linux/mm/vmscan.c
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   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/gfp.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/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/compaction.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#include <linux/memcontrol.h>
  41#include <linux/delayacct.h>
  42#include <linux/sysctl.h>
  43#include <linux/oom.h>
  44#include <linux/prefetch.h>
  45
  46#include <asm/tlbflush.h>
  47#include <asm/div64.h>
  48
  49#include <linux/swapops.h>
  50
  51#include "internal.h"
  52
  53#define CREATE_TRACE_POINTS
  54#include <trace/events/vmscan.h>
  55
  56struct scan_control {
  57        /* Incremented by the number of inactive pages that were scanned */
  58        unsigned long nr_scanned;
  59
  60        /* Number of pages freed so far during a call to shrink_zones() */
  61        unsigned long nr_reclaimed;
  62
  63        /* How many pages shrink_list() should reclaim */
  64        unsigned long nr_to_reclaim;
  65
  66        unsigned long hibernation_mode;
  67
  68        /* This context's GFP mask */
  69        gfp_t gfp_mask;
  70
  71        int may_writepage;
  72
  73        /* Can mapped pages be reclaimed? */
  74        int may_unmap;
  75
  76        /* Can pages be swapped as part of reclaim? */
  77        int may_swap;
  78
  79        int order;
  80
  81        /* Scan (total_size >> priority) pages at once */
  82        int priority;
  83
  84        /*
  85         * The memory cgroup that hit its limit and as a result is the
  86         * primary target of this reclaim invocation.
  87         */
  88        struct mem_cgroup *target_mem_cgroup;
  89
  90        /*
  91         * Nodemask of nodes allowed by the caller. If NULL, all nodes
  92         * are scanned.
  93         */
  94        nodemask_t      *nodemask;
  95};
  96
  97#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  98
  99#ifdef ARCH_HAS_PREFETCH
 100#define prefetch_prev_lru_page(_page, _base, _field)                    \
 101        do {                                                            \
 102                if ((_page)->lru.prev != _base) {                       \
 103                        struct page *prev;                              \
 104                                                                        \
 105                        prev = lru_to_page(&(_page->lru));              \
 106                        prefetch(&prev->_field);                        \
 107                }                                                       \
 108        } while (0)
 109#else
 110#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
 111#endif
 112
 113#ifdef ARCH_HAS_PREFETCHW
 114#define prefetchw_prev_lru_page(_page, _base, _field)                   \
 115        do {                                                            \
 116                if ((_page)->lru.prev != _base) {                       \
 117                        struct page *prev;                              \
 118                                                                        \
 119                        prev = lru_to_page(&(_page->lru));              \
 120                        prefetchw(&prev->_field);                       \
 121                }                                                       \
 122        } while (0)
 123#else
 124#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 125#endif
 126
 127/*
 128 * From 0 .. 100.  Higher means more swappy.
 129 */
 130int vm_swappiness = 60;
 131long vm_total_pages;    /* The total number of pages which the VM controls */
 132
 133static LIST_HEAD(shrinker_list);
 134static DECLARE_RWSEM(shrinker_rwsem);
 135
 136#ifdef CONFIG_MEMCG
 137static bool global_reclaim(struct scan_control *sc)
 138{
 139        return !sc->target_mem_cgroup;
 140}
 141#else
 142static bool global_reclaim(struct scan_control *sc)
 143{
 144        return true;
 145}
 146#endif
 147
 148static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
 149{
 150        if (!mem_cgroup_disabled())
 151                return mem_cgroup_get_lru_size(lruvec, lru);
 152
 153        return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
 154}
 155
 156/*
 157 * Add a shrinker callback to be called from the vm
 158 */
 159void register_shrinker(struct shrinker *shrinker)
 160{
 161        atomic_long_set(&shrinker->nr_in_batch, 0);
 162        down_write(&shrinker_rwsem);
 163        list_add_tail(&shrinker->list, &shrinker_list);
 164        up_write(&shrinker_rwsem);
 165}
 166EXPORT_SYMBOL(register_shrinker);
 167
 168/*
 169 * Remove one
 170 */
 171void unregister_shrinker(struct shrinker *shrinker)
 172{
 173        down_write(&shrinker_rwsem);
 174        list_del(&shrinker->list);
 175        up_write(&shrinker_rwsem);
 176}
 177EXPORT_SYMBOL(unregister_shrinker);
 178
 179static inline int do_shrinker_shrink(struct shrinker *shrinker,
 180                                     struct shrink_control *sc,
 181                                     unsigned long nr_to_scan)
 182{
 183        sc->nr_to_scan = nr_to_scan;
 184        return (*shrinker->shrink)(shrinker, sc);
 185}
 186
 187#define SHRINK_BATCH 128
 188/*
 189 * Call the shrink functions to age shrinkable caches
 190 *
 191 * Here we assume it costs one seek to replace a lru page and that it also
 192 * takes a seek to recreate a cache object.  With this in mind we age equal
 193 * percentages of the lru and ageable caches.  This should balance the seeks
 194 * generated by these structures.
 195 *
 196 * If the vm encountered mapped pages on the LRU it increase the pressure on
 197 * slab to avoid swapping.
 198 *
 199 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 200 *
 201 * `lru_pages' represents the number of on-LRU pages in all the zones which
 202 * are eligible for the caller's allocation attempt.  It is used for balancing
 203 * slab reclaim versus page reclaim.
 204 *
 205 * Returns the number of slab objects which we shrunk.
 206 */
 207unsigned long shrink_slab(struct shrink_control *shrink,
 208                          unsigned long nr_pages_scanned,
 209                          unsigned long lru_pages)
 210{
 211        struct shrinker *shrinker;
 212        unsigned long ret = 0;
 213
 214        if (nr_pages_scanned == 0)
 215                nr_pages_scanned = SWAP_CLUSTER_MAX;
 216
 217        if (!down_read_trylock(&shrinker_rwsem)) {
 218                /* Assume we'll be able to shrink next time */
 219                ret = 1;
 220                goto out;
 221        }
 222
 223        list_for_each_entry(shrinker, &shrinker_list, list) {
 224                unsigned long long delta;
 225                long total_scan;
 226                long max_pass;
 227                int shrink_ret = 0;
 228                long nr;
 229                long new_nr;
 230                long batch_size = shrinker->batch ? shrinker->batch
 231                                                  : SHRINK_BATCH;
 232
 233                max_pass = do_shrinker_shrink(shrinker, shrink, 0);
 234                if (max_pass <= 0)
 235                        continue;
 236
 237                /*
 238                 * copy the current shrinker scan count into a local variable
 239                 * and zero it so that other concurrent shrinker invocations
 240                 * don't also do this scanning work.
 241                 */
 242                nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
 243
 244                total_scan = nr;
 245                delta = (4 * nr_pages_scanned) / shrinker->seeks;
 246                delta *= max_pass;
 247                do_div(delta, lru_pages + 1);
 248                total_scan += delta;
 249                if (total_scan < 0) {
 250                        printk(KERN_ERR "shrink_slab: %pF negative objects to "
 251                               "delete nr=%ld\n",
 252                               shrinker->shrink, total_scan);
 253                        total_scan = max_pass;
 254                }
 255
 256                /*
 257                 * We need to avoid excessive windup on filesystem shrinkers
 258                 * due to large numbers of GFP_NOFS allocations causing the
 259                 * shrinkers to return -1 all the time. This results in a large
 260                 * nr being built up so when a shrink that can do some work
 261                 * comes along it empties the entire cache due to nr >>>
 262                 * max_pass.  This is bad for sustaining a working set in
 263                 * memory.
 264                 *
 265                 * Hence only allow the shrinker to scan the entire cache when
 266                 * a large delta change is calculated directly.
 267                 */
 268                if (delta < max_pass / 4)
 269                        total_scan = min(total_scan, max_pass / 2);
 270
 271                /*
 272                 * Avoid risking looping forever due to too large nr value:
 273                 * never try to free more than twice the estimate number of
 274                 * freeable entries.
 275                 */
 276                if (total_scan > max_pass * 2)
 277                        total_scan = max_pass * 2;
 278
 279                trace_mm_shrink_slab_start(shrinker, shrink, nr,
 280                                        nr_pages_scanned, lru_pages,
 281                                        max_pass, delta, total_scan);
 282
 283                while (total_scan >= batch_size) {
 284                        int nr_before;
 285
 286                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
 287                        shrink_ret = do_shrinker_shrink(shrinker, shrink,
 288                                                        batch_size);
 289                        if (shrink_ret == -1)
 290                                break;
 291                        if (shrink_ret < nr_before)
 292                                ret += nr_before - shrink_ret;
 293                        count_vm_events(SLABS_SCANNED, batch_size);
 294                        total_scan -= batch_size;
 295
 296                        cond_resched();
 297                }
 298
 299                /*
 300                 * move the unused scan count back into the shrinker in a
 301                 * manner that handles concurrent updates. If we exhausted the
 302                 * scan, there is no need to do an update.
 303                 */
 304                if (total_scan > 0)
 305                        new_nr = atomic_long_add_return(total_scan,
 306                                        &shrinker->nr_in_batch);
 307                else
 308                        new_nr = atomic_long_read(&shrinker->nr_in_batch);
 309
 310                trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
 311        }
 312        up_read(&shrinker_rwsem);
 313out:
 314        cond_resched();
 315        return ret;
 316}
 317
 318static inline int is_page_cache_freeable(struct page *page)
 319{
 320        /*
 321         * A freeable page cache page is referenced only by the caller
 322         * that isolated the page, the page cache radix tree and
 323         * optional buffer heads at page->private.
 324         */
 325        return page_count(page) - page_has_private(page) == 2;
 326}
 327
 328static int may_write_to_queue(struct backing_dev_info *bdi,
 329                              struct scan_control *sc)
 330{
 331        if (current->flags & PF_SWAPWRITE)
 332                return 1;
 333        if (!bdi_write_congested(bdi))
 334                return 1;
 335        if (bdi == current->backing_dev_info)
 336                return 1;
 337        return 0;
 338}
 339
 340/*
 341 * We detected a synchronous write error writing a page out.  Probably
 342 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 343 * fsync(), msync() or close().
 344 *
 345 * The tricky part is that after writepage we cannot touch the mapping: nothing
 346 * prevents it from being freed up.  But we have a ref on the page and once
 347 * that page is locked, the mapping is pinned.
 348 *
 349 * We're allowed to run sleeping lock_page() here because we know the caller has
 350 * __GFP_FS.
 351 */
 352static void handle_write_error(struct address_space *mapping,
 353                                struct page *page, int error)
 354{
 355        lock_page(page);
 356        if (page_mapping(page) == mapping)
 357                mapping_set_error(mapping, error);
 358        unlock_page(page);
 359}
 360
 361/* possible outcome of pageout() */
 362typedef enum {
 363        /* failed to write page out, page is locked */
 364        PAGE_KEEP,
 365        /* move page to the active list, page is locked */
 366        PAGE_ACTIVATE,
 367        /* page has been sent to the disk successfully, page is unlocked */
 368        PAGE_SUCCESS,
 369        /* page is clean and locked */
 370        PAGE_CLEAN,
 371} pageout_t;
 372
 373/*
 374 * pageout is called by shrink_page_list() for each dirty page.
 375 * Calls ->writepage().
 376 */
 377static pageout_t pageout(struct page *page, struct address_space *mapping,
 378                         struct scan_control *sc)
 379{
 380        /*
 381         * If the page is dirty, only perform writeback if that write
 382         * will be non-blocking.  To prevent this allocation from being
 383         * stalled by pagecache activity.  But note that there may be
 384         * stalls if we need to run get_block().  We could test
 385         * PagePrivate for that.
 386         *
 387         * If this process is currently in __generic_file_aio_write() against
 388         * this page's queue, we can perform writeback even if that
 389         * will block.
 390         *
 391         * If the page is swapcache, write it back even if that would
 392         * block, for some throttling. This happens by accident, because
 393         * swap_backing_dev_info is bust: it doesn't reflect the
 394         * congestion state of the swapdevs.  Easy to fix, if needed.
 395         */
 396        if (!is_page_cache_freeable(page))
 397                return PAGE_KEEP;
 398        if (!mapping) {
 399                /*
 400                 * Some data journaling orphaned pages can have
 401                 * page->mapping == NULL while being dirty with clean buffers.
 402                 */
 403                if (page_has_private(page)) {
 404                        if (try_to_free_buffers(page)) {
 405                                ClearPageDirty(page);
 406                                printk("%s: orphaned page\n", __func__);
 407                                return PAGE_CLEAN;
 408                        }
 409                }
 410                return PAGE_KEEP;
 411        }
 412        if (mapping->a_ops->writepage == NULL)
 413                return PAGE_ACTIVATE;
 414        if (!may_write_to_queue(mapping->backing_dev_info, sc))
 415                return PAGE_KEEP;
 416
 417        if (clear_page_dirty_for_io(page)) {
 418                int res;
 419                struct writeback_control wbc = {
 420                        .sync_mode = WB_SYNC_NONE,
 421                        .nr_to_write = SWAP_CLUSTER_MAX,
 422                        .range_start = 0,
 423                        .range_end = LLONG_MAX,
 424                        .for_reclaim = 1,
 425                };
 426
 427                SetPageReclaim(page);
 428                res = mapping->a_ops->writepage(page, &wbc);
 429                if (res < 0)
 430                        handle_write_error(mapping, page, res);
 431                if (res == AOP_WRITEPAGE_ACTIVATE) {
 432                        ClearPageReclaim(page);
 433                        return PAGE_ACTIVATE;
 434                }
 435
 436                if (!PageWriteback(page)) {
 437                        /* synchronous write or broken a_ops? */
 438                        ClearPageReclaim(page);
 439                }
 440                trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
 441                inc_zone_page_state(page, NR_VMSCAN_WRITE);
 442                return PAGE_SUCCESS;
 443        }
 444
 445        return PAGE_CLEAN;
 446}
 447
 448/*
 449 * Same as remove_mapping, but if the page is removed from the mapping, it
 450 * gets returned with a refcount of 0.
 451 */
 452static int __remove_mapping(struct address_space *mapping, struct page *page)
 453{
 454        BUG_ON(!PageLocked(page));
 455        BUG_ON(mapping != page_mapping(page));
 456
 457        spin_lock_irq(&mapping->tree_lock);
 458        /*
 459         * The non racy check for a busy page.
