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/vmstat.h>
  23 #include <linux/file.h>
  24 #include <linux/writeback.h>
  25 #include <linux/blkdev.h>
  26 #include <linux/buffer_head.h>  /* for try_to_release_page(),
  27                                         buffer_heads_over_limit */
  28 #include <linux/mm_inline.h>
  29 #include <linux/pagevec.h>
  30 #include <linux/backing-dev.h>
  31 #include <linux/rmap.h>
  32 #include <linux/topology.h>
  33 #include <linux/cpu.h>
  34 #include <linux/cpuset.h>
  35 #include <linux/notifier.h>
  36 #include <linux/rwsem.h>
  37 #include <linux/delay.h>
  38 #include <linux/kthread.h>
  39 #include <linux/freezer.h>
  40
  41 #include <asm/tlbflush.h>
  42 #include <asm/div64.h>
  43
  44 #include <linux/swapops.h>
  45
  46 #include "internal.h"
  47
  48 struct scan_control {
  49         /* Incremented by the number of inactive pages that were scanned */
  50         unsigned long nr_scanned;
  51
  52         /* This context's GFP mask */
  53         gfp_t gfp_mask;
  54
  55         int may_writepage;
  56
  57         /* Can pages be swapped as part of reclaim? */
  58         int may_swap;
  59
  60         /* This context's SWAP_CLUSTER_MAX. If freeing memory for
  61          * suspend, we effectively ignore SWAP_CLUSTER_MAX.
  62          * In this context, it doesn't matter that we scan the
  63          * whole list at once. */
  64         int swap_cluster_max;
  65
  66         int swappiness;
  67
  68         int all_unreclaimable;
  69 };
  70
  71 /*
  72  * The list of shrinker callbacks used by to apply pressure to
  73  * ageable caches.
  74  */
  75 struct shrinker {
  76         shrinker_t              shrinker;
  77         struct list_head        list;
  78         int                     seeks;  /* seeks to recreate an obj */
  79         long                    nr;     /* objs pending delete */
  80 };
  81
  82 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  83
  84 #ifdef ARCH_HAS_PREFETCH
  85 #define prefetch_prev_lru_page(_page, _base, _field)                    \
  86         do {                                                            \
  87                 if ((_page)->lru.prev != _base) {                       \
  88                         struct page *prev;                              \
  89                                                                         \
  90                         prev = lru_to_page(&(_page->lru));              \
  91                         prefetch(&prev->_field);                        \
  92                 }                                                       \
  93         } while (0)
  94 #else
  95 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
  96 #endif
  97
  98 #ifdef ARCH_HAS_PREFETCHW
  99 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
 100         do {                                                            \
 101                 if ((_page)->lru.prev != _base) {                       \
 102                         struct page *prev;                              \
 103                                                                         \
 104                         prev = lru_to_page(&(_page->lru));              \
 105                         prefetchw(&prev->_field);                       \
 106                 }                                                       \
 107         } while (0)
 108 #else
 109 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 110 #endif
 111
 112 /*
 113  * From 0 .. 100.  Higher means more swappy.
 114  */
 115 int vm_swappiness = 60;
 116 long vm_total_pages;    /* The total number of pages which the VM controls */
 117
 118 static LIST_HEAD(shrinker_list);
 119 static DECLARE_RWSEM(shrinker_rwsem);
 120
 121 /*
 122  * Add a shrinker callback to be called from the vm
 123  */
 124 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
 125 {
 126         struct shrinker *shrinker;
 127
 128         shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
 129         if (shrinker) {
 130                 shrinker->shrinker = theshrinker;
 131                 shrinker->seeks = seeks;
 132                 shrinker->nr = 0;
 133                 down_write(&shrinker_rwsem);
 134                 list_add_tail(&shrinker->list, &shrinker_list);
 135                 up_write(&shrinker_rwsem);
 136         }
 137         return shrinker;
 138 }
 139 EXPORT_SYMBOL(set_shrinker);
 140
 141 /*
 142  * Remove one
 143  */
 144 void remove_shrinker(struct shrinker *shrinker)
 145 {
 146         down_write(&shrinker_rwsem);
 147         list_del(&shrinker->list);
 148         up_write(&shrinker_rwsem);
 149         kfree(shrinker);
 150 }
 151 EXPORT_SYMBOL(remove_shrinker);
 152
 153 #define SHRINK_BATCH 128
 154 /*
 155  * Call the shrink functions to age shrinkable caches
 156  *
 157  * Here we assume it costs one seek to replace a lru page and that it also
 158  * takes a seek to recreate a cache object.  With this in mind we age equal
 159  * percentages of the lru and ageable caches.  This should balance the seeks
 160  * generated by these structures.
 161  *
 162  * If the vm encounted mapped pages on the LRU it increase the pressure on
 163  * slab to avoid swapping.
 164  *
 165  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 166  *
 167  * `lru_pages' represents the number of on-LRU pages in all the zones which
 168  * are eligible for the caller's allocation attempt.  It is used for balancing
 169  * slab reclaim versus page reclaim.
 170  *
 171  * Returns the number of slab objects which we shrunk.
 172  */
 173 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 174                         unsigned long lru_pages)
 175 {
 176         struct shrinker *shrinker;
 177         unsigned long ret = 0;
 178
 179         if (scanned == 0)
 180                 scanned = SWAP_CLUSTER_MAX;
 181
 182         if (!down_read_trylock(&shrinker_rwsem))
 183                 return 1;       /* Assume we'll be able to shrink next time */
 184
 185         list_for_each_entry(shrinker, &shrinker_list, list) {
 186                 unsigned long long delta;
 187                 unsigned long total_scan;
 188                 unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
 189
 190                 delta = (4 * scanned) / shrinker->seeks;
 191                 delta *= max_pass;
 192                 do_div(delta, lru_pages + 1);
 193                 shrinker->nr += delta;
 194                 if (shrinker->nr < 0) {
 195                         printk(KERN_ERR "%s: nr=%ld\n",
 196                                         __FUNCTION__, shrinker->nr);
 197                         shrinker->nr = max_pass;
 198                 }
 199
 200                 /*
 201                  * Avoid risking looping forever due to too large nr value:
 202                  * never try to free more than twice the estimate number of
 203                  * freeable entries.
 204                  */
 205                 if (shrinker->nr > max_pass * 2)
 206                         shrinker->nr = max_pass * 2;
 207
 208                 total_scan = shrinker->nr;
 209                 shrinker->nr = 0;
 210
 211                 while (total_scan >= SHRINK_BATCH) {
 212                         long this_scan = SHRINK_BATCH;
 213                         int shrink_ret;
 214                         int nr_before;
 215
 216                         nr_before = (*shrinker->shrinker)(0, gfp_mask);
 217                         shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
 218                         if (shrink_ret == -1)
 219                                 break;
 220                         if (shrink_ret < nr_before)
 221                                 ret += nr_before - shrink_ret;
 222                         count_vm_events(SLABS_SCANNED, this_scan);
 223                         total_scan -= this_scan;
 224
 225                         cond_resched();
 226                 }
 227
 228                 shrinker->nr += total_scan;
 229         }
 230         up_read(&shrinker_rwsem);
 231         return ret;
 232 }
 233
 234 /* Called without lock on whether page is mapped, so answer is unstable */
 235 static inline int page_mapping_inuse(struct page *page)
 236 {
 237         struct address_space *mapping;
 238
 239         /* Page is in somebody's page tables. */
 240         if (page_mapped(page))
 241                 return 1;
 242
 243         /* Be more reluctant to reclaim swapcache than pagecache */
 244         if (PageSwapCache(page))
 245                 return 1;
 246
 247         mapping = page_mapping(page);
 248         if (!mapping)
 249                 return 0;
 250
 251         /* File is mmap'd by somebody? */
 252         return mapping_mapped(mapping);
 253 }
 254
 255 static inline int is_page_cache_freeable(struct page *page)
 256 {
 257         return page_count(page) - !!PagePrivate(page) == 2;
 258 }
 259
 260 static int may_write_to_queue(struct backing_dev_info *bdi)
 261 {
 262         if (current->flags & PF_SWAPWRITE)
 263                 return 1;
 264         if (!bdi_write_congested(bdi))
 265                 return 1;
 266         if (bdi == current->backing_dev_info)
 267                 return 1;
 268         return 0;
 269 }
 270
 271 /*
 272  * We detected a synchronous write error writing a page out.  Probably
 273  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 274  * fsync(), msync() or close().
