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         /* Ask shrink_caches, or shrink_zone to scan at this priority */
  67         unsigned int priority;
  68
  69         /* This context's GFP mask */
  70         gfp_t gfp_mask;
  71
  72         int may_writepage;
  73
  74         /* Can pages be swapped as part of reclaim? */
  75         int may_swap;
  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  * Returns the number of slab objects which we shrunk.
 185  */
 186 int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
 187 {
 188         struct shrinker *shrinker;
 189         int ret = 0;
 190
 191         if (scanned == 0)
 192                 scanned = SWAP_CLUSTER_MAX;
 193
 194         if (!down_read_trylock(&shrinker_rwsem))
 195                 return 1;       /* Assume we'll be able to shrink next time */
 196
 197         list_for_each_entry(shrinker, &shrinker_list, list) {
 198                 unsigned long long delta;
 199                 unsigned long total_scan;
 200                 unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
 201
 202                 delta = (4 * scanned) / shrinker->seeks;
 203                 delta *= max_pass;
 204                 do_div(delta, lru_pages + 1);
 205                 shrinker->nr += delta;
 206                 if (shrinker->nr < 0) {
 207                         printk(KERN_ERR "%s: nr=%ld\n",
 208                                         __FUNCTION__, shrinker->nr);
 209                         shrinker->nr = max_pass;
 210                 }
 211
 212                 /*
 213                  * Avoid risking looping forever due to too large nr value:
 214                  * never try to free more than twice the estimate number of
 215                  * freeable entries.
 216                  */
 217                 if (shrinker->nr > max_pass * 2)
 218                         shrinker->nr = max_pass * 2;
 219
 220                 total_scan = shrinker->nr;
 221                 shrinker->nr = 0;
 222
 223                 while (total_scan >= SHRINK_BATCH) {
 224                         long this_scan = SHRINK_BATCH;
 225                         int shrink_ret;
 226                         int nr_before;
 227
 228                         nr_before = (*shrinker->shrinker)(0, gfp_mask);
 229                         shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
 230                         if (shrink_ret == -1)
 231                                 break;
 232                         if (shrink_ret < nr_before)
 233                                 ret += nr_before - shrink_ret;
 234                         mod_page_state(slabs_scanned, this_scan);
 235                         total_scan -= this_scan;
 236
 237                         cond_resched();
 238                 }
 239
 240                 shrinker->nr += total_scan;
 241         }
 242         up_read(&shrinker_rwsem);
 243         return ret;
 244 }
 245
 246 /* Called without lock on whether page is mapped, so answer is unstable */
 247 static inline int page_mapping_inuse(struct page *page)
 248 {
 249         struct address_space *mapping;
 250
 251         /* Page is in somebody's page tables. */
 252         if (page_mapped(page))
 253                 return 1;
 254
 255         /* Be more reluctant to reclaim swapcache than pagecache */
 256         if (PageSwapCache(page))
 257                 return 1;
 258
 259         mapping = page_mapping(page);
 260         if (!mapping)
 261                 return 0;
 262
 263         /* File is mmap'd by somebody? */
 264         return mapping_mapped(mapping);
 265 }
 266
 267 static inline int is_page_cache_freeable(struct page *page)
 268 {
 269         return page_count(page) - !!PagePrivate(page) == 2;
 270 }
 271
 272 static int may_write_to_queue(struct backing_dev_info *bdi)
 273 {
 274         if (current->flags & PF_SWAPWRITE)
 275                 return 1;
 276         if (!bdi_write_congested(bdi))
 277                 return 1;
 278         if (bdi == current->backing_dev_info)
 279                 return 1;
 280         return 0;
 281 }
 282
 283 /*
 284  * We detected a synchronous write error writing a page out.  Probably
 285  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 286  * fsync(), msync() or close().
 287  *
 288  * The tricky part is that after writepage we cannot touch the mapping: nothing
 289  * prevents it from being freed up.  But we have a ref on the page and once
 290  * that page is locked, the mapping is pinned.
 291  *
 292  * We're allowed to run sleeping lock_page() here because we know the caller has
 293  * __GFP_FS.
 294  */
 295 static void handle_write_error(struct address_space *mapping,
 296                                 struct page *page, int error)
 297 {
 298         lock_page(page);
 299         if (page_mapping(page) == mapping) {
 300                 if (error == -ENOSPC)
 301                         set_bit(AS_ENOSPC, &mapping->flags);
 302                 else
 303                         set_bit(AS_EIO, &mapping->flags);
 304         }
 305         unlock_page(page);
 306 }
 307
 308 /*
 309  * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
 310  */
 311 static pageout_t pageout(struct page *page, struct address_space *mapping)
 312 {
 313         /*
 314          * If the page is dirty, only perform writeback if that write
 315          * will be non-blocking.  To prevent this allocation from being
 316          * stalled by pagecache activity.  But note that there may be
 317          * stalls if we need to run get_block().  We could test
 318          * PagePrivate for that.
 319          *
 320          * If this process is currently in generic_file_write() against
 321          * this page's queue, we can perform writeback even if that
 322          * will block.
 323          *
 324          * If the page is swapcache, write it back even if that would
 325          * block, for some throttling. This happens by accident, because
 326          * swap_backing_dev_info is bust: it doesn't reflect the
 327          * congestion state of the swapdevs.  Easy to fix, if needed.
 328          * See swapfile.c:page_queue_congested().
 329          */
 330         if (!is_page_cache_freeable(page))
 331                 return PAGE_KEEP;
 332         if (!mapping) {
 333                 /*
 334                  * Some data journaling orphaned pages can have
 335                  * page->mapping == NULL while being dirty with clean buffers.
