Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus
[firefly-linux-kernel-4.4.55.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 static void pagevec_lru_move_fn(struct pagevec *pvec,
240         void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
241         void *arg)
242 {
243         int i;
244         struct zone *zone = NULL;
245         struct lruvec *lruvec;
246         unsigned long flags = 0;
247
248         for (i = 0; i < pagevec_count(pvec); i++) {
249                 struct page *page = pvec->pages[i];
250                 struct zone *pagezone = page_zone(page);
251
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);
257                 }
258
259                 lruvec = mem_cgroup_page_lruvec(page, zone);
260                 (*move_fn)(page, lruvec, arg);
261         }
262         if (zone)
263                 spin_unlock_irqrestore(&zone->lru_lock, flags);
264         release_pages(pvec->pages, pvec->nr, pvec->cold);
265         pagevec_reinit(pvec);
266 }
267
268 static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
269                                  void *arg)
270 {
271         int *pgmoved = arg;
272
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)++;
277         }
278 }
279
280 /*
281  * pagevec_move_tail() must be called with IRQ disabled.
282  * Otherwise this may cause nasty races.
283  */
284 static void pagevec_move_tail(struct pagevec *pvec)
285 {
286         int pgmoved = 0;
287
288         pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
289         __count_vm_events(PGROTATED, pgmoved);
290 }
291
292 /*
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.
296  */
297 void rotate_reclaimable_page(struct page *page)
298 {
299         if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
300             !PageUnevictable(page) && PageLRU(page)) {
301                 struct pagevec *pvec;
302                 unsigned long flags;
303
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);
310         }
311 }
312
313 static void update_page_reclaim_stat(struct lruvec *lruvec,
314                                      int file, int rotated)
315 {
316         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
317
318         reclaim_stat->recent_scanned[file]++;
319         if (rotated)
320                 reclaim_stat->recent_rotated[file]++;
321 }
322
323 static void __activate_page(struct page *page, struct lruvec *lruvec,
324                             void *arg)
325 {
326         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
327                 int file = page_is_file_cache(page);
328                 int lru = page_lru_base_type(page);
329
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);
334
335                 __count_vm_event(PGACTIVATE);
336                 update_page_reclaim_stat(lruvec, file, 1);
337         }
338 }
339
340 #ifdef CONFIG_SMP
341 static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
342
343 static void activate_page_drain(int cpu)
344 {
345         struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
346
347         if (pagevec_count(pvec))
348                 pagevec_lru_move_fn(pvec, __activate_page, NULL);
349 }
350
351 void activate_page(struct page *page)
352 {
353         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
354                 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
355
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);
360         }
361 }
362
363 #else
364 static inline void activate_page_drain(int cpu)
365 {
366 }
367
368 void activate_page(struct page *page)
369 {
370         struct zone *zone = page_zone(page);
371
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);
375 }
376 #endif
377
378 /*
379  * Mark a page as having seen activity.
380  *
381  * inactive,unreferenced        ->      inactive,referenced
382  * inactive,referenced          ->      active,unreferenced
383  * active,unreferenced          ->      active,referenced
384  */
385 void mark_page_accessed(struct page *page)
386 {
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);
393         }
394 }
395 EXPORT_SYMBOL(mark_page_accessed);
396
397 void __lru_cache_add(struct page *page, enum lru_list lru)
398 {
399         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
400
401         page_cache_get(page);
402         if (!pagevec_add(pvec, page))
403                 __pagevec_lru_add(pvec, lru);
404         put_cpu_var(lru_add_pvecs);
405 }
406 EXPORT_SYMBOL(__lru_cache_add);
407
408 /**
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.
412  */
413 void lru_cache_add_lru(struct page *page, enum lru_list lru)
414 {
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);
421         }
422
423         VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
424         __lru_cache_add(page, lru);
425 }
426
427 /**
428  * add_page_to_unevictable_list - add a page to the unevictable list
429  * @page:  the page to be added to the unevictable list
430  *
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.
436  */
437 void add_page_to_unevictable_list(struct page *page)
438 {
439         struct zone *zone = page_zone(page);
440         struct lruvec *lruvec;
441
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);
448 }
449
450 /*
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.
456  *
457  * If the page isn't page_mapped and dirty/writeback, the page
458  * could reclaim asap using PG_reclaim.
459  *
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
466  *
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.
470  */
471 static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
472                               void *arg)
473 {
474         int lru, file;
475         bool active;
476
477         if (!PageLRU(page))
478                 return;
479
480         if (PageUnevictable(page))
481                 return;
482
483         /* Some processes are using the page */
484         if (page_mapped(page))
485                 return;
486
487         active = PageActive(page);
488         file = page_is_file_cache(page);
489         lru = page_lru_base_type(page);
490
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);
495
496         if (PageWriteback(page) || PageDirty(page)) {
497                 /*
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.
501                  */
502                 SetPageReclaim(page);
503         } else {
504                 /*
505                  * The page's writeback ends up during pagevec
506                  * We moves tha page into tail of inactive.
507                  */
508                 list_move_tail(&page->lru, &lruvec->lists[lru]);
509                 __count_vm_event(PGROTATED);
510         }
511
512         if (active)
513                 __count_vm_event(PGDEACTIVATE);
514         update_page_reclaim_stat(lruvec, file, 0);
515 }
516
517 /*
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.
