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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  15
  16#include <linux/mm.h>
  17#include <linux/module.h>
  18#include <linux/gfp.h>
  19#include <linux/kernel_stat.h>
  20#include <linux/swap.h>
  21#include <linux/pagemap.h>
  22#include <linux/init.h>
  23#include <linux/highmem.h>
  24#include <linux/vmpressure.h>
  25#include <linux/vmstat.h>
  26#include <linux/file.h>
  27#include <linux/writeback.h>
  28#include <linux/blkdev.h>
  29#include <linux/buffer_head.h>  /* for try_to_release_page(),
  30                                        buffer_heads_over_limit */
  31#include <linux/mm_inline.h>
  32#include <linux/backing-dev.h>
  33#include <linux/rmap.h>
  34#include <linux/topology.h>
  35#include <linux/cpu.h>
  36#include <linux/cpuset.h>
  37#include <linux/compaction.h>
  38#include <linux/notifier.h>
  39#include <linux/rwsem.h>
  40#include <linux/delay.h>
  41#include <linux/kthread.h>
  42#include <linux/freezer.h>
  43#include <linux/memcontrol.h>
  44#include <linux/delayacct.h>
  45#include <linux/sysctl.h>
  46#include <linux/oom.h>
  47#include <linux/prefetch.h>
  48#include <linux/printk.h>
  49#include <linux/dax.h>
  50
  51#include <asm/tlbflush.h>
  52#include <asm/div64.h>
  53
  54#include <linux/swapops.h>
  55#include <linux/balloon_compaction.h>
  56
  57#include "internal.h"
  58
  59#define CREATE_TRACE_POINTS
  60#include <trace/events/vmscan.h>
  61
  62struct scan_control {
  63        /* How many pages shrink_list() should reclaim */
  64        unsigned long nr_to_reclaim;
  65
  66        /* This context's GFP mask */
  67        gfp_t gfp_mask;
  68
  69        /* Allocation order */
  70        int order;
  71
  72        /*
  73         * Nodemask of nodes allowed by the caller. If NULL, all nodes
  74         * are scanned.
  75         */
  76        nodemask_t      *nodemask;
  77
  78        /*
  79         * The memory cgroup that hit its limit and as a result is the
  80         * primary target of this reclaim invocation.
  81         */
  82        struct mem_cgroup *target_mem_cgroup;
  83
  84        /* Scan (total_size >> priority) pages at once */
  85        int priority;
  86
  87        /* The highest zone to isolate pages for reclaim from */
  88        enum zone_type reclaim_idx;
  89
  90        unsigned int may_writepage:1;
  91
  92        /* Can mapped pages be reclaimed? */
  93        unsigned int may_unmap:1;
  94
  95        /* Can pages be swapped as part of reclaim? */
  96        unsigned int may_swap:1;
  97
  98        /* Can cgroups be reclaimed below their normal consumption range? */
  99        unsigned int may_thrash:1;
 100
 101        unsigned int hibernation_mode:1;
 102
 103        /* One of the zones is ready for compaction */
 104        unsigned int compaction_ready:1;
 105
 106        /* Incremented by the number of inactive pages that were scanned */
 107        unsigned long nr_scanned;
 108
 109        /* Number of pages freed so far during a call to shrink_zones() */
 110        unsigned long nr_reclaimed;
 111};
 112
 113#ifdef ARCH_HAS_PREFETCH
 114#define prefetch_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                        prefetch(&prev->_field);                        \
 121                }                                                       \
 122        } while (0)
 123#else
 124#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
 125#endif
 126
 127#ifdef ARCH_HAS_PREFETCHW
 128#define prefetchw_prev_lru_page(_page, _base, _field)                   \
 129        do {                                                            \
 130                if ((_page)->lru.prev != _base) {                       \
 131                        struct page *prev;                              \
 132                                                                        \
 133                        prev = lru_to_page(&(_page->lru));              \
 134                        prefetchw(&prev->_field);                       \
 135                }                                                       \
 136        } while (0)
 137#else
 138#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 139#endif
 140
 141/*
 142 * From 0 .. 100.  Higher means more swappy.
 143 */
 144int vm_swappiness = 60;
 145/*
 146 * The total number of pages which are beyond the high watermark within all
 147 * zones.
 148 */
 149unsigned long vm_total_pages;
 150
 151static LIST_HEAD(shrinker_list);
 152static DECLARE_RWSEM(shrinker_rwsem);
 153
 154#ifdef CONFIG_MEMCG
 155static bool global_reclaim(struct scan_control *sc)
 156{
 157        return !sc->target_mem_cgroup;
 158}
 159
 160/**
 161 * sane_reclaim - is the usual dirty throttling mechanism operational?
 162 * @sc: scan_control in question
 163 *
 164 * The normal page dirty throttling mechanism in balance_dirty_pages() is
 165 * completely broken with the legacy memcg and direct stalling in
 166 * shrink_page_list() is used for throttling instead, which lacks all the
 167 * niceties such as fairness, adaptive pausing, bandwidth proportional
 168 * allocation and configurability.
 169 *
 170 * This function tests whether the vmscan currently in progress can assume
 171 * that the normal dirty throttling mechanism is operational.
 172 */
 173static bool sane_reclaim(struct scan_control *sc)
 174{
 175        struct mem_cgroup *memcg = sc->target_mem_cgroup;
 176
 177        if (!memcg)
 178                return true;
 179#ifdef CONFIG_CGROUP_WRITEBACK
 180        if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
 181                return true;
 182#endif
 183        return false;
 184}
 185#else
 186static bool global_reclaim(struct scan_control *sc)
 187{
 188        return true;
 189}
 190
 191static bool sane_reclaim(struct scan_control *sc)
 192{
 193        return true;
 194}
 195#endif
 196
 197/*
 198 * This misses isolated pages which are not accounted for to save counters.
 199 * As the data only determines if reclaim or compaction continues, it is
 200 * not expected that isolated pages will be a dominating factor.
 201 */
 202unsigned long zone_reclaimable_pages(struct zone *zone)
 203{
 204        unsigned long nr;
 205
 206        nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
 207                zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
 208        if (get_nr_swap_pages() > 0)
 209                nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
 210                        zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
 211
 212        return nr;
 213}
 214
 215unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
 216{
 217        unsigned long nr;
 218
 219        nr = node_page_state_snapshot(pgdat, NR_ACTIVE_FILE) +
 220             node_page_state_snapshot(pgdat, NR_INACTIVE_FILE) +
 221             node_page_state_snapshot(pgdat, NR_ISOLATED_FILE);
 222
 223        if (get_nr_swap_pages() > 0)
 224                nr += node_page_state_snapshot(pgdat, NR_ACTIVE_ANON) +
 225                      node_page_state_snapshot(pgdat, NR_INACTIVE_ANON) +
 226                      node_page_state_snapshot(pgdat, NR_ISOLATED_ANON);
 227
 228        return nr;
 229}
 230
 231bool pgdat_reclaimable(struct pglist_data *pgdat)
 232{
 233        return node_page_state_snapshot(pgdat, NR_PAGES_SCANNED) <
 234                pgdat_reclaimable_pages(pgdat) * 6;
 235}
 236
 237unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru)
 238{
 239        if (!mem_cgroup_disabled())
 240                return mem_cgroup_get_lru_size(lruvec, lru);
 241
 242        return node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
 243}
 244
 245/*
 246 * Add a shrinker callback to be called from the vm.
 247 */
 248int register_shrinker(struct shrinker *shrinker)
 249{
 250        size_t size = sizeof(*shrinker->nr_deferred);
 251
 252        if (shrinker->flags & SHRINKER_NUMA_AWARE)
 253                size *= nr_node_ids;
 254
 255        shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
 256        if (!shrinker->nr_deferred)
 257                return -ENOMEM;
 258
 259        down_write(&shrinker_rwsem);
 260        list_add_tail(&shrinker->list, &shrinker_list);
 261        up_write(&shrinker_rwsem);
 262        return 0;
 263}
 264EXPORT_SYMBOL(register_shrinker);
 265
 266/*
 267 * Remove one
 268 */
 269void unregister_shrinker(struct shrinker *shrinker)
 270{
 271        down_write(&shrinker_rwsem);
 272        list_del(&shrinker->list);
 273        up_write(&shrinker_rwsem);
 274        kfree(shrinker->nr_deferred);
 275}
 276EXPORT_SYMBOL(unregister_shrinker);
 277
 278#define SHRINK_BATCH 128
 279
 280static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 281                                    struct shrinker *shrinker,
 282                                    unsigned long nr_scanned,
 283                                    unsigned long nr_eligible)
 284{
 285        unsigned long freed = 0;
 286        unsigned long long delta;
 287        long total_scan;
 288        long freeable;
 289        long nr;
 290        long new_nr;
 291        int nid = shrinkctl->nid;
 292        long batch_size = shrinker->batch ? shrinker->batch
 293                                          : SHRINK_BATCH;
 294
 295        freeable = shrinker->count_objects(shrinker, shrinkctl);
 296        if (freeable == 0)
 297                return 0;
 298
 299        /*
 300         * copy the current shrinker scan count into a local variable
 301         * and zero it so that other concurrent shrinker invocations
 302         * don't also do this scanning work.
 303         */
 304        nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
 305
 306        total_scan = nr;
 307        delta = (4 * nr_scanned) / shrinker->seeks;
 308        delta *= freeable;
 309        do_div(delta, nr_eligible + 1);
 310        total_scan += delta;
 311        if (total_scan < 0) {
 312                pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
 313                       shrinker->scan_objects, total_scan);
 314                total_scan = freeable;
 315        }
 316
 317        /*
 318         * We need to avoid excessive windup on filesystem shrinkers
 319         * due to large numbers of GFP_NOFS allocations causing the
 320         * shrinkers to return -1 all the time. This results in a large
 321         * nr being built up so when a shrink that can do some work
 322         * comes along it empties the entire cache due to nr >>>
 323         * freeable. This is bad for sustaining a working set in
 324         * memory.
 325         *
 326         * Hence only allow the shrinker to scan the entire cache when
 327         * a large delta change is calculated directly.
 328         */
 329        if (delta < freeable / 4)
 330                total_scan = min(total_scan, freeable / 2);
 331
 332        /*
 333         * Avoid risking looping forever due to too large nr value:
 334         * never try to free more than twice the estimate number of
 335         * freeable entries.
 336         */
 337        if (total_scan > freeable * 2)
 338                total_scan = freeable * 2;
 339
 340        trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
 341                                   nr_scanned, nr_eligible,
 342                                   freeable, delta, total_scan);
 343
 344        /*
 345         * Normally, we should not scan less than batch_size objects in one
 346         * pass to avoid too frequent shrinker calls, but if the slab has less
 347         * than batch_size objects in total and we are really tight on memory,
 348         * we will try to reclaim all available objects, otherwise we can end
 349         * up failing allocations although there are plenty of reclaimable
 350         * objects spread over several slabs with usage less than the
 351         * batch_size.
 352         *
 353         * We detect the "tight on memory" situations by looking at the total
 354         * number of objects we want to scan (total_scan). If it is greater
 355         * than the total number of objects on slab (freeable), we must be
 356         * scanning at high prio and therefore should try to reclaim as much as
 357         * possible.
 358         */
 359        while (total_scan >= batch_size ||
 360               total_scan >= freeable) {
 361                unsigned long ret;
 362                unsigned long nr_to_scan = min(batch_size, total_scan);
 363
 364                shrinkctl->nr_to_scan = nr_to_scan;
 365                ret = shrinker->scan_objects(shrinker, shrinkctl);
 366                if (ret == SHRINK_STOP)
 367                        break;
 368                freed += ret;
 369
 370                count_vm_events(SLABS_SCANNED, nr_to_scan);
 371                total_scan -= nr_to_scan;
 372
 373                cond_resched();
 374        }
 375
 376        /*
 377         * move the unused scan count back into the shrinker in a
 378         * manner that handles concurrent updates. If we exhausted the
 379         * scan, there is no need to do an update.
 380         */
 381        if (total_scan > 0)
 382                new_nr = atomic_long_add_return(total_scan,
 383                                                &shrinker->nr_deferred[nid]);
 384        else
 385                new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
 386
 387        trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
 388        return freed;
 389}
 390
 391/**
 392 * shrink_slab - shrink slab caches
 393 * @gfp_mask: allocation context
 394 * @nid: node whose slab caches to target
 395 * @memcg: memory cgroup whose slab caches to target
 396 * @nr_scanned: pressure numerator
 397 * @nr_eligible: pressure denominator
 398 *
 399 * Call the shrink functions to age shrinkable caches.
 400 *
 401 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
 402 * unaware shrinkers will receive a node id of 0 instead.
 403 *
 404 * @memcg specifies the memory cgroup to target. If it is not NULL,
 405 * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
 406 * objects from the memory cgroup specified. Otherwise, only unaware
 407 * shrinkers are called.
 408 *
 409 * @nr_scanned and @nr_eligible form a ratio that indicate how much of
 410 * the available objects should be scanned.  Page reclaim for example
 411 * passes the number of pages scanned and the number of pages on the
 412 * LRU lists that it considered on @nid, plus a bias in @nr_scanned
 413 * when it encountered mapped pages.  The ratio is further biased by
 414 * the ->seeks setting of the shrink function, which indicates the
 415 * cost to recreate an object relative to that of an LRU page.
 416 *
 417 * Returns the number of reclaimed slab objects.