 336                  */
 337                 if (PagePrivate(page)) {
 338                         if (try_to_free_buffers(page)) {
 339                                 ClearPageDirty(page);
 340                                 printk("%s: orphaned page\n", __FUNCTION__);
 341                                 return PAGE_CLEAN;
 342                         }
 343                 }
 344                 return PAGE_KEEP;
 345         }
 346         if (mapping->a_ops->writepage == NULL)
 347                 return PAGE_ACTIVATE;
 348         if (!may_write_to_queue(mapping->backing_dev_info))
 349                 return PAGE_KEEP;
 350
 351         if (clear_page_dirty_for_io(page)) {
 352                 int res;
 353                 struct writeback_control wbc = {
 354                         .sync_mode = WB_SYNC_NONE,
 355                         .nr_to_write = SWAP_CLUSTER_MAX,
 356                         .nonblocking = 1,
 357                         .for_reclaim = 1,
 358                 };
 359
 360                 SetPageReclaim(page);
 361                 res = mapping->a_ops->writepage(page, &wbc);
 362                 if (res < 0)
 363                         handle_write_error(mapping, page, res);
 364                 if (res == AOP_WRITEPAGE_ACTIVATE) {
 365                         ClearPageReclaim(page);
 366                         return PAGE_ACTIVATE;
 367                 }
 368                 if (!PageWriteback(page)) {
 369                         /* synchronous write or broken a_ops? */
 370                         ClearPageReclaim(page);
 371                 }
 372
 373                 return PAGE_SUCCESS;
 374         }
 375
 376         return PAGE_CLEAN;
 377 }
 378
 379 static int remove_mapping(struct address_space *mapping, struct page *page)
 380 {
 381         if (!mapping)
 382                 return 0;               /* truncate got there first */
 383
 384         write_lock_irq(&mapping->tree_lock);
 385
 386         /*
 387          * The non-racy check for busy page.  It is critical to check
 388          * PageDirty _after_ making sure that the page is freeable and
 389          * not in use by anybody.       (pagecache + us == 2)
 390          */
 391         if (unlikely(page_count(page) != 2))
 392                 goto cannot_free;
 393         smp_rmb();
 394         if (unlikely(PageDirty(page)))
 395                 goto cannot_free;
 396
 397         if (PageSwapCache(page)) {
 398                 swp_entry_t swap = { .val = page_private(page) };
 399                 __delete_from_swap_cache(page);
 400                 write_unlock_irq(&mapping->tree_lock);
 401                 swap_free(swap);
 402                 __put_page(page);       /* The pagecache ref */
 403                 return 1;
 404         }
 405
 406         __remove_from_page_cache(page);
 407         write_unlock_irq(&mapping->tree_lock);
 408         __put_page(page);
 409         return 1;
 410
 411 cannot_free:
 412         write_unlock_irq(&mapping->tree_lock);
 413         return 0;
 414 }
 415
 416 /*
 417  * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
 418  */
 419 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
 420 {
 421         LIST_HEAD(ret_pages);
 422         struct pagevec freed_pvec;
 423         int pgactivate = 0;
 424         int reclaimed = 0;
 425
 426         cond_resched();
 427
 428         pagevec_init(&freed_pvec, 1);
 429         while (!list_empty(page_list)) {
 430                 struct address_space *mapping;
 431                 struct page *page;
 432                 int may_enter_fs;
 433                 int referenced;
 434
 435                 cond_resched();
 436
 437                 page = lru_to_page(page_list);
 438                 list_del(&page->lru);
 439
 440                 if (TestSetPageLocked(page))
 441                         goto keep;
 442
 443                 BUG_ON(PageActive(page));
 444
 445                 sc->nr_scanned++;
 446                 /* Double the slab pressure for mapped and swapcache pages */
 447                 if (page_mapped(page) || PageSwapCache(page))
 448                         sc->nr_scanned++;
 449
 450                 if (PageWriteback(page))
 451                         goto keep_locked;
 452
 453                 referenced = page_referenced(page, 1);
 454                 /* In active use or really unfreeable?  Activate it. */
 455                 if (referenced && page_mapping_inuse(page))
 456                         goto activate_locked;
 457
 458 #ifdef CONFIG_SWAP
 459                 /*
 460                  * Anonymous process memory has backing store?
 461                  * Try to allocate it some swap space here.
 462                  */
 463                 if (PageAnon(page) && !PageSwapCache(page)) {
 464                         if (!sc->may_swap)
 465                                 goto keep_locked;
 466                         if (!add_to_swap(page, GFP_ATOMIC))
 467                                 goto activate_locked;
 468                 }
 469 #endif /* CONFIG_SWAP */
 470
 471                 mapping = page_mapping(page);
 472                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 473                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 474
 475                 /*
 476                  * The page is mapped into the page tables of one or more
 477                  * processes. Try to unmap it here.
 478                  */
 479                 if (page_mapped(page) && mapping) {
 480                         /*
 481                          * No unmapping if we do not swap
 482                          */
 483                         if (!sc->may_swap)
 484                                 goto keep_locked;
 485
 486                         switch (try_to_unmap(page, 0)) {
 487                         case SWAP_FAIL:
 488                                 goto activate_locked;
 489                         case SWAP_AGAIN:
 490                                 goto keep_locked;
 491                         case SWAP_SUCCESS:
 492                                 ; /* try to free the page below */
 493                         }
 494                 }
 495
 496                 if (PageDirty(page)) {
 497                         if (referenced)
 498                                 goto keep_locked;
 499                         if (!may_enter_fs)
 500                                 goto keep_locked;
 501                         if (!sc->may_writepage)
 502                                 goto keep_locked;
 503
 504                         /* Page is dirty, try to write it out here */
 505                         switch(pageout(page, mapping)) {
 506                         case PAGE_KEEP:
 507                                 goto keep_locked;
 508                         case PAGE_ACTIVATE:
 509                                 goto activate_locked;
 510                         case PAGE_SUCCESS:
 511                                 if (PageWriteback(page) || PageDirty(page))
 512                                         goto keep;
 513                                 /*
 514                                  * A synchronous write - probably a ramdisk.  Go
 515                                  * ahead and try to reclaim the page.
 516                                  */
 517                                 if (TestSetPageLocked(page))
 518                                         goto keep;
 519                                 if (PageDirty(page) || PageWriteback(page))
 520                                         goto keep_locked;
 521                                 mapping = page_mapping(page);
 522                         case PAGE_CLEAN:
 523                                 ; /* try to free the page below */
 524                         }
 525                 }
 526
 527                 /*
 528                  * If the page has buffers, try to free the buffer mappings
 529                  * associated with this page. If we succeed we try to free
 530                  * the page as well.
 531                  *
 532                  * We do this even if the page is PageDirty().
 533                  * try_to_release_page() does not perform I/O, but it is
 534                  * possible for a page to have PageDirty set, but it is actually
 535                  * clean (all its buffers are clean).  This happens if the
 536                  * buffers were written out directly, with submit_bh(). ext3
 537                  * will do this, as well as the blockdev mapping.
 538                  * try_to_release_page() will discover that cleanness and will
 539                  * drop the buffers and mark the page clean - it can be freed.
 540                  *
 541                  * Rarely, pages can have buffers and no ->mapping.  These are
 542                  * the pages which were not successfully invalidated in
 543                  * truncate_complete_page().  We try to drop those buffers here
 544                  * and if that worked, and the page is no longer mapped into
 545                  * process address space (page_count == 1) it can be freed.
 546                  * Otherwise, leave the page on the LRU so it is swappable.
 547                  */
 548                 if (PagePrivate(page)) {
 549                         if (!try_to_release_page(page, sc->gfp_mask))
 550                                 goto activate_locked;
 551                         if (!mapping && page_count(page) == 1)
 552                                 goto free_it;
 553                 }
 554
 555                 if (!remove_mapping(mapping, page))
 556                         goto keep_locked;
 557
 558 free_it:
 559                 unlock_page(page);
 560                 reclaimed++;
 561                 if (!pagevec_add(&freed_pvec, page))
 562                         __pagevec_release_nonlru(&freed_pvec);
 563                 continue;
 564
 565 activate_locked:
 566                 SetPageActive(page);
 567                 pgactivate++;
 568 keep_locked:
 569                 unlock_page(page);
 570 keep:
 571                 list_add(&page->lru, &ret_pages);
 572                 BUG_ON(PageLRU(page));
 573         }
 574         list_splice(&ret_pages, page_list);
 575         if (pagevec_count(&freed_pvec))
 576                 __pagevec_release_nonlru(&freed_pvec);
 577         mod_page_state(pgactivate, pgactivate);
 578         sc->nr_reclaimed += reclaimed;
 579         return reclaimed;
 580 }
 581
 582 #ifdef CONFIG_MIGRATION
 583 static inline void move_to_lru(struct page *page)
 584 {
 585         list_del(&page->lru);
 586         if (PageActive(page)) {
 587                 /*
 588                  * lru_cache_add_active checks that
 589                  * the PG_active bit is off.
 590                  */
 591                 ClearPageActive(page);
 592                 lru_cache_add_active(page);
 593         } else {
 594                 lru_cache_add(page);
 595         }
 596         put_page(page);
 597 }
 598
 599 /*
 600  * Add isolated pages on the list back to the LRU.
 601  *
 602  * returns the number of pages put back.
