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? */
  38 int page_cluster;
  39
  40 static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
  41 static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
  42 static 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  */
  48 static 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
  62 static void __put_single_page(struct page *page)
  63 {
  64         __page_cache_release(page);
  65         free_hot_cold_page(page, 0);
  66 }
  67
  68 static 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
  77 static 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
 154 void 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 }
 161 EXPORT_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  */
 170 void 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 }
 180 EXPORT_SYMBOL(put_pages_list);
 181
 182 /*
 183  * pagevec_move_tail() must be called with IRQ disabled.
 184  * Otherwise this may cause nasty races.
 185  */
 186 static void pagevec_move_tail(struct pagevec *pvec)
 187 {
 188         int i;
 189         int pgmoved = 0;
 190         struct zone *zone = NULL;
 191
 192         for (i = 0; i < pagevec_count(pvec); i++) {
 193                 struct page *page = pvec->pages[i];
 194                 struct zone *pagezone = page_zone(page);
 195
 196                 if (pagezone != zone) {
 197                         if (zone)
 198                                 spin_unlock(&zone->lru_lock);
 199                         zone = pagezone;
 200                         spin_lock(&zone->lru_lock);
 201                 }
 202                 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
 203                         enum lru_list lru = page_lru_base_type(page);
 204                         list_move_tail(&page->lru, &zone->lru[lru].list);
 205                         mem_cgroup_rotate_reclaimable_page(page);
 206                         pgmoved++;
 207                 }
 208         }
 209         if (zone)
 210                 spin_unlock(&zone->lru_lock);
 211         __count_vm_events(PGROTATED, pgmoved);
 212         release_pages(pvec->pages, pvec->nr, pvec->cold);
 213         pagevec_reinit(pvec);
 214 }
 215
 216 /*
 217  * Writeback is about to end against a page which has been marked for immediate
 218  * reclaim.  If it still appears to be reclaimable, move it to the tail of the
 219  * inactive list.
 220  */
 221 void  rotate_reclaimable_page(struct page *page)
 222 {
 223         if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
 224             !PageUnevictable(page) && PageLRU(page)) {
 225                 struct pagevec *pvec;
 226                 unsigned long flags;
 227
 228                 page_cache_get(page);
 229                 local_irq_save(flags);
 230                 pvec = &__get_cpu_var(lru_rotate_pvecs);
 231                 if (!pagevec_add(pvec, page))
 232                         pagevec_move_tail(pvec);
 233                 local_irq_restore(flags);
 234         }
 235 }
 236
 237 static void update_page_reclaim_stat(struct zone *zone, struct page *page,
 238                                      int file, int rotated)
 239 {
 240         struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat;
 241         struct zone_reclaim_stat *memcg_reclaim_stat;
 242
 243         memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page);
 244
 245         reclaim_stat->recent_scanned[file]++;
 246         if (rotated)
 247                 reclaim_stat->recent_rotated[file]++;
 248
 249         if (!memcg_reclaim_stat)
 250                 return;
 251
 252         memcg_reclaim_stat->recent_scanned[file]++;
 253         if (rotated)
 254                 memcg_reclaim_stat->recent_rotated[file]++;
 255 }
 256
 257 /*
 258  * FIXME: speed this up?
 259  */
 260 void activate_page(struct page *page)
 261 {
 262         struct zone *zone = page_zone(page);
 263
 264         spin_lock_irq(&zone->lru_lock);
 265         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
 266                 int file = page_is_file_cache(page);
 267                 int lru = page_lru_base_type(page);
 268                 del_page_from_lru_list(zone, page, lru);
 269
 270                 SetPageActive(page);
 271                 lru += LRU_ACTIVE;
 272                 add_page_to_lru_list(zone, page, lru);
 273                 __count_vm_event(PGACTIVATE);
 274
 275                 update_page_reclaim_stat(zone, page, file, 1);
 276         }
 277         spin_unlock_irq(&zone->lru_lock);
 278 }
 279
 280 /*
 281  * Mark a page as having seen activity.
