activation.
605         *
606         * Note: the mark is set for activated pages as well
607         * so that recently deactivated but used pages are
608         * quickly recovered.
609         */
610        SetPageReferenced(page);
611
612        if (referenced_page)
613            return PAGEREF_ACTIVATE;
614
615        return PAGEREF_KEEP;
616    }
617
618    /* Reclaim if clean, defer dirty pages to writeback */
619    if (referenced_page)
620        return PAGEREF_RECLAIM_CLEAN;
621
622    return PAGEREF_RECLAIM;
623}
624
625static noinline_for_stack void free_page_list(struct list_head *free_pages)
626{
627    struct pagevec freed_pvec;
628    struct page *page, *tmp;
629
630    pagevec_init(&freed_pvec, 1);
631
632    list_for_each_entry_safe(page, tmp, free_pages, lru) {
633        list_del(&page->lru);
634        if (!pagevec_add(&freed_pvec, page)) {
635            __pagevec_free(&freed_pvec);
636            pagevec_reinit(&freed_pvec);
637        }
638    }
639
640    pagevec_free(&freed_pvec);
641}
642
643/*
644 * shrink_page_list() returns the number of reclaimed pages
645 */
646static unsigned long shrink_page_list(struct list_head *page_list,
647                    struct scan_control *sc,
648                    enum pageout_io sync_writeback)
649{
650    LIST_HEAD(ret_pages);
651    LIST_HEAD(free_pages);
652    int pgactivate = 0;
653    unsigned long nr_reclaimed = 0;
654
655    cond_resched();
656
657    while (!list_empty(page_list)) {
658        enum page_references references;
659        struct address_space *mapping;
660        struct page *page;
661        int may_enter_fs;
662
663        cond_resched();
664
665        page = lru_to_page(page_list);
666        list_del(&page->lru);
667
668        if (!trylock_page(page))
669            goto keep;
670
671        VM_BUG_ON(PageActive(page));
672
673        sc->nr_scanned++;
674
675        if (unlikely(!page_evictable(page, NULL)))
676            goto cull_mlocked;
677
678        if (!sc->may_unmap && page_mapped(page))
679            goto keep_locked;
680
681        /* Double the slab pressure for mapped and swapcache pages */
682        if (page_mapped(page) || PageSwapCache(page))
683            sc->nr_scanned++;
684
685        may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
686            (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
687
688        if (PageWriteback(page)) {
689            /*
690             * Synchronous reclaim is performed in two passes,
691             * first an asynchronous pass over the list to
692             * start parallel writeback, and a second synchronous
693             * pass to wait for the IO to complete. Wait here
694             * for any page for which writeback has already
695             * started.
696             */
697            if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
698                wait_on_page_writeback(page);
699            else
700                goto keep_locked;
701        }
702
703        references = page_check_references(page, sc);
704        switch (references) {
705        case PAGEREF_ACTIVATE:
706            goto activate_locked;
707        case PAGEREF_KEEP:
708            goto keep_locked;
709        case PAGEREF_RECLAIM:
710        case PAGEREF_RECLAIM_CLEAN:
711            ; /* try to reclaim the page below */
712        }
713
714        /*
715         * Anonymous process memory has backing store?
716         * Try to allocate it some swap space here.
717         */
718        if (PageAnon(page) && !PageSwapCache(page)) {
719            if (!(sc->gfp_mask & __GFP_IO))
720                goto keep_locked;
721            if (!add_to_swap(page))
722                goto activate_locked;
723            may_enter_fs = 1;
724        }
725
726        mapping = page_mapping(page);
727
728        /*
729         * The page is mapped into the page tables of one or more
730         * processes. Try to unmap it here.
731         */
732        if (page_mapped(page) && mapping) {
733            switch (try_to_unmap(page, TTU_UNMAP)) {
734            case SWAP_FAIL:
735                goto activate_locked;
736            case SWAP_AGAIN:
737                goto keep_locked;
738            case SWAP_MLOCK:
739                goto cull_mlocked;
740            case SWAP_SUCCESS:
741                ; /* try to free the page below */
742            }
743        }
744
745        if (PageDirty(page)) {
746            if (references == PAGEREF_RECLAIM_CLEAN)
747                goto keep_locked;
748            if (!may_enter_fs)
749                goto keep_locked;
750            if (!sc->may_writepage)
751                goto keep_locked;
752
753            /* Page is dirty, try to write it out here */
754            switch (pageout(page, mapping, sync_writeback)) {
755            case PAGE_KEEP:
756                goto keep_locked;
757            case PAGE_ACTIVATE:
758                goto activate_locked;
759            case PAGE_SUCCESS:
760                if (PageWriteback(page) || PageDirty(page))
761                    goto keep;
762                /*
763                 * A synchronous write - probably a ramdisk. Go
764                 * ahead and try to reclaim the page.
765                 */
766                if (!trylock_page(page))
767                    goto keep;
768                if (PageDirty(page) || PageWriteback(page))
769                    goto keep_locked;
770                mapping = page_mapping(page);
771            case PAGE_CLEAN:
772                ; /* try to free the page below */
773            }
774        }
775
776        /*
777         * If the page has buffers, try to free the buffer mappings
778         * associated with this page. If we succeed we try to free
779         * the page as well.
780         *
781         * We do this even if the page is PageDirty().
782         * try_to_release_page() does not perform I/O, but it is
783         * possible for a page to have PageDirty set, but it is actually
784         * clean (all its buffers are clean). This happens if the
785         * buffers were written out directly, with submit_bh(). ext3
786         * will do this, as well as the blockdev mapping.
787         * try_to_release_page() will discover that cleanness and will
788         * drop the buffers and mark the page clean - it can be freed.
789         *
790         * Rarely, pages can have buffers and no ->mapping. These are
791         * the pages which were not successfully invalidated in
792         * truncate_complete_page(). We try to drop those buffers here
793         * and if that worked, and the page is no longer mapped into
794         * process address space (page_count == 1) it can be freed.
795         * Otherwise, leave the page on the LRU so it is swappable.
796         */
797        if (page_has_private(page)) {
798            if (!try_to_release_page(page, sc->gfp_mask))
799                goto activate_locked;
800            if (!mapping && page_count(page) == 1) {
801                unlock_page(page);
802                if (put_page_testzero(page))
803                    goto free_it;
804                else {
805                    /*
806                     * rare race with speculative reference.
807                     * the speculative reference will free
808                     * this page shortly, so we may
809                     * increment nr_reclaimed here (and
810                     * leave it off the LRU).
811                     */
812                    nr_reclaimed++;
813                    continue;
814                }
815            }
816        }
817
818        if (!mapping || !__remove_mapping(mapping, page))
819            goto keep_locked;
820
821        /*
822         * At this point, we have no other references and there is
823         * no way to pick any more up (removed from LRU, removed
824         * from pagecache). Can use non-atomic bitops now (and
825         * we obviously don't have to worry about waking up a process
826         * waiting on the page lock, because there are no references.
827         */
828        __clear_page_locked(page);
829free_it:
830        nr_reclaimed++;
831
832        /*
833         * Is there need to periodically free_page_list? It would
834         * appear not as the counts should be low
835         */
836        list_add(&page->lru, &free_pages);
837        continue;
838
839cull_mlocked:
840        if (PageSwapCache(page))
841            try_to_free_swap(page);
842        unlock_page(page);
843        putback_lru_page(page);
844        continue;
845
846activate_locked:
847        /* Not a candidate for swapping, so reclaim swap space. */
848        if (PageSwapCache(page) && vm_swap_full())
849            try_to_free_swap(page);
850        VM_BUG_ON(PageActive(page));
851        SetPageActive(page);
852        pgactivate++;
853keep_locked:
854        unlock_page(page);
855keep:
856        list_add(&page->lru, &ret_pages);
857        VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
858    }
859
860    free_page_list(&free_pages);
861
862    list_splice(&ret_pages, page_list);
863    count_vm_events(PGACTIVATE, pgactivate);
864    return nr_reclaimed;
865}
866
867/*
868 * Attempt to remove the specified page from its LRU. Only take this page
869 * if it is of the appropriate PageActive status. Pages which are being
870 * freed elsewhere are also ignored.
871 *
872 * page: page to consider
873 * mode: one of the LRU isolation modes defined above
874 *
875 * returns 0 on success, -ve errno on failure.
876 */
877int __isolate_lru_page(struct page *page, int mode, int file)
878{
879    int ret = -EINVAL;
880
881    /* Only take pages on the LRU. */
882    if (!PageLRU(page))
883        return ret;
884
885    /*
886     * When checking the active state, we need to be sure we are
887     * dealing with comparible boolean values. Take the logical not
888     * of each.
889     */
890    if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
891        return ret;
892
893    if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
894        return ret;
895
896    /*
897     * When this function is being called for lumpy reclaim, we
898     * initially look into all LRU pages, active, inactive and
899     * unevictable; only give shrink_page_list evictable pages.
900     */
901    if (PageUnevictable(page))
902        return ret;
903
904    ret = -EBUSY;
905
906    if (likely(get_page_unless_zero(page))) {
907        /*
908         * Be careful not to clear PageLRU until after we're
909         * sure the page is not being freed elsewhere -- the
910         * page release code relies on it.
911         */
912        ClearPageLRU(page);
913        ret = 0;
914    }
915
916    return ret;
917}
918
919/*
920 * zone->lru_lock is heavily contended. Some of the functions that
921 * shrink the lists perform better by taking out a batch of pages
922 * and working on them outside the LRU lock.
923 *
924 * For pagecache intensive workloads, this function is the hottest
925 * spot in the kernel (apart from copy_*_user functions).
