mm/vmscan.c

   1 /*
   2  *  linux/mm/vmscan.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5  *
   6  *  Swap reorganised 29.12.95, Stephen Tweedie.
   7  *  kswapd added: 7.1.96  sct
   8  *  Removed kswapd_ctl limits, and swap out as many pages as needed
   9  *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
  10  *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
  11  *  Multiqueue VM started 5.8.00, Rik van Riel.
  12  */
  13
  14 #include <linux/mm.h>
  15 #include <linux/module.h>
  16 #include <linux/slab.h>
  17 #include <linux/kernel_stat.h>
  18 #include <linux/swap.h>
  19 #include <linux/pagemap.h>
  20 #include <linux/init.h>
  21 #include <linux/highmem.h>
  22 #include <linux/file.h>
  23 #include <linux/writeback.h>
  24 #include <linux/blkdev.h>
  25 #include <linux/buffer_head.h>  /* for try_to_release_page(),
  26                                         buffer_heads_over_limit */
  27 #include <linux/mm_inline.h>
  28 #include <linux/pagevec.h>
  29 #include <linux/backing-dev.h>
  30 #include <linux/rmap.h>
  31 #include <linux/topology.h>
  32 #include <linux/cpu.h>
  33 #include <linux/cpuset.h>
  34 #include <linux/notifier.h>
  35 #include <linux/rwsem.h>
  36
  37 #include <asm/tlbflush.h>
  38 #include <asm/div64.h>
  39
  40 #include <linux/swapops.h>
  41
  42 /* possible outcome of pageout() */
  43 typedef enum {
  44         /* failed to write page out, page is locked */
  45         PAGE_KEEP,
  46         /* move page to the active list, page is locked */
  47         PAGE_ACTIVATE,
  48         /* page has been sent to the disk successfully, page is unlocked */
  49         PAGE_SUCCESS,
  50         /* page is clean and locked */
  51         PAGE_CLEAN,
  52 } pageout_t;
  53
  54 struct scan_control {
  55         /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
  56         unsigned long nr_to_scan;
  57
  58         /* Incremented by the number of inactive pages that were scanned */
  59         unsigned long nr_scanned;
  60
  61         /* Incremented by the number of pages reclaimed */
  62         unsigned long nr_reclaimed;
  63
  64         unsigned long nr_mapped;        /* From page_state */
  65
  66         /* How many pages shrink_cache() should reclaim */
  67         int nr_to_reclaim;
  68
  69         /* Ask shrink_caches, or shrink_zone to scan at this priority */
  70         unsigned int priority;
  71
  72         /* This context's GFP mask */
  73         unsigned int gfp_mask;
  74
  75         int may_writepage;
  76
  77         /* This context's SWAP_CLUSTER_MAX. If freeing memory for
  78          * suspend, we effectively ignore SWAP_CLUSTER_MAX.
  79          * In this context, it doesn't matter that we scan the
  80          * whole list at once. */
  81         int swap_cluster_max;
  82 };
  83
  84 /*
  85  * The list of shrinker callbacks used by to apply pressure to
  86  * ageable caches.
  87  */
  88 struct shrinker {
  89         shrinker_t              shrinker;
  90         struct list_head        list;
  91         int                     seeks;  /* seeks to recreate an obj */
  92         long                    nr;     /* objs pending delete */
  93 };
  94
  95 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  96
  97 #ifdef ARCH_HAS_PREFETCH
  98 #define prefetch_prev_lru_page(_page, _base, _field)                    \
  99         do {                                                            \
 100                 if ((_page)->lru.prev != _base) {                       \
 101                         struct page *prev;                              \
 102                                                                         \
 103                         prev = lru_to_page(&(_page->lru));              \
 104                         prefetch(&prev->_field);                        \
 105                 }                                                       \
 106         } while (0)
 107 #else
 108 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
 109 #endif
 110
 111 #ifdef ARCH_HAS_PREFETCHW
 112 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
 113         do {                                                            \
 114                 if ((_page)->lru.prev != _base) {                       \
 115                         struct page *prev;                              \
 116                                                                         \
 117                         prev = lru_to_page(&(_page->lru));              \
 118                         prefetchw(&prev->_field);                       \
 119                 }                                                       \
 120         } while (0)
 121 #else
 122 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 123 #endif
 124
 125 /*
 126  * From 0 .. 100.  Higher means more swappy.
 127  */
 128 int vm_swappiness = 60;
 129 static long total_memory;
 130
 131 static LIST_HEAD(shrinker_list);
 132 static DECLARE_RWSEM(shrinker_rwsem);
 133
 134 /*
 135  * Add a shrinker callback to be called from the vm
 136  */
 137 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
 138 {
 139         struct shrinker *shrinker;
 140
 141         shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
 142         if (shrinker) {
 143                 shrinker->shrinker = theshrinker;
 144                 shrinker->seeks = seeks;
 145                 shrinker->nr = 0;
 146                 down_write(&shrinker_rwsem);
 147                 list_add_tail(&shrinker->list, &shrinker_list);
 148                 up_write(&shrinker_rwsem);
 149         }
 150         return shrinker;
 151 }
 152 EXPORT_SYMBOL(set_shrinker);
 153
 154 /*
 155  * Remove one
 156  */
 157 void remove_shrinker(struct shrinker *shrinker)
 158 {
 159         down_write(&shrinker_rwsem);
 160         list_del(&shrinker->list);
 161         up_write(&shrinker_rwsem);
 162         kfree(shrinker);
 163 }
 164 EXPORT_SYMBOL(remove_shrinker);
 165
 166 #define SHRINK_BATCH 128
 167 /*
 168  * Call the shrink functions to age shrinkable caches
 169  *
 170  * Here we assume it costs one seek to replace a lru page and that it also
 171  * takes a seek to recreate a cache object.  With this in mind we age equal
 172  * percentages of the lru and ageable caches.  This should balance the seeks
 173  * generated by these structures.
