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 #include <linux/delay.h>
  37
  38 #include <asm/tlbflush.h>
  39 #include <asm/div64.h>
  40
  41 #include <linux/swapops.h>
  42
  43 #include "internal.h"
  44
  45 struct scan_control {
  46         /* Incremented by the number of inactive pages that were scanned */
  47         unsigned long nr_scanned;
  48
  49         unsigned long nr_mapped;        /* From page_state */
  50
  51         /* This context's GFP mask */
  52         gfp_t gfp_mask;
  53
  54         int may_writepage;
  55
  56         /* Can pages be swapped as part of reclaim? */
  57         int may_swap;
  58
  59         /* This context's SWAP_CLUSTER_MAX. If freeing memory for
  60          * suspend, we effectively ignore SWAP_CLUSTER_MAX.
  61          * In this context, it doesn't matter that we scan the
  62          * whole list at once. */
  63         int swap_cluster_max;
  64
  65         int swappiness;
  66 };
  67
  68 /*
  69  * The list of shrinker callbacks used by to apply pressure to
  70  * ageable caches.
  71  */
  72 struct shrinker {
  73         shrinker_t              shrinker;
  74         struct list_head        list;
  75         int                     seeks;  /* seeks to recreate an obj */
  76         long                    nr;     /* objs pending delete */
  77 };
  78
  79 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  80
  81 #ifdef ARCH_HAS_PREFETCH
  82 #define prefetch_prev_lru_page(_page, _base, _field)                    \
  83         do {                                                            \
  84                 if ((_page)->lru.prev != _base) {                       \
  85                         struct page *prev;                              \
  86                                                                         \
  87                         prev = lru_to_page(&(_page->lru));              \
  88                         prefetch(&prev->_field);                        \
  89                 }                                                       \
  90         } while (0)
  91 #else
  92 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
  93 #endif
  94
  95 #ifdef ARCH_HAS_PREFETCHW
  96 #define prefetchw_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                         prefetchw(&prev->_field);                       \
 103                 }                                                       \
 104         } while (0)
 105 #else
 106 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 107 #endif
 108
 109 /*
 110  * From 0 .. 100.  Higher means more swappy.
 111  */
 112 int vm_swappiness = 60;
 113 static long total_memory;
 114
 115 static LIST_HEAD(shrinker_list);
 116 static DECLARE_RWSEM(shrinker_rwsem);
 117
 118 /*
 119  * Add a shrinker callback to be called from the vm
 120  */
 121 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
 122 {
 123         struct shrinker *shrinker;
 124
 125         shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
 126         if (shrinker) {
 127                 shrinker->shrinker = theshrinker;
 128                 shrinker->seeks = seeks;
 129                 shrinker->nr = 0;
 130                 down_write(&shrinker_rwsem);
 131                 list_add_tail(&shrinker->list, &shrinker_list);
 132                 up_write(&shrinker_rwsem);
 133         }
 134         return shrinker;
 135 }
 136 EXPORT_SYMBOL(set_shrinker);
 137
 138 /*
 139  * Remove one
 140  */
 141 void remove_shrinker(struct shrinker *shrinker)
 142 {
 143         down_write(&shrinker_rwsem);
 144         list_del(&shrinker->list);
 145         up_write(&shrinker_rwsem);
 146         kfree(shrinker);
 147 }
 148 EXPORT_SYMBOL(remove_shrinker);
 149
 150 #define SHRINK_BATCH 128
 151 /*
 152  * Call the shrink functions to age shrinkable caches
 153  *
 154  * Here we assume it costs one seek to replace a lru page and that it also
 155  * takes a seek to recreate a cache object.  With this in mind we age equal
 156  * percentages of the lru and ageable caches.  This should balance the seeks
 157  * generated by these structures.
 158  *
 159  * If the vm encounted mapped pages on the LRU it increase the pressure on
 160  * slab to avoid swapping.
 161  *
 162  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 163  *
 164  * `lru_pages' represents the number of on-LRU pages in all the zones which
 165  * are eligible for the caller's allocation attempt.  It is used for balancing
 166  * slab reclaim versus page reclaim.
 167  *
 168  * Returns the number of slab objects which we shrunk.
 169  */
 170 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 171                         unsigned long lru_pages)
 172 {
 173         struct shrinker *shrinker;
 174         unsigned long ret = 0;
 175
 176         if (scanned == 0)
 177                 scanned = SWAP_CLUSTER_MAX;
 178
 179         if (!down_read_trylock(&shrinker_rwsem))
 180                 return 1;       /* Assume we'll be able to shrink next time */
 181
 182         list_for_each_entry(shrinker, &shrinker_list, list) {
 183                 unsigned long long delta;
 184                 unsigned long total_scan;
 185                 unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
 186
 187                 delta = (4 * scanned) / shrinker->seeks;
 188                 delta *= max_pass;
 189                 do_div(delta, lru_pages + 1);
 190                 shrinker->nr += delta;
 191                 if (shrinker->nr < 0) {
 192                         printk(KERN_ERR "%s: nr=%ld\n",
 193                                         __FUNCTION__, shrinker->nr);
 194                         shrinker->nr = max_pass;
 195                 }
 196
 197                 /*
 198                  * Avoid risking looping forever due to too large nr value:
 199                  * never try to free more than twice the estimate number of
 200                  * freeable entries.
 201                  */
 202                 if (shrinker->nr > max_pass * 2)
 203                         shrinker->nr = max_pass * 2;
 204
 205                 total_scan = shrinker->nr;
 206                 shrinker->nr = 0;
 207
 208                 while (total_scan >= SHRINK_BATCH) {
 209                         long this_scan = SHRINK_BATCH;
 210                         int shrink_ret;
 211                         int nr_before;
 212
 213                         nr_before = (*shrinker->shrinker)(0, gfp_mask);
 214                         shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
 215                         if (shrink_ret == -1)
 216                                 break;
 217                         if (shrink_ret < nr_before)
 218                                 ret += nr_before - shrink_ret;
 219                         mod_page_state(slabs_scanned, this_scan);
 220                         total_scan -= this_scan;
 221
 222                         cond_resched();
 223                 }
 224
 225                 shrinker->nr += total_scan;
 226         }
 227         up_read(&shrinker_rwsem);
 228         return ret;
 229 }
 230
 231 /* Called without lock on whether page is mapped, so answer is unstable */
 232 static inline int page_mapping_inuse(struct page *page)
 233 {
 234         struct address_space *mapping;
 235
 236         /* Page is in somebody's page tables. */
 237         if (page_mapped(page))
 238                 return 1;
 239
 240         /* Be more reluctant to reclaim swapcache than pagecache */
 241         if (PageSwapCache(page))
 242                 return 1;
 243
 244         mapping = page_mapping(page);
 245         if (!mapping)
 246                 return 0;
 247
 248         /* File is mmap'd by somebody? */
 249         return mapping_mapped(mapping);
 250 }
 251
 252 static inline int is_page_cache_freeable(struct page *page)
 253 {
 254         return page_count(page) - !!PagePrivate(page) == 2;
 255 }
 256
 257 static int may_write_to_queue(struct backing_dev_info *bdi)
 258 {
 259         if (current->flags & PF_SWAPWRITE)
 260                 return 1;
 261         if (!bdi_write_congested(bdi))
 262                 return 1;
 263         if (bdi == current->backing_dev_info)
 264                 return 1;
 265         return 0;
 266 }
 267
 268 /*
 269  * We detected a synchronous write error writing a page out.  Probably
 270  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 271  * fsync(), msync() or close().