926 *
927 * Appropriate locks must be held before calling this function.
928 *
929 * @nr_to_scan: The number of pages to look through on the list.
930 * @src: The LRU list to pull pages off.
931 * @dst: The temp list to put pages on to.
932 * @scanned: The number of pages that were scanned.
933 * @order: The caller's attempted allocation order
934 * @mode: One of the LRU isolation modes
935 * @file: True [1] if isolating file [!anon] pages
936 *
937 * returns how many pages were moved onto *@dst.
938 */
939static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
940        struct list_head *src, struct list_head *dst,
941        unsigned long *scanned, int order, int mode, int file)
942{
943    unsigned long nr_taken = 0;
944    unsigned long nr_lumpy_taken = 0;
945    unsigned long nr_lumpy_dirty = 0;
946    unsigned long nr_lumpy_failed = 0;
947    unsigned long scan;
948
949    for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
950        struct page *page;
951        unsigned long pfn;
952        unsigned long end_pfn;
953        unsigned long page_pfn;
954        int zone_id;
955
956        page = lru_to_page(src);
957        prefetchw_prev_lru_page(page, src, flags);
958
959        VM_BUG_ON(!PageLRU(page));
960
961        switch (__isolate_lru_page(page, mode, file)) {
962        case 0:
963            list_move(&page->lru, dst);
964            mem_cgroup_del_lru(page);
965            nr_taken++;
966            break;
967
968        case -EBUSY:
969            /* else it is being freed elsewhere */
970            list_move(&page->lru, src);
971            mem_cgroup_rotate_lru_list(page, page_lru(page));
972            continue;
973
974        default:
975            BUG();
976        }
977
978        if (!order)
979            continue;
980
981        /*
982         * Attempt to take all pages in the order aligned region
983         * surrounding the tag page. Only take those pages of
984         * the same active state as that tag page. We may safely
985         * round the target page pfn down to the requested order
986         * as the mem_map is guarenteed valid out to MAX_ORDER,
987         * where that page is in a different zone we will detect
988         * it from its zone id and abort this block scan.
989         */
990        zone_id = page_zone_id(page);
991        page_pfn = page_to_pfn(page);
992        pfn = page_pfn & ~((1 << order) - 1);
993        end_pfn = pfn + (1 << order);
994        for (; pfn < end_pfn; pfn++) {
995            struct page *cursor_page;
996
997            /* The target page is in the block, ignore it. */
998            if (unlikely(pfn == page_pfn))
999                continue;
1000
1001            /* Avoid holes within the zone. */
1002            if (unlikely(!pfn_valid_within(pfn)))
1003                break;
1004
1005            cursor_page = pfn_to_page(pfn);
1006
1007            /* Check that we have not crossed a zone boundary. */
1008            if (unlikely(page_zone_id(cursor_page) != zone_id))
1009                continue;
1010
1011            /*
1012             * If we don't have enough swap space, reclaiming of
1013             * anon page which don't already have a swap slot is
1014             * pointless.
1015             */
1016            if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
1017                    !PageSwapCache(cursor_page))
1018                continue;
1019
1020            if (__isolate_lru_page(cursor_page, mode, file) == 0) {
1021                list_move(&cursor_page->lru, dst);
1022                mem_cgroup_del_lru(cursor_page);
1023                nr_taken++;
1024                nr_lumpy_taken++;
1025                if (PageDirty(cursor_page))
1026                    nr_lumpy_dirty++;
1027                scan++;
1028            } else {
1029                if (mode == ISOLATE_BOTH &&
1030                        page_count(cursor_page))
1031                    nr_lumpy_failed++;
1032            }
1033        }
1034    }
1035
1036    *scanned = scan;
1037
1038    trace_mm_vmscan_lru_isolate(order,
1039            nr_to_scan, scan,
1040            nr_taken,
1041            nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
1042            mode);
1043    return nr_taken;
1044}
1045
1046static unsigned long isolate_pages_global(unsigned long nr,
1047                    struct list_head *dst,
1048                    unsigned long *scanned, int order,
1049                    int mode, struct zone *z,
1050                    int active, int file)
1051{
1052    int lru = LRU_BASE;
1053    if (active)
1054        lru += LRU_ACTIVE;
1055    if (file)
1056        lru += LRU_FILE;
1057    return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
1058                                mode, file);
1059}
1060
1061/*
1062 * clear_active_flags() is a helper for shrink_active_list(), clearing
1063 * any active bits from the pages in the list.
1064 */
1065static unsigned long clear_active_flags(struct list_head *page_list,
1066                    unsigned int *count)
1067{
1068    int nr_active = 0;
1069    int lru;
1070    struct page *page;
1071
1072    list_for_each_entry(page, page_list, lru) {
1073        lru = page_lru_base_type(page);
1074        if (PageActive(page)) {
1075            lru += LRU_ACTIVE;
1076            ClearPageActive(page);
1077            nr_active++;
1078        }
1079        if (count)
1080            count[lru]++;
1081    }
1082
1083    return nr_active;
1084}
1085
1086/**
1087 * isolate_lru_page - tries to isolate a page from its LRU list
1088 * @page: page to isolate from its LRU list
1089 *
1090 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1091 * vmstat statistic corresponding to whatever LRU list the page was on.
1092 *
1093 * Returns 0 if the page was removed from an LRU list.
1094 * Returns -EBUSY if the page was not on an LRU list.
1095 *
1096 * The returned page will have PageLRU() cleared. If it was found on
1097 * the active list, it will have PageActive set. If it was found on
1098 * the unevictable list, it will have the PageUnevictable bit set. That flag
1099 * may need to be cleared by the caller before letting the page go.
1100 *
1101 * The vmstat statistic corresponding to the list on which the page was
1102 * found will be decremented.
1103 *
1104 * Restrictions:
1105 * (1) Must be called with an elevated refcount on the page. This is a
1106 * fundamentnal difference from isolate_lru_pages (which is called
1107 * without a stable reference).
1108 * (2) the lru_lock must not be held.
1109 * (3) interrupts must be enabled.
1110 */
1111int isolate_lru_page(struct page *page)
1112{
1113    int ret = -EBUSY;
1114
1115    if (PageLRU(page)) {
1116        struct zone *zone = page_zone(page);
1117
1118        spin_lock_irq(&zone->lru_lock);
1119        if (PageLRU(page) && get_page_unless_zero(page)) {
1120            int lru = page_lru(page);
1121            ret = 0;
1122            ClearPageLRU(page);
1123
1124            del_page_from_lru_list(zone, page, lru);
1125        }
1126        spin_unlock_irq(&zone->lru_lock);
1127    }
1128    return ret;
1129}
1130
1131/*
1132 * Are there way too many processes in the direct reclaim path already?
1133 */
1134static int too_many_isolated(struct zone *zone, int file,
1135        struct scan_control *sc)
1136{
1137    unsigned long inactive, isolated;
1138
1139    if (current_is_kswapd())
1140        return 0;
1141
1142    if (!scanning_global_lru(sc))
1143        return 0;
1144
1145    if (file) {
1146        inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1147        isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1148    } else {
1149        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1150        isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1151    }
1152
1153    return isolated > inactive;
1154}
1155
1156/*
1157 * TODO: Try merging with migrations version of putback_lru_pages
1158 */
1159static noinline_for_stack void
1160putback_lru_pages(struct zone *zone, struct scan_control *sc,
1161                unsigned long nr_anon, unsigned long nr_file,
1162                struct list_head *page_list)
1163{
1164    struct page *page;
1165    struct pagevec pvec;
1166    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1167
1168    pagevec_init(&pvec, 1);
1169
1170    /*
1171     * Put back any unfreeable pages.
1172     */
1173    spin_lock(&zone->lru_lock);
1174    while (!list_empty(page_list)) {
1175        int lru;
1176        page = lru_to_page(page_list);
1177        VM_BUG_ON(PageLRU(page));
1178        list_del(&page->lru);
1179        if (unlikely(!page_evictable(page, NULL))) {
1180            spin_unlock_irq(&zone->lru_lock);
1181            putback_lru_page(page);
1182            spin_lock_irq(&zone->lru_lock);
1183            continue;
1184        }
1185        SetPageLRU(page);
1186        lru = page_lru(page);
1187        add_page_to_lru_list(zone, page, lru);
1188        if (is_active_lru(lru)) {
1189            int file = is_file_lru(lru);
1190            reclaim_stat->recent_rotated[file]++;
1191        }
1192        if (!pagevec_add(&pvec, page)) {
1193            spin_unlock_irq(&zone->lru_lock);
1194            __pagevec_release(&pvec);
1195            spin_lock_irq(&zone->lru_lock);
1196        }
1197    }
1198    __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1199    __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1200
1201    spin_unlock_irq(&zone->lru_lock);
1202    pagevec_release(&pvec);
1203}
1204
1205static noinline_for_stack void update_isolated_counts(struct zone *zone,
1206                    struct scan_control *sc,
1207                    unsigned long *nr_anon,
1208                    unsigned long *nr_file,
1209                    struct list_head *isolated_list)
1210{
1211    unsigned long nr_active;
1212    unsigned int count[NR_LRU_LISTS] = { 0, };
1213    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1214
1215    nr_active = clear_active_flags(isolated_list, count);
1216    __count_vm_events(PGDEACTIVATE, nr_active);
1217
1218    __mod_zone_page_state(zone, NR_ACTIVE_FILE,
1219                  -count[LRU_ACTIVE_FILE]);
1220    __mod_zone_page_state(zone, NR_INACTIVE_FILE,
1221                  -count[LRU_INACTIVE_FILE]);
1222    __mod_zone_page_state(zone, NR_ACTIVE_ANON,
1223                  -count[LRU_ACTIVE_ANON]);
1224    __mod_zone_page_state(zone, NR_INACTIVE_ANON,
1225                  -count[LRU_INACTIVE_ANON]);
1226
1227    *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1228    *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1229    __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
1230    __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
1231
1232    reclaim_stat->recent_scanned[0] += *nr_anon;
1233    reclaim_stat->recent_scanned[1] += *nr_file;
1234}
1235
1236/*
1237 * Returns true if the caller should wait to clean dirty/writeback pages.