 174  *
 175  * If the vm encounted mapped pages on the LRU it increase the pressure on
 176  * slab to avoid swapping.
 177  *
 178  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 179  *
 180  * `lru_pages' represents the number of on-LRU pages in all the zones which
 181  * are eligible for the caller's allocation attempt.  It is used for balancing
 182  * slab reclaim versus page reclaim.
 183  */
 184 static int shrink_slab(unsigned long scanned, unsigned int gfp_mask,
 185                         unsigned long lru_pages)
 186 {
 187         struct shrinker *shrinker;
 188
 189         if (scanned == 0)
 190                 scanned = SWAP_CLUSTER_MAX;
 191
 192         if (!down_read_trylock(&shrinker_rwsem))
 193                 return 0;
 194
 195         list_for_each_entry(shrinker, &shrinker_list, list) {
 196                 unsigned long long delta;
 197                 unsigned long total_scan;
 198
 199                 delta = (4 * scanned) / shrinker->seeks;
 200                 delta *= (*shrinker->shrinker)(0, gfp_mask);
 201                 do_div(delta, lru_pages + 1);
 202                 shrinker->nr += delta;
 203                 if (shrinker->nr < 0)
 204                         shrinker->nr = LONG_MAX;        /* It wrapped! */
 205
 206                 total_scan = shrinker->nr;
 207                 shrinker->nr = 0;
 208
 209                 while (total_scan >= SHRINK_BATCH) {
 210                         long this_scan = SHRINK_BATCH;
 211                         int shrink_ret;
 212
 213                         shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
 214                         if (shrink_ret == -1)
 215                                 break;
 216                         mod_page_state(slabs_scanned, this_scan);
 217                         total_scan -= this_scan;
 218
 219                         cond_resched();
 220                 }
 221
 222                 shrinker->nr += total_scan;
 223         }
 224         up_read(&shrinker_rwsem);
 225         return 0;
 226 }
 227
 228 /* Called without lock on whether page is mapped, so answer is unstable */
 229 static inline int page_mapping_inuse(struct page *page)
 230 {
 231         struct address_space *mapping;
 232
 233         /* Page is in somebody's page tables. */
 234         if (page_mapped(page))
 235                 return 1;
 236
 237         /* Be more reluctant to reclaim swapcache than pagecache */
 238         if (PageSwapCache(page))
 239                 return 1;
 240
 241         mapping = page_mapping(page);
 242         if (!mapping)
 243                 return 0;
 244
 245         /* File is mmap'd by somebody? */
 246         return mapping_mapped(mapping);
 247 }
 248
 249 static inline int is_page_cache_freeable(struct page *page)
 250 {
 251         return page_count(page) - !!PagePrivate(page) == 2;
 252 }
 253
 254 static int may_write_to_queue(struct backing_dev_info *bdi)
 255 {
 256         if (current_is_kswapd())
 257                 return 1;
 258         if (current_is_pdflush())       /* This is unlikely, but why not... */
 259                 return 1;
 260         if (!bdi_write_congested(bdi))
 261                 return 1;
 262         if (bdi == current->backing_dev_info)
 263                 return 1;
 264         return 0;
 265 }
 266
 267 /*
 268  * We detected a synchronous write error writing a page out.  Probably
 269  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 270  * fsync(), msync() or close().
 271  *
 272  * The tricky part is that after writepage we cannot touch the mapping: nothing
 273  * prevents it from being freed up.  But we have a ref on the page and once
 274  * that page is locked, the mapping is pinned.
 275  *
 276  * We're allowed to run sleeping lock_page() here because we know the caller has
 277  * __GFP_FS.
 278  */
 279 static void handle_write_error(struct address_space *mapping,
 280                                 struct page *page, int error)
 281 {
 282         lock_page(page);
 283         if (page_mapping(page) == mapping) {
 284                 if (error == -ENOSPC)
 285                         set_bit(AS_ENOSPC, &mapping->flags);
 286                 else
 287                         set_bit(AS_EIO, &mapping->flags);
 288         }
 289         unlock_page(page);
 290 }
 291
 292 /*
 293  * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
 294  */
 295 static pageout_t pageout(struct page *page, struct address_space *mapping)
 296 {
 297         /*
 298          * If the page is dirty, only perform writeback if that write
 299          * will be non-blocking.  To prevent this allocation from being
 300          * stalled by pagecache activity.  But note that there may be
 301          * stalls if we need to run get_block().  We could test
 302          * PagePrivate for that.
 303          *
 304          * If this process is currently in generic_file_write() against
 305          * this page's queue, we can perform writeback even if that
 306          * will block.
 307          *
 308          * If the page is swapcache, write it back even if that would
 309          * block, for some throttling. This happens by accident, because
 310          * swap_backing_dev_info is bust: it doesn't reflect the
 311          * congestion state of the swapdevs.  Easy to fix, if needed.
 312          * See swapfile.c:page_queue_congested().
 313          */
 314         if (!is_page_cache_freeable(page))
 315                 return PAGE_KEEP;
 316         if (!mapping) {
 317                 /*
 318                  * Some data journaling orphaned pages can have
 319                  * page->mapping == NULL while being dirty with clean buffers.