 418 */
 419static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 420                                 struct mem_cgroup *memcg,
 421                                 unsigned long nr_scanned,
 422                                 unsigned long nr_eligible)
 423{
 424        struct shrinker *shrinker;
 425        unsigned long freed = 0;
 426
 427        if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
 428                return 0;
 429
 430        if (nr_scanned == 0)
 431                nr_scanned = SWAP_CLUSTER_MAX;
 432
 433        if (!down_read_trylock(&shrinker_rwsem)) {
 434                /*
 435                 * If we would return 0, our callers would understand that we
 436                 * have nothing else to shrink and give up trying. By returning
 437                 * 1 we keep it going and assume we'll be able to shrink next
 438                 * time.
 439                 */
 440                freed = 1;
 441                goto out;
 442        }
 443
 444        list_for_each_entry(shrinker, &shrinker_list, list) {
 445                struct shrink_control sc = {
 446                        .gfp_mask = gfp_mask,
 447                        .nid = nid,
 448                        .memcg = memcg,
 449                };
 450
 451                /*
 452                 * If kernel memory accounting is disabled, we ignore
 453                 * SHRINKER_MEMCG_AWARE flag and call all shrinkers
 454                 * passing NULL for memcg.
 455                 */
 456                if (memcg_kmem_enabled() &&
 457                    !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
 458                        continue;
 459
 460                if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
 461                        sc.nid = 0;
 462
 463                freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
 464        }
 465
 466        up_read(&shrinker_rwsem);
 467out:
 468        cond_resched();
 469        return freed;
 470}
 471
 472void drop_slab_node(int nid)
 473{
 474        unsigned long freed;
 475
 476        do {
 477                struct mem_cgroup *memcg = NULL;
 478
 479                freed = 0;
 480                do {
 481                        freed += shrink_slab(GFP_KERNEL, nid, memcg,
 482                                             1000, 1000);
 483                } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 484        } while (freed > 10);
 485}
 486
 487void drop_slab(void)
 488{
 489        int nid;
 490
 491        for_each_online_node(nid)
 492                drop_slab_node(nid);
 493}
 494
 495static inline int is_page_cache_freeable(struct page *page)
 496{
 497        /*
 498         * A freeable page cache page is referenced only by the caller
 499         * that isolated the page, the page cache radix tree and
 500         * optional buffer heads at page->private.
 501         */
 502        return page_count(page) - page_has_private(page) == 2;
 503}
 504
 505static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
 506{
 507        if (current->flags & PF_SWAPWRITE)
 508                return 1;
 509        if (!inode_write_congested(inode))
 510                return 1;
 511        if (inode_to_bdi(inode) == current->backing_dev_info)
 512                return 1;
 513        return 0;
 514}
 515
 516/*
 517 * We detected a synchronous write error writing a page out.  Probably
 518 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 519 * fsync(), msync() or close().
 520 *
 521 * The tricky part is that after writepage we cannot touch the mapping: nothing
 522 * prevents it from being freed up.  But we have a ref on the page and once
 523 * that page is locked, the mapping is pinned.
 524 *
 525 * We're allowed to run sleeping lock_page() here because we know the caller has
 526 * __GFP_FS.
 527 */
 528static void handle_write_error(struct address_space *mapping,
 529                                struct page *page, int error)
 530{
 531        lock_page(page);
 532        if (page_mapping(page) == mapping)
 533                mapping_set_error(mapping, error);
 534        unlock_page(page);
 535}
 536
 537/* possible outcome of pageout() */
 538typedef enum {
 539        /* failed to write page out, page is locked */
 540        PAGE_KEEP,
 541        /* move page to the active list, page is locked */
 542        PAGE_ACTIVATE,
 543        /* page has been sent to the disk successfully, page is unlocked */
 544        PAGE_SUCCESS,
 545        /* page is clean and locked */
 546        PAGE_CLEAN,
 547} pageout_t;
 548
 549/*
 550 * pageout is called by shrink_page_list() for each dirty page.
 551 * Calls ->writepage().
 552 */
 553static pageout_t pageout(struct page *page, struct address_space *mapping,
 554                         struct scan_control *sc)
 555{
 556        /*
 557         * If the page is dirty, only perform writeback if that write
 558         * will be non-blocking.  To prevent this allocation from being
 559         * stalled by pagecache activity.  But note that there may be
 560         * stalls if we need to run get_block().  We could test
 561         * PagePrivate for that.
 562         *
 563         * If this process is currently in __generic_file_write_iter() against
 564         * this page's queue, we can perform writeback even if that
 565         * will block.
 566         *
 567         * If the page is swapcache, write it back even if that would
 568         * block, for some throttling. This happens by accident, because
 569         * swap_backing_dev_info is bust: it doesn't reflect the
 570         * congestion state of the swapdevs.  Easy to fix, if needed.
 571         */
 572        if (!is_page_cache_freeable(page))
 573                return PAGE_KEEP;
 574        if (!mapping) {
 575                /*
 576                 * Some data journaling orphaned pages can have
 577                 * page->mapping == NULL while being dirty with clean buffers.
 578                 */
 579                if (page_has_private(page)) {
 580                        if (try_to_free_buffers(page)) {
 581                                ClearPageDirty(page);
 582                                pr_info("%s: orphaned page\n", __func__);
 583                                return PAGE_CLEAN;
 584                        }
 585                }
 586                return PAGE_KEEP;
 587        }
 588        if (mapping->a_ops->writepage == NULL)
 589                return PAGE_ACTIVATE;
 590        if (!may_write_to_inode(mapping->host, sc))
 591                return PAGE_KEEP;
 592
 593        if (clear_page_dirty_for_io(page)) {
 594                int res;
 595                struct writeback_control wbc = {
 596                        .sync_mode = WB_SYNC_NONE,
 597                        .nr_to_write = SWAP_CLUSTER_MAX,
 598                        .range_start = 0,
 599                        .range_end = LLONG_MAX,
 600                        .for_reclaim = 1,
 601                };
 602
 603                SetPageReclaim(page);
 604                res = mapping->a_ops->writepage(page, &wbc);
 605                if (res < 0)
 606                        handle_write_error(mapping, page, res);
 607                if (res == AOP_WRITEPAGE_ACTIVATE) {
 608                        ClearPageReclaim(page);
 609                        return PAGE_ACTIVATE;
 610                }
 611
 612                if (!PageWriteback(page)) {
 613                        /* synchronous write or broken a_ops? */
 614                        ClearPageReclaim(page);
 615                }
 616                trace_mm_vmscan_writepage(page);
 617                inc_node_page_state(page, NR_VMSCAN_WRITE);
 618                return PAGE_SUCCESS;
 619        }
 620
 621        return PAGE_CLEAN;
 622}
 623
 624/*
 625 * Same as remove_mapping, but if the page is removed from the mapping, it
 626 * gets returned with a refcount of 0.
 627 */
 628static int __remove_mapping(struct address_space *mapping, struct page *page,
 629                            bool reclaimed)
 630{
 631        unsigned long flags;
 632
 633        BUG_ON(!PageLocked(page));
 634        BUG_ON(mapping != page_mapping(page));
 635
 636        spin_lock_irqsave(&mapping->tree_lock, flags);
 637        /*
 638         * The non racy check for a busy page.
 639         *
 640         * Must be careful with the order of the tests. When someone has
 641         * a ref to the page, it may be possible that they dirty it then
 642         * drop the reference. So if PageDirty is tested before page_count
 643         * here, then the following race may occur:
 644         *
 645         * get_user_pages(&page);
 646         * [user mapping goes away]
 647         * write_to(page);
 648         *                              !PageDirty(page)    [good]
 649         * SetPageDirty(page);
 650         * put_page(page);
 651         *                              !page_count(page)   [good, discard it]
 652         *
 653         * [oops, our write_to data is lost]
 654         *
 655         * Reversing the order of the tests ensures such a situation cannot
 656         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 657         * load is not satisfied before that of page->_refcount.
 658         *
 659         * Note that if SetPageDirty is always performed via set_page_dirty,
 660         * and thus under tree_lock, then this ordering is not required.
 661         */
 662        if (!page_ref_freeze(page, 2))
 663                goto cannot_free;
 664        /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
 665        if (unlikely(PageDirty(page))) {
 666                page_ref_unfreeze(page, 2);
 667                goto cannot_free;
 668        }
 669
 670        if (PageSwapCache(page)) {
 671                swp_entry_t swap = { .val = page_private(page) };
 672                mem_cgroup_swapout(page, swap);
 673                __delete_from_swap_cache(page);
 674                spin_unlock_irqrestore(&mapping->tree_lock, flags);
 675                swapcache_free(swap);
 676        } else {
 677                void (*freepage)(struct page *);
 678                void *shadow = NULL;
 679
 680                freepage = mapping->a_ops->freepage;
 681                /*
 682                 * Remember a shadow entry for reclaimed file cache in
 683                 * order to detect refaults, thus thrashing, later on.
 684                 *
 685                 * But don't store shadows in an address space that is
 686                 * already exiting.  This is not just an optizimation,
 687                 * inode reclaim needs to empty out the radix tree or
 688                 * the nodes are lost.  Don't plant shadows behind its
 689                 * back.
 690                 *
 691                 * We also don't store shadows for DAX mappings because the
 692                 * only page cache pages found in these are zero pages
 693                 * covering holes, and because we don't want to mix DAX
 694                 * exceptional entries and shadow exceptional entries in the
 695                 * same page_tree.
 696                 */
 697                if (reclaimed && page_is_file_cache(page) &&
 698                    !mapping_exiting(mapping) && !dax_mapping(mapping))
 699                        shadow = workingset_eviction(mapping, page);
 700                __delete_from_page_cache(page, shadow);
 701                spin_unlock_irqrestore(&mapping->tree_lock, flags);
 702
 703                if (freepage != NULL)
 704                        freepage(page);
 705        }
 706
 707        return 1;
 708
 709cannot_free:
 710        spin_unlock_irqrestore(&mapping->tree_lock, flags);
 711        return 0;
 712}
 713
 714/*
 715 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 716 * someone else has a ref on the page, abort and return 0.  If it was
 717 * successfully detached, return 1.  Assumes the caller has a single ref on
 718 * this page.
 719 */
 720int remove_mapping(struct address_space *mapping, struct page *page)
 721{
 722        if (__remove_mapping(mapping, page, false)) {
 723                /*
 724                 * Unfreezing the refcount with 1 rather than 2 effectively
 725                 * drops the pagecache ref for us without requiring another
 726                 * atomic operation.
 727                 */
 728                page_ref_unfreeze(page, 1);
 729                return 1;
 730        }
 731        return 0;
 732}
 733
 734/**
 735 * putback_lru_page - put previously isolated page onto appropriate LRU list
 736 * @page: page to be put back to appropriate lru list
 737 *
 738 * Add previously isolated @page to appropriate LRU list.
 739 * Page may still be unevictable for other reasons.
 740 *
 741 * lru_lock must not be held, interrupts must be enabled.
 742 */
 743void putback_lru_page(struct page *page)
 744{
 745        bool is_unevictable;
 746        int was_unevictable = PageUnevictable(page);
 747
 748        VM_BUG_ON_PAGE(PageLRU(page), page);
 749
 750redo:
 751        ClearPageUnevictable(page);
 752
 753        if (page_evictable(page)) {
 754                /*
 755                 * For evictable pages, we can use the cache.
 756                 * In event of a race, worst case is we end up with an
 757                 * unevictable page on [in]active list.
 758                 * We know how to handle that.
 759                 */
 760                is_unevictable = false;
 761                lru_cache_add(page);
 762        } else {
 763                /*
 764                 * Put unevictable pages directly on zone's unevictable
 765                 * list.
 766                 */
 767                is_unevictable = true;
 768                add_page_to_unevictable_list(page);
 769                /*
 770                 * When racing with an mlock or AS_UNEVICTABLE clearing
 771                 * (page is unlocked) make sure that if the other thread
 772                 * does not observe our setting of PG_lru and fails
 773                 * isolation/check_move_unevictable_pages,
 774                 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
 775                 * the page back to the evictable list.
 776                 *
 777                 * The other side is TestClearPageMlocked() or shmem_lock().
 778                 */
 779                smp_mb();
 780        }
 781
 782        /*
 783         * page's status can change while we move it among lru. If an evictable
 784         * page is on unevictable list, it never be freed. To avoid that,
 785         * check after we added it to the list, again.
 786         */
 787        if (is_unevictable && page_evictable(page)) {
 788                if (!isolate_lru_page(page)) {
 789                        put_page(page);
 790                        goto redo;
 791                }
 792                /* This means someone else dropped this page from LRU
 793                 * So, it will be freed or putback to LRU again. There is
 794                 * nothing to do here.
 795                 */
 796        }
 797
 798        if (was_unevictable && !is_unevictable)
 799                count_vm_event(UNEVICTABLE_PGRESCUED);
 800        else if (!was_unevictable && is_unevictable)
 801                count_vm_event(UNEVICTABLE_PGCULLED);
 802
 803        put_page(page);         /* drop ref from isolate */
 804}
 805
 806enum page_references {
 807        PAGEREF_RECLAIM,
 808        PAGEREF_RECLAIM_CLEAN,
 809        PAGEREF_KEEP,
 810        PAGEREF_ACTIVATE,
 811};
 812
 813static enum page_references page_check_references(struct page *page,
 814                                                  struct scan_control *sc)
 815{
 816        int referenced_ptes, referenced_page;
 817        unsigned long vm_flags;
 818
 819        referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
 820                                          &vm_flags);
 821        referenced_page = TestClearPageReferenced(page);
 822
 823        /*
 824         * Mlock lost the isolation race with us.  Let try_to_unmap()
 825         * move the page to the unevictable list.
