perf evsel: Make some methods private
[linux-2.6.git] / mm / swap.c
blob4e7e2ec67078f783750eb43e8dc45db5600b1b94
1 /*
2 * linux/mm/swap.c
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 */
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.
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/export.h>
25 #include <linux/mm_inline.h>
26 #include <linux/percpu_counter.h>
27 #include <linux/percpu.h>
28 #include <linux/cpu.h>
29 #include <linux/notifier.h>
30 #include <linux/backing-dev.h>
31 #include <linux/memcontrol.h>
32 #include <linux/gfp.h>
34 #include "internal.h"
36 /* How many pages do we try to swap or page in/out together? */
37 int page_cluster;
39 static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
40 static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
41 static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
44 * This path almost never happens for VM activity - pages are normally
45 * freed via pagevecs. But it gets used by networking.
47 static void __page_cache_release(struct page *page)
49 if (PageLRU(page)) {
50 struct zone *zone = page_zone(page);
51 struct lruvec *lruvec;
52 unsigned long flags;
54 spin_lock_irqsave(&zone->lru_lock, flags);
55 lruvec = mem_cgroup_page_lruvec(page, zone);
56 VM_BUG_ON(!PageLRU(page));
57 __ClearPageLRU(page);
58 del_page_from_lru_list(page, lruvec, page_off_lru(page));
59 spin_unlock_irqrestore(&zone->lru_lock, flags);
63 static void __put_single_page(struct page *page)
65 __page_cache_release(page);
66 free_hot_cold_page(page, 0);
69 static void __put_compound_page(struct page *page)
71 compound_page_dtor *dtor;
73 __page_cache_release(page);
74 dtor = get_compound_page_dtor(page);
75 (*dtor)(page);
78 static void put_compound_page(struct page *page)
80 if (unlikely(PageTail(page))) {
81 /* __split_huge_page_refcount can run under us */
82 struct page *page_head = compound_trans_head(page);
84 if (likely(page != page_head &&
85 get_page_unless_zero(page_head))) {
86 unsigned long flags;
89 * THP can not break up slab pages so avoid taking
90 * compound_lock(). Slab performs non-atomic bit ops
91 * on page->flags for better performance. In particular
92 * slab_unlock() in slub used to be a hot path. It is
93 * still hot on arches that do not support
94 * this_cpu_cmpxchg_double().
96 if (PageSlab(page_head)) {
97 if (PageTail(page)) {
98 if (put_page_testzero(page_head))
99 VM_BUG_ON(1);
101 atomic_dec(&page->_mapcount);
102 goto skip_lock_tail;
103 } else
104 goto skip_lock;
107 * page_head wasn't a dangling pointer but it
108 * may not be a head page anymore by the time
109 * we obtain the lock. That is ok as long as it
110 * can't be freed from under us.
112 flags = compound_lock_irqsave(page_head);
113 if (unlikely(!PageTail(page))) {
114 /* __split_huge_page_refcount run before us */
115 compound_unlock_irqrestore(page_head, flags);
116 skip_lock:
117 if (put_page_testzero(page_head))
118 __put_single_page(page_head);
119 out_put_single:
120 if (put_page_testzero(page))
121 __put_single_page(page);
122 return;
124 VM_BUG_ON(page_head != page->first_page);
126 * We can release the refcount taken by
127 * get_page_unless_zero() now that
128 * __split_huge_page_refcount() is blocked on
129 * the compound_lock.
131 if (put_page_testzero(page_head))
132 VM_BUG_ON(1);
133 /* __split_huge_page_refcount will wait now */
134 VM_BUG_ON(page_mapcount(page) <= 0);
135 atomic_dec(&page->_mapcount);
136 VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
137 VM_BUG_ON(atomic_read(&page->_count) != 0);
138 compound_unlock_irqrestore(page_head, flags);
140 skip_lock_tail:
141 if (put_page_testzero(page_head)) {
142 if (PageHead(page_head))
143 __put_compound_page(page_head);
144 else
145 __put_single_page(page_head);
147 } else {
148 /* page_head is a dangling pointer */
149 VM_BUG_ON(PageTail(page));
150 goto out_put_single;
152 } else if (put_page_testzero(page)) {
153 if (PageHead(page))
154 __put_compound_page(page);
155 else
156 __put_single_page(page);
160 void put_page(struct page *page)
162 if (unlikely(PageCompound(page)))
163 put_compound_page(page);
164 else if (put_page_testzero(page))
165 __put_single_page(page);
167 EXPORT_SYMBOL(put_page);
170 * This function is exported but must not be called by anything other
171 * than get_page(). It implements the slow path of get_page().