 320                  */
 321                 if (PagePrivate(page)) {
 322                         if (try_to_free_buffers(page)) {
 323                                 ClearPageDirty(page);
 324                                 printk("%s: orphaned page\n", __FUNCTION__);
 325                                 return PAGE_CLEAN;
 326                         }
 327                 }
 328                 return PAGE_KEEP;
 329         }
 330         if (mapping->a_ops->writepage == NULL)
 331                 return PAGE_ACTIVATE;
 332         if (!may_write_to_queue(mapping->backing_dev_info))
 333                 return PAGE_KEEP;
 334
 335         if (clear_page_dirty_for_io(page)) {
 336                 int res;
 337                 struct writeback_control wbc = {
 338                         .sync_mode = WB_SYNC_NONE,
 339                         .nr_to_write = SWAP_CLUSTER_MAX,
 340                         .nonblocking = 1,
 341                         .for_reclaim = 1,
 342                 };
 343
 344                 SetPageReclaim(page);
 345                 res = mapping->a_ops->writepage(page, &wbc);
 346                 if (res < 0)
 347                         handle_write_error(mapping, page, res);
 348                 if (res == WRITEPAGE_ACTIVATE) {
 349                         ClearPageReclaim(page);
 350                         return PAGE_ACTIVATE;
 351                 }
 352                 if (!PageWriteback(page)) {
 353                         /* synchronous write or broken a_ops? */
 354                         ClearPageReclaim(page);
 355                 }
 356
 357                 return PAGE_SUCCESS;
 358         }
 359
 360         return PAGE_CLEAN;
 361 }
 362
 363 /*
 364  * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
 365  */
 366 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
 367 {
 368         LIST_HEAD(ret_pages);
 369         struct pagevec freed_pvec;
 370         int pgactivate = 0;
 371         int reclaimed = 0;
 372
 373         cond_resched();
 374
 375         pagevec_init(&freed_pvec, 1);
 376         while (!list_empty(page_list)) {
 377                 struct address_space *mapping;
 378                 struct page *page;
 379                 int may_enter_fs;
 380                 int referenced;
 381
 382                 cond_resched();
 383
 384                 page = lru_to_page(page_list);
 385                 list_del(&page->lru);
 386
 387                 if (TestSetPageLocked(page))
 388                         goto keep;
 389
 390                 BUG_ON(PageActive(page));
 391
 392                 sc->nr_scanned++;
 393                 /* Double the slab pressure for mapped and swapcache pages */
 394                 if (page_mapped(page) || PageSwapCache(page))
 395                         sc->nr_scanned++;
 396
 397                 if (PageWriteback(page))
 398                         goto keep_locked;
 399
 400                 referenced = page_referenced(page, 1, sc->priority <= 0);
 401                 /* In active use or really unfreeable?  Activate it. */
 402                 if (referenced && page_mapping_inuse(page))
 403                         goto activate_locked;
 404
 405 #ifdef CONFIG_SWAP
 406                 /*
 407                  * Anonymous process memory has backing store?
 408                  * Try to allocate it some swap space here.
 409                  */
 410                 if (PageAnon(page) && !PageSwapCache(page)) {
 411                         if (!add_to_swap(page))
 412                                 goto activate_locked;
 413                 }
 414 #endif /* CONFIG_SWAP */
 415
 416                 mapping = page_mapping(page);
 417                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 418                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 419
 420                 /*
 421                  * The page is mapped into the page tables of one or more
 422                  * processes. Try to unmap it here.
 423                  */
 424                 if (page_mapped(page) && mapping) {
 425                         switch (try_to_unmap(page)) {
 426                         case SWAP_FAIL:
 427                                 goto activate_locked;
 428                         case SWAP_AGAIN:
 429                                 goto keep_locked;
 430                         case SWAP_SUCCESS:
 431                                 ; /* try to free the page below */
 432                         }
 433                 }
 434
 435                 if (PageDirty(page)) {
 436                         if (referenced)
 437                                 goto keep_locked;
 438                         if (!may_enter_fs)
 439                                 goto keep_locked;
 440                         if (laptop_mode && !sc->may_writepage)
 441                                 goto keep_locked;
 442
 443                         /* Page is dirty, try to write it out here */
 444                         switch(pageout(page, mapping)) {
 445                         case PAGE_KEEP:
 446                                 goto keep_locked;
 447                         case PAGE_ACTIVATE:
 448                                 goto activate_locked;
 449                         case PAGE_SUCCESS:
 450                                 if (PageWriteback(page) || PageDirty(page))
 451                                         goto keep;
 452                                 /*
 453                                  * A synchronous write - probably a ramdisk.  Go
 454                                  * ahead and try to reclaim the page.
 455                                  */
 456                                 if (TestSetPageLocked(page))
 457                                         goto keep;
 458                                 if (PageDirty(page) || PageWriteback(page))
 459                                         goto keep_locked;
 460                                 mapping = page_mapping(page);
 461                         case PAGE_CLEAN:
 462                                 ; /* try to free the page below */
 463                         }
 464                 }
 465
 466                 /*
 467                  * If the page has buffers, try to free the buffer mappings
 468                  * associated with this page. If we succeed we try to free
 469                  * the page as well.
 470                  *
 471                  * We do this even if the page is PageDirty().
 472                  * try_to_release_page() does not perform I/O, but it is
 473                  * possible for a page to have PageDirty set, but it is actually
 474                  * clean (all its buffers are clean).  This happens if the
 475                  * buffers were written out directly, with submit_bh(). ext3
 476                  * will do this, as well as the blockdev mapping.
 477                  * try_to_release_page() will discover that cleanness and will
 478                  * drop the buffers and mark the page clean - it can be freed.
 479                  *
 480                  * Rarely, pages can have buffers and no ->mapping.  These are
 481                  * the pages which were not successfully invalidated in
 482                  * truncate_complete_page().  We try to drop those buffers here
 483                  * and if that worked, and the page is no longer mapped into
 484                  * process address space (page_count == 1) it can be freed.
 485                  * Otherwise, leave the page on the LRU so it is swappable.