 460         *
 461         * Must be careful with the order of the tests. When someone has
 462         * a ref to the page, it may be possible that they dirty it then
 463         * drop the reference. So if PageDirty is tested before page_count
 464         * here, then the following race may occur:
 465         *
 466         * get_user_pages(&page);
 467         * [user mapping goes away]
 468         * write_to(page);
 469         *                              !PageDirty(page)    [good]
 470         * SetPageDirty(page);
 471         * put_page(page);
 472         *                              !page_count(page)   [good, discard it]
 473         *
 474         * [oops, our write_to data is lost]
 475         *
 476         * Reversing the order of the tests ensures such a situation cannot
 477         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 478         * load is not satisfied before that of page->_count.
 479         *
 480         * Note that if SetPageDirty is always performed via set_page_dirty,
 481         * and thus under tree_lock, then this ordering is not required.
 482         */
 483        if (!page_freeze_refs(page, 2))
 484                goto cannot_free;
 485        /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
 486        if (unlikely(PageDirty(page))) {
 487                page_unfreeze_refs(page, 2);
 488                goto cannot_free;
 489        }
 490
 491        if (PageSwapCache(page)) {
 492                swp_entry_t swap = { .val = page_private(page) };
 493                __delete_from_swap_cache(page);
 494                spin_unlock_irq(&mapping->tree_lock);
 495                swapcache_free(swap, page);
 496        } else {
 497                void (*freepage)(struct page *);
 498
 499                freepage = mapping->a_ops->freepage;
 500
 501                __delete_from_page_cache(page);
 502                spin_unlock_irq(&mapping->tree_lock);
 503                mem_cgroup_uncharge_cache_page(page);
 504
 505                if (freepage != NULL)
 506                        freepage(page);
 507        }
 508
 509        return 1;
 510
 511cannot_free:
 512        spin_unlock_irq(&mapping->tree_lock);
 513        return 0;
 514}
 515
 516/*
 517 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 518 * someone else has a ref on the page, abort and return 0.  If it was
 519 * successfully detached, return 1.  Assumes the caller has a single ref on
 520 * this page.
 521 */
 522int remove_mapping(struct address_space *mapping, struct page *page)
 523{
 524        if (__remove_mapping(mapping, page)) {
 525                /*
 526                 * Unfreezing the refcount with 1 rather than 2 effectively
 527                 * drops the pagecache ref for us without requiring another
 528                 * atomic operation.
 529                 */
 530                page_unfreeze_refs(page, 1);
 531                return 1;
 532        }
 533        return 0;
 534}
 535
 536/**
 537 * putback_lru_page - put previously isolated page onto appropriate LRU list
 538 * @page: page to be put back to appropriate lru list
 539 *
 540 * Add previously isolated @page to appropriate LRU list.
 541 * Page may still be unevictable for other reasons.
 542 *
 543 * lru_lock must not be held, interrupts must be enabled.
 544 */
 545void putback_lru_page(struct page *page)
 546{
 547        int lru;
 548        int active = !!TestClearPageActive(page);
 549        int was_unevictable = PageUnevictable(page);
 550
 551        VM_BUG_ON(PageLRU(page));
 552
 553redo:
 554        ClearPageUnevictable(page);
 555
 556        if (page_evictable(page)) {
 557                /*
 558                 * For evictable pages, we can use the cache.
 559                 * In event of a race, worst case is we end up with an
 560                 * unevictable page on [in]active list.
 561                 * We know how to handle that.
 562                 */
 563                lru = active + page_lru_base_type(page);
 564                lru_cache_add_lru(page, lru);
 565        } else {
 566                /*
 567                 * Put unevictable pages directly on zone's unevictable
 568                 * list.
 569                 */
 570                lru = LRU_UNEVICTABLE;
 571                add_page_to_unevictable_list(page);
 572                /*
 573                 * When racing with an mlock or AS_UNEVICTABLE clearing
 574                 * (page is unlocked) make sure that if the other thread
 575                 * does not observe our setting of PG_lru and fails
 576                 * isolation/check_move_unevictable_pages,
 577                 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
 578                 * the page back to the evictable list.
 579                 *
 580                 * The other side is TestClearPageMlocked() or shmem_lock().
 581                 */
 582                smp_mb();
 583        }
 584
 585        /*
 586         * page's status can change while we move it among lru. If an evictable
 587         * page is on unevictable list, it never be freed. To avoid that,
 588         * check after we added it to the list, again.
 589         */
 590        if (lru == LRU_UNEVICTABLE && page_evictable(page)) {
 591                if (!isolate_lru_page(page)) {
 592                        put_page(page);
 593                        goto redo;
 594                }
 595                /* This means someone else dropped this page from LRU
 596                 * So, it will be freed or putback to LRU again. There is
 597                 * nothing to do here.
 598                 */
 599        }
 600
 601        if (was_unevictable && lru != LRU_UNEVICTABLE)
 602                count_vm_event(UNEVICTABLE_PGRESCUED);
 603        else if (!was_unevictable && lru == LRU_UNEVICTABLE)
 604                count_vm_event(UNEVICTABLE_PGCULLED);
 605
 606        put_page(page);         /* drop ref from isolate */
 607}
 608
 609enum page_references {
 610        PAGEREF_RECLAIM,
 611        PAGEREF_RECLAIM_CLEAN,
 612        PAGEREF_KEEP,
 613        PAGEREF_ACTIVATE,
 614};
 615
 616static enum page_references page_check_references(struct page *page,
 617                                                  struct scan_control *sc)
 618{
 619        int referenced_ptes, referenced_page;
 620        unsigned long vm_flags;
 621
 622        referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
 623                                          &vm_flags);
 624        referenced_page = TestClearPageReferenced(page);
 625
 626        /*
 627         * Mlock lost the isolation race with us.  Let try_to_unmap()
 628         * move the page to the unevictable list.
 629         */
 630        if (vm_flags & VM_LOCKED)
 631                return PAGEREF_RECLAIM;
 632
 633        if (referenced_ptes) {
 634                if (PageSwapBacked(page))
 635                        return PAGEREF_ACTIVATE;
 636                /*
 637                 * All mapped pages start out with page table
 638                 * references from the instantiating fault, so we need
 639                 * to look twice if a mapped file page is used more
 640                 * than once.
 641                 *
 642                 * Mark it and spare it for another trip around the
 643                 * inactive list.  Another page table reference will
 644                 * lead to its activation.
 645                 *
 646                 * Note: the mark is set for activated pages as well
 647                 * so that recently deactivated but used pages are
 648                 * quickly recovered.
 649                 */
 650                SetPageReferenced(page);
 651
 652                if (referenced_page || referenced_ptes > 1)
 653                        return PAGEREF_ACTIVATE;
 654
 655                /*
 656                 * Activate file-backed executable pages after first usage.
 657                 */
 658                if (vm_flags & VM_EXEC)
 659                        return PAGEREF_ACTIVATE;
 660
 661                return PAGEREF_KEEP;
 662        }
 663
 664        /* Reclaim if clean, defer dirty pages to writeback */
 665        if (referenced_page && !PageSwapBacked(page))
 666                return PAGEREF_RECLAIM_CLEAN;
 667
 668        return PAGEREF_RECLAIM;
 669}
 670
 671/*
 672 * shrink_page_list() returns the number of reclaimed pages
 673 */
 674static unsigned long shrink_page_list(struct list_head *page_list,
 675                                      struct zone *zone,
 676                                      struct scan_control *sc,
 677                                      enum ttu_flags ttu_flags,
 678                                      unsigned long *ret_nr_dirty,
 679                                      unsigned long *ret_nr_writeback,
 680                                      bool force_reclaim)
 681{
 682        LIST_HEAD(ret_pages);
 683        LIST_HEAD(free_pages);
 684        int pgactivate = 0;
 685        unsigned long nr_dirty = 0;
 686        unsigned long nr_congested = 0;
 687        unsigned long nr_reclaimed = 0;
 688        unsigned long nr_writeback = 0;
 689
 690        cond_resched();
 691
 692        mem_cgroup_uncharge_start();
 693        while (!list_empty(page_list)) {
 694                struct address_space *mapping;
 695                struct page *page;
 696                int may_enter_fs;
 697                enum page_references references = PAGEREF_RECLAIM_CLEAN;
 698
 699                cond_resched();
 700
 701                page = lru_to_page(page_list);
 702                list_del(&page->lru);
 703
 704                if (!trylock_page(page))
 705                        goto keep;
 706
 707                VM_BUG_ON(PageActive(page));
 708                VM_BUG_ON(page_zone(page) != zone);
 709
 710                sc->nr_scanned++;
 711
 712                if (unlikely(!page_evictable(page)))
 713                        goto cull_mlocked;
 714
 715                if (!sc->may_unmap && page_mapped(page))
 716                        goto keep_locked;
 717
 718                /* Double the slab pressure for mapped and swapcache pages */
 719                if (page_mapped(page) || PageSwapCache(page))
 720                        sc->nr_scanned++;
 721
 722                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 723                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 724
 725                if (PageWriteback(page)) {
 726                        /*
 727                         * memcg doesn't have any dirty pages throttling so we
 728                         * could easily OOM just because too many pages are in
 729                         * writeback and there is nothing else to reclaim.
 730                         *
 731                         * Check __GFP_IO, certainly because a loop driver
 732                         * thread might enter reclaim, and deadlock if it waits
 733                         * on a page for which it is needed to do the write
 734                         * (loop masks off __GFP_IO|__GFP_FS for this reason);
 735                         * but more thought would probably show more reasons.
 736                         *
 737                         * Don't require __GFP_FS, since we're not going into
 738                         * the FS, just waiting on its writeback completion.
 739                         * Worryingly, ext4 gfs2 and xfs allocate pages with
 740                         * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
 741                         * testing may_enter_fs here is liable to OOM on them.
 742                         */
 743                        if (global_reclaim(sc) ||
 744                            !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
 745                                /*
 746                                 * This is slightly racy - end_page_writeback()
 747                                 * might have just cleared PageReclaim, then
 748                                 * setting PageReclaim here end up interpreted
 749                                 * as PageReadahead - but that does not matter
 750                                 * enough to care.  What we do want is for this
 751                                 * page to have PageReclaim set next time memcg
 752                                 * reclaim reaches the tests above, so it will
 753                                 * then wait_on_page_writeback() to avoid OOM;
 754                                 * and it's also appropriate in global reclaim.
 755                                 */
 756                                SetPageReclaim(page);
 757                                nr_writeback++;
 758                                goto keep_locked;
 759                        }
 760                        wait_on_page_writeback(page);
 761                }
 762
 763                if (!force_reclaim)
 764                        references = page_check_references(page, sc);
 765
 766                switch (references) {
 767                case PAGEREF_ACTIVATE:
 768                        goto activate_locked;
 769                case PAGEREF_KEEP:
 770                        goto keep_locked;
 771                case PAGEREF_RECLAIM:
 772                case PAGEREF_RECLAIM_CLEAN:
 773                        ; /* try to reclaim the page below */
 774                }
 775
 776                /*
 777                 * Anonymous process memory has backing store?
 778                 * Try to allocate it some swap space here.
 779                 */
 780                if (PageAnon(page) && !PageSwapCache(page)) {
 781                        if (!(sc->gfp_mask & __GFP_IO))
 782                                goto keep_locked;
 783                        if (!add_to_swap(page))
 784                                goto activate_locked;
 785                        may_enter_fs = 1;
 786                }
 787
 788                mapping = page_mapping(page);
 789
 790                /*
 791                 * The page is mapped into the page tables of one or more
 792                 * processes. Try to unmap it here.
 793                 */
 794                if (page_mapped(page) && mapping) {
 795                        switch (try_to_unmap(page, ttu_flags)) {
 796                        case SWAP_FAIL:
 797                                goto activate_locked;
 798                        case SWAP_AGAIN:
 799                                goto keep_locked;
 800                        case SWAP_MLOCK:
 801                                goto cull_mlocked;
 802                        case SWAP_SUCCESS:
 803                                ; /* try to free the page below */
 804                        }
 805                }
 806
 807                if (PageDirty(page)) {
 808                        nr_dirty++;
 809
 810                        /*
 811                         * Only kswapd can writeback filesystem pages to
 812                         * avoid risk of stack overflow but do not writeback
 813                         * unless under significant pressure.
 814                         */
 815                        if (page_is_file_cache(page) &&
 816                                        (!current_is_kswapd() ||
 817                                         sc->priority >= DEF_PRIORITY - 2)) {
 818                                /*
 819                                 * Immediately reclaim when written back.
 820                                 * Similar in principal to deactivate_page()
 821                                 * except we already have the page isolated
 822                                 * and know it's dirty
 823                                 */
 824                                inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
 825                                SetPageReclaim(page);
 826
 827                                goto keep_locked;
 828                        }
 829
 830                        if (references == PAGEREF_RECLAIM_CLEAN)
 831                                goto keep_locked;
 832                        if (!may_enter_fs)
 833                                goto keep_locked;
 834                        if (!sc->may_writepage)
 835                                goto keep_locked;
 836
 837                        /* Page is dirty, try to write it out here */
 838                        switch (pageout(page, mapping, sc)) {
 839                        case PAGE_KEEP:
 840                                nr_congested++;
 841                                goto keep_locked;
 842                        case PAGE_ACTIVATE:
 843                                goto activate_locked;
 844                        case PAGE_SUCCESS:
 845                                if (PageWriteback(page))
 846                                        goto keep;
 847                                if (PageDirty(page))
 848                                        goto keep;
 849
 850                                /*
 851                                 * A synchronous write - probably a ramdisk.  Go
 852                                 * ahead and try to reclaim the page.
 853                                 */
 854                                if (!trylock_page(page))
 855                                        goto keep;
 856                                if (PageDirty(page) || PageWriteback(page))
 857                                        goto keep_locked;
 858                                mapping = page_mapping(page);
 859                        case PAGE_CLEAN:
 860                                ; /* try to free the page below */
 861                        }
 862                }
 863
 864                /*
 865                 * If the page has buffers, try to free the buffer mappings
 866                 * associated with this page. If we succeed we try to free
 867                 * the page as well.
 868                 *
 869                 * We do this even if the page is PageDirty().
 870                 * try_to_release_page() does not perform I/O, but it is
 871                 * possible for a page to have PageDirty set, but it is actually
 872                 * clean (all its buffers are clean).  This happens if the
 873                 * buffers were written out directly, with submit_bh(). ext3
 874                 * will do this, as well as the blockdev mapping.