 282  *
 283  * inactive,unreferenced        ->      inactive,referenced
 284  * inactive,referenced          ->      active,unreferenced
 285  * active,unreferenced          ->      active,referenced
 286  */
 287 void mark_page_accessed(struct page *page)
 288 {
 289         if (!PageActive(page) && !PageUnevictable(page) &&
 290                         PageReferenced(page) && PageLRU(page)) {
 291                 activate_page(page);
 292                 ClearPageReferenced(page);
 293         } else if (!PageReferenced(page)) {
 294                 SetPageReferenced(page);
 295         }
 296 }
 297
 298 EXPORT_SYMBOL(mark_page_accessed);
 299
 300 void __lru_cache_add(struct page *page, enum lru_list lru)
 301 {
 302         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
 303
 304         page_cache_get(page);
 305         if (!pagevec_add(pvec, page))
 306                 ____pagevec_lru_add(pvec, lru);
 307         put_cpu_var(lru_add_pvecs);
 308 }
 309 EXPORT_SYMBOL(__lru_cache_add);
 310
 311 /**
 312  * lru_cache_add_lru - add a page to a page list
 313  * @page: the page to be added to the LRU.
 314  * @lru: the LRU list to which the page is added.
 315  */
 316 void lru_cache_add_lru(struct page *page, enum lru_list lru)
 317 {
 318         if (PageActive(page)) {
 319                 VM_BUG_ON(PageUnevictable(page));
 320                 ClearPageActive(page);
 321         } else if (PageUnevictable(page)) {
 322                 VM_BUG_ON(PageActive(page));
 323                 ClearPageUnevictable(page);
 324         }
 325
 326         VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
 327         __lru_cache_add(page, lru);
 328 }
 329
 330 /**
 331  * add_page_to_unevictable_list - add a page to the unevictable list
 332  * @page:  the page to be added to the unevictable list
 333  *
 334  * Add page directly to its zone's unevictable list.  To avoid races with
 335  * tasks that might be making the page evictable, through eg. munlock,
 336  * munmap or exit, while it's not on the lru, we want to add the page
 337  * while it's locked or otherwise "invisible" to other tasks.  This is
 338  * difficult to do when using the pagevec cache, so bypass that.
 339  */
 340 void add_page_to_unevictable_list(struct page *page)
 341 {
 342         struct zone *zone = page_zone(page);
 343
 344         spin_lock_irq(&zone->lru_lock);
 345         SetPageUnevictable(page);
 346         SetPageLRU(page);
 347         add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
 348         spin_unlock_irq(&zone->lru_lock);
 349 }
 350
 351 /*
 352  * If the page can not be invalidated, it is moved to the
 353  * inactive list to speed up its reclaim.  It is moved to the
 354  * head of the list, rather than the tail, to give the flusher
 355  * threads some time to write it out, as this is much more
 356  * effective than the single-page writeout from reclaim.
 357  *
 358  * If the page isn't page_mapped and dirty/writeback, the page
 359  * could reclaim asap using PG_reclaim.
 360  *
 361  * 1. active, mapped page -> none
 362  * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
 363  * 3. inactive, mapped page -> none
 364  * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
 365  * 5. inactive, clean -> inactive, tail
 366  * 6. Others -> none
 367  *
 368  * In 4, why it moves inactive's head, the VM expects the page would
 369  * be write it out by flusher threads as this is much more effective
 370  * than the single-page writeout from reclaim.
 371  */
 372 static void lru_deactivate(struct page *page, struct zone *zone)
 373 {
 374         int lru, file;
 375         bool active;
 376
 377         if (!PageLRU(page))
 378                 return;
 379
 380         /* Some processes are using the page */
 381         if (page_mapped(page))
 382                 return;
 383
 384         active = PageActive(page);
 385
 386         file = page_is_file_cache(page);
 387         lru = page_lru_base_type(page);
 388         del_page_from_lru_list(zone, page, lru + active);
 389         ClearPageActive(page);
 390         ClearPageReferenced(page);
 391         add_page_to_lru_list(zone, page, lru);
 392
 393         if (PageWriteback(page) || PageDirty(page)) {
 394                 /*
 395                  * PG_reclaim could be raced with end_page_writeback
 396                  * It can make readahead confusing.  But race window
 397                  * is _really_ small and  it's non-critical problem.