 486                  */
 487                 if (PagePrivate(page)) {
 488                         if (!try_to_release_page(page, sc->gfp_mask))
 489                                 goto activate_locked;
 490                         if (!mapping && page_count(page) == 1)
 491                                 goto free_it;
 492                 }
 493
 494                 if (!mapping)
 495                         goto keep_locked;       /* truncate got there first */
 496
 497                 write_lock_irq(&mapping->tree_lock);
 498
 499                 /*
 500                  * The non-racy check for busy page.  It is critical to check
 501                  * PageDirty _after_ making sure that the page is freeable and
 502                  * not in use by anybody.       (pagecache + us == 2)
 503                  */
 504                 if (page_count(page) != 2 || PageDirty(page)) {
 505                         write_unlock_irq(&mapping->tree_lock);
 506                         goto keep_locked;
 507                 }
 508
 509 #ifdef CONFIG_SWAP
 510                 if (PageSwapCache(page)) {
 511                         swp_entry_t swap = { .val = page->private };
 512                         __delete_from_swap_cache(page);
 513                         write_unlock_irq(&mapping->tree_lock);
 514                         swap_free(swap);
 515                         __put_page(page);       /* The pagecache ref */
 516                         goto free_it;
 517                 }
 518 #endif /* CONFIG_SWAP */
 519
 520                 __remove_from_page_cache(page);
 521                 write_unlock_irq(&mapping->tree_lock);
 522                 __put_page(page);
 523
 524 free_it:
 525                 unlock_page(page);
 526                 reclaimed++;
 527                 if (!pagevec_add(&freed_pvec, page))
 528                         __pagevec_release_nonlru(&freed_pvec);
 529                 continue;
 530
 531 activate_locked:
 532                 SetPageActive(page);
 533                 pgactivate++;
 534 keep_locked:
 535                 unlock_page(page);
 536 keep:
 537                 list_add(&page->lru, &ret_pages);
 538                 BUG_ON(PageLRU(page));
 539         }
 540         list_splice(&ret_pages, page_list);
 541         if (pagevec_count(&freed_pvec))
 542                 __pagevec_release_nonlru(&freed_pvec);
 543         mod_page_state(pgactivate, pgactivate);
 544         sc->nr_reclaimed += reclaimed;
 545         return reclaimed;
 546 }
 547
 548 /*
 549  * zone->lru_lock is heavily contended.  Some of the functions that
 550  * shrink the lists perform better by taking out a batch of pages
 551  * and working on them outside the LRU lock.
 552  *
 553  * For pagecache intensive workloads, this function is the hottest
 554  * spot in the kernel (apart from copy_*_user functions).
 555  *
 556  * Appropriate locks must be held before calling this function.
 557  *
 558  * @nr_to_scan: The number of pages to look through on the list.
 559  * @src:        The LRU list to pull pages off.
 560  * @dst:        The temp list to put pages on to.
 561  * @scanned:    The number of pages that were scanned.
 562  *
 563  * returns how many pages were moved onto *@dst.
 564  */
 565 static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
 566                              struct list_head *dst, int *scanned)
 567 {
 568         int nr_taken = 0;
 569         struct page *page;
 570         int scan = 0;
 571
 572         while (scan++ < nr_to_scan && !list_empty(src)) {
 573                 page = lru_to_page(src);
 574                 prefetchw_prev_lru_page(page, src, flags);
 575
 576                 if (!TestClearPageLRU(page))
 577                         BUG();
 578                 list_del(&page->lru);
 579                 if (get_page_testone(page)) {
 580                         /*
 581                          * It is being freed elsewhere
 582                          */
 583                         __put_page(page);
 584                         SetPageLRU(page);
 585                         list_add(&page->lru, src);
 586                         continue;
 587                 } else {
 588                         list_add(&page->lru, dst);
 589                         nr_taken++;
 590                 }
 591         }
 592
 593         *scanned = scan;
 594         return nr_taken;
 595 }
 596
 597 /*
 598  * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
 599  */
 600 static void shrink_cache(struct zone *zone, struct scan_control *sc)
 601 {
 602         LIST_HEAD(page_list);
 603         struct pagevec pvec;
 604         int max_scan = sc->nr_to_scan;
 605
 606         pagevec_init(&pvec, 1);
 607
 608         lru_add_drain();
 609         spin_lock_irq(&zone->lru_lock);
 610         while (max_scan > 0) {
 611                 struct page *page;
 612                 int nr_taken;
 613                 int nr_scan;
 614                 int nr_freed;
 615
 616                 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
 617                                              &zone->inactive_list,
 618                                              &page_list, &nr_scan);
 619                 zone->nr_inactive -= nr_taken;
 620                 zone->pages_scanned += nr_scan;
 621                 spin_unlock_irq(&zone->lru_lock);
 622
 623                 if (nr_taken == 0)
 624                         goto done;
 625
 626                 max_scan -= nr_scan;
 627                 if (current_is_kswapd())
 628                         mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
 629                 else
 630                         mod_page_state_zone(zone, pgscan_direct, nr_scan);
 631                 nr_freed = shrink_list(&page_list, sc);
 632                 if (current_is_kswapd())
 633                         mod_page_state(kswapd_steal, nr_freed);
 634                 mod_page_state_zone(zone, pgsteal, nr_freed);
 635                 sc->nr_to_reclaim -= nr_freed;
 636
 637                 spin_lock_irq(&zone->lru_lock);
 638                 /*
 639                  * Put back any unfreeable pages.
 640                  */
 641                 while (!list_empty(&page_list)) {
 642                         page = lru_to_page(&page_list);
 643                         if (TestSetPageLRU(page))
 644                                 BUG();
 645                         list_del(&page->lru);
 646                         if (PageActive(page))
 647                                 add_page_to_active_list(zone, page);
 648                         else
 649                                 add_page_to_inactive_list(zone, page);
 650                         if (!pagevec_add(&pvec, page)) {
 651                                 spin_unlock_irq(&zone->lru_lock);
 652                                 __pagevec_release(&pvec);
 653                                 spin_lock_irq(&zone->lru_lock);
 654                         }
 655                 }
 656         }
 657         spin_unlock_irq(&zone->lru_lock);
 658 done:
 659         pagevec_release(&pvec);
 660 }
 661
 662 /*
 663  * This moves pages from the active list to the inactive list.
 664  *
 665  * We move them the other way if the page is referenced by one or more
 666  * processes, from rmap.
