Root/mm/swap.c

1/*
2 * linux/mm/swap.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 */
6
7/*
8 * This file contains the default values for the operation of the
9 * Linux VM subsystem. Fine-tuning documentation can be found in
10 * Documentation/sysctl/vm.txt.
11 * Started 18.12.91
12 * Swap aging added 23.2.95, Stephen Tweedie.
13 * Buffermem limits added 12.3.98, Rik van Riel.
14 */
15
16#include <linux/mm.h>
17#include <linux/sched.h>
18#include <linux/kernel_stat.h>
19#include <linux/swap.h>
20#include <linux/mman.h>
21#include <linux/pagemap.h>
22#include <linux/pagevec.h>
23#include <linux/init.h>
24#include <linux/module.h>
25#include <linux/mm_inline.h>
26#include <linux/buffer_head.h> /* for try_to_release_page() */
27#include <linux/percpu_counter.h>
28#include <linux/percpu.h>
29#include <linux/cpu.h>
30#include <linux/notifier.h>
31#include <linux/backing-dev.h>
32#include <linux/memcontrol.h>
33#include <linux/gfp.h>
34
35#include "internal.h"
36
37/* How many pages do we try to swap or page in/out together? */
38int page_cluster;
39
40static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
41static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
42static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
43
44/*
45 * This path almost never happens for VM activity - pages are normally
46 * freed via pagevecs. But it gets used by networking.
47 */
48static void __page_cache_release(struct page *page)
49{
50    if (PageLRU(page)) {
51        unsigned long flags;
52        struct zone *zone = page_zone(page);
53
54        spin_lock_irqsave(&zone->lru_lock, flags);
55        VM_BUG_ON(!PageLRU(page));
56        __ClearPageLRU(page);
57        del_page_from_lru(zone, page);
58        spin_unlock_irqrestore(&zone->lru_lock, flags);
59    }
60}
61
62static void __put_single_page(struct page *page)
63{
64    __page_cache_release(page);
65    free_hot_cold_page(page, 0);
66}
67
68static void __put_compound_page(struct page *page)
69{
70    compound_page_dtor *dtor;
71
72    __page_cache_release(page);
73    dtor = get_compound_page_dtor(page);
74    (*dtor)(page);
75}
76
77static void put_compound_page(struct page *page)
78{
79    if (unlikely(PageTail(page))) {
80        /* __split_huge_page_refcount can run under us */
81        struct page *page_head = page->first_page;
82        smp_rmb();
83        /*
84         * If PageTail is still set after smp_rmb() we can be sure
85         * that the page->first_page we read wasn't a dangling pointer.
86         * See __split_huge_page_refcount() smp_wmb().
87         */
88        if (likely(PageTail(page) && get_page_unless_zero(page_head))) {
89            unsigned long flags;
90            /*
91             * Verify that our page_head wasn't converted
92             * to a a regular page before we got a
93             * reference on it.
94             */
95            if (unlikely(!PageHead(page_head))) {
96                /* PageHead is cleared after PageTail */
97                smp_rmb();
98                VM_BUG_ON(PageTail(page));
99                goto out_put_head;
100            }
101            /*
102             * Only run compound_lock on a valid PageHead,
103             * after having it pinned with
104             * get_page_unless_zero() above.
105             */
106            smp_mb();
107            /* page_head wasn't a dangling pointer */
108            flags = compound_lock_irqsave(page_head);
109            if (unlikely(!PageTail(page))) {
110                /* __split_huge_page_refcount run before us */
111                compound_unlock_irqrestore(page_head, flags);
112                VM_BUG_ON(PageHead(page_head));
113            out_put_head:
114                if (put_page_testzero(page_head))
115                    __put_single_page(page_head);
116            out_put_single:
117                if (put_page_testzero(page))
118                    __put_single_page(page);
119                return;
120            }
121            VM_BUG_ON(page_head != page->first_page);
122            /*
123             * We can release the refcount taken by
124             * get_page_unless_zero now that
125             * split_huge_page_refcount is blocked on the
126             * compound_lock.