 272  *
 273  * The tricky part is that after writepage we cannot touch the mapping: nothing
 274  * prevents it from being freed up.  But we have a ref on the page and once
 275  * that page is locked, the mapping is pinned.
 276  *
 277  * We're allowed to run sleeping lock_page() here because we know the caller has
 278  * __GFP_FS.
 279  */
 280 static void handle_write_error(struct address_space *mapping,
 281                                 struct page *page, int error)
 282 {
 283         lock_page(page);
 284         if (page_mapping(page) == mapping) {
 285                 if (error == -ENOSPC)
 286                         set_bit(AS_ENOSPC, &mapping->flags);
 287                 else
 288                         set_bit(AS_EIO, &mapping->flags);
 289         }
 290         unlock_page(page);
 291 }
 292
 293 /*
 294  * pageout is called by shrink_page_list() for each dirty page.
 295  * Calls ->writepage().
 296  */
 297 pageout_t pageout(struct page *page, struct address_space *mapping)
 298 {
 299         /*
 300          * If the page is dirty, only perform writeback if that write
 301          * will be non-blocking.  To prevent this allocation from being
 302          * stalled by pagecache activity.  But note that there may be
 303          * stalls if we need to run get_block().  We could test
 304          * PagePrivate for that.
 305          *
 306          * If this process is currently in generic_file_write() against
 307          * this page's queue, we can perform writeback even if that
 308          * will block.
 309          *
 310          * If the page is swapcache, write it back even if that would
 311          * block, for some throttling. This happens by accident, because
 312          * swap_backing_dev_info is bust: it doesn't reflect the
 313          * congestion state of the swapdevs.  Easy to fix, if needed.
 314          * See swapfile.c:page_queue_congested().
 315          */
 316         if (!is_page_cache_freeable(page))
 317                 return PAGE_KEEP;
 318         if (!mapping) {
 319                 /*
 320                  * Some data journaling orphaned pages can have
 321                  * page->mapping == NULL while being dirty with clean buffers.
 322                  */
 323                 if (PagePrivate(page)) {
 324                         if (try_to_free_buffers(page)) {
 325                                 ClearPageDirty(page);
 326                                 printk("%s: orphaned page\n", __FUNCTION__);
 327                                 return PAGE_CLEAN;
 328                         }
 329                 }
 330                 return PAGE_KEEP;
 331         }
 332         if (mapping->a_ops->writepage == NULL)
 333                 return PAGE_ACTIVATE;
 334         if (!may_write_to_queue(mapping->backing_dev_info))
 335                 return PAGE_KEEP;
 336
 337         if (clear_page_dirty_for_io(page)) {
 338                 int res;
 339                 struct writeback_control wbc = {
 340                         .sync_mode = WB_SYNC_NONE,
 341                         .nr_to_write = SWAP_CLUSTER_MAX,
 342                         .nonblocking = 1,
 343                         .for_reclaim = 1,
 344                 };
 345
 346                 SetPageReclaim(page);
 347                 res = mapping->a_ops->writepage(page, &wbc);
 348                 if (res < 0)
 349                         handle_write_error(mapping, page, res);
 350                 if (res == AOP_WRITEPAGE_ACTIVATE) {
 351                         ClearPageReclaim(page);
 352                         return PAGE_ACTIVATE;
 353                 }
 354                 if (!PageWriteback(page)) {
 355                         /* synchronous write or broken a_ops? */
 356                         ClearPageReclaim(page);
 357                 }
 358
 359                 return PAGE_SUCCESS;
 360         }
 361
 362         return PAGE_CLEAN;
 363 }
 364
 365 int remove_mapping(struct address_space *mapping, struct page *page)
 366 {
 367         if (!mapping)
 368                 return 0;               /* truncate got there first */
 369
 370         write_lock_irq(&mapping->tree_lock);
 371
 372         /*
 373          * The non-racy check for busy page.  It is critical to check
 374          * PageDirty _after_ making sure that the page is freeable and
 375          * not in use by anybody.       (pagecache + us == 2)
 376          */
 377         if (unlikely(page_count(page) != 2))
 378                 goto cannot_free;
 379         smp_rmb();
 380         if (unlikely(PageDirty(page)))
 381                 goto cannot_free;
 382
 383         if (PageSwapCache(page)) {
 384                 swp_entry_t swap = { .val = page_private(page) };
 385                 __delete_from_swap_cache(page);
 386                 write_unlock_irq(&mapping->tree_lock);
 387                 swap_free(swap);
 388                 __put_page(page);       /* The pagecache ref */
 389                 return 1;
 390         }
 391
 392         __remove_from_page_cache(page);
 393         write_unlock_irq(&mapping->tree_lock);
 394         __put_page(page);
 395         return 1;
 396
 397 cannot_free:
 398         write_unlock_irq(&mapping->tree_lock);
 399         return 0;
 400 }
 401
 402 /*
 403  * shrink_page_list() returns the number of reclaimed pages
 404  */
 405 static unsigned long shrink_page_list(struct list_head *page_list,
 406                                         struct scan_control *sc)
 407 {
 408         LIST_HEAD(ret_pages);
 409         struct pagevec freed_pvec;
 410         int pgactivate = 0;
 411         unsigned long nr_reclaimed = 0;
 412
 413         cond_resched();
 414
 415         pagevec_init(&freed_pvec, 1);
 416         while (!list_empty(page_list)) {
 417                 struct address_space *mapping;
 418                 struct page *page;
 419                 int may_enter_fs;
 420                 int referenced;
 421
 422                 cond_resched();
 423
 424                 page = lru_to_page(page_list);
 425                 list_del(&page->lru);
 426
 427                 if (TestSetPageLocked(page))
 428                         goto keep;
 429
 430                 BUG_ON(PageActive(page));
 431
 432                 sc->nr_scanned++;
 433
 434                 if (!sc->may_swap && page_mapped(page))
 435                         goto keep_locked;
 436
 437                 /* Double the slab pressure for mapped and swapcache pages */
 438                 if (page_mapped(page) || PageSwapCache(page))
 439                         sc->nr_scanned++;
 440
 441                 if (PageWriteback(page))
 442                         goto keep_locked;
 443
 444                 referenced = page_referenced(page, 1);
 445                 /* In active use or really unfreeable?  Activate it. */
 446                 if (referenced && page_mapping_inuse(page))
 447                         goto activate_locked;
 448
 449 #ifdef CONFIG_SWAP
 450                 /*
 451                  * Anonymous process memory has backing store?
 452                  * Try to allocate it some swap space here.