1238 *
1239 * If we are direct reclaiming for contiguous pages and we do not reclaim
1240 * everything in the list, try again and wait for writeback IO to complete.
1241 * This will stall high-order allocations noticeably. Only do that when really
1242 * need to free the pages under high memory pressure.
1243 */
1244static inline bool should_reclaim_stall(unsigned long nr_taken,
1245                    unsigned long nr_freed,
1246                    int priority,
1247                    struct scan_control *sc)
1248{
1249    int lumpy_stall_priority;
1250
1251    /* kswapd should not stall on sync IO */
1252    if (current_is_kswapd())
1253        return false;
1254
1255    /* Only stall on lumpy reclaim */
1256    if (!sc->lumpy_reclaim_mode)
1257        return false;
1258
1259    /* If we have relaimed everything on the isolated list, no stall */
1260    if (nr_freed == nr_taken)
1261        return false;
1262
1263    /*
1264     * For high-order allocations, there are two stall thresholds.
1265     * High-cost allocations stall immediately where as lower
1266     * order allocations such as stacks require the scanning
1267     * priority to be much higher before stalling.
1268     */
1269    if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1270        lumpy_stall_priority = DEF_PRIORITY;
1271    else
1272        lumpy_stall_priority = DEF_PRIORITY / 3;
1273
1274    return priority <= lumpy_stall_priority;
1275}
1276
1277/*
1278 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1279 * of reclaimed pages
1280 */
1281static noinline_for_stack unsigned long
1282shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
1283            struct scan_control *sc, int priority, int file)
1284{
1285    LIST_HEAD(page_list);
1286    unsigned long nr_scanned;
1287    unsigned long nr_reclaimed = 0;
1288    unsigned long nr_taken;
1289    unsigned long nr_active;
1290    unsigned long nr_anon;
1291    unsigned long nr_file;
1292
1293    while (unlikely(too_many_isolated(zone, file, sc))) {
1294        congestion_wait(BLK_RW_ASYNC, HZ/10);
1295
1296        /* We are about to die and free our memory. Return now. */
1297        if (fatal_signal_pending(current))
1298            return SWAP_CLUSTER_MAX;
1299    }
1300
1301
1302    lru_add_drain();
1303    spin_lock_irq(&zone->lru_lock);
1304
1305    if (scanning_global_lru(sc)) {
1306        nr_taken = isolate_pages_global(nr_to_scan,
1307            &page_list, &nr_scanned, sc->order,
1308            sc->lumpy_reclaim_mode ?
1309                ISOLATE_BOTH : ISOLATE_INACTIVE,
1310            zone, 0, file);
1311        zone->pages_scanned += nr_scanned;
1312        if (current_is_kswapd())
1313            __count_zone_vm_events(PGSCAN_KSWAPD, zone,
1314                           nr_scanned);
1315        else
1316            __count_zone_vm_events(PGSCAN_DIRECT, zone,
1317                           nr_scanned);
1318    } else {
1319        nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
1320            &page_list, &nr_scanned, sc->order,
1321            sc->lumpy_reclaim_mode ?
1322                ISOLATE_BOTH : ISOLATE_INACTIVE,
1323            zone, sc->mem_cgroup,
1324            0, file);
1325        /*
1326         * mem_cgroup_isolate_pages() keeps track of
1327         * scanned pages on its own.
1328         */
1329    }
1330
1331    if (nr_taken == 0) {
1332        spin_unlock_irq(&zone->lru_lock);
1333        return 0;
1334    }
1335
1336    update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
1337
1338    spin_unlock_irq(&zone->lru_lock);
1339
1340    nr_reclaimed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
1341
1342    /* Check if we should syncronously wait for writeback */
1343    if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
1344        congestion_wait(BLK_RW_ASYNC, HZ/10);
1345
1346        /*
1347         * The attempt at page out may have made some
1348         * of the pages active, mark them inactive again.
1349         */
1350        nr_active = clear_active_flags(&page_list, NULL);
1351        count_vm_events(PGDEACTIVATE, nr_active);
1352
1353        nr_reclaimed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC);
1354    }
1355
1356    local_irq_disable();
1357    if (current_is_kswapd())
1358        __count_vm_events(KSWAPD_STEAL, nr_reclaimed);
1359    __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
1360
1361    putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);
1362    return nr_reclaimed;
1363}
1364
1365/*
1366 * This moves pages from the active list to the inactive list.
1367 *
1368 * We move them the other way if the page is referenced by one or more
1369 * processes, from rmap.
1370 *
1371 * If the pages are mostly unmapped, the processing is fast and it is
1372 * appropriate to hold zone->lru_lock across the whole operation. But if
1373 * the pages are mapped, the processing is slow (page_referenced()) so we
1374 * should drop zone->lru_lock around each page. It's impossible to balance
1375 * this, so instead we remove the pages from the LRU while processing them.
1376 * It is safe to rely on PG_active against the non-LRU pages in here because
1377 * nobody will play with that bit on a non-LRU page.
1378 *
1379 * The downside is that we have to touch page->_count against each page.
1380 * But we had to alter page->flags anyway.
1381 */
1382
1383static void move_active_pages_to_lru(struct zone *zone,
1384                     struct list_head *list,
1385                     enum lru_list lru)
1386{
1387    unsigned long pgmoved = 0;
1388    struct pagevec pvec;
1389    struct page *page;
1390
1391    pagevec_init(&pvec, 1);
1392
1393    while (!list_empty(list)) {
1394        page = lru_to_page(list);
1395
1396        VM_BUG_ON(PageLRU(page));
1397        SetPageLRU(page);
1398
1399        list_move(&page->lru, &zone->lru[lru].list);
1400        mem_cgroup_add_lru_list(page, lru);
1401        pgmoved++;
1402
1403        if (!pagevec_add(&pvec, page) || list_empty(list)) {
1404            spin_unlock_irq(&zone->lru_lock);
1405            if (buffer_heads_over_limit)
1406                pagevec_strip(&pvec);
1407            __pagevec_release(&pvec);
1408            spin_lock_irq(&zone->lru_lock);
1409        }
1410    }
1411    __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1412    if (!is_active_lru(lru))
1413        __count_vm_events(PGDEACTIVATE, pgmoved);
1414}
1415
1416static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1417            struct scan_control *sc, int priority, int file)
1418{
1419    unsigned long nr_taken;
1420    unsigned long pgscanned;
1421    unsigned long vm_flags;
1422    LIST_HEAD(l_hold); /* The pages which were snipped off */
1423    LIST_HEAD(l_active);
1424    LIST_HEAD(l_inactive);
1425    struct page *page;
1426    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1427    unsigned long nr_rotated = 0;
1428
1429    lru_add_drain();
1430    spin_lock_irq(&zone->lru_lock);
1431    if (scanning_global_lru(sc)) {
1432        nr_taken = isolate_pages_global(nr_pages, &l_hold,
1433                        &pgscanned, sc->order,
1434                        ISOLATE_ACTIVE, zone,
1435                        1, file);
1436        zone->pages_scanned += pgscanned;
1437    } else {
1438        nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
1439                        &pgscanned, sc->order,
1440                        ISOLATE_ACTIVE, zone,
1441                        sc->mem_cgroup, 1, file);
1442        /*
1443         * mem_cgroup_isolate_pages() keeps track of
1444         * scanned pages on its own.
1445         */
1446    }
1447
1448    reclaim_stat->recent_scanned[file] += nr_taken;
1449
1450    __count_zone_vm_events(PGREFILL, zone, pgscanned);
1451    if (file)
1452        __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1453    else
1454        __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1455    __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1456    spin_unlock_irq(&zone->lru_lock);
1457
1458    while (!list_empty(&l_hold)) {
1459        cond_resched();
1460        page = lru_to_page(&l_hold);
1461        list_del(&page->lru);
1462
1463        if (unlikely(!page_evictable(page, NULL))) {
1464            putback_lru_page(page);
1465            continue;
1466        }
1467
1468        if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1469            nr_rotated++;
1470            /*
1471             * Identify referenced, file-backed active pages and
1472             * give them one more trip around the active list. So
1473             * that executable code get better chances to stay in
1474             * memory under moderate memory pressure. Anon pages
1475             * are not likely to be evicted by use-once streaming
1476             * IO, plus JVM can create lots of anon VM_EXEC pages,
1477             * so we ignore them here.
1478             */
1479            if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1480                list_add(&page->lru, &l_active);
1481                continue;
1482            }
1483        }
1484
1485        ClearPageActive(page); /* we are de-activating */
1486        list_add(&page->lru, &l_inactive);
1487    }
1488
1489    /*
1490     * Move pages back to the lru list.
1491     */
1492    spin_lock_irq(&zone->lru_lock);
1493    /*
1494     * Count referenced pages from currently used mappings as rotated,
1495     * even though only some of them are actually re-activated. This
1496     * helps balance scan pressure between file and anonymous pages in
1497     * get_scan_ratio.
