mm: have order > 0 compaction start near a pageblock with free pages
[linux-3.10.git] / 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/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>
33
34 #include "internal.h"
35
36 /* How many pages do we try to swap or page in/out together? */
37 int page_cluster;
38
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);
42
43 /*
44  * This path almost never happens for VM activity - pages are normally
45  * freed via pagevecs.  But it gets used by networking.
46  */
47 static void __page_cache_release(struct page *page)
48 {
49         if (PageLRU(page)) {
50                 struct zone *zone = page_zone(page);
51                 struct lruvec *lruvec;
52                 unsigned long flags;
53
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);
60         }
61 }
62
63 static void __put_single_page(struct page *page)
64 {
65         __page_cache_release(page);
66         free_hot_cold_page(page, 0);
67 }
68
69 static void __put_compound_page(struct page *page)
70 {
71         compound_page_dtor *dtor;
72
73         __page_cache_release(page);
74         dtor = get_compound_page_dtor(page);
75         (*dtor)(page);
76 }
77
78 static void put_compound_page(struct page *page)
79 {
80         if (unlikely(PageTail(page))) {
81                 /* __split_huge_page_refcount can run under us */
82                 struct page *page_head = compound_trans_head(page);
83
84                 if (likely(page != page_head &&
85                            get_page_unless_zero(page_head))) {
86                         unsigned long flags;
87
88                         /*
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().
95                          */
96                         if (PageSlab(page_head)) {
97                                 if (PageTail(page)) {
98                                         if (put_page_testzero(page_head))
99                                                 VM_BUG_ON(1);
100
101                                         atomic_dec(&page->_mapcount);
102                                         goto skip_lock_tail;
103                                 } else
104                                         goto skip_lock;
105                         }
106                         /*
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.
111                          */
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;
123                         }
124                         VM_BUG_ON(page_head != page->first_page);
125                         /*
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.
130                          */
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);
139
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);
146                         }
147                 } else {
148                         /* page_head is a dangling pointer */
149                         VM_BUG_ON(PageTail(page));
150                         goto out_put_single;
151                 }
152         } else if (put_page_testzero(page)) {
153                 if (PageHead(page))
154                         __put_compound_page(page);
155                 else
156                         __put_single_page(page);
157         }
158 }
159
160 void put_page(struct page *page)
161 {
162         if (unlikely(PageCompound(page)))
163                 put_compound_page(page);
164         else if (put_page_testzero(page))
165                 __put_single_page(page);
166 }
167 EXPORT_SYMBOL(put_page);
168
169 /*
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().
172  */
173 bool __get_page_tail(struct page *page)
174 {
175         /*
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().
182          */
183         unsigned long flags;
184         bool got = false;
185         struct page *page_head = compound_trans_head(page);
186
187         if (likely(page != page_head && get_page_unless_zero(page_head))) {
188
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;
197                         }
198                 }
199
200                 /*
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.
205                  */
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;
211                 }
212                 compound_unlock_irqrestore(page_head, flags);
213                 if (unlikely(!got))
214                         put_page(page_head);
215         }
216         return got;
217 }
218 EXPORT_SYMBOL(__get_page_tail);
219
220 /**
221  * put_pages_list() - release a list of pages
222  * @pages: list of pages threaded on page->lru
223  *
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.
226  */
227 void put_pages_list(struct list_head *pages)
228 {
229         while (!list_empty(pages)) {
230                 struct page *victim;
231
232                 victim = list_entry(pages->prev, struct page, lru);
233                 list_del(&victim->lru);
234                 page_cache_release(victim);
235         }
236 }
237 EXPORT_SYMBOL(put_pages_list);
238
239 /*
240  * get_kernel_pages() - pin kernel pages in memory
241  * @kiov:       An array of struct kvec structures
242  * @nr_segs:    number of segments to pin
243  * @write:      pinning for read/write, currently ignored
244  * @pages:      array that receives pointers to the pages pinned.