 826         */
 827        if (vm_flags & VM_LOCKED)
 828                return PAGEREF_RECLAIM;
 829
 830        if (referenced_ptes) {
 831                if (PageSwapBacked(page))
 832                        return PAGEREF_ACTIVATE;
 833                /*
 834                 * All mapped pages start out with page table
 835                 * references from the instantiating fault, so we need
 836                 * to look twice if a mapped file page is used more
 837                 * than once.
 838                 *
 839                 * Mark it and spare it for another trip around the
 840                 * inactive list.  Another page table reference will
 841                 * lead to its activation.
 842                 *
 843                 * Note: the mark is set for activated pages as well
 844                 * so that recently deactivated but used pages are
 845                 * quickly recovered.
 846                 */
 847                SetPageReferenced(page);
 848
 849                if (referenced_page || referenced_ptes > 1)
 850                        return PAGEREF_ACTIVATE;
 851
 852                /*
 853                 * Activate file-backed executable pages after first usage.
 854                 */
 855                if (vm_flags & VM_EXEC)
 856                        return PAGEREF_ACTIVATE;
 857
 858                return PAGEREF_KEEP;
 859        }
 860
 861        /* Reclaim if clean, defer dirty pages to writeback */
 862        if (referenced_page && !PageSwapBacked(page))
 863                return PAGEREF_RECLAIM_CLEAN;
 864
 865        return PAGEREF_RECLAIM;
 866}
 867
 868/* Check if a page is dirty or under writeback */
 869static void page_check_dirty_writeback(struct page *page,
 870                                       bool *dirty, bool *writeback)
 871{
 872        struct address_space *mapping;
 873
 874        /*
 875         * Anonymous pages are not handled by flushers and must be written
 876         * from reclaim context. Do not stall reclaim based on them
 877         */
 878        if (!page_is_file_cache(page)) {
 879                *dirty = false;
 880                *writeback = false;
 881                return;
 882        }
 883
 884        /* By default assume that the page flags are accurate */
 885        *dirty = PageDirty(page);
 886        *writeback = PageWriteback(page);
 887
 888        /* Verify dirty/writeback state if the filesystem supports it */
 889        if (!page_has_private(page))
 890                return;
 891
 892        mapping = page_mapping(page);
 893        if (mapping && mapping->a_ops->is_dirty_writeback)
 894                mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
 895}
 896
 897/*
 898 * shrink_page_list() returns the number of reclaimed pages
 899 */
 900static unsigned long shrink_page_list(struct list_head *page_list,
 901                                      struct pglist_data *pgdat,
 902                                      struct scan_control *sc,
 903                                      enum ttu_flags ttu_flags,
 904                                      unsigned long *ret_nr_dirty,
 905                                      unsigned long *ret_nr_unqueued_dirty,
 906                                      unsigned long *ret_nr_congested,
 907                                      unsigned long *ret_nr_writeback,
 908                                      unsigned long *ret_nr_immediate,
 909                                      bool force_reclaim)
 910{
 911        LIST_HEAD(ret_pages);
 912        LIST_HEAD(free_pages);
 913        int pgactivate = 0;
 914        unsigned long nr_unqueued_dirty = 0;
 915        unsigned long nr_dirty = 0;
 916        unsigned long nr_congested = 0;
 917        unsigned long nr_reclaimed = 0;
 918        unsigned long nr_writeback = 0;
 919        unsigned long nr_immediate = 0;
 920
 921        cond_resched();
 922
 923        while (!list_empty(page_list)) {
 924                struct address_space *mapping;
 925                struct page *page;
 926                int may_enter_fs;
 927                enum page_references references = PAGEREF_RECLAIM_CLEAN;
 928                bool dirty, writeback;
 929                bool lazyfree = false;
 930                int ret = SWAP_SUCCESS;
 931
 932                cond_resched();
 933
 934                page = lru_to_page(page_list);
 935                list_del(&page->lru);
 936
 937                if (!trylock_page(page))
 938                        goto keep;
 939
 940                VM_BUG_ON_PAGE(PageActive(page), page);
 941
 942                sc->nr_scanned++;
 943
 944                if (unlikely(!page_evictable(page)))
 945                        goto cull_mlocked;
 946
 947                if (!sc->may_unmap && page_mapped(page))
 948                        goto keep_locked;
 949
 950                /* Double the slab pressure for mapped and swapcache pages */
 951                if (page_mapped(page) || PageSwapCache(page))
 952                        sc->nr_scanned++;
 953
 954                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 955                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 956
 957                /*
 958                 * The number of dirty pages determines if a zone is marked
 959                 * reclaim_congested which affects wait_iff_congested. kswapd
 960                 * will stall and start writing pages if the tail of the LRU
 961                 * is all dirty unqueued pages.
 962                 */
 963                page_check_dirty_writeback(page, &dirty, &writeback);
 964                if (dirty || writeback)
 965                        nr_dirty++;
 966
 967                if (dirty && !writeback)
 968                        nr_unqueued_dirty++;
 969
 970                /*
 971                 * Treat this page as congested if the underlying BDI is or if
 972                 * pages are cycling through the LRU so quickly that the
 973                 * pages marked for immediate reclaim are making it to the
 974                 * end of the LRU a second time.
 975                 */
 976                mapping = page_mapping(page);
 977                if (((dirty || writeback) && mapping &&
 978                     inode_write_congested(mapping->host)) ||
 979                    (writeback && PageReclaim(page)))
 980                        nr_congested++;
 981
 982                /*
 983                 * If a page at the tail of the LRU is under writeback, there
 984                 * are three cases to consider.
 985                 *
 986                 * 1) If reclaim is encountering an excessive number of pages
 987                 *    under writeback and this page is both under writeback and
 988                 *    PageReclaim then it indicates that pages are being queued
 989                 *    for IO but are being recycled through the LRU before the
 990                 *    IO can complete. Waiting on the page itself risks an
 991                 *    indefinite stall if it is impossible to writeback the
 992                 *    page due to IO error or disconnected storage so instead
 993                 *    note that the LRU is being scanned too quickly and the
 994                 *    caller can stall after page list has been processed.
 995                 *
 996                 * 2) Global or new memcg reclaim encounters a page that is
 997                 *    not marked for immediate reclaim, or the caller does not
 998                 *    have __GFP_FS (or __GFP_IO if it's simply going to swap,
 999                 *    not to fs). In this case mark the page for immediate
1000                 *    reclaim and continue scanning.
1001                 *
1002                 *    Require may_enter_fs because we would wait on fs, which
1003                 *    may not have submitted IO yet. And the loop driver might
1004                 *    enter reclaim, and deadlock if it waits on a page for
1005                 *    which it is needed to do the write (loop masks off
1006                 *    __GFP_IO|__GFP_FS for this reason); but more thought
1007                 *    would probably show more reasons.
1008                 *
1009                 * 3) Legacy memcg encounters a page that is already marked
1010                 *    PageReclaim. memcg does not have any dirty pages
1011                 *    throttling so we could easily OOM just because too many
1012                 *    pages are in writeback and there is nothing else to
1013                 *    reclaim. Wait for the writeback to complete.
1014                 */
1015                if (PageWriteback(page)) {
1016                        /* Case 1 above */
1017                        if (current_is_kswapd() &&
1018                            PageReclaim(page) &&
1019                            test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1020                                nr_immediate++;
1021                                goto keep_locked;
1022
1023                        /* Case 2 above */
1024                        } else if (sane_reclaim(sc) ||
1025                            !PageReclaim(page) || !may_enter_fs) {
1026                                /*
1027                                 * This is slightly racy - end_page_writeback()
1028                                 * might have just cleared PageReclaim, then
1029                                 * setting PageReclaim here end up interpreted
1030                                 * as PageReadahead - but that does not matter
1031                                 * enough to care.  What we do want is for this
1032                                 * page to have PageReclaim set next time memcg
1033                                 * reclaim reaches the tests above, so it will
1034                                 * then wait_on_page_writeback() to avoid OOM;
1035                                 * and it's also appropriate in global reclaim.
1036                                 */
1037                                SetPageReclaim(page);
1038                                nr_writeback++;
1039                                goto keep_locked;
1040
1041                        /* Case 3 above */
1042                        } else {
1043                                unlock_page(page);
1044                                wait_on_page_writeback(page);
1045                                /* then go back and try same page again */
1046                                list_add_tail(&page->lru, page_list);
1047                                continue;
1048                        }
1049                }
1050
1051                if (!force_reclaim)
1052                        references = page_check_references(page, sc);
1053
1054                switch (references) {
1055                case PAGEREF_ACTIVATE:
1056                        goto activate_locked;
1057                case PAGEREF_KEEP:
1058                        goto keep_locked;
1059                case PAGEREF_RECLAIM:
1060                case PAGEREF_RECLAIM_CLEAN:
1061                        ; /* try to reclaim the page below */
1062                }
1063
1064                /*
1065                 * Anonymous process memory has backing store?
1066                 * Try to allocate it some swap space here.
1067                 */
1068                if (PageAnon(page) && !PageSwapCache(page)) {
1069                        if (!(sc->gfp_mask & __GFP_IO))
1070                                goto keep_locked;
1071                        if (!add_to_swap(page, page_list))
1072                                goto activate_locked;
1073                        lazyfree = true;
1074                        may_enter_fs = 1;
1075
1076                        /* Adding to swap updated mapping */
1077                        mapping = page_mapping(page);
1078                } else if (unlikely(PageTransHuge(page))) {
1079                        /* Split file THP */
1080                        if (split_huge_page_to_list(page, page_list))
1081                                goto keep_locked;
1082                }
1083
1084                VM_BUG_ON_PAGE(PageTransHuge(page), page);
1085
1086                /*
1087                 * The page is mapped into the page tables of one or more
1088                 * processes. Try to unmap it here.
1089                 */
1090                if (page_mapped(page) && mapping) {
1091                        switch (ret = try_to_unmap(page, lazyfree ?
1092                                (ttu_flags | TTU_BATCH_FLUSH | TTU_LZFREE) :
1093                                (ttu_flags | TTU_BATCH_FLUSH))) {
1094                        case SWAP_FAIL:
1095                                goto activate_locked;
1096                        case SWAP_AGAIN:
1097                                goto keep_locked;
1098                        case SWAP_MLOCK:
1099                                goto cull_mlocked;
1100                        case SWAP_LZFREE:
1101                                goto lazyfree;
1102                        case SWAP_SUCCESS:
1103                                ; /* try to free the page below */
1104                        }
1105                }
1106
1107                if (PageDirty(page)) {
1108                        /*
1109                         * Only kswapd can writeback filesystem pages to
1110                         * avoid risk of stack overflow but only writeback
1111                         * if many dirty pages have been encountered.
1112                         */
1113                        if (page_is_file_cache(page) &&
1114                                        (!current_is_kswapd() ||
1115                                         !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1116                                /*
1117                                 * Immediately reclaim when written back.
1118                                 * Similar in principal to deactivate_page()
1119                                 * except we already have the page isolated
1120                                 * and know it's dirty
1121                                 */
1122                                inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1123                                SetPageReclaim(page);
1124
1125                                goto keep_locked;
1126                        }
1127
1128                        if (references == PAGEREF_RECLAIM_CLEAN)
1129                                goto keep_locked;
1130                        if (!may_enter_fs)
1131                                goto keep_locked;
1132                        if (!sc->may_writepage)
1133                                goto keep_locked;
1134
1135                        /*
1136                         * Page is dirty. Flush the TLB if a writable entry
1137                         * potentially exists to avoid CPU writes after IO
1138                         * starts and then write it out here.
1139                         */
1140                        try_to_unmap_flush_dirty();
1141                        switch (pageout(page, mapping, sc)) {
1142                        case PAGE_KEEP:
1143                                goto keep_locked;
1144                        case PAGE_ACTIVATE:
1145                                goto activate_locked;
1146                        case PAGE_SUCCESS:
1147                                if (PageWriteback(page))
1148                                        goto keep;
1149                                if (PageDirty(page))
1150                                        goto keep;
1151
1152                                /*
1153                                 * A synchronous write - probably a ramdisk.  Go
1154                                 * ahead and try to reclaim the page.
1155                                 */
1156                                if (!trylock_page(page))
1157                                        goto keep;
1158                                if (PageDirty(page) || PageWriteback(page))
1159                                        goto keep_locked;
1160                                mapping = page_mapping(page);
1161                        case PAGE_CLEAN:
1162                                ; /* try to free the page below */
1163                        }
1164                }
1165
1166                /*
1167                 * If the page has buffers, try to free the buffer mappings
1168                 * associated with this page. If we succeed we try to free
1169                 * the page as well.
1170                 *
1171                 * We do this even if the page is PageDirty().
1172                 * try_to_release_page() does not perform I/O, but it is
1173                 * possible for a page to have PageDirty set, but it is actually
1174                 * clean (all its buffers are clean).  This happens if the
1175                 * buffers were written out directly, with submit_bh(). ext3
1176                 * will do this, as well as the blockdev mapping.
1177                 * try_to_release_page() will discover that cleanness and will
1178                 * drop the buffers and mark the page clean - it can be freed.
1179                 *
1180                 * Rarely, pages can have buffers and no ->mapping.  These are
1181                 * the pages which were not successfully invalidated in
1182                 * truncate_complete_page().  We try to drop those buffers here
1183                 * and if that worked, and the page is no longer mapped into
1184                 * process address space (page_count == 1) it can be freed.
1185                 * Otherwise, leave the page on the LRU so it is swappable.
1186                 */
1187                if (page_has_private(page)) {
1188                        if (!try_to_release_page(page, sc->gfp_mask))
1189                                goto activate_locked;
1190                        if (!mapping && page_count(page) == 1) {
1191                                unlock_page(page);
1192                                if (put_page_testzero(page))
1193                                        goto free_it;
1194                                else {
1195                                        /*
1196                                         * rare race with speculative reference.