 453                  */
 454                 if (PageAnon(page) && !PageSwapCache(page))
 455                         if (!add_to_swap(page, GFP_ATOMIC))
 456                                 goto activate_locked;
 457 #endif /* CONFIG_SWAP */
 458
 459                 mapping = page_mapping(page);
 460                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 461                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 462
 463                 /*
 464                  * The page is mapped into the page tables of one or more
 465                  * processes. Try to unmap it here.
 466                  */
 467                 if (page_mapped(page) && mapping) {
 468                         switch (try_to_unmap(page, 0)) {
 469                         case SWAP_FAIL:
 470                                 goto activate_locked;
 471                         case SWAP_AGAIN:
 472                                 goto keep_locked;
 473                         case SWAP_SUCCESS:
 474                                 ; /* try to free the page below */
 475                         }
 476                 }
 477
 478                 if (PageDirty(page)) {
 479                         if (referenced)
 480                                 goto keep_locked;
 481                         if (!may_enter_fs)
 482                                 goto keep_locked;
 483                         if (!sc->may_writepage)
 484                                 goto keep_locked;
 485
 486                         /* Page is dirty, try to write it out here */
 487                         switch(pageout(page, mapping)) {
 488                         case PAGE_KEEP:
 489                                 goto keep_locked;
 490                         case PAGE_ACTIVATE:
 491                                 goto activate_locked;
 492                         case PAGE_SUCCESS:
 493                                 if (PageWriteback(page) || PageDirty(page))
 494                                         goto keep;
 495                                 /*
 496                                  * A synchronous write - probably a ramdisk.  Go
 497                                  * ahead and try to reclaim the page.
 498                                  */
 499                                 if (TestSetPageLocked(page))
 500                                         goto keep;
 501                                 if (PageDirty(page) || PageWriteback(page))
 502                                         goto keep_locked;
 503                                 mapping = page_mapping(page);
 504                         case PAGE_CLEAN:
 505                                 ; /* try to free the page below */
 506                         }
 507                 }
 508
 509                 /*
 510                  * If the page has buffers, try to free the buffer mappings
 511                  * associated with this page. If we succeed we try to free
 512                  * the page as well.
 513                  *
 514                  * We do this even if the page is PageDirty().
 515                  * try_to_release_page() does not perform I/O, but it is
 516                  * possible for a page to have PageDirty set, but it is actually
 517                  * clean (all its buffers are clean).  This happens if the
 518                  * buffers were written out directly, with submit_bh(). ext3
 519                  * will do this, as well as the blockdev mapping.
 520                  * try_to_release_page() will discover that cleanness and will
 521                  * drop the buffers and mark the page clean - it can be freed.
 522                  *
 523                  * Rarely, pages can have buffers and no ->mapping.  These are
 524                  * the pages which were not successfully invalidated in
 525                  * truncate_complete_page().  We try to drop those buffers here
 526                  * and if that worked, and the page is no longer mapped into
 527                  * process address space (page_count == 1) it can be freed.
 528                  * Otherwise, leave the page on the LRU so it is swappable.
 529                  */
 530                 if (PagePrivate(page)) {
 531                         if (!try_to_release_page(page, sc->gfp_mask))
 532                                 goto activate_locked;
 533                         if (!mapping && page_count(page) == 1)
 534                                 goto free_it;
 535                 }
 536
 537                 if (!remove_mapping(mapping, page))
 538                         goto keep_locked;
 539
 540 free_it:
 541                 unlock_page(page);
 542                 nr_reclaimed++;
 543                 if (!pagevec_add(&freed_pvec, page))
 544                         __pagevec_release_nonlru(&freed_pvec);
 545                 continue;
 546
 547 activate_locked:
 548                 SetPageActive(page);
 549                 pgactivate++;
 550 keep_locked:
 551                 unlock_page(page);
 552 keep:
 553                 list_add(&page->lru, &ret_pages);
 554                 BUG_ON(PageLRU(page));
 555         }
 556         list_splice(&ret_pages, page_list);
 557         if (pagevec_count(&freed_pvec))
 558                 __pagevec_release_nonlru(&freed_pvec);
 559         mod_page_state(pgactivate, pgactivate);
 560         return nr_reclaimed;
 561 }
 562
 563 /*
 564  * zone->lru_lock is heavily contended.  Some of the functions that
 565  * shrink the lists perform better by taking out a batch of pages
 566  * and working on them outside the LRU lock.
 567  *
 568  * For pagecache intensive workloads, this function is the hottest
 569  * spot in the kernel (apart from copy_*_user functions).
 570  *
 571  * Appropriate locks must be held before calling this function.
 572  *
 573  * @nr_to_scan: The number of pages to look through on the list.
 574  * @src:        The LRU list to pull pages off.
 575  * @dst:        The temp list to put pages on to.
 576  * @scanned:    The number of pages that were scanned.
 577  *
 578  * returns how many pages were moved onto *@dst.
 579  */
 580 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 581                 struct list_head *src, struct list_head *dst,
 582                 unsigned long *scanned)
 583 {
 584         unsigned long nr_taken = 0;
 585         struct page *page;
 586         unsigned long scan;
 587
 588         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
 589                 struct list_head *target;
 590                 page = lru_to_page(src);
 591                 prefetchw_prev_lru_page(page, src, flags);
 592
 593                 BUG_ON(!PageLRU(page));
 594
 595                 list_del(&page->lru);
 596                 target = src;
 597                 if (likely(get_page_unless_zero(page))) {
 598                         /*
 599                          * Be careful not to clear PageLRU until after we're
 600                          * sure the page is not being freed elsewhere -- the
 601                          * page release code relies on it.
 602                          */
 603                         ClearPageLRU(page);
 604                         target = dst;
 605                         nr_taken++;
 606                 } /* else it is being freed elsewhere */
 607
 608                 list_add(&page->lru, target);
 609         }
 610
 611         *scanned = scan;
 612         return nr_taken;
 613 }
 614
 615 /*
 616  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
 617  * of reclaimed pages
 618  */
 619 static unsigned long shrink_inactive_list(unsigned long max_scan,
 620                                 struct zone *zone, struct scan_control *sc)
 621 {
 622         LIST_HEAD(page_list);
 623         struct pagevec pvec;
 624         unsigned long nr_scanned = 0;
 625         unsigned long nr_reclaimed = 0;
 626
 627         pagevec_init(&pvec, 1);
 628
 629         lru_add_drain();
 630         spin_lock_irq(&zone->lru_lock);
 631         do {
 632                 struct page *page;
 633                 unsigned long nr_taken;
 634                 unsigned long nr_scan;
 635                 unsigned long nr_freed;
 636
 637                 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
 638                                              &zone->inactive_list,
 639                                              &page_list, &nr_scan);
 640                 zone->nr_inactive -= nr_taken;
 641                 zone->pages_scanned += nr_scan;
 642                 spin_unlock_irq(&zone->lru_lock);
 643
 644                 nr_scanned += nr_scan;
 645                 nr_freed = shrink_page_list(&page_list, sc);
 646                 nr_reclaimed += nr_freed;
 647                 local_irq_disable();
 648                 if (current_is_kswapd()) {
 649                         __mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
 650                         __mod_page_state(kswapd_steal, nr_freed);
 651                 } else
 652                         __mod_page_state_zone(zone, pgscan_direct, nr_scan);
 653                 __mod_page_state_zone(zone, pgsteal, nr_freed);
 654
 655                 if (nr_taken == 0)
 656                         goto done;
 657
 658                 spin_lock(&zone->lru_lock);
 659                 /*
 660                  * Put back any unfreeable pages.