245  *              Should be at least nr_segs long.
246  *
247  * Returns number of pages pinned. This may be fewer than the number
248  * requested. If nr_pages is 0 or negative, returns 0. If no pages
249  * were pinned, returns -errno. Each page returned must be released
250  * with a put_page() call when it is finished with.
251  */
252 int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
253                 struct page **pages)
254 {
255         int seg;
256
257         for (seg = 0; seg < nr_segs; seg++) {
258                 if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
259                         return seg;
260
261                 pages[seg] = kmap_to_page(kiov[seg].iov_base);
262                 page_cache_get(pages[seg]);
263         }
264
265         return seg;
266 }
267 EXPORT_SYMBOL_GPL(get_kernel_pages);
268
269 /*
270  * get_kernel_page() - pin a kernel page in memory
271  * @start:      starting kernel address
272  * @write:      pinning for read/write, currently ignored
273  * @pages:      array that receives pointer to the page pinned.
274  *              Must be at least nr_segs long.
275  *
276  * Returns 1 if page is pinned. If the page was not pinned, returns
277  * -errno. The page returned must be released with a put_page() call
278  * when it is finished with.
279  */
280 int get_kernel_page(unsigned long start, int write, struct page **pages)
281 {
282         const struct kvec kiov = {
283                 .iov_base = (void *)start,
284                 .iov_len = PAGE_SIZE
285         };
286
287         return get_kernel_pages(&kiov, 1, write, pages);
288 }
289 EXPORT_SYMBOL_GPL(get_kernel_page);
290
291 static void pagevec_lru_move_fn(struct pagevec *pvec,
292         void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
293         void *arg)
294 {
295         int i;
296         struct zone *zone = NULL;
297         struct lruvec *lruvec;
298         unsigned long flags = 0;
299
300         for (i = 0; i < pagevec_count(pvec); i++) {
301                 struct page *page = pvec->pages[i];
302                 struct zone *pagezone = page_zone(page);
303
304                 if (pagezone != zone) {
305                         if (zone)
306                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
307                         zone = pagezone;
308                         spin_lock_irqsave(&zone->lru_lock, flags);
309                 }
310
311                 lruvec = mem_cgroup_page_lruvec(page, zone);
312                 (*move_fn)(page, lruvec, arg);
313         }
314         if (zone)
315                 spin_unlock_irqrestore(&zone->lru_lock, flags);
316         release_pages(pvec->pages, pvec->nr, pvec->cold);
317         pagevec_reinit(pvec);
318 }
319
320 static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
321                                  void *arg)
322 {
323         int *pgmoved = arg;
324
325         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
326                 enum lru_list lru = page_lru_base_type(page);
327                 list_move_tail(&page->lru, &lruvec->lists[lru]);
328                 (*pgmoved)++;
329         }
330 }
331
332 /*
333  * pagevec_move_tail() must be called with IRQ disabled.
334  * Otherwise this may cause nasty races.
335  */
336 static void pagevec_move_tail(struct pagevec *pvec)
337 {
338         int pgmoved = 0;
339
340         pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
341         __count_vm_events(PGROTATED, pgmoved);
342 }
343
344 /*
345  * Writeback is about to end against a page which has been marked for immediate
346  * reclaim.  If it still appears to be reclaimable, move it to the tail of the
347  * inactive list.