1498     */
1499    reclaim_stat->recent_rotated[file] += nr_rotated;
1500
1501    move_active_pages_to_lru(zone, &l_active,
1502                        LRU_ACTIVE + file * LRU_FILE);
1503    move_active_pages_to_lru(zone, &l_inactive,
1504                        LRU_BASE + file * LRU_FILE);
1505    __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1506    spin_unlock_irq(&zone->lru_lock);
1507}
1508
1509static int inactive_anon_is_low_global(struct zone *zone)
1510{
1511    unsigned long active, inactive;
1512
1513    active = zone_page_state(zone, NR_ACTIVE_ANON);
1514    inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1515
1516    if (inactive * zone->inactive_ratio < active)
1517        return 1;
1518
1519    return 0;
1520}
1521
1522/**
1523 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1524 * @zone: zone to check
1525 * @sc: scan control of this context
1526 *
1527 * Returns true if the zone does not have enough inactive anon pages,
1528 * meaning some active anon pages need to be deactivated.
1529 */
1530static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1531{
1532    int low;
1533
1534    if (scanning_global_lru(sc))
1535        low = inactive_anon_is_low_global(zone);
1536    else
1537        low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1538    return low;
1539}
1540
1541static int inactive_file_is_low_global(struct zone *zone)
1542{
1543    unsigned long active, inactive;
1544
1545    active = zone_page_state(zone, NR_ACTIVE_FILE);
1546    inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1547
1548    return (active > inactive);
1549}
1550
1551/**
1552 * inactive_file_is_low - check if file pages need to be deactivated
1553 * @zone: zone to check
1554 * @sc: scan control of this context
1555 *
1556 * When the system is doing streaming IO, memory pressure here
1557 * ensures that active file pages get deactivated, until more
1558 * than half of the file pages are on the inactive list.
1559 *
1560 * Once we get to that situation, protect the system's working
1561 * set from being evicted by disabling active file page aging.
1562 *
1563 * This uses a different ratio than the anonymous pages, because
1564 * the page cache uses a use-once replacement algorithm.
1565 */
1566static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1567{
1568    int low;
1569
1570    if (scanning_global_lru(sc))
1571        low = inactive_file_is_low_global(zone);
1572    else
1573        low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1574    return low;
1575}
1576
1577static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1578                int file)
1579{
1580    if (file)
1581        return inactive_file_is_low(zone, sc);
1582    else
1583        return inactive_anon_is_low(zone, sc);
1584}
1585
1586static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1587    struct zone *zone, struct scan_control *sc, int priority)
1588{
1589    int file = is_file_lru(lru);
1590
1591    if (is_active_lru(lru)) {
1592        if (inactive_list_is_low(zone, sc, file))
1593            shrink_active_list(nr_to_scan, zone, sc, priority, file);
1594        return 0;
1595    }
1596
1597    return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1598}
1599
1600/*
1601 * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
1602 * until we collected @swap_cluster_max pages to scan.
1603 */
1604static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
1605                       unsigned long *nr_saved_scan)
1606{
1607    unsigned long nr;
1608
1609    *nr_saved_scan += nr_to_scan;
1610    nr = *nr_saved_scan;
1611
1612    if (nr >= SWAP_CLUSTER_MAX)
1613        *nr_saved_scan = 0;
1614    else
1615        nr = 0;
1616
1617    return nr;
1618}
1619
1620/*
1621 * Determine how aggressively the anon and file LRU lists should be
1622 * scanned. The relative value of each set of LRU lists is determined
1623 * by looking at the fraction of the pages scanned we did rotate back
1624 * onto the active list instead of evict.
1625 *
1626 * nr[0] = anon pages to scan; nr[1] = file pages to scan
1627 */
1628static void get_scan_count(struct zone *zone, struct scan_control *sc,
1629                    unsigned long *nr, int priority)
1630{
1631    unsigned long anon, file, free;
1632    unsigned long anon_prio, file_prio;
1633    unsigned long ap, fp;
1634    struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1635    u64 fraction[2], denominator;
1636    enum lru_list l;
1637    int noswap = 0;
1638
1639    /* If we have no swap space, do not bother scanning anon pages. */
1640    if (!sc->may_swap || (nr_swap_pages <= 0)) {
1641        noswap = 1;
1642        fraction[0] = 0;
1643        fraction[1] = 1;
1644        denominator = 1;
1645        goto out;
1646    }
1647
1648    anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1649        zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1650    file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1651        zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1652
1653    if (scanning_global_lru(sc)) {
1654        free = zone_page_state(zone, NR_FREE_PAGES);
1655        /* If we have very few page cache pages,
1656           force-scan anon pages. */
1657        if (unlikely(file + free <= high_wmark_pages(zone))) {
1658            fraction[0] = 1;
1659            fraction[1] = 0;
1660            denominator = 1;
1661            goto out;
1662        }
1663    }
1664
1665    /*
1666     * With swappiness at 100, anonymous and file have the same priority.
1667     * This scanning priority is essentially the inverse of IO cost.
1668     */
1669    anon_prio = sc->swappiness;
1670    file_prio = 200 - sc->swappiness;
1671
1672    /*
1673     * OK, so we have swap space and a fair amount of page cache
1674     * pages. We use the recently rotated / recently scanned
1675     * ratios to determine how valuable each cache is.
1676     *
1677     * Because workloads change over time (and to avoid overflow)
1678     * we keep these statistics as a floating average, which ends
1679     * up weighing recent references more than old ones.
1680     *
1681     * anon in [0], file in [1]
1682     */
1683    spin_lock_irq(&zone->lru_lock);
1684    if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1685        reclaim_stat->recent_scanned[0] /= 2;
1686        reclaim_stat->recent_rotated[0] /= 2;
1687    }
1688
1689    if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1690        reclaim_stat->recent_scanned[1] /= 2;
1691        reclaim_stat->recent_rotated[1] /= 2;
1692    }
1693
1694    /*
1695     * The amount of pressure on anon vs file pages is inversely
1696     * proportional to the fraction of recently scanned pages on
1697     * each list that were recently referenced and in active use.
1698     */
1699    ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1700    ap /= reclaim_stat->recent_rotated[0] + 1;
1701
1702    fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1703    fp /= reclaim_stat->recent_rotated[1] + 1;
1704    spin_unlock_irq(&zone->lru_lock);
1705
1706    fraction[0] = ap;
1707    fraction[1] = fp;
1708    denominator = ap + fp + 1;
1709out:
1710    for_each_evictable_lru(l) {
1711        int file = is_file_lru(l);
1712        unsigned long scan;
1713
1714        scan = zone_nr_lru_pages(zone, sc, l);
1715        if (priority || noswap) {
1716            scan >>= priority;
1717            scan = div64_u64(scan * fraction[file], denominator);
1718        }
1719        nr[l] = nr_scan_try_batch(scan,
1720                      &reclaim_stat->nr_saved_scan[l]);
1721    }
1722}
1723
1724static void set_lumpy_reclaim_mode(int priority, struct scan_control *sc)
1725{
1726    /*
1727     * If we need a large contiguous chunk of memory, or have
1728     * trouble getting a small set of contiguous pages, we
1729     * will reclaim both active and inactive pages.
1730     */
1731    if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1732        sc->lumpy_reclaim_mode = 1;
1733    else if (sc->order && priority < DEF_PRIORITY - 2)
1734        sc->lumpy_reclaim_mode = 1;
1735    else
1736        sc->lumpy_reclaim_mode = 0;
1737}
1738
1739/*
1740 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1741 */
1742static void shrink_zone(int priority, struct zone *zone,
1743                struct scan_control *sc)
1744{
1745    unsigned long nr[NR_LRU_LISTS];
1746    unsigned long nr_to_scan;
1747    enum lru_list l;
1748    unsigned long nr_reclaimed = sc->nr_reclaimed;
1749    unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1750
1751    get_scan_count(zone, sc, nr, priority);
1752
1753    set_lumpy_reclaim_mode(priority, sc);
1754
1755    while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1756                    nr[LRU_INACTIVE_FILE]) {
1757        for_each_evictable_lru(l) {
1758            if (nr[l]) {
1759                nr_to_scan = min_t(unsigned long,
1760                           nr[l], SWAP_CLUSTER_MAX);
1761                nr[l] -= nr_to_scan;
1762
1763                nr_reclaimed += shrink_list(l, nr_to_scan,
1764                                zone, sc, priority);
1765            }
1766        }
1767        /*
1768         * On large memory systems, scan >> priority can become
1769         * really large. This is fine for the starting priority;
1770         * we want to put equal scanning pressure on each zone.
1771         * However, if the VM has a harder time of freeing pages,
1772         * with multiple processes reclaiming pages, the total
1773         * freeing target can get unreasonably large.
1774         */
1775        if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
1776            break;
1777    }
1778
1779    sc->nr_reclaimed = nr_reclaimed;
1780
1781    /*
1782     * Even if we did not try to evict anon pages at all, we want to
1783     * rebalance the anon lru active/inactive ratio.
1784     */
1785    if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)
1786        shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
1787
1788    throttle_vm_writeout(sc->gfp_mask);
1789}
1790
1791/*
1792 * This is the direct reclaim path, for page-allocating processes. We only
1793 * try to reclaim pages from zones which will satisfy the caller's allocation
1794 * request.
1795 *
1796 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1797 * Because:
1798 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1799 * allocation or
1800 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1801 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1802 * zone defense algorithm.
1803 *
1804 * If a zone is deemed to be full of pinned pages then just give it a light
1805 * scan then give up on it.
1806 */
1807static void shrink_zones(int priority, struct zonelist *zonelist,
1808                    struct scan_control *sc)
1809{
1810    struct zoneref *z;
1811    struct zone *zone;
1812
1813    for_each_zone_zonelist_nodemask(zone, z, zonelist,
1814                    gfp_zone(sc->gfp_mask), sc->nodemask) {
1815        if (!populated_zone(zone))
1816            continue;
1817        /*
1818         * Take care memory controller reclaiming has small influence
1819         * to global LRU.