 661                  */
 662                 while (!list_empty(&page_list)) {
 663                         page = lru_to_page(&page_list);
 664                         BUG_ON(PageLRU(page));
 665                         SetPageLRU(page);
 666                         list_del(&page->lru);
 667                         if (PageActive(page))
 668                                 add_page_to_active_list(zone, page);
 669                         else
 670                                 add_page_to_inactive_list(zone, page);
 671                         if (!pagevec_add(&pvec, page)) {
 672                                 spin_unlock_irq(&zone->lru_lock);
 673                                 __pagevec_release(&pvec);
 674                                 spin_lock_irq(&zone->lru_lock);
 675                         }
 676                 }
 677         } while (nr_scanned < max_scan);
 678         spin_unlock(&zone->lru_lock);
 679 done:
 680         local_irq_enable();
 681         pagevec_release(&pvec);
 682         return nr_reclaimed;
 683 }
 684
 685 /*
 686  * This moves pages from the active list to the inactive list.
 687  *
 688  * We move them the other way if the page is referenced by one or more
 689  * processes, from rmap.
 690  *
 691  * If the pages are mostly unmapped, the processing is fast and it is
 692  * appropriate to hold zone->lru_lock across the whole operation.  But if
 693  * the pages are mapped, the processing is slow (page_referenced()) so we
 694  * should drop zone->lru_lock around each page.  It's impossible to balance
 695  * this, so instead we remove the pages from the LRU while processing them.
 696  * It is safe to rely on PG_active against the non-LRU pages in here because
 697  * nobody will play with that bit on a non-LRU page.
 698  *
 699  * The downside is that we have to touch page->_count against each page.
 700  * But we had to alter page->flags anyway.
 701  */
 702 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 703                                 struct scan_control *sc)
 704 {
 705         unsigned long pgmoved;
 706         int pgdeactivate = 0;
 707         unsigned long pgscanned;
 708         LIST_HEAD(l_hold);      /* The pages which were snipped off */
 709         LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
 710         LIST_HEAD(l_active);    /* Pages to go onto the active_list */
 711         struct page *page;
 712         struct pagevec pvec;
 713         int reclaim_mapped = 0;
 714
 715         if (sc->may_swap) {
 716                 long mapped_ratio;
 717                 long distress;
 718                 long swap_tendency;
 719
 720                 /*
 721                  * `distress' is a measure of how much trouble we're having
 722                  * reclaiming pages.  0 -> no problems.  100 -> great trouble.
 723                  */
 724                 distress = 100 >> zone->prev_priority;
 725
 726                 /*
 727                  * The point of this algorithm is to decide when to start
 728                  * reclaiming mapped memory instead of just pagecache.  Work out
 729                  * how much memory
 730                  * is mapped.
 731                  */
 732                 mapped_ratio = (sc->nr_mapped * 100) / total_memory;
 733
 734                 /*
 735                  * Now decide how much we really want to unmap some pages.  The
 736                  * mapped ratio is downgraded - just because there's a lot of
 737                  * mapped memory doesn't necessarily mean that page reclaim
 738                  * isn't succeeding.
 739                  *
 740                  * The distress ratio is important - we don't want to start
 741                  * going oom.
 742                  *
 743                  * A 100% value of vm_swappiness overrides this algorithm
 744                  * altogether.
 745                  */
 746                 swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;
 747
 748                 /*
 749                  * Now use this metric to decide whether to start moving mapped
 750                  * memory onto the inactive list.
 751                  */
 752                 if (swap_tendency >= 100)
 753                         reclaim_mapped = 1;
 754         }
 755
 756         lru_add_drain();
 757         spin_lock_irq(&zone->lru_lock);
 758         pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
 759                                     &l_hold, &pgscanned);
 760         zone->pages_scanned += pgscanned;
 761         zone->nr_active -= pgmoved;
 762         spin_unlock_irq(&zone->lru_lock);
 763
 764         while (!list_empty(&l_hold)) {
 765                 cond_resched();
 766                 page = lru_to_page(&l_hold);
 767                 list_del(&page->lru);
 768                 if (page_mapped(page)) {
 769                         if (!reclaim_mapped ||
 770                             (total_swap_pages == 0 && PageAnon(page)) ||
 771                             page_referenced(page, 0)) {
 772                                 list_add(&page->lru, &l_active);
 773                                 continue;
 774                         }
 775                 }
 776                 list_add(&page->lru, &l_inactive);
 777         }
 778
 779         pagevec_init(&pvec, 1);
 780         pgmoved = 0;
 781         spin_lock_irq(&zone->lru_lock);
 782         while (!list_empty(&l_inactive)) {
 783                 page = lru_to_page(&l_inactive);
 784                 prefetchw_prev_lru_page(page, &l_inactive, flags);
 785                 BUG_ON(PageLRU(page));
 786                 SetPageLRU(page);
 787                 BUG_ON(!PageActive(page));
 788                 ClearPageActive(page);
 789
 790                 list_move(&page->lru, &zone->inactive_list);
 791                 pgmoved++;
 792                 if (!pagevec_add(&pvec, page)) {
 793                         zone->nr_inactive += pgmoved;
 794                         spin_unlock_irq(&zone->lru_lock);
 795                         pgdeactivate += pgmoved;
 796                         pgmoved = 0;
 797                         if (buffer_heads_over_limit)
 798                                 pagevec_strip(&pvec);
 799                         __pagevec_release(&pvec);
 800                         spin_lock_irq(&zone->lru_lock);
 801                 }
 802         }
 803         zone->nr_inactive += pgmoved;
 804         pgdeactivate += pgmoved;
 805         if (buffer_heads_over_limit) {
 806                 spin_unlock_irq(&zone->lru_lock);
 807                 pagevec_strip(&pvec);
 808                 spin_lock_irq(&zone->lru_lock);
 809         }
 810
 811         pgmoved = 0;
 812         while (!list_empty(&l_active)) {
 813                 page = lru_to_page(&l_active);
 814                 prefetchw_prev_lru_page(page, &l_active, flags);
 815                 BUG_ON(PageLRU(page));
 816                 SetPageLRU(page);
 817                 BUG_ON(!PageActive(page));
 818                 list_move(&page->lru, &zone->active_list);
 819                 pgmoved++;
 820                 if (!pagevec_add(&pvec, page)) {
 821                         zone->nr_active += pgmoved;
 822                         pgmoved = 0;
 823                         spin_unlock_irq(&zone->lru_lock);
 824                         __pagevec_release(&pvec);
 825                         spin_lock_irq(&zone->lru_lock);
 826                 }
 827         }
 828         zone->nr_active += pgmoved;
 829         spin_unlock(&zone->lru_lock);
 830
 831         __mod_page_state_zone(zone, pgrefill, pgscanned);
 832         __mod_page_state(pgdeactivate, pgdeactivate);
 833         local_irq_enable();
 834
 835         pagevec_release(&pvec);
 836 }
 837
 838 /*
 839  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 840  */
 841 static unsigned long shrink_zone(int priority, struct zone *zone,
 842                                 struct scan_control *sc)
 843 {
 844         unsigned long nr_active;
 845         unsigned long nr_inactive;
 846         unsigned long nr_to_scan;
 847         unsigned long nr_reclaimed = 0;
 848
 849         atomic_inc(&zone->reclaim_in_progress);
 850
 851         /*
 852          * Add one to `nr_to_scan' just to make sure that the kernel will
 853          * slowly sift through the active list.