 603  */
 604 int putback_lru_pages(struct list_head *l)
 605 {
 606         struct page *page;
 607         struct page *page2;
 608         int count = 0;
 609
 610         list_for_each_entry_safe(page, page2, l, lru) {
 611                 move_to_lru(page);
 612                 count++;
 613         }
 614         return count;
 615 }
 616
 617 /*
 618  * Non migratable page
 619  */
 620 int fail_migrate_page(struct page *newpage, struct page *page)
 621 {
 622         return -EIO;
 623 }
 624 EXPORT_SYMBOL(fail_migrate_page);
 625
 626 /*
 627  * swapout a single page
 628  * page is locked upon entry, unlocked on exit
 629  */
 630 static int swap_page(struct page *page)
 631 {
 632         struct address_space *mapping = page_mapping(page);
 633
 634         if (page_mapped(page) && mapping)
 635                 if (try_to_unmap(page, 0) != SWAP_SUCCESS)
 636                         goto unlock_retry;
 637
 638         if (PageDirty(page)) {
 639                 /* Page is dirty, try to write it out here */
 640                 switch(pageout(page, mapping)) {
 641                 case PAGE_KEEP:
 642                 case PAGE_ACTIVATE:
 643                         goto unlock_retry;
 644
 645                 case PAGE_SUCCESS:
 646                         goto retry;
 647
 648                 case PAGE_CLEAN:
 649                         ; /* try to free the page below */
 650                 }
 651         }
 652
 653         if (PagePrivate(page)) {
 654                 if (!try_to_release_page(page, GFP_KERNEL) ||
 655                     (!mapping && page_count(page) == 1))
 656                         goto unlock_retry;
 657         }
 658
 659         if (remove_mapping(mapping, page)) {
 660                 /* Success */
 661                 unlock_page(page);
 662                 return 0;
 663         }
 664
 665 unlock_retry:
 666         unlock_page(page);
 667
 668 retry:
 669         return -EAGAIN;
 670 }
 671 EXPORT_SYMBOL(swap_page);
 672
 673 /*
 674  * Page migration was first developed in the context of the memory hotplug
 675  * project. The main authors of the migration code are:
 676  *
 677  * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
 678  * Hirokazu Takahashi <taka@valinux.co.jp>
 679  * Dave Hansen <haveblue@us.ibm.com>
 680  * Christoph Lameter <clameter@sgi.com>
 681  */
 682
 683 /*
 684  * Remove references for a page and establish the new page with the correct
 685  * basic settings to be able to stop accesses to the page.
 686  */
 687 int migrate_page_remove_references(struct page *newpage,
 688                                 struct page *page, int nr_refs)
 689 {
 690         struct address_space *mapping = page_mapping(page);
 691         struct page **radix_pointer;
 692
 693         /*
 694          * Avoid doing any of the following work if the page count
 695          * indicates that the page is in use or truncate has removed
 696          * the page.
 697          */
 698         if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
 699                 return 1;
 700
 701         /*
 702          * Establish swap ptes for anonymous pages or destroy pte
 703          * maps for files.
 704          *
 705          * In order to reestablish file backed mappings the fault handlers
 706          * will take the radix tree_lock which may then be used to stop
 707          * processses from accessing this page until the new page is ready.
 708          *
 709          * A process accessing via a swap pte (an anonymous page) will take a
 710          * page_lock on the old page which will block the process until the
 711          * migration attempt is complete. At that time the PageSwapCache bit
 712          * will be examined. If the page was migrated then the PageSwapCache
 713          * bit will be clear and the operation to retrieve the page will be
 714          * retried which will find the new page in the radix tree. Then a new
 715          * direct mapping may be generated based on the radix tree contents.
 716          *
 717          * If the page was not migrated then the PageSwapCache bit
 718          * is still set and the operation may continue.
 719          */
 720         try_to_unmap(page, 1);
 721
 722         /*
 723          * Give up if we were unable to remove all mappings.
 724          */
 725         if (page_mapcount(page))
 726                 return 1;
 727
 728         write_lock_irq(&mapping->tree_lock);
 729
 730         radix_pointer = (struct page **)radix_tree_lookup_slot(
 731                                                 &mapping->page_tree,
 732                                                 page_index(page));
 733
 734         if (!page_mapping(page) || page_count(page) != nr_refs ||
 735                         *radix_pointer != page) {
 736                 write_unlock_irq(&mapping->tree_lock);
 737                 return 1;
 738         }
 739
 740         /*
 741          * Now we know that no one else is looking at the page.
 742          *
 743          * Certain minimal information about a page must be available
 744          * in order for other subsystems to properly handle the page if they
 745          * find it through the radix tree update before we are finished
 746          * copying the page.
 747          */
 748         get_page(newpage);
 749         newpage->index = page->index;
 750         newpage->mapping = page->mapping;
 751         if (PageSwapCache(page)) {
 752                 SetPageSwapCache(newpage);
 753                 set_page_private(newpage, page_private(page));
 754         }
 755
 756         *radix_pointer = newpage;
 757         __put_page(page);
 758         write_unlock_irq(&mapping->tree_lock);
 759
 760         return 0;
 761 }
 762 EXPORT_SYMBOL(migrate_page_remove_references);
 763
 764 /*
 765  * Copy the page to its new location
 766  */
 767 void migrate_page_copy(struct page *newpage, struct page *page)
 768 {
 769         copy_highpage(newpage, page);
 770
 771         if (PageError(page))
 772                 SetPageError(newpage);
 773         if (PageReferenced(page))
 774                 SetPageReferenced(newpage);
 775         if (PageUptodate(page))
 776                 SetPageUptodate(newpage);
 777         if (PageActive(page))
 778                 SetPageActive(newpage);
 779         if (PageChecked(page))
 780                 SetPageChecked(newpage);
 781         if (PageMappedToDisk(page))
 782                 SetPageMappedToDisk(newpage);
 783
 784         if (PageDirty(page)) {
 785                 clear_page_dirty_for_io(page);
 786                 set_page_dirty(newpage);
 787         }
 788
 789         ClearPageSwapCache(page);
 790         ClearPageActive(page);
 791         ClearPagePrivate(page);
 792         set_page_private(page, 0);
 793         page->mapping = NULL;
 794
 795         /*
 796          * If any waiters have accumulated on the new page then
 797          * wake them up.
 798          */
 799         if (PageWriteback(newpage))
 800                 end_page_writeback(newpage);
 801 }
 802 EXPORT_SYMBOL(migrate_page_copy);
 803
 804 /*
 805  * Common logic to directly migrate a single page suitable for
 806  * pages that do not use PagePrivate.
 807  *
 808  * Pages are locked upon entry and exit.
 809  */
 810 int migrate_page(struct page *newpage, struct page *page)
 811 {
 812         BUG_ON(PageWriteback(page));    /* Writeback must be complete */
 813
 814         if (migrate_page_remove_references(newpage, page, 2))
 815                 return -EAGAIN;
 816
 817         migrate_page_copy(newpage, page);
 818
 819         /*
 820          * Remove auxiliary swap entries and replace
 821          * them with real ptes.
 822          *
 823          * Note that a real pte entry will allow processes that are not
 824          * waiting on the page lock to use the new page via the page tables
 825          * before the new page is unlocked.
 826          */
 827         remove_from_swap(newpage);
 828         return 0;
 829 }
 830 EXPORT_SYMBOL(migrate_page);
 831
 832 /*
 833  * migrate_pages
 834  *
 835  * Two lists are passed to this function. The first list
 836  * contains the pages isolated from the LRU to be migrated.