1820         */
1821        if (scanning_global_lru(sc)) {
1822            if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1823                continue;
1824            if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1825                continue; /* Let kswapd poll it */
1826        }
1827
1828        shrink_zone(priority, zone, sc);
1829    }
1830}
1831
1832static bool zone_reclaimable(struct zone *zone)
1833{
1834    return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
1835}
1836
1837/*
1838 * As hibernation is going on, kswapd is freezed so that it can't mark
1839 * the zone into all_unreclaimable. It can't handle OOM during hibernation.
1840 * So let's check zone's unreclaimable in direct reclaim as well as kswapd.
1841 */
1842static bool all_unreclaimable(struct zonelist *zonelist,
1843        struct scan_control *sc)
1844{
1845    struct zoneref *z;
1846    struct zone *zone;
1847    bool all_unreclaimable = true;
1848
1849    for_each_zone_zonelist_nodemask(zone, z, zonelist,
1850            gfp_zone(sc->gfp_mask), sc->nodemask) {
1851        if (!populated_zone(zone))
1852            continue;
1853        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1854            continue;
1855        if (zone_reclaimable(zone)) {
1856            all_unreclaimable = false;
1857            break;
1858        }
1859    }
1860
1861    return all_unreclaimable;
1862}
1863
1864/*
1865 * This is the main entry point to direct page reclaim.
1866 *
1867 * If a full scan of the inactive list fails to free enough memory then we
1868 * are "out of memory" and something needs to be killed.
1869 *
1870 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1871 * high - the zone may be full of dirty or under-writeback pages, which this
1872 * caller can't do much about. We kick the writeback threads and take explicit
1873 * naps in the hope that some of these pages can be written. But if the
1874 * allocating task holds filesystem locks which prevent writeout this might not
1875 * work, and the allocation attempt will fail.
1876 *
1877 * returns: 0, if no pages reclaimed
1878 * else, the number of pages reclaimed
1879 */
1880static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
1881                    struct scan_control *sc)
1882{
1883    int priority;
1884    unsigned long total_scanned = 0;
1885    struct reclaim_state *reclaim_state = current->reclaim_state;
1886    struct zoneref *z;
1887    struct zone *zone;
1888    unsigned long writeback_threshold;
1889
1890    get_mems_allowed();
1891    delayacct_freepages_start();
1892
1893    if (scanning_global_lru(sc))
1894        count_vm_event(ALLOCSTALL);
1895
1896    for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1897        sc->nr_scanned = 0;
1898        if (!priority)
1899            disable_swap_token();
1900        shrink_zones(priority, zonelist, sc);
1901        /*
1902         * Don't shrink slabs when reclaiming memory from
1903         * over limit cgroups
1904         */
1905        if (scanning_global_lru(sc)) {
1906            unsigned long lru_pages = 0;
1907            for_each_zone_zonelist(zone, z, zonelist,
1908                    gfp_zone(sc->gfp_mask)) {
1909                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1910                    continue;
1911
1912                lru_pages += zone_reclaimable_pages(zone);
1913            }
1914
1915            shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
1916            if (reclaim_state) {
1917                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
1918                reclaim_state->reclaimed_slab = 0;
1919            }
1920        }
1921        total_scanned += sc->nr_scanned;
1922        if (sc->nr_reclaimed >= sc->nr_to_reclaim)
1923            goto out;
1924
1925        /*
1926         * Try to write back as many pages as we just scanned. This
1927         * tends to cause slow streaming writers to write data to the
1928         * disk smoothly, at the dirtying rate, which is nice. But
1929         * that's undesirable in laptop mode, where we *want* lumpy
1930         * writeout. So in laptop mode, write out the whole world.
1931         */
1932        writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
1933        if (total_scanned > writeback_threshold) {
1934            wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
1935            sc->may_writepage = 1;
1936        }
1937
1938        /* Take a nap, wait for some writeback to complete */
1939        if (!sc->hibernation_mode && sc->nr_scanned &&
1940            priority < DEF_PRIORITY - 2)
1941            congestion_wait(BLK_RW_ASYNC, HZ/10);
1942    }
1943
1944out:
1945    /*
1946     * Now that we've scanned all the zones at this priority level, note
1947     * that level within the zone so that the next thread which performs
1948     * scanning of this zone will immediately start out at this priority
1949     * level. This affects only the decision whether or not to bring
1950     * mapped pages onto the inactive list.
1951     */
1952    if (priority < 0)
1953        priority = 0;
1954
1955    delayacct_freepages_end();
1956    put_mems_allowed();
1957
1958    if (sc->nr_reclaimed)
1959        return sc->nr_reclaimed;
1960
1961    /* top priority shrink_zones still had more to do? don't OOM, then */
1962    if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
1963        return 1;
1964
1965    return 0;
1966}
1967
1968unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
1969                gfp_t gfp_mask, nodemask_t *nodemask)
1970{
1971    unsigned long nr_reclaimed;
1972    struct scan_control sc = {
1973        .gfp_mask = gfp_mask,
1974        .may_writepage = !laptop_mode,
1975        .nr_to_reclaim = SWAP_CLUSTER_MAX,
1976        .may_unmap = 1,
1977        .may_swap = 1,
1978        .swappiness = vm_swappiness,
1979        .order = order,
1980        .mem_cgroup = NULL,
1981        .nodemask = nodemask,
1982    };
1983
1984    trace_mm_vmscan_direct_reclaim_begin(order,
1985                sc.may_writepage,
1986                gfp_mask);
1987
1988    nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
1989
1990    trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
1991
1992    return nr_reclaimed;
1993}
1994
1995#ifdef CONFIG_CGROUP_MEM_RES_CTLR
1996
1997unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
1998                        gfp_t gfp_mask, bool noswap,
1999                        unsigned int swappiness,
2000                        struct zone *zone)
2001{
2002    struct scan_control sc = {
2003        .nr_to_reclaim = SWAP_CLUSTER_MAX,
2004        .may_writepage = !laptop_mode,
2005        .may_unmap = 1,
2006        .may_swap = !noswap,
2007        .swappiness = swappiness,
2008        .order = 0,
2009        .mem_cgroup = mem,
2010    };
2011    sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2012            (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2013
2014    trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
2015                              sc.may_writepage,
2016                              sc.gfp_mask);
2017
2018    /*
2019     * NOTE: Although we can get the priority field, using it
2020     * here is not a good idea, since it limits the pages we can scan.
2021     * if we don't reclaim here, the shrink_zone from balance_pgdat
2022     * will pick up pages from other mem cgroup's as well. We hack
2023     * the priority and make it zero.
2024     */
2025    shrink_zone(0, zone, &sc);
2026
2027    trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2028
2029    return sc.nr_reclaimed;
2030}
2031
2032unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
2033                       gfp_t gfp_mask,
2034                       bool noswap,
2035                       unsigned int swappiness)
2036{
2037    struct zonelist *zonelist;
2038    unsigned long nr_reclaimed;
2039    struct scan_control sc = {
2040        .may_writepage = !laptop_mode,
2041        .may_unmap = 1,
2042        .may_swap = !noswap,
2043        .nr_to_reclaim = SWAP_CLUSTER_MAX,
2044        .swappiness = swappiness,
2045        .order = 0,
2046        .mem_cgroup = mem_cont,
2047        .nodemask = NULL, /* we don't care the placement */
2048    };
2049
2050    sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2051            (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2052    zonelist = NODE_DATA(numa_node_id())->node_zonelists;
2053
2054    trace_mm_vmscan_memcg_reclaim_begin(0,
2055                        sc.may_writepage,
2056                        sc.gfp_mask);
2057
2058    nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2059
2060    trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2061
2062    return nr_reclaimed;
2063}
2064#endif
2065
2066/* is kswapd sleeping prematurely? */
2067static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
2068{
2069    int i;
2070
2071    /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2072    if (remaining)
2073        return 1;
2074
2075    /* If after HZ/10, a zone is below the high mark, it's premature */
2076    for (i = 0; i < pgdat->nr_zones; i++) {
2077        struct zone *zone = pgdat->node_zones + i;
2078
2079        if (!populated_zone(zone))
2080            continue;
2081
2082        if (zone->all_unreclaimable)
2083            continue;
2084
2085        if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
2086                                0, 0))
2087            return 1;
2088    }
2089
2090    return 0;
2091}
2092
2093/*
2094 * For kswapd, balance_pgdat() will work across all this node's zones until
2095 * they are all at high_wmark_pages(zone).
2096 *
2097 * Returns the number of pages which were actually freed.
2098 *
2099 * There is special handling here for zones which are full of pinned pages.
2100 * This can happen if the pages are all mlocked, or if they are all used by
2101 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
2102 * What we do is to detect the case where all pages in the zone have been
2103 * scanned twice and there has been zero successful reclaim. Mark the zone as
2104 * dead and from now on, only perform a short scan. Basically we're polling
2105 * the zone for when the problem goes away.
2106 *
2107 * kswapd scans the zones in the highmem->normal->dma direction. It skips
2108 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2109 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2110 * lower zones regardless of the number of free pages in the lower zones. This
2111 * interoperates with the page allocator fallback scheme to ensure that aging
2112 * of pages is balanced across the zones.