 875                 * try_to_release_page() will discover that cleanness and will
 876                 * drop the buffers and mark the page clean - it can be freed.
 877                 *
 878                 * Rarely, pages can have buffers and no ->mapping.  These are
 879                 * the pages which were not successfully invalidated in
 880                 * truncate_complete_page().  We try to drop those buffers here
 881                 * and if that worked, and the page is no longer mapped into
 882                 * process address space (page_count == 1) it can be freed.
 883                 * Otherwise, leave the page on the LRU so it is swappable.
 884                 */
 885                if (page_has_private(page)) {
 886                        if (!try_to_release_page(page, sc->gfp_mask))
 887                                goto activate_locked;
 888                        if (!mapping && page_count(page) == 1) {
 889                                unlock_page(page);
 890                                if (put_page_testzero(page))
 891                                        goto free_it;
 892                                else {
 893                                        /*
 894                                         * rare race with speculative reference.
 895                                         * the speculative reference will free
 896                                         * this page shortly, so we may
 897                                         * increment nr_reclaimed here (and
 898                                         * leave it off the LRU).
 899                                         */
 900                                        nr_reclaimed++;
 901                                        continue;
 902                                }
 903                        }
 904                }
 905
 906                if (!mapping || !__remove_mapping(mapping, page))
 907                        goto keep_locked;
 908
 909                /*
 910                 * At this point, we have no other references and there is
 911                 * no way to pick any more up (removed from LRU, removed
 912                 * from pagecache). Can use non-atomic bitops now (and
 913                 * we obviously don't have to worry about waking up a process
 914                 * waiting on the page lock, because there are no references.
 915                 */
 916                __clear_page_locked(page);
 917free_it:
 918                nr_reclaimed++;
 919
 920                /*
 921                 * Is there need to periodically free_page_list? It would
 922                 * appear not as the counts should be low
 923                 */
 924                list_add(&page->lru, &free_pages);
 925                continue;
 926
 927cull_mlocked:
 928                if (PageSwapCache(page))
 929                        try_to_free_swap(page);
 930                unlock_page(page);
 931                putback_lru_page(page);
 932                continue;
 933
 934activate_locked:
 935                /* Not a candidate for swapping, so reclaim swap space. */
 936                if (PageSwapCache(page) && vm_swap_full())
 937                        try_to_free_swap(page);
 938                VM_BUG_ON(PageActive(page));
 939                SetPageActive(page);
 940                pgactivate++;
 941keep_locked:
 942                unlock_page(page);
 943keep:
 944                list_add(&page->lru, &ret_pages);
 945                VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 946        }
 947
 948        /*
 949         * Tag a zone as congested if all the dirty pages encountered were
 950         * backed by a congested BDI. In this case, reclaimers should just
 951         * back off and wait for congestion to clear because further reclaim
 952         * will encounter the same problem
 953         */
 954        if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
 955                zone_set_flag(zone, ZONE_CONGESTED);
 956
 957        free_hot_cold_page_list(&free_pages, 1);
 958
 959        list_splice(&ret_pages, page_list);
 960        count_vm_events(PGACTIVATE, pgactivate);
 961        mem_cgroup_uncharge_end();
 962        *ret_nr_dirty += nr_dirty;
 963        *ret_nr_writeback += nr_writeback;
 964        return nr_reclaimed;
 965}
 966
 967unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 968                                            struct list_head *page_list)
 969{
 970        struct scan_control sc = {
 971                .gfp_mask = GFP_KERNEL,
 972                .priority = DEF_PRIORITY,
 973                .may_unmap = 1,
 974        };
 975        unsigned long ret, dummy1, dummy2;
 976        struct page *page, *next;
 977        LIST_HEAD(clean_pages);
 978
 979        list_for_each_entry_safe(page, next, page_list, lru) {
 980                if (page_is_file_cache(page) && !PageDirty(page)) {
 981                        ClearPageActive(page);
 982                        list_move(&page->lru, &clean_pages);
 983                }
 984        }
 985
 986        ret = shrink_page_list(&clean_pages, zone, &sc,
 987                                TTU_UNMAP|TTU_IGNORE_ACCESS,
 988                                &dummy1, &dummy2, true);
 989        list_splice(&clean_pages, page_list);
 990        __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
 991        return ret;
 992}
 993
 994/*
 995 * Attempt to remove the specified page from its LRU.  Only take this page
 996 * if it is of the appropriate PageActive status.  Pages which are being
 997 * freed elsewhere are also ignored.
 998 *
 999 * page:        page to consider
1000 * mode:        one of the LRU isolation modes defined above
1001 *
1002 * returns 0 on success, -ve errno on failure.
1003 */
1004int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1005{
1006        int ret = -EINVAL;
1007
1008        /* Only take pages on the LRU. */
1009        if (!PageLRU(page))
1010                return ret;
1011
1012        /* Compaction should not handle unevictable pages but CMA can do so */
1013        if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1014                return ret;
1015
1016        ret = -EBUSY;
1017
1018        /*
1019         * To minimise LRU disruption, the caller can indicate that it only
1020         * wants to isolate pages it will be able to operate on without
1021         * blocking - clean pages for the most part.
1022         *
1023         * ISOLATE_CLEAN means that only clean pages should be isolated. This
1024         * is used by reclaim when it is cannot write to backing storage
1025         *
1026         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1027         * that it is possible to migrate without blocking
1028         */
1029        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1030                /* All the caller can do on PageWriteback is block */
1031                if (PageWriteback(page))
1032                        return ret;
1033
1034                if (PageDirty(page)) {
1035                        struct address_space *mapping;
1036
1037                        /* ISOLATE_CLEAN means only clean pages */
1038                        if (mode & ISOLATE_CLEAN)
1039                                return ret;
1040
1041                        /*
1042                         * Only pages without mappings or that have a
1043                         * ->migratepage callback are possible to migrate
1044                         * without blocking
1045                         */
1046                        mapping = page_mapping(page);
1047                        if (mapping && !mapping->a_ops->migratepage)
1048                                return ret;
1049                }
1050        }
1051
1052        if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1053                return ret;
1054
1055        if (likely(get_page_unless_zero(page))) {
1056                /*
1057                 * Be careful not to clear PageLRU until after we're
1058                 * sure the page is not being freed elsewhere -- the
1059                 * page release code relies on it.
1060                 */
1061                ClearPageLRU(page);
1062                ret = 0;
1063        }
1064
1065        return ret;
1066}
1067
1068/*
1069 * zone->lru_lock is heavily contended.  Some of the functions that
1070 * shrink the lists perform better by taking out a batch of pages
1071 * and working on them outside the LRU lock.
1072 *
1073 * For pagecache intensive workloads, this function is the hottest
1074 * spot in the kernel (apart from copy_*_user functions).
1075 *
1076 * Appropriate locks must be held before calling this function.
1077 *
1078 * @nr_to_scan: The number of pages to look through on the list.
1079 * @lruvec:     The LRU vector to pull pages from.
1080 * @dst:        The temp list to put pages on to.
1081 * @nr_scanned: The number of pages that were scanned.
1082 * @sc:         The scan_control struct for this reclaim session
1083 * @mode:       One of the LRU isolation modes
1084 * @lru:        LRU list id for isolating
1085 *
1086 * returns how many pages were moved onto *@dst.
1087 */
1088static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1089                struct lruvec *lruvec, struct list_head *dst,
1090                unsigned long *nr_scanned, struct scan_control *sc,
1091                isolate_mode_t mode, enum lru_list lru)
1092{
1093        struct list_head *src = &lruvec->lists[lru];
1094        unsigned long nr_taken = 0;
1095        unsigned long scan;
1096
1097        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1098                struct page *page;
1099                int nr_pages;
1100
1101                page = lru_to_page(src);
1102                prefetchw_prev_lru_page(page, src, flags);
1103
1104                VM_BUG_ON(!PageLRU(page));
1105
1106                switch (__isolate_lru_page(page, mode)) {
1107                case 0:
1108                        nr_pages = hpage_nr_pages(page);
1109                        mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1110                        list_move(&page->lru, dst);
1111                        nr_taken += nr_pages;
1112                        break;
1113
1114                case -EBUSY:
1115                        /* else it is being freed elsewhere */
1116                        list_move(&page->lru, src);
1117                        continue;
1118
1119                default:
1120                        BUG();
1121                }
1122        }
1123
1124        *nr_scanned = scan;
1125        trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1126                                    nr_taken, mode, is_file_lru(lru));
1127        return nr_taken;
1128}
1129
1130/**
1131 * isolate_lru_page - tries to isolate a page from its LRU list
1132 * @page: page to isolate from its LRU list
1133 *
1134 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1135 * vmstat statistic corresponding to whatever LRU list the page was on.
1136 *
1137 * Returns 0 if the page was removed from an LRU list.
1138 * Returns -EBUSY if the page was not on an LRU list.
1139 *
1140 * The returned page will have PageLRU() cleared.  If it was found on
1141 * the active list, it will have PageActive set.  If it was found on
1142 * the unevictable list, it will have the PageUnevictable bit set. That flag
1143 * may need to be cleared by the caller before letting the page go.
1144 *
1145 * The vmstat statistic corresponding to the list on which the page was
1146 * found will be decremented.
1147 *
1148 * Restrictions:
1149 * (1) Must be called with an elevated refcount on the page. This is a
1150 *     fundamentnal difference from isolate_lru_pages (which is called
1151 *     without a stable reference).
1152 * (2) the lru_lock must not be held.
1153 * (3) interrupts must be enabled.
1154 */
1155int isolate_lru_page(struct page *page)
1156{
1157        int ret = -EBUSY;
1158
1159        VM_BUG_ON(!page_count(page));
1160
1161        if (PageLRU(page)) {
1162                struct zone *zone = page_zone(page);
1163                struct lruvec *lruvec;
1164
1165                spin_lock_irq(&zone->lru_lock);
1166                lruvec = mem_cgroup_page_lruvec(page, zone);
1167                if (PageLRU(page)) {
1168                        int lru = page_lru(page);
1169                        get_page(page);
1170                        ClearPageLRU(page);
1171                        del_page_from_lru_list(page, lruvec, lru);
1172                        ret = 0;
1173                }
1174                spin_unlock_irq(&zone->lru_lock);
1175        }
1176        return ret;
1177}
1178
1179/*
1180 * Are there way too many processes in the direct reclaim path already?
1181 */
1182static int too_many_isolated(struct zone *zone, int file,
1183                struct scan_control *sc)
1184{
1185        unsigned long inactive, isolated;
1186
1187        if (current_is_kswapd())
1188                return 0;
1189
1190        if (!global_reclaim(sc))
1191                return 0;
1192
1193        if (file) {
1194                inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1195                isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1196        } else {
1197                inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1198                isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1199        }
1200
1201        return isolated > inactive;
1202}
1203
1204static noinline_for_stack void
1205putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1206{
1207        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1208        struct zone *zone = lruvec_zone(lruvec);
1209        LIST_HEAD(pages_to_free);
1210
1211        /*
1212         * Put back any unfreeable pages.
1213         */
1214        while (!list_empty(page_list)) {
1215                struct page *page = lru_to_page(page_list);
1216                int lru;
1217
1218                VM_BUG_ON(PageLRU(page));
1219                list_del(&page->lru);
1220                if (unlikely(!page_evictable(page))) {
1221                        spin_unlock_irq(&zone->lru_lock);
1222                        putback_lru_page(page);
1223                        spin_lock_irq(&zone->lru_lock);
1224                        continue;
1225                }
1226
1227                lruvec = mem_cgroup_page_lruvec(page, zone);
1228
1229                SetPageLRU(page);
1230                lru = page_lru(page);
1231                add_page_to_lru_list(page, lruvec, lru);
1232
1233                if (is_active_lru(lru)) {
1234                        int file = is_file_lru(lru);
1235                        int numpages = hpage_nr_pages(page);
1236                        reclaim_stat->recent_rotated[file] += numpages;
1237                }
1238                if (put_page_testzero(page)) {
1239                        __ClearPageLRU(page);
1240                        __ClearPageActive(page);
1241                        del_page_from_lru_list(page, lruvec, lru);
1242
1243                        if (unlikely(PageCompound(page))) {
1244                                spin_unlock_irq(&zone->lru_lock);
1245                                (*get_compound_page_dtor(page))(page);
1246                                spin_lock_irq(&zone->lru_lock);
1247                        } else
1248                                list_add(&page->lru, &pages_to_free);
1249                }
1250        }
1251
1252        /*
1253         * To save our caller's stack, now use input list for pages to free.
1254         */
1255        list_splice(&pages_to_free, page_list);
1256}
1257
1258/*
1259 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1260 * of reclaimed pages
1261 */
1262static noinline_for_stack unsigned long
1263shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1264                     struct scan_control *sc, enum lru_list lru)
1265{
1266        LIST_HEAD(page_list);
1267        unsigned long nr_scanned;
1268        unsigned long nr_reclaimed = 0;
1269        unsigned long nr_taken;
1270        unsigned long nr_dirty = 0;
1271        unsigned long nr_writeback = 0;
1272        isolate_mode_t isolate_mode = 0;
1273        int file = is_file_lru(lru);
1274        struct zone *zone = lruvec_zone(lruvec);
1275        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1276
1277        while (unlikely(too_many_isolated(zone, file, sc))) {
1278                congestion_wait(BLK_RW_ASYNC, HZ/10);
1279
1280                /* We are about to die and free our memory. Return now. */
1281                if (fatal_signal_pending(current))
1282                        return SWAP_CLUSTER_MAX;
1283        }
1284
1285        lru_add_drain();
1286
1287        if (!sc->may_unmap)
1288                isolate_mode |= ISOLATE_UNMAPPED;
1289        if (!sc->may_writepage)
1290                isolate_mode |= ISOLATE_CLEAN;
1291
1292        spin_lock_irq(&zone->lru_lock);
1293
1294        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1295                                     &nr_scanned, sc, isolate_mode, lru);
1296
1297        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1298        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1299
1300        if (global_reclaim(sc)) {
1301                zone->pages_scanned += nr_scanned;
1302                if (current_is_kswapd())
1303                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1304                else
1305                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1306        }
1307        spin_unlock_irq(&zone->lru_lock);
1308
1309        if (nr_taken == 0)
1310                return 0;
1311
1312        nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1313                                        &nr_dirty, &nr_writeback, false);
1314
1315        spin_lock_irq(&zone->lru_lock);
1316
1317        reclaim_stat->recent_scanned[file] += nr_taken;
1318
1319        if (global_reclaim(sc)) {
1320                if (current_is_kswapd())
1321                        __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1322                                               nr_reclaimed);
1323                else
1324                        __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1325                                               nr_reclaimed);
1326        }
1327
1328        putback_inactive_pages(lruvec, &page_list);
1329
1330        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1331
1332        spin_unlock_irq(&zone->lru_lock);
1333
1334        free_hot_cold_page_list(&page_list, 1);
1335
1336        /*
1337         * If reclaim is isolating dirty pages under writeback, it implies
1338         * that the long-lived page allocation rate is exceeding the page
1339         * laundering rate. Either the global limits are not being effective
1340         * at throttling processes due to the page distribution throughout
1341         * zones or there is heavy usage of a slow backing device. The
1342         * only option is to throttle from reclaim context which is not ideal
1343         * as there is no guarantee the dirtying process is throttled in the
1344         * same way balance_dirty_pages() manages.