 275  *
 276  * The tricky part is that after writepage we cannot touch the mapping: nothing
 277  * prevents it from being freed up.  But we have a ref on the page and once
 278  * that page is locked, the mapping is pinned.
 279  *
 280  * We're allowed to run sleeping lock_page() here because we know the caller has
 281  * __GFP_FS.
 282  */
 283 static void handle_write_error(struct address_space *mapping,
 284                                 struct page *page, int error)
 285 {
 286         lock_page(page);
 287         if (page_mapping(page) == mapping)
 288                 mapping_set_error(mapping, error);
 289         unlock_page(page);
 290 }
 291
 292 /* possible outcome of pageout() */
 293 typedef enum {
 294         /* failed to write page out, page is locked */
 295         PAGE_KEEP,
 296         /* move page to the active list, page is locked */
 297         PAGE_ACTIVATE,
 298         /* page has been sent to the disk successfully, page is unlocked */
 299         PAGE_SUCCESS,
 300         /* page is clean and locked */
 301         PAGE_CLEAN,
 302 } pageout_t;
 303
 304 /*
 305  * pageout is called by shrink_page_list() for each dirty page.
 306  * Calls ->writepage().
 307  */
 308 static pageout_t pageout(struct page *page, struct address_space *mapping)
 309 {
 310         /*
 311          * If the page is dirty, only perform writeback if that write
 312          * will be non-blocking.  To prevent this allocation from being
 313          * stalled by pagecache activity.  But note that there may be
 314          * stalls if we need to run get_block().  We could test
 315          * PagePrivate for that.
 316          *
 317          * If this process is currently in generic_file_write() against
 318          * this page's queue, we can perform writeback even if that
 319          * will block.
 320          *
 321          * If the page is swapcache, write it back even if that would
 322          * block, for some throttling. This happens by accident, because
 323          * swap_backing_dev_info is bust: it doesn't reflect the
 324          * congestion state of the swapdevs.  Easy to fix, if needed.
 325          * See swapfile.c:page_queue_congested().
 326          */
 327         if (!is_page_cache_freeable(page))
 328                 return PAGE_KEEP;
 329         if (!mapping) {
 330                 /*
 331                  * Some data journaling orphaned pages can have
 332                  * page->mapping == NULL while being dirty with clean buffers.
 333                  */
 334                 if (PagePrivate(page)) {
 335                         if (try_to_free_buffers(page)) {
 336                                 ClearPageDirty(page);
 337                                 printk("%s: orphaned page\n", __FUNCTION__);
 338                                 return PAGE_CLEAN;
 339                         }
 340                 }
 341                 return PAGE_KEEP;
 342         }
 343         if (mapping->a_ops->writepage == NULL)
 344                 return PAGE_ACTIVATE;
 345         if (!may_write_to_queue(mapping->backing_dev_info))
 346                 return PAGE_KEEP;
 347
 348         if (clear_page_dirty_for_io(page)) {
 349                 int res;
 350                 struct writeback_control wbc = {
 351                         .sync_mode = WB_SYNC_NONE,
 352                         .nr_to_write = SWAP_CLUSTER_MAX,
 353                         .range_start = 0,
 354                         .range_end = LLONG_MAX,
 355                         .nonblocking = 1,
 356                         .for_reclaim = 1,
 357                 };
 358
 359                 SetPageReclaim(page);
 360                 res = mapping->a_ops->writepage(page, &wbc);
 361                 if (res < 0)
 362                         handle_write_error(mapping, page, res);
 363                 if (res == AOP_WRITEPAGE_ACTIVATE) {
 364                         ClearPageReclaim(page);
 365                         return PAGE_ACTIVATE;
 366                 }
 367                 if (!PageWriteback(page)) {
 368                         /* synchronous write or broken a_ops? */
 369                         ClearPageReclaim(page);
 370                 }
 371                 inc_zone_page_state(page, NR_VMSCAN_WRITE);
 372                 return PAGE_SUCCESS;
 373         }
 374
 375         return PAGE_CLEAN;
 376 }
 377
 378 /*
 379  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 380  * someone else has a ref on the page, abort and return 0.  If it was
 381  * successfully detached, return 1.  Assumes the caller has a single ref on
 382  * this page.
 383  */
 384 int remove_mapping(struct address_space *mapping, struct page *page)
 385 {
 386         BUG_ON(!PageLocked(page));
 387         BUG_ON(mapping != page_mapping(page));
 388
 389         write_lock_irq(&mapping->tree_lock);
 390         /*
 391          * The non racy check for a busy page.
 392          *
 393          * Must be careful with the order of the tests. When someone has
 394          * a ref to the page, it may be possible that they dirty it then
 395          * drop the reference. So if PageDirty is tested before page_count
 396          * here, then the following race may occur:
 397          *
 398          * get_user_pages(&page);
 399          * [user mapping goes away]
 400          * write_to(page);
 401          *                              !PageDirty(page)    [good]
 402          * SetPageDirty(page);
 403          * put_page(page);
 404          *                              !page_count(page)   [good, discard it]
 405          *
 406          * [oops, our write_to data is lost]
 407          *
 408          * Reversing the order of the tests ensures such a situation cannot
 409          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 410          * load is not satisfied before that of page->_count.
 411          *
 412          * Note that if SetPageDirty is always performed via set_page_dirty,
 413          * and thus under tree_lock, then this ordering is not required.
 414          */
 415         if (unlikely(page_count(page) != 2))
 416                 goto cannot_free;
 417         smp_rmb();
 418         if (unlikely(PageDirty(page)))
 419                 goto cannot_free;
 420
 421         if (PageSwapCache(page)) {
 422                 swp_entry_t swap = { .val = page_private(page) };
 423                 __delete_from_swap_cache(page);
 424                 write_unlock_irq(&mapping->tree_lock);
 425                 swap_free(swap);
 426                 __put_page(page);       /* The pagecache ref */
 427                 return 1;
 428         }
 429
 430         __remove_from_page_cache(page);
 431         write_unlock_irq(&mapping->tree_lock);
 432         __put_page(page);
 433         return 1;
 434
 435 cannot_free:
 436         write_unlock_irq(&mapping->tree_lock);
 437         return 0;
 438 }
 439
 440 /*
 441  * shrink_page_list() returns the number of reclaimed pages
 442  */
 443 static unsigned long shrink_page_list(struct list_head *page_list,
 444                                         struct scan_control *sc)
 445 {
 446         LIST_HEAD(ret_pages);
 447         struct pagevec freed_pvec;
 448         int pgactivate = 0;
 449         unsigned long nr_reclaimed = 0;
 450
 451         cond_resched();
 452
 453         pagevec_init(&freed_pvec, 1);
 454         while (!list_empty(page_list)) {
 455                 struct address_space *mapping;
 456                 struct page *page;
 457                 int may_enter_fs;
 458                 int referenced;
 459
 460                 cond_resched();
 461
 462                 page = lru_to_page(page_list);
 463                 list_del(&page->lru);
 464
 465                 if (TestSetPageLocked(page))
 466                         goto keep;
 467
 468                 VM_BUG_ON(PageActive(page));
 469
 470                 sc->nr_scanned++;
 471
 472                 if (!sc->may_swap && page_mapped(page))
 473                         goto keep_locked;
 474
 475                 /* Double the slab pressure for mapped and swapcache pages */
 476                 if (page_mapped(page) || PageSwapCache(page))
 477                         sc->nr_scanned++;
 478
 479                 if (PageWriteback(page))
 480                         goto keep_locked;
 481
 482                 referenced = page_referenced(page, 1);
 483                 /* In active use or really unfreeable?  Activate it. */
 484                 if (referenced && page_mapping_inuse(page))
 485                         goto activate_locked;
 486
 487 #ifdef CONFIG_SWAP
 488                 /*
 489                  * Anonymous process memory has backing store?
