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
  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                 unsigned long flags;
  51                 struct zone *zone = page_zone(page);
  52
  53                 spin_lock_irqsave(&zone->lru_lock, flags);
  54                 VM_BUG_ON(!PageLRU(page));
  55                 __ClearPageLRU(page);
  56                 del_page_from_lru(zone, page);
  57                 spin_unlock_irqrestore(&zone->lru_lock, flags);
  58         }
  59 }
  60
  61 static void __put_single_page(struct page *page)
  62 {
  63         __page_cache_release(page);
  64         free_hot_cold_page(page, 0);
  65 }
  66
  67 static void __put_compound_page(struct page *page)
  68 {
  69         compound_page_dtor *dtor;
  70
  71         __page_cache_release(page);
  72         dtor = get_compound_page_dtor(page);
  73         (*dtor)(page);
  74 }
  75
  76 static void put_compound_page(struct page *page)
  77 {
  78         if (unlikely(PageTail(page))) {
  79                 /* __split_huge_page_refcount can run under us */
  80                 struct page *page_head = page->first_page;
  81                 smp_rmb();
  82                 /*
  83                  * If PageTail is still set after smp_rmb() we can be sure
  84                  * that the page->first_page we read wasn't a dangling pointer.
  85                  * See __split_huge_page_refcount() smp_wmb().
  86                  */
  87                 if (likely(PageTail(page) && get_page_unless_zero(page_head))) {
  88                         unsigned long flags;
  89                         /*
  90                          * Verify that our page_head wasn't converted
  91                          * to a a regular page before we got a
  92                          * reference on it.
  93                          */
  94                         if (unlikely(!PageHead(page_head))) {
  95                                 /* PageHead is cleared after PageTail */
  96                                 smp_rmb();
  97                                 VM_BUG_ON(PageTail(page));
  98                                 goto out_put_head;
  99                         }
 100                         /*
 101                          * Only run compound_lock on a valid PageHead,
 102                          * after having it pinned with
 103                          * get_page_unless_zero() above.
 104                          */
 105                         smp_mb();
 106                         /* page_head wasn't a dangling pointer */
 107                         flags = compound_lock_irqsave(page_head);
 108                         if (unlikely(!PageTail(page))) {
 109                                 /* __split_huge_page_refcount run before us */
 110                                 compound_unlock_irqrestore(page_head, flags);
 111                                 VM_BUG_ON(PageHead(page_head));
 112                         out_put_head:
 113                                 if (put_page_testzero(page_head))
 114                                         __put_single_page(page_head);
 115                         out_put_single:
 116                                 if (put_page_testzero(page))
 117                                         __put_single_page(page);
 118                                 return;
 119                         }
 120                         VM_BUG_ON(page_head != page->first_page);
 121                         /*
 122                          * We can release the refcount taken by
 123                          * get_page_unless_zero now that
 124                          * split_huge_page_refcount is blocked on the
 125                          * compound_lock.
 126                          */
 127                         if (put_page_testzero(page_head))
 128                                 VM_BUG_ON(1);
 129                         /* __split_huge_page_refcount will wait now */
 130                         VM_BUG_ON(atomic_read(&page->_count) <= 0);
 131                         atomic_dec(&page->_count);
 132                         VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
 133                         compound_unlock_irqrestore(page_head, flags);
 134                         if (put_page_testzero(page_head)) {
 135                                 if (PageHead(page_head))
 136                                         __put_compound_page(page_head);
 137                                 else
 138                                         __put_single_page(page_head);
 139                         }
 140                 } else {
 141                         /* page_head is a dangling pointer */
 142                         VM_BUG_ON(PageTail(page));
 143                         goto out_put_single;
 144                 }
 145         } else if (put_page_testzero(page)) {
 146                 if (PageHead(page))
 147                         __put_compound_page(page);
 148                 else
 149                         __put_single_page(page);
 150         }
 151 }
 152
 153 void put_page(struct page *page)
 154 {
 155         if (unlikely(PageCompound(page)))
 156                 put_compound_page(page);
 157         else if (put_page_testzero(page))
 158                 __put_single_page(page);
 159 }
 160 EXPORT_SYMBOL(put_page);
 161
 162 /**
 163  * put_pages_list() - release a list of pages
 164  * @pages: list of pages threaded on page->lru
 165  *
 166  * Release a list of pages which are strung together on page.lru.  Currently
 167  * used by read_cache_pages() and related error recovery code.