348  */
349 void rotate_reclaimable_page(struct page *page)
350 {
351         if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
352             !PageUnevictable(page) && PageLRU(page)) {
353                 struct pagevec *pvec;
354                 unsigned long flags;
355
356                 page_cache_get(page);
357                 local_irq_save(flags);
358                 pvec = &__get_cpu_var(lru_rotate_pvecs);
359                 if (!pagevec_add(pvec, page))
360                         pagevec_move_tail(pvec);
361                 local_irq_restore(flags);
362         }
363 }
364
365 static void update_page_reclaim_stat(struct lruvec *lruvec,
366                                      int file, int rotated)
367 {
368         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
369
370         reclaim_stat->recent_scanned[file]++;
371         if (rotated)
372                 reclaim_stat->recent_rotated[file]++;
373 }
374
375 static void __activate_page(struct page *page, struct lruvec *lruvec,
376                             void *arg)
377 {
378         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
379                 int file = page_is_file_cache(page);
380                 int lru = page_lru_base_type(page);
381
382                 del_page_from_lru_list(page, lruvec, lru);
383                 SetPageActive(page);
384                 lru += LRU_ACTIVE;
385                 add_page_to_lru_list(page, lruvec, lru);
386
387                 __count_vm_event(PGACTIVATE);
388                 update_page_reclaim_stat(lruvec, file, 1);
389         }
390 }
391
392 #ifdef CONFIG_SMP
393 static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
394
395 static void activate_page_drain(int cpu)
396 {
397         struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
398
399         if (pagevec_count(pvec))
400                 pagevec_lru_move_fn(pvec, __activate_page, NULL);
401 }
402
403 void activate_page(struct page *page)
404 {
405         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
406                 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
407
408                 page_cache_get(page);
409                 if (!pagevec_add(pvec, page))
410                         pagevec_lru_move_fn(pvec, __activate_page, NULL);
411                 put_cpu_var(activate_page_pvecs);
412         }
413 }
414
415 #else
416 static inline void activate_page_drain(int cpu)
417 {
418 }
419
420 void activate_page(struct page *page)
421 {
422         struct zone *zone = page_zone(page);
423
424         spin_lock_irq(&zone->lru_lock);
425         __activate_page(page, mem_cgroup_page_lruvec(page, zone), NULL);
426         spin_unlock_irq(&zone->lru_lock);
427 }
428 #endif
429
430 /*
431  * Mark a page as having seen activity.
432  *
433  * inactive,unreferenced        ->      inactive,referenced
434  * inactive,referenced          ->      active,unreferenced
435  * active,unreferenced          ->      active,referenced
436  */
437 void mark_page_accessed(struct page *page)
438 {
439         if (!PageActive(page) && !PageUnevictable(page) &&
440                         PageReferenced(page) && PageLRU(page)) {
441                 activate_page(page);
442                 ClearPageReferenced(page);
443         } else if (!PageReferenced(page)) {
444                 SetPageReferenced(page);
445         }
446 }
447 EXPORT_SYMBOL(mark_page_accessed);
448
449 void __lru_cache_add(struct page *page, enum lru_list lru)
450 {
451         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
452
453         page_cache_get(page);
454         if (!pagevec_add(pvec, page))
455                 __pagevec_lru_add(pvec, lru);
456         put_cpu_var(lru_add_pvecs);
457 }
458 EXPORT_SYMBOL(__lru_cache_add);
459
460 /**
461  * lru_cache_add_lru - add a page to a page list
462  * @page: the page to be added to the LRU.
463  * @lru: the LRU list to which the page is added.
464  */
465 void lru_cache_add_lru(struct page *page, enum lru_list lru)
466 {
467         if (PageActive(page)) {
468                 VM_BUG_ON(PageUnevictable(page));
469                 ClearPageActive(page);
470         } else if (PageUnevictable(page)) {
471                 VM_BUG_ON(PageActive(page));
472                 ClearPageUnevictable(page);
473         }
474
475         VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
476         __lru_cache_add(page, lru);
477 }
478
479 /**
480  * add_page_to_unevictable_list - add a page to the unevictable list
481  * @page:  the page to be added to the unevictable list
482  *
483  * Add page directly to its zone's unevictable list.  To avoid races with
484  * tasks that might be making the page evictable, through eg. munlock,
485  * munmap or exit, while it's not on the lru, we want to add the page
486  * while it's locked or otherwise "invisible" to other tasks.  This is
487  * difficult to do when using the pagevec cache, so bypass that.