 667  *
 668  * If the pages are mostly unmapped, the processing is fast and it is
 669  * appropriate to hold zone->lru_lock across the whole operation.  But if
 670  * the pages are mapped, the processing is slow (page_referenced()) so we
 671  * should drop zone->lru_lock around each page.  It's impossible to balance
 672  * this, so instead we remove the pages from the LRU while processing them.
 673  * It is safe to rely on PG_active against the non-LRU pages in here because
 674  * nobody will play with that bit on a non-LRU page.
 675  *
 676  * The downside is that we have to touch page->_count against each page.
 677  * But we had to alter page->flags anyway.
 678  */
 679 static void
 680 refill_inactive_zone(struct zone *zone, struct scan_control *sc)
 681 {
 682         int pgmoved;
 683         int pgdeactivate = 0;
 684         int pgscanned;
 685         int nr_pages = sc->nr_to_scan;
 686         LIST_HEAD(l_hold);      /* The pages which were snipped off */
 687         LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
 688         LIST_HEAD(l_active);    /* Pages to go onto the active_list */
 689         struct page *page;
 690         struct pagevec pvec;
 691         int reclaim_mapped = 0;
 692         long mapped_ratio;
 693         long distress;
 694         long swap_tendency;
 695
 696         lru_add_drain();
 697         spin_lock_irq(&zone->lru_lock);
 698         pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
 699                                     &l_hold, &pgscanned);
 700         zone->pages_scanned += pgscanned;
 701         zone->nr_active -= pgmoved;
 702         spin_unlock_irq(&zone->lru_lock);
 703
 704         /*
 705          * `distress' is a measure of how much trouble we're having reclaiming
 706          * pages.  0 -> no problems.  100 -> great trouble.
 707          */
 708         distress = 100 >> zone->prev_priority;
 709
 710         /*
 711          * The point of this algorithm is to decide when to start reclaiming
 712          * mapped memory instead of just pagecache.  Work out how much memory
 713          * is mapped.
 714          */
 715         mapped_ratio = (sc->nr_mapped * 100) / total_memory;
 716
 717         /*
 718          * Now decide how much we really want to unmap some pages.  The mapped
 719          * ratio is downgraded - just because there's a lot of mapped memory
 720          * doesn't necessarily mean that page reclaim isn't succeeding.
 721          *
 722          * The distress ratio is important - we don't want to start going oom.
 723          *
 724          * A 100% value of vm_swappiness overrides this algorithm altogether.
 725          */
 726         swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
 727
 728         /*
 729          * Now use this metric to decide whether to start moving mapped memory
 730          * onto the inactive list.
 731          */
 732         if (swap_tendency >= 100)
 733                 reclaim_mapped = 1;
 734
 735         while (!list_empty(&l_hold)) {
 736                 cond_resched();
 737                 page = lru_to_page(&l_hold);
 738                 list_del(&page->lru);
 739                 if (page_mapped(page)) {
 740                         if (!reclaim_mapped ||
 741                             (total_swap_pages == 0 && PageAnon(page)) ||
 742                             page_referenced(page, 0, sc->priority <= 0)) {
 743                                 list_add(&page->lru, &l_active);
 744                                 continue;
 745                         }
 746                 }
 747                 list_add(&page->lru, &l_inactive);
 748         }
 749
 750         pagevec_init(&pvec, 1);
 751         pgmoved = 0;
 752         spin_lock_irq(&zone->lru_lock);
 753         while (!list_empty(&l_inactive)) {
 754                 page = lru_to_page(&l_inactive);
 755                 prefetchw_prev_lru_page(page, &l_inactive, flags);
 756                 if (TestSetPageLRU(page))
 757                         BUG();
 758                 if (!TestClearPageActive(page))
 759                         BUG();
 760                 list_move(&page->lru, &zone->inactive_list);
 761                 pgmoved++;
 762                 if (!pagevec_add(&pvec, page)) {
 763                         zone->nr_inactive += pgmoved;
 764                         spin_unlock_irq(&zone->lru_lock);
 765                         pgdeactivate += pgmoved;
 766                         pgmoved = 0;
 767                         if (buffer_heads_over_limit)
 768                                 pagevec_strip(&pvec);
 769                         __pagevec_release(&pvec);
 770                         spin_lock_irq(&zone->lru_lock);
 771                 }
 772         }
 773         zone->nr_inactive += pgmoved;
 774         pgdeactivate += pgmoved;
 775         if (buffer_heads_over_limit) {
 776                 spin_unlock_irq(&zone->lru_lock);
 777                 pagevec_strip(&pvec);
 778                 spin_lock_irq(&zone->lru_lock);
 779         }
 780
 781         pgmoved = 0;
 782         while (!list_empty(&l_active)) {
 783                 page = lru_to_page(&l_active);
 784                 prefetchw_prev_lru_page(page, &l_active, flags);
 785                 if (TestSetPageLRU(page))
 786                         BUG();
 787                 BUG_ON(!PageActive(page));
 788                 list_move(&page->lru, &zone->active_list);
 789                 pgmoved++;
 790                 if (!pagevec_add(&pvec, page)) {
 791                         zone->nr_active += pgmoved;
 792                         pgmoved = 0;
 793                         spin_unlock_irq(&zone->lru_lock);
 794                         __pagevec_release(&pvec);
 795                         spin_lock_irq(&zone->lru_lock);
 796                 }
 797         }
 798         zone->nr_active += pgmoved;
 799         spin_unlock_irq(&zone->lru_lock);
 800         pagevec_release(&pvec);
 801
 802         mod_page_state_zone(zone, pgrefill, pgscanned);
 803         mod_page_state(pgdeactivate, pgdeactivate);
 804 }
 805
 806 /*
 807  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 808  */
 809 static void
 810 shrink_zone(struct zone *zone, struct scan_control *sc)
 811 {
 812         unsigned long nr_active;
 813         unsigned long nr_inactive;
 814
 815         /*
 816          * Add one to `nr_to_scan' just to make sure that the kernel will
 817          * slowly sift through the active list.