 398                  */
 399                 SetPageReclaim(page);
 400         } else {
 401                 /*
 402                  * The page's writeback ends up during pagevec
 403                  * We moves tha page into tail of inactive.
 404                  */
 405                 list_move_tail(&page->lru, &zone->lru[lru].list);
 406                 mem_cgroup_rotate_reclaimable_page(page);
 407                 __count_vm_event(PGROTATED);
 408         }
 409
 410         if (active)
 411                 __count_vm_event(PGDEACTIVATE);
 412         update_page_reclaim_stat(zone, page, file, 0);
 413 }
 414
 415 static void ____pagevec_lru_deactivate(struct pagevec *pvec)
 416 {
 417         int i;
 418         struct zone *zone = NULL;
 419
 420         for (i = 0; i < pagevec_count(pvec); i++) {
 421                 struct page *page = pvec->pages[i];
 422                 struct zone *pagezone = page_zone(page);
 423
 424                 if (pagezone != zone) {
 425                         if (zone)
 426                                 spin_unlock_irq(&zone->lru_lock);
 427                         zone = pagezone;
 428                         spin_lock_irq(&zone->lru_lock);
 429                 }
 430                 lru_deactivate(page, zone);
 431         }
 432         if (zone)
 433                 spin_unlock_irq(&zone->lru_lock);
 434
 435         release_pages(pvec->pages, pvec->nr, pvec->cold);
 436         pagevec_reinit(pvec);
 437 }
 438
 439
 440 /*
 441  * Drain pages out of the cpu's pagevecs.
 442  * Either "cpu" is the current CPU, and preemption has already been
 443  * disabled; or "cpu" is being hot-unplugged, and is already dead.
 444  */
 445 static void drain_cpu_pagevecs(int cpu)
 446 {
 447         struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
 448         struct pagevec *pvec;
 449         int lru;
 450
 451         for_each_lru(lru) {
 452                 pvec = &pvecs[lru - LRU_BASE];
 453                 if (pagevec_count(pvec))
 454                         ____pagevec_lru_add(pvec, lru);
 455         }
 456
 457         pvec = &per_cpu(lru_rotate_pvecs, cpu);
 458         if (pagevec_count(pvec)) {
 459                 unsigned long flags;
 460
 461                 /* No harm done if a racing interrupt already did this */
 462                 local_irq_save(flags);
 463                 pagevec_move_tail(pvec);
 464                 local_irq_restore(flags);
 465         }
 466
 467         pvec = &per_cpu(lru_deactivate_pvecs, cpu);
 468         if (pagevec_count(pvec))
 469                 ____pagevec_lru_deactivate(pvec);
 470 }
 471
 472 /**
 473  * deactivate_page - forcefully deactivate a page
 474  * @page: page to deactivate
 475  *
 476  * This function hints the VM that @page is a good reclaim candidate,
 477  * for example if its invalidation fails due to the page being dirty
 478  * or under writeback.
 479  */
 480 void deactivate_page(struct page *page)
 481 {
 482         if (likely(get_page_unless_zero(page))) {
 483                 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
 484
 485                 if (!pagevec_add(pvec, page))
 486                         ____pagevec_lru_deactivate(pvec);
 487                 put_cpu_var(lru_deactivate_pvecs);
 488         }
 489 }
 490
 491 void lru_add_drain(void)
 492 {
 493         drain_cpu_pagevecs(get_cpu());
 494         put_cpu();
 495 }
 496
 497 static void lru_add_drain_per_cpu(struct work_struct *dummy)
 498 {
 499         lru_add_drain();
 500 }
 501
 502 /*
 503  * Returns 0 for success
 504  */
 505 int lru_add_drain_all(void)
 506 {
 507         return schedule_on_each_cpu(lru_add_drain_per_cpu);
 508 }
 509
 510 /*
 511  * Batched page_cache_release().  Decrement the reference count on all the
 512  * passed pages.  If it fell to zero then remove the page from the LRU and
 513  * free it.