488  */
489 void add_page_to_unevictable_list(struct page *page)
490 {
491         struct zone *zone = page_zone(page);
492         struct lruvec *lruvec;
493
494         spin_lock_irq(&zone->lru_lock);
495         lruvec = mem_cgroup_page_lruvec(page, zone);
496         SetPageUnevictable(page);
497         SetPageLRU(page);
498         add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
499         spin_unlock_irq(&zone->lru_lock);
500 }
501
502 /*
503  * If the page can not be invalidated, it is moved to the
504  * inactive list to speed up its reclaim.  It is moved to the
505  * head of the list, rather than the tail, to give the flusher
506  * threads some time to write it out, as this is much more
507  * effective than the single-page writeout from reclaim.
508  *
509  * If the page isn't page_mapped and dirty/writeback, the page
510  * could reclaim asap using PG_reclaim.
511  *
512  * 1. active, mapped page -> none
513  * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
514  * 3. inactive, mapped page -> none
515  * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
516  * 5. inactive, clean -> inactive, tail
517  * 6. Others -> none
518  *
519  * In 4, why it moves inactive's head, the VM expects the page would
520  * be write it out by flusher threads as this is much more effective
521  * than the single-page writeout from reclaim.
522  */
523 static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
524                               void *arg)
525 {
526         int lru, file;
527         bool active;
528
529         if (!PageLRU(page))
530                 return;
531
532         if (PageUnevictable(page))
533                 return;
534
535         /* Some processes are using the page */
536         if (page_mapped(page))
537                 return;
538
539         active = PageActive(page);
540         file = page_is_file_cache(page);
541         lru = page_lru_base_type(page);
542
543         del_page_from_lru_list(page, lruvec, lru + active);
544         ClearPageActive(page);
545         ClearPageReferenced(page);
546         add_page_to_lru_list(page, lruvec, lru);
547
548         if (PageWriteback(page) || PageDirty(page)) {
549                 /*
550                  * PG_reclaim could be raced with end_page_writeback
551                  * It can make readahead confusing.  But race window
552                  * is _really_ small and  it's non-critical problem.
553                  */
554                 SetPageReclaim(page);
555         } else {
556                 /*
557                  * The page's writeback ends up during pagevec
558                  * We moves tha page into tail of inactive.
559                  */
560                 list_move_tail(&page->lru, &lruvec->lists[lru]);
561                 __count_vm_event(PGROTATED);
562         }
563
564         if (active)
565                 __count_vm_event(PGDEACTIVATE);
566         update_page_reclaim_stat(lruvec, file, 0);
567 }
568
569 /*
570  * Drain pages out of the cpu's pagevecs.
571  * Either "cpu" is the current CPU, and preemption has already been
572  * disabled; or "cpu" is being hot-unplugged, and is already dead.
573  */
574 void lru_add_drain_cpu(int cpu)
575 {
576         struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
577         struct pagevec *pvec;
578         int lru;
579
580         for_each_lru(lru) {
581                 pvec = &pvecs[lru - LRU_BASE];
582                 if (pagevec_count(pvec))
583                         __pagevec_lru_add(pvec, lru);
584         }
585
586         pvec = &per_cpu(lru_rotate_pvecs, cpu);
587         if (pagevec_count(pvec)) {
588                 unsigned long flags;
589
590                 /* No harm done if a racing interrupt already did this */
591                 local_irq_save(flags);
592                 pagevec_move_tail(pvec);
593                 local_irq_restore(flags);
594         }
595
596         pvec = &per_cpu(lru_deactivate_pvecs, cpu);
597         if (pagevec_count(pvec))
598                 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
599
600         activate_page_drain(cpu);
601 }
602
603 /**
604  * deactivate_page - forcefully deactivate a page
605  * @page: page to deactivate
606  *
607  * This function hints the VM that @page is a good reclaim candidate,
608  * for example if its invalidation fails due to the page being dirty
609  * or under writeback.