1345         *
1346         * This scales the number of dirty pages that must be under writeback
1347         * before throttling depending on priority. It is a simple backoff
1348         * function that has the most effect in the range DEF_PRIORITY to
1349         * DEF_PRIORITY-2 which is the priority reclaim is considered to be
1350         * in trouble and reclaim is considered to be in trouble.
1351         *
1352         * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle
1353         * DEF_PRIORITY-1  50% must be PageWriteback
1354         * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble
1355         * ...
1356         * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1357         *                     isolated page is PageWriteback
1358         */
1359        if (nr_writeback && nr_writeback >=
1360                        (nr_taken >> (DEF_PRIORITY - sc->priority)))
1361                wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1362
1363        trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1364                zone_idx(zone),
1365                nr_scanned, nr_reclaimed,
1366                sc->priority,
1367                trace_shrink_flags(file));
1368        return nr_reclaimed;
1369}
1370
1371/*
1372 * This moves pages from the active list to the inactive list.
1373 *
1374 * We move them the other way if the page is referenced by one or more
1375 * processes, from rmap.
1376 *
1377 * If the pages are mostly unmapped, the processing is fast and it is
1378 * appropriate to hold zone->lru_lock across the whole operation.  But if
1379 * the pages are mapped, the processing is slow (page_referenced()) so we
1380 * should drop zone->lru_lock around each page.  It's impossible to balance
1381 * this, so instead we remove the pages from the LRU while processing them.
1382 * It is safe to rely on PG_active against the non-LRU pages in here because
1383 * nobody will play with that bit on a non-LRU page.
1384 *
1385 * The downside is that we have to touch page->_count against each page.
1386 * But we had to alter page->flags anyway.
1387 */
1388
1389static void move_active_pages_to_lru(struct lruvec *lruvec,
1390                                     struct list_head *list,
1391                                     struct list_head *pages_to_free,
1392                                     enum lru_list lru)
1393{
1394        struct zone *zone = lruvec_zone(lruvec);
1395        unsigned long pgmoved = 0;
1396        struct page *page;
1397        int nr_pages;
1398
1399        while (!list_empty(list)) {
1400                page = lru_to_page(list);
1401                lruvec = mem_cgroup_page_lruvec(page, zone);
1402
1403                VM_BUG_ON(PageLRU(page));
1404                SetPageLRU(page);
1405
1406                nr_pages = hpage_nr_pages(page);
1407                mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1408                list_move(&page->lru, &lruvec->lists[lru]);
1409                pgmoved += nr_pages;
1410
1411                if (put_page_testzero(page)) {
1412                        __ClearPageLRU(page);
1413                        __ClearPageActive(page);
1414                        del_page_from_lru_list(page, lruvec, lru);
1415
1416                        if (unlikely(PageCompound(page))) {
1417                                spin_unlock_irq(&zone->lru_lock);
1418                                (*get_compound_page_dtor(page))(page);
1419                                spin_lock_irq(&zone->lru_lock);
1420                        } else
1421                                list_add(&page->lru, pages_to_free);
1422                }
1423        }
1424        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1425        if (!is_active_lru(lru))
1426                __count_vm_events(PGDEACTIVATE, pgmoved);
1427}
1428
1429static void shrink_active_list(unsigned long nr_to_scan,
1430                               struct lruvec *lruvec,
1431                               struct scan_control *sc,
1432                               enum lru_list lru)
1433{
1434        unsigned long nr_taken;
1435        unsigned long nr_scanned;
1436        unsigned long vm_flags;
1437        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1438        LIST_HEAD(l_active);
1439        LIST_HEAD(l_inactive);
1440        struct page *page;
1441        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1442        unsigned long nr_rotated = 0;
1443        isolate_mode_t isolate_mode = 0;
1444        int file = is_file_lru(lru);
1445        struct zone *zone = lruvec_zone(lruvec);
1446
1447        lru_add_drain();
1448
1449        if (!sc->may_unmap)
1450                isolate_mode |= ISOLATE_UNMAPPED;
1451        if (!sc->may_writepage)
1452                isolate_mode |= ISOLATE_CLEAN;
1453
1454        spin_lock_irq(&zone->lru_lock);
1455
1456        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1457                                     &nr_scanned, sc, isolate_mode, lru);
1458        if (global_reclaim(sc))
1459                zone->pages_scanned += nr_scanned;
1460
1461        reclaim_stat->recent_scanned[file] += nr_taken;
1462
1463        __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1464        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1465        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1466        spin_unlock_irq(&zone->lru_lock);
1467
1468        while (!list_empty(&l_hold)) {
1469                cond_resched();
1470                page = lru_to_page(&l_hold);
1471                list_del(&page->lru);
1472
1473                if (unlikely(!page_evictable(page))) {
1474                        putback_lru_page(page);
1475                        continue;
1476                }
1477
1478                if (unlikely(buffer_heads_over_limit)) {
1479                        if (page_has_private(page) && trylock_page(page)) {
1480                                if (page_has_private(page))
1481                                        try_to_release_page(page, 0);
1482                                unlock_page(page);
1483                        }
1484                }
1485
1486                if (page_referenced(page, 0, sc->target_mem_cgroup,
1487                                    &vm_flags)) {
1488                        nr_rotated += hpage_nr_pages(page);
1489                        /*
1490                         * Identify referenced, file-backed active pages and
1491                         * give them one more trip around the active list. So
1492                         * that executable code get better chances to stay in
1493                         * memory under moderate memory pressure.  Anon pages
1494                         * are not likely to be evicted by use-once streaming
1495                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1496                         * so we ignore them here.
1497                         */
1498                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1499                                list_add(&page->lru, &l_active);
1500                                continue;
1501                        }
1502                }
1503
1504                ClearPageActive(page);  /* we are de-activating */
1505                list_add(&page->lru, &l_inactive);
1506        }
1507
1508        /*
1509         * Move pages back to the lru list.
1510         */
1511        spin_lock_irq(&zone->lru_lock);
1512        /*
1513         * Count referenced pages from currently used mappings as rotated,
1514         * even though only some of them are actually re-activated.  This
1515         * helps balance scan pressure between file and anonymous pages in
1516         * get_scan_ratio.
1517         */
1518        reclaim_stat->recent_rotated[file] += nr_rotated;
1519
1520        move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1521        move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1522        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1523        spin_unlock_irq(&zone->lru_lock);
1524
1525        free_hot_cold_page_list(&l_hold, 1);
1526}
1527
1528#ifdef CONFIG_SWAP
1529static int inactive_anon_is_low_global(struct zone *zone)
1530{
1531        unsigned long active, inactive;
1532
1533        active = zone_page_state(zone, NR_ACTIVE_ANON);
1534        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1535
1536        if (inactive * zone->inactive_ratio < active)
1537                return 1;
1538
1539        return 0;
1540}
1541
1542/**
1543 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1544 * @lruvec: LRU vector to check
1545 *
1546 * Returns true if the zone does not have enough inactive anon pages,
1547 * meaning some active anon pages need to be deactivated.
1548 */
1549static int inactive_anon_is_low(struct lruvec *lruvec)
1550{
1551        /*
1552         * If we don't have swap space, anonymous page deactivation
1553         * is pointless.
1554         */
1555        if (!total_swap_pages)
1556                return 0;
1557
1558        if (!mem_cgroup_disabled())
1559                return mem_cgroup_inactive_anon_is_low(lruvec);
1560
1561        return inactive_anon_is_low_global(lruvec_zone(lruvec));
1562}
1563#else
1564static inline int inactive_anon_is_low(struct lruvec *lruvec)
1565{
1566        return 0;
1567}
1568#endif
1569
1570static int inactive_file_is_low_global(struct zone *zone)
1571{
1572        unsigned long active, inactive;
1573
1574        active = zone_page_state(zone, NR_ACTIVE_FILE);
1575        inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1576
1577        return (active > inactive);
1578}
1579
1580/**
1581 * inactive_file_is_low - check if file pages need to be deactivated
1582 * @lruvec: LRU vector to check
1583 *
1584 * When the system is doing streaming IO, memory pressure here
1585 * ensures that active file pages get deactivated, until more
1586 * than half of the file pages are on the inactive list.
1587 *
1588 * Once we get to that situation, protect the system's working
1589 * set from being evicted by disabling active file page aging.
1590 *
1591 * This uses a different ratio than the anonymous pages, because
1592 * the page cache uses a use-once replacement algorithm.
1593 */
1594static int inactive_file_is_low(struct lruvec *lruvec)
1595{
1596        if (!mem_cgroup_disabled())
1597                return mem_cgroup_inactive_file_is_low(lruvec);
1598
1599        return inactive_file_is_low_global(lruvec_zone(lruvec));
1600}
1601
1602static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1603{
1604        if (is_file_lru(lru))
1605                return inactive_file_is_low(lruvec);
1606        else
1607                return inactive_anon_is_low(lruvec);
1608}
1609
1610static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1611                                 struct lruvec *lruvec, struct scan_control *sc)
1612{
1613        if (is_active_lru(lru)) {
1614                if (inactive_list_is_low(lruvec, lru))
1615                        shrink_active_list(nr_to_scan, lruvec, sc, lru);
1616                return 0;
1617        }
1618
1619        return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1620}
1621
1622static int vmscan_swappiness(struct scan_control *sc)
1623{
1624        if (global_reclaim(sc))
1625                return vm_swappiness;
1626        return mem_cgroup_swappiness(sc->target_mem_cgroup);
1627}
1628
1629/*
1630 * Determine how aggressively the anon and file LRU lists should be
1631 * scanned.  The relative value of each set of LRU lists is determined
1632 * by looking at the fraction of the pages scanned we did rotate back
1633 * onto the active list instead of evict.
1634 *
1635 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1636 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1637 */
1638static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1639                           unsigned long *nr)
1640{
1641        unsigned long anon, file, free;
1642        unsigned long anon_prio, file_prio;
1643        unsigned long ap, fp;
1644        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1645        u64 fraction[2], denominator;
1646        enum lru_list lru;
1647        int noswap = 0;
1648        bool force_scan = false;
1649        struct zone *zone = lruvec_zone(lruvec);
1650
1651        /*
1652         * If the zone or memcg is small, nr[l] can be 0.  This
1653         * results in no scanning on this priority and a potential
1654         * priority drop.  Global direct reclaim can go to the next
1655         * zone and tends to have no problems. Global kswapd is for
1656         * zone balancing and it needs to scan a minimum amount. When
1657         * reclaiming for a memcg, a priority drop can cause high
1658         * latencies, so it's better to scan a minimum amount there as
1659         * well.
1660         */
1661        if (current_is_kswapd() && zone->all_unreclaimable)
1662                force_scan = true;
1663        if (!global_reclaim(sc))
1664                force_scan = true;
1665
1666        /* If we have no swap space, do not bother scanning anon pages. */
1667        if (!sc->may_swap || (nr_swap_pages <= 0)) {
1668                noswap = 1;
1669                fraction[0] = 0;
1670                fraction[1] = 1;
1671                denominator = 1;
1672                goto out;
1673        }
1674
1675        anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1676                get_lru_size(lruvec, LRU_INACTIVE_ANON);
1677        file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1678                get_lru_size(lruvec, LRU_INACTIVE_FILE);
1679
1680        if (global_reclaim(sc)) {
1681                free  = zone_page_state(zone, NR_FREE_PAGES);
1682                /* If we have very few page cache pages,
1683                   force-scan anon pages. */
1684                if (unlikely(file + free <= high_wmark_pages(zone))) {
1685                        fraction[0] = 1;
1686                        fraction[1] = 0;
1687                        denominator = 1;
1688                        goto out;
1689                }
1690        }
1691
1692        /*
1693         * With swappiness at 100, anonymous and file have the same priority.
1694         * This scanning priority is essentially the inverse of IO cost.
1695         */
1696        anon_prio = vmscan_swappiness(sc);
1697        file_prio = 200 - anon_prio;
1698
1699        /*
1700         * OK, so we have swap space and a fair amount of page cache
1701         * pages.  We use the recently rotated / recently scanned
1702         * ratios to determine how valuable each cache is.
1703         *
1704         * Because workloads change over time (and to avoid overflow)
1705         * we keep these statistics as a floating average, which ends
1706         * up weighing recent references more than old ones.
1707         *
1708         * anon in [0], file in [1]
1709         */
1710        spin_lock_irq(&zone->lru_lock);
1711        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1712                reclaim_stat->recent_scanned[0] /= 2;
1713                reclaim_stat->recent_rotated[0] /= 2;
1714        }
1715
1716        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1717                reclaim_stat->recent_scanned[1] /= 2;
1718                reclaim_stat->recent_rotated[1] /= 2;
1719        }
1720
1721        /*
1722         * The amount of pressure on anon vs file pages is inversely
1723         * proportional to the fraction of recently scanned pages on
1724         * each list that were recently referenced and in active use.