127             */
128            if (put_page_testzero(page_head))
129                VM_BUG_ON(1);
130            /* __split_huge_page_refcount will wait now */
131            VM_BUG_ON(atomic_read(&page->_count) <= 0);
132            atomic_dec(&page->_count);
133            VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
134            compound_unlock_irqrestore(page_head, flags);
135            if (put_page_testzero(page_head)) {
136                if (PageHead(page_head))
137                    __put_compound_page(page_head);
138                else
139                    __put_single_page(page_head);
140            }
141        } else {
142            /* page_head is a dangling pointer */
143            VM_BUG_ON(PageTail(page));
144            goto out_put_single;
145        }
146    } else if (put_page_testzero(page)) {
147        if (PageHead(page))
148            __put_compound_page(page);
149        else
150            __put_single_page(page);
151    }
152}
153
154void put_page(struct page *page)
155{
156    if (unlikely(PageCompound(page)))
157        put_compound_page(page);
158    else if (put_page_testzero(page))
159        __put_single_page(page);
160}
161EXPORT_SYMBOL(put_page);
162
163/**
164 * put_pages_list() - release a list of pages
165 * @pages: list of pages threaded on page->lru
166 *
167 * Release a list of pages which are strung together on page.lru. Currently
168 * used by read_cache_pages() and related error recovery code.
169 */
170void put_pages_list(struct list_head *pages)
171{
172    while (!list_empty(pages)) {
173        struct page *victim;
174
175        victim = list_entry(pages->prev, struct page, lru);
176        list_del(&victim->lru);
177        page_cache_release(victim);
178    }
179}
180EXPORT_SYMBOL(put_pages_list);
181
182static void pagevec_lru_move_fn(struct pagevec *pvec,
183                void (*move_fn)(struct page *page, void *arg),
184                void *arg)
185{
186    int i;
187    struct zone *zone = NULL;
188    unsigned long flags = 0;
189
190    for (i = 0; i < pagevec_count(pvec); i++) {
191        struct page *page = pvec->pages[i];
192        struct zone *pagezone = page_zone(page);
193
194        if (pagezone != zone) {
195            if (zone)
196                spin_unlock_irqrestore(&zone->lru_lock, flags);
197            zone = pagezone;
198            spin_lock_irqsave(&zone->lru_lock, flags);
199        }
200
201        (*move_fn)(page, arg);
202    }
203    if (zone)
204        spin_unlock_irqrestore(&zone->lru_lock, flags);
205    release_pages(pvec->pages, pvec->nr, pvec->cold);
206    pagevec_reinit(pvec);
207}
208
209static void pagevec_move_tail_fn(struct page *page, void *arg)
210{
211    int *pgmoved = arg;
212    struct zone *zone = page_zone(page);
213
214    if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
215        enum lru_list lru = page_lru_base_type(page);
216        list_move_tail(&page->lru, &zone->lru[lru].list);
217        mem_cgroup_rotate_reclaimable_page(page);
218        (*pgmoved)++;
219    }
220}
221
222/*
223 * pagevec_move_tail() must be called with IRQ disabled.
224 * Otherwise this may cause nasty races.
225 */
226static void pagevec_move_tail(struct pagevec *pvec)
227{
228    int pgmoved = 0;
229
230    pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
231    __count_vm_events(PGROTATED, pgmoved);
232}
233
234/*
235 * Writeback is about to end against a page which has been marked for immediate
236 * reclaim. If it still appears to be reclaimable, move it to the tail of the
237 * inactive list.