610  */
611 void deactivate_page(struct page *page)
612 {
613         /*
614          * In a workload with many unevictable page such as mprotect, unevictable
615          * page deactivation for accelerating reclaim is pointless.
616          */
617         if (PageUnevictable(page))
618                 return;
619
620         if (likely(get_page_unless_zero(page))) {
621                 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
622
623                 if (!pagevec_add(pvec, page))
624                         pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
625                 put_cpu_var(lru_deactivate_pvecs);
626         }
627 }
628
629 void lru_add_drain(void)
630 {
631         lru_add_drain_cpu(get_cpu());
632         put_cpu();
633 }
634
635 static void lru_add_drain_per_cpu(struct work_struct *dummy)
636 {
637         lru_add_drain();
638 }
639
640 /*
641  * Returns 0 for success
642  */
643 int lru_add_drain_all(void)
644 {
645         return schedule_on_each_cpu(lru_add_drain_per_cpu);
646 }
647
648 /*
649  * Batched page_cache_release().  Decrement the reference count on all the
650  * passed pages.  If it fell to zero then remove the page from the LRU and
651  * free it.
652  *
653  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
654  * for the remainder of the operation.
655  *
656  * The locking in this function is against shrink_inactive_list(): we recheck
657  * the page count inside the lock to see whether shrink_inactive_list()
658  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
659  * will free it.
660  */
661 void release_pages(struct page **pages, int nr, int cold)
662 {
663         int i;
664         LIST_HEAD(pages_to_free);
665         struct zone *zone = NULL;
666         struct lruvec *lruvec;
667         unsigned long uninitialized_var(flags);
668
669         for (i = 0; i < nr; i++) {
670                 struct page *page = pages[i];
671
672                 if (unlikely(PageCompound(page))) {
673                         if (zone) {
674                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
675                                 zone = NULL;
676                         }
677                         put_compound_page(page);
678                         continue;
679                 }
680
681                 if (!put_page_testzero(page))
682                         continue;
683
684                 if (PageLRU(page)) {
685                         struct zone *pagezone = page_zone(page);
686
687                         if (pagezone != zone) {
688                                 if (zone)
689                                         spin_unlock_irqrestore(&zone->lru_lock,
690                                                                         flags);
691                                 zone = pagezone;
692                                 spin_lock_irqsave(&zone->lru_lock, flags);
693                         }
694
695                         lruvec = mem_cgroup_page_lruvec(page, zone);
696                         VM_BUG_ON(!PageLRU(page));
697                         __ClearPageLRU(page);
698                         del_page_from_lru_list(page, lruvec, page_off_lru(page));
699                 }
700
701                 list_add(&page->lru, &pages_to_free);
702         }
703         if (zone)
704                 spin_unlock_irqrestore(&zone->lru_lock, flags);
705
706         free_hot_cold_page_list(&pages_to_free, cold);
707 }
708 EXPORT_SYMBOL(release_pages);
709
710 /*
711  * The pages which we're about to release may be in the deferred lru-addition
712  * queues.  That would prevent them from really being freed right now.  That's
713  * OK from a correctness point of view but is inefficient - those pages may be
714  * cache-warm and we want to give them back to the page allocator ASAP.
715  *
716  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
717  * and __pagevec_lru_add_active() call release_pages() directly to avoid
718  * mutual recursion.