 837  * The second list contains new pages that the pages isolated
 838  * can be moved to. If the second list is NULL then all
 839  * pages are swapped out.
 840  *
 841  * The function returns after 10 attempts or if no pages
 842  * are movable anymore because t has become empty
 843  * or no retryable pages exist anymore.
 844  *
 845  * Return: Number of pages not migrated when "to" ran empty.
 846  */
 847 int migrate_pages(struct list_head *from, struct list_head *to,
 848                   struct list_head *moved, struct list_head *failed)
 849 {
 850         int retry;
 851         int nr_failed = 0;
 852         int pass = 0;
 853         struct page *page;
 854         struct page *page2;
 855         int swapwrite = current->flags & PF_SWAPWRITE;
 856         int rc;
 857
 858         if (!swapwrite)
 859                 current->flags |= PF_SWAPWRITE;
 860
 861 redo:
 862         retry = 0;
 863
 864         list_for_each_entry_safe(page, page2, from, lru) {
 865                 struct page *newpage = NULL;
 866                 struct address_space *mapping;
 867
 868                 cond_resched();
 869
 870                 rc = 0;
 871                 if (page_count(page) == 1)
 872                         /* page was freed from under us. So we are done. */
 873                         goto next;
 874
 875                 if (to && list_empty(to))
 876                         break;
 877
 878                 /*
 879                  * Skip locked pages during the first two passes to give the
 880                  * functions holding the lock time to release the page. Later we
 881                  * use lock_page() to have a higher chance of acquiring the
 882                  * lock.
 883                  */
 884                 rc = -EAGAIN;
 885                 if (pass > 2)
 886                         lock_page(page);
 887                 else
 888                         if (TestSetPageLocked(page))
 889                                 goto next;
 890
 891                 /*
 892                  * Only wait on writeback if we have already done a pass where
 893                  * we we may have triggered writeouts for lots of pages.
 894                  */
 895                 if (pass > 0) {
 896                         wait_on_page_writeback(page);
 897                 } else {
 898                         if (PageWriteback(page))
 899                                 goto unlock_page;
 900                 }
 901
 902                 /*
 903                  * Anonymous pages must have swap cache references otherwise
 904                  * the information contained in the page maps cannot be
 905                  * preserved.
 906                  */
 907                 if (PageAnon(page) && !PageSwapCache(page)) {
 908                         if (!add_to_swap(page, GFP_KERNEL)) {
 909                                 rc = -ENOMEM;
 910                                 goto unlock_page;
 911                         }
 912                 }
 913
 914                 if (!to) {
 915                         rc = swap_page(page);
 916                         goto next;
 917                 }
 918
 919                 newpage = lru_to_page(to);
 920                 lock_page(newpage);
 921
 922                 /*
 923                  * Pages are properly locked and writeback is complete.
 924                  * Try to migrate the page.
 925                  */
 926                 mapping = page_mapping(page);
 927                 if (!mapping)
 928                         goto unlock_both;
 929
 930                 if (mapping->a_ops->migratepage) {
 931                         rc = mapping->a_ops->migratepage(newpage, page);
 932                         goto unlock_both;
 933                 }
 934
 935                 /*
 936                  * Trigger writeout if page is dirty
 937                  */
 938                 if (PageDirty(page)) {
 939                         switch (pageout(page, mapping)) {
 940                         case PAGE_KEEP:
 941                         case PAGE_ACTIVATE:
 942                                 goto unlock_both;
 943
 944                         case PAGE_SUCCESS:
 945                                 unlock_page(newpage);
 946                                 goto next;
 947
 948                         case PAGE_CLEAN:
 949                                 ; /* try to migrate the page below */
 950                         }
 951                 }
 952                 /*
 953                  * If we have no buffer or can release the buffer
 954                  * then do a simple migration.
 955                  */
 956                 if (!page_has_buffers(page) ||
 957                     try_to_release_page(page, GFP_KERNEL)) {
 958                         rc = migrate_page(newpage, page);
 959                         goto unlock_both;
 960                 }
 961
 962                 /*
 963                  * On early passes with mapped pages simply
 964                  * retry. There may be a lock held for some
 965                  * buffers that may go away. Later
 966                  * swap them out.
 967                  */
 968                 if (pass > 4) {
 969                         unlock_page(newpage);
 970                         newpage = NULL;
 971                         rc = swap_page(page);
 972                         goto next;
 973                 }
 974
 975 unlock_both:
 976                 unlock_page(newpage);
 977
 978 unlock_page:
 979                 unlock_page(page);
 980
 981 next:
 982                 if (rc == -EAGAIN) {
 983                         retry++;
 984                 } else if (rc) {
 985                         /* Permanent failure */
 986                         list_move(&page->lru, failed);
 987                         nr_failed++;
 988                 } else {
 989                         if (newpage) {
 990                                 /* Successful migration. Return page to LRU */
 991                                 move_to_lru(newpage);
 992                         }
 993                         list_move(&page->lru, moved);
 994                 }
 995         }
 996         if (retry && pass++ < 10)
 997                 goto redo;
 998
 999         if (!swapwrite)
1000                 current->flags &= ~PF_SWAPWRITE;
1001
1002         return nr_failed + retry;
1003 }
1004
1005 /*
1006  * Isolate one page from the LRU lists and put it on the
1007  * indicated list with elevated refcount.
1008  *
1009  * Result:
1010  *  0 = page not on LRU list
1011  *  1 = page removed from LRU list and added to the specified list.
1012  */
1013 int isolate_lru_page(struct page *page)
1014 {
1015         int ret = 0;
1016
1017         if (PageLRU(page)) {
1018                 struct zone *zone = page_zone(page);
1019                 spin_lock_irq(&zone->lru_lock);
1020                 if (TestClearPageLRU(page)) {
1021                         ret = 1;
1022                         get_page(page);
1023                         if (PageActive(page))
1024                                 del_page_from_active_list(zone, page);
1025                         else
1026                                 del_page_from_inactive_list(zone, page);
1027                 }
1028                 spin_unlock_irq(&zone->lru_lock);
1029         }
1030
1031         return ret;
1032 }
1033 #endif
1034
1035 /*
1036  * zone->lru_lock is heavily contended.  Some of the functions that
1037  * shrink the lists perform better by taking out a batch of pages
1038  * and working on them outside the LRU lock.
1039  *
1040  * For pagecache intensive workloads, this function is the hottest
1041  * spot in the kernel (apart from copy_*_user functions).
1042  *
1043  * Appropriate locks must be held before calling this function.
1044  *
1045  * @nr_to_scan: The number of pages to look through on the list.
1046  * @src:        The LRU list to pull pages off.
1047  * @dst:        The temp list to put pages on to.
1048  * @scanned:    The number of pages that were scanned.
1049  *
1050  * returns how many pages were moved onto *@dst.