 168  */
 169 void put_pages_list(struct list_head *pages)
 170 {
 171         while (!list_empty(pages)) {
 172                 struct page *victim;
 173
 174                 victim = list_entry(pages->prev, struct page, lru);
 175                 list_del(&victim->lru);
 176                 page_cache_release(victim);
 177         }
 178 }
 179 EXPORT_SYMBOL(put_pages_list);
 180
 181 static void pagevec_lru_move_fn(struct pagevec *pvec,
 182                                 void (*move_fn)(struct page *page, void *arg),
 183                                 void *arg)
 184 {
 185         int i;
 186         struct zone *zone = NULL;
 187         unsigned long flags = 0;
 188
 189         for (i = 0; i < pagevec_count(pvec); i++) {
 190                 struct page *page = pvec->pages[i];
 191                 struct zone *pagezone = page_zone(page);
 192
 193                 if (pagezone != zone) {
 194                         if (zone)
 195                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 196                         zone = pagezone;
 197                         spin_lock_irqsave(&zone->lru_lock, flags);
 198                 }
 199
 200                 (*move_fn)(page, arg);
 201         }
 202         if (zone)
 203                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 204         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
 205         pagevec_reinit(pvec);
 206 }
 207
 208 static void pagevec_move_tail_fn(struct page *page, void *arg)
 209 {
 210         int *pgmoved = arg;
 211         struct zone *zone = page_zone(page);
 212
 213         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
 214                 int lru = page_lru_base_type(page);
 215                 list_move_tail(&page->lru, &zone->lru[lru].list);
 216                 (*pgmoved)++;
 217         }
 218 }
 219
 220 /*
 221  * pagevec_move_tail() must be called with IRQ disabled.
 222  * Otherwise this may cause nasty races.
 223  */
 224 static void pagevec_move_tail(struct pagevec *pvec)
 225 {
 226         int pgmoved = 0;
 227
 228         pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
 229         __count_vm_events(PGROTATED, pgmoved);
 230 }
 231
 232 /*
 233  * Writeback is about to end against a page which has been marked for immediate
 234  * reclaim.  If it still appears to be reclaimable, move it to the tail of the
 235  * inactive list.
 236  */
 237 void rotate_reclaimable_page(struct page *page)
 238 {
 239         if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
 240             !PageUnevictable(page) && PageLRU(page)) {
 241                 struct pagevec *pvec;
 242                 unsigned long flags;
 243
 244                 page_cache_get(page);
 245                 local_irq_save(flags);
 246                 pvec = &__get_cpu_var(lru_rotate_pvecs);
 247                 if (!pagevec_add(pvec, page))
 248                         pagevec_move_tail(pvec);
 249                 local_irq_restore(flags);
 250         }
 251 }
 252
 253 static void update_page_reclaim_stat(struct zone *zone, struct page *page,
 254                                      int file, int rotated)
 255 {
 256         struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat;
 257         struct zone_reclaim_stat *memcg_reclaim_stat;
 258
 259         memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page);
 260
 261         reclaim_stat->recent_scanned[file]++;
 262         if (rotated)
 263                 reclaim_stat->recent_rotated[file]++;
 264
 265         if (!memcg_reclaim_stat)
 266                 return;
 267
 268         memcg_reclaim_stat->recent_scanned[file]++;
 269         if (rotated)
 270                 memcg_reclaim_stat->recent_rotated[file]++;
 271 }
 272
 273 /*
 274  * A page will go to active list either by activate_page or putback_lru_page.
 275  * In the activate_page case, the page hasn't active bit set. The page might
 276  * not in LRU list because it's isolated before it gets a chance to be moved to
 277  * active list. The window is small because pagevec just stores several pages.
 278  * For such case, we do nothing for such page.