1197                                         * the speculative reference will free
1198                                         * this page shortly, so we may
1199                                         * increment nr_reclaimed here (and
1200                                         * leave it off the LRU).
1201                                         */
1202                                        nr_reclaimed++;
1203                                        continue;
1204                                }
1205                        }
1206                }
1207
1208lazyfree:
1209                if (!mapping || !__remove_mapping(mapping, page, true))
1210                        goto keep_locked;
1211
1212                /*
1213                 * At this point, we have no other references and there is
1214                 * no way to pick any more up (removed from LRU, removed
1215                 * from pagecache). Can use non-atomic bitops now (and
1216                 * we obviously don't have to worry about waking up a process
1217                 * waiting on the page lock, because there are no references.
1218                 */
1219                __ClearPageLocked(page);
1220free_it:
1221                if (ret == SWAP_LZFREE)
1222                        count_vm_event(PGLAZYFREED);
1223
1224                nr_reclaimed++;
1225
1226                /*
1227                 * Is there need to periodically free_page_list? It would
1228                 * appear not as the counts should be low
1229                 */
1230                list_add(&page->lru, &free_pages);
1231                continue;
1232
1233cull_mlocked:
1234                if (PageSwapCache(page))
1235                        try_to_free_swap(page);
1236                unlock_page(page);
1237                list_add(&page->lru, &ret_pages);
1238                continue;
1239
1240activate_locked:
1241                /* Not a candidate for swapping, so reclaim swap space. */
1242                if (PageSwapCache(page) && mem_cgroup_swap_full(page))
1243                        try_to_free_swap(page);
1244                VM_BUG_ON_PAGE(PageActive(page), page);
1245                SetPageActive(page);
1246                pgactivate++;
1247keep_locked:
1248                unlock_page(page);
1249keep:
1250                list_add(&page->lru, &ret_pages);
1251                VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1252        }
1253
1254        mem_cgroup_uncharge_list(&free_pages);
1255        try_to_unmap_flush();
1256        free_hot_cold_page_list(&free_pages, true);
1257
1258        list_splice(&ret_pages, page_list);
1259        count_vm_events(PGACTIVATE, pgactivate);
1260
1261        *ret_nr_dirty += nr_dirty;
1262        *ret_nr_congested += nr_congested;
1263        *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1264        *ret_nr_writeback += nr_writeback;
1265        *ret_nr_immediate += nr_immediate;
1266        return nr_reclaimed;
1267}
1268
1269unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1270                                            struct list_head *page_list)
1271{
1272        struct scan_control sc = {
1273                .gfp_mask = GFP_KERNEL,
1274                .priority = DEF_PRIORITY,
1275                .may_unmap = 1,
1276        };
1277        unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1278        struct page *page, *next;
1279        LIST_HEAD(clean_pages);
1280
1281        list_for_each_entry_safe(page, next, page_list, lru) {
1282                if (page_is_file_cache(page) && !PageDirty(page) &&
1283                    !__PageMovable(page)) {
1284                        ClearPageActive(page);
1285                        list_move(&page->lru, &clean_pages);
1286                }
1287        }
1288
1289        ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
1290                        TTU_UNMAP|TTU_IGNORE_ACCESS,
1291                        &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1292        list_splice(&clean_pages, page_list);
1293        mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1294        return ret;
1295}
1296
1297/*
1298 * Attempt to remove the specified page from its LRU.  Only take this page
1299 * if it is of the appropriate PageActive status.  Pages which are being
1300 * freed elsewhere are also ignored.
1301 *
1302 * page:        page to consider
1303 * mode:        one of the LRU isolation modes defined above
1304 *
1305 * returns 0 on success, -ve errno on failure.
1306 */
1307int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1308{
1309        int ret = -EINVAL;
1310
1311        /* Only take pages on the LRU. */
1312        if (!PageLRU(page))
1313                return ret;
1314
1315        /* Compaction should not handle unevictable pages but CMA can do so */
1316        if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1317                return ret;
1318
1319        ret = -EBUSY;
1320
1321        /*
1322         * To minimise LRU disruption, the caller can indicate that it only
1323         * wants to isolate pages it will be able to operate on without
1324         * blocking - clean pages for the most part.
1325         *
1326         * ISOLATE_CLEAN means that only clean pages should be isolated. This
1327         * is used by reclaim when it is cannot write to backing storage
1328         *
1329         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1330         * that it is possible to migrate without blocking
1331         */
1332        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1333                /* All the caller can do on PageWriteback is block */
1334                if (PageWriteback(page))
1335                        return ret;
1336
1337                if (PageDirty(page)) {
1338                        struct address_space *mapping;
1339
1340                        /* ISOLATE_CLEAN means only clean pages */
1341                        if (mode & ISOLATE_CLEAN)
1342                                return ret;
1343
1344                        /*
1345                         * Only pages without mappings or that have a
1346                         * ->migratepage callback are possible to migrate
1347                         * without blocking
1348                         */
1349                        mapping = page_mapping(page);
1350                        if (mapping && !mapping->a_ops->migratepage)
1351                                return ret;
1352                }
1353        }
1354
1355        if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1356                return ret;
1357
1358        if (likely(get_page_unless_zero(page))) {
1359                /*
1360                 * Be careful not to clear PageLRU until after we're
1361                 * sure the page is not being freed elsewhere -- the
1362                 * page release code relies on it.
1363                 */
1364                ClearPageLRU(page);
1365                ret = 0;
1366        }
1367
1368        return ret;
1369}
1370
1371
1372/*
1373 * Update LRU sizes after isolating pages. The LRU size updates must
1374 * be complete before mem_cgroup_update_lru_size due to a santity check.
1375 */
1376static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1377                        enum lru_list lru, unsigned long *nr_zone_taken,
1378                        unsigned long nr_taken)
1379{
1380        int zid;
1381
1382        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1383                if (!nr_zone_taken[zid])
1384                        continue;
1385
1386                __update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1387        }
1388
1389#ifdef CONFIG_MEMCG
1390        mem_cgroup_update_lru_size(lruvec, lru, -nr_taken);
1391#endif
1392}
1393
1394/*
1395 * zone_lru_lock is heavily contended.  Some of the functions that
1396 * shrink the lists perform better by taking out a batch of pages
1397 * and working on them outside the LRU lock.
1398 *
1399 * For pagecache intensive workloads, this function is the hottest
1400 * spot in the kernel (apart from copy_*_user functions).
1401 *
1402 * Appropriate locks must be held before calling this function.
1403 *
1404 * @nr_to_scan: The number of pages to look through on the list.
1405 * @lruvec:     The LRU vector to pull pages from.
1406 * @dst:        The temp list to put pages on to.
1407 * @nr_scanned: The number of pages that were scanned.
1408 * @sc:         The scan_control struct for this reclaim session
1409 * @mode:       One of the LRU isolation modes
1410 * @lru:        LRU list id for isolating
1411 *
1412 * returns how many pages were moved onto *@dst.
1413 */
1414static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1415                struct lruvec *lruvec, struct list_head *dst,
1416                unsigned long *nr_scanned, struct scan_control *sc,
1417                isolate_mode_t mode, enum lru_list lru)
1418{
1419        struct list_head *src = &lruvec->lists[lru];
1420        unsigned long nr_taken = 0;
1421        unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1422        unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1423        unsigned long scan, nr_pages;
1424        LIST_HEAD(pages_skipped);
1425
1426        for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
1427                                        !list_empty(src);) {
1428                struct page *page;
1429
1430                page = lru_to_page(src);
1431                prefetchw_prev_lru_page(page, src, flags);
1432
1433                VM_BUG_ON_PAGE(!PageLRU(page), page);
1434
1435                if (page_zonenum(page) > sc->reclaim_idx) {
1436                        list_move(&page->lru, &pages_skipped);
1437                        nr_skipped[page_zonenum(page)]++;
1438                        continue;
1439                }
1440
1441                /*
1442                 * Account for scanned and skipped separetly to avoid the pgdat
1443                 * being prematurely marked unreclaimable by pgdat_reclaimable.
1444                 */
1445                scan++;
1446
1447                switch (__isolate_lru_page(page, mode)) {
1448                case 0:
1449                        nr_pages = hpage_nr_pages(page);
1450                        nr_taken += nr_pages;
1451                        nr_zone_taken[page_zonenum(page)] += nr_pages;
1452                        list_move(&page->lru, dst);
1453                        break;
1454
1455                case -EBUSY:
1456                        /* else it is being freed elsewhere */
1457                        list_move(&page->lru, src);
1458                        continue;
1459
1460                default:
1461                        BUG();
1462                }
1463        }
1464
1465        /*
1466         * Splice any skipped pages to the start of the LRU list. Note that
1467         * this disrupts the LRU order when reclaiming for lower zones but
1468         * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
1469         * scanning would soon rescan the same pages to skip and put the
1470         * system at risk of premature OOM.
1471         */
1472        if (!list_empty(&pages_skipped)) {
1473                int zid;
1474                unsigned long total_skipped = 0;
1475
1476                for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1477                        if (!nr_skipped[zid])
1478                                continue;
1479
1480                        __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1481                        total_skipped += nr_skipped[zid];
1482                }
1483
1484                /*
1485                 * Account skipped pages as a partial scan as the pgdat may be
1486                 * close to unreclaimable. If the LRU list is empty, account
1487                 * skipped pages as a full scan.
1488                 */
1489                scan += list_empty(src) ? total_skipped : total_skipped >> 2;
1490
1491                list_splice(&pages_skipped, src);
1492        }
1493        *nr_scanned = scan;
1494        trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,
1495                                    nr_taken, mode, is_file_lru(lru));
1496        update_lru_sizes(lruvec, lru, nr_zone_taken, nr_taken);
1497        return nr_taken;
1498}
1499
1500/**
1501 * isolate_lru_page - tries to isolate a page from its LRU list
1502 * @page: page to isolate from its LRU list
1503 *
1504 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1505 * vmstat statistic corresponding to whatever LRU list the page was on.
1506 *
1507 * Returns 0 if the page was removed from an LRU list.
1508 * Returns -EBUSY if the page was not on an LRU list.
1509 *
1510 * The returned page will have PageLRU() cleared.  If it was found on
1511 * the active list, it will have PageActive set.  If it was found on
1512 * the unevictable list, it will have the PageUnevictable bit set. That flag
1513 * may need to be cleared by the caller before letting the page go.
1514 *
1515 * The vmstat statistic corresponding to the list on which the page was
1516 * found will be decremented.
1517 *
1518 * Restrictions:
1519 * (1) Must be called with an elevated refcount on the page. This is a
1520 *     fundamentnal difference from isolate_lru_pages (which is called
1521 *     without a stable reference).
1522 * (2) the lru_lock must not be held.
1523 * (3) interrupts must be enabled.
1524 */
1525int isolate_lru_page(struct page *page)
1526{
1527        int ret = -EBUSY;
1528
1529        VM_BUG_ON_PAGE(!page_count(page), page);
1530        WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1531
1532        if (PageLRU(page)) {
1533                struct zone *zone = page_zone(page);
1534                struct lruvec *lruvec;
1535
1536                spin_lock_irq(zone_lru_lock(zone));
1537                lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
1538                if (PageLRU(page)) {
1539                        int lru = page_lru(page);
1540                        get_page(page);
1541                        ClearPageLRU(page);
1542                        del_page_from_lru_list(page, lruvec, lru);
1543                        ret = 0;
1544                }
1545                spin_unlock_irq(zone_lru_lock(zone));
1546        }
1547        return ret;
1548}
1549
1550/*
1551 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1552 * then get resheduled. When there are massive number of tasks doing page
1553 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1554 * the LRU list will go small and be scanned faster than necessary, leading to
1555 * unnecessary swapping, thrashing and OOM.
1556 */
1557static int too_many_isolated(struct pglist_data *pgdat, int file,
1558                struct scan_control *sc)
1559{
1560        unsigned long inactive, isolated;
1561
1562        if (current_is_kswapd())
1563                return 0;
1564
1565        if (!sane_reclaim(sc))
1566                return 0;
1567
1568        if (file) {
1569                inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
1570                isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1571        } else {
1572                inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
1573                isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1574        }
1575
1576        /*
1577         * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1578         * won't get blocked by normal direct-reclaimers, forming a circular
1579         * deadlock.
1580         */
1581        if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1582                inactive >>= 3;
1583
1584        return isolated > inactive;
1585}
1586
1587static noinline_for_stack void
1588putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1589{
1590        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1591        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1592        LIST_HEAD(pages_to_free);
1593
1594        /*
1595         * Put back any unfreeable pages.
1596         */
1597        while (!list_empty(page_list)) {
1598                struct page *page = lru_to_page(page_list);
1599                int lru;
1600
1601                VM_BUG_ON_PAGE(PageLRU(page), page);
1602                list_del(&page->lru);
1603                if (unlikely(!page_evictable(page))) {
1604                        spin_unlock_irq(&pgdat->lru_lock);
1605                        putback_lru_page(page);
1606                        spin_lock_irq(&pgdat->lru_lock);
1607                        continue;
1608                }
1609
1610                lruvec = mem_cgroup_page_lruvec(page, pgdat);
1611
1612                SetPageLRU(page);
1613                lru = page_lru(page);
1614                add_page_to_lru_list(page, lruvec, lru);
1615
1616                if (is_active_lru(lru)) {
1617                        int file = is_file_lru(lru);
1618                        int numpages = hpage_nr_pages(page);
1619                        reclaim_stat->recent_rotated[file] += numpages;
1620                }
1621                if (put_page_testzero(page)) {
1622                        __ClearPageLRU(page);
1623                        __ClearPageActive(page);
1624                        del_page_from_lru_list(page, lruvec, lru);
1625
1626                        if (unlikely(PageCompound(page))) {
1627                                spin_unlock_irq(&pgdat->lru_lock);
1628                                mem_cgroup_uncharge(page);
1629                                (*get_compound_page_dtor(page))(page);
1630                                spin_lock_irq(&pgdat->lru_lock);
1631                        } else
1632                                list_add(&page->lru, &pages_to_free);
1633                }
1634        }
1635
1636        /*
1637         * To save our caller's stack, now use input list for pages to free.