 490                  * Try to allocate it some swap space here.
 491                  */
 492                 if (PageAnon(page) && !PageSwapCache(page))
 493                         if (!add_to_swap(page, GFP_ATOMIC))
 494                                 goto activate_locked;
 495 #endif /* CONFIG_SWAP */
 496
 497                 mapping = page_mapping(page);
 498                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 499                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 500
 501                 /*
 502                  * The page is mapped into the page tables of one or more
 503                  * processes. Try to unmap it here.
 504                  */
 505                 if (page_mapped(page) && mapping) {
 506                         switch (try_to_unmap(page, 0)) {
 507                         case SWAP_FAIL:
 508                                 goto activate_locked;
 509                         case SWAP_AGAIN:
 510                                 goto keep_locked;
 511                         case SWAP_SUCCESS:
 512                                 ; /* try to free the page below */
 513                         }
 514                 }
 515
 516                 if (PageDirty(page)) {
 517                         if (referenced)
 518                                 goto keep_locked;
 519                         if (!may_enter_fs)
 520                                 goto keep_locked;
 521                         if (!sc->may_writepage)
 522                                 goto keep_locked;
 523
 524                         /* Page is dirty, try to write it out here */
 525                         switch(pageout(page, mapping)) {
 526                         case PAGE_KEEP:
 527                                 goto keep_locked;
 528                         case PAGE_ACTIVATE:
 529                                 goto activate_locked;
 530                         case PAGE_SUCCESS:
 531                                 if (PageWriteback(page) || PageDirty(page))
 532                                         goto keep;
 533                                 /*
 534                                  * A synchronous write - probably a ramdisk.  Go
 535                                  * ahead and try to reclaim the page.
 536                                  */
 537                                 if (TestSetPageLocked(page))
 538                                         goto keep;
 539                                 if (PageDirty(page) || PageWriteback(page))
 540                                         goto keep_locked;
 541                                 mapping = page_mapping(page);
 542                         case PAGE_CLEAN:
 543                                 ; /* try to free the page below */
 544                         }
 545                 }
 546
 547                 /*
 548                  * If the page has buffers, try to free the buffer mappings
 549                  * associated with this page. If we succeed we try to free
 550                  * the page as well.
 551                  *
 552                  * We do this even if the page is PageDirty().
 553                  * try_to_release_page() does not perform I/O, but it is
 554                  * possible for a page to have PageDirty set, but it is actually
 555                  * clean (all its buffers are clean).  This happens if the
 556                  * buffers were written out directly, with submit_bh(). ext3
 557                  * will do this, as well as the blockdev mapping.
 558                  * try_to_release_page() will discover that cleanness and will
 559                  * drop the buffers and mark the page clean - it can be freed.
 560                  *
 561                  * Rarely, pages can have buffers and no ->mapping.  These are
 562                  * the pages which were not successfully invalidated in
 563                  * truncate_complete_page().  We try to drop those buffers here
 564                  * and if that worked, and the page is no longer mapped into
 565                  * process address space (page_count == 1) it can be freed.
 566                  * Otherwise, leave the page on the LRU so it is swappable.
 567                  */
 568                 if (PagePrivate(page)) {
 569                         if (!try_to_release_page(page, sc->gfp_mask))
 570                                 goto activate_locked;
 571                         if (!mapping && page_count(page) == 1)
 572                                 goto free_it;
 573                 }
 574
 575                 if (!mapping || !remove_mapping(mapping, page))
 576                         goto keep_locked;
 577
 578 free_it:
 579                 unlock_page(page);
 580                 nr_reclaimed++;
 581                 if (!pagevec_add(&freed_pvec, page))
 582                         __pagevec_release_nonlru(&freed_pvec);
 583                 continue;
 584
 585 activate_locked:
 586                 SetPageActive(page);
 587                 pgactivate++;
 588 keep_locked:
 589                 unlock_page(page);
 590 keep:
 591                 list_add(&page->lru, &ret_pages);
 592                 VM_BUG_ON(PageLRU(page));
 593         }
 594         list_splice(&ret_pages, page_list);
 595         if (pagevec_count(&freed_pvec))
 596                 __pagevec_release_nonlru(&freed_pvec);
 597         count_vm_events(PGACTIVATE, pgactivate);
 598         return nr_reclaimed;
 599 }
 600
 601 /*
 602  * zone->lru_lock is heavily contended.  Some of the functions that
 603  * shrink the lists perform better by taking out a batch of pages
 604  * and working on them outside the LRU lock.
 605  *
 606  * For pagecache intensive workloads, this function is the hottest
 607  * spot in the kernel (apart from copy_*_user functions).
 608  *
 609  * Appropriate locks must be held before calling this function.
 610  *
 611  * @nr_to_scan: The number of pages to look through on the list.
 612  * @src:        The LRU list to pull pages off.
 613  * @dst:        The temp list to put pages on to.
 614  * @scanned:    The number of pages that were scanned.
 615  *
 616  * returns how many pages were moved onto *@dst.
 617  */
 618 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 619                 struct list_head *src, struct list_head *dst,
 620                 unsigned long *scanned)
 621 {
 622         unsigned long nr_taken = 0;
 623         struct page *page;
 624         unsigned long scan;
 625
 626         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
 627                 struct list_head *target;
 628                 page = lru_to_page(src);
 629                 prefetchw_prev_lru_page(page, src, flags);
 630
 631                 VM_BUG_ON(!PageLRU(page));
 632
 633                 list_del(&page->lru);
 634                 target = src;
 635                 if (likely(get_page_unless_zero(page))) {
 636                         /*
 637                          * Be careful not to clear PageLRU until after we're
 638                          * sure the page is not being freed elsewhere -- the
 639                          * page release code relies on it.
