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