 279  * In the putback_lru_page case, the page isn't in lru list but has active
 280  * bit set
 281  */
 282 static void __activate_page(struct page *page, void *arg)
 283 {
 284         struct zone *zone = page_zone(page);
 285         int file = page_is_file_cache(page);
 286         int lru = page_lru_base_type(page);
 287         bool putback = !PageLRU(page);
 288
 289         /* The page is isolated before it's moved to active list */
 290         if (!PageLRU(page) && !PageActive(page))
 291                 return;
 292         if ((PageLRU(page) && PageActive(page)) || PageUnevictable(page))
 293                 return;
 294
 295         if (!putback)
 296                 del_page_from_lru_list(zone, page, lru);
 297         else
 298                 SetPageLRU(page);
 299
 300         SetPageActive(page);
 301         lru += LRU_ACTIVE;
 302         add_page_to_lru_list(zone, page, lru);
 303
 304         if (putback)
 305                 return;
 306         __count_vm_event(PGACTIVATE);
 307         update_page_reclaim_stat(zone, page, file, 1);
 308 }
 309
 310 #ifdef CONFIG_SMP
 311 static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
 312
 313 static void activate_page_drain(int cpu)
 314 {
 315         struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
 316
 317         if (pagevec_count(pvec))
 318                 pagevec_lru_move_fn(pvec, __activate_page, NULL);
 319 }
 320
 321 void activate_page(struct page *page)
 322 {
 323         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
 324                 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
 325
 326                 page_cache_get(page);
 327                 if (!pagevec_add(pvec, page))
 328                         pagevec_lru_move_fn(pvec, __activate_page, NULL);
 329                 put_cpu_var(activate_page_pvecs);
 330         }
 331 }
 332
 333 /* Caller should hold zone->lru_lock */
 334 int putback_active_lru_page(struct zone *zone, struct page *page)
 335 {
 336         struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
 337
 338         if (!pagevec_add(pvec, page)) {
 339                 spin_unlock_irq(&zone->lru_lock);
 340                 pagevec_lru_move_fn(pvec, __activate_page, NULL);
 341                 spin_lock_irq(&zone->lru_lock);
 342         }
 343         put_cpu_var(activate_page_pvecs);
 344         return 1;
 345 }
 346
 347 #else
 348 static inline void activate_page_drain(int cpu)
 349 {
 350 }
 351
 352 void activate_page(struct page *page)
 353 {
 354         struct zone *zone = page_zone(page);
 355
 356         spin_lock_irq(&zone->lru_lock);
 357         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page))
 358                 __activate_page(page, NULL);
 359         spin_unlock_irq(&zone->lru_lock);
 360 }
 361 #endif
 362
 363 /*
 364  * Mark a page as having seen activity.
 365  *
 366  * inactive,unreferenced        ->      inactive,referenced
 367  * inactive,referenced          ->      active,unreferenced
 368  * active,unreferenced          ->      active,referenced
 369  */
 370 void mark_page_accessed(struct page *page)
 371 {
 372         if (!PageActive(page) && !PageUnevictable(page) &&
 373                         PageReferenced(page) && PageLRU(page)) {
 374                 activate_page(page);
 375                 ClearPageReferenced(page);
 376         } else if (!PageReferenced(page)) {
 377                 SetPageReferenced(page);
 378         }
 379 }
 380
 381 EXPORT_SYMBOL(mark_page_accessed);
 382
 383 void __lru_cache_add(struct page *page, enum lru_list lru)
 384 {
 385         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
 386
 387         page_cache_get(page);
 388         if (!pagevec_add(pvec, page))
 389                 ____pagevec_lru_add(pvec, lru);
 390         put_cpu_var(lru_add_pvecs);
 391 }
 392 EXPORT_SYMBOL(__lru_cache_add);
 393
 394 /**
 395  * lru_cache_add_lru - add a page to a page list
 396  * @page: the page to be added to the LRU.
 397  * @lru: the LRU list to which the page is added.
 398  */
 399 void lru_cache_add_lru(struct page *page, enum lru_list lru)
 400 {
 401         if (PageActive(page)) {
 402                 VM_BUG_ON(PageUnevictable(page));
 403                 ClearPageActive(page);
 404         } else if (PageUnevictable(page)) {
 405                 VM_BUG_ON(PageActive(page));
 406                 ClearPageUnevictable(page);
 407         }
 408
 409         VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
 410         __lru_cache_add(page, lru);
 411 }
 412
 413 /**
 414  * add_page_to_unevictable_list - add a page to the unevictable list
 415  * @page:  the page to be added to the unevictable list
 416  *
 417  * Add page directly to its zone's unevictable list.  To avoid races with
 418  * tasks that might be making the page evictable, through eg. munlock,
 419  * munmap or exit, while it's not on the lru, we want to add the page
 420  * while it's locked or otherwise "invisible" to other tasks.  This is
 421  * difficult to do when using the pagevec cache, so bypass that.
 422  */
 423 void add_page_to_unevictable_list(struct page *page)
 424 {
 425         struct zone *zone = page_zone(page);
 426
 427         spin_lock_irq(&zone->lru_lock);
 428         SetPageUnevictable(page);
 429         SetPageLRU(page);
 430         add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
 431         spin_unlock_irq(&zone->lru_lock);
 432 }
 433
 434 /*
 435  * Drain pages out of the cpu's pagevecs.