 514  *
 515  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
 516  * for the remainder of the operation.
 517  *
 518  * The locking in this function is against shrink_inactive_list(): we recheck
 519  * the page count inside the lock to see whether shrink_inactive_list()
 520  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
 521  * will free it.
 522  */
 523 void release_pages(struct page **pages, int nr, int cold)
 524 {
 525         int i;
 526         struct pagevec pages_to_free;
 527         struct zone *zone = NULL;
 528         unsigned long uninitialized_var(flags);
 529
 530         pagevec_init(&pages_to_free, cold);
 531         for (i = 0; i < nr; i++) {
 532                 struct page *page = pages[i];
 533
 534                 if (unlikely(PageCompound(page))) {
 535                         if (zone) {
 536                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 537                                 zone = NULL;
 538                         }
 539                         put_compound_page(page);
 540                         continue;
 541                 }
 542
 543                 if (!put_page_testzero(page))
 544                         continue;
 545
 546                 if (PageLRU(page)) {
 547                         struct zone *pagezone = page_zone(page);
 548
 549                         if (pagezone != zone) {
 550                                 if (zone)
 551                                         spin_unlock_irqrestore(&zone->lru_lock,
 552                                                                         flags);
 553                                 zone = pagezone;
 554                                 spin_lock_irqsave(&zone->lru_lock, flags);
 555                         }
 556                         VM_BUG_ON(!PageLRU(page));
 557                         __ClearPageLRU(page);
 558                         del_page_from_lru(zone, page);
 559                 }
 560
 561                 if (!pagevec_add(&pages_to_free, page)) {
 562                         if (zone) {
 563                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 564                                 zone = NULL;
 565                         }
 566                         __pagevec_free(&pages_to_free);
 567                         pagevec_reinit(&pages_to_free);
 568                 }
 569         }
 570         if (zone)
 571                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 572
 573         pagevec_free(&pages_to_free);
 574 }
 575 EXPORT_SYMBOL(release_pages);
 576
 577 /*
 578  * The pages which we're about to release may be in the deferred lru-addition
 579  * queues.  That would prevent them from really being freed right now.  That's
 580  * OK from a correctness point of view but is inefficient - those pages may be
 581  * cache-warm and we want to give them back to the page allocator ASAP.
 582  *
 583  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
 584  * and __pagevec_lru_add_active() call release_pages() directly to avoid
 585  * mutual recursion.
 586  */
 587 void __pagevec_release(struct pagevec *pvec)
 588 {
 589         lru_add_drain();
 590         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
 591         pagevec_reinit(pvec);
 592 }
 593
 594 EXPORT_SYMBOL(__pagevec_release);
 595
 596 /* used by __split_huge_page_refcount() */
 597 void lru_add_page_tail(struct zone* zone,
 598                        struct page *page, struct page *page_tail)
 599 {
 600         int active;
 601         enum lru_list lru;
 602         const int file = 0;
 603         struct list_head *head;
 604
 605         VM_BUG_ON(!PageHead(page));
 606         VM_BUG_ON(PageCompound(page_tail));
 607         VM_BUG_ON(PageLRU(page_tail));
 608         VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
 609
 610         SetPageLRU(page_tail);
 611
 612         if (page_evictable(page_tail, NULL)) {
 613                 if (PageActive(page)) {
 614                         SetPageActive(page_tail);
 615                         active = 1;
 616                         lru = LRU_ACTIVE_ANON;
 617                 } else {
 618                         active = 0;
 619                         lru = LRU_INACTIVE_ANON;
 620                 }
 621                 update_page_reclaim_stat(zone, page_tail, file, active);
 622                 if (likely(PageLRU(page)))
 623                         head = page->lru.prev;
 624                 else
 625                         head = &zone->lru[lru].list;
 626                 __add_page_to_lru_list(zone, page_tail, lru, head);
 627         } else {
 628                 SetPageUnevictable(page_tail);
 629                 add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
 630         }
 631 }
 632
 633 /*
 634  * Add the passed pages to the LRU, then drop the caller's refcount
 635  * on them.  Reinitialises the caller's pagevec.