1051  */
1052 static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
1053                              struct list_head *dst, int *scanned)
1054 {
1055         int nr_taken = 0;
1056         struct page *page;
1057         int scan = 0;
1058
1059         while (scan++ < nr_to_scan && !list_empty(src)) {
1060                 page = lru_to_page(src);
1061                 prefetchw_prev_lru_page(page, src, flags);
1062
1063                 if (!TestClearPageLRU(page))
1064                         BUG();
1065                 list_del(&page->lru);
1066                 if (get_page_testone(page)) {
1067                         /*
1068                          * It is being freed elsewhere
1069                          */
1070                         __put_page(page);
1071                         SetPageLRU(page);
1072                         list_add(&page->lru, src);
1073                         continue;
1074                 } else {
1075                         list_add(&page->lru, dst);
1076                         nr_taken++;
1077                 }
1078         }
1079
1080         *scanned = scan;
1081         return nr_taken;
1082 }
1083
1084 /*
1085  * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
1086  */
1087 static void shrink_cache(struct zone *zone, struct scan_control *sc)
1088 {
1089         LIST_HEAD(page_list);
1090         struct pagevec pvec;
1091         int max_scan = sc->nr_to_scan;
1092
1093         pagevec_init(&pvec, 1);
1094
1095         lru_add_drain();
1096         spin_lock_irq(&zone->lru_lock);
1097         while (max_scan > 0) {
1098                 struct page *page;
1099                 int nr_taken;
1100                 int nr_scan;
1101                 int nr_freed;
1102
1103                 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
1104                                              &zone->inactive_list,
1105                                              &page_list, &nr_scan);
1106                 zone->nr_inactive -= nr_taken;
1107                 zone->pages_scanned += nr_scan;
1108                 spin_unlock_irq(&zone->lru_lock);
1109
1110                 if (nr_taken == 0)
1111                         goto done;
1112
1113                 max_scan -= nr_scan;
1114                 nr_freed = shrink_list(&page_list, sc);
1115
1116                 local_irq_disable();
1117                 if (current_is_kswapd()) {
1118                         __mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
1119                         __mod_page_state(kswapd_steal, nr_freed);
1120                 } else
1121                         __mod_page_state_zone(zone, pgscan_direct, nr_scan);
1122                 __mod_page_state_zone(zone, pgsteal, nr_freed);
1123
1124                 spin_lock(&zone->lru_lock);
1125                 /*
1126                  * Put back any unfreeable pages.
1127                  */
1128                 while (!list_empty(&page_list)) {
1129                         page = lru_to_page(&page_list);
1130                         if (TestSetPageLRU(page))
1131                                 BUG();
1132                         list_del(&page->lru);
1133                         if (PageActive(page))
1134                                 add_page_to_active_list(zone, page);
1135                         else
1136                                 add_page_to_inactive_list(zone, page);
1137                         if (!pagevec_add(&pvec, page)) {
1138                                 spin_unlock_irq(&zone->lru_lock);
1139                                 __pagevec_release(&pvec);
1140                                 spin_lock_irq(&zone->lru_lock);
1141                         }
1142                 }
1143         }
1144         spin_unlock_irq(&zone->lru_lock);
1145 done:
1146         pagevec_release(&pvec);
1147 }
1148
1149 /*
1150  * This moves pages from the active list to the inactive list.
1151  *
1152  * We move them the other way if the page is referenced by one or more
1153  * processes, from rmap.
1154  *
1155  * If the pages are mostly unmapped, the processing is fast and it is
1156  * appropriate to hold zone->lru_lock across the whole operation.  But if
1157  * the pages are mapped, the processing is slow (page_referenced()) so we
1158  * should drop zone->lru_lock around each page.  It's impossible to balance
1159  * this, so instead we remove the pages from the LRU while processing them.
1160  * It is safe to rely on PG_active against the non-LRU pages in here because
1161  * nobody will play with that bit on a non-LRU page.
1162  *
1163  * The downside is that we have to touch page->_count against each page.
1164  * But we had to alter page->flags anyway.
1165  */
1166 static void
1167 refill_inactive_zone(struct zone *zone, struct scan_control *sc)
1168 {
1169         int pgmoved;
1170         int pgdeactivate = 0;
1171         int pgscanned;
1172         int nr_pages = sc->nr_to_scan;
1173         LIST_HEAD(l_hold);      /* The pages which were snipped off */
1174         LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
1175         LIST_HEAD(l_active);    /* Pages to go onto the active_list */
1176         struct page *page;
1177         struct pagevec pvec;
1178         int reclaim_mapped = 0;
1179         long mapped_ratio;
1180         long distress;
1181         long swap_tendency;
1182
1183         lru_add_drain();
1184         spin_lock_irq(&zone->lru_lock);
1185         pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
1186                                     &l_hold, &pgscanned);
1187         zone->pages_scanned += pgscanned;
1188         zone->nr_active -= pgmoved;
1189         spin_unlock_irq(&zone->lru_lock);
1190
1191         /*
1192          * `distress' is a measure of how much trouble we're having reclaiming
1193          * pages.  0 -> no problems.  100 -> great trouble.
1194          */
1195         distress = 100 >> zone->prev_priority;
1196
1197         /*
1198          * The point of this algorithm is to decide when to start reclaiming
1199          * mapped memory instead of just pagecache.  Work out how much memory
1200          * is mapped.
1201          */
1202         mapped_ratio = (sc->nr_mapped * 100) / total_memory;
1203
1204         /*
1205          * Now decide how much we really want to unmap some pages.  The mapped
1206          * ratio is downgraded - just because there's a lot of mapped memory
1207          * doesn't necessarily mean that page reclaim isn't succeeding.
1208          *
1209          * The distress ratio is important - we don't want to start going oom.
1210          *
1211          * A 100% value of vm_swappiness overrides this algorithm altogether.
1212          */
1213         swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
1214
1215         /*
1216          * Now use this metric to decide whether to start moving mapped memory
1217          * onto the inactive list.
1218          */
1219         if (swap_tendency >= 100)
1220                 reclaim_mapped = 1;
1221
1222         while (!list_empty(&l_hold)) {
1223                 cond_resched();
1224                 page = lru_to_page(&l_hold);
1225                 list_del(&page->lru);
1226                 if (page_mapped(page)) {
1227                         if (!reclaim_mapped ||
1228                             (total_swap_pages == 0 && PageAnon(page)) ||
1229                             page_referenced(page, 0)) {
1230                                 list_add(&page->lru, &l_active);
1231                                 continue;
1232                         }
1233                 }
1234                 list_add(&page->lru, &l_inactive);
1235         }
1236
1237         pagevec_init(&pvec, 1);
1238         pgmoved = 0;
1239         spin_lock_irq(&zone->lru_lock);
1240         while (!list_empty(&l_inactive)) {
1241                 page = lru_to_page(&l_inactive);
1242                 prefetchw_prev_lru_page(page, &l_inactive, flags);
1243                 if (TestSetPageLRU(page))
1244                         BUG();
1245                 if (!TestClearPageActive(page))
1246                         BUG();
1247                 list_move(&page->lru, &zone->inactive_list);
1248                 pgmoved++;
1249                 if (!pagevec_add(&pvec, page)) {
1250                         zone->nr_inactive += pgmoved;
1251                         spin_unlock_irq(&zone->lru_lock);
1252                         pgdeactivate += pgmoved;
1253                         pgmoved = 0;
1254                         if (buffer_heads_over_limit)
1255                                 pagevec_strip(&pvec);
1256                         __pagevec_release(&pvec);
1257                         spin_lock_irq(&zone->lru_lock);
1258                 }
1259         }
1260         zone->nr_inactive += pgmoved;
1261         pgdeactivate += pgmoved;
1262         if (buffer_heads_over_limit) {
1263                 spin_unlock_irq(&zone->lru_lock);
1264                 pagevec_strip(&pvec);
1265                 spin_lock_irq(&zone->lru_lock);
1266         }
1267
1268         pgmoved = 0;
1269         while (!list_empty(&l_active)) {
1270                 page = lru_to_page(&l_active);
1271                 prefetchw_prev_lru_page(page, &l_active, flags);
1272                 if (TestSetPageLRU(page))
1273                         BUG();
1274                 BUG_ON(!PageActive(page));
1275                 list_move(&page->lru, &zone->active_list);
1276                 pgmoved++;
1277                 if (!pagevec_add(&pvec, page)) {
1278                         zone->nr_active += pgmoved;
1279                         pgmoved = 0;
1280                         spin_unlock_irq(&zone->lru_lock);
1281                         __pagevec_release(&pvec);
1282                         spin_lock_irq(&zone->lru_lock);
1283                 }
1284         }
1285         zone->nr_active += pgmoved;
1286         spin_unlock(&zone->lru_lock);
1287
1288         __mod_page_state_zone(zone, pgrefill, pgscanned);
1289         __mod_page_state(pgdeactivate, pgdeactivate);
1290         local_irq_enable();
1291
1292         pagevec_release(&pvec);
1293 }
1294
1295 /*
1296  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1297  */
1298 static void
1299 shrink_zone(struct zone *zone, struct scan_control *sc)
1300 {
1301         unsigned long nr_active;
1302         unsigned long nr_inactive;
1303
1304         atomic_inc(&zone->reclaim_in_progress);
1305
1306         /*
1307          * Add one to `nr_to_scan' just to make sure that the kernel will
1308          * slowly sift through the active list.