1638         */
1639        list_splice(&pages_to_free, page_list);
1640}
1641
1642/*
1643 * If a kernel thread (such as nfsd for loop-back mounts) services
1644 * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
1645 * In that case we should only throttle if the backing device it is
1646 * writing to is congested.  In other cases it is safe to throttle.
1647 */
1648static int current_may_throttle(void)
1649{
1650        return !(current->flags & PF_LESS_THROTTLE) ||
1651                current->backing_dev_info == NULL ||
1652                bdi_write_congested(current->backing_dev_info);
1653}
1654
1655static bool inactive_reclaimable_pages(struct lruvec *lruvec,
1656                                struct scan_control *sc, enum lru_list lru)
1657{
1658        int zid;
1659        struct zone *zone;
1660        int file = is_file_lru(lru);
1661        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1662
1663        if (!global_reclaim(sc))
1664                return true;
1665
1666        for (zid = sc->reclaim_idx; zid >= 0; zid--) {
1667                zone = &pgdat->node_zones[zid];
1668                if (!managed_zone(zone))
1669                        continue;
1670
1671                if (zone_page_state_snapshot(zone, NR_ZONE_LRU_BASE +
1672                                LRU_FILE * file) >= SWAP_CLUSTER_MAX)
1673                        return true;
1674        }
1675
1676        return false;
1677}
1678
1679/*
1680 * shrink_inactive_list() is a helper for shrink_node().  It returns the number
1681 * of reclaimed pages
1682 */
1683static noinline_for_stack unsigned long
1684shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1685                     struct scan_control *sc, enum lru_list lru)
1686{
1687        LIST_HEAD(page_list);
1688        unsigned long nr_scanned;
1689        unsigned long nr_reclaimed = 0;
1690        unsigned long nr_taken;
1691        unsigned long nr_dirty = 0;
1692        unsigned long nr_congested = 0;
1693        unsigned long nr_unqueued_dirty = 0;
1694        unsigned long nr_writeback = 0;
1695        unsigned long nr_immediate = 0;
1696        isolate_mode_t isolate_mode = 0;
1697        int file = is_file_lru(lru);
1698        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1699        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1700
1701        if (!inactive_reclaimable_pages(lruvec, sc, lru))
1702                return 0;
1703
1704        while (unlikely(too_many_isolated(pgdat, file, sc))) {
1705                congestion_wait(BLK_RW_ASYNC, HZ/10);
1706
1707                /* We are about to die and free our memory. Return now. */
1708                if (fatal_signal_pending(current))
1709                        return SWAP_CLUSTER_MAX;
1710        }
1711
1712        lru_add_drain();
1713
1714        if (!sc->may_unmap)
1715                isolate_mode |= ISOLATE_UNMAPPED;
1716        if (!sc->may_writepage)
1717                isolate_mode |= ISOLATE_CLEAN;
1718
1719        spin_lock_irq(&pgdat->lru_lock);
1720
1721        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1722                                     &nr_scanned, sc, isolate_mode, lru);
1723
1724        __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1725        reclaim_stat->recent_scanned[file] += nr_taken;
1726
1727        if (global_reclaim(sc)) {
1728                __mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
1729                if (current_is_kswapd())
1730                        __count_vm_events(PGSCAN_KSWAPD, nr_scanned);
1731                else
1732                        __count_vm_events(PGSCAN_DIRECT, nr_scanned);
1733        }
1734        spin_unlock_irq(&pgdat->lru_lock);
1735
1736        if (nr_taken == 0)
1737                return 0;
1738
1739        nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, TTU_UNMAP,
1740                                &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1741                                &nr_writeback, &nr_immediate,
1742                                false);
1743
1744        spin_lock_irq(&pgdat->lru_lock);
1745
1746        if (global_reclaim(sc)) {
1747                if (current_is_kswapd())
1748                        __count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
1749                else
1750                        __count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
1751        }
1752
1753        putback_inactive_pages(lruvec, &page_list);
1754
1755        __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1756
1757        spin_unlock_irq(&pgdat->lru_lock);
1758
1759        mem_cgroup_uncharge_list(&page_list);
1760        free_hot_cold_page_list(&page_list, true);
1761
1762        /*
1763         * If reclaim is isolating dirty pages under writeback, it implies
1764         * that the long-lived page allocation rate is exceeding the page
1765         * laundering rate. Either the global limits are not being effective
1766         * at throttling processes due to the page distribution throughout
1767         * zones or there is heavy usage of a slow backing device. The
1768         * only option is to throttle from reclaim context which is not ideal
1769         * as there is no guarantee the dirtying process is throttled in the
1770         * same way balance_dirty_pages() manages.
1771         *
1772         * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1773         * of pages under pages flagged for immediate reclaim and stall if any
1774         * are encountered in the nr_immediate check below.
1775         */
1776        if (nr_writeback && nr_writeback == nr_taken)
1777                set_bit(PGDAT_WRITEBACK, &pgdat->flags);
1778
1779        /*
1780         * Legacy memcg will stall in page writeback so avoid forcibly
1781         * stalling here.
1782         */
1783        if (sane_reclaim(sc)) {
1784                /*
1785                 * Tag a zone as congested if all the dirty pages scanned were
1786                 * backed by a congested BDI and wait_iff_congested will stall.
1787                 */
1788                if (nr_dirty && nr_dirty == nr_congested)
1789                        set_bit(PGDAT_CONGESTED, &pgdat->flags);
1790
1791                /*
1792                 * If dirty pages are scanned that are not queued for IO, it
1793                 * implies that flushers are not keeping up. In this case, flag
1794                 * the pgdat PGDAT_DIRTY and kswapd will start writing pages from
1795                 * reclaim context.
1796                 */
1797                if (nr_unqueued_dirty == nr_taken)
1798                        set_bit(PGDAT_DIRTY, &pgdat->flags);
1799
1800                /*
1801                 * If kswapd scans pages marked marked for immediate
1802                 * reclaim and under writeback (nr_immediate), it implies
1803                 * that pages are cycling through the LRU faster than
1804                 * they are written so also forcibly stall.
1805                 */
1806                if (nr_immediate && current_may_throttle())
1807                        congestion_wait(BLK_RW_ASYNC, HZ/10);
1808        }
1809
1810        /*
1811         * Stall direct reclaim for IO completions if underlying BDIs or zone
1812         * is congested. Allow kswapd to continue until it starts encountering
1813         * unqueued dirty pages or cycling through the LRU too quickly.
1814         */
1815        if (!sc->hibernation_mode && !current_is_kswapd() &&
1816            current_may_throttle())
1817                wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);
1818
1819        trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
1820                        nr_scanned, nr_reclaimed,
1821                        sc->priority, file);
1822        return nr_reclaimed;
1823}
1824
1825/*
1826 * This moves pages from the active list to the inactive list.
1827 *
1828 * We move them the other way if the page is referenced by one or more
1829 * processes, from rmap.
1830 *
1831 * If the pages are mostly unmapped, the processing is fast and it is
1832 * appropriate to hold zone_lru_lock across the whole operation.  But if
1833 * the pages are mapped, the processing is slow (page_referenced()) so we
1834 * should drop zone_lru_lock around each page.  It's impossible to balance
1835 * this, so instead we remove the pages from the LRU while processing them.
1836 * It is safe to rely on PG_active against the non-LRU pages in here because
1837 * nobody will play with that bit on a non-LRU page.
1838 *
1839 * The downside is that we have to touch page->_refcount against each page.
1840 * But we had to alter page->flags anyway.
1841 */
1842
1843static void move_active_pages_to_lru(struct lruvec *lruvec,
1844                                     struct list_head *list,
1845                                     struct list_head *pages_to_free,
1846                                     enum lru_list lru)
1847{
1848        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1849        unsigned long pgmoved = 0;
1850        struct page *page;
1851        int nr_pages;
1852
1853        while (!list_empty(list)) {
1854                page = lru_to_page(list);
1855                lruvec = mem_cgroup_page_lruvec(page, pgdat);
1856
1857                VM_BUG_ON_PAGE(PageLRU(page), page);
1858                SetPageLRU(page);
1859
1860                nr_pages = hpage_nr_pages(page);
1861                update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
1862                list_move(&page->lru, &lruvec->lists[lru]);
1863                pgmoved += nr_pages;
1864
1865                if (put_page_testzero(page)) {
1866                        __ClearPageLRU(page);
1867                        __ClearPageActive(page);
1868                        del_page_from_lru_list(page, lruvec, lru);
1869
1870                        if (unlikely(PageCompound(page))) {
1871                                spin_unlock_irq(&pgdat->lru_lock);
1872                                mem_cgroup_uncharge(page);
1873                                (*get_compound_page_dtor(page))(page);
1874                                spin_lock_irq(&pgdat->lru_lock);
1875                        } else
1876                                list_add(&page->lru, pages_to_free);
1877                }
1878        }
1879
1880        if (!is_active_lru(lru))
1881                __count_vm_events(PGDEACTIVATE, pgmoved);
1882}
1883
1884static void shrink_active_list(unsigned long nr_to_scan,
1885                               struct lruvec *lruvec,
1886                               struct scan_control *sc,
1887                               enum lru_list lru)
1888{
1889        unsigned long nr_taken;
1890        unsigned long nr_scanned;
1891        unsigned long vm_flags;
1892        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1893        LIST_HEAD(l_active);
1894        LIST_HEAD(l_inactive);
1895        struct page *page;
1896        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1897        unsigned long nr_rotated = 0;
1898        isolate_mode_t isolate_mode = 0;
1899        int file = is_file_lru(lru);
1900        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1901
1902        lru_add_drain();
1903
1904        if (!sc->may_unmap)
1905                isolate_mode |= ISOLATE_UNMAPPED;
1906        if (!sc->may_writepage)
1907                isolate_mode |= ISOLATE_CLEAN;
1908
1909        spin_lock_irq(&pgdat->lru_lock);
1910
1911        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1912                                     &nr_scanned, sc, isolate_mode, lru);
1913
1914        __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1915        reclaim_stat->recent_scanned[file] += nr_taken;
1916
1917        if (global_reclaim(sc))
1918                __mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
1919        __count_vm_events(PGREFILL, nr_scanned);
1920
1921        spin_unlock_irq(&pgdat->lru_lock);
1922
1923        while (!list_empty(&l_hold)) {
1924                cond_resched();
1925                page = lru_to_page(&l_hold);
1926                list_del(&page->lru);
1927
1928                if (unlikely(!page_evictable(page))) {
1929                        putback_lru_page(page);
1930                        continue;
1931                }
1932
1933                if (unlikely(buffer_heads_over_limit)) {
1934                        if (page_has_private(page) && trylock_page(page)) {
1935                                if (page_has_private(page))
1936                                        try_to_release_page(page, 0);
1937                                unlock_page(page);
1938                        }
1939                }
1940
1941                if (page_referenced(page, 0, sc->target_mem_cgroup,
1942                                    &vm_flags)) {
1943                        nr_rotated += hpage_nr_pages(page);
1944                        /*
1945                         * Identify referenced, file-backed active pages and
1946                         * give them one more trip around the active list. So
1947                         * that executable code get better chances to stay in
1948                         * memory under moderate memory pressure.  Anon pages
1949                         * are not likely to be evicted by use-once streaming
1950                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1951                         * so we ignore them here.
1952                         */
1953                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1954                                list_add(&page->lru, &l_active);
1955                                continue;
1956                        }
1957                }
1958
1959                ClearPageActive(page);  /* we are de-activating */
1960                list_add(&page->lru, &l_inactive);
1961        }
1962
1963        /*
1964         * Move pages back to the lru list.
1965         */
1966        spin_lock_irq(&pgdat->lru_lock);
1967        /*
1968         * Count referenced pages from currently used mappings as rotated,
1969         * even though only some of them are actually re-activated.  This
1970         * helps balance scan pressure between file and anonymous pages in
1971         * get_scan_count.
1972         */
1973        reclaim_stat->recent_rotated[file] += nr_rotated;
1974
1975        move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1976        move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1977        __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1978        spin_unlock_irq(&pgdat->lru_lock);
1979
1980        mem_cgroup_uncharge_list(&l_hold);
1981        free_hot_cold_page_list(&l_hold, true);
1982}
1983
1984/*
1985 * The inactive anon list should be small enough that the VM never has
1986 * to do too much work.
1987 *
1988 * The inactive file list should be small enough to leave most memory
1989 * to the established workingset on the scan-resistant active list,
1990 * but large enough to avoid thrashing the aggregate readahead window.
1991 *
1992 * Both inactive lists should also be large enough that each inactive
1993 * page has a chance to be referenced again before it is reclaimed.