 818          */
 819         zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
 820         nr_active = zone->nr_scan_active;
 821         if (nr_active >= sc->swap_cluster_max)
 822                 zone->nr_scan_active = 0;
 823         else
 824                 nr_active = 0;
 825
 826         zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
 827         nr_inactive = zone->nr_scan_inactive;
 828         if (nr_inactive >= sc->swap_cluster_max)
 829                 zone->nr_scan_inactive = 0;
 830         else
 831                 nr_inactive = 0;
 832
 833         sc->nr_to_reclaim = sc->swap_cluster_max;
 834
 835         while (nr_active || nr_inactive) {
 836                 if (nr_active) {
 837                         sc->nr_to_scan = min(nr_active,
 838                                         (unsigned long)sc->swap_cluster_max);
 839                         nr_active -= sc->nr_to_scan;
 840                         refill_inactive_zone(zone, sc);
 841                 }
 842
 843                 if (nr_inactive) {
 844                         sc->nr_to_scan = min(nr_inactive,
 845                                         (unsigned long)sc->swap_cluster_max);
 846                         nr_inactive -= sc->nr_to_scan;
 847                         shrink_cache(zone, sc);
 848                         if (sc->nr_to_reclaim <= 0)
 849                                 break;
 850                 }
 851         }
 852
 853         throttle_vm_writeout();
 854 }
 855
 856 /*
 857  * This is the direct reclaim path, for page-allocating processes.  We only
 858  * try to reclaim pages from zones which will satisfy the caller's allocation
 859  * request.
 860  *
 861  * We reclaim from a zone even if that zone is over pages_high.  Because:
 862  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 863  *    allocation or
 864  * b) The zones may be over pages_high but they must go *over* pages_high to
 865  *    satisfy the `incremental min' zone defense algorithm.
 866  *
 867  * Returns the number of reclaimed pages.
 868  *
 869  * If a zone is deemed to be full of pinned pages then just give it a light
 870  * scan then give up on it.
 871  */
 872 static void
 873 shrink_caches(struct zone **zones, struct scan_control *sc)
 874 {
 875         int i;
 876
 877         for (i = 0; zones[i] != NULL; i++) {
 878                 struct zone *zone = zones[i];
 879
 880                 if (zone->present_pages == 0)
 881                         continue;
 882
 883                 if (!cpuset_zone_allowed(zone))
 884                         continue;
 885
 886                 zone->temp_priority = sc->priority;
 887                 if (zone->prev_priority > sc->priority)
 888                         zone->prev_priority = sc->priority;
 889
 890                 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
 891                         continue;       /* Let kswapd poll it */
 892
 893                 shrink_zone(zone, sc);
 894         }
 895 }
 896
 897 /*
 898  * This is the main entry point to direct page reclaim.
 899  *
 900  * If a full scan of the inactive list fails to free enough memory then we
 901  * are "out of memory" and something needs to be killed.
 902  *
 903  * If the caller is !__GFP_FS then the probability of a failure is reasonably
 904  * high - the zone may be full of dirty or under-writeback pages, which this
 905  * caller can't do much about.  We kick pdflush and take explicit naps in the
 906  * hope that some of these pages can be written.  But if the allocating task
 907  * holds filesystem locks which prevent writeout this might not work, and the
 908  * allocation attempt will fail.
 909  */
 910 int try_to_free_pages(struct zone **zones,
 911                 unsigned int gfp_mask, unsigned int order)
 912 {
 913         int priority;
 914         int ret = 0;
 915         int total_scanned = 0, total_reclaimed = 0;
 916         struct reclaim_state *reclaim_state = current->reclaim_state;
 917         struct scan_control sc;
 918         unsigned long lru_pages = 0;
 919         int i;
 920
 921         sc.gfp_mask = gfp_mask;
 922         sc.may_writepage = 0;
 923
 924         inc_page_state(allocstall);
 925
 926         for (i = 0; zones[i] != NULL; i++) {
 927                 struct zone *zone = zones[i];
 928
 929                 if (!cpuset_zone_allowed(zone))
 930                         continue;
 931
 932                 zone->temp_priority = DEF_PRIORITY;
 933                 lru_pages += zone->nr_active + zone->nr_inactive;
 934         }
 935
 936         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
 937                 sc.nr_mapped = read_page_state(nr_mapped);
 938                 sc.nr_scanned = 0;
 939                 sc.nr_reclaimed = 0;
 940                 sc.priority = priority;
 941                 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
 942                 shrink_caches(zones, &sc);
 943                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
 944                 if (reclaim_state) {
 945                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
 946                         reclaim_state->reclaimed_slab = 0;
 947                 }
 948                 total_scanned += sc.nr_scanned;
 949                 total_reclaimed += sc.nr_reclaimed;
 950                 if (total_reclaimed >= sc.swap_cluster_max) {
 951                         ret = 1;
 952                         goto out;
 953                 }
 954
 955                 /*
 956                  * Try to write back as many pages as we just scanned.  This
 957                  * tends to cause slow streaming writers to write data to the
 958                  * disk smoothly, at the dirtying rate, which is nice.   But
 959                  * that's undesirable in laptop mode, where we *want* lumpy
 960                  * writeout.  So in laptop mode, write out the whole world.
 961                  */
 962                 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
 963                         wakeup_bdflush(laptop_mode ? 0 : total_scanned);
 964                         sc.may_writepage = 1;
 965                 }
 966
 967                 /* Take a nap, wait for some writeback to complete */
 968                 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
 969                         blk_congestion_wait(WRITE, HZ/10);
 970         }
 971 out:
 972         for (i = 0; zones[i] != 0; i++) {
 973                 struct zone *zone = zones[i];
 974
 975                 if (!cpuset_zone_allowed(zone))
 976                         continue;
 977
 978                 zone->prev_priority = zone->temp_priority;
 979         }
 980         return ret;
 981 }
 982
 983 /*
 984  * For kswapd, balance_pgdat() will work across all this node's zones until
 985  * they are all at pages_high.