1725         */
1726        ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1727        ap /= reclaim_stat->recent_rotated[0] + 1;
1728
1729        fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1730        fp /= reclaim_stat->recent_rotated[1] + 1;
1731        spin_unlock_irq(&zone->lru_lock);
1732
1733        fraction[0] = ap;
1734        fraction[1] = fp;
1735        denominator = ap + fp + 1;
1736out:
1737        for_each_evictable_lru(lru) {
1738                int file = is_file_lru(lru);
1739                unsigned long scan;
1740
1741                scan = get_lru_size(lruvec, lru);
1742                if (sc->priority || noswap || !vmscan_swappiness(sc)) {
1743                        scan >>= sc->priority;
1744                        if (!scan && force_scan)
1745                                scan = SWAP_CLUSTER_MAX;
1746                        scan = div64_u64(scan * fraction[file], denominator);
1747                }
1748                nr[lru] = scan;
1749        }
1750}
1751
1752/* Use reclaim/compaction for costly allocs or under memory pressure */
1753static bool in_reclaim_compaction(struct scan_control *sc)
1754{
1755        if (COMPACTION_BUILD && sc->order &&
1756                        (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1757                         sc->priority < DEF_PRIORITY - 2))
1758                return true;
1759
1760        return false;
1761}
1762
1763/*
1764 * Reclaim/compaction is used for high-order allocation requests. It reclaims
1765 * order-0 pages before compacting the zone. should_continue_reclaim() returns
1766 * true if more pages should be reclaimed such that when the page allocator
1767 * calls try_to_compact_zone() that it will have enough free pages to succeed.
1768 * It will give up earlier than that if there is difficulty reclaiming pages.
1769 */
1770static inline bool should_continue_reclaim(struct lruvec *lruvec,
1771                                        unsigned long nr_reclaimed,
1772                                        unsigned long nr_scanned,
1773                                        struct scan_control *sc)
1774{
1775        unsigned long pages_for_compaction;
1776        unsigned long inactive_lru_pages;
1777
1778        /* If not in reclaim/compaction mode, stop */
1779        if (!in_reclaim_compaction(sc))
1780                return false;
1781
1782        /* Consider stopping depending on scan and reclaim activity */
1783        if (sc->gfp_mask & __GFP_REPEAT) {
1784                /*
1785                 * For __GFP_REPEAT allocations, stop reclaiming if the
1786                 * full LRU list has been scanned and we are still failing
1787                 * to reclaim pages. This full LRU scan is potentially
1788                 * expensive but a __GFP_REPEAT caller really wants to succeed
1789                 */
1790                if (!nr_reclaimed && !nr_scanned)
1791                        return false;
1792        } else {
1793                /*
1794                 * For non-__GFP_REPEAT allocations which can presumably
1795                 * fail without consequence, stop if we failed to reclaim
1796                 * any pages from the last SWAP_CLUSTER_MAX number of
1797                 * pages that were scanned. This will return to the
1798                 * caller faster at the risk reclaim/compaction and
1799                 * the resulting allocation attempt fails
1800                 */
1801                if (!nr_reclaimed)
1802                        return false;
1803        }
1804
1805        /*
1806         * If we have not reclaimed enough pages for compaction and the
1807         * inactive lists are large enough, continue reclaiming
1808         */
1809        pages_for_compaction = (2UL << sc->order);
1810        inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1811        if (nr_swap_pages > 0)
1812                inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
1813        if (sc->nr_reclaimed < pages_for_compaction &&
1814                        inactive_lru_pages > pages_for_compaction)
1815                return true;
1816
1817        /* If compaction would go ahead or the allocation would succeed, stop */
1818        switch (compaction_suitable(lruvec_zone(lruvec), sc->order)) {
1819        case COMPACT_PARTIAL:
1820        case COMPACT_CONTINUE:
1821                return false;
1822        default:
1823                return true;
1824        }
1825}
1826
1827/*
1828 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1829 */
1830static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1831{
1832        unsigned long nr[NR_LRU_LISTS];
1833        unsigned long nr_to_scan;
1834        enum lru_list lru;
1835        unsigned long nr_reclaimed, nr_scanned;
1836        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1837        struct blk_plug plug;
1838
1839restart:
1840        nr_reclaimed = 0;
1841        nr_scanned = sc->nr_scanned;
1842        get_scan_count(lruvec, sc, nr);
1843
1844        blk_start_plug(&plug);
1845        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1846                                        nr[LRU_INACTIVE_FILE]) {
1847                for_each_evictable_lru(lru) {
1848                        if (nr[lru]) {
1849                                nr_to_scan = min_t(unsigned long,
1850                                                   nr[lru], SWAP_CLUSTER_MAX);
1851                                nr[lru] -= nr_to_scan;
1852
1853                                nr_reclaimed += shrink_list(lru, nr_to_scan,
1854                                                            lruvec, sc);
1855                        }
1856                }
1857                /*
1858                 * On large memory systems, scan >> priority can become
1859                 * really large. This is fine for the starting priority;
1860                 * we want to put equal scanning pressure on each zone.
1861                 * However, if the VM has a harder time of freeing pages,
1862                 * with multiple processes reclaiming pages, the total
1863                 * freeing target can get unreasonably large.
1864                 */
1865                if (nr_reclaimed >= nr_to_reclaim &&
1866                    sc->priority < DEF_PRIORITY)
1867                        break;
1868        }
1869        blk_finish_plug(&plug);
1870        sc->nr_reclaimed += nr_reclaimed;
1871
1872        /*
1873         * Even if we did not try to evict anon pages at all, we want to
1874         * rebalance the anon lru active/inactive ratio.
1875         */
1876        if (inactive_anon_is_low(lruvec))
1877                shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1878                                   sc, LRU_ACTIVE_ANON);
1879
1880        /* reclaim/compaction might need reclaim to continue */
1881        if (should_continue_reclaim(lruvec, nr_reclaimed,
1882                                    sc->nr_scanned - nr_scanned, sc))
1883                goto restart;
1884
1885        throttle_vm_writeout(sc->gfp_mask);
1886}
1887
1888static void shrink_zone(struct zone *zone, struct scan_control *sc)
1889{
1890        struct mem_cgroup *root = sc->target_mem_cgroup;
1891        struct mem_cgroup_reclaim_cookie reclaim = {
1892                .zone = zone,
1893                .priority = sc->priority,
1894        };
1895        struct mem_cgroup *memcg;
1896
1897        memcg = mem_cgroup_iter(root, NULL, &reclaim);
1898        do {
1899                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1900
1901                shrink_lruvec(lruvec, sc);
1902
1903                /*
1904                 * Limit reclaim has historically picked one memcg and
1905                 * scanned it with decreasing priority levels until
1906                 * nr_to_reclaim had been reclaimed.  This priority
1907                 * cycle is thus over after a single memcg.
1908                 *
1909                 * Direct reclaim and kswapd, on the other hand, have
1910                 * to scan all memory cgroups to fulfill the overall
1911                 * scan target for the zone.
1912                 */
1913                if (!global_reclaim(sc)) {
1914                        mem_cgroup_iter_break(root, memcg);
1915                        break;
1916                }
1917                memcg = mem_cgroup_iter(root, memcg, &reclaim);
1918        } while (memcg);
1919}
1920
1921/* Returns true if compaction should go ahead for a high-order request */
1922static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
1923{
1924        unsigned long balance_gap, watermark;
1925        bool watermark_ok;
1926
1927        /* Do not consider compaction for orders reclaim is meant to satisfy */
1928        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
1929                return false;
1930
1931        /*
1932         * Compaction takes time to run and there are potentially other
1933         * callers using the pages just freed. Continue reclaiming until
1934         * there is a buffer of free pages available to give compaction
1935         * a reasonable chance of completing and allocating the page
1936         */
1937        balance_gap = min(low_wmark_pages(zone),
1938                (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
1939                        KSWAPD_ZONE_BALANCE_GAP_RATIO);
1940        watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
1941        watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
1942
1943        /*
1944         * If compaction is deferred, reclaim up to a point where
1945         * compaction will have a chance of success when re-enabled
1946         */
1947        if (compaction_deferred(zone, sc->order))
1948                return watermark_ok;
1949
1950        /* If compaction is not ready to start, keep reclaiming */
1951        if (!compaction_suitable(zone, sc->order))
1952                return false;
1953
1954        return watermark_ok;
1955}
1956
1957/*
1958 * This is the direct reclaim path, for page-allocating processes.  We only
1959 * try to reclaim pages from zones which will satisfy the caller's allocation
1960 * request.
1961 *
1962 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1963 * Because:
1964 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1965 *    allocation or
1966 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1967 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1968 *    zone defense algorithm.
1969 *
1970 * If a zone is deemed to be full of pinned pages then just give it a light
1971 * scan then give up on it.
1972 *
1973 * This function returns true if a zone is being reclaimed for a costly
1974 * high-order allocation and compaction is ready to begin. This indicates to
1975 * the caller that it should consider retrying the allocation instead of
1976 * further reclaim.
1977 */
1978static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
1979{
1980        struct zoneref *z;
1981        struct zone *zone;
1982        unsigned long nr_soft_reclaimed;
1983        unsigned long nr_soft_scanned;
1984        bool aborted_reclaim = false;
1985
1986        /*
1987         * If the number of buffer_heads in the machine exceeds the maximum
1988         * allowed level, force direct reclaim to scan the highmem zone as
1989         * highmem pages could be pinning lowmem pages storing buffer_heads
1990         */
1991        if (buffer_heads_over_limit)
1992                sc->gfp_mask |= __GFP_HIGHMEM;
1993
1994        for_each_zone_zonelist_nodemask(zone, z, zonelist,
1995                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
1996                if (!populated_zone(zone))
1997                        continue;
1998                /*
1999                 * Take care memory controller reclaiming has small influence
2000                 * to global LRU.
2001                 */
2002                if (global_reclaim(sc)) {
2003                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2004                                continue;
2005                        if (zone->all_unreclaimable &&
2006                                        sc->priority != DEF_PRIORITY)
2007                                continue;       /* Let kswapd poll it */
2008                        if (COMPACTION_BUILD) {
2009                                /*
2010                                 * If we already have plenty of memory free for
2011                                 * compaction in this zone, don't free any more.
2012                                 * Even though compaction is invoked for any
2013                                 * non-zero order, only frequent costly order
2014                                 * reclamation is disruptive enough to become a
2015                                 * noticeable problem, like transparent huge
2016                                 * page allocations.
2017                                 */
2018                                if (compaction_ready(zone, sc)) {
2019                                        aborted_reclaim = true;
2020                                        continue;
2021                                }
2022                        }
2023                        /*
2024                         * This steals pages from memory cgroups over softlimit
2025                         * and returns the number of reclaimed pages and
2026                         * scanned pages. This works for global memory pressure
2027                         * and balancing, not for a memcg's limit.
2028                         */
2029                        nr_soft_scanned = 0;
2030                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2031                                                sc->order, sc->gfp_mask,
2032                                                &nr_soft_scanned);
2033                        sc->nr_reclaimed += nr_soft_reclaimed;
2034                        sc->nr_scanned += nr_soft_scanned;
2035                        /* need some check for avoid more shrink_zone() */
2036                }
2037
2038                shrink_zone(zone, sc);
2039        }
2040
2041        return aborted_reclaim;
2042}
2043
2044static bool zone_reclaimable(struct zone *zone)
2045{
2046        return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2047}
2048
2049/* All zones in zonelist are unreclaimable? */
2050static bool all_unreclaimable(struct zonelist *zonelist,
2051                struct scan_control *sc)
2052{
2053        struct zoneref *z;
2054        struct zone *zone;
2055
2056        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2057                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2058                if (!populated_zone(zone))
2059                        continue;
2060                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2061                        continue;
2062                if (!zone->all_unreclaimable)
2063                        return false;
2064        }
2065
2066        return true;
2067}
2068
2069/*
2070 * This is the main entry point to direct page reclaim.
2071 *
2072 * If a full scan of the inactive list fails to free enough memory then we
2073 * are "out of memory" and something needs to be killed.
2074 *
2075 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2076 * high - the zone may be full of dirty or under-writeback pages, which this
2077 * caller can't do much about.  We kick the writeback threads and take explicit
2078 * naps in the hope that some of these pages can be written.  But if the
2079 * allocating task holds filesystem locks which prevent writeout this might not
2080 * work, and the allocation attempt will fail.
2081 *
2082 * returns:     0, if no pages reclaimed
2083 *              else, the number of pages reclaimed
2084 */
2085static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2086                                        struct scan_control *sc,
2087                                        struct shrink_control *shrink)
2088{
2089        unsigned long total_scanned = 0;
2090        struct reclaim_state *reclaim_state = current->reclaim_state;
2091        struct zoneref *z;
2092        struct zone *zone;
2093        unsigned long writeback_threshold;
2094        bool aborted_reclaim;
2095
2096        delayacct_freepages_start();
2097
2098        if (global_reclaim(sc))
2099                count_vm_event(ALLOCSTALL);
2100
2101        do {
2102                sc->nr_scanned = 0;
2103                aborted_reclaim = shrink_zones(zonelist, sc);
2104
2105                /*
2106                 * Don't shrink slabs when reclaiming memory from
2107                 * over limit cgroups
2108                 */
2109                if (global_reclaim(sc)) {
2110                        unsigned long lru_pages = 0;
2111                        for_each_zone_zonelist(zone, z, zonelist,
2112                                        gfp_zone(sc->gfp_mask)) {
2113                                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2114                                        continue;
2115
2116                                lru_pages += zone_reclaimable_pages(zone);
2117                        }
2118
2119                        shrink_slab(shrink, sc->nr_scanned, lru_pages);
2120                        if (reclaim_state) {
2121                                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2122                                reclaim_state->reclaimed_slab = 0;
2123                        }
2124                }
2125                total_scanned += sc->nr_scanned;
2126                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2127                        goto out;
2128
2129                /*
2130                 * Try to write back as many pages as we just scanned.  This
2131                 * tends to cause slow streaming writers to write data to the
2132                 * disk smoothly, at the dirtying rate, which is nice.   But
2133                 * that's undesirable in laptop mode, where we *want* lumpy
2134                 * writeout.  So in laptop mode, write out the whole world.
2135                 */
2136                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2137                if (total_scanned > writeback_threshold) {
2138                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2139                                                WB_REASON_TRY_TO_FREE_PAGES);
2140                        sc->may_writepage = 1;
2141                }
2142
2143                /* Take a nap, wait for some writeback to complete */
2144                if (!sc->hibernation_mode && sc->nr_scanned &&
2145                    sc->priority < DEF_PRIORITY - 2) {
2146                        struct zone *preferred_zone;
2147
2148                        first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2149                                                &cpuset_current_mems_allowed,
2150                                                &preferred_zone);
2151                        wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2152                }
2153        } while (--sc->priority >= 0);
2154
2155out:
2156        delayacct_freepages_end();
2157
2158        if (sc->nr_reclaimed)
2159                return sc->nr_reclaimed;
2160
2161        /*
2162         * As hibernation is going on, kswapd is freezed so that it can't mark
2163         * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2164         * check.