 854          */
 855         zone->nr_scan_active += (zone->nr_active >> priority) + 1;
 856         nr_active = zone->nr_scan_active;
 857         if (nr_active >= sc->swap_cluster_max)
 858                 zone->nr_scan_active = 0;
 859         else
 860                 nr_active = 0;
 861
 862         zone->nr_scan_inactive += (zone->nr_inactive >> priority) + 1;
 863         nr_inactive = zone->nr_scan_inactive;
 864         if (nr_inactive >= sc->swap_cluster_max)
 865                 zone->nr_scan_inactive = 0;
 866         else
 867                 nr_inactive = 0;
 868
 869         while (nr_active || nr_inactive) {
 870                 if (nr_active) {
 871                         nr_to_scan = min(nr_active,
 872                                         (unsigned long)sc->swap_cluster_max);
 873                         nr_active -= nr_to_scan;
 874                         shrink_active_list(nr_to_scan, zone, sc);
 875                 }
 876
 877                 if (nr_inactive) {
 878                         nr_to_scan = min(nr_inactive,
 879                                         (unsigned long)sc->swap_cluster_max);
 880                         nr_inactive -= nr_to_scan;
 881                         nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
 882                                                                 sc);
 883                 }
 884         }
 885
 886         throttle_vm_writeout();
 887
 888         atomic_dec(&zone->reclaim_in_progress);
 889         return nr_reclaimed;
 890 }
 891
 892 /*
 893  * This is the direct reclaim path, for page-allocating processes.  We only
 894  * try to reclaim pages from zones which will satisfy the caller's allocation
 895  * request.
 896  *
 897  * We reclaim from a zone even if that zone is over pages_high.  Because:
 898  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 899  *    allocation or
 900  * b) The zones may be over pages_high but they must go *over* pages_high to
 901  *    satisfy the `incremental min' zone defense algorithm.
 902  *
 903  * Returns the number of reclaimed pages.
 904  *
 905  * If a zone is deemed to be full of pinned pages then just give it a light
 906  * scan then give up on it.
 907  */
 908 static unsigned long shrink_zones(int priority, struct zone **zones,
 909                                         struct scan_control *sc)
 910 {
 911         unsigned long nr_reclaimed = 0;
 912         int i;
 913
 914         for (i = 0; zones[i] != NULL; i++) {
 915                 struct zone *zone = zones[i];
 916
 917                 if (!populated_zone(zone))
 918                         continue;
 919
 920                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
 921                         continue;
 922
 923                 zone->temp_priority = priority;
 924                 if (zone->prev_priority > priority)
 925                         zone->prev_priority = priority;
 926
 927                 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
 928                         continue;       /* Let kswapd poll it */
 929
 930                 nr_reclaimed += shrink_zone(priority, zone, sc);
 931         }
 932         return nr_reclaimed;
 933 }
 934
 935 /*
 936  * This is the main entry point to direct page reclaim.
 937  *
 938  * If a full scan of the inactive list fails to free enough memory then we
 939  * are "out of memory" and something needs to be killed.
 940  *
 941  * If the caller is !__GFP_FS then the probability of a failure is reasonably
 942  * high - the zone may be full of dirty or under-writeback pages, which this
 943  * caller can't do much about.  We kick pdflush and take explicit naps in the
 944  * hope that some of these pages can be written.  But if the allocating task
 945  * holds filesystem locks which prevent writeout this might not work, and the
 946  * allocation attempt will fail.
 947  */
 948 unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
 949 {
 950         int priority;
 951         int ret = 0;
 952         unsigned long total_scanned = 0;
 953         unsigned long nr_reclaimed = 0;
 954         struct reclaim_state *reclaim_state = current->reclaim_state;
 955         unsigned long lru_pages = 0;
 956         int i;
 957         struct scan_control sc = {
 958                 .gfp_mask = gfp_mask,
 959                 .may_writepage = !laptop_mode,
 960                 .swap_cluster_max = SWAP_CLUSTER_MAX,
 961                 .may_swap = 1,
 962                 .swappiness = vm_swappiness,
 963         };
 964
 965         inc_page_state(allocstall);
 966
 967         for (i = 0; zones[i] != NULL; i++) {
 968                 struct zone *zone = zones[i];
 969
 970                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
 971                         continue;
 972
 973                 zone->temp_priority = DEF_PRIORITY;
 974                 lru_pages += zone->nr_active + zone->nr_inactive;
 975         }
 976
 977         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
 978                 sc.nr_mapped = read_page_state(nr_mapped);
 979                 sc.nr_scanned = 0;
 980                 if (!priority)
 981                         disable_swap_token();
 982                 nr_reclaimed += shrink_zones(priority, zones, &sc);
 983                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
 984                 if (reclaim_state) {
 985                         nr_reclaimed += reclaim_state->reclaimed_slab;
 986                         reclaim_state->reclaimed_slab = 0;
 987                 }
 988                 total_scanned += sc.nr_scanned;
 989                 if (nr_reclaimed >= sc.swap_cluster_max) {
 990                         ret = 1;
 991                         goto out;
 992                 }
 993
 994                 /*
 995                  * Try to write back as many pages as we just scanned.  This
 996                  * tends to cause slow streaming writers to write data to the
 997                  * disk smoothly, at the dirtying rate, which is nice.   But
 998                  * that's undesirable in laptop mode, where we *want* lumpy
 999                  * writeout.  So in laptop mode, write out the whole world.
1000                  */
1001                 if (total_scanned > sc.swap_cluster_max +
1002                                         sc.swap_cluster_max / 2) {
1003                         wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1004                         sc.may_writepage = 1;
1005                 }
1006
1007                 /* Take a nap, wait for some writeback to complete */
1008                 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1009                         blk_congestion_wait(WRITE, HZ/10);
1010         }
1011 out:
1012         for (i = 0; zones[i] != 0; i++) {
1013                 struct zone *zone = zones[i];
1014
1015                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1016                         continue;
1017
1018                 zone->prev_priority = zone->temp_priority;
1019         }
1020         return ret;
1021 }
1022
1023 /*
1024  * For kswapd, balance_pgdat() will work across all this node's zones until
1025  * they are all at pages_high.