173 bool __get_page_tail(struct page *page)
176 * This takes care of get_page() if run on a tail page
177 * returned by one of the get_user_pages/follow_page variants.
178 * get_user_pages/follow_page itself doesn't need the compound
179 * lock because it runs __get_page_tail_foll() under the
180 * proper PT lock that already serializes against
181 * split_huge_page().
183 unsigned long flags;
184 bool got = false;
185 struct page *page_head = compound_trans_head(page);
187 if (likely(page != page_head && get_page_unless_zero(page_head))) {
189 /* Ref to put_compound_page() comment. */
190 if (PageSlab(page_head)) {
191 if (likely(PageTail(page))) {
192 __get_page_tail_foll(page, false);
193 return true;
194 } else {
195 put_page(page_head);
196 return false;
201 * page_head wasn't a dangling pointer but it
202 * may not be a head page anymore by the time
203 * we obtain the lock. That is ok as long as it
204 * can't be freed from under us.
206 flags = compound_lock_irqsave(page_head);
207 /* here __split_huge_page_refcount won't run anymore */
208 if (likely(PageTail(page))) {
209 __get_page_tail_foll(page, false);
210 got = true;
212 compound_unlock_irqrestore(page_head, flags);
213 if (unlikely(!got))
214 put_page(page_head);
216 return got;
218 EXPORT_SYMBOL(__get_page_tail);
221 * put_pages_list() - release a list of pages
222 * @pages: list of pages threaded on page->lru
224 * Release a list of pages which are strung together on page.lru. Currently
225 * used by read_cache_pages() and related error recovery code.
227 void put_pages_list(struct list_head *pages)
229 while (!list_empty(pages)) {
230 struct page *victim;
232 victim = list_entry(pages->prev, struct page, lru);
233 list_del(&victim->lru);
234 page_cache_release(victim);
237 EXPORT_SYMBOL(put_pages_list);
239 static void pagevec_lru_move_fn(struct pagevec *pvec,
240 void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
241 void *arg)
243 int i;
244 struct zone *zone = NULL;
245 struct lruvec *lruvec;
246 unsigned long flags = 0;
248 for (i = 0; i < pagevec_count(pvec); i++) {
249 struct page *page = pvec->pages[i];
250 struct zone *pagezone = page_zone(page);
252 if (pagezone != zone) {
253 if (zone)
254 spin_unlock_irqrestore(&zone->lru_lock, flags);
255 zone = pagezone;
256 spin_lock_irqsave(&zone->lru_lock, flags);
259 lruvec = mem_cgroup_page_lruvec(page, zone);
260 (*move_fn)(page, lruvec, arg);
262 if (zone)
263 spin_unlock_irqrestore(&zone->lru_lock, flags);
264 release_pages(pvec->pages, pvec->nr, pvec->cold);
265 pagevec_reinit(pvec);
268 static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
269 void *arg)
271 int *pgmoved = arg;
273 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
274 enum lru_list lru = page_lru_base_type(page);
275 list_move_tail(&page->lru, &lruvec->lists[lru]);
276 (*pgmoved)++;
281 * pagevec_move_tail() must be called with IRQ disabled.
282 * Otherwise this may cause nasty races.
284 static void pagevec_move_tail(struct pagevec *pvec)
286 int pgmoved = 0;
288 pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
289 __count_vm_events(PGROTATED, pgmoved);
293 * Writeback is about to end against a page which has been marked for immediate
294 * reclaim. If it still appears to be reclaimable, move it to the tail of the
295 * inactive list.