 640                          */
 641                         ClearPageLRU(page);
 642                         target = dst;
 643                         nr_taken++;
 644                 } /* else it is being freed elsewhere */
 645
 646                 list_add(&page->lru, target);
 647         }
 648
 649         *scanned = scan;
 650         return nr_taken;
 651 }
 652
 653 /*
 654  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
 655  * of reclaimed pages
 656  */
 657 static unsigned long shrink_inactive_list(unsigned long max_scan,
 658                                 struct zone *zone, struct scan_control *sc)
 659 {
 660         LIST_HEAD(page_list);
 661         struct pagevec pvec;
 662         unsigned long nr_scanned = 0;
 663         unsigned long nr_reclaimed = 0;
 664
 665         pagevec_init(&pvec, 1);
 666
 667         lru_add_drain();
 668         spin_lock_irq(&zone->lru_lock);
 669         do {
 670                 struct page *page;
 671                 unsigned long nr_taken;
 672                 unsigned long nr_scan;
 673                 unsigned long nr_freed;
 674
 675                 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
 676                                              &zone->inactive_list,
 677                                              &page_list, &nr_scan);
 678                 __mod_zone_page_state(zone, NR_INACTIVE, -nr_taken);
 679                 zone->pages_scanned += nr_scan;
 680                 spin_unlock_irq(&zone->lru_lock);
 681
 682                 nr_scanned += nr_scan;
 683                 nr_freed = shrink_page_list(&page_list, sc);
 684                 nr_reclaimed += nr_freed;
 685                 local_irq_disable();
 686                 if (current_is_kswapd()) {
 687                         __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan);
 688                         __count_vm_events(KSWAPD_STEAL, nr_freed);
 689                 } else
 690                         __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan);
 691                 __count_zone_vm_events(PGSTEAL, zone, nr_freed);
 692
 693                 if (nr_taken == 0)
 694                         goto done;
 695
 696                 spin_lock(&zone->lru_lock);
 697                 /*
 698                  * Put back any unfreeable pages.
 699                  */
 700                 while (!list_empty(&page_list)) {
 701                         page = lru_to_page(&page_list);
 702                         VM_BUG_ON(PageLRU(page));
 703                         SetPageLRU(page);
 704                         list_del(&page->lru);
 705                         if (PageActive(page))
 706                                 add_page_to_active_list(zone, page);
 707                         else
 708                                 add_page_to_inactive_list(zone, page);
 709                         if (!pagevec_add(&pvec, page)) {
 710                                 spin_unlock_irq(&zone->lru_lock);
 711                                 __pagevec_release(&pvec);
 712                                 spin_lock_irq(&zone->lru_lock);
 713                         }
 714                 }
 715         } while (nr_scanned < max_scan);
 716         spin_unlock(&zone->lru_lock);
 717 done:
 718         local_irq_enable();
 719         pagevec_release(&pvec);
 720         return nr_reclaimed;
 721 }
 722
 723 /*
 724  * We are about to scan this zone at a certain priority level.  If that priority
 725  * level is smaller (ie: more urgent) than the previous priority, then note
 726  * that priority level within the zone.  This is done so that when the next
 727  * process comes in to scan this zone, it will immediately start out at this
 728  * priority level rather than having to build up its own scanning priority.
 729  * Here, this priority affects only the reclaim-mapped threshold.
 730  */
 731 static inline void note_zone_scanning_priority(struct zone *zone, int priority)
 732 {
 733         if (priority < zone->prev_priority)
 734                 zone->prev_priority = priority;
 735 }
 736
 737 static inline int zone_is_near_oom(struct zone *zone)
 738 {
 739         return zone->pages_scanned >= (zone_page_state(zone, NR_ACTIVE)
 740                                 + zone_page_state(zone, NR_INACTIVE))*3;
 741 }
 742
 743 /*
 744  * This moves pages from the active list to the inactive list.
 745  *
 746  * We move them the other way if the page is referenced by one or more
 747  * processes, from rmap.
 748  *
 749  * If the pages are mostly unmapped, the processing is fast and it is
 750  * appropriate to hold zone->lru_lock across the whole operation.  But if
 751  * the pages are mapped, the processing is slow (page_referenced()) so we
 752  * should drop zone->lru_lock around each page.  It's impossible to balance
 753  * this, so instead we remove the pages from the LRU while processing them.
 754  * It is safe to rely on PG_active against the non-LRU pages in here because
 755  * nobody will play with that bit on a non-LRU page.
 756  *
 757  * The downside is that we have to touch page->_count against each page.
 758  * But we had to alter page->flags anyway.
 759  */
 760 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 761                                 struct scan_control *sc, int priority)
 762 {
 763         unsigned long pgmoved;
 764         int pgdeactivate = 0;
 765         unsigned long pgscanned;
 766         LIST_HEAD(l_hold);      /* The pages which were snipped off */
 767         LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
 768         LIST_HEAD(l_active);    /* Pages to go onto the active_list */
 769         struct page *page;
 770         struct pagevec pvec;
 771         int reclaim_mapped = 0;
 772
 773         if (sc->may_swap) {
 774                 long mapped_ratio;
 775                 long distress;
 776                 long swap_tendency;
 777
 778                 if (zone_is_near_oom(zone))
 779                         goto force_reclaim_mapped;
 780
 781                 /*
 782                  * `distress' is a measure of how much trouble we're having
 783                  * reclaiming pages.  0 -> no problems.  100 -> great trouble.
 784                  */
 785                 distress = 100 >> min(zone->prev_priority, priority);
 786
 787                 /*
 788                  * The point of this algorithm is to decide when to start
 789                  * reclaiming mapped memory instead of just pagecache.  Work out
 790                  * how much memory
 791                  * is mapped.
 792                  */
 793                 mapped_ratio = ((global_page_state(NR_FILE_MAPPED) +
 794                                 global_page_state(NR_ANON_PAGES)) * 100) /
 795                                         vm_total_pages;
 796
 797                 /*
 798                  * Now decide how much we really want to unmap some pages.  The
 799                  * mapped ratio is downgraded - just because there's a lot of
 800                  * mapped memory doesn't necessarily mean that page reclaim
 801                  * isn't succeeding.
 802                  *
 803                  * The distress ratio is important - we don't want to start
 804                  * going oom.
 805                  *
 806                  * A 100% value of vm_swappiness overrides this algorithm
 807                  * altogether.
 808                  */
 809                 swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;
 810
 811                 /*
 812                  * Now use this metric to decide whether to start moving mapped
 813                  * memory onto the inactive list.
 814                  */
 815                 if (swap_tendency >= 100)
 816 force_reclaim_mapped:
 817                         reclaim_mapped = 1;
 818         }
 819
 820         lru_add_drain();
 821         spin_lock_irq(&zone->lru_lock);
 822         pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
 823                                     &l_hold, &pgscanned);
 824         zone->pages_scanned += pgscanned;
 825         __mod_zone_page_state(zone, NR_ACTIVE, -pgmoved);
 826         spin_unlock_irq(&zone->lru_lock);
 827
 828         while (!list_empty(&l_hold)) {
 829                 cond_resched();
 830                 page = lru_to_page(&l_hold);
 831                 list_del(&page->lru);
 832                 if (page_mapped(page)) {
 833                         if (!reclaim_mapped ||
 834                             (total_swap_pages == 0 && PageAnon(page)) ||
 835                             page_referenced(page, 0)) {
 836                                 list_add(&page->lru, &l_active);
 837                                 continue;
 838                         }
 839                 }
 840                 list_add(&page->lru, &l_inactive);
 841         }
 842
 843         pagevec_init(&pvec, 1);
 844         pgmoved = 0;
 845         spin_lock_irq(&zone->lru_lock);
 846         while (!list_empty(&l_inactive)) {
 847                 page = lru_to_page(&l_inactive);
 848                 prefetchw_prev_lru_page(page, &l_inactive, flags);
 849                 VM_BUG_ON(PageLRU(page));
 850                 SetPageLRU(page);
 851                 VM_BUG_ON(!PageActive(page));
 852                 ClearPageActive(page);
 853
 854                 list_move(&page->lru, &zone->inactive_list);
 855                 pgmoved++;
 856                 if (!pagevec_add(&pvec, page)) {
 857                         __mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
 858                         spin_unlock_irq(&zone->lru_lock);
 859                         pgdeactivate += pgmoved;
 860                         pgmoved = 0;
 861                         if (buffer_heads_over_limit)
 862                                 pagevec_strip(&pvec);
 863                         __pagevec_release(&pvec);
 864                         spin_lock_irq(&zone->lru_lock);
 865                 }
 866         }
 867         __mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
 868         pgdeactivate += pgmoved;
 869         if (buffer_heads_over_limit) {
 870                 spin_unlock_irq(&zone->lru_lock);
 871                 pagevec_strip(&pvec);
 872                 spin_lock_irq(&zone->lru_lock);
 873         }
 874
 875         pgmoved = 0;
 876         while (!list_empty(&l_active)) {
 877                 page = lru_to_page(&l_active);
 878                 prefetchw_prev_lru_page(page, &l_active, flags);
 879                 VM_BUG_ON(PageLRU(page));
 880                 SetPageLRU(page);
 881                 VM_BUG_ON(!PageActive(page));
 882                 list_move(&page->lru, &zone->active_list);
 883                 pgmoved++;
 884                 if (!pagevec_add(&pvec, page)) {
 885                         __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
 886                         pgmoved = 0;
 887                         spin_unlock_irq(&zone->lru_lock);
 888                         __pagevec_release(&pvec);
 889                         spin_lock_irq(&zone->lru_lock);
 890                 }
 891         }
 892         __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
 893
 894         __count_zone_vm_events(PGREFILL, zone, pgscanned);
 895         __count_vm_events(PGDEACTIVATE, pgdeactivate);
 896         spin_unlock_irq(&zone->lru_lock);
 897
 898         pagevec_release(&pvec);
 899 }
 900
 901 /*
 902  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 903  */
 904 static unsigned long shrink_zone(int priority, struct zone *zone,
 905                                 struct scan_control *sc)
 906 {
 907         unsigned long nr_active;
 908         unsigned long nr_inactive;
 909         unsigned long nr_to_scan;
 910         unsigned long nr_reclaimed = 0;
 911
 912         atomic_inc(&zone->reclaim_in_progress);
 913
 914         /*
 915          * Add one to `nr_to_scan' just to make sure that the kernel will
 916          * slowly sift through the active list.