 986  *
 987  * If `nr_pages' is non-zero then it is the number of pages which are to be
 988  * reclaimed, regardless of the zone occupancies.  This is a software suspend
 989  * special.
 990  *
 991  * Returns the number of pages which were actually freed.
 992  *
 993  * There is special handling here for zones which are full of pinned pages.
 994  * This can happen if the pages are all mlocked, or if they are all used by
 995  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
 996  * What we do is to detect the case where all pages in the zone have been
 997  * scanned twice and there has been zero successful reclaim.  Mark the zone as
 998  * dead and from now on, only perform a short scan.  Basically we're polling
 999  * the zone for when the problem goes away.
1000  *
1001  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1002  * zones which have free_pages > pages_high, but once a zone is found to have
1003  * free_pages <= pages_high, we scan that zone and the lower zones regardless
1004  * of the number of free pages in the lower zones.  This interoperates with
1005  * the page allocator fallback scheme to ensure that aging of pages is balanced
1006  * across the zones.
1007  */
1008 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
1009 {
1010         int to_free = nr_pages;
1011         int all_zones_ok;
1012         int priority;
1013         int i;
1014         int total_scanned, total_reclaimed;
1015         struct reclaim_state *reclaim_state = current->reclaim_state;
1016         struct scan_control sc;
1017
1018 loop_again:
1019         total_scanned = 0;
1020         total_reclaimed = 0;
1021         sc.gfp_mask = GFP_KERNEL;
1022         sc.may_writepage = 0;
1023         sc.nr_mapped = read_page_state(nr_mapped);
1024
1025         inc_page_state(pageoutrun);
1026
1027         for (i = 0; i < pgdat->nr_zones; i++) {
1028                 struct zone *zone = pgdat->node_zones + i;
1029
1030                 zone->temp_priority = DEF_PRIORITY;
1031         }
1032
1033         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1034                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1035                 unsigned long lru_pages = 0;
1036
1037                 all_zones_ok = 1;
1038
1039                 if (nr_pages == 0) {
1040                         /*
1041                          * Scan in the highmem->dma direction for the highest
1042                          * zone which needs scanning
1043                          */
1044                         for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1045                                 struct zone *zone = pgdat->node_zones + i;
1046
1047                                 if (zone->present_pages == 0)
1048                                         continue;
1049
1050                                 if (zone->all_unreclaimable &&
1051                                                 priority != DEF_PRIORITY)
1052                                         continue;
1053
1054                                 if (!zone_watermark_ok(zone, order,
1055                                                 zone->pages_high, 0, 0, 0)) {
1056                                         end_zone = i;
1057                                         goto scan;
1058                                 }
1059                         }
1060                         goto out;
1061                 } else {
1062                         end_zone = pgdat->nr_zones - 1;
1063                 }
1064 scan:
1065                 for (i = 0; i <= end_zone; i++) {
1066                         struct zone *zone = pgdat->node_zones + i;
1067
1068                         lru_pages += zone->nr_active + zone->nr_inactive;
1069                 }
1070
1071                 /*
1072                  * Now scan the zone in the dma->highmem direction, stopping
1073                  * at the last zone which needs scanning.
1074                  *
1075                  * We do this because the page allocator works in the opposite
1076                  * direction.  This prevents the page allocator from allocating
1077                  * pages behind kswapd's direction of progress, which would
1078                  * cause too much scanning of the lower zones.
1079                  */
1080                 for (i = 0; i <= end_zone; i++) {
1081                         struct zone *zone = pgdat->node_zones + i;
1082
1083                         if (zone->present_pages == 0)
1084                                 continue;
1085
1086                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1087                                 continue;
1088
1089                         if (nr_pages == 0) {    /* Not software suspend */
1090                                 if (!zone_watermark_ok(zone, order,
1091                                                 zone->pages_high, end_zone, 0, 0))
1092                                         all_zones_ok = 0;
1093                         }
1094                         zone->temp_priority = priority;
1095                         if (zone->prev_priority > priority)
1096                                 zone->prev_priority = priority;
1097                         sc.nr_scanned = 0;
1098                         sc.nr_reclaimed = 0;
1099                         sc.priority = priority;
1100                         sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
1101                         shrink_zone(zone, &sc);
1102                         reclaim_state->reclaimed_slab = 0;
1103                         shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
1104                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1105                         total_reclaimed += sc.nr_reclaimed;
1106                         total_scanned += sc.nr_scanned;
1107                         if (zone->all_unreclaimable)
1108                                 continue;
1109                         if (zone->pages_scanned >= (zone->nr_active +
1110                                                         zone->nr_inactive) * 4)
1111                                 zone->all_unreclaimable = 1;
1112                         /*
1113                          * If we've done a decent amount of scanning and
1114                          * the reclaim ratio is low, start doing writepage
1115                          * even in laptop mode
1116                          */
1117                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1118                             total_scanned > total_reclaimed+total_reclaimed/2)
1119                                 sc.may_writepage = 1;
1120                 }
1121                 if (nr_pages && to_free > total_reclaimed)
1122                         continue;       /* swsusp: need to do more work */
1123                 if (all_zones_ok)
1124                         break;          /* kswapd: all done */
1125                 /*
1126                  * OK, kswapd is getting into trouble.  Take a nap, then take
1127                  * another pass across the zones.
1128                  */
1129                 if (total_scanned && priority < DEF_PRIORITY - 2)
1130                         blk_congestion_wait(WRITE, HZ/10);
1131
1132                 /*
1133                  * We do this so kswapd doesn't build up large priorities for
1134                  * example when it is freeing in parallel with allocators. It
1135                  * matches the direct reclaim path behaviour in terms of impact
1136                  * on zone->*_priority.