1309          */
1310         zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
1311         nr_active = zone->nr_scan_active;
1312         if (nr_active >= sc->swap_cluster_max)
1313                 zone->nr_scan_active = 0;
1314         else
1315                 nr_active = 0;
1316
1317         zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
1318         nr_inactive = zone->nr_scan_inactive;
1319         if (nr_inactive >= sc->swap_cluster_max)
1320                 zone->nr_scan_inactive = 0;
1321         else
1322                 nr_inactive = 0;
1323
1324         while (nr_active || nr_inactive) {
1325                 if (nr_active) {
1326                         sc->nr_to_scan = min(nr_active,
1327                                         (unsigned long)sc->swap_cluster_max);
1328                         nr_active -= sc->nr_to_scan;
1329                         refill_inactive_zone(zone, sc);
1330                 }
1331
1332                 if (nr_inactive) {
1333                         sc->nr_to_scan = min(nr_inactive,
1334                                         (unsigned long)sc->swap_cluster_max);
1335                         nr_inactive -= sc->nr_to_scan;
1336                         shrink_cache(zone, sc);
1337                 }
1338         }
1339
1340         throttle_vm_writeout();
1341
1342         atomic_dec(&zone->reclaim_in_progress);
1343 }
1344
1345 /*
1346  * This is the direct reclaim path, for page-allocating processes.  We only
1347  * try to reclaim pages from zones which will satisfy the caller's allocation
1348  * request.
1349  *
1350  * We reclaim from a zone even if that zone is over pages_high.  Because:
1351  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1352  *    allocation or
1353  * b) The zones may be over pages_high but they must go *over* pages_high to
1354  *    satisfy the `incremental min' zone defense algorithm.
1355  *
1356  * Returns the number of reclaimed pages.
1357  *
1358  * If a zone is deemed to be full of pinned pages then just give it a light
1359  * scan then give up on it.
1360  */
1361 static void
1362 shrink_caches(struct zone **zones, struct scan_control *sc)
1363 {
1364         int i;
1365
1366         for (i = 0; zones[i] != NULL; i++) {
1367                 struct zone *zone = zones[i];
1368
1369                 if (!populated_zone(zone))
1370                         continue;
1371
1372                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1373                         continue;
1374
1375                 zone->temp_priority = sc->priority;
1376                 if (zone->prev_priority > sc->priority)
1377                         zone->prev_priority = sc->priority;
1378
1379                 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
1380                         continue;       /* Let kswapd poll it */
1381
1382                 shrink_zone(zone, sc);
1383         }
1384 }
1385
1386 /*
1387  * This is the main entry point to direct page reclaim.
1388  *
1389  * If a full scan of the inactive list fails to free enough memory then we
1390  * are "out of memory" and something needs to be killed.
1391  *
1392  * If the caller is !__GFP_FS then the probability of a failure is reasonably
1393  * high - the zone may be full of dirty or under-writeback pages, which this
1394  * caller can't do much about.  We kick pdflush and take explicit naps in the
1395  * hope that some of these pages can be written.  But if the allocating task
1396  * holds filesystem locks which prevent writeout this might not work, and the
1397  * allocation attempt will fail.
1398  */
1399 int try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
1400 {
1401         int priority;
1402         int ret = 0;
1403         int total_scanned = 0, total_reclaimed = 0;
1404         struct reclaim_state *reclaim_state = current->reclaim_state;
1405         struct scan_control sc;
1406         unsigned long lru_pages = 0;
1407         int i;
1408
1409         sc.gfp_mask = gfp_mask;
1410         sc.may_writepage = !laptop_mode;
1411         sc.may_swap = 1;
1412
1413         inc_page_state(allocstall);
1414
1415         for (i = 0; zones[i] != NULL; i++) {
1416                 struct zone *zone = zones[i];
1417
1418                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1419                         continue;
1420
1421                 zone->temp_priority = DEF_PRIORITY;
1422                 lru_pages += zone->nr_active + zone->nr_inactive;
1423         }
1424
1425         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1426                 sc.nr_mapped = read_page_state(nr_mapped);
1427                 sc.nr_scanned = 0;
1428                 sc.nr_reclaimed = 0;
1429                 sc.priority = priority;
1430                 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1431                 if (!priority)
1432                         disable_swap_token();
1433                 shrink_caches(zones, &sc);
1434                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
1435                 if (reclaim_state) {
1436                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1437                         reclaim_state->reclaimed_slab = 0;
1438                 }
1439                 total_scanned += sc.nr_scanned;
1440                 total_reclaimed += sc.nr_reclaimed;
1441                 if (total_reclaimed >= sc.swap_cluster_max) {
1442                         ret = 1;
1443                         goto out;
1444                 }
1445
1446                 /*
1447                  * Try to write back as many pages as we just scanned.  This
1448                  * tends to cause slow streaming writers to write data to the
1449                  * disk smoothly, at the dirtying rate, which is nice.   But
1450                  * that's undesirable in laptop mode, where we *want* lumpy
1451                  * writeout.  So in laptop mode, write out the whole world.
1452                  */
1453                 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
1454                         wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1455                         sc.may_writepage = 1;
1456                 }
1457
1458                 /* Take a nap, wait for some writeback to complete */
1459                 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1460                         blk_congestion_wait(WRITE, HZ/10);
1461         }
1462 out:
1463         for (i = 0; zones[i] != 0; i++) {
1464                 struct zone *zone = zones[i];
1465
1466                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1467                         continue;
1468
1469                 zone->prev_priority = zone->temp_priority;
1470         }
1471         return ret;
1472 }
1473
1474 /*
1475  * For kswapd, balance_pgdat() will work across all this node's zones until
1476  * they are all at pages_high.
1477  *
1478  * If `nr_pages' is non-zero then it is the number of pages which are to be
1479  * reclaimed, regardless of the zone occupancies.  This is a software suspend
1480  * special.
1481  *
1482  * Returns the number of pages which were actually freed.
1483  *
1484  * There is special handling here for zones which are full of pinned pages.
1485  * This can happen if the pages are all mlocked, or if they are all used by
1486  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1487  * What we do is to detect the case where all pages in the zone have been
1488  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1489  * dead and from now on, only perform a short scan.  Basically we're polling
1490  * the zone for when the problem goes away.