719  */
720 void __pagevec_release(struct pagevec *pvec)
721 {
722         lru_add_drain();
723         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
724         pagevec_reinit(pvec);
725 }
726 EXPORT_SYMBOL(__pagevec_release);
727
728 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
729 /* used by __split_huge_page_refcount() */
730 void lru_add_page_tail(struct page *page, struct page *page_tail,
731                        struct lruvec *lruvec)
732 {
733         int uninitialized_var(active);
734         enum lru_list lru;
735         const int file = 0;
736
737         VM_BUG_ON(!PageHead(page));
738         VM_BUG_ON(PageCompound(page_tail));
739         VM_BUG_ON(PageLRU(page_tail));
740         VM_BUG_ON(NR_CPUS != 1 &&
741                   !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
742
743         SetPageLRU(page_tail);
744
745         if (page_evictable(page_tail, NULL)) {
746                 if (PageActive(page)) {
747                         SetPageActive(page_tail);
748                         active = 1;
749                         lru = LRU_ACTIVE_ANON;
750                 } else {
751                         active = 0;
752                         lru = LRU_INACTIVE_ANON;
753                 }
754         } else {
755                 SetPageUnevictable(page_tail);
756                 lru = LRU_UNEVICTABLE;
757         }
758
759         if (likely(PageLRU(page)))
760                 list_add_tail(&page_tail->lru, &page->lru);
761         else {
762                 struct list_head *list_head;
763                 /*
764                  * Head page has not yet been counted, as an hpage,
765                  * so we must account for each subpage individually.
766                  *
767                  * Use the standard add function to put page_tail on the list,
768                  * but then correct its position so they all end up in order.
769                  */
770                 add_page_to_lru_list(page_tail, lruvec, lru);
771                 list_head = page_tail->lru.prev;
772                 list_move_tail(&page_tail->lru, list_head);
773         }
774
775         if (!PageUnevictable(page))
776                 update_page_reclaim_stat(lruvec, file, active);
777 }
778 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
779
780 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
781                                  void *arg)
782 {
783         enum lru_list lru = (enum lru_list)arg;
784         int file = is_file_lru(lru);
785         int active = is_active_lru(lru);
786
787         VM_BUG_ON(PageActive(page));
788         VM_BUG_ON(PageUnevictable(page));
789         VM_BUG_ON(PageLRU(page));
790
791         SetPageLRU(page);
792         if (active)
793                 SetPageActive(page);
794         add_page_to_lru_list(page, lruvec, lru);
795         update_page_reclaim_stat(lruvec, file, active);
796 }
797
798 /*
799  * Add the passed pages to the LRU, then drop the caller's refcount
800  * on them.  Reinitialises the caller's pagevec.
801  */
802 void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
803 {
804         VM_BUG_ON(is_unevictable_lru(lru));
805
806         pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)lru);
807 }
808 EXPORT_SYMBOL(__pagevec_lru_add);
809
810 /**
811  * pagevec_lookup - gang pagecache lookup
812  * @pvec:       Where the resulting pages are placed
813  * @mapping:    The address_space to search
814  * @start:      The starting page index
815  * @nr_pages:   The maximum number of pages
816  *
817  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
818  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
819  * reference against the pages in @pvec.
820  *
821  * The search returns a group of mapping-contiguous pages with ascending
822  * indexes.  There may be holes in the indices due to not-present pages.
823  *
824  * pagevec_lookup() returns the number of pages which were found.
825  */
826 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
827                 pgoff_t start, unsigned nr_pages)
828 {
829         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
830         return pagevec_count(pvec);
831 }
832 EXPORT_SYMBOL(pagevec_lookup);
833
834 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
835                 pgoff_t *index, int tag, unsigned nr_pages)
836 {
837         pvec->nr = find_get_pages_tag(mapping, index, tag,
838                                         nr_pages, pvec->pages);
839         return pagevec_count(pvec);
840 }
841 EXPORT_SYMBOL(pagevec_lookup_tag);
842
843 /*
844  * Perform any setup for the swap system
845  */
846 void __init swap_setup(void)
847 {
848         unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
849
850 #ifdef CONFIG_SWAP
851         bdi_init(swapper_space.backing_dev_info);
852 #endif
853
854         /* Use a smaller cluster for small-memory machines */
855         if (megs < 16)
856                 page_cluster = 2;
857         else
858                 page_cluster = 3;
859         /*
860          * Right now other parts of the system means that we
861          * _really_ don't want to cluster much more
862          */
863 }