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