1994 *
1995 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
1996 * on this LRU, maintained by the pageout code. A zone->inactive_ratio
1997 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
1998 *
1999 * total     target    max
2000 * memory    ratio     inactive
2001 * -------------------------------------
2002 *   10MB       1         5MB
2003 *  100MB       1        50MB
2004 *    1GB       3       250MB
2005 *   10GB      10       0.9GB
2006 *  100GB      31         3GB
2007 *    1TB     101        10GB
2008 *   10TB     320        32GB
2009 */
2010static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2011                                                struct scan_control *sc)
2012{
2013        unsigned long inactive_ratio;
2014        unsigned long inactive;
2015        unsigned long active;
2016        unsigned long gb;
2017        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2018        int zid;
2019
2020        /*
2021         * If we don't have swap space, anonymous page deactivation
2022         * is pointless.
2023         */
2024        if (!file && !total_swap_pages)
2025                return false;
2026
2027        inactive = lruvec_lru_size(lruvec, file * LRU_FILE);
2028        active = lruvec_lru_size(lruvec, file * LRU_FILE + LRU_ACTIVE);
2029
2030        /*
2031         * For zone-constrained allocations, it is necessary to check if
2032         * deactivations are required for lowmem to be reclaimed. This
2033         * calculates the inactive/active pages available in eligible zones.
2034         */
2035        for (zid = sc->reclaim_idx + 1; zid < MAX_NR_ZONES; zid++) {
2036                struct zone *zone = &pgdat->node_zones[zid];
2037                unsigned long inactive_zone, active_zone;
2038
2039                if (!managed_zone(zone))
2040                        continue;
2041
2042                inactive_zone = zone_page_state(zone,
2043                                NR_ZONE_LRU_BASE + (file * LRU_FILE));
2044                active_zone = zone_page_state(zone,
2045                                NR_ZONE_LRU_BASE + (file * LRU_FILE) + LRU_ACTIVE);
2046
2047                inactive -= min(inactive, inactive_zone);
2048                active -= min(active, active_zone);
2049        }
2050
2051        gb = (inactive + active) >> (30 - PAGE_SHIFT);
2052        if (gb)
2053                inactive_ratio = int_sqrt(10 * gb);
2054        else
2055                inactive_ratio = 1;
2056
2057        return inactive * inactive_ratio < active;
2058}
2059
2060static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2061                                 struct lruvec *lruvec, struct scan_control *sc)
2062{
2063        if (is_active_lru(lru)) {
2064                if (inactive_list_is_low(lruvec, is_file_lru(lru), sc))
2065                        shrink_active_list(nr_to_scan, lruvec, sc, lru);
2066                return 0;
2067        }
2068
2069        return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2070}
2071
2072enum scan_balance {
2073        SCAN_EQUAL,
2074        SCAN_FRACT,
2075        SCAN_ANON,
2076        SCAN_FILE,
2077};
2078
2079/*
2080 * Determine how aggressively the anon and file LRU lists should be
2081 * scanned.  The relative value of each set of LRU lists is determined
2082 * by looking at the fraction of the pages scanned we did rotate back
2083 * onto the active list instead of evict.
2084 *
2085 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
2086 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
2087 */
2088static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2089                           struct scan_control *sc, unsigned long *nr,
2090                           unsigned long *lru_pages)
2091{
2092        int swappiness = mem_cgroup_swappiness(memcg);
2093        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2094        u64 fraction[2];
2095        u64 denominator = 0;    /* gcc */
2096        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2097        unsigned long anon_prio, file_prio;
2098        enum scan_balance scan_balance;
2099        unsigned long anon, file;
2100        bool force_scan = false;
2101        unsigned long ap, fp;
2102        enum lru_list lru;
2103        bool some_scanned;
2104        int pass;
2105
2106        /*
2107         * If the zone or memcg is small, nr[l] can be 0.  This
2108         * results in no scanning on this priority and a potential
2109         * priority drop.  Global direct reclaim can go to the next
2110         * zone and tends to have no problems. Global kswapd is for
2111         * zone balancing and it needs to scan a minimum amount. When
2112         * reclaiming for a memcg, a priority drop can cause high
2113         * latencies, so it's better to scan a minimum amount there as
2114         * well.
2115         */
2116        if (current_is_kswapd()) {
2117                if (!pgdat_reclaimable(pgdat))
2118                        force_scan = true;
2119                if (!mem_cgroup_online(memcg))
2120                        force_scan = true;
2121        }
2122        if (!global_reclaim(sc))
2123                force_scan = true;
2124
2125        /* If we have no swap space, do not bother scanning anon pages. */
2126        if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2127                scan_balance = SCAN_FILE;
2128                goto out;
2129        }
2130
2131        /*
2132         * Global reclaim will swap to prevent OOM even with no
2133         * swappiness, but memcg users want to use this knob to
2134         * disable swapping for individual groups completely when
2135         * using the memory controller's swap limit feature would be
2136         * too expensive.
2137         */
2138        if (!global_reclaim(sc) && !swappiness) {
2139                scan_balance = SCAN_FILE;
2140                goto out;
2141        }
2142
2143        /*
2144         * Do not apply any pressure balancing cleverness when the
2145         * system is close to OOM, scan both anon and file equally
2146         * (unless the swappiness setting disagrees with swapping).
2147         */
2148        if (!sc->priority && swappiness) {
2149                scan_balance = SCAN_EQUAL;
2150                goto out;
2151        }
2152
2153        /*
2154         * Prevent the reclaimer from falling into the cache trap: as
2155         * cache pages start out inactive, every cache fault will tip
2156         * the scan balance towards the file LRU.  And as the file LRU
2157         * shrinks, so does the window for rotation from references.
2158         * This means we have a runaway feedback loop where a tiny
2159         * thrashing file LRU becomes infinitely more attractive than
2160         * anon pages.  Try to detect this based on file LRU size.
2161         */
2162        if (global_reclaim(sc)) {
2163                unsigned long pgdatfile;
2164                unsigned long pgdatfree;
2165                int z;
2166                unsigned long total_high_wmark = 0;
2167
2168                pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
2169                pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
2170                           node_page_state(pgdat, NR_INACTIVE_FILE);
2171
2172                for (z = 0; z < MAX_NR_ZONES; z++) {
2173                        struct zone *zone = &pgdat->node_zones[z];
2174                        if (!managed_zone(zone))
2175                                continue;
2176
2177                        total_high_wmark += high_wmark_pages(zone);
2178                }
2179
2180                if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2181                        scan_balance = SCAN_ANON;
2182                        goto out;
2183                }
2184        }
2185
2186        /*
2187         * If there is enough inactive page cache, i.e. if the size of the
2188         * inactive list is greater than that of the active list *and* the
2189         * inactive list actually has some pages to scan on this priority, we
2190         * do not reclaim anything from the anonymous working set right now.
2191         * Without the second condition we could end up never scanning an
2192         * lruvec even if it has plenty of old anonymous pages unless the
2193         * system is under heavy pressure.
2194         */
2195        if (!inactive_list_is_low(lruvec, true, sc) &&
2196            lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
2197                scan_balance = SCAN_FILE;
2198                goto out;
2199        }
2200
2201        scan_balance = SCAN_FRACT;
2202
2203        /*
2204         * With swappiness at 100, anonymous and file have the same priority.
2205         * This scanning priority is essentially the inverse of IO cost.
2206         */
2207        anon_prio = swappiness;
2208        file_prio = 200 - anon_prio;
2209
2210        /*
2211         * OK, so we have swap space and a fair amount of page cache
2212         * pages.  We use the recently rotated / recently scanned
2213         * ratios to determine how valuable each cache is.
2214         *
2215         * Because workloads change over time (and to avoid overflow)
2216         * we keep these statistics as a floating average, which ends
2217         * up weighing recent references more than old ones.
2218         *
2219         * anon in [0], file in [1]
2220         */
2221
2222        anon  = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON) +
2223                lruvec_lru_size(lruvec, LRU_INACTIVE_ANON);
2224        file  = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE) +
2225                lruvec_lru_size(lruvec, LRU_INACTIVE_FILE);
2226
2227        spin_lock_irq(&pgdat->lru_lock);
2228        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
2229                reclaim_stat->recent_scanned[0] /= 2;
2230                reclaim_stat->recent_rotated[0] /= 2;
2231        }
2232
2233        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
2234                reclaim_stat->recent_scanned[1] /= 2;
2235                reclaim_stat->recent_rotated[1] /= 2;
2236        }
2237
2238        /*
2239         * The amount of pressure on anon vs file pages is inversely
2240         * proportional to the fraction of recently scanned pages on
2241         * each list that were recently referenced and in active use.
2242         */
2243        ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2244        ap /= reclaim_stat->recent_rotated[0] + 1;
2245
2246        fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2247        fp /= reclaim_stat->recent_rotated[1] + 1;
2248        spin_unlock_irq(&pgdat->lru_lock);
2249
2250        fraction[0] = ap;
2251        fraction[1] = fp;
2252        denominator = ap + fp + 1;
2253out:
2254        some_scanned = false;
2255        /* Only use force_scan on second pass. */
2256        for (pass = 0; !some_scanned && pass < 2; pass++) {
2257                *lru_pages = 0;
2258                for_each_evictable_lru(lru) {
2259                        int file = is_file_lru(lru);
2260                        unsigned long size;
2261                        unsigned long scan;
2262
2263                        size = lruvec_lru_size(lruvec, lru);
2264                        scan = size >> sc->priority;
2265
2266                        if (!scan && pass && force_scan)
2267                                scan = min(size, SWAP_CLUSTER_MAX);
2268
2269                        switch (scan_balance) {
2270                        case SCAN_EQUAL:
2271                                /* Scan lists relative to size */
2272                                break;
2273                        case SCAN_FRACT:
2274                                /*
2275                                 * Scan types proportional to swappiness and
2276                                 * their relative recent reclaim efficiency.
2277                                 */
2278                                scan = div64_u64(scan * fraction[file],
2279                                                        denominator);
2280                                break;
2281                        case SCAN_FILE:
2282                        case SCAN_ANON:
2283                                /* Scan one type exclusively */
2284                                if ((scan_balance == SCAN_FILE) != file) {
2285                                        size = 0;
2286                                        scan = 0;
2287                                }
2288                                break;
2289                        default:
2290                                /* Look ma, no brain */
2291                                BUG();
2292                        }
2293
2294                        *lru_pages += size;
2295                        nr[lru] = scan;
2296
2297                        /*
2298                         * Skip the second pass and don't force_scan,
2299                         * if we found something to scan.
2300                         */
2301                        some_scanned |= !!scan;
2302                }
2303        }
2304}
2305
2306/*
2307 * This is a basic per-node page freer.  Used by both kswapd and direct reclaim.
2308 */
2309static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2310                              struct scan_control *sc, unsigned long *lru_pages)
2311{
2312        struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2313        unsigned long nr[NR_LRU_LISTS];
2314        unsigned long targets[NR_LRU_LISTS];
2315        unsigned long nr_to_scan;
2316        enum lru_list lru;
2317        unsigned long nr_reclaimed = 0;
2318        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2319        struct blk_plug plug;
2320        bool scan_adjusted;
2321
2322        get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2323
2324        /* Record the original scan target for proportional adjustments later */
2325        memcpy(targets, nr, sizeof(nr));
2326
2327        /*
2328         * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2329         * event that can occur when there is little memory pressure e.g.
2330         * multiple streaming readers/writers. Hence, we do not abort scanning
2331         * when the requested number of pages are reclaimed when scanning at
2332         * DEF_PRIORITY on the assumption that the fact we are direct
2333         * reclaiming implies that kswapd is not keeping up and it is best to
2334         * do a batch of work at once. For memcg reclaim one check is made to
2335         * abort proportional reclaim if either the file or anon lru has already
2336         * dropped to zero at the first pass.
2337         */
2338        scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
2339                         sc->priority == DEF_PRIORITY);
2340
2341        blk_start_plug(&plug);
2342        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2343                                        nr[LRU_INACTIVE_FILE]) {
2344                unsigned long nr_anon, nr_file, percentage;
2345                unsigned long nr_scanned;
2346
2347                for_each_evictable_lru(lru) {
2348                        if (nr[lru]) {
2349                                nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2350                                nr[lru] -= nr_to_scan;
2351
2352                                nr_reclaimed += shrink_list(lru, nr_to_scan,
2353                                                            lruvec, sc);
2354                        }
2355                }
2356
2357                cond_resched();
2358
2359                if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2360                        continue;
2361
2362                /*
2363                 * For kswapd and memcg, reclaim at least the number of pages
2364                 * requested. Ensure that the anon and file LRUs are scanned
2365                 * proportionally what was requested by get_scan_count(). We
2366                 * stop reclaiming one LRU and reduce the amount scanning
2367                 * proportional to the original scan target.
2368                 */
2369                nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2370                nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2371
2372                /*
2373                 * It's just vindictive to attack the larger once the smaller
2374                 * has gone to zero.  And given the way we stop scanning the
2375                 * smaller below, this makes sure that we only make one nudge
2376                 * towards proportionality once we've got nr_to_reclaim.
2377                 */
2378                if (!nr_file || !nr_anon)
2379                        break;
2380
2381                if (nr_file > nr_anon) {
2382                        unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2383                                                targets[LRU_ACTIVE_ANON] + 1;
2384                        lru = LRU_BASE;
2385                        percentage = nr_anon * 100 / scan_target;
2386                } else {
2387                        unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2388                                                targets[LRU_ACTIVE_FILE] + 1;
2389                        lru = LRU_FILE;
2390                        percentage = nr_file * 100 / scan_target;
2391                }
2392
2393                /* Stop scanning the smaller of the LRU */
2394                nr[lru] = 0;
2395                nr[lru + LRU_ACTIVE] = 0;
2396
2397                /*
2398                 * Recalculate the other LRU scan count based on its original
2399                 * scan target and the percentage scanning already complete
2400                 */
2401                lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2402                nr_scanned = targets[lru] - nr[lru];
2403                nr[lru] = targets[lru] * (100 - percentage) / 100;
2404                nr[lru] -= min(nr[lru], nr_scanned);
2405
2406                lru += LRU_ACTIVE;
2407                nr_scanned = targets[lru] - nr[lru];
2408                nr[lru] = targets[lru] * (100 - percentage) / 100;
2409                nr[lru] -= min(nr[lru], nr_scanned);
2410
2411                scan_adjusted = true;
2412        }
2413        blk_finish_plug(&plug);
2414        sc->nr_reclaimed += nr_reclaimed;
2415
2416        /*
2417         * Even if we did not try to evict anon pages at all, we want to
2418         * rebalance the anon lru active/inactive ratio.