238 */
239void rotate_reclaimable_page(struct page *page)
240{
241    if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
242        !PageUnevictable(page) && PageLRU(page)) {
243        struct pagevec *pvec;
244        unsigned long flags;
245
246        page_cache_get(page);
247        local_irq_save(flags);
248        pvec = &__get_cpu_var(lru_rotate_pvecs);
249        if (!pagevec_add(pvec, page))
250            pagevec_move_tail(pvec);
251        local_irq_restore(flags);
252    }
253}
254
255static void update_page_reclaim_stat(struct zone *zone, struct page *page,
256                     int file, int rotated)
257{
258    struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat;
259    struct zone_reclaim_stat *memcg_reclaim_stat;
260
261    memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page);
262
263    reclaim_stat->recent_scanned[file]++;
264    if (rotated)
265        reclaim_stat->recent_rotated[file]++;
266
267    if (!memcg_reclaim_stat)
268        return;
269
270    memcg_reclaim_stat->recent_scanned[file]++;
271    if (rotated)
272        memcg_reclaim_stat->recent_rotated[file]++;
273}
274
275static void __activate_page(struct page *page, void *arg)
276{
277    struct zone *zone = page_zone(page);
278
279    if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
280        int file = page_is_file_cache(page);
281        int lru = page_lru_base_type(page);
282        del_page_from_lru_list(zone, page, lru);
283
284        SetPageActive(page);
285        lru += LRU_ACTIVE;
286        add_page_to_lru_list(zone, page, lru);
287        __count_vm_event(PGACTIVATE);
288
289        update_page_reclaim_stat(zone, page, file, 1);
290    }
291}
292
293#ifdef CONFIG_SMP
294static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
295
296static void activate_page_drain(int cpu)
297{
298    struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
299
300    if (pagevec_count(pvec))
301        pagevec_lru_move_fn(pvec, __activate_page, NULL);
302}
303
304void activate_page(struct page *page)
305{
306    if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
307        struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
308
309        page_cache_get(page);
310        if (!pagevec_add(pvec, page))
311            pagevec_lru_move_fn(pvec, __activate_page, NULL);
312        put_cpu_var(activate_page_pvecs);
313    }
314}
315
316#else
317static inline void activate_page_drain(int cpu)
318{
319}
320
321void activate_page(struct page *page)
322{
323    struct zone *zone = page_zone(page);
324
325    spin_lock_irq(&zone->lru_lock);
326    __activate_page(page, NULL);
327    spin_unlock_irq(&zone->lru_lock);
328}
329#endif
330
331/*
332 * Mark a page as having seen activity.
333 *
334 * inactive,unreferenced -> inactive,referenced
335 * inactive,referenced -> active,unreferenced
336 * active,unreferenced -> active,referenced
337 */
338void mark_page_accessed(struct page *page)
339{
340    if (!PageActive(page) && !PageUnevictable(page) &&
341            PageReferenced(page) && PageLRU(page)) {
342        activate_page(page);
343        ClearPageReferenced(page);
344    } else if (!PageReferenced(page)) {
345        SetPageReferenced(page);
346    }
347}
348
349EXPORT_SYMBOL(mark_page_accessed);
350
351void __lru_cache_add(struct page *page, enum lru_list lru)
352{
353    struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
354
355    page_cache_get(page);
356    if (!pagevec_add(pvec, page))
357        ____pagevec_lru_add(pvec, lru);
358    put_cpu_var(lru_add_pvecs);
359}
360EXPORT_SYMBOL(__lru_cache_add);
361
362/**
363 * lru_cache_add_lru - add a page to a page list
364 * @page: the page to be added to the LRU.
365 * @lru: the LRU list to which the page is added.
366 */
367void lru_cache_add_lru(struct page *page, enum lru_list lru)
368{
369    if (PageActive(page)) {
370        VM_BUG_ON(PageUnevictable(page));
371        ClearPageActive(page);
372    } else if (PageUnevictable(page)) {
373        VM_BUG_ON(PageActive(page));
374        ClearPageUnevictable(page);
375    }
376
377    VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
378    __lru_cache_add(page, lru);
379}
380
381/**
382 * add_page_to_unevictable_list - add a page to the unevictable list
383 * @page: the page to be added to the unevictable list
384 *
385 * Add page directly to its zone's unevictable list. To avoid races with
386 * tasks that might be making the page evictable, through eg. munlock,
387 * munmap or exit, while it's not on the lru, we want to add the page
388 * while it's locked or otherwise "invisible" to other tasks. This is
389 * difficult to do when using the pagevec cache, so bypass that.