297 void rotate_reclaimable_page(struct page *page)
299 if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
300 !PageUnevictable(page) && PageLRU(page)) {
301 struct pagevec *pvec;
302 unsigned long flags;
304 page_cache_get(page);
305 local_irq_save(flags);
306 pvec = &__get_cpu_var(lru_rotate_pvecs);
307 if (!pagevec_add(pvec, page))
308 pagevec_move_tail(pvec);
309 local_irq_restore(flags);
313 static void update_page_reclaim_stat(struct lruvec *lruvec,
314 int file, int rotated)
316 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
318 reclaim_stat->recent_scanned[file]++;
319 if (rotated)
320 reclaim_stat->recent_rotated[file]++;
323 static void __activate_page(struct page *page, struct lruvec *lruvec,
324 void *arg)
326 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
327 int file = page_is_file_cache(page);
328 int lru = page_lru_base_type(page);
330 del_page_from_lru_list(page, lruvec, lru);
331 SetPageActive(page);
332 lru += LRU_ACTIVE;
333 add_page_to_lru_list(page, lruvec, lru);
335 __count_vm_event(PGACTIVATE);
336 update_page_reclaim_stat(lruvec, file, 1);
340 #ifdef CONFIG_SMP
341 static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
343 static void activate_page_drain(int cpu)
345 struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
347 if (pagevec_count(pvec))
348 pagevec_lru_move_fn(pvec, __activate_page, NULL);
351 void activate_page(struct page *page)
353 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
354 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
356 page_cache_get(page);
357 if (!pagevec_add(pvec, page))
358 pagevec_lru_move_fn(pvec, __activate_page, NULL);
359 put_cpu_var(activate_page_pvecs);
363 #else
364 static inline void activate_page_drain(int cpu)
368 void activate_page(struct page *page)
370 struct zone *zone = page_zone(page);
372 spin_lock_irq(&zone->lru_lock);
373 __activate_page(page, mem_cgroup_page_lruvec(page, zone), NULL);
374 spin_unlock_irq(&zone->lru_lock);
376 #endif
379 * Mark a page as having seen activity.
381 * inactive,unreferenced -> inactive,referenced
382 * inactive,referenced -> active,unreferenced
383 * active,unreferenced -> active,referenced
385 void mark_page_accessed(struct page *page)
387 if (!PageActive(page) && !PageUnevictable(page) &&
388 PageReferenced(page) && PageLRU(page)) {
389 activate_page(page);
390 ClearPageReferenced(page);
391 } else if (!PageReferenced(page)) {
392 SetPageReferenced(page);
395 EXPORT_SYMBOL(mark_page_accessed);
397 void __lru_cache_add(struct page *page, enum lru_list lru)
399 struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
401 page_cache_get(page);
402 if (!pagevec_add(pvec, page))
403 __pagevec_lru_add(pvec, lru);
404 put_cpu_var(lru_add_pvecs);
406 EXPORT_SYMBOL(__lru_cache_add);
409 * lru_cache_add_lru - add a page to a page list
410 * @page: the page to be added to the LRU.
411 * @lru: the LRU list to which the page is added.
413 void lru_cache_add_lru(struct page *page, enum lru_list lru)
415 if (PageActive(page)) {
416 VM_BUG_ON(PageUnevictable(page));
417 ClearPageActive(page);
418 } else if (PageUnevictable(page)) {
419 VM_BUG_ON(PageActive(page));
420 ClearPageUnevictable(page);
423 VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
424 __lru_cache_add(page, lru);
428 * add_page_to_unevictable_list - add a page to the unevictable list
429 * @page: the page to be added to the unevictable list
431 * Add page directly to its zone's unevictable list. To avoid races with
432 * tasks that might be making the page evictable, through eg. munlock,
433 * munmap or exit, while it's not on the lru, we want to add the page
434 * while it's locked or otherwise "invisible" to other tasks. This is
435 * difficult to do when using the pagevec cache, so bypass that.
437 void add_page_to_unevictable_list(struct page *page)
439 struct zone *zone = page_zone(page);
440 struct lruvec *lruvec;
442 spin_lock_irq(&zone->lru_lock);
443 lruvec = mem_cgroup_page_lruvec(page, zone);
444 SetPageUnevictable(page);
445 SetPageLRU(page);
446 add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
447 spin_unlock_irq(&zone->lru_lock);
451 * If the page can not be invalidated, it is moved to the
452 * inactive list to speed up its reclaim. It is moved to the
453 * head of the list, rather than the tail, to give the flusher
454 * threads some time to write it out, as this is much more
455 * effective than the single-page writeout from reclaim.
457 * If the page isn't page_mapped and dirty/writeback, the page
458 * could reclaim asap using PG_reclaim.
460 * 1. active, mapped page -> none
461 * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
462 * 3. inactive, mapped page -> none
463 * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
464 * 5. inactive, clean -> inactive, tail
465 * 6. Others -> none
467 * In 4, why it moves inactive's head, the VM expects the page would
468 * be write it out by flusher threads as this is much more effective
469 * than the single-page writeout from reclaim.
471 static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
472 void *arg)
474 int lru, file;
475 bool active;
477 if (!PageLRU(page))
478 return;
480 if (PageUnevictable(page))
481 return;
483 /* Some processes are using the page */
484 if (page_mapped(page))
485 return;
487 active = PageActive(page);
488 file = page_is_file_cache(page);
489 lru = page_lru_base_type(page);
491 del_page_from_lru_list(page, lruvec, lru + active);
492 ClearPageActive(page);
493 ClearPageReferenced(page);
494 add_page_to_lru_list(page, lruvec, lru);
496 if (PageWriteback(page) || PageDirty(page)) {
498 * PG_reclaim could be raced with end_page_writeback
499 * It can make readahead confusing. But race window
500 * is _really_ small and it's non-critical problem.