2165         */
2166        if (oom_killer_disabled)
2167                return 0;
2168
2169        /* Aborted reclaim to try compaction? don't OOM, then */
2170        if (aborted_reclaim)
2171                return 1;
2172
2173        /* top priority shrink_zones still had more to do? don't OOM, then */
2174        if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2175                return 1;
2176
2177        return 0;
2178}
2179
2180static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2181{
2182        struct zone *zone;
2183        unsigned long pfmemalloc_reserve = 0;
2184        unsigned long free_pages = 0;
2185        int i;
2186        bool wmark_ok;
2187
2188        for (i = 0; i <= ZONE_NORMAL; i++) {
2189                zone = &pgdat->node_zones[i];
2190                pfmemalloc_reserve += min_wmark_pages(zone);
2191                free_pages += zone_page_state(zone, NR_FREE_PAGES);
2192        }
2193
2194        wmark_ok = free_pages > pfmemalloc_reserve / 2;
2195
2196        /* kswapd must be awake if processes are being throttled */
2197        if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2198                pgdat->classzone_idx = min(pgdat->classzone_idx,
2199                                                (enum zone_type)ZONE_NORMAL);
2200                wake_up_interruptible(&pgdat->kswapd_wait);
2201        }
2202
2203        return wmark_ok;
2204}
2205
2206/*
2207 * Throttle direct reclaimers if backing storage is backed by the network
2208 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2209 * depleted. kswapd will continue to make progress and wake the processes
2210 * when the low watermark is reached.
2211 *
2212 * Returns true if a fatal signal was delivered during throttling. If this
2213 * happens, the page allocator should not consider triggering the OOM killer.
2214 */
2215static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2216                                        nodemask_t *nodemask)
2217{
2218        struct zone *zone;
2219        int high_zoneidx = gfp_zone(gfp_mask);
2220        pg_data_t *pgdat;
2221
2222        /*
2223         * Kernel threads should not be throttled as they may be indirectly
2224         * responsible for cleaning pages necessary for reclaim to make forward
2225         * progress. kjournald for example may enter direct reclaim while
2226         * committing a transaction where throttling it could forcing other
2227         * processes to block on log_wait_commit().
2228         */
2229        if (current->flags & PF_KTHREAD)
2230                goto out;
2231
2232        /*
2233         * If a fatal signal is pending, this process should not throttle.
2234         * It should return quickly so it can exit and free its memory
2235         */
2236        if (fatal_signal_pending(current))
2237                goto out;
2238
2239        /* Check if the pfmemalloc reserves are ok */
2240        first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2241        pgdat = zone->zone_pgdat;
2242        if (pfmemalloc_watermark_ok(pgdat))
2243                goto out;
2244
2245        /* Account for the throttling */
2246        count_vm_event(PGSCAN_DIRECT_THROTTLE);
2247
2248        /*
2249         * If the caller cannot enter the filesystem, it's possible that it
2250         * is due to the caller holding an FS lock or performing a journal
2251         * transaction in the case of a filesystem like ext[3|4]. In this case,
2252         * it is not safe to block on pfmemalloc_wait as kswapd could be
2253         * blocked waiting on the same lock. Instead, throttle for up to a
2254         * second before continuing.
2255         */
2256        if (!(gfp_mask & __GFP_FS)) {
2257                wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2258                        pfmemalloc_watermark_ok(pgdat), HZ);
2259
2260                goto check_pending;
2261        }
2262
2263        /* Throttle until kswapd wakes the process */
2264        wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2265                pfmemalloc_watermark_ok(pgdat));
2266
2267check_pending:
2268        if (fatal_signal_pending(current))
2269                return true;
2270
2271out:
2272        return false;
2273}
2274
2275unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2276                                gfp_t gfp_mask, nodemask_t *nodemask)
2277{
2278        unsigned long nr_reclaimed;
2279        struct scan_control sc = {
2280                .gfp_mask = gfp_mask,
2281                .may_writepage = !laptop_mode,
2282                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2283                .may_unmap = 1,
2284                .may_swap = 1,
2285                .order = order,
2286                .priority = DEF_PRIORITY,
2287                .target_mem_cgroup = NULL,
2288                .nodemask = nodemask,
2289        };
2290        struct shrink_control shrink = {
2291                .gfp_mask = sc.gfp_mask,
2292        };
2293
2294        /*
2295         * Do not enter reclaim if fatal signal was delivered while throttled.
2296         * 1 is returned so that the page allocator does not OOM kill at this
2297         * point.
2298         */
2299        if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2300                return 1;
2301
2302        trace_mm_vmscan_direct_reclaim_begin(order,
2303                                sc.may_writepage,
2304                                gfp_mask);
2305
2306        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2307
2308        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2309
2310        return nr_reclaimed;
2311}
2312
2313#ifdef CONFIG_MEMCG
2314
2315unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2316                                                gfp_t gfp_mask, bool noswap,
2317                                                struct zone *zone,
2318                                                unsigned long *nr_scanned)
2319{
2320        struct scan_control sc = {
2321                .nr_scanned = 0,
2322                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2323                .may_writepage = !laptop_mode,
2324                .may_unmap = 1,
2325                .may_swap = !noswap,
2326                .order = 0,
2327                .priority = 0,
2328                .target_mem_cgroup = memcg,
2329        };
2330        struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2331
2332        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2333                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2334
2335        trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2336                                                      sc.may_writepage,
2337                                                      sc.gfp_mask);
2338
2339        /*
2340         * NOTE: Although we can get the priority field, using it
2341         * here is not a good idea, since it limits the pages we can scan.
2342         * if we don't reclaim here, the shrink_zone from balance_pgdat
2343         * will pick up pages from other mem cgroup's as well. We hack
2344         * the priority and make it zero.
2345         */
2346        shrink_lruvec(lruvec, &sc);
2347
2348        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2349
2350        *nr_scanned = sc.nr_scanned;
2351        return sc.nr_reclaimed;
2352}
2353
2354unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2355                                           gfp_t gfp_mask,
2356                                           bool noswap)
2357{
2358        struct zonelist *zonelist;
2359        unsigned long nr_reclaimed;
2360        int nid;
2361        struct scan_control sc = {
2362                .may_writepage = !laptop_mode,
2363                .may_unmap = 1,
2364                .may_swap = !noswap,
2365                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2366                .order = 0,
2367                .priority = DEF_PRIORITY,
2368                .target_mem_cgroup = memcg,
2369                .nodemask = NULL, /* we don't care the placement */
2370                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2371                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2372        };
2373        struct shrink_control shrink = {
2374                .gfp_mask = sc.gfp_mask,
2375        };
2376
2377        /*
2378         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2379         * take care of from where we get pages. So the node where we start the
2380         * scan does not need to be the current node.
2381         */
2382        nid = mem_cgroup_select_victim_node(memcg);
2383
2384        zonelist = NODE_DATA(nid)->node_zonelists;
2385
2386        trace_mm_vmscan_memcg_reclaim_begin(0,
2387                                            sc.may_writepage,
2388                                            sc.gfp_mask);
2389
2390        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2391
2392        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2393
2394        return nr_reclaimed;
2395}
2396#endif
2397
2398static void age_active_anon(struct zone *zone, struct scan_control *sc)
2399{
2400        struct mem_cgroup *memcg;
2401
2402        if (!total_swap_pages)
2403                return;
2404
2405        memcg = mem_cgroup_iter(NULL, NULL, NULL);
2406        do {
2407                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2408
2409                if (inactive_anon_is_low(lruvec))
2410                        shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2411                                           sc, LRU_ACTIVE_ANON);
2412
2413                memcg = mem_cgroup_iter(NULL, memcg, NULL);
2414        } while (memcg);
2415}
2416
2417static bool zone_balanced(struct zone *zone, int order,
2418                          unsigned long balance_gap, int classzone_idx)
2419{
2420        if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2421                                    balance_gap, classzone_idx, 0))
2422                return false;
2423
2424        if (COMPACTION_BUILD && order && !compaction_suitable(zone, order))
2425                return false;
2426
2427        return true;
2428}
2429
2430/*
2431 * pgdat_balanced is used when checking if a node is balanced for high-order
2432 * allocations. Only zones that meet watermarks and are in a zone allowed
2433 * by the callers classzone_idx are added to balanced_pages. The total of
2434 * balanced pages must be at least 25% of the zones allowed by classzone_idx
2435 * for the node to be considered balanced. Forcing all zones to be balanced
2436 * for high orders can cause excessive reclaim when there are imbalanced zones.
2437 * The choice of 25% is due to
2438 *   o a 16M DMA zone that is balanced will not balance a zone on any
2439 *     reasonable sized machine
2440 *   o On all other machines, the top zone must be at least a reasonable
2441 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2442 *     would need to be at least 256M for it to be balance a whole node.
2443 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2444 *     to balance a node on its own. These seemed like reasonable ratios.
2445 */
2446static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2447                                                int classzone_idx)
2448{
2449        unsigned long present_pages = 0;
2450        int i;
2451
2452        for (i = 0; i <= classzone_idx; i++)
2453                present_pages += pgdat->node_zones[i].present_pages;
2454
2455        /* A special case here: if zone has no page, we think it's balanced */
2456        return balanced_pages >= (present_pages >> 2);
2457}
2458
2459/*
2460 * Prepare kswapd for sleeping. This verifies that there are no processes
2461 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2462 *
2463 * Returns true if kswapd is ready to sleep
2464 */
2465static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2466                                        int classzone_idx)
2467{
2468        int i;
2469        unsigned long balanced = 0;
2470        bool all_zones_ok = true;
2471
2472        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2473        if (remaining)
2474                return false;
2475
2476        /*
2477         * There is a potential race between when kswapd checks its watermarks
2478         * and a process gets throttled. There is also a potential race if
2479         * processes get throttled, kswapd wakes, a large process exits therby
2480         * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2481         * is going to sleep, no process should be sleeping on pfmemalloc_wait
2482         * so wake them now if necessary. If necessary, processes will wake
2483         * kswapd and get throttled again
2484         */
2485        if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2486                wake_up(&pgdat->pfmemalloc_wait);
2487                return false;
2488        }
2489
2490        /* Check the watermark levels */
2491        for (i = 0; i <= classzone_idx; i++) {
2492                struct zone *zone = pgdat->node_zones + i;
2493
2494                if (!populated_zone(zone))
2495                        continue;
2496
2497                /*
2498                 * balance_pgdat() skips over all_unreclaimable after
2499                 * DEF_PRIORITY. Effectively, it considers them balanced so
2500                 * they must be considered balanced here as well if kswapd
2501                 * is to sleep
2502                 */
2503                if (zone->all_unreclaimable) {
2504                        balanced += zone->present_pages;
2505                        continue;
2506                }
2507
2508                if (!zone_balanced(zone, order, 0, i))
2509                        all_zones_ok = false;
2510                else
2511                        balanced += zone->present_pages;
2512        }
2513
2514        /*
2515         * For high-order requests, the balanced zones must contain at least
2516         * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2517         * must be balanced
2518         */
2519        if (order)
2520                return pgdat_balanced(pgdat, balanced, classzone_idx);
2521        else
2522                return all_zones_ok;
2523}
2524
2525/*
2526 * For kswapd, balance_pgdat() will work across all this node's zones until
2527 * they are all at high_wmark_pages(zone).
2528 *
2529 * Returns the final order kswapd was reclaiming at
2530 *
2531 * There is special handling here for zones which are full of pinned pages.
2532 * This can happen if the pages are all mlocked, or if they are all used by
2533 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2534 * What we do is to detect the case where all pages in the zone have been
2535 * scanned twice and there has been zero successful reclaim.  Mark the zone as
2536 * dead and from now on, only perform a short scan.  Basically we're polling
2537 * the zone for when the problem goes away.
2538 *
2539 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2540 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2541 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2542 * lower zones regardless of the number of free pages in the lower zones. This
2543 * interoperates with the page allocator fallback scheme to ensure that aging
2544 * of pages is balanced across the zones.
2545 */
2546static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2547                                                        int *classzone_idx)
2548{
2549        int all_zones_ok;
2550        unsigned long balanced;
2551        int i;
2552        int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2553        unsigned long total_scanned;
2554        struct reclaim_state *reclaim_state = current->reclaim_state;
2555        unsigned long nr_soft_reclaimed;
2556        unsigned long nr_soft_scanned;
2557        struct scan_control sc = {
2558                .gfp_mask = GFP_KERNEL,
2559                .may_unmap = 1,
2560                .may_swap = 1,
2561                /*
2562                 * kswapd doesn't want to be bailed out while reclaim. because
2563                 * we want to put equal scanning pressure on each zone.
2564                 */
2565                .nr_to_reclaim = ULONG_MAX,
2566                .order = order,
2567                .target_mem_cgroup = NULL,
2568        };
2569        struct shrink_control shrink = {
2570                .gfp_mask = sc.gfp_mask,
2571        };
2572loop_again:
2573        total_scanned = 0;
2574        sc.priority = DEF_PRIORITY;
2575        sc.nr_reclaimed = 0;
2576        sc.may_writepage = !laptop_mode;
2577        count_vm_event(PAGEOUTRUN);
2578
2579        do {
2580                unsigned long lru_pages = 0;
2581                int has_under_min_watermark_zone = 0;
2582
2583                all_zones_ok = 1;
2584                balanced = 0;
2585
2586                /*
2587                 * Scan in the highmem->dma direction for the highest
2588                 * zone which needs scanning
2589                 */
2590                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2591                        struct zone *zone = pgdat->node_zones + i;
2592
2593                        if (!populated_zone(zone))
2594                                continue;
2595
2596                        if (zone->all_unreclaimable &&
2597                            sc.priority != DEF_PRIORITY)
2598                                continue;
2599
2600                        /*
2601                         * Do some background aging of the anon list, to give
2602                         * pages a chance to be referenced before reclaiming.
2603                         */
2604                        age_active_anon(zone, &sc);
2605
2606                        /*
2607                         * If the number of buffer_heads in the machine
2608                         * exceeds the maximum allowed level and this node
2609                         * has a highmem zone, force kswapd to reclaim from
2610                         * it to relieve lowmem pressure.