1491  *
1492  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1493  * zones which have free_pages > pages_high, but once a zone is found to have
1494  * free_pages <= pages_high, we scan that zone and the lower zones regardless
1495  * of the number of free pages in the lower zones.  This interoperates with
1496  * the page allocator fallback scheme to ensure that aging of pages is balanced
1497  * across the zones.
1498  */
1499 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
1500 {
1501         int to_free = nr_pages;
1502         int all_zones_ok;
1503         int priority;
1504         int i;
1505         int total_scanned, total_reclaimed;
1506         struct reclaim_state *reclaim_state = current->reclaim_state;
1507         struct scan_control sc;
1508
1509 loop_again:
1510         total_scanned = 0;
1511         total_reclaimed = 0;
1512         sc.gfp_mask = GFP_KERNEL;
1513         sc.may_writepage = !laptop_mode;
1514         sc.may_swap = 1;
1515         sc.nr_mapped = read_page_state(nr_mapped);
1516
1517         inc_page_state(pageoutrun);
1518
1519         for (i = 0; i < pgdat->nr_zones; i++) {
1520                 struct zone *zone = pgdat->node_zones + i;
1521
1522                 zone->temp_priority = DEF_PRIORITY;
1523         }
1524
1525         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1526                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1527                 unsigned long lru_pages = 0;
1528
1529                 /* The swap token gets in the way of swapout... */
1530                 if (!priority)
1531                         disable_swap_token();
1532
1533                 all_zones_ok = 1;
1534
1535                 if (nr_pages == 0) {
1536                         /*
1537                          * Scan in the highmem->dma direction for the highest
1538                          * zone which needs scanning
1539                          */
1540                         for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1541                                 struct zone *zone = pgdat->node_zones + i;
1542
1543                                 if (!populated_zone(zone))
1544                                         continue;
1545
1546                                 if (zone->all_unreclaimable &&
1547                                                 priority != DEF_PRIORITY)
1548                                         continue;
1549
1550                                 if (!zone_watermark_ok(zone, order,
1551                                                 zone->pages_high, 0, 0)) {
1552                                         end_zone = i;
1553                                         goto scan;
1554                                 }
1555                         }
1556                         goto out;
1557                 } else {
1558                         end_zone = pgdat->nr_zones - 1;
1559                 }
1560 scan:
1561                 for (i = 0; i <= end_zone; i++) {
1562                         struct zone *zone = pgdat->node_zones + i;
1563
1564                         lru_pages += zone->nr_active + zone->nr_inactive;
1565                 }
1566
1567                 /*
1568                  * Now scan the zone in the dma->highmem direction, stopping
1569                  * at the last zone which needs scanning.
1570                  *
1571                  * We do this because the page allocator works in the opposite
1572                  * direction.  This prevents the page allocator from allocating
1573                  * pages behind kswapd's direction of progress, which would
1574                  * cause too much scanning of the lower zones.
1575                  */
1576                 for (i = 0; i <= end_zone; i++) {
1577                         struct zone *zone = pgdat->node_zones + i;
1578                         int nr_slab;
1579
1580                         if (!populated_zone(zone))
1581                                 continue;
1582
1583                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1584                                 continue;
1585
1586                         if (nr_pages == 0) {    /* Not software suspend */
1587                                 if (!zone_watermark_ok(zone, order,
1588                                                 zone->pages_high, end_zone, 0))
1589                                         all_zones_ok = 0;
1590                         }
1591                         zone->temp_priority = priority;
1592                         if (zone->prev_priority > priority)
1593                                 zone->prev_priority = priority;
1594                         sc.nr_scanned = 0;
1595                         sc.nr_reclaimed = 0;
1596                         sc.priority = priority;
1597                         sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
1598                         atomic_inc(&zone->reclaim_in_progress);
1599                         shrink_zone(zone, &sc);
1600                         atomic_dec(&zone->reclaim_in_progress);
1601                         reclaim_state->reclaimed_slab = 0;
1602                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1603                                                 lru_pages);
1604                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1605                         total_reclaimed += sc.nr_reclaimed;
1606                         total_scanned += sc.nr_scanned;
1607                         if (zone->all_unreclaimable)
1608                                 continue;
1609                         if (nr_slab == 0 && zone->pages_scanned >=
1610                                     (zone->nr_active + zone->nr_inactive) * 4)
1611                                 zone->all_unreclaimable = 1;
1612                         /*
1613                          * If we've done a decent amount of scanning and
1614                          * the reclaim ratio is low, start doing writepage
1615                          * even in laptop mode
1616                          */
1617                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1618                             total_scanned > total_reclaimed+total_reclaimed/2)
1619                                 sc.may_writepage = 1;
1620                 }
1621                 if (nr_pages && to_free > total_reclaimed)
1622                         continue;       /* swsusp: need to do more work */
1623                 if (all_zones_ok)
1624                         break;          /* kswapd: all done */
1625                 /*
1626                  * OK, kswapd is getting into trouble.  Take a nap, then take
1627                  * another pass across the zones.
1628                  */
1629                 if (total_scanned && priority < DEF_PRIORITY - 2)
1630                         blk_congestion_wait(WRITE, HZ/10);
1631
1632                 /*
1633                  * We do this so kswapd doesn't build up large priorities for
1634                  * example when it is freeing in parallel with allocators. It
1635                  * matches the direct reclaim path behaviour in terms of impact
1636                  * on zone->*_priority.
1637                  */
1638                 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
1639                         break;
1640         }
1641 out:
1642         for (i = 0; i < pgdat->nr_zones; i++) {
1643                 struct zone *zone = pgdat->node_zones + i;
1644
1645                 zone->prev_priority = zone->temp_priority;
1646         }
1647         if (!all_zones_ok) {
1648                 cond_resched();
1649                 goto loop_again;
1650         }
1651
1652         return total_reclaimed;
1653 }
1654
1655 /*
1656  * The background pageout daemon, started as a kernel thread
1657  * from the init process.
1658  *
1659  * This basically trickles out pages so that we have _some_
1660  * free memory available even if there is no other activity
1661  * that frees anything up. This is needed for things like routing
1662  * etc, where we otherwise might have all activity going on in
1663  * asynchronous contexts that cannot page things out.
1664  *
1665  * If there are applications that are active memory-allocators
1666  * (most normal use), this basically shouldn't matter.
1667  */
1668 static int kswapd(void *p)
1669 {
1670         unsigned long order;
1671         pg_data_t *pgdat = (pg_data_t*)p;
1672         struct task_struct *tsk = current;
1673         DEFINE_WAIT(wait);
1674         struct reclaim_state reclaim_state = {
1675                 .reclaimed_slab = 0,
1676         };
1677         cpumask_t cpumask;
1678
1679         daemonize("kswapd%d", pgdat->node_id);
1680         cpumask = node_to_cpumask(pgdat->node_id);
1681         if (!cpus_empty(cpumask))
1682                 set_cpus_allowed(tsk, cpumask);
1683         current->reclaim_state = &reclaim_state;
1684
1685         /*
1686          * Tell the memory management that we're a "memory allocator",
1687          * and that if we need more memory we should get access to it
1688          * regardless (see "__alloc_pages()"). "kswapd" should
1689          * never get caught in the normal page freeing logic.
1690          *
1691          * (Kswapd normally doesn't need memory anyway, but sometimes
1692          * you need a small amount of memory in order to be able to
1693          * page out something else, and this flag essentially protects
1694          * us from recursively trying to free more memory as we're
1695          * trying to free the first piece of memory in the first place).