502 SetPageReclaim(page);
503 } else {
505 * The page's writeback ends up during pagevec
506 * We moves tha page into tail of inactive.
508 list_move_tail(&page->lru, &lruvec->lists[lru]);
509 __count_vm_event(PGROTATED);
512 if (active)
513 __count_vm_event(PGDEACTIVATE);
514 update_page_reclaim_stat(lruvec, file, 0);
518 * Drain pages out of the cpu's pagevecs.
519 * Either "cpu" is the current CPU, and preemption has already been
520 * disabled; or "cpu" is being hot-unplugged, and is already dead.
522 void lru_add_drain_cpu(int cpu)
524 struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
525 struct pagevec *pvec;
526 int lru;
528 for_each_lru(lru) {
529 pvec = &pvecs[lru - LRU_BASE];
530 if (pagevec_count(pvec))
531 __pagevec_lru_add(pvec, lru);
534 pvec = &per_cpu(lru_rotate_pvecs, cpu);
535 if (pagevec_count(pvec)) {
536 unsigned long flags;
538 /* No harm done if a racing interrupt already did this */
539 local_irq_save(flags);
540 pagevec_move_tail(pvec);
541 local_irq_restore(flags);
544 pvec = &per_cpu(lru_deactivate_pvecs, cpu);
545 if (pagevec_count(pvec))
546 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
548 activate_page_drain(cpu);
552 * deactivate_page - forcefully deactivate a page
553 * @page: page to deactivate
555 * This function hints the VM that @page is a good reclaim candidate,
556 * for example if its invalidation fails due to the page being dirty
557 * or under writeback.
559 void deactivate_page(struct page *page)
562 * In a workload with many unevictable page such as mprotect, unevictable
563 * page deactivation for accelerating reclaim is pointless.
565 if (PageUnevictable(page))
566 return;
568 if (likely(get_page_unless_zero(page))) {
569 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
571 if (!pagevec_add(pvec, page))
572 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
573 put_cpu_var(lru_deactivate_pvecs);
577 void lru_add_drain(void)
579 lru_add_drain_cpu(get_cpu());
580 put_cpu();
583 static void lru_add_drain_per_cpu(struct work_struct *dummy)
585 lru_add_drain();
589 * Returns 0 for success
591 int lru_add_drain_all(void)
593 return schedule_on_each_cpu(lru_add_drain_per_cpu);
597 * Batched page_cache_release(). Decrement the reference count on all the
598 * passed pages. If it fell to zero then remove the page from the LRU and
599 * free it.
601 * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
602 * for the remainder of the operation.
604 * The locking in this function is against shrink_inactive_list(): we recheck
605 * the page count inside the lock to see whether shrink_inactive_list()
606 * grabbed the page via the LRU. If it did, give up: shrink_inactive_list()
607 * will free it.
609 void release_pages(struct page **pages, int nr, int cold)
611 int i;
612 LIST_HEAD(pages_to_free);
613 struct zone *zone = NULL;
614 struct lruvec *lruvec;
615 unsigned long uninitialized_var(flags);
617 for (i = 0; i < nr; i++) {
618 struct page *page = pages[i];
620 if (unlikely(PageCompound(page))) {
621 if (zone) {
622 spin_unlock_irqrestore(&zone->lru_lock, flags);
623 zone = NULL;
625 put_compound_page(page);
626 continue;
629 if (!put_page_testzero(page))
630 continue;
632 if (PageLRU(page)) {
633 struct zone *pagezone = page_zone(page);
635 if (pagezone != zone) {
636 if (zone)
637 spin_unlock_irqrestore(&zone->lru_lock,
638 flags);
639 zone = pagezone;
640 spin_lock_irqsave(&zone->lru_lock, flags);
643 lruvec = mem_cgroup_page_lruvec(page, zone);
644 VM_BUG_ON(!PageLRU(page));
645 __ClearPageLRU(page);
646 del_page_from_lru_list(page, lruvec, page_off_lru(page));
649 list_add(&page->lru, &pages_to_free);
651 if (zone)
652 spin_unlock_irqrestore(&zone->lru_lock, flags);
654 free_hot_cold_page_list(&pages_to_free, cold);
656 EXPORT_SYMBOL(release_pages);
659 * The pages which we're about to release may be in the deferred lru-addition
660 * queues. That would prevent them from really being freed right now. That's
661 * OK from a correctness point of view but is inefficient - those pages may be
662 * cache-warm and we want to give them back to the page allocator ASAP.