521  */
522 void lru_add_drain_cpu(int cpu)
523 {
524         struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
525         struct pagevec *pvec;
526         int lru;
527
528         for_each_lru(lru) {
529                 pvec = &pvecs[lru - LRU_BASE];
530                 if (pagevec_count(pvec))
531                         __pagevec_lru_add(pvec, lru);
532         }
533
534         pvec = &per_cpu(lru_rotate_pvecs, cpu);
535         if (pagevec_count(pvec)) {
536                 unsigned long flags;
537
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);
542         }
543
544         pvec = &per_cpu(lru_deactivate_pvecs, cpu);
545         if (pagevec_count(pvec))
546                 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
547
548         activate_page_drain(cpu);
549 }
550
551 /**
552  * deactivate_page - forcefully deactivate a page
553  * @page: page to deactivate
554  *
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.
558  */
559 void deactivate_page(struct page *page)
560 {
561         /*
562          * In a workload with many unevictable page such as mprotect, unevictable
563          * page deactivation for accelerating reclaim is pointless.
564          */
565         if (PageUnevictable(page))
566                 return;
567
568         if (likely(get_page_unless_zero(page))) {
569                 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
570
571                 if (!pagevec_add(pvec, page))
572                         pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
573                 put_cpu_var(lru_deactivate_pvecs);
574         }
575 }
576
577 void lru_add_drain(void)
578 {
579         lru_add_drain_cpu(get_cpu());
580         put_cpu();
581 }
582
583 static void lru_add_drain_per_cpu(struct work_struct *dummy)
584 {
585         lru_add_drain();
586 }
587
588 /*
589  * Returns 0 for success
590  */
591 int lru_add_drain_all(void)
592 {
593         return schedule_on_each_cpu(lru_add_drain_per_cpu);
594 }
595
596 /*
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.
600  *
601  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
602  * for the remainder of the operation.
603  *
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.
608  */
609 void release_pages(struct page **pages, int nr, int cold)
610 {
611         int i;
612         LIST_HEAD(pages_to_free);
613         struct zone *zone = NULL;
614         struct lruvec *lruvec;
615         unsigned long uninitialized_var(flags);
616
617         for (i = 0; i < nr; i++) {
618                 struct page *page = pages[i];
619
620                 if (unlikely(PageCompound(page))) {
621                         if (zone) {
622                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
623                                 zone = NULL;
624                         }
625                         put_compound_page(page);
626                         continue;
627                 }
628
629                 if (!put_page_testzero(page))
630                         continue;
631
632                 if (PageLRU(page)) {
633                         struct zone *pagezone = page_zone(page);
634
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);
641                         }
642
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));
647                 }
648
649                 list_add(&page->lru, &pages_to_free);
650         }
651         if (zone)
652                 spin_unlock_irqrestore(&zone->lru_lock, flags);
653
654         free_hot_cold_page_list(&pages_to_free, cold);
655 }
656 EXPORT_SYMBOL(release_pages);
657
658 /*
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.
663  *
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.
667  */
668 void __pagevec_release(struct pagevec *pvec)
669 {
670         lru_add_drain();
671         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
672         pagevec_reinit(pvec);
673 }
674 EXPORT_SYMBOL(__pagevec_release);
675
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)
680 {
681         int uninitialized_var(active);
682         enum lru_list lru;
683         const int file = 0;
684
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));
690
691         SetPageLRU(page_tail);
692
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;
701                 }
702         } else {
703                 SetPageUnevictable(page_tail);
704                 lru = LRU_UNEVICTABLE;
705         }
706
707         if (likely(PageLRU(page)))
708                 list_add_tail(&page_tail->lru, &page->lru);
709         else {
710                 struct list_head *list_head;
711                 /*
712                  * Head page has not yet been counted, as an hpage,
713                  * so we must account for each subpage individually.
714                  *
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.
717                  */
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);
721         }
722
723         if (!PageUnevictable(page))
724                 update_page_reclaim_stat(lruvec, file, active);
725 }
726 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
727
728 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
729                                  void *arg)
730 {
731         enum lru_list lru = (enum lru_list)arg;
732         int file = is_file_lru(lru);
733         int active = is_active_lru(lru);
734
735         VM_BUG_ON(PageActive(page));
736         VM_BUG_ON(PageUnevictable(page));
737         VM_BUG_ON(PageLRU(page));
738
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);
744 }
745
746 /*
747  * Add the passed pages to the LRU, then drop the caller's refcount
748  * on them.  Reinitialises the caller's pagevec.
749  */
750 void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
751 {
752         VM_BUG_ON(is_unevictable_lru(lru));
753
754         pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)lru);
755 }
756 EXPORT_SYMBOL(__pagevec_lru_add);
757
758 /**
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
764  *
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.
768  *
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.
771  *
772  * pagevec_lookup() returns the number of pages which were found.
773  */
774 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
775                 pgoff_t start, unsigned nr_pages)
776 {
777         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
778         return pagevec_count(pvec);
779 }
780 EXPORT_SYMBOL(pagevec_lookup);
781
782 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
783                 pgoff_t *index, int tag, unsigned nr_pages)
784 {
785         pvec->nr = find_get_pages_tag(mapping, index, tag,
786                                         nr_pages, pvec->pages);
787         return pagevec_count(pvec);
788 }
789 EXPORT_SYMBOL(pagevec_lookup_tag);
790
791 /*
792  * Perform any setup for the swap system
793  */
794 void __init swap_setup(void)
795 {
796         unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
797
798 #ifdef CONFIG_SWAP
799         bdi_init(swapper_space.backing_dev_info);
800 #endif
801
802         /* Use a smaller cluster for small-memory machines */
803         if (megs < 16)
804                 page_cluster = 2;
805         else
806                 page_cluster = 3;
807         /*
808          * Right now other parts of the system means that we
809          * _really_ don't want to cluster much more
810          */
811 }