1026  *
1027  * Returns the number of pages which were actually freed.
1028  *
1029  * There is special handling here for zones which are full of pinned pages.
1030  * This can happen if the pages are all mlocked, or if they are all used by
1031  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1032  * What we do is to detect the case where all pages in the zone have been
1033  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1034  * dead and from now on, only perform a short scan.  Basically we're polling
1035  * the zone for when the problem goes away.
1036  *
1037  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1038  * zones which have free_pages > pages_high, but once a zone is found to have
1039  * free_pages <= pages_high, we scan that zone and the lower zones regardless
1040  * of the number of free pages in the lower zones.  This interoperates with
1041  * the page allocator fallback scheme to ensure that aging of pages is balanced
1042  * across the zones.
1043  */
1044 static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1045 {
1046         int all_zones_ok;
1047         int priority;
1048         int i;
1049         unsigned long total_scanned;
1050         unsigned long nr_reclaimed;
1051         struct reclaim_state *reclaim_state = current->reclaim_state;
1052         struct scan_control sc = {
1053                 .gfp_mask = GFP_KERNEL,
1054                 .may_swap = 1,
1055                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1056                 .swappiness = vm_swappiness,
1057         };
1058
1059 loop_again:
1060         total_scanned = 0;
1061         nr_reclaimed = 0;
1062         sc.may_writepage = !laptop_mode;
1063         sc.nr_mapped = read_page_state(nr_mapped);
1064
1065         inc_page_state(pageoutrun);
1066
1067         for (i = 0; i < pgdat->nr_zones; i++) {
1068                 struct zone *zone = pgdat->node_zones + i;
1069
1070                 zone->temp_priority = DEF_PRIORITY;
1071         }
1072
1073         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1074                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1075                 unsigned long lru_pages = 0;
1076
1077                 /* The swap token gets in the way of swapout... */
1078                 if (!priority)
1079                         disable_swap_token();
1080
1081                 all_zones_ok = 1;
1082
1083                 /*
1084                  * Scan in the highmem->dma direction for the highest
1085                  * zone which needs scanning
1086                  */
1087                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1088                         struct zone *zone = pgdat->node_zones + i;
1089
1090                         if (!populated_zone(zone))
1091                                 continue;
1092
1093                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1094                                 continue;
1095
1096                         if (!zone_watermark_ok(zone, order, zone->pages_high,
1097                                                0, 0)) {
1098                                 end_zone = i;
1099                                 goto scan;
1100                         }
1101                 }
1102                 goto out;
1103 scan:
1104                 for (i = 0; i <= end_zone; i++) {
1105                         struct zone *zone = pgdat->node_zones + i;
1106
1107                         lru_pages += zone->nr_active + zone->nr_inactive;
1108                 }
1109
1110                 /*
1111                  * Now scan the zone in the dma->highmem direction, stopping
1112                  * at the last zone which needs scanning.
1113                  *
1114                  * We do this because the page allocator works in the opposite
1115                  * direction.  This prevents the page allocator from allocating
1116                  * pages behind kswapd's direction of progress, which would
1117                  * cause too much scanning of the lower zones.
1118                  */
1119                 for (i = 0; i <= end_zone; i++) {
1120                         struct zone *zone = pgdat->node_zones + i;
1121                         int nr_slab;
1122
1123                         if (!populated_zone(zone))
1124                                 continue;
1125
1126                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1127                                 continue;
1128
1129                         if (!zone_watermark_ok(zone, order, zone->pages_high,
1130                                                end_zone, 0))
1131                                 all_zones_ok = 0;
1132                         zone->temp_priority = priority;
1133                         if (zone->prev_priority > priority)
1134                                 zone->prev_priority = priority;
1135                         sc.nr_scanned = 0;
1136                         nr_reclaimed += shrink_zone(priority, zone, &sc);
1137                         reclaim_state->reclaimed_slab = 0;
1138                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1139                                                 lru_pages);
1140                         nr_reclaimed += reclaim_state->reclaimed_slab;
1141                         total_scanned += sc.nr_scanned;
1142                         if (zone->all_unreclaimable)
1143                                 continue;
1144                         if (nr_slab == 0 && zone->pages_scanned >=
1145                                     (zone->nr_active + zone->nr_inactive) * 4)
1146                                 zone->all_unreclaimable = 1;
1147                         /*
1148                          * If we've done a decent amount of scanning and
1149                          * the reclaim ratio is low, start doing writepage
1150                          * even in laptop mode
1151                          */
1152                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1153                             total_scanned > nr_reclaimed + nr_reclaimed / 2)
1154                                 sc.may_writepage = 1;
1155                 }
1156                 if (all_zones_ok)
1157                         break;          /* kswapd: all done */
1158                 /*
1159                  * OK, kswapd is getting into trouble.  Take a nap, then take
1160                  * another pass across the zones.
1161                  */
1162                 if (total_scanned && priority < DEF_PRIORITY - 2)
1163                         blk_congestion_wait(WRITE, HZ/10);
1164
1165                 /*
1166                  * We do this so kswapd doesn't build up large priorities for
1167                  * example when it is freeing in parallel with allocators. It
1168                  * matches the direct reclaim path behaviour in terms of impact
1169                  * on zone->*_priority.
1170                  */
1171                 if (nr_reclaimed >= SWAP_CLUSTER_MAX)
1172                         break;
1173         }
1174 out:
1175         for (i = 0; i < pgdat->nr_zones; i++) {
1176                 struct zone *zone = pgdat->node_zones + i;
1177
1178                 zone->prev_priority = zone->temp_priority;
1179         }
1180         if (!all_zones_ok) {
1181                 cond_resched();
1182                 goto loop_again;
1183         }
1184
1185         return nr_reclaimed;
1186 }
1187
1188 /*
1189  * The background pageout daemon, started as a kernel thread
1190  * from the init process.
1191  *
1192  * This basically trickles out pages so that we have _some_
1193  * free memory available even if there is no other activity
1194  * that frees anything up. This is needed for things like routing
1195  * etc, where we otherwise might have all activity going on in
1196  * asynchronous contexts that cannot page things out.
1197  *
1198  * If there are applications that are active memory-allocators
1199  * (most normal use), this basically shouldn't matter.
1200  */
1201 static int kswapd(void *p)
1202 {
1203         unsigned long order;
1204         pg_data_t *pgdat = (pg_data_t*)p;
1205         struct task_struct *tsk = current;
1206         DEFINE_WAIT(wait);
1207         struct reclaim_state reclaim_state = {
1208                 .reclaimed_slab = 0,
1209         };
1210         cpumask_t cpumask;
1211
1212         daemonize("kswapd%d", pgdat->node_id);
1213         cpumask = node_to_cpumask(pgdat->node_id);
1214         if (!cpus_empty(cpumask))
1215                 set_cpus_allowed(tsk, cpumask);
1216         current->reclaim_state = &reclaim_state;
1217
1218         /*
1219          * Tell the memory management that we're a "memory allocator",
1220          * and that if we need more memory we should get access to it
1221          * regardless (see "__alloc_pages()"). "kswapd" should
1222          * never get caught in the normal page freeing logic.