 436  * Either "cpu" is the current CPU, and preemption has already been
 437  * disabled; or "cpu" is being hot-unplugged, and is already dead.
 438  */
 439 static void drain_cpu_pagevecs(int cpu)
 440 {
 441         struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
 442         struct pagevec *pvec;
 443         int lru;
 444
 445         for_each_lru(lru) {
 446                 pvec = &pvecs[lru - LRU_BASE];
 447                 if (pagevec_count(pvec))
 448                         ____pagevec_lru_add(pvec, lru);
 449         }
 450
 451         pvec = &per_cpu(lru_rotate_pvecs, cpu);
 452         if (pagevec_count(pvec)) {
 453                 unsigned long flags;
 454
 455                 /* No harm done if a racing interrupt already did this */
 456                 local_irq_save(flags);
 457                 pagevec_move_tail(pvec);
 458                 local_irq_restore(flags);
 459         }
 460         activate_page_drain(cpu);
 461 }
 462
 463 void lru_add_drain(void)
 464 {
 465         drain_cpu_pagevecs(get_cpu());
 466         put_cpu();
 467 }
 468
 469 static void lru_add_drain_per_cpu(struct work_struct *dummy)
 470 {
 471         lru_add_drain();
 472 }
 473
 474 /*
 475  * Returns 0 for success
 476  */
 477 int lru_add_drain_all(void)
 478 {
 479         return schedule_on_each_cpu(lru_add_drain_per_cpu);
 480 }
 481
 482 /*
 483  * Batched page_cache_release().  Decrement the reference count on all the
 484  * passed pages.  If it fell to zero then remove the page from the LRU and
 485  * free it.
 486  *
 487  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
 488  * for the remainder of the operation.
 489  *
 490  * The locking in this function is against shrink_inactive_list(): we recheck
 491  * the page count inside the lock to see whether shrink_inactive_list()
 492  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
 493  * will free it.
 494  */
 495 void release_pages(struct page **pages, int nr, int cold)
 496 {
 497         int i;
 498         struct pagevec pages_to_free;
 499         struct zone *zone = NULL;
 500         unsigned long uninitialized_var(flags);
 501
 502         pagevec_init(&pages_to_free, cold);
 503         for (i = 0; i < nr; i++) {
 504                 struct page *page = pages[i];
 505
 506                 if (unlikely(PageCompound(page))) {
 507                         if (zone) {
 508                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 509                                 zone = NULL;
 510                         }
 511                         put_compound_page(page);
 512                         continue;
 513                 }
 514
 515                 if (!put_page_testzero(page))
 516                         continue;
 517
 518                 if (PageLRU(page)) {
 519                         struct zone *pagezone = page_zone(page);
 520
 521                         if (pagezone != zone) {
 522                                 if (zone)
 523                                         spin_unlock_irqrestore(&zone->lru_lock,
 524                                                                         flags);
 525                                 zone = pagezone;
 526                                 spin_lock_irqsave(&zone->lru_lock, flags);
 527                         }
 528                         VM_BUG_ON(!PageLRU(page));
 529                         __ClearPageLRU(page);
 530                         del_page_from_lru(zone, page);
 531                 }
 532
 533                 if (!pagevec_add(&pages_to_free, page)) {
 534                         if (zone) {
 535                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 536                                 zone = NULL;
 537                         }
 538                         __pagevec_free(&pages_to_free);
 539                         pagevec_reinit(&pages_to_free);
 540                 }
 541         }
 542         if (zone)
 543                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 544
 545         pagevec_free(&pages_to_free);
 546 }
 547 EXPORT_SYMBOL(release_pages);
 548
 549 /*
 550  * The pages which we're about to release may be in the deferred lru-addition
 551  * queues.  That would prevent them from really being freed right now.  That's
 552  * OK from a correctness point of view but is inefficient - those pages may be
 553  * cache-warm and we want to give them back to the page allocator ASAP.
 554  *
 555  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
 556  * and __pagevec_lru_add_active() call release_pages() directly to avoid
 557  * mutual recursion.