 917          */
 918         zone->nr_scan_active +=
 919                 (zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
 920         nr_active = zone->nr_scan_active;
 921         if (nr_active >= sc->swap_cluster_max)
 922                 zone->nr_scan_active = 0;
 923         else
 924                 nr_active = 0;
 925
 926         zone->nr_scan_inactive +=
 927                 (zone_page_state(zone, NR_INACTIVE) >> priority) + 1;
 928         nr_inactive = zone->nr_scan_inactive;
 929         if (nr_inactive >= sc->swap_cluster_max)
 930                 zone->nr_scan_inactive = 0;
 931         else
 932                 nr_inactive = 0;
 933
 934         while (nr_active || nr_inactive) {
 935                 if (nr_active) {
 936                         nr_to_scan = min(nr_active,
 937                                         (unsigned long)sc->swap_cluster_max);
 938                         nr_active -= nr_to_scan;
 939                         shrink_active_list(nr_to_scan, zone, sc, priority);
 940                 }
 941
 942                 if (nr_inactive) {
 943                         nr_to_scan = min(nr_inactive,
 944                                         (unsigned long)sc->swap_cluster_max);
 945                         nr_inactive -= nr_to_scan;
 946                         nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
 947                                                                 sc);
 948                 }
 949         }
 950
 951         throttle_vm_writeout(sc->gfp_mask);
 952
 953         atomic_dec(&zone->reclaim_in_progress);
 954         return nr_reclaimed;
 955 }
 956
 957 /*
 958  * This is the direct reclaim path, for page-allocating processes.  We only
 959  * try to reclaim pages from zones which will satisfy the caller's allocation
 960  * request.
 961  *
 962  * We reclaim from a zone even if that zone is over pages_high.  Because:
 963  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 964  *    allocation or
 965  * b) The zones may be over pages_high but they must go *over* pages_high to
 966  *    satisfy the `incremental min' zone defense algorithm.
 967  *
 968  * Returns the number of reclaimed pages.
 969  *
 970  * If a zone is deemed to be full of pinned pages then just give it a light
 971  * scan then give up on it.
 972  */
 973 static unsigned long shrink_zones(int priority, struct zone **zones,
 974                                         struct scan_control *sc)
 975 {
 976         unsigned long nr_reclaimed = 0;
 977         int i;
 978
 979         sc->all_unreclaimable = 1;
 980         for (i = 0; zones[i] != NULL; i++) {
 981                 struct zone *zone = zones[i];
 982
 983                 if (!populated_zone(zone))
 984                         continue;
 985
 986                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
 987                         continue;
 988
 989                 note_zone_scanning_priority(zone, priority);
 990
 991                 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
 992                         continue;       /* Let kswapd poll it */
 993
 994                 sc->all_unreclaimable = 0;
 995
 996                 nr_reclaimed += shrink_zone(priority, zone, sc);
 997         }
 998         return nr_reclaimed;
 999 }
1000
1001 /*
1002  * This is the main entry point to direct page reclaim.
1003  *
1004  * If a full scan of the inactive list fails to free enough memory then we
1005  * are "out of memory" and something needs to be killed.
1006  *
1007  * If the caller is !__GFP_FS then the probability of a failure is reasonably
1008  * high - the zone may be full of dirty or under-writeback pages, which this
1009  * caller can't do much about.  We kick pdflush and take explicit naps in the
1010  * hope that some of these pages can be written.  But if the allocating task
1011  * holds filesystem locks which prevent writeout this might not work, and the
1012  * allocation attempt will fail.
1013  */
1014 unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
1015 {
1016         int priority;
1017         int ret = 0;
1018         unsigned long total_scanned = 0;
1019         unsigned long nr_reclaimed = 0;
1020         struct reclaim_state *reclaim_state = current->reclaim_state;
1021         unsigned long lru_pages = 0;
1022         int i;
1023         struct scan_control sc = {
1024                 .gfp_mask = gfp_mask,
1025                 .may_writepage = !laptop_mode,
1026                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1027                 .may_swap = 1,
1028                 .swappiness = vm_swappiness,
1029         };
1030
1031         count_vm_event(ALLOCSTALL);
1032
1033         for (i = 0; zones[i] != NULL; i++) {
1034                 struct zone *zone = zones[i];
1035
1036                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1037                         continue;
1038
1039                 lru_pages += zone_page_state(zone, NR_ACTIVE)
1040                                 + zone_page_state(zone, NR_INACTIVE);
1041         }
1042
1043         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1044                 sc.nr_scanned = 0;
1045                 if (!priority)
1046                         disable_swap_token();
1047                 nr_reclaimed += shrink_zones(priority, zones, &sc);
1048                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
1049                 if (reclaim_state) {
1050                         nr_reclaimed += reclaim_state->reclaimed_slab;
1051                         reclaim_state->reclaimed_slab = 0;
1052                 }
1053                 total_scanned += sc.nr_scanned;
1054                 if (nr_reclaimed >= sc.swap_cluster_max) {
1055                         ret = 1;
1056                         goto out;
1057                 }
1058
1059                 /*
1060                  * Try to write back as many pages as we just scanned.  This
1061                  * tends to cause slow streaming writers to write data to the
1062                  * disk smoothly, at the dirtying rate, which is nice.   But
1063                  * that's undesirable in laptop mode, where we *want* lumpy
1064                  * writeout.  So in laptop mode, write out the whole world.