2419         */
2420        if (inactive_list_is_low(lruvec, false, sc))
2421                shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2422                                   sc, LRU_ACTIVE_ANON);
2423}
2424
2425/* Use reclaim/compaction for costly allocs or under memory pressure */
2426static bool in_reclaim_compaction(struct scan_control *sc)
2427{
2428        if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2429                        (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2430                         sc->priority < DEF_PRIORITY - 2))
2431                return true;
2432
2433        return false;
2434}
2435
2436/*
2437 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2438 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2439 * true if more pages should be reclaimed such that when the page allocator
2440 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2441 * It will give up earlier than that if there is difficulty reclaiming pages.
2442 */
2443static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2444                                        unsigned long nr_reclaimed,
2445                                        unsigned long nr_scanned,
2446                                        struct scan_control *sc)
2447{
2448        unsigned long pages_for_compaction;
2449        unsigned long inactive_lru_pages;
2450        int z;
2451
2452        /* If not in reclaim/compaction mode, stop */
2453        if (!in_reclaim_compaction(sc))
2454                return false;
2455
2456        /* Consider stopping depending on scan and reclaim activity */
2457        if (sc->gfp_mask & __GFP_REPEAT) {
2458                /*
2459                 * For __GFP_REPEAT allocations, stop reclaiming if the
2460                 * full LRU list has been scanned and we are still failing
2461                 * to reclaim pages. This full LRU scan is potentially
2462                 * expensive but a __GFP_REPEAT caller really wants to succeed
2463                 */
2464                if (!nr_reclaimed && !nr_scanned)
2465                        return false;
2466        } else {
2467                /*
2468                 * For non-__GFP_REPEAT allocations which can presumably
2469                 * fail without consequence, stop if we failed to reclaim
2470                 * any pages from the last SWAP_CLUSTER_MAX number of
2471                 * pages that were scanned. This will return to the
2472                 * caller faster at the risk reclaim/compaction and
2473                 * the resulting allocation attempt fails
2474                 */
2475                if (!nr_reclaimed)
2476                        return false;
2477        }
2478
2479        /*
2480         * If we have not reclaimed enough pages for compaction and the
2481         * inactive lists are large enough, continue reclaiming
2482         */
2483        pages_for_compaction = compact_gap(sc->order);
2484        inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2485        if (get_nr_swap_pages() > 0)
2486                inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2487        if (sc->nr_reclaimed < pages_for_compaction &&
2488                        inactive_lru_pages > pages_for_compaction)
2489                return true;
2490
2491        /* If compaction would go ahead or the allocation would succeed, stop */
2492        for (z = 0; z <= sc->reclaim_idx; z++) {
2493                struct zone *zone = &pgdat->node_zones[z];
2494                if (!managed_zone(zone))
2495                        continue;
2496
2497                switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2498                case COMPACT_SUCCESS:
2499                case COMPACT_CONTINUE:
2500                        return false;
2501                default:
2502                        /* check next zone */
2503                        ;
2504                }
2505        }
2506        return true;
2507}
2508
2509static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
2510{
2511        struct reclaim_state *reclaim_state = current->reclaim_state;
2512        unsigned long nr_reclaimed, nr_scanned;
2513        bool reclaimable = false;
2514
2515        do {
2516                struct mem_cgroup *root = sc->target_mem_cgroup;
2517                struct mem_cgroup_reclaim_cookie reclaim = {
2518                        .pgdat = pgdat,
2519                        .priority = sc->priority,
2520                };
2521                unsigned long node_lru_pages = 0;
2522                struct mem_cgroup *memcg;
2523
2524                nr_reclaimed = sc->nr_reclaimed;
2525                nr_scanned = sc->nr_scanned;
2526
2527                memcg = mem_cgroup_iter(root, NULL, &reclaim);
2528                do {
2529                        unsigned long lru_pages;
2530                        unsigned long reclaimed;
2531                        unsigned long scanned;
2532
2533                        if (mem_cgroup_low(root, memcg)) {
2534                                if (!sc->may_thrash)
2535                                        continue;
2536                                mem_cgroup_events(memcg, MEMCG_LOW, 1);
2537                        }
2538
2539                        reclaimed = sc->nr_reclaimed;
2540                        scanned = sc->nr_scanned;
2541
2542                        shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
2543                        node_lru_pages += lru_pages;
2544
2545                        if (memcg)
2546                                shrink_slab(sc->gfp_mask, pgdat->node_id,
2547                                            memcg, sc->nr_scanned - scanned,
2548                                            lru_pages);
2549
2550                        /* Record the group's reclaim efficiency */
2551                        vmpressure(sc->gfp_mask, memcg, false,
2552                                   sc->nr_scanned - scanned,
2553                                   sc->nr_reclaimed - reclaimed);
2554
2555                        /*
2556                         * Direct reclaim and kswapd have to scan all memory
2557                         * cgroups to fulfill the overall scan target for the
2558                         * node.
2559                         *
2560                         * Limit reclaim, on the other hand, only cares about
2561                         * nr_to_reclaim pages to be reclaimed and it will
2562                         * retry with decreasing priority if one round over the
2563                         * whole hierarchy is not sufficient.
2564                         */
2565                        if (!global_reclaim(sc) &&
2566                                        sc->nr_reclaimed >= sc->nr_to_reclaim) {
2567                                mem_cgroup_iter_break(root, memcg);
2568                                break;
2569                        }
2570                } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2571
2572                /*
2573                 * Shrink the slab caches in the same proportion that
2574                 * the eligible LRU pages were scanned.
2575                 */
2576                if (global_reclaim(sc))
2577                        shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
2578                                    sc->nr_scanned - nr_scanned,
2579                                    node_lru_pages);
2580
2581                if (reclaim_state) {
2582                        sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2583                        reclaim_state->reclaimed_slab = 0;
2584                }
2585
2586                /* Record the subtree's reclaim efficiency */
2587                vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2588                           sc->nr_scanned - nr_scanned,
2589                           sc->nr_reclaimed - nr_reclaimed);
2590
2591                if (sc->nr_reclaimed - nr_reclaimed)
2592                        reclaimable = true;
2593
2594        } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2595                                         sc->nr_scanned - nr_scanned, sc));
2596
2597        return reclaimable;
2598}
2599
2600/*
2601 * Returns true if compaction should go ahead for a costly-order request, or
2602 * the allocation would already succeed without compaction. Return false if we
2603 * should reclaim first.
2604 */
2605static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2606{
2607        unsigned long watermark;
2608        enum compact_result suitable;
2609
2610        suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
2611        if (suitable == COMPACT_SUCCESS)
2612                /* Allocation should succeed already. Don't reclaim. */
2613                return true;
2614        if (suitable == COMPACT_SKIPPED)
2615                /* Compaction cannot yet proceed. Do reclaim. */
2616                return false;
2617
2618        /*
2619         * Compaction is already possible, but it takes time to run and there
2620         * are potentially other callers using the pages just freed. So proceed
2621         * with reclaim to make a buffer of free pages available to give
2622         * compaction a reasonable chance of completing and allocating the page.
2623         * Note that we won't actually reclaim the whole buffer in one attempt
2624         * as the target watermark in should_continue_reclaim() is lower. But if
2625         * we are already above the high+gap watermark, don't reclaim at all.
2626         */
2627        watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2628
2629        return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2630}
2631
2632/*
2633 * This is the direct reclaim path, for page-allocating processes.  We only
2634 * try to reclaim pages from zones which will satisfy the caller's allocation
2635 * request.
2636 *
2637 * If a zone is deemed to be full of pinned pages then just give it a light
2638 * scan then give up on it.
2639 */
2640static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2641{
2642        struct zoneref *z;
2643        struct zone *zone;
2644        unsigned long nr_soft_reclaimed;
2645        unsigned long nr_soft_scanned;
2646        gfp_t orig_mask;
2647        pg_data_t *last_pgdat = NULL;
2648
2649        /*
2650         * If the number of buffer_heads in the machine exceeds the maximum
2651         * allowed level, force direct reclaim to scan the highmem zone as
2652         * highmem pages could be pinning lowmem pages storing buffer_heads
2653         */
2654        orig_mask = sc->gfp_mask;
2655        if (buffer_heads_over_limit) {
2656                sc->gfp_mask |= __GFP_HIGHMEM;
2657                sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2658        }
2659
2660        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2661                                        sc->reclaim_idx, sc->nodemask) {
2662                /*
2663                 * Take care memory controller reclaiming has small influence
2664                 * to global LRU.
2665                 */
2666                if (global_reclaim(sc)) {
2667                        if (!cpuset_zone_allowed(zone,
2668                                                 GFP_KERNEL | __GFP_HARDWALL))
2669                                continue;
2670
2671                        if (sc->priority != DEF_PRIORITY &&
2672                            !pgdat_reclaimable(zone->zone_pgdat))
2673                                continue;       /* Let kswapd poll it */
2674
2675                        /*
2676                         * If we already have plenty of memory free for
2677                         * compaction in this zone, don't free any more.
2678                         * Even though compaction is invoked for any
2679                         * non-zero order, only frequent costly order
2680                         * reclamation is disruptive enough to become a
2681                         * noticeable problem, like transparent huge
2682                         * page allocations.
2683                         */
2684                        if (IS_ENABLED(CONFIG_COMPACTION) &&
2685                            sc->order > PAGE_ALLOC_COSTLY_ORDER &&
2686                            compaction_ready(zone, sc)) {
2687                                sc->compaction_ready = true;
2688                                continue;
2689                        }
2690
2691                        /*
2692                         * Shrink each node in the zonelist once. If the
2693                         * zonelist is ordered by zone (not the default) then a
2694                         * node may be shrunk multiple times but in that case
2695                         * the user prefers lower zones being preserved.
2696                         */
2697                        if (zone->zone_pgdat == last_pgdat)
2698                                continue;
2699
2700                        /*
2701                         * This steals pages from memory cgroups over softlimit
2702                         * and returns the number of reclaimed pages and
2703                         * scanned pages. This works for global memory pressure
2704                         * and balancing, not for a memcg's limit.
2705                         */
2706                        nr_soft_scanned = 0;
2707                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2708                                                sc->order, sc->gfp_mask,
2709                                                &nr_soft_scanned);
2710                        sc->nr_reclaimed += nr_soft_reclaimed;
2711                        sc->nr_scanned += nr_soft_scanned;
2712                        /* need some check for avoid more shrink_zone() */
2713                }
2714
2715                /* See comment about same check for global reclaim above */
2716                if (zone->zone_pgdat == last_pgdat)
2717                        continue;
2718                last_pgdat = zone->zone_pgdat;
2719                shrink_node(zone->zone_pgdat, sc);
2720        }
2721
2722        /*
2723         * Restore to original mask to avoid the impact on the caller if we
2724         * promoted it to __GFP_HIGHMEM.
2725         */
2726        sc->gfp_mask = orig_mask;
2727}
2728
2729/*
2730 * This is the main entry point to direct page reclaim.
2731 *
2732 * If a full scan of the inactive list fails to free enough memory then we
2733 * are "out of memory" and something needs to be killed.
2734 *
2735 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2736 * high - the zone may be full of dirty or under-writeback pages, which this
2737 * caller can't do much about.  We kick the writeback threads and take explicit
2738 * naps in the hope that some of these pages can be written.  But if the
2739 * allocating task holds filesystem locks which prevent writeout this might not
2740 * work, and the allocation attempt will fail.
2741 *
2742 * returns:     0, if no pages reclaimed
2743 *              else, the number of pages reclaimed
2744 */
2745static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2746                                          struct scan_control *sc)
2747{
2748        int initial_priority = sc->priority;
2749        unsigned long total_scanned = 0;
2750        unsigned long writeback_threshold;
2751retry:
2752        delayacct_freepages_start();
2753
2754        if (global_reclaim(sc))
2755                __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
2756
2757        do {
2758                vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2759                                sc->priority);
2760                sc->nr_scanned = 0;
2761                shrink_zones(zonelist, sc);
2762
2763                total_scanned += sc->nr_scanned;
2764                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2765                        break;
2766
2767                if (sc->compaction_ready)
2768                        break;
2769
2770                /*
2771                 * If we're getting trouble reclaiming, start doing
2772                 * writepage even in laptop mode.
2773                 */
2774                if (sc->priority < DEF_PRIORITY - 2)
2775                        sc->may_writepage = 1;
2776
2777                /*
2778                 * Try to write back as many pages as we just scanned.  This
2779                 * tends to cause slow streaming writers to write data to the
2780                 * disk smoothly, at the dirtying rate, which is nice.   But
2781                 * that's undesirable in laptop mode, where we *want* lumpy
2782                 * writeout.  So in laptop mode, write out the whole world.