664 * So __pagevec_release() will drain those queues here. __pagevec_lru_add()
665 * and __pagevec_lru_add_active() call release_pages() directly to avoid
666 * mutual recursion.
668 void __pagevec_release(struct pagevec *pvec)
670 lru_add_drain();
671 release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
672 pagevec_reinit(pvec);
674 EXPORT_SYMBOL(__pagevec_release);
676 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
677 /* used by __split_huge_page_refcount() */
678 void lru_add_page_tail(struct page *page, struct page *page_tail,
679 struct lruvec *lruvec)
681 int uninitialized_var(active);
682 enum lru_list lru;
683 const int file = 0;
685 VM_BUG_ON(!PageHead(page));
686 VM_BUG_ON(PageCompound(page_tail));
687 VM_BUG_ON(PageLRU(page_tail));
688 VM_BUG_ON(NR_CPUS != 1 &&
689 !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
691 SetPageLRU(page_tail);
693 if (page_evictable(page_tail, NULL)) {
694 if (PageActive(page)) {
695 SetPageActive(page_tail);
696 active = 1;
697 lru = LRU_ACTIVE_ANON;
698 } else {
699 active = 0;
700 lru = LRU_INACTIVE_ANON;
702 } else {
703 SetPageUnevictable(page_tail);
704 lru = LRU_UNEVICTABLE;
707 if (likely(PageLRU(page)))
708 list_add_tail(&page_tail->lru, &page->lru);
709 else {
710 struct list_head *list_head;
712 * Head page has not yet been counted, as an hpage,
713 * so we must account for each subpage individually.
715 * Use the standard add function to put page_tail on the list,
716 * but then correct its position so they all end up in order.
718 add_page_to_lru_list(page_tail, lruvec, lru);
719 list_head = page_tail->lru.prev;
720 list_move_tail(&page_tail->lru, list_head);
723 if (!PageUnevictable(page))
724 update_page_reclaim_stat(lruvec, file, active);
726 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
728 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
729 void *arg)
731 enum lru_list lru = (enum lru_list)arg;
732 int file = is_file_lru(lru);
733 int active = is_active_lru(lru);
735 VM_BUG_ON(PageActive(page));
736 VM_BUG_ON(PageUnevictable(page));
737 VM_BUG_ON(PageLRU(page));
739 SetPageLRU(page);
740 if (active)
741 SetPageActive(page);
742 add_page_to_lru_list(page, lruvec, lru);
743 update_page_reclaim_stat(lruvec, file, active);
747 * Add the passed pages to the LRU, then drop the caller's refcount
748 * on them. Reinitialises the caller's pagevec.
750 void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
752 VM_BUG_ON(is_unevictable_lru(lru));
754 pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)lru);
756 EXPORT_SYMBOL(__pagevec_lru_add);
759 * pagevec_lookup - gang pagecache lookup
760 * @pvec: Where the resulting pages are placed
761 * @mapping: The address_space to search
762 * @start: The starting page index
763 * @nr_pages: The maximum number of pages
765 * pagevec_lookup() will search for and return a group of up to @nr_pages pages
766 * in the mapping. The pages are placed in @pvec. pagevec_lookup() takes a
767 * reference against the pages in @pvec.
769 * The search returns a group of mapping-contiguous pages with ascending
770 * indexes. There may be holes in the indices due to not-present pages.
772 * pagevec_lookup() returns the number of pages which were found.
774 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
775 pgoff_t start, unsigned nr_pages)
777 pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
778 return pagevec_count(pvec);
780 EXPORT_SYMBOL(pagevec_lookup);
782 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
783 pgoff_t *index, int tag, unsigned nr_pages)
785 pvec->nr = find_get_pages_tag(mapping, index, tag,
786 nr_pages, pvec->pages);
787 return pagevec_count(pvec);
789 EXPORT_SYMBOL(pagevec_lookup_tag);
792 * Perform any setup for the swap system
794 void __init swap_setup(void)
796 unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
798 #ifdef CONFIG_SWAP
799 bdi_init(swapper_space.backing_dev_info);
800 #endif
802 /* Use a smaller cluster for small-memory machines */
803 if (megs < 16)
804 page_cluster = 2;
805 else
806 page_cluster = 3;
808 * Right now other parts of the system means that we
809 * _really_ don't want to cluster much more