1065                  */
1066                 if (total_scanned > sc.swap_cluster_max +
1067                                         sc.swap_cluster_max / 2) {
1068                         wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1069                         sc.may_writepage = 1;
1070                 }
1071
1072                 /* Take a nap, wait for some writeback to complete */
1073                 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1074                         congestion_wait(WRITE, HZ/10);
1075         }
1076         /* top priority shrink_caches still had more to do? don't OOM, then */
1077         if (!sc.all_unreclaimable)
1078                 ret = 1;
1079 out:
1080         /*
1081          * Now that we've scanned all the zones at this priority level, note
1082          * that level within the zone so that the next thread which performs
1083          * scanning of this zone will immediately start out at this priority
1084          * level.  This affects only the decision whether or not to bring
1085          * mapped pages onto the inactive list.
1086          */
1087         if (priority < 0)
1088                 priority = 0;
1089         for (i = 0; zones[i] != 0; i++) {
1090                 struct zone *zone = zones[i];
1091
1092                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1093                         continue;
1094
1095                 zone->prev_priority = priority;
1096         }
1097         return ret;
1098 }
1099
1100 /*
1101  * For kswapd, balance_pgdat() will work across all this node's zones until
1102  * they are all at pages_high.
1103  *
1104  * Returns the number of pages which were actually freed.
1105  *
1106  * There is special handling here for zones which are full of pinned pages.
1107  * This can happen if the pages are all mlocked, or if they are all used by
1108  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1109  * What we do is to detect the case where all pages in the zone have been
1110  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1111  * dead and from now on, only perform a short scan.  Basically we're polling
1112  * the zone for when the problem goes away.
1113  *
1114  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1115  * zones which have free_pages > pages_high, but once a zone is found to have
1116  * free_pages <= pages_high, we scan that zone and the lower zones regardless
1117  * of the number of free pages in the lower zones.  This interoperates with
1118  * the page allocator fallback scheme to ensure that aging of pages is balanced
1119  * across the zones.
1120  */
1121 static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1122 {
1123         int all_zones_ok;
1124         int priority;
1125         int i;
1126         unsigned long total_scanned;
1127         unsigned long nr_reclaimed;
1128         struct reclaim_state *reclaim_state = current->reclaim_state;
1129         struct scan_control sc = {
1130                 .gfp_mask = GFP_KERNEL,
1131                 .may_swap = 1,
1132                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1133                 .swappiness = vm_swappiness,
1134         };
1135         /*
1136          * temp_priority is used to remember the scanning priority at which
1137          * this zone was successfully refilled to free_pages == pages_high.
1138          */
1139         int temp_priority[MAX_NR_ZONES];
1140
1141 loop_again:
1142         total_scanned = 0;
1143         nr_reclaimed = 0;
1144         sc.may_writepage = !laptop_mode;
1145         count_vm_event(PAGEOUTRUN);
1146
1147         for (i = 0; i < pgdat->nr_zones; i++)
1148                 temp_priority[i] = DEF_PRIORITY;
1149
1150         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1151                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1152                 unsigned long lru_pages = 0;
1153
1154                 /* The swap token gets in the way of swapout... */
1155                 if (!priority)
1156                         disable_swap_token();
1157
1158                 all_zones_ok = 1;
1159
1160                 /*
1161                  * Scan in the highmem->dma direction for the highest
1162                  * zone which needs scanning
1163                  */
1164                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1165                         struct zone *zone = pgdat->node_zones + i;
1166
1167                         if (!populated_zone(zone))
1168                                 continue;
1169
1170                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1171                                 continue;
1172
1173                         if (!zone_watermark_ok(zone, order, zone->pages_high,
1174                                                0, 0)) {
1175                                 end_zone = i;
1176                                 break;
1177                         }
1178                 }
1179                 if (i < 0)
1180                         goto out;
1181
1182                 for (i = 0; i <= end_zone; i++) {
1183                         struct zone *zone = pgdat->node_zones + i;
1184
1185                         lru_pages += zone_page_state(zone, NR_ACTIVE)
1186                                         + zone_page_state(zone, NR_INACTIVE);
1187                 }
1188
1189                 /*
1190                  * Now scan the zone in the dma->highmem direction, stopping
1191                  * at the last zone which needs scanning.
1192                  *
1193                  * We do this because the page allocator works in the opposite
1194                  * direction.  This prevents the page allocator from allocating
1195                  * pages behind kswapd's direction of progress, which would
1196                  * cause too much scanning of the lower zones.
1197                  */
1198                 for (i = 0; i <= end_zone; i++) {
1199                         struct zone *zone = pgdat->node_zones + i;
1200                         int nr_slab;
1201
1202                         if (!populated_zone(zone))
1203                                 continue;
1204
1205                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1206                                 continue;
1207
1208                         if (!zone_watermark_ok(zone, order, zone->pages_high,
1209                                                end_zone, 0))
1210                                 all_zones_ok = 0;
1211                         temp_priority[i] = priority;
1212                         sc.nr_scanned = 0;
1213                         note_zone_scanning_priority(zone, priority);
1214                         nr_reclaimed += shrink_zone(priority, zone, &sc);
1215                         reclaim_state->reclaimed_slab = 0;
1216                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1217                                                 lru_pages);
1218                         nr_reclaimed += reclaim_state->reclaimed_slab;
1219                         total_scanned += sc.nr_scanned;
1220                         if (zone->all_unreclaimable)
1221                                 continue;
1222                         if (nr_slab == 0 && zone->pages_scanned >=
1223                                 (zone_page_state(zone, NR_ACTIVE)
1224                                 + zone_page_state(zone, NR_INACTIVE)) * 6)
1225                                         zone->all_unreclaimable = 1;
1226                         /*
1227                          * If we've done a decent amount of scanning and
1228                          * the reclaim ratio is low, start doing writepage
1229                          * even in laptop mode
1230                          */
1231                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1232                             total_scanned > nr_reclaimed + nr_reclaimed / 2)
1233                                 sc.may_writepage = 1;
1234                 }
1235                 if (all_zones_ok)
1236                         break;          /* kswapd: all done */
1237                 /*
1238                  * OK, kswapd is getting into trouble.  Take a nap, then take
1239                  * another pass across the zones.
1240                  */
1241                 if (total_scanned && priority < DEF_PRIORITY - 2)
1242                         congestion_wait(WRITE, HZ/10);
1243
1244                 /*
1245                  * We do this so kswapd doesn't build up large priorities for
1246                  * example when it is freeing in parallel with allocators. It
1247                  * matches the direct reclaim path behaviour in terms of impact
1248                  * on zone->*_priority.
1249                  */
1250                 if (nr_reclaimed >= SWAP_CLUSTER_MAX)
1251                         break;
1252         }
1253 out:
1254         /*
1255          * Note within each zone the priority level at which this zone was
1256          * brought into a happy state.  So that the next thread which scans this
1257          * zone will start out at that priority level.
1258          */
1259         for (i = 0; i < pgdat->nr_zones; i++) {
1260                 struct zone *zone = pgdat->node_zones + i;
1261
1262                 zone->prev_priority = temp_priority[i];
1263         }
1264         if (!all_zones_ok) {
1265                 cond_resched();
1266
1267                 try_to_freeze();
1268
1269                 goto loop_again;
1270         }
1271
1272         return nr_reclaimed;
1273 }
1274
1275 /*
1276  * The background pageout daemon, started as a kernel thread
1277  * from the init process.
1278  *
1279  * This basically trickles out pages so that we have _some_
1280  * free memory available even if there is no other activity
1281  * that frees anything up. This is needed for things like routing
1282  * etc, where we otherwise might have all activity going on in
1283  * asynchronous contexts that cannot page things out.
1284  *
1285  * If there are applications that are active memory-allocators
1286  * (most normal use), this basically shouldn't matter.