 636  */
 637 void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
 638 {
 639         int i;
 640         struct zone *zone = NULL;
 641
 642         VM_BUG_ON(is_unevictable_lru(lru));
 643
 644         for (i = 0; i < pagevec_count(pvec); i++) {
 645                 struct page *page = pvec->pages[i];
 646                 struct zone *pagezone = page_zone(page);
 647                 int file;
 648                 int active;
 649
 650                 if (pagezone != zone) {
 651                         if (zone)
 652                                 spin_unlock_irq(&zone->lru_lock);
 653                         zone = pagezone;
 654                         spin_lock_irq(&zone->lru_lock);
 655                 }
 656                 VM_BUG_ON(PageActive(page));
 657                 VM_BUG_ON(PageUnevictable(page));
 658                 VM_BUG_ON(PageLRU(page));
 659                 SetPageLRU(page);
 660                 active = is_active_lru(lru);
 661                 file = is_file_lru(lru);
 662                 if (active)
 663                         SetPageActive(page);
 664                 update_page_reclaim_stat(zone, page, file, active);
 665                 add_page_to_lru_list(zone, page, lru);
 666         }
 667         if (zone)
 668                 spin_unlock_irq(&zone->lru_lock);
 669         release_pages(pvec->pages, pvec->nr, pvec->cold);
 670         pagevec_reinit(pvec);
 671 }
 672
 673 EXPORT_SYMBOL(____pagevec_lru_add);
 674
 675 /*
 676  * Try to drop buffers from the pages in a pagevec
 677  */
 678 void pagevec_strip(struct pagevec *pvec)
 679 {
 680         int i;
 681
 682         for (i = 0; i < pagevec_count(pvec); i++) {
 683                 struct page *page = pvec->pages[i];
 684
 685                 if (page_has_private(page) && trylock_page(page)) {
 686                         if (page_has_private(page))
 687                                 try_to_release_page(page, 0);
 688                         unlock_page(page);
 689                 }
 690         }
 691 }
 692
 693 /**
 694  * pagevec_lookup - gang pagecache lookup
 695  * @pvec:       Where the resulting pages are placed
 696  * @mapping:    The address_space to search
 697  * @start:      The starting page index
 698  * @nr_pages:   The maximum number of pages
 699  *
 700  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
 701  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
 702  * reference against the pages in @pvec.
 703  *
 704  * The search returns a group of mapping-contiguous pages with ascending
 705  * indexes.  There may be holes in the indices due to not-present pages.
 706  *
 707  * pagevec_lookup() returns the number of pages which were found.
 708  */
 709 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 710                 pgoff_t start, unsigned nr_pages)
 711 {
 712         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
 713         return pagevec_count(pvec);
 714 }
 715
 716 EXPORT_SYMBOL(pagevec_lookup);
 717
 718 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
 719                 pgoff_t *index, int tag, unsigned nr_pages)
 720 {
 721         pvec->nr = find_get_pages_tag(mapping, index, tag,
 722                                         nr_pages, pvec->pages);
 723         return pagevec_count(pvec);
 724 }
 725
 726 EXPORT_SYMBOL(pagevec_lookup_tag);
 727
 728 /*
 729  * Perform any setup for the swap system
 730  */
 731 void __init swap_setup(void)
 732 {
 733         unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
 734
 735 #ifdef CONFIG_SWAP
 736         bdi_init(swapper_space.backing_dev_info);
 737 #endif
 738
 739         /* Use a smaller cluster for small-memory machines */
 740         if (megs < 16)
 741                 page_cluster = 2;
 742         else
 743                 page_cluster = 3;
 744         /*
 745          * Right now other parts of the system means that we
 746          * _really_ don't want to cluster much more
 747          */
 748 }