 558  */
 559 void __pagevec_release(struct pagevec *pvec)
 560 {
 561         lru_add_drain();
 562         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
 563         pagevec_reinit(pvec);
 564 }
 565
 566 EXPORT_SYMBOL(__pagevec_release);
 567
 568 /* used by __split_huge_page_refcount() */
 569 void lru_add_page_tail(struct zone* zone,
 570                        struct page *page, struct page *page_tail)
 571 {
 572         int active;
 573         enum lru_list lru;
 574         const int file = 0;
 575         struct list_head *head;
 576
 577         VM_BUG_ON(!PageHead(page));
 578         VM_BUG_ON(PageCompound(page_tail));
 579         VM_BUG_ON(PageLRU(page_tail));
 580         VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
 581
 582         SetPageLRU(page_tail);
 583
 584         if (page_evictable(page_tail, NULL)) {
 585                 if (PageActive(page)) {
 586                         SetPageActive(page_tail);
 587                         active = 1;
 588                         lru = LRU_ACTIVE_ANON;
 589                 } else {
 590                         active = 0;
 591                         lru = LRU_INACTIVE_ANON;
 592                 }
 593                 update_page_reclaim_stat(zone, page_tail, file, active);
 594                 if (likely(PageLRU(page)))
 595                         head = page->lru.prev;
 596                 else
 597                         head = &zone->lru[lru].list;
 598                 __add_page_to_lru_list(zone, page_tail, lru, head);
 599         } else {
 600                 SetPageUnevictable(page_tail);
 601                 add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
 602         }
 603 }
 604
 605 static void ____pagevec_lru_add_fn(struct page *page, void *arg)
 606 {
 607         enum lru_list lru = (enum lru_list)arg;
 608         struct zone *zone = page_zone(page);
 609         int file = is_file_lru(lru);
 610         int active = is_active_lru(lru);
 611
 612         VM_BUG_ON(PageActive(page));
 613         VM_BUG_ON(PageUnevictable(page));
 614         VM_BUG_ON(PageLRU(page));
 615
 616         SetPageLRU(page);
 617         if (active)
 618                 SetPageActive(page);
 619         update_page_reclaim_stat(zone, page, file, active);
 620         add_page_to_lru_list(zone, page, lru);
 621 }
 622
 623 /*
 624  * Add the passed pages to the LRU, then drop the caller's refcount
 625  * on them.  Reinitialises the caller's pagevec.
 626  */
 627 void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
 628 {
 629         VM_BUG_ON(is_unevictable_lru(lru));
 630
 631         pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
 632 }
 633
 634 EXPORT_SYMBOL(____pagevec_lru_add);
 635
 636 /*
 637  * Try to drop buffers from the pages in a pagevec
 638  */
 639 void pagevec_strip(struct pagevec *pvec)
 640 {
 641         int i;
 642
 643         for (i = 0; i < pagevec_count(pvec); i++) {
 644                 struct page *page = pvec->pages[i];
 645
 646                 if (page_has_private(page) && trylock_page(page)) {
 647                         if (page_has_private(page))
 648                                 try_to_release_page(page, 0);
 649                         unlock_page(page);
 650                 }
 651         }
 652 }
 653
 654 /**
 655  * pagevec_lookup - gang pagecache lookup
 656  * @pvec:       Where the resulting pages are placed
 657  * @mapping:    The address_space to search
 658  * @start:      The starting page index
 659  * @nr_pages:   The maximum number of pages
 660  *
 661  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
 662  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
 663  * reference against the pages in @pvec.
 664  *
 665  * The search returns a group of mapping-contiguous pages with ascending
 666  * indexes.  There may be holes in the indices due to not-present pages.
 667  *
 668  * pagevec_lookup() returns the number of pages which were found.
 669  */
 670 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 671                 pgoff_t start, unsigned nr_pages)
 672 {
 673         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
 674         return pagevec_count(pvec);
 675 }
 676
 677 EXPORT_SYMBOL(pagevec_lookup);
 678
 679 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
 680                 pgoff_t *index, int tag, unsigned nr_pages)
 681 {
 682         pvec->nr = find_get_pages_tag(mapping, index, tag,
 683                                         nr_pages, pvec->pages);
 684         return pagevec_count(pvec);
 685 }
 686
 687 EXPORT_SYMBOL(pagevec_lookup_tag);
 688
 689 /*
 690  * Perform any setup for the swap system
 691  */
 692 void __init swap_setup(void)
 693 {
 694         unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
 695
 696 #ifdef CONFIG_SWAP
 697         bdi_init(swapper_space.backing_dev_info);
 698 #endif
 699
 700         /* Use a smaller cluster for small-memory machines */
 701         if (megs < 16)
 702                 page_cluster = 2;
 703         else
 704                 page_cluster = 3;
 705         /*
 706          * Right now other parts of the system means that we
 707          * _really_ don't want to cluster much more
 708          */
 709 }