1287  */
1288 static int kswapd(void *p)
1289 {
1290         unsigned long order;
1291         pg_data_t *pgdat = (pg_data_t*)p;
1292         struct task_struct *tsk = current;
1293         DEFINE_WAIT(wait);
1294         struct reclaim_state reclaim_state = {
1295                 .reclaimed_slab = 0,
1296         };
1297         cpumask_t cpumask;
1298
1299         cpumask = node_to_cpumask(pgdat->node_id);
1300         if (!cpus_empty(cpumask))
1301                 set_cpus_allowed(tsk, cpumask);
1302         current->reclaim_state = &reclaim_state;
1303
1304         /*
1305          * Tell the memory management that we're a "memory allocator",
1306          * and that if we need more memory we should get access to it
1307          * regardless (see "__alloc_pages()"). "kswapd" should
1308          * never get caught in the normal page freeing logic.
1309          *
1310          * (Kswapd normally doesn't need memory anyway, but sometimes
1311          * you need a small amount of memory in order to be able to
1312          * page out something else, and this flag essentially protects
1313          * us from recursively trying to free more memory as we're
1314          * trying to free the first piece of memory in the first place).
1315          */
1316         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1317
1318         order = 0;
1319         for ( ; ; ) {
1320                 unsigned long new_order;
1321
1322                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1323                 new_order = pgdat->kswapd_max_order;
1324                 pgdat->kswapd_max_order = 0;
1325                 if (order < new_order) {
1326                         /*
1327                          * Don't sleep if someone wants a larger 'order'
1328                          * allocation
1329                          */
1330                         order = new_order;
1331                 } else {
1332                         if (!freezing(current))
1333                                 schedule();
1334
1335                         order = pgdat->kswapd_max_order;
1336                 }
1337                 finish_wait(&pgdat->kswapd_wait, &wait);
1338
1339                 if (!try_to_freeze()) {
1340                         /* We can speed up thawing tasks if we don't call
1341                          * balance_pgdat after returning from the refrigerator
1342                          */
1343                         balance_pgdat(pgdat, order);
1344                 }
1345         }
1346         return 0;
1347 }
1348
1349 /*
1350  * A zone is low on free memory, so wake its kswapd task to service it.
1351  */
1352 void wakeup_kswapd(struct zone *zone, int order)
1353 {
1354         pg_data_t *pgdat;
1355
1356         if (!populated_zone(zone))
1357                 return;
1358
1359         pgdat = zone->zone_pgdat;
1360         if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1361                 return;
1362         if (pgdat->kswapd_max_order < order)
1363                 pgdat->kswapd_max_order = order;
1364         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1365                 return;
1366         if (!waitqueue_active(&pgdat->kswapd_wait))
1367                 return;
1368         wake_up_interruptible(&pgdat->kswapd_wait);
1369 }
1370
1371 #ifdef CONFIG_PM
1372 /*
1373  * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
1374  * from LRU lists system-wide, for given pass and priority, and returns the
1375  * number of reclaimed pages
1376  *
1377  * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1378  */
1379 static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
1380                                       int pass, struct scan_control *sc)
1381 {
1382         struct zone *zone;
1383         unsigned long nr_to_scan, ret = 0;
1384
1385         for_each_zone(zone) {
1386
1387                 if (!populated_zone(zone))
1388                         continue;
1389
1390                 if (zone->all_unreclaimable && prio != DEF_PRIORITY)
1391                         continue;
1392
1393                 /* For pass = 0 we don't shrink the active list */
1394                 if (pass > 0) {
1395                         zone->nr_scan_active +=
1396                                 (zone_page_state(zone, NR_ACTIVE) >> prio) + 1;
1397                         if (zone->nr_scan_active >= nr_pages || pass > 3) {
1398                                 zone->nr_scan_active = 0;
1399                                 nr_to_scan = min(nr_pages,
1400                                         zone_page_state(zone, NR_ACTIVE));
1401                                 shrink_active_list(nr_to_scan, zone, sc, prio);
1402                         }
1403                 }
1404
1405                 zone->nr_scan_inactive +=
1406                         (zone_page_state(zone, NR_INACTIVE) >> prio) + 1;
1407                 if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
1408                         zone->nr_scan_inactive = 0;
1409                         nr_to_scan = min(nr_pages,
1410                                 zone_page_state(zone, NR_INACTIVE));
1411                         ret += shrink_inactive_list(nr_to_scan, zone, sc);
1412                         if (ret >= nr_pages)
1413                                 return ret;
1414                 }
1415         }
1416
1417         return ret;
1418 }
1419
1420 static unsigned long count_lru_pages(void)
1421 {
1422         return global_page_state(NR_ACTIVE) + global_page_state(NR_INACTIVE);
1423 }
1424
1425 /*
1426  * Try to free `nr_pages' of memory, system-wide, and return the number of
1427  * freed pages.
1428  *
1429  * Rather than trying to age LRUs the aim is to preserve the overall
1430  * LRU order by reclaiming preferentially
1431  * inactive > active > active referenced > active mapped
1432  */
1433 unsigned long shrink_all_memory(unsigned long nr_pages)
1434 {
1435         unsigned long lru_pages, nr_slab;
1436         unsigned long ret = 0;
1437         int pass;
1438         struct reclaim_state reclaim_state;
1439         struct scan_control sc = {
1440                 .gfp_mask = GFP_KERNEL,
1441                 .may_swap = 0,
1442                 .swap_cluster_max = nr_pages,
1443                 .may_writepage = 1,
1444                 .swappiness = vm_swappiness,
1445         };
1446
1447         current->reclaim_state = &reclaim_state;
1448
1449         lru_pages = count_lru_pages();
1450         nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
1451         /* If slab caches are huge, it's better to hit them first */
1452         while (nr_slab >= lru_pages) {
1453                 reclaim_state.reclaimed_slab = 0;
1454                 shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1455                 if (!reclaim_state.reclaimed_slab)
1456                         break;
1457
1458                 ret += reclaim_state.reclaimed_slab;
1459                 if (ret >= nr_pages)
1460                         goto out;
1461
1462                 nr_slab -= reclaim_state.reclaimed_slab;
1463         }
1464
1465         /*
1466          * We try to shrink LRUs in 5 passes:
1467          * 0 = Reclaim from inactive_list only
1468          * 1 = Reclaim from active list but don't reclaim mapped
1469          * 2 = 2nd pass of type 1
1470          * 3 = Reclaim mapped (normal reclaim)
1471          * 4 = 2nd pass of type 3
1472          */
1473         for (pass = 0; pass < 5; pass++) {
1474                 int prio;
1475
1476                 /* Force reclaiming mapped pages in the passes #3 and #4 */
1477                 if (pass > 2) {
1478                         sc.may_swap = 1;
1479                         sc.swappiness = 100;
1480                 }
1481
1482                 for (prio = DEF_PRIORITY; prio >= 0; prio--) {
1483                         unsigned long nr_to_scan = nr_pages - ret;
1484
1485                         sc.nr_scanned = 0;
1486                         ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
1487                         if (ret >= nr_pages)
1488                                 goto out;
1489
1490                         reclaim_state.reclaimed_slab = 0;
1491                         shrink_slab(sc.nr_scanned, sc.gfp_mask,
1492                                         count_lru_pages());
1493                         ret += reclaim_state.reclaimed_slab;
1494                         if (ret >= nr_pages)
1495                                 goto out;
1496
1497                         if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
1498                                 congestion_wait(WRITE, HZ / 10);
1499                 }
1500         }
1501
1502         /*
1503          * If ret = 0, we could not shrink LRUs, but there may be something
1504          * in slab caches
1505          */
1506         if (!ret) {
1507                 do {
1508                         reclaim_state.reclaimed_slab = 0;
1509                         shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages());
1510                         ret += reclaim_state.reclaimed_slab;
1511                 } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
1512         }
1513
1514 out:
1515         current->reclaim_state = NULL;
1516
1517         return ret;
1518 }
1519 #endif
1520
1521 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1522    not required for correctness.  So if the last cpu in a node goes
1523    away, we get changed to run anywhere: as the first one comes back,
1524    restore their cpu bindings. */
1525 static int __devinit cpu_callback(struct notifier_block *nfb,
1526                                   unsigned long action, void *hcpu)
1527 {
1528         pg_data_t *pgdat;
1529         cpumask_t mask;
1530
1531         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
1532                 for_each_online_pgdat(pgdat) {
1533                         mask = node_to_cpumask(pgdat->node_id);
1534                         if (any_online_cpu(mask) != NR_CPUS)
1535                                 /* One of our CPUs online: restore mask */
1536                                 set_cpus_allowed(pgdat->kswapd, mask);
1537                 }
1538         }
1539         return NOTIFY_OK;
1540 }
1541
1542 /*
1543  * This kswapd start function will be called by init and node-hot-add.