2611                         */
2612                        if (buffer_heads_over_limit && is_highmem_idx(i)) {
2613                                end_zone = i;
2614                                break;
2615                        }
2616
2617                        if (!zone_balanced(zone, order, 0, 0)) {
2618                                end_zone = i;
2619                                break;
2620                        } else {
2621                                /* If balanced, clear the congested flag */
2622                                zone_clear_flag(zone, ZONE_CONGESTED);
2623                        }
2624                }
2625                if (i < 0)
2626                        goto out;
2627
2628                for (i = 0; i <= end_zone; i++) {
2629                        struct zone *zone = pgdat->node_zones + i;
2630
2631                        lru_pages += zone_reclaimable_pages(zone);
2632                }
2633
2634                /*
2635                 * Now scan the zone in the dma->highmem direction, stopping
2636                 * at the last zone which needs scanning.
2637                 *
2638                 * We do this because the page allocator works in the opposite
2639                 * direction.  This prevents the page allocator from allocating
2640                 * pages behind kswapd's direction of progress, which would
2641                 * cause too much scanning of the lower zones.
2642                 */
2643                for (i = 0; i <= end_zone; i++) {
2644                        struct zone *zone = pgdat->node_zones + i;
2645                        int nr_slab, testorder;
2646                        unsigned long balance_gap;
2647
2648                        if (!populated_zone(zone))
2649                                continue;
2650
2651                        if (zone->all_unreclaimable &&
2652                            sc.priority != DEF_PRIORITY)
2653                                continue;
2654
2655                        sc.nr_scanned = 0;
2656
2657                        nr_soft_scanned = 0;
2658                        /*
2659                         * Call soft limit reclaim before calling shrink_zone.
2660                         */
2661                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2662                                                        order, sc.gfp_mask,
2663                                                        &nr_soft_scanned);
2664                        sc.nr_reclaimed += nr_soft_reclaimed;
2665                        total_scanned += nr_soft_scanned;
2666
2667                        /*
2668                         * We put equal pressure on every zone, unless
2669                         * one zone has way too many pages free
2670                         * already. The "too many pages" is defined
2671                         * as the high wmark plus a "gap" where the
2672                         * gap is either the low watermark or 1%
2673                         * of the zone, whichever is smaller.
2674                         */
2675                        balance_gap = min(low_wmark_pages(zone),
2676                                (zone->present_pages +
2677                                        KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2678                                KSWAPD_ZONE_BALANCE_GAP_RATIO);
2679                        /*
2680                         * Kswapd reclaims only single pages with compaction
2681                         * enabled. Trying too hard to reclaim until contiguous
2682                         * free pages have become available can hurt performance
2683                         * by evicting too much useful data from memory.
2684                         * Do not reclaim more than needed for compaction.
2685                         */
2686                        testorder = order;
2687                        if (COMPACTION_BUILD && order &&
2688                                        compaction_suitable(zone, order) !=
2689                                                COMPACT_SKIPPED)
2690                                testorder = 0;
2691
2692                        if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2693                            !zone_balanced(zone, testorder,
2694                                           balance_gap, end_zone)) {
2695                                shrink_zone(zone, &sc);
2696
2697                                reclaim_state->reclaimed_slab = 0;
2698                                nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2699                                sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2700                                total_scanned += sc.nr_scanned;
2701
2702                                if (nr_slab == 0 && !zone_reclaimable(zone))
2703                                        zone->all_unreclaimable = 1;
2704                        }
2705
2706                        /*
2707                         * If we've done a decent amount of scanning and
2708                         * the reclaim ratio is low, start doing writepage
2709                         * even in laptop mode
2710                         */
2711                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2712                            total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2713                                sc.may_writepage = 1;
2714
2715                        if (zone->all_unreclaimable) {
2716                                if (end_zone && end_zone == i)
2717                                        end_zone--;
2718                                continue;
2719                        }
2720
2721                        if (!zone_balanced(zone, testorder, 0, end_zone)) {
2722                                all_zones_ok = 0;
2723                                /*
2724                                 * We are still under min water mark.  This
2725                                 * means that we have a GFP_ATOMIC allocation
2726                                 * failure risk. Hurry up!
2727                                 */
2728                                if (!zone_watermark_ok_safe(zone, order,
2729                                            min_wmark_pages(zone), end_zone, 0))
2730                                        has_under_min_watermark_zone = 1;
2731                        } else {
2732                                /*
2733                                 * If a zone reaches its high watermark,
2734                                 * consider it to be no longer congested. It's
2735                                 * possible there are dirty pages backed by
2736                                 * congested BDIs but as pressure is relieved,
2737                                 * speculatively avoid congestion waits
2738                                 */
2739                                zone_clear_flag(zone, ZONE_CONGESTED);
2740                                if (i <= *classzone_idx)
2741                                        balanced += zone->present_pages;
2742                        }
2743
2744                }
2745
2746                /*
2747                 * If the low watermark is met there is no need for processes
2748                 * to be throttled on pfmemalloc_wait as they should not be
2749                 * able to safely make forward progress. Wake them
2750                 */
2751                if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
2752                                pfmemalloc_watermark_ok(pgdat))
2753                        wake_up(&pgdat->pfmemalloc_wait);
2754
2755                if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2756                        break;          /* kswapd: all done */
2757                /*
2758                 * OK, kswapd is getting into trouble.  Take a nap, then take
2759                 * another pass across the zones.
2760                 */
2761                if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
2762                        if (has_under_min_watermark_zone)
2763                                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2764                        else
2765                                congestion_wait(BLK_RW_ASYNC, HZ/10);
2766                }
2767
2768                /*
2769                 * We do this so kswapd doesn't build up large priorities for
2770                 * example when it is freeing in parallel with allocators. It
2771                 * matches the direct reclaim path behaviour in terms of impact
2772                 * on zone->*_priority.
2773                 */
2774                if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2775                        break;
2776        } while (--sc.priority >= 0);
2777out:
2778
2779        /*
2780         * order-0: All zones must meet high watermark for a balanced node
2781         * high-order: Balanced zones must make up at least 25% of the node
2782         *             for the node to be balanced
2783         */
2784        if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2785                cond_resched();
2786
2787                try_to_freeze();
2788
2789                /*
2790                 * Fragmentation may mean that the system cannot be
2791                 * rebalanced for high-order allocations in all zones.
2792                 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2793                 * it means the zones have been fully scanned and are still
2794                 * not balanced. For high-order allocations, there is
2795                 * little point trying all over again as kswapd may
2796                 * infinite loop.
2797                 *
2798                 * Instead, recheck all watermarks at order-0 as they
2799                 * are the most important. If watermarks are ok, kswapd will go
2800                 * back to sleep. High-order users can still perform direct
2801                 * reclaim if they wish.
2802                 */
2803                if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2804                        order = sc.order = 0;
2805
2806                goto loop_again;
2807        }
2808
2809        /*
2810         * If kswapd was reclaiming at a higher order, it has the option of
2811         * sleeping without all zones being balanced. Before it does, it must
2812         * ensure that the watermarks for order-0 on *all* zones are met and
2813         * that the congestion flags are cleared. The congestion flag must
2814         * be cleared as kswapd is the only mechanism that clears the flag
2815         * and it is potentially going to sleep here.
2816         */
2817        if (order) {
2818                int zones_need_compaction = 1;
2819
2820                for (i = 0; i <= end_zone; i++) {
2821                        struct zone *zone = pgdat->node_zones + i;
2822
2823                        if (!populated_zone(zone))
2824                                continue;
2825
2826                        /* Check if the memory needs to be defragmented. */
2827                        if (zone_watermark_ok(zone, order,
2828                                    low_wmark_pages(zone), *classzone_idx, 0))
2829                                zones_need_compaction = 0;
2830                }
2831
2832                if (zones_need_compaction)
2833                        compact_pgdat(pgdat, order);
2834        }
2835
2836        /*
2837         * Return the order we were reclaiming at so prepare_kswapd_sleep()
2838         * makes a decision on the order we were last reclaiming at. However,
2839         * if another caller entered the allocator slow path while kswapd
2840         * was awake, order will remain at the higher level
2841         */
2842        *classzone_idx = end_zone;
2843        return order;
2844}
2845
2846static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2847{
2848        long remaining = 0;
2849        DEFINE_WAIT(wait);
2850
2851        if (freezing(current) || kthread_should_stop())
2852                return;
2853
2854        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2855
2856        /* Try to sleep for a short interval */
2857        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2858                remaining = schedule_timeout(HZ/10);
2859                finish_wait(&pgdat->kswapd_wait, &wait);
2860                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2861        }
2862
2863        /*
2864         * After a short sleep, check if it was a premature sleep. If not, then
2865         * go fully to sleep until explicitly woken up.
2866         */
2867        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2868                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2869
2870                /*
2871                 * vmstat counters are not perfectly accurate and the estimated
2872                 * value for counters such as NR_FREE_PAGES can deviate from the
2873                 * true value by nr_online_cpus * threshold. To avoid the zone
2874                 * watermarks being breached while under pressure, we reduce the
2875                 * per-cpu vmstat threshold while kswapd is awake and restore
2876                 * them before going back to sleep.
2877                 */
2878                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2879
2880                /*
2881                 * Compaction records what page blocks it recently failed to
2882                 * isolate pages from and skips them in the future scanning.
2883                 * When kswapd is going to sleep, it is reasonable to assume
2884                 * that pages and compaction may succeed so reset the cache.
2885                 */
2886                reset_isolation_suitable(pgdat);
2887
2888                if (!kthread_should_stop())
2889                        schedule();
2890
2891                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2892        } else {
2893                if (remaining)
2894                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2895                else
2896                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2897        }
2898        finish_wait(&pgdat->kswapd_wait, &wait);
2899}
2900
2901/*
2902 * The background pageout daemon, started as a kernel thread
2903 * from the init process.
2904 *
2905 * This basically trickles out pages so that we have _some_
2906 * free memory available even if there is no other activity
2907 * that frees anything up. This is needed for things like routing
2908 * etc, where we otherwise might have all activity going on in
2909 * asynchronous contexts that cannot page things out.
2910 *
2911 * If there are applications that are active memory-allocators
2912 * (most normal use), this basically shouldn't matter.
2913 */
2914static int kswapd(void *p)
2915{
2916        unsigned long order, new_order;
2917        unsigned balanced_order;
2918        int classzone_idx, new_classzone_idx;
2919        int balanced_classzone_idx;
2920        pg_data_t *pgdat = (pg_data_t*)p;
2921        struct task_struct *tsk = current;
2922
2923        struct reclaim_state reclaim_state = {
2924                .reclaimed_slab = 0,
2925        };
2926        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2927
2928        lockdep_set_current_reclaim_state(GFP_KERNEL);
2929
2930        if (!cpumask_empty(cpumask))
2931                set_cpus_allowed_ptr(tsk, cpumask);
2932        current->reclaim_state = &reclaim_state;
2933
2934        /*
2935         * Tell the memory management that we're a "memory allocator",
2936         * and that if we need more memory we should get access to it
2937         * regardless (see "__alloc_pages()"). "kswapd" should
2938         * never get caught in the normal page freeing logic.
2939         *
2940         * (Kswapd normally doesn't need memory anyway, but sometimes
2941         * you need a small amount of memory in order to be able to
2942         * page out something else, and this flag essentially protects
2943         * us from recursively trying to free more memory as we're
2944         * trying to free the first piece of memory in the first place).
2945         */
2946        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2947        set_freezable();
2948
2949        order = new_order = 0;
2950        balanced_order = 0;
2951        classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2952        balanced_classzone_idx = classzone_idx;
2953        for ( ; ; ) {
2954                int ret;
2955
2956                /*
2957                 * If the last balance_pgdat was unsuccessful it's unlikely a
2958                 * new request of a similar or harder type will succeed soon
2959                 * so consider going to sleep on the basis we reclaimed at
2960                 */
2961                if (balanced_classzone_idx >= new_classzone_idx &&
2962                                        balanced_order == new_order) {
2963                        new_order = pgdat->kswapd_max_order;
2964                        new_classzone_idx = pgdat->classzone_idx;
2965                        pgdat->kswapd_max_order =  0;
2966                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2967                }
2968
2969                if (order < new_order || classzone_idx > new_classzone_idx) {
2970                        /*
2971                         * Don't sleep if someone wants a larger 'order'
2972                         * allocation or has tigher zone constraints
2973                         */
2974                        order = new_order;
2975                        classzone_idx = new_classzone_idx;
2976                } else {
2977                        kswapd_try_to_sleep(pgdat, balanced_order,
2978                                                balanced_classzone_idx);
2979                        order = pgdat->kswapd_max_order;
2980                        classzone_idx = pgdat->classzone_idx;
2981                        new_order = order;
2982                        new_classzone_idx = classzone_idx;
2983                        pgdat->kswapd_max_order = 0;
2984                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2985                }
2986
2987                ret = try_to_freeze();
2988                if (kthread_should_stop())
2989                        break;
2990
2991                /*
2992                 * We can speed up thawing tasks if we don't call balance_pgdat
2993                 * after returning from the refrigerator
2994                 */
2995                if (!ret) {
2996                        trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2997                        balanced_classzone_idx = classzone_idx;
2998                        balanced_order = balance_pgdat(pgdat, order,
2999                                                &balanced_classzone_idx);
3000                }
3001        }
3002
3003        current->reclaim_state = NULL;
3004        return 0;
3005}
3006
3007/*
3008 * A zone is low on free memory, so wake its kswapd task to service it.
3009 */
3010void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3011{
3012        pg_data_t *pgdat;
3013
3014        if (!populated_zone(zone))
3015                return;
3016
3017        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3018                return;
3019        pgdat = zone->zone_pgdat;
3020        if (pgdat->kswapd_max_order < order) {
3021                pgdat->kswapd_max_order = order;
3022                pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3023        }
3024        if (!waitqueue_active(&pgdat->kswapd_wait))
3025                return;
3026        if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
3027                return;
3028
3029        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3030        wake_up_interruptible(&pgdat->kswapd_wait);
3031}
3032
3033/*
3034 * The reclaimable count would be mostly accurate.
3035 * The less reclaimable pages may be
3036 * - mlocked pages, which will be moved to unevictable list when encountered
3037 * - mapped pages, which may require several travels to be reclaimed
3038 * - dirty pages, which is not "instantly" reclaimable
3039 */
3040unsigned long global_reclaimable_pages(void)
3041{
3042        int nr;
3043
3044        nr = global_page_state(NR_ACTIVE_FILE) +
3045             global_page_state(NR_INACTIVE_FILE);
3046
3047        if (nr_swap_pages > 0)
3048                nr += global_page_state(NR_ACTIVE_ANON) +
3049                      global_page_state(NR_INACTIVE_ANON);
3050
3051        return nr;
3052}
3053
3054unsigned long zone_reclaimable_pages(struct zone *zone)
3055{
3056        int nr;
3057
3058        nr = zone_page_state(zone, NR_ACTIVE_FILE) +
3059             zone_page_state(zone, NR_INACTIVE_FILE);
3060
3061        if (nr_swap_pages > 0)
3062                nr += zone_page_state(zone, NR_ACTIVE_ANON) +
3063                      zone_page_state(zone, NR_INACTIVE_ANON);
3064
3065        return nr;
3066}
3067
3068#ifdef CONFIG_HIBERNATION
3069/*
3070 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3071 * freed pages.