1223          *
1224          * (Kswapd normally doesn't need memory anyway, but sometimes
1225          * you need a small amount of memory in order to be able to
1226          * page out something else, and this flag essentially protects
1227          * us from recursively trying to free more memory as we're
1228          * trying to free the first piece of memory in the first place).
1229          */
1230         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1231
1232         order = 0;
1233         for ( ; ; ) {
1234                 unsigned long new_order;
1235
1236                 try_to_freeze();
1237
1238                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1239                 new_order = pgdat->kswapd_max_order;
1240                 pgdat->kswapd_max_order = 0;
1241                 if (order < new_order) {
1242                         /*
1243                          * Don't sleep if someone wants a larger 'order'
1244                          * allocation
1245                          */
1246                         order = new_order;
1247                 } else {
1248                         schedule();
1249                         order = pgdat->kswapd_max_order;
1250                 }
1251                 finish_wait(&pgdat->kswapd_wait, &wait);
1252
1253                 balance_pgdat(pgdat, order);
1254         }
1255         return 0;
1256 }
1257
1258 /*
1259  * A zone is low on free memory, so wake its kswapd task to service it.
1260  */
1261 void wakeup_kswapd(struct zone *zone, int order)
1262 {
1263         pg_data_t *pgdat;
1264
1265         if (!populated_zone(zone))
1266                 return;
1267
1268         pgdat = zone->zone_pgdat;
1269         if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1270                 return;
1271         if (pgdat->kswapd_max_order < order)
1272                 pgdat->kswapd_max_order = order;
1273         if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1274                 return;
1275         if (!waitqueue_active(&pgdat->kswapd_wait))
1276                 return;
1277         wake_up_interruptible(&pgdat->kswapd_wait);
1278 }
1279
1280 #ifdef CONFIG_PM
1281 /*
1282  * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
1283  * from LRU lists system-wide, for given pass and priority, and returns the
1284  * number of reclaimed pages
1285  *
1286  * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1287  */
1288 static unsigned long shrink_all_zones(unsigned long nr_pages, int pass,
1289                                       int prio, struct scan_control *sc)
1290 {
1291         struct zone *zone;
1292         unsigned long nr_to_scan, ret = 0;
1293
1294         for_each_zone(zone) {
1295
1296                 if (!populated_zone(zone))
1297                         continue;
1298
1299                 if (zone->all_unreclaimable && prio != DEF_PRIORITY)
1300                         continue;
1301
1302                 /* For pass = 0 we don't shrink the active list */
1303                 if (pass > 0) {
1304                         zone->nr_scan_active += (zone->nr_active >> prio) + 1;
1305                         if (zone->nr_scan_active >= nr_pages || pass > 3) {
1306                                 zone->nr_scan_active = 0;
1307                                 nr_to_scan = min(nr_pages, zone->nr_active);
1308                                 shrink_active_list(nr_to_scan, zone, sc);
1309                         }
1310                 }
1311
1312                 zone->nr_scan_inactive += (zone->nr_inactive >> prio) + 1;
1313                 if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
1314                         zone->nr_scan_inactive = 0;
1315                         nr_to_scan = min(nr_pages, zone->nr_inactive);
1316                         ret += shrink_inactive_list(nr_to_scan, zone, sc);
1317                         if (ret >= nr_pages)
1318                                 return ret;
1319                 }
1320         }
1321
1322         return ret;
1323 }
1324
1325 /*
1326  * Try to free `nr_pages' of memory, system-wide, and return the number of
1327  * freed pages.
1328  *
1329  * Rather than trying to age LRUs the aim is to preserve the overall
1330  * LRU order by reclaiming preferentially
1331  * inactive > active > active referenced > active mapped
1332  */
1333 unsigned long shrink_all_memory(unsigned long nr_pages)
1334 {
1335         unsigned long lru_pages, nr_slab;
1336         unsigned long ret = 0;
1337         int pass;
1338         struct reclaim_state reclaim_state;
1339         struct zone *zone;
1340         struct scan_control sc = {
1341                 .gfp_mask = GFP_KERNEL,
1342                 .may_swap = 0,
1343                 .swap_cluster_max = nr_pages,
1344                 .may_writepage = 1,
1345                 .swappiness = vm_swappiness,
1346         };
1347
1348         current->reclaim_state = &reclaim_state;
1349
1350         lru_pages = 0;
1351         for_each_zone(zone)
1352                 lru_pages += zone->nr_active + zone->nr_inactive;
1353
1354         nr_slab = read_page_state(nr_slab);
1355         /* If slab caches are huge, it's better to hit them first */
1356         while (nr_slab >= lru_pages) {
1357                 reclaim_state.reclaimed_slab = 0;
1358                 shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1359                 if (!reclaim_state.reclaimed_slab)
1360                         break;
1361
1362                 ret += reclaim_state.reclaimed_slab;
1363                 if (ret >= nr_pages)
1364                         goto out;
1365
1366                 nr_slab -= reclaim_state.reclaimed_slab;
1367         }
1368
1369         /*
1370          * We try to shrink LRUs in 5 passes:
1371          * 0 = Reclaim from inactive_list only
1372          * 1 = Reclaim from active list but don't reclaim mapped
1373          * 2 = 2nd pass of type 1
1374          * 3 = Reclaim mapped (normal reclaim)
1375          * 4 = 2nd pass of type 3
1376          */
1377         for (pass = 0; pass < 5; pass++) {
1378                 int prio;
1379
1380                 /* Needed for shrinking slab caches later on */
1381                 if (!lru_pages)
1382                         for_each_zone(zone) {
1383                                 lru_pages += zone->nr_active;
1384                                 lru_pages += zone->nr_inactive;
1385                         }
1386
1387                 /* Force reclaiming mapped pages in the passes #3 and #4 */
1388                 if (pass > 2) {
1389                         sc.may_swap = 1;
1390                         sc.swappiness = 100;
1391                 }
1392
1393                 for (prio = DEF_PRIORITY; prio >= 0; prio--) {
1394                         unsigned long nr_to_scan = nr_pages - ret;
1395
1396                         sc.nr_mapped = read_page_state(nr_mapped);
1397                         sc.nr_scanned = 0;
1398
1399                         ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
1400                         if (ret >= nr_pages)
1401                                 goto out;
1402
1403                         reclaim_state.reclaimed_slab = 0;
1404                         shrink_slab(sc.nr_scanned, sc.gfp_mask, lru_pages);
1405                         ret += reclaim_state.reclaimed_slab;
1406                         if (ret >= nr_pages)
1407                                 goto out;
1408
1409                         if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
1410                                 blk_congestion_wait(WRITE, HZ / 10);
1411                 }
1412
1413                 lru_pages = 0;
1414         }
1415
1416         /*
1417          * If ret = 0, we could not shrink LRUs, but there may be something
1418          * in slab caches
1419          */
1420         if (!ret)
1421                 do {
1422                         reclaim_state.reclaimed_slab = 0;
1423                         shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1424                         ret += reclaim_state.reclaimed_slab;
1425                 } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
1426
1427 out:
1428         current->reclaim_state = NULL;
1429
1430         return ret;
1431 }
1432 #endif
1433
1434 #ifdef CONFIG_HOTPLUG_CPU
1435 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1436    not required for correctness.  So if the last cpu in a node goes
1437    away, we get changed to run anywhere: as the first one comes back,
1438    restore their cpu bindings. */
1439 static int cpu_callback(struct notifier_block *nfb,
1440                                   unsigned long action, void *hcpu)
1441 {
1442         pg_data_t *pgdat;
1443         cpumask_t mask;
1444
1445         if (action == CPU_ONLINE) {
1446                 for_each_online_pgdat(pgdat) {
1447                         mask = node_to_cpumask(pgdat->node_id);
1448                         if (any_online_cpu(mask) != NR_CPUS)
1449                                 /* One of our CPUs online: restore mask */
1450                                 set_cpus_allowed(pgdat->kswapd, mask);
1451                 }
1452         }
1453         return NOTIFY_OK;
1454 }
1455 #endif /* CONFIG_HOTPLUG_CPU */
1456
1457 static int __init kswapd_init(void)
1458 {
1459         pg_data_t *pgdat;
1460
1461         swap_setup();
1462         for_each_online_pgdat(pgdat) {
1463                 pid_t pid;
1464
1465                 pid = kernel_thread(kswapd, pgdat, CLONE_KERNEL);
1466                 BUG_ON(pid < 0);
1467                 read_lock(&tasklist_lock);
1468                 pgdat->kswapd = find_task_by_pid(pid);
1469                 read_unlock(&tasklist_lock);
1470         }
1471         total_memory = nr_free_pagecache_pages();
1472         hotcpu_notifier(cpu_callback, 0);
1473         return 0;
1474 }
1475
1476 module_init(kswapd_init)
1477
1478 #ifdef CONFIG_NUMA
1479 /*
1480  * Zone reclaim mode
1481  *
1482  * If non-zero call zone_reclaim when the number of free pages falls below
1483  * the watermarks.