1544  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
1545  */
1546 int kswapd_run(int nid)
1547 {
1548         pg_data_t *pgdat = NODE_DATA(nid);
1549         int ret = 0;
1550
1551         if (pgdat->kswapd)
1552                 return 0;
1553
1554         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
1555         if (IS_ERR(pgdat->kswapd)) {
1556                 /* failure at boot is fatal */
1557                 BUG_ON(system_state == SYSTEM_BOOTING);
1558                 printk("Failed to start kswapd on node %d\n",nid);
1559                 ret = -1;
1560         }
1561         return ret;
1562 }
1563
1564 static int __init kswapd_init(void)
1565 {
1566         int nid;
1567
1568         swap_setup();
1569         for_each_online_node(nid)
1570                 kswapd_run(nid);
1571         hotcpu_notifier(cpu_callback, 0);
1572         return 0;
1573 }
1574
1575 module_init(kswapd_init)
1576
1577 #ifdef CONFIG_NUMA
1578 /*
1579  * Zone reclaim mode
1580  *
1581  * If non-zero call zone_reclaim when the number of free pages falls below
1582  * the watermarks.
1583  */
1584 int zone_reclaim_mode __read_mostly;
1585
1586 #define RECLAIM_OFF 0
1587 #define RECLAIM_ZONE (1<<0)     /* Run shrink_cache on the zone */
1588 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
1589 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
1590
1591 /*
1592  * Priority for ZONE_RECLAIM. This determines the fraction of pages
1593  * of a node considered for each zone_reclaim. 4 scans 1/16th of
1594  * a zone.
1595  */
1596 #define ZONE_RECLAIM_PRIORITY 4
1597
1598 /*
1599  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
1600  * occur.
1601  */
1602 int sysctl_min_unmapped_ratio = 1;
1603
1604 /*
1605  * If the number of slab pages in a zone grows beyond this percentage then
1606  * slab reclaim needs to occur.
1607  */
1608 int sysctl_min_slab_ratio = 5;
1609
1610 /*
1611  * Try to free up some pages from this zone through reclaim.
1612  */
1613 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1614 {
1615         /* Minimum pages needed in order to stay on node */
1616         const unsigned long nr_pages = 1 << order;
1617         struct task_struct *p = current;
1618         struct reclaim_state reclaim_state;
1619         int priority;
1620         unsigned long nr_reclaimed = 0;
1621         struct scan_control sc = {
1622                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
1623                 .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
1624                 .swap_cluster_max = max_t(unsigned long, nr_pages,
1625                                         SWAP_CLUSTER_MAX),
1626                 .gfp_mask = gfp_mask,
1627                 .swappiness = vm_swappiness,
1628         };
1629         unsigned long slab_reclaimable;
1630
1631         disable_swap_token();
1632         cond_resched();
1633         /*
1634          * We need to be able to allocate from the reserves for RECLAIM_SWAP
1635          * and we also need to be able to write out pages for RECLAIM_WRITE
1636          * and RECLAIM_SWAP.
1637          */
1638         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
1639         reclaim_state.reclaimed_slab = 0;
1640         p->reclaim_state = &reclaim_state;
1641
1642         if (zone_page_state(zone, NR_FILE_PAGES) -
1643                 zone_page_state(zone, NR_FILE_MAPPED) >
1644                 zone->min_unmapped_pages) {
1645                 /*
1646                  * Free memory by calling shrink zone with increasing
1647                  * priorities until we have enough memory freed.
1648                  */
1649                 priority = ZONE_RECLAIM_PRIORITY;
1650                 do {
1651                         note_zone_scanning_priority(zone, priority);
1652                         nr_reclaimed += shrink_zone(priority, zone, &sc);
1653                         priority--;
1654                 } while (priority >= 0 && nr_reclaimed < nr_pages);
1655         }
1656
1657         slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
1658         if (slab_reclaimable > zone->min_slab_pages) {
1659                 /*
1660                  * shrink_slab() does not currently allow us to determine how
1661                  * many pages were freed in this zone. So we take the current
1662                  * number of slab pages and shake the slab until it is reduced
1663                  * by the same nr_pages that we used for reclaiming unmapped
1664                  * pages.
1665                  *
1666                  * Note that shrink_slab will free memory on all zones and may
1667                  * take a long time.
1668                  */
1669                 while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
1670                         zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
1671                                 slab_reclaimable - nr_pages)
1672                         ;
1673
1674                 /*
1675                  * Update nr_reclaimed by the number of slab pages we
1676                  * reclaimed from this zone.
1677                  */
1678                 nr_reclaimed += slab_reclaimable -
1679                         zone_page_state(zone, NR_SLAB_RECLAIMABLE);
1680         }
1681
1682         p->reclaim_state = NULL;
1683         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
1684         return nr_reclaimed >= nr_pages;
1685 }
1686
1687 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1688 {
1689         cpumask_t mask;
1690         int node_id;
1691
1692         /*
1693          * Zone reclaim reclaims unmapped file backed pages and
1694          * slab pages if we are over the defined limits.
1695          *
1696          * A small portion of unmapped file backed pages is needed for
1697          * file I/O otherwise pages read by file I/O will be immediately
1698          * thrown out if the zone is overallocated. So we do not reclaim
1699          * if less than a specified percentage of the zone is used by
1700          * unmapped file backed pages.
1701          */
1702         if (zone_page_state(zone, NR_FILE_PAGES) -
1703             zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages
1704             && zone_page_state(zone, NR_SLAB_RECLAIMABLE)
1705                         <= zone->min_slab_pages)
1706                 return 0;
1707
1708         /*
1709          * Avoid concurrent zone reclaims, do not reclaim in a zone that does
1710          * not have reclaimable pages and if we should not delay the allocation
1711          * then do not scan.
1712          */
1713         if (!(gfp_mask & __GFP_WAIT) ||
1714                 zone->all_unreclaimable ||
1715                 atomic_read(&zone->reclaim_in_progress) > 0 ||
1716                 (current->flags & PF_MEMALLOC))
1717                         return 0;
1718
1719         /*
1720          * Only run zone reclaim on the local zone or on zones that do not
1721          * have associated processors. This will favor the local processor
1722          * over remote processors and spread off node memory allocations
1723          * as wide as possible.
1724          */
1725         node_id = zone_to_nid(zone);
1726         mask = node_to_cpumask(node_id);
1727         if (!cpus_empty(mask) && node_id != numa_node_id())
1728                 return 0;
1729         return __zone_reclaim(zone, gfp_mask, order);
1730 }
1731 #endif