2113 */
2114static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
2115{
2116    int all_zones_ok;
2117    int priority;
2118    int i;
2119    unsigned long total_scanned;
2120    struct reclaim_state *reclaim_state = current->reclaim_state;
2121    struct scan_control sc = {
2122        .gfp_mask = GFP_KERNEL,
2123        .may_unmap = 1,
2124        .may_swap = 1,
2125        /*
2126         * kswapd doesn't want to be bailed out while reclaim. because
2127         * we want to put equal scanning pressure on each zone.
2128         */
2129        .nr_to_reclaim = ULONG_MAX,
2130        .swappiness = vm_swappiness,
2131        .order = order,
2132        .mem_cgroup = NULL,
2133    };
2134loop_again:
2135    total_scanned = 0;
2136    sc.nr_reclaimed = 0;
2137    sc.may_writepage = !laptop_mode;
2138    count_vm_event(PAGEOUTRUN);
2139
2140    for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2141        int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2142        unsigned long lru_pages = 0;
2143        int has_under_min_watermark_zone = 0;
2144
2145        /* The swap token gets in the way of swapout... */
2146        if (!priority)
2147            disable_swap_token();
2148
2149        all_zones_ok = 1;
2150
2151        /*
2152         * Scan in the highmem->dma direction for the highest
2153         * zone which needs scanning
2154         */
2155        for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2156            struct zone *zone = pgdat->node_zones + i;
2157
2158            if (!populated_zone(zone))
2159                continue;
2160
2161            if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2162                continue;
2163
2164            /*
2165             * Do some background aging of the anon list, to give
2166             * pages a chance to be referenced before reclaiming.
2167             */
2168            if (inactive_anon_is_low(zone, &sc))
2169                shrink_active_list(SWAP_CLUSTER_MAX, zone,
2170                            &sc, priority, 0);
2171
2172            if (!zone_watermark_ok(zone, order,
2173                    high_wmark_pages(zone), 0, 0)) {
2174                end_zone = i;
2175                break;
2176            }
2177        }
2178        if (i < 0)
2179            goto out;
2180
2181        for (i = 0; i <= end_zone; i++) {
2182            struct zone *zone = pgdat->node_zones + i;
2183
2184            lru_pages += zone_reclaimable_pages(zone);
2185        }
2186
2187        /*
2188         * Now scan the zone in the dma->highmem direction, stopping
2189         * at the last zone which needs scanning.
2190         *
2191         * We do this because the page allocator works in the opposite
2192         * direction. This prevents the page allocator from allocating
2193         * pages behind kswapd's direction of progress, which would
2194         * cause too much scanning of the lower zones.
2195         */
2196        for (i = 0; i <= end_zone; i++) {
2197            struct zone *zone = pgdat->node_zones + i;
2198            int nr_slab;
2199
2200            if (!populated_zone(zone))
2201                continue;
2202
2203            if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2204                continue;
2205
2206            sc.nr_scanned = 0;
2207
2208            /*
2209             * Call soft limit reclaim before calling shrink_zone.
2210             * For now we ignore the return value
2211             */
2212            mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask);
2213
2214            /*
2215             * We put equal pressure on every zone, unless one
2216             * zone has way too many pages free already.
2217             */
2218            if (!zone_watermark_ok(zone, order,
2219                    8*high_wmark_pages(zone), end_zone, 0))
2220                shrink_zone(priority, zone, &sc);
2221            reclaim_state->reclaimed_slab = 0;
2222            nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
2223                        lru_pages);
2224            sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2225            total_scanned += sc.nr_scanned;
2226            if (zone->all_unreclaimable)
2227                continue;
2228            if (nr_slab == 0 && !zone_reclaimable(zone))
2229                zone->all_unreclaimable = 1;
2230            /*
2231             * If we've done a decent amount of scanning and
2232             * the reclaim ratio is low, start doing writepage
2233             * even in laptop mode
2234             */
2235            if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2236                total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2237                sc.may_writepage = 1;
2238
2239            if (!zone_watermark_ok(zone, order,
2240                    high_wmark_pages(zone), end_zone, 0)) {
2241                all_zones_ok = 0;
2242                /*
2243                 * We are still under min water mark. This
2244                 * means that we have a GFP_ATOMIC allocation
2245                 * failure risk. Hurry up!
2246                 */
2247                if (!zone_watermark_ok(zone, order,
2248                        min_wmark_pages(zone), end_zone, 0))
2249                    has_under_min_watermark_zone = 1;
2250            }
2251
2252        }
2253        if (all_zones_ok)
2254            break; /* kswapd: all done */
2255        /*
2256         * OK, kswapd is getting into trouble. Take a nap, then take
2257         * another pass across the zones.
2258         */
2259        if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2260            if (has_under_min_watermark_zone)
2261                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2262            else
2263                congestion_wait(BLK_RW_ASYNC, HZ/10);
2264        }
2265
2266        /*
2267         * We do this so kswapd doesn't build up large priorities for
2268         * example when it is freeing in parallel with allocators. It
2269         * matches the direct reclaim path behaviour in terms of impact
2270         * on zone->*_priority.
2271         */
2272        if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2273            break;
2274    }
2275out:
2276    if (!all_zones_ok) {
2277        cond_resched();
2278
2279        try_to_freeze();
2280
2281        /*
2282         * Fragmentation may mean that the system cannot be
2283         * rebalanced for high-order allocations in all zones.
2284         * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2285         * it means the zones have been fully scanned and are still
2286         * not balanced. For high-order allocations, there is
2287         * little point trying all over again as kswapd may
2288         * infinite loop.
2289         *
2290         * Instead, recheck all watermarks at order-0 as they
2291         * are the most important. If watermarks are ok, kswapd will go
2292         * back to sleep. High-order users can still perform direct
2293         * reclaim if they wish.
2294         */
2295        if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2296            order = sc.order = 0;
2297
2298        goto loop_again;
2299    }
2300
2301    return sc.nr_reclaimed;
2302}
2303
2304/*
2305 * The background pageout daemon, started as a kernel thread
2306 * from the init process.
2307 *
2308 * This basically trickles out pages so that we have _some_
2309 * free memory available even if there is no other activity
2310 * that frees anything up. This is needed for things like routing
2311 * etc, where we otherwise might have all activity going on in
2312 * asynchronous contexts that cannot page things out.
2313 *
2314 * If there are applications that are active memory-allocators
2315 * (most normal use), this basically shouldn't matter.
2316 */
2317static int kswapd(void *p)
2318{
2319    unsigned long order;
2320    pg_data_t *pgdat = (pg_data_t*)p;
2321    struct task_struct *tsk = current;
2322    DEFINE_WAIT(wait);
2323    struct reclaim_state reclaim_state = {
2324        .reclaimed_slab = 0,
2325    };
2326    const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2327
2328    lockdep_set_current_reclaim_state(GFP_KERNEL);
2329
2330    if (!cpumask_empty(cpumask))
2331        set_cpus_allowed_ptr(tsk, cpumask);
2332    current->reclaim_state = &reclaim_state;
2333
2334    /*
2335     * Tell the memory management that we're a "memory allocator",
2336     * and that if we need more memory we should get access to it
2337     * regardless (see "__alloc_pages()"). "kswapd" should
2338     * never get caught in the normal page freeing logic.
2339     *
2340     * (Kswapd normally doesn't need memory anyway, but sometimes
2341     * you need a small amount of memory in order to be able to
2342     * page out something else, and this flag essentially protects
2343     * us from recursively trying to free more memory as we're
2344     * trying to free the first piece of memory in the first place).
2345     */
2346    tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2347    set_freezable();
2348
2349    order = 0;
2350    for ( ; ; ) {
2351        unsigned long new_order;
2352        int ret;
2353
2354        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2355        new_order = pgdat->kswapd_max_order;
2356        pgdat->kswapd_max_order = 0;
2357        if (order < new_order) {
2358            /*
2359             * Don't sleep if someone wants a larger 'order'
2360             * allocation
2361             */
2362            order = new_order;
2363        } else {
2364            if (!freezing(current) && !kthread_should_stop()) {
2365                long remaining = 0;
2366
2367                /* Try to sleep for a short interval */
2368                if (!sleeping_prematurely(pgdat, order, remaining)) {
2369                    remaining = schedule_timeout(HZ/10);
2370                    finish_wait(&pgdat->kswapd_wait, &wait);
2371                    prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2372                }
2373
2374                /*
2375                 * After a short sleep, check if it was a
2376                 * premature sleep. If not, then go fully
2377                 * to sleep until explicitly woken up
2378                 */
2379                if (!sleeping_prematurely(pgdat, order, remaining)) {
2380                    trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2381                    schedule();
2382                } else {
2383                    if (remaining)
2384                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2385                    else
2386                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2387                }
2388            }
2389
2390            order = pgdat->kswapd_max_order;
2391        }
2392        finish_wait(&pgdat->kswapd_wait, &wait);
2393
2394        ret = try_to_freeze();
2395        if (kthread_should_stop())
2396            break;
2397
2398        /*
2399         * We can speed up thawing tasks if we don't call balance_pgdat
2400         * after returning from the refrigerator
2401         */
2402        if (!ret) {
2403            trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2404            balance_pgdat(pgdat, order);
2405        }
2406    }
2407    return 0;
2408}
2409
2410/*
2411 * A zone is low on free memory, so wake its kswapd task to service it.
2412 */
2413void wakeup_kswapd(struct zone *zone, int order)
2414{
2415    pg_data_t *pgdat;
2416
2417    if (!populated_zone(zone))
2418        return;
2419
2420    pgdat = zone->zone_pgdat;
2421    if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
2422        return;
2423    if (pgdat->kswapd_max_order < order)
2424        pgdat->kswapd_max_order = order;
2425    trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2426    if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2427        return;
2428    if (!waitqueue_active(&pgdat->kswapd_wait))
2429        return;
2430    wake_up_interruptible(&pgdat->kswapd_wait);
2431}
2432
2433/*
2434 * The reclaimable count would be mostly accurate.