2783                 */
2784                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2785                if (total_scanned > writeback_threshold) {
2786                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2787                                                WB_REASON_TRY_TO_FREE_PAGES);
2788                        sc->may_writepage = 1;
2789                }
2790        } while (--sc->priority >= 0);
2791
2792        delayacct_freepages_end();
2793
2794        if (sc->nr_reclaimed)
2795                return sc->nr_reclaimed;
2796
2797        /* Aborted reclaim to try compaction? don't OOM, then */
2798        if (sc->compaction_ready)
2799                return 1;
2800
2801        /* Untapped cgroup reserves?  Don't OOM, retry. */
2802        if (!sc->may_thrash) {
2803                sc->priority = initial_priority;
2804                sc->may_thrash = 1;
2805                goto retry;
2806        }
2807
2808        return 0;
2809}
2810
2811static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2812{
2813        struct zone *zone;
2814        unsigned long pfmemalloc_reserve = 0;
2815        unsigned long free_pages = 0;
2816        int i;
2817        bool wmark_ok;
2818
2819        for (i = 0; i <= ZONE_NORMAL; i++) {
2820                zone = &pgdat->node_zones[i];
2821                if (!managed_zone(zone) ||
2822                    pgdat_reclaimable_pages(pgdat) == 0)
2823                        continue;
2824
2825                pfmemalloc_reserve += min_wmark_pages(zone);
2826                free_pages += zone_page_state(zone, NR_FREE_PAGES);
2827        }
2828
2829        /* If there are no reserves (unexpected config) then do not throttle */
2830        if (!pfmemalloc_reserve)
2831                return true;
2832
2833        wmark_ok = free_pages > pfmemalloc_reserve / 2;
2834
2835        /* kswapd must be awake if processes are being throttled */
2836        if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2837                pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
2838                                                (enum zone_type)ZONE_NORMAL);
2839                wake_up_interruptible(&pgdat->kswapd_wait);
2840        }
2841
2842        return wmark_ok;
2843}
2844
2845/*
2846 * Throttle direct reclaimers if backing storage is backed by the network
2847 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2848 * depleted. kswapd will continue to make progress and wake the processes
2849 * when the low watermark is reached.
2850 *
2851 * Returns true if a fatal signal was delivered during throttling. If this
2852 * happens, the page allocator should not consider triggering the OOM killer.
2853 */
2854static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2855                                        nodemask_t *nodemask)
2856{
2857        struct zoneref *z;
2858        struct zone *zone;
2859        pg_data_t *pgdat = NULL;
2860
2861        /*
2862         * Kernel threads should not be throttled as they may be indirectly
2863         * responsible for cleaning pages necessary for reclaim to make forward
2864         * progress. kjournald for example may enter direct reclaim while
2865         * committing a transaction where throttling it could forcing other
2866         * processes to block on log_wait_commit().
2867         */
2868        if (current->flags & PF_KTHREAD)
2869                goto out;
2870
2871        /*
2872         * If a fatal signal is pending, this process should not throttle.
2873         * It should return quickly so it can exit and free its memory
2874         */
2875        if (fatal_signal_pending(current))
2876                goto out;
2877
2878        /*
2879         * Check if the pfmemalloc reserves are ok by finding the first node
2880         * with a usable ZONE_NORMAL or lower zone. The expectation is that
2881         * GFP_KERNEL will be required for allocating network buffers when
2882         * swapping over the network so ZONE_HIGHMEM is unusable.
2883         *
2884         * Throttling is based on the first usable node and throttled processes
2885         * wait on a queue until kswapd makes progress and wakes them. There
2886         * is an affinity then between processes waking up and where reclaim
2887         * progress has been made assuming the process wakes on the same node.
2888         * More importantly, processes running on remote nodes will not compete
2889         * for remote pfmemalloc reserves and processes on different nodes
2890         * should make reasonable progress.
2891         */
2892        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2893                                        gfp_zone(gfp_mask), nodemask) {
2894                if (zone_idx(zone) > ZONE_NORMAL)
2895                        continue;
2896
2897                /* Throttle based on the first usable node */
2898                pgdat = zone->zone_pgdat;
2899                if (pfmemalloc_watermark_ok(pgdat))
2900                        goto out;
2901                break;
2902        }
2903
2904        /* If no zone was usable by the allocation flags then do not throttle */
2905        if (!pgdat)
2906                goto out;
2907
2908        /* Account for the throttling */
2909        count_vm_event(PGSCAN_DIRECT_THROTTLE);
2910
2911        /*
2912         * If the caller cannot enter the filesystem, it's possible that it
2913         * is due to the caller holding an FS lock or performing a journal
2914         * transaction in the case of a filesystem like ext[3|4]. In this case,
2915         * it is not safe to block on pfmemalloc_wait as kswapd could be
2916         * blocked waiting on the same lock. Instead, throttle for up to a
2917         * second before continuing.
2918         */
2919        if (!(gfp_mask & __GFP_FS)) {
2920                wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2921                        pfmemalloc_watermark_ok(pgdat), HZ);
2922
2923                goto check_pending;
2924        }
2925
2926        /* Throttle until kswapd wakes the process */
2927        wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2928                pfmemalloc_watermark_ok(pgdat));
2929
2930check_pending:
2931        if (fatal_signal_pending(current))
2932                return true;
2933
2934out:
2935        return false;
2936}
2937
2938unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2939                                gfp_t gfp_mask, nodemask_t *nodemask)
2940{
2941        unsigned long nr_reclaimed;
2942        struct scan_control sc = {
2943                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2944                .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2945                .reclaim_idx = gfp_zone(gfp_mask),
2946                .order = order,
2947                .nodemask = nodemask,
2948                .priority = DEF_PRIORITY,
2949                .may_writepage = !laptop_mode,
2950                .may_unmap = 1,
2951                .may_swap = 1,
2952        };
2953
2954        /*
2955         * Do not enter reclaim if fatal signal was delivered while throttled.
2956         * 1 is returned so that the page allocator does not OOM kill at this
2957         * point.
2958         */
2959        if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2960                return 1;
2961
2962        trace_mm_vmscan_direct_reclaim_begin(order,
2963                                sc.may_writepage,
2964                                gfp_mask,
2965                                sc.reclaim_idx);
2966
2967        nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2968
2969        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2970
2971        return nr_reclaimed;
2972}
2973
2974#ifdef CONFIG_MEMCG
2975
2976unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
2977                                                gfp_t gfp_mask, bool noswap,
2978                                                pg_data_t *pgdat,
2979                                                unsigned long *nr_scanned)
2980{
2981        struct scan_control sc = {
2982                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2983                .target_mem_cgroup = memcg,
2984                .may_writepage = !laptop_mode,
2985                .may_unmap = 1,
2986                .reclaim_idx = MAX_NR_ZONES - 1,
2987                .may_swap = !noswap,
2988        };
2989        unsigned long lru_pages;
2990
2991        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2992                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2993
2994        trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2995                                                      sc.may_writepage,
2996                                                      sc.gfp_mask,
2997                                                      sc.reclaim_idx);
2998
2999        /*
3000         * NOTE: Although we can get the priority field, using it
3001         * here is not a good idea, since it limits the pages we can scan.
3002         * if we don't reclaim here, the shrink_node from balance_pgdat
3003         * will pick up pages from other mem cgroup's as well. We hack
3004         * the priority and make it zero.
3005         */
3006        shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3007
3008        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
3009
3010        *nr_scanned = sc.nr_scanned;
3011        return sc.nr_reclaimed;
3012}
3013
3014unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3015                                           unsigned long nr_pages,
3016                                           gfp_t gfp_mask,
3017                                           bool may_swap)
3018{
3019        struct zonelist *zonelist;
3020        unsigned long nr_reclaimed;
3021        int nid;
3022        struct scan_control sc = {
3023                .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3024                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3025                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3026                .reclaim_idx = MAX_NR_ZONES - 1,
3027                .target_mem_cgroup = memcg,
3028                .priority = DEF_PRIORITY,
3029                .may_writepage = !laptop_mode,
3030                .may_unmap = 1,
3031                .may_swap = may_swap,
3032        };
3033
3034        /*
3035         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
3036         * take care of from where we get pages. So the node where we start the
3037         * scan does not need to be the current node.
3038         */
3039        nid = mem_cgroup_select_victim_node(memcg);
3040
3041        zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3042
3043        trace_mm_vmscan_memcg_reclaim_begin(0,
3044                                            sc.may_writepage,
3045                                            sc.gfp_mask,
3046                                            sc.reclaim_idx);
3047
3048        current->flags |= PF_MEMALLOC;
3049        nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3050        current->flags &= ~PF_MEMALLOC;
3051
3052        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
3053
3054        return nr_reclaimed;
3055}
3056#endif
3057
3058static void age_active_anon(struct pglist_data *pgdat,
3059                                struct scan_control *sc)
3060{
3061        struct mem_cgroup *memcg;
3062
3063        if (!total_swap_pages)
3064                return;
3065
3066        memcg = mem_cgroup_iter(NULL, NULL, NULL);
3067        do {
3068                struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3069
3070                if (inactive_list_is_low(lruvec, false, sc))
3071                        shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3072                                           sc, LRU_ACTIVE_ANON);
3073
3074                memcg = mem_cgroup_iter(NULL, memcg, NULL);
3075        } while (memcg);
3076}
3077
3078static bool zone_balanced(struct zone *zone, int order, int classzone_idx)
3079{
3080        unsigned long mark = high_wmark_pages(zone);
3081
3082        if (!zone_watermark_ok_safe(zone, order, mark, classzone_idx))
3083                return false;
3084
3085        /*
3086         * If any eligible zone is balanced then the node is not considered
3087         * to be congested or dirty
3088         */
3089        clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
3090        clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
3091
3092        return true;
3093}
3094
3095/*
3096 * Prepare kswapd for sleeping. This verifies that there are no processes
3097 * waiting in throttle_direct_reclaim() and that watermarks have been met.
3098 *
3099 * Returns true if kswapd is ready to sleep
3100 */
3101static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3102{
3103        int i;
3104
3105        /*
3106         * The throttled processes are normally woken up in balance_pgdat() as
3107         * soon as pfmemalloc_watermark_ok() is true. But there is a potential
3108         * race between when kswapd checks the watermarks and a process gets
3109         * throttled. There is also a potential race if processes get
3110         * throttled, kswapd wakes, a large process exits thereby balancing the
3111         * zones, which causes kswapd to exit balance_pgdat() before reaching
3112         * the wake up checks. If kswapd is going to sleep, no process should
3113         * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
3114         * the wake up is premature, processes will wake kswapd and get
3115         * throttled again. The difference from wake ups in balance_pgdat() is
3116         * that here we are under prepare_to_wait().
3117         */
3118        if (waitqueue_active(&pgdat->pfmemalloc_wait))
3119                wake_up_all(&pgdat->pfmemalloc_wait);
3120
3121        for (i = 0; i <= classzone_idx; i++) {
3122                struct zone *zone = pgdat->node_zones + i;
3123
3124                if (!managed_zone(zone))
3125                        continue;
3126
3127                if (!zone_balanced(zone, order, classzone_idx))
3128                        return false;
3129        }
3130
3131        return true;
3132}
3133
3134/*
3135 * kswapd shrinks a node of pages that are at or below the highest usable
3136 * zone that is currently unbalanced.
3137 *
3138 * Returns true if kswapd scanned at least the requested number of pages to
3139 * reclaim or if the lack of progress was due to pages under writeback.
3140 * This is used to determine if the scanning priority needs to be raised.
3141 */
3142static bool kswapd_shrink_node(pg_data_t *pgdat,
3143                               struct scan_control *sc)
3144{
3145        struct zone *zone;
3146        int z;
3147
3148        /* Reclaim a number of pages proportional to the number of zones */
3149        sc->nr_to_reclaim = 0;
3150        for (z = 0; z <= sc->reclaim_idx; z++) {
3151                zone = pgdat->node_zones + z;
3152                if (!managed_zone(zone))
3153                        continue;
3154
3155                sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
3156        }
3157
3158        /*
3159         * Historically care was taken to put equal pressure on all zones but
3160         * now pressure is applied based on node LRU order.
3161         */
3162        shrink_node(pgdat, sc);
3163
3164        /*
3165         * Fragmentation may mean that the system cannot be rebalanced for
3166         * high-order allocations. If twice the allocation size has been
3167         * reclaimed then recheck watermarks only at order-0 to prevent
3168         * excessive reclaim. Assume that a process requested a high-order
3169         * can direct reclaim/compact.
3170         */
3171        if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3172                sc->order = 0;
3173
3174        return sc->nr_scanned >= sc->nr_to_reclaim;
3175}
3176
3177/*
3178 * For kswapd, balance_pgdat() will reclaim pages across a node from zones
3179 * that are eligible for use by the caller until at least one zone is
3180 * balanced.
3181 *
3182 * Returns the order kswapd finished reclaiming at.
3183 *
3184 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
3185 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3186 * found to have free_pages <= high_wmark_pages(zone), any page is that zone
3187 * or lower is eligible for reclaim until at least one usable zone is
3188 * balanced.
3189 */
3190static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
3191{
3192        int i;
3193        unsigned long nr_soft_reclaimed;
3194        unsigned long nr_soft_scanned;
3195        struct zone *zone;
3196        struct scan_control sc = {
3197                .gfp_mask = GFP_KERNEL,
3198                .order = order,
3199                .priority = DEF_PRIORITY,
3200                .may_writepage = !laptop_mode,
3201                .may_unmap = 1,
3202                .may_swap = 1,
3203        };
3204        count_vm_event(PAGEOUTRUN);
3205
3206        do {
3207                bool raise_priority = true;
3208
3209                sc.nr_reclaimed = 0;
3210                sc.reclaim_idx = classzone_idx;
3211
3212