390 */
391void add_page_to_unevictable_list(struct page *page)
392{
393    struct zone *zone = page_zone(page);
394
395    spin_lock_irq(&zone->lru_lock);
396    SetPageUnevictable(page);
397    SetPageLRU(page);
398    add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
399    spin_unlock_irq(&zone->lru_lock);
400}
401
402/*
403 * If the page can not be invalidated, it is moved to the
404 * inactive list to speed up its reclaim. It is moved to the
405 * head of the list, rather than the tail, to give the flusher
406 * threads some time to write it out, as this is much more
407 * effective than the single-page writeout from reclaim.
408 *
409 * If the page isn't page_mapped and dirty/writeback, the page
410 * could reclaim asap using PG_reclaim.
411 *
412 * 1. active, mapped page -> none
413 * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
414 * 3. inactive, mapped page -> none
415 * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
416 * 5. inactive, clean -> inactive, tail
417 * 6. Others -> none
418 *
419 * In 4, why it moves inactive's head, the VM expects the page would
420 * be write it out by flusher threads as this is much more effective
421 * than the single-page writeout from reclaim.
422 */
423static void lru_deactivate_fn(struct page *page, void *arg)
424{
425    int lru, file;
426    bool active;
427    struct zone *zone = page_zone(page);
428
429    if (!PageLRU(page))
430        return;
431
432    if (PageUnevictable(page))
433        return;
434
435    /* Some processes are using the page */
436    if (page_mapped(page))
437        return;
438
439    active = PageActive(page);
440
441    file = page_is_file_cache(page);
442    lru = page_lru_base_type(page);
443    del_page_from_lru_list(zone, page, lru + active);
444    ClearPageActive(page);
445    ClearPageReferenced(page);
446    add_page_to_lru_list(zone, page, lru);
447
448    if (PageWriteback(page) || PageDirty(page)) {
449        /*
450         * PG_reclaim could be raced with end_page_writeback
451         * It can make readahead confusing. But race window
452         * is _really_ small and it's non-critical problem.
453         */
454        SetPageReclaim(page);
455    } else {
456        /*
457         * The page's writeback ends up during pagevec
458         * We moves tha page into tail of inactive.
459         */
460        list_move_tail(&page->lru, &zone->lru[lru].list);
461        mem_cgroup_rotate_reclaimable_page(page);
462        __count_vm_event(PGROTATED);
463    }
464
465    if (active)
466        __count_vm_event(PGDEACTIVATE);
467    update_page_reclaim_stat(zone, page, file, 0);
468}
469
470/*
471 * Drain pages out of the cpu's pagevecs.
472 * Either "cpu" is the current CPU, and preemption has already been
473 * disabled; or "cpu" is being hot-unplugged, and is already dead.
474 */
475static void drain_cpu_pagevecs(int cpu)
476{
477    struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
478    struct pagevec *pvec;
479    int lru;
480
481    for_each_lru(lru) {
482        pvec = &pvecs[lru - LRU_BASE];
483        if (pagevec_count(pvec))
484            ____pagevec_lru_add(pvec, lru);
485    }
486
487    pvec = &per_cpu(lru_rotate_pvecs, cpu);
488    if (pagevec_count(pvec)) {
489        unsigned long flags;
490
491        /* No harm done if a racing interrupt already did this */
492        local_irq_save(flags);
493        pagevec_move_tail(pvec);
494        local_irq_restore(flags);
495    }
496
497    pvec = &per_cpu(lru_deactivate_pvecs, cpu);
498    if (pagevec_count(pvec))
499        pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
500
501    activate_page_drain(cpu);
502}
503
504/**
505 * deactivate_page - forcefully deactivate a page
506 * @page: page to deactivate
507 *
508 * This function hints the VM that @page is a good reclaim candidate,
509 * for example if its invalidation fails due to the page being dirty
510 * or under writeback.