2435 * The less reclaimable pages may be
2436 * - mlocked pages, which will be moved to unevictable list when encountered
2437 * - mapped pages, which may require several travels to be reclaimed
2438 * - dirty pages, which is not "instantly" reclaimable
2439 */
2440unsigned long global_reclaimable_pages(void)
2441{
2442    int nr;
2443
2444    nr = global_page_state(NR_ACTIVE_FILE) +
2445         global_page_state(NR_INACTIVE_FILE);
2446
2447    if (nr_swap_pages > 0)
2448        nr += global_page_state(NR_ACTIVE_ANON) +
2449              global_page_state(NR_INACTIVE_ANON);
2450
2451    return nr;
2452}
2453
2454unsigned long zone_reclaimable_pages(struct zone *zone)
2455{
2456    int nr;
2457
2458    nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2459         zone_page_state(zone, NR_INACTIVE_FILE);
2460
2461    if (nr_swap_pages > 0)
2462        nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2463              zone_page_state(zone, NR_INACTIVE_ANON);
2464
2465    return nr;
2466}
2467
2468#ifdef CONFIG_HIBERNATION
2469/*
2470 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2471 * freed pages.
2472 *
2473 * Rather than trying to age LRUs the aim is to preserve the overall
2474 * LRU order by reclaiming preferentially
2475 * inactive > active > active referenced > active mapped
2476 */
2477unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2478{
2479    struct reclaim_state reclaim_state;
2480    struct scan_control sc = {
2481        .gfp_mask = GFP_HIGHUSER_MOVABLE,
2482        .may_swap = 1,
2483        .may_unmap = 1,
2484        .may_writepage = 1,
2485        .nr_to_reclaim = nr_to_reclaim,
2486        .hibernation_mode = 1,
2487        .swappiness = vm_swappiness,
2488        .order = 0,
2489    };
2490    struct zonelist * zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2491    struct task_struct *p = current;
2492    unsigned long nr_reclaimed;
2493
2494    p->flags |= PF_MEMALLOC;
2495    lockdep_set_current_reclaim_state(sc.gfp_mask);
2496    reclaim_state.reclaimed_slab = 0;
2497    p->reclaim_state = &reclaim_state;
2498
2499    nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2500
2501    p->reclaim_state = NULL;
2502    lockdep_clear_current_reclaim_state();
2503    p->flags &= ~PF_MEMALLOC;
2504
2505    return nr_reclaimed;
2506}
2507#endif /* CONFIG_HIBERNATION */
2508
2509/* It's optimal to keep kswapds on the same CPUs as their memory, but
2510   not required for correctness. So if the last cpu in a node goes
2511   away, we get changed to run anywhere: as the first one comes back,
2512   restore their cpu bindings. */
2513static int __devinit cpu_callback(struct notifier_block *nfb,
2514                  unsigned long action, void *hcpu)
2515{
2516    int nid;
2517
2518    if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2519        for_each_node_state(nid, N_HIGH_MEMORY) {
2520            pg_data_t *pgdat = NODE_DATA(nid);
2521            const struct cpumask *mask;
2522
2523            mask = cpumask_of_node(pgdat->node_id);
2524
2525            if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2526                /* One of our CPUs online: restore mask */
2527                set_cpus_allowed_ptr(pgdat->kswapd, mask);
2528        }
2529    }
2530    return NOTIFY_OK;
2531}
2532
2533/*
2534 * This kswapd start function will be called by init and node-hot-add.
2535 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2536 */
2537int kswapd_run(int nid)
2538{
2539    pg_data_t *pgdat = NODE_DATA(nid);
2540    int ret = 0;
2541
2542    if (pgdat->kswapd)
2543        return 0;
2544
2545    pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2546    if (IS_ERR(pgdat->kswapd)) {
2547        /* failure at boot is fatal */
2548        BUG_ON(system_state == SYSTEM_BOOTING);
2549        printk("Failed to start kswapd on node %d\n",nid);
2550        ret = -1;
2551    }
2552    return ret;
2553}
2554
2555/*
2556 * Called by memory hotplug when all memory in a node is offlined.
2557 */
2558void kswapd_stop(int nid)
2559{
2560    struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2561
2562    if (kswapd)
2563        kthread_stop(kswapd);
2564}
2565
2566static int __init kswapd_init(void)
2567{
2568    int nid;
2569
2570    swap_setup();
2571    for_each_node_state(nid, N_HIGH_MEMORY)
2572         kswapd_run(nid);
2573    hotcpu_notifier(cpu_callback, 0);
2574    return 0;
2575}
2576
2577module_init(kswapd_init)
2578
2579#ifdef CONFIG_NUMA
2580/*
2581 * Zone reclaim mode
2582 *
2583 * If non-zero call zone_reclaim when the number of free pages falls below
2584 * the watermarks.
2585 */
2586int zone_reclaim_mode __read_mostly;
2587
2588#define RECLAIM_OFF 0
2589#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
2590#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
2591#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
2592
2593/*
2594 * Priority for ZONE_RECLAIM. This determines the fraction of pages
2595 * of a node considered for each zone_reclaim. 4 scans 1/16th of
2596 * a zone.
2597 */
2598#define ZONE_RECLAIM_PRIORITY 4
2599
2600/*
2601 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
2602 * occur.
2603 */
2604int sysctl_min_unmapped_ratio = 1;
2605
2606/*
2607 * If the number of slab pages in a zone grows beyond this percentage then
2608 * slab reclaim needs to occur.
2609 */
2610int sysctl_min_slab_ratio = 5;
2611
2612static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
2613{
2614    unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
2615    unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
2616        zone_page_state(zone, NR_ACTIVE_FILE);
2617
2618    /*
2619     * It's possible for there to be more file mapped pages than
2620     * accounted for by the pages on the file LRU lists because
2621     * tmpfs pages accounted for as ANON can also be FILE_MAPPED
2622     */
2623    return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
2624}
2625
2626/* Work out how many page cache pages we can reclaim in this reclaim_mode */
2627static long zone_pagecache_reclaimable(struct zone *zone)
2628{
2629    long nr_pagecache_reclaimable;
2630    long delta = 0;
2631
2632    /*
2633     * If RECLAIM_SWAP is set, then all file pages are considered
2634     * potentially reclaimable. Otherwise, we have to worry about
2635     * pages like swapcache and zone_unmapped_file_pages() provides
2636     * a better estimate
2637     */
2638    if (zone_reclaim_mode & RECLAIM_SWAP)
2639        nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
2640    else
2641        nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
2642
2643    /* If we can't clean pages, remove dirty pages from consideration */
2644    if (!(zone_reclaim_mode & RECLAIM_WRITE))
2645        delta += zone_page_state(zone, NR_FILE_DIRTY);
2646
2647    /* Watch for any possible underflows due to delta */
2648    if (unlikely(delta > nr_pagecache_reclaimable))
2649        delta = nr_pagecache_reclaimable;
2650
2651    return nr_pagecache_reclaimable - delta;
2652}
2653
2654/*
2655 * Try to free up some pages from this zone through reclaim.
2656 */
2657static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2658{
2659    /* Minimum pages needed in order to stay on node */
2660    const unsigned long nr_pages = 1 << order;
2661    struct task_struct *p = current;
2662    struct reclaim_state reclaim_state;
2663    int priority;
2664    struct scan_control sc = {
2665        .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
2666        .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
2667        .may_swap = 1,
2668        .nr_to_reclaim = max_t(unsigned long, nr_pages,
2669                       SWAP_CLUSTER_MAX),
2670        .gfp_mask = gfp_mask,
2671        .swappiness = vm_swappiness,
2672        .order = order,
2673    };
2674    unsigned long nr_slab_pages0, nr_slab_pages1;
2675
2676    cond_resched();
2677    /*
2678     * We need to be able to allocate from the reserves for RECLAIM_SWAP
2679     * and we also need to be able to write out pages for RECLAIM_WRITE
2680     * and RECLAIM_SWAP.
2681     */
2682    p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
2683    lockdep_set_current_reclaim_state(gfp_mask);
2684    reclaim_state.reclaimed_slab = 0;
2685    p->reclaim_state = &reclaim_state;
2686
2687    if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
2688        /*
2689         * Free memory by calling shrink zone with increasing
2690         * priorities until we have enough memory freed.
2691         */
2692        priority = ZONE_RECLAIM_PRIORITY;
2693        do {
2694            shrink_zone(priority, zone, &sc);
2695            priority--;
2696        } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
2697    }
2698
2699    nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2700    if (nr_slab_pages0 > zone->min_slab_pages) {
2701        /*
2702         * shrink_slab() does not currently allow us to determine how
2703         * many pages were freed in this zone. So we take the current
2704         * number of slab pages and shake the slab until it is reduced
2705         * by the same nr_pages that we used for reclaiming unmapped
2706         * pages.
2707         *
2708         * Note that shrink_slab will free memory on all zones and may
2709         * take a long time.
2710         */
2711        for (;;) {
2712            unsigned long lru_pages = zone_reclaimable_pages(zone);
2713
2714            /* No reclaimable slab or very low memory pressure */
2715            if (!shrink_slab(sc.nr_scanned, gfp_mask, lru_pages))
2716                break;
2717
2718            /* Freed enough memory */
2719            nr_slab_pages1 = zone_page_state(zone,
2720                            NR_SLAB_RECLAIMABLE);
2721            if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
2722                break;
2723        }
2724
2725        /*
2726         * Update nr_reclaimed by the number of slab pages we
2727         * reclaimed from this zone.