3072 *
3073 * Rather than trying to age LRUs the aim is to preserve the overall
3074 * LRU order by reclaiming preferentially
3075 * inactive > active > active referenced > active mapped
3076 */
3077unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3078{
3079        struct reclaim_state reclaim_state;
3080        struct scan_control sc = {
3081                .gfp_mask = GFP_HIGHUSER_MOVABLE,
3082                .may_swap = 1,
3083                .may_unmap = 1,
3084                .may_writepage = 1,
3085                .nr_to_reclaim = nr_to_reclaim,
3086                .hibernation_mode = 1,
3087                .order = 0,
3088                .priority = DEF_PRIORITY,
3089        };
3090        struct shrink_control shrink = {
3091                .gfp_mask = sc.gfp_mask,
3092        };
3093        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3094        struct task_struct *p = current;
3095        unsigned long nr_reclaimed;
3096
3097        p->flags |= PF_MEMALLOC;
3098        lockdep_set_current_reclaim_state(sc.gfp_mask);
3099        reclaim_state.reclaimed_slab = 0;
3100        p->reclaim_state = &reclaim_state;
3101
3102        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3103
3104        p->reclaim_state = NULL;
3105        lockdep_clear_current_reclaim_state();
3106        p->flags &= ~PF_MEMALLOC;
3107
3108        return nr_reclaimed;
3109}
3110#endif /* CONFIG_HIBERNATION */
3111
3112/* It's optimal to keep kswapds on the same CPUs as their memory, but
3113   not required for correctness.  So if the last cpu in a node goes
3114   away, we get changed to run anywhere: as the first one comes back,
3115   restore their cpu bindings. */
3116static int __devinit cpu_callback(struct notifier_block *nfb,
3117                                  unsigned long action, void *hcpu)
3118{
3119        int nid;
3120
3121        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3122                for_each_node_state(nid, N_HIGH_MEMORY) {
3123                        pg_data_t *pgdat = NODE_DATA(nid);
3124                        const struct cpumask *mask;
3125
3126                        mask = cpumask_of_node(pgdat->node_id);
3127
3128                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3129                                /* One of our CPUs online: restore mask */
3130                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
3131                }
3132        }
3133        return NOTIFY_OK;
3134}
3135
3136/*
3137 * This kswapd start function will be called by init and node-hot-add.
3138 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3139 */
3140int kswapd_run(int nid)
3141{
3142        pg_data_t *pgdat = NODE_DATA(nid);
3143        int ret = 0;
3144
3145        if (pgdat->kswapd)
3146                return 0;
3147
3148        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3149        if (IS_ERR(pgdat->kswapd)) {
3150                /* failure at boot is fatal */
3151                BUG_ON(system_state == SYSTEM_BOOTING);
3152                pgdat->kswapd = NULL;
3153                pr_err("Failed to start kswapd on node %d\n", nid);
3154                ret = PTR_ERR(pgdat->kswapd);
3155        }
3156        return ret;
3157}
3158
3159/*
3160 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3161 * hold lock_memory_hotplug().
3162 */
3163void kswapd_stop(int nid)
3164{
3165        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3166
3167        if (kswapd) {
3168                kthread_stop(kswapd);
3169                NODE_DATA(nid)->kswapd = NULL;
3170        }
3171}
3172
3173static int __init kswapd_init(void)
3174{
3175        int nid;
3176
3177        swap_setup();
3178        for_each_node_state(nid, N_HIGH_MEMORY)
3179                kswapd_run(nid);
3180        hotcpu_notifier(cpu_callback, 0);
3181        return 0;
3182}
3183
3184module_init(kswapd_init)
3185
3186#ifdef CONFIG_NUMA
3187/*
3188 * Zone reclaim mode
3189 *
3190 * If non-zero call zone_reclaim when the number of free pages falls below
3191 * the watermarks.
3192 */
3193int zone_reclaim_mode __read_mostly;
3194
3195#define RECLAIM_OFF 0
3196#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3197#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3198#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3199
3200/*
3201 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3202 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3203 * a zone.
3204 */
3205#define ZONE_RECLAIM_PRIORITY 4
3206
3207/*
3208 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3209 * occur.
3210 */
3211int sysctl_min_unmapped_ratio = 1;
3212
3213/*
3214 * If the number of slab pages in a zone grows beyond this percentage then
3215 * slab reclaim needs to occur.
3216 */
3217int sysctl_min_slab_ratio = 5;
3218
3219static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3220{
3221        unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3222        unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3223                zone_page_state(zone, NR_ACTIVE_FILE);
3224
3225        /*
3226         * It's possible for there to be more file mapped pages than
3227         * accounted for by the pages on the file LRU lists because
3228         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3229         */
3230        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3231}
3232
3233/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3234static long zone_pagecache_reclaimable(struct zone *zone)
3235{
3236        long nr_pagecache_reclaimable;
3237        long delta = 0;
3238
3239        /*
3240         * If RECLAIM_SWAP is set, then all file pages are considered
3241         * potentially reclaimable. Otherwise, we have to worry about
3242         * pages like swapcache and zone_unmapped_file_pages() provides
3243         * a better estimate
3244         */
3245        if (zone_reclaim_mode & RECLAIM_SWAP)
3246                nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3247        else
3248                nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3249
3250        /* If we can't clean pages, remove dirty pages from consideration */
3251        if (!(zone_reclaim_mode & RECLAIM_WRITE))
3252                delta += zone_page_state(zone, NR_FILE_DIRTY);
3253
3254        /* Watch for any possible underflows due to delta */
3255        if (unlikely(delta > nr_pagecache_reclaimable))
3256                delta = nr_pagecache_reclaimable;
3257
3258        return nr_pagecache_reclaimable - delta;
3259}
3260
3261/*
3262 * Try to free up some pages from this zone through reclaim.
3263 */
3264static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3265{
3266        /* Minimum pages needed in order to stay on node */
3267        const unsigned long nr_pages = 1 << order;
3268        struct task_struct *p = current;
3269        struct reclaim_state reclaim_state;
3270        struct scan_control sc = {
3271                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3272                .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3273                .may_swap = 1,
3274                .nr_to_reclaim = max_t(unsigned long, nr_pages,
3275                                       SWAP_CLUSTER_MAX),
3276                .gfp_mask = gfp_mask,
3277                .order = order,
3278                .priority = ZONE_RECLAIM_PRIORITY,
3279        };
3280        struct shrink_control shrink = {
3281                .gfp_mask = sc.gfp_mask,
3282        };
3283        unsigned long nr_slab_pages0, nr_slab_pages1;
3284
3285        cond_resched();
3286        /*
3287         * We need to be able to allocate from the reserves for RECLAIM_SWAP
3288         * and we also need to be able to write out pages for RECLAIM_WRITE
3289         * and RECLAIM_SWAP.
3290         */
3291        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3292        lockdep_set_current_reclaim_state(gfp_mask);
3293        reclaim_state.reclaimed_slab = 0;
3294        p->reclaim_state = &reclaim_state;
3295
3296        if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3297                /*
3298                 * Free memory by calling shrink zone with increasing
3299                 * priorities until we have enough memory freed.
3300                 */
3301                do {
3302                        shrink_zone(zone, &sc);
3303                } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3304        }
3305
3306        nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3307        if (nr_slab_pages0 > zone->min_slab_pages) {
3308                /*
3309                 * shrink_slab() does not currently allow us to determine how
3310                 * many pages were freed in this zone. So we take the current
3311                 * number of slab pages and shake the slab until it is reduced
3312                 * by the same nr_pages that we used for reclaiming unmapped
3313                 * pages.
3314                 *
3315                 * Note that shrink_slab will free memory on all zones and may
3316                 * take a long time.
3317                 */
3318                for (;;) {
3319                        unsigned long lru_pages = zone_reclaimable_pages(zone);
3320
3321                        /* No reclaimable slab or very low memory pressure */
3322                        if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3323                                break;
3324
3325                        /* Freed enough memory */
3326                        nr_slab_pages1 = zone_page_state(zone,
3327                                                        NR_SLAB_RECLAIMABLE);
3328                        if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3329                                break;
3330                }
3331
3332                /*
3333                 * Update nr_reclaimed by the number of slab pages we
3334                 * reclaimed from this zone.
3335                 */
3336                nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3337                if (nr_slab_pages1 < nr_slab_pages0)
3338                        sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3339        }
3340
3341        p->reclaim_state = NULL;
3342        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3343        lockdep_clear_current_reclaim_state();
3344        return sc.nr_reclaimed >= nr_pages;
3345}
3346
3347int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3348{
3349        int node_id;
3350        int ret;
3351
3352        /*
3353         * Zone reclaim reclaims unmapped file backed pages and
3354         * slab pages if we are over the defined limits.
3355         *
3356         * A small portion of unmapped file backed pages is needed for
3357         * file I/O otherwise pages read by file I/O will be immediately
3358         * thrown out if the zone is overallocated. So we do not reclaim
3359         * if less than a specified percentage of the zone is used by
3360         * unmapped file backed pages.
3361         */
3362        if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3363            zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3364                return ZONE_RECLAIM_FULL;
3365
3366        if (zone->all_unreclaimable)
3367                return ZONE_RECLAIM_FULL;
3368
3369        /*
3370         * Do not scan if the allocation should not be delayed.
3371         */
3372        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3373                return ZONE_RECLAIM_NOSCAN;
3374
3375        /*
3376         * Only run zone reclaim on the local zone or on zones that do not
3377         * have associated processors. This will favor the local processor
3378         * over remote processors and spread off node memory allocations
3379         * as wide as possible.
3380         */
3381        node_id = zone_to_nid(zone);
3382        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3383                return ZONE_RECLAIM_NOSCAN;
3384
3385        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3386                return ZONE_RECLAIM_NOSCAN;
3387
3388        ret = __zone_reclaim(zone, gfp_mask, order);
3389        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3390
3391        if (!ret)
3392                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3393
3394        return ret;
3395}
3396#endif
3397
3398/*
3399 * page_evictable - test whether a page is evictable
3400 * @page: the page to test
3401 *
3402 * Test whether page is evictable--i.e., should be placed on active/inactive
3403 * lists vs unevictable list.
3404 *
3405 * Reasons page might not be evictable:
3406 * (1) page's mapping marked unevictable
3407 * (2) page is part of an mlocked VMA
3408 *
3409 */
3410int page_evictable(struct page *page)
3411{
3412        return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3413}
3414
3415#ifdef CONFIG_SHMEM
3416/**
3417 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3418 * @pages:      array of pages to check
3419 * @nr_pages:   number of pages to check
3420 *
3421 * Checks pages for evictability and moves them to the appropriate lru list.
3422 *
3423 * This function is only used for SysV IPC SHM_UNLOCK.
3424 */
3425void check_move_unevictable_pages(struct page **pages, int nr_pages)
3426{
3427        struct lruvec *lruvec;
3428        struct zone *zone = NULL;
3429        int pgscanned = 0;
3430        int pgrescued = 0;
3431        int i;
3432
3433        for (i = 0; i < nr_pages; i++) {
3434                struct page *page = pages[i];
3435                struct zone *pagezone;
3436
3437                pgscanned++;
3438                pagezone = page_zone(page);
3439                if (pagezone != zone) {
3440                        if (zone)
3441                                spin_unlock_irq(&zone->lru_lock);
3442                        zone = pagezone;
3443                        spin_lock_irq(&zone->lru_lock);
3444                }
3445                lruvec = mem_cgroup_page_lruvec(page, zone);
3446
3447                if (!PageLRU(page) || !PageUnevictable(page))
3448                        continue;
3449
3450                if (page_evictable(page)) {
3451                        enum lru_list lru = page_lru_base_type(page);
3452
3453                        VM_BUG_ON(PageActive(page));
3454                        ClearPageUnevictable(page);
3455                        del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3456                        add_page_to_lru_list(page, lruvec, lru);
3457                        pgrescued++;
3458                }
3459        }
3460
3461        if (zone) {
3462                __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3463                __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3464                spin_unlock_irq(&zone->lru_lock);
3465        }
3466}
3467#endif /* CONFIG_SHMEM */
3468
3469static void warn_scan_unevictable_pages(void)
3470{
3471        printk_once(KERN_WARNING
3472                    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3473                    "disabled for lack of a legitimate use case.  If you have "
3474                    "one, please send an email to linux-mm@kvack.org.\n",
3475                    current->comm);
3476}
3477
3478/*
3479 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3480 * all nodes' unevictable lists for evictable pages
3481 */
3482unsigned long scan_unevictable_pages;
3483
3484int scan_unevictable_handler(struct ctl_table *table, int write,
3485                           void __user *buffer,
3486                           size_t *length, loff_t *ppos)
3487{
3488        warn_scan_unevictable_pages();
3489        proc_doulongvec_minmax(table, write, buffer, length, ppos);
3490        scan_unevictable_pages = 0;
3491        return 0;
3492}
3493
3494#ifdef CONFIG_NUMA
3495/*
3496 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3497 * a specified node's per zone unevictable lists for evictable pages.
3498 */
3499
3500static ssize_t read_scan_unevictable_node(struct device *dev,
3501                                          struct device_attribute *attr,
3502                                          char *buf)
3503{
3504        warn_scan_unevictable_pages();
3505        return sprintf(buf, "0\n");     /* always zero; should fit... */
3506}
3507
3508static ssize_t write_scan_unevictable_node(struct device *dev,
3509                                           struct device_attribute *attr,
3510                                        const char *buf, size_t count)
3511{
3512        warn_scan_unevictable_pages();
3513        return 1;
3514}
3515
3516
3517static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3518                        read_scan_unevictable_node,
3519                        write_scan_unevictable_node);
3520
3521int scan_unevictable_register_node(struct node *node)
3522{
3523        return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3524}
3525
3526void scan_unevictable_unregister_node(struct node *node)
3527{
3528        device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3529}
3530#endif
3531
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