511 */
512void deactivate_page(struct page *page)
513{
514    /*
515     * In a workload with many unevictable page such as mprotect, unevictable
516     * page deactivation for accelerating reclaim is pointless.
517     */
518    if (PageUnevictable(page))
519        return;
520
521    if (likely(get_page_unless_zero(page))) {
522        struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
523
524        if (!pagevec_add(pvec, page))
525            pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
526        put_cpu_var(lru_deactivate_pvecs);
527    }
528}
529
530void lru_add_drain(void)
531{
532    drain_cpu_pagevecs(get_cpu());
533    put_cpu();
534}
535
536static void lru_add_drain_per_cpu(struct work_struct *dummy)
537{
538    lru_add_drain();
539}
540
541/*
542 * Returns 0 for success
543 */
544int lru_add_drain_all(void)
545{
546    return schedule_on_each_cpu(lru_add_drain_per_cpu);
547}
548
549/*
550 * Batched page_cache_release(). Decrement the reference count on all the
551 * passed pages. If it fell to zero then remove the page from the LRU and
552 * free it.
553 *
554 * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
555 * for the remainder of the operation.
556 *
557 * The locking in this function is against shrink_inactive_list(): we recheck
558 * the page count inside the lock to see whether shrink_inactive_list()
559 * grabbed the page via the LRU. If it did, give up: shrink_inactive_list()
560 * will free it.
561 */
562void release_pages(struct page **pages, int nr, int cold)
563{
564    int i;
565    struct pagevec pages_to_free;
566    struct zone *zone = NULL;
567    unsigned long uninitialized_var(flags);
568
569    pagevec_init(&pages_to_free, cold);
570    for (i = 0; i < nr; i++) {
571        struct page *page = pages[i];
572
573        if (unlikely(PageCompound(page))) {
574            if (zone) {
575                spin_unlock_irqrestore(&zone->lru_lock, flags);
576                zone = NULL;
577            }
578            put_compound_page(page);
579            continue;
580        }
581
582        if (!put_page_testzero(page))
583            continue;
584
585        if (PageLRU(page)) {
586            struct zone *pagezone = page_zone(page);
587
588            if (pagezone != zone) {
589                if (zone)
590                    spin_unlock_irqrestore(&zone->lru_lock,
591                                    flags);
592                zone = pagezone;
593                spin_lock_irqsave(&zone->lru_lock, flags);
594            }
595            VM_BUG_ON(!PageLRU(page));
596            __ClearPageLRU(page);
597            del_page_from_lru(zone, page);
598        }
599
600        if (!pagevec_add(&pages_to_free, page)) {
601            if (zone) {
602                spin_unlock_irqrestore(&zone->lru_lock, flags);
603                zone = NULL;
604            }
605            __pagevec_free(&pages_to_free);
606            pagevec_reinit(&pages_to_free);
607          }
608    }
609    if (zone)
610        spin_unlock_irqrestore(&zone->lru_lock, flags);
611
612    pagevec_free(&pages_to_free);
613}
614EXPORT_SYMBOL(release_pages);
615
616/*
617 * The pages which we're about to release may be in the deferred lru-addition
618 * queues. That would prevent them from really being freed right now. That's
619 * OK from a correctness point of view but is inefficient - those pages may be
620 * cache-warm and we want to give them back to the page allocator ASAP.
621 *
622 * So __pagevec_release() will drain those queues here. __pagevec_lru_add()
623 * and __pagevec_lru_add_active() call release_pages() directly to avoid
624 * mutual recursion.