1696          */
1697         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1698
1699         order = 0;
1700         for ( ; ; ) {
1701                 unsigned long new_order;
1702
1703                 try_to_freeze();
1704
1705                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1706                 new_order = pgdat->kswapd_max_order;
1707                 pgdat->kswapd_max_order = 0;
1708                 if (order < new_order) {
1709                         /*
1710                          * Don't sleep if someone wants a larger 'order'
1711                          * allocation
1712                          */
1713                         order = new_order;
1714                 } else {
1715                         schedule();
1716                         order = pgdat->kswapd_max_order;
1717                 }
1718                 finish_wait(&pgdat->kswapd_wait, &wait);
1719
1720                 balance_pgdat(pgdat, 0, order);
1721         }
1722         return 0;
1723 }
1724
1725 /*
1726  * A zone is low on free memory, so wake its kswapd task to service it.
1727  */
1728 void wakeup_kswapd(struct zone *zone, int order)
1729 {
1730         pg_data_t *pgdat;
1731
1732         if (!populated_zone(zone))
1733                 return;
1734
1735         pgdat = zone->zone_pgdat;
1736         if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1737                 return;
1738         if (pgdat->kswapd_max_order < order)
1739                 pgdat->kswapd_max_order = order;
1740         if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1741                 return;
1742         if (!waitqueue_active(&pgdat->kswapd_wait))
1743                 return;
1744         wake_up_interruptible(&pgdat->kswapd_wait);
1745 }
1746
1747 #ifdef CONFIG_PM
1748 /*
1749  * Try to free `nr_pages' of memory, system-wide.  Returns the number of freed
1750  * pages.
1751  */
1752 int shrink_all_memory(int nr_pages)
1753 {
1754         pg_data_t *pgdat;
1755         int nr_to_free = nr_pages;
1756         int ret = 0;
1757         struct reclaim_state reclaim_state = {
1758                 .reclaimed_slab = 0,
1759         };
1760
1761         current->reclaim_state = &reclaim_state;
1762         for_each_pgdat(pgdat) {
1763                 int freed;
1764                 freed = balance_pgdat(pgdat, nr_to_free, 0);
1765                 ret += freed;
1766                 nr_to_free -= freed;
1767                 if (nr_to_free <= 0)
1768                         break;
1769         }
1770         current->reclaim_state = NULL;
1771         return ret;
1772 }
1773 #endif
1774
1775 #ifdef CONFIG_HOTPLUG_CPU
1776 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1777    not required for correctness.  So if the last cpu in a node goes
1778    away, we get changed to run anywhere: as the first one comes back,
1779    restore their cpu bindings. */
1780 static int __devinit cpu_callback(struct notifier_block *nfb,
1781                                   unsigned long action,
1782                                   void *hcpu)
1783 {
1784         pg_data_t *pgdat;
1785         cpumask_t mask;
1786
1787         if (action == CPU_ONLINE) {
1788                 for_each_pgdat(pgdat) {
1789                         mask = node_to_cpumask(pgdat->node_id);
1790                         if (any_online_cpu(mask) != NR_CPUS)
1791                                 /* One of our CPUs online: restore mask */
1792                                 set_cpus_allowed(pgdat->kswapd, mask);
1793                 }
1794         }
1795         return NOTIFY_OK;
1796 }
1797 #endif /* CONFIG_HOTPLUG_CPU */
1798
1799 static int __init kswapd_init(void)
1800 {
1801         pg_data_t *pgdat;
1802         swap_setup();
1803         for_each_pgdat(pgdat)
1804                 pgdat->kswapd
1805                 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1806         total_memory = nr_free_pagecache_pages();
1807         hotcpu_notifier(cpu_callback, 0);
1808         return 0;
1809 }
1810
1811 module_init(kswapd_init)
1812
1813 #ifdef CONFIG_NUMA
1814 /*
1815  * Zone reclaim mode
1816  *
1817  * If non-zero call zone_reclaim when the number of free pages falls below
1818  * the watermarks.
1819  *
1820  * In the future we may add flags to the mode. However, the page allocator
1821  * should only have to check that zone_reclaim_mode != 0 before calling
1822  * zone_reclaim().
1823  */
1824 int zone_reclaim_mode __read_mostly;
1825
1826 #define RECLAIM_OFF 0
1827 #define RECLAIM_ZONE (1<<0)     /* Run shrink_cache on the zone */
1828 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
1829 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
1830 #define RECLAIM_SLAB (1<<3)     /* Do a global slab shrink if the zone is out of memory */
1831
1832 /*
1833  * Mininum time between zone reclaim scans
1834  */
1835 int zone_reclaim_interval __read_mostly = 30*HZ;
1836
1837 /*
1838  * Priority for ZONE_RECLAIM. This determines the fraction of pages
1839  * of a node considered for each zone_reclaim. 4 scans 1/16th of
1840  * a zone.
1841  */
1842 #define ZONE_RECLAIM_PRIORITY 4
1843
1844 /*
1845  * Try to free up some pages from this zone through reclaim.
1846  */
1847 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1848 {
1849         int nr_pages;
1850         struct task_struct *p = current;
1851         struct reclaim_state reclaim_state;
1852         struct scan_control sc;
1853         cpumask_t mask;
1854         int node_id;
1855
1856         if (time_before(jiffies,
1857                 zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval))
1858                         return 0;
1859
1860         if (!(gfp_mask & __GFP_WAIT) ||
1861                 zone->all_unreclaimable ||
1862                 atomic_read(&zone->reclaim_in_progress) > 0)
1863                         return 0;
1864
1865         node_id = zone->zone_pgdat->node_id;
1866         mask = node_to_cpumask(node_id);
1867         if (!cpus_empty(mask) && node_id != numa_node_id())
1868                 return 0;
1869
1870         sc.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE);
1871         sc.may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP);
1872         sc.nr_scanned = 0;
1873         sc.nr_reclaimed = 0;
1874         sc.priority = ZONE_RECLAIM_PRIORITY + 1;
1875         sc.nr_mapped = read_page_state(nr_mapped);
1876         sc.gfp_mask = gfp_mask;
1877
1878         disable_swap_token();
1879
1880         nr_pages = 1 << order;
1881         if (nr_pages > SWAP_CLUSTER_MAX)
1882                 sc.swap_cluster_max = nr_pages;
1883         else
1884                 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1885
1886         cond_resched();
1887         p->flags |= PF_MEMALLOC;
1888         reclaim_state.reclaimed_slab = 0;
1889         p->reclaim_state = &reclaim_state;
1890
1891         /*
1892          * Free memory by calling shrink zone with increasing priorities
1893          * until we have enough memory freed.
1894          */
1895         do {
1896                 sc.priority--;
1897                 shrink_zone(zone, &sc);
1898
1899         } while (sc.nr_reclaimed < nr_pages && sc.priority > 0);
1900
1901         if (sc.nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) {
1902                 /*
1903                  * shrink_slab does not currently allow us to determine
1904                  * how many pages were freed in the zone. So we just
1905                  * shake the slab and then go offnode for a single allocation.
1906                  *
1907                  * shrink_slab will free memory on all zones and may take
1908                  * a long time.
1909                  */
1910                 shrink_slab(sc.nr_scanned, gfp_mask, order);
1911                 sc.nr_reclaimed = 1;    /* Avoid getting the off node timeout */
1912         }
1913
1914         p->reclaim_state = NULL;
1915         current->flags &= ~PF_MEMALLOC;
1916
1917         if (sc.nr_reclaimed == 0)
1918                 zone->last_unsuccessful_zone_reclaim = jiffies;
1919
1920         return sc.nr_reclaimed >= nr_pages;
1921 }
1922 #endif
1923