2728         */
2729        nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2730        if (nr_slab_pages1 < nr_slab_pages0)
2731            sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
2732    }
2733
2734    p->reclaim_state = NULL;
2735    current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
2736    lockdep_clear_current_reclaim_state();
2737    return sc.nr_reclaimed >= nr_pages;
2738}
2739
2740int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2741{
2742    int node_id;
2743    int ret;
2744
2745    /*
2746     * Zone reclaim reclaims unmapped file backed pages and
2747     * slab pages if we are over the defined limits.
2748     *
2749     * A small portion of unmapped file backed pages is needed for
2750     * file I/O otherwise pages read by file I/O will be immediately
2751     * thrown out if the zone is overallocated. So we do not reclaim
2752     * if less than a specified percentage of the zone is used by
2753     * unmapped file backed pages.
2754     */
2755    if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
2756        zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
2757        return ZONE_RECLAIM_FULL;
2758
2759    if (zone->all_unreclaimable)
2760        return ZONE_RECLAIM_FULL;
2761
2762    /*
2763     * Do not scan if the allocation should not be delayed.
2764     */
2765    if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
2766        return ZONE_RECLAIM_NOSCAN;
2767
2768    /*
2769     * Only run zone reclaim on the local zone or on zones that do not
2770     * have associated processors. This will favor the local processor
2771     * over remote processors and spread off node memory allocations
2772     * as wide as possible.
2773     */
2774    node_id = zone_to_nid(zone);
2775    if (node_state(node_id, N_CPU) && node_id != numa_node_id())
2776        return ZONE_RECLAIM_NOSCAN;
2777
2778    if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
2779        return ZONE_RECLAIM_NOSCAN;
2780
2781    ret = __zone_reclaim(zone, gfp_mask, order);
2782    zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
2783
2784    if (!ret)
2785        count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
2786
2787    return ret;
2788}
2789#endif
2790
2791/*
2792 * page_evictable - test whether a page is evictable
2793 * @page: the page to test
2794 * @vma: the VMA in which the page is or will be mapped, may be NULL
2795 *
2796 * Test whether page is evictable--i.e., should be placed on active/inactive
2797 * lists vs unevictable list. The vma argument is !NULL when called from the
2798 * fault path to determine how to instantate a new page.
2799 *
2800 * Reasons page might not be evictable:
2801 * (1) page's mapping marked unevictable
2802 * (2) page is part of an mlocked VMA
2803 *
2804 */
2805int page_evictable(struct page *page, struct vm_area_struct *vma)
2806{
2807
2808    if (mapping_unevictable(page_mapping(page)))
2809        return 0;
2810
2811    if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
2812        return 0;
2813
2814    return 1;
2815}
2816
2817/**
2818 * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
2819 * @page: page to check evictability and move to appropriate lru list
2820 * @zone: zone page is in
2821 *
2822 * Checks a page for evictability and moves the page to the appropriate
2823 * zone lru list.
2824 *
2825 * Restrictions: zone->lru_lock must be held, page must be on LRU and must
2826 * have PageUnevictable set.
2827 */
2828static void check_move_unevictable_page(struct page *page, struct zone *zone)
2829{
2830    VM_BUG_ON(PageActive(page));
2831
2832retry:
2833    ClearPageUnevictable(page);
2834    if (page_evictable(page, NULL)) {
2835        enum lru_list l = page_lru_base_type(page);
2836
2837        __dec_zone_state(zone, NR_UNEVICTABLE);
2838        list_move(&page->lru, &zone->lru[l].list);
2839        mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
2840        __inc_zone_state(zone, NR_INACTIVE_ANON + l);
2841        __count_vm_event(UNEVICTABLE_PGRESCUED);
2842    } else {
2843        /*
2844         * rotate unevictable list
2845         */
2846        SetPageUnevictable(page);
2847        list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
2848        mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
2849        if (page_evictable(page, NULL))
2850            goto retry;
2851    }
2852}
2853
2854/**
2855 * scan_mapping_unevictable_pages - scan an address space for evictable pages
2856 * @mapping: struct address_space to scan for evictable pages
2857 *
2858 * Scan all pages in mapping. Check unevictable pages for
2859 * evictability and move them to the appropriate zone lru list.
2860 */
2861void scan_mapping_unevictable_pages(struct address_space *mapping)
2862{
2863    pgoff_t next = 0;
2864    pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
2865             PAGE_CACHE_SHIFT;
2866    struct zone *zone;
2867    struct pagevec pvec;
2868
2869    if (mapping->nrpages == 0)
2870        return;
2871
2872    pagevec_init(&pvec, 0);
2873    while (next < end &&
2874        pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
2875        int i;
2876        int pg_scanned = 0;
2877
2878        zone = NULL;
2879
2880        for (i = 0; i < pagevec_count(&pvec); i++) {
2881            struct page *page = pvec.pages[i];
2882            pgoff_t page_index = page->index;
2883            struct zone *pagezone = page_zone(page);
2884
2885            pg_scanned++;
2886            if (page_index > next)
2887                next = page_index;
2888            next++;
2889
2890            if (pagezone != zone) {
2891                if (zone)
2892                    spin_unlock_irq(&zone->lru_lock);
2893                zone = pagezone;
2894                spin_lock_irq(&zone->lru_lock);
2895            }
2896
2897            if (PageLRU(page) && PageUnevictable(page))
2898                check_move_unevictable_page(page, zone);
2899        }
2900        if (zone)
2901            spin_unlock_irq(&zone->lru_lock);
2902        pagevec_release(&pvec);
2903
2904        count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
2905    }
2906
2907}
2908
2909/**
2910 * scan_zone_unevictable_pages - check unevictable list for evictable pages
2911 * @zone - zone of which to scan the unevictable list
2912 *
2913 * Scan @zone's unevictable LRU lists to check for pages that have become
2914 * evictable. Move those that have to @zone's inactive list where they
2915 * become candidates for reclaim, unless shrink_inactive_zone() decides
2916 * to reactivate them. Pages that are still unevictable are rotated
2917 * back onto @zone's unevictable list.
2918 */
2919#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
2920static void scan_zone_unevictable_pages(struct zone *zone)
2921{
2922    struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
2923    unsigned long scan;
2924    unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
2925
2926    while (nr_to_scan > 0) {
2927        unsigned long batch_size = min(nr_to_scan,
2928                        SCAN_UNEVICTABLE_BATCH_SIZE);
2929
2930        spin_lock_irq(&zone->lru_lock);
2931        for (scan = 0; scan < batch_size; scan++) {
2932            struct page *page = lru_to_page(l_unevictable);
2933
2934            if (!trylock_page(page))
2935                continue;
2936
2937            prefetchw_prev_lru_page(page, l_unevictable, flags);
2938
2939            if (likely(PageLRU(page) && PageUnevictable(page)))
2940                check_move_unevictable_page(page, zone);
2941
2942            unlock_page(page);
2943        }
2944        spin_unlock_irq(&zone->lru_lock);
2945
2946        nr_to_scan -= batch_size;
2947    }
2948}
2949
2950
2951/**
2952 * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
2953 *
2954 * A really big hammer: scan all zones' unevictable LRU lists to check for
2955 * pages that have become evictable. Move those back to the zones'
2956 * inactive list where they become candidates for reclaim.
2957 * This occurs when, e.g., we have unswappable pages on the unevictable lists,
2958 * and we add swap to the system. As such, it runs in the context of a task
2959 * that has possibly/probably made some previously unevictable pages
2960 * evictable.
2961 */
2962static void scan_all_zones_unevictable_pages(void)
2963{
2964    struct zone *zone;
2965
2966    for_each_zone(zone) {
2967        scan_zone_unevictable_pages(zone);
2968    }
2969}
2970
2971/*
2972 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
2973 * all nodes' unevictable lists for evictable pages
2974 */
2975unsigned long scan_unevictable_pages;
2976
2977int scan_unevictable_handler(struct ctl_table *table, int write,
2978               void __user *buffer,
2979               size_t *length, loff_t *ppos)
2980{
2981    proc_doulongvec_minmax(table, write, buffer, length, ppos);
2982
2983    if (write && *(unsigned long *)table->data)
2984        scan_all_zones_unevictable_pages();
2985
2986    scan_unevictable_pages = 0;
2987    return 0;
2988}
2989
2990/*
2991 * per node 'scan_unevictable_pages' attribute. On demand re-scan of
2992 * a specified node's per zone unevictable lists for evictable pages.
2993 */
2994
2995static ssize_t read_scan_unevictable_node(struct sys_device *dev,
2996                      struct sysdev_attribute *attr,
2997                      char *buf)
2998{
2999    return sprintf(buf, "0\n"); /* always zero; should fit... */
3000}
3001
3002static ssize_t write_scan_unevictable_node(struct sys_device *dev,
3003                       struct sysdev_attribute *attr,
3004                    const char *buf, size_t count)
3005{
3006    struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
3007    struct zone *zone;
3008    unsigned long res;
3009    unsigned long req = strict_strtoul(buf, 10, &res);
3010
3011    if (!req)
3012        return 1; /* zero is no-op */
3013
3014    for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
3015        if (!populated_zone(zone))
3016            continue;
3017        scan_zone_unevictable_pages(zone);
3018    }
3019    return 1;
3020}
3021
3022
3023static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3024            read_scan_unevictable_node,
3025            write_scan_unevictable_node);
3026
3027int scan_unevictable_register_node(struct node *node)
3028{
3029    return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
3030}
3031
3032void scan_unevictable_unregister_node(struct node *node)
3033{
3034    sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
3035}
3036
3037

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