1137                  */
1138                 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
1139                         break;
1140         }
1141 out:
1142         for (i = 0; i < pgdat->nr_zones; i++) {
1143                 struct zone *zone = pgdat->node_zones + i;
1144
1145                 zone->prev_priority = zone->temp_priority;
1146         }
1147         if (!all_zones_ok) {
1148                 cond_resched();
1149                 goto loop_again;
1150         }
1151
1152         return total_reclaimed;
1153 }
1154
1155 /*
1156  * The background pageout daemon, started as a kernel thread
1157  * from the init process.
1158  *
1159  * This basically trickles out pages so that we have _some_
1160  * free memory available even if there is no other activity
1161  * that frees anything up. This is needed for things like routing
1162  * etc, where we otherwise might have all activity going on in
1163  * asynchronous contexts that cannot page things out.
1164  *
1165  * If there are applications that are active memory-allocators
1166  * (most normal use), this basically shouldn't matter.
1167  */
1168 static int kswapd(void *p)
1169 {
1170         unsigned long order;
1171         pg_data_t *pgdat = (pg_data_t*)p;
1172         struct task_struct *tsk = current;
1173         DEFINE_WAIT(wait);
1174         struct reclaim_state reclaim_state = {
1175                 .reclaimed_slab = 0,
1176         };
1177         cpumask_t cpumask;
1178
1179         daemonize("kswapd%d", pgdat->node_id);
1180         cpumask = node_to_cpumask(pgdat->node_id);
1181         if (!cpus_empty(cpumask))
1182                 set_cpus_allowed(tsk, cpumask);
1183         current->reclaim_state = &reclaim_state;
1184
1185         /*
1186          * Tell the memory management that we're a "memory allocator",
1187          * and that if we need more memory we should get access to it
1188          * regardless (see "__alloc_pages()"). "kswapd" should
1189          * never get caught in the normal page freeing logic.
1190          *
1191          * (Kswapd normally doesn't need memory anyway, but sometimes
1192          * you need a small amount of memory in order to be able to
1193          * page out something else, and this flag essentially protects
1194          * us from recursively trying to free more memory as we're
1195          * trying to free the first piece of memory in the first place).
1196          */
1197         tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
1198
1199         order = 0;
1200         for ( ; ; ) {
1201                 unsigned long new_order;
1202                 if (current->flags & PF_FREEZE)
1203                         refrigerator(PF_FREEZE);
1204
1205                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1206                 new_order = pgdat->kswapd_max_order;
1207                 pgdat->kswapd_max_order = 0;
1208                 if (order < new_order) {
1209                         /*
1210                          * Don't sleep if someone wants a larger 'order'
1211                          * allocation
1212                          */
1213                         order = new_order;
1214                 } else {
1215                         schedule();
1216                         order = pgdat->kswapd_max_order;
1217                 }
1218                 finish_wait(&pgdat->kswapd_wait, &wait);
1219
1220                 balance_pgdat(pgdat, 0, order);
1221         }
1222         return 0;
1223 }
1224
1225 /*
1226  * A zone is low on free memory, so wake its kswapd task to service it.
1227  */
1228 void wakeup_kswapd(struct zone *zone, int order)
1229 {
1230         pg_data_t *pgdat;
1231
1232         if (zone->present_pages == 0)
1233                 return;
1234
1235         pgdat = zone->zone_pgdat;
1236         if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0, 0))
1237                 return;
1238         if (pgdat->kswapd_max_order < order)
1239                 pgdat->kswapd_max_order = order;
1240         if (!cpuset_zone_allowed(zone))
1241                 return;
1242         if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
1243                 return;
1244         wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
1245 }
1246
1247 #ifdef CONFIG_PM
1248 /*
1249  * Try to free `nr_pages' of memory, system-wide.  Returns the number of freed
1250  * pages.
1251  */
1252 int shrink_all_memory(int nr_pages)
1253 {
1254         pg_data_t *pgdat;
1255         int nr_to_free = nr_pages;
1256         int ret = 0;
1257         struct reclaim_state reclaim_state = {
1258                 .reclaimed_slab = 0,
1259         };
1260
1261         current->reclaim_state = &reclaim_state;
1262         for_each_pgdat(pgdat) {
1263                 int freed;
1264                 freed = balance_pgdat(pgdat, nr_to_free, 0);
1265                 ret += freed;
1266                 nr_to_free -= freed;
1267                 if (nr_to_free <= 0)
1268                         break;
1269         }
1270         current->reclaim_state = NULL;
1271         return ret;
1272 }
1273 #endif
1274
1275 #ifdef CONFIG_HOTPLUG_CPU
1276 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1277    not required for correctness.  So if the last cpu in a node goes
1278    away, we get changed to run anywhere: as the first one comes back,
1279    restore their cpu bindings. */
1280 static int __devinit cpu_callback(struct notifier_block *nfb,
1281                                   unsigned long action,
1282                                   void *hcpu)
1283 {
1284         pg_data_t *pgdat;
1285         cpumask_t mask;
1286
1287         if (action == CPU_ONLINE) {
1288                 for_each_pgdat(pgdat) {
1289                         mask = node_to_cpumask(pgdat->node_id);
1290                         if (any_online_cpu(mask) != NR_CPUS)
1291                                 /* One of our CPUs online: restore mask */
1292                                 set_cpus_allowed(pgdat->kswapd, mask);
1293                 }
1294         }
1295         return NOTIFY_OK;
1296 }
1297 #endif /* CONFIG_HOTPLUG_CPU */
1298
1299 static int __init kswapd_init(void)
1300 {
1301         pg_data_t *pgdat;
1302         swap_setup();
1303         for_each_pgdat(pgdat)
1304                 pgdat->kswapd
1305                 = find_task_by_real_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1306         total_memory = nr_free_pagecache_pages();
1307         hotcpu_notifier(cpu_callback, 0);
1308         return 0;
1309 }
1310
1311 module_init(kswapd_init)