1484  *
1485  * In the future we may add flags to the mode. However, the page allocator
1486  * should only have to check that zone_reclaim_mode != 0 before calling
1487  * zone_reclaim().
1488  */
1489 int zone_reclaim_mode __read_mostly;
1490
1491 #define RECLAIM_OFF 0
1492 #define RECLAIM_ZONE (1<<0)     /* Run shrink_cache on the zone */
1493 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
1494 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
1495 #define RECLAIM_SLAB (1<<3)     /* Do a global slab shrink if the zone is out of memory */
1496
1497 /*
1498  * Mininum time between zone reclaim scans
1499  */
1500 int zone_reclaim_interval __read_mostly = 30*HZ;
1501
1502 /*
1503  * Priority for ZONE_RECLAIM. This determines the fraction of pages
1504  * of a node considered for each zone_reclaim. 4 scans 1/16th of
1505  * a zone.
1506  */
1507 #define ZONE_RECLAIM_PRIORITY 4
1508
1509 /*
1510  * Try to free up some pages from this zone through reclaim.
1511  */
1512 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1513 {
1514         /* Minimum pages needed in order to stay on node */
1515         const unsigned long nr_pages = 1 << order;
1516         struct task_struct *p = current;
1517         struct reclaim_state reclaim_state;
1518         int priority;
1519         unsigned long nr_reclaimed = 0;
1520         struct scan_control sc = {
1521                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
1522                 .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
1523                 .nr_mapped = read_page_state(nr_mapped),
1524                 .swap_cluster_max = max_t(unsigned long, nr_pages,
1525                                         SWAP_CLUSTER_MAX),
1526                 .gfp_mask = gfp_mask,
1527                 .swappiness = vm_swappiness,
1528         };
1529
1530         disable_swap_token();
1531         cond_resched();
1532         /*
1533          * We need to be able to allocate from the reserves for RECLAIM_SWAP
1534          * and we also need to be able to write out pages for RECLAIM_WRITE
1535          * and RECLAIM_SWAP.
1536          */
1537         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
1538         reclaim_state.reclaimed_slab = 0;
1539         p->reclaim_state = &reclaim_state;
1540
1541         /*
1542          * Free memory by calling shrink zone with increasing priorities
1543          * until we have enough memory freed.
1544          */
1545         priority = ZONE_RECLAIM_PRIORITY;
1546         do {
1547                 nr_reclaimed += shrink_zone(priority, zone, &sc);
1548                 priority--;
1549         } while (priority >= 0 && nr_reclaimed < nr_pages);
1550
1551         if (nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) {
1552                 /*
1553                  * shrink_slab() does not currently allow us to determine how
1554                  * many pages were freed in this zone. So we just shake the slab
1555                  * a bit and then go off node for this particular allocation
1556                  * despite possibly having freed enough memory to allocate in
1557                  * this zone.  If we freed local memory then the next
1558                  * allocations will be local again.
1559                  *
1560                  * shrink_slab will free memory on all zones and may take
1561                  * a long time.
1562                  */
1563                 shrink_slab(sc.nr_scanned, gfp_mask, order);
1564         }
1565
1566         p->reclaim_state = NULL;
1567         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
1568
1569         if (nr_reclaimed == 0) {
1570                 /*
1571                  * We were unable to reclaim enough pages to stay on node.  We
1572                  * now allow off node accesses for a certain time period before
1573                  * trying again to reclaim pages from the local zone.
1574                  */
1575                 zone->last_unsuccessful_zone_reclaim = jiffies;
1576         }
1577
1578         return nr_reclaimed >= nr_pages;
1579 }
1580
1581 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1582 {
1583         cpumask_t mask;
1584         int node_id;
1585
1586         /*
1587          * Do not reclaim if there was a recent unsuccessful attempt at zone
1588          * reclaim.  In that case we let allocations go off node for the
1589          * zone_reclaim_interval.  Otherwise we would scan for each off-node
1590          * page allocation.
1591          */
1592         if (time_before(jiffies,
1593                 zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval))
1594                         return 0;
1595
1596         /*
1597          * Avoid concurrent zone reclaims, do not reclaim in a zone that does
1598          * not have reclaimable pages and if we should not delay the allocation
1599          * then do not scan.
1600          */
1601         if (!(gfp_mask & __GFP_WAIT) ||
1602                 zone->all_unreclaimable ||
1603                 atomic_read(&zone->reclaim_in_progress) > 0 ||
1604                 (current->flags & PF_MEMALLOC))
1605                         return 0;
1606
1607         /*
1608          * Only run zone reclaim on the local zone or on zones that do not
1609          * have associated processors. This will favor the local processor
1610          * over remote processors and spread off node memory allocations
1611          * as wide as possible.
1612          */
1613         node_id = zone->zone_pgdat->node_id;
1614         mask = node_to_cpumask(node_id);
1615         if (!cpus_empty(mask) && node_id != numa_node_id())
1616                 return 0;
1617         return __zone_reclaim(zone, gfp_mask, order);
1618 }
1619 #endif