625 */
626void __pagevec_release(struct pagevec *pvec)
627{
628    lru_add_drain();
629    release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
630    pagevec_reinit(pvec);
631}
632
633EXPORT_SYMBOL(__pagevec_release);
634
635/* used by __split_huge_page_refcount() */
636void lru_add_page_tail(struct zone* zone,
637               struct page *page, struct page *page_tail)
638{
639    int active;
640    enum lru_list lru;
641    const int file = 0;
642    struct list_head *head;
643
644    VM_BUG_ON(!PageHead(page));
645    VM_BUG_ON(PageCompound(page_tail));
646    VM_BUG_ON(PageLRU(page_tail));
647    VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
648
649    SetPageLRU(page_tail);
650
651    if (page_evictable(page_tail, NULL)) {
652        if (PageActive(page)) {
653            SetPageActive(page_tail);
654            active = 1;
655            lru = LRU_ACTIVE_ANON;
656        } else {
657            active = 0;
658            lru = LRU_INACTIVE_ANON;
659        }
660        update_page_reclaim_stat(zone, page_tail, file, active);
661        if (likely(PageLRU(page)))
662            head = page->lru.prev;
663        else
664            head = &zone->lru[lru].list;
665        __add_page_to_lru_list(zone, page_tail, lru, head);
666    } else {
667        SetPageUnevictable(page_tail);
668        add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
669    }
670}
671
672static void ____pagevec_lru_add_fn(struct page *page, void *arg)
673{
674    enum lru_list lru = (enum lru_list)arg;
675    struct zone *zone = page_zone(page);
676    int file = is_file_lru(lru);
677    int active = is_active_lru(lru);
678
679    VM_BUG_ON(PageActive(page));
680    VM_BUG_ON(PageUnevictable(page));
681    VM_BUG_ON(PageLRU(page));
682
683    SetPageLRU(page);
684    if (active)
685        SetPageActive(page);
686    update_page_reclaim_stat(zone, page, file, active);
687    add_page_to_lru_list(zone, page, lru);
688}
689
690/*
691 * Add the passed pages to the LRU, then drop the caller's refcount
692 * on them. Reinitialises the caller's pagevec.
693 */
694void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
695{
696    VM_BUG_ON(is_unevictable_lru(lru));
697
698    pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
699}
700
701EXPORT_SYMBOL(____pagevec_lru_add);
702
703/*
704 * Try to drop buffers from the pages in a pagevec
705 */
706void pagevec_strip(struct pagevec *pvec)
707{
708    int i;
709
710    for (i = 0; i < pagevec_count(pvec); i++) {
711        struct page *page = pvec->pages[i];
712
713        if (page_has_private(page) && trylock_page(page)) {
714            if (page_has_private(page))
715                try_to_release_page(page, 0);
716            unlock_page(page);
717        }
718    }
719}
720
721/**
722 * pagevec_lookup - gang pagecache lookup
723 * @pvec: Where the resulting pages are placed
724 * @mapping: The address_space to search
725 * @start: The starting page index
726 * @nr_pages: The maximum number of pages
727 *
728 * pagevec_lookup() will search for and return a group of up to @nr_pages pages
729 * in the mapping. The pages are placed in @pvec. pagevec_lookup() takes a
730 * reference against the pages in @pvec.
731 *
732 * The search returns a group of mapping-contiguous pages with ascending
733 * indexes. There may be holes in the indices due to not-present pages.
734 *
735 * pagevec_lookup() returns the number of pages which were found.
736 */
737unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
738        pgoff_t start, unsigned nr_pages)
739{
740    pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
741    return pagevec_count(pvec);
742}
743
744EXPORT_SYMBOL(pagevec_lookup);
745
746unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
747        pgoff_t *index, int tag, unsigned nr_pages)
748{
749    pvec->nr = find_get_pages_tag(mapping, index, tag,
750                    nr_pages, pvec->pages);
751    return pagevec_count(pvec);
752}
753
754EXPORT_SYMBOL(pagevec_lookup_tag);
755
756/*
757 * Perform any setup for the swap system
758 */
759void __init swap_setup(void)
760{
761    unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
762
763#ifdef CONFIG_SWAP
764    bdi_init(swapper_space.backing_dev_info);
765#endif
766
767    /* Use a smaller cluster for small-memory machines */
768    if (megs < 16)
769        page_cluster = 2;
770    else
771        page_cluster = 3;
772    /*
773     * Right now other parts of the system means that we
774     * _really_ don't want to cluster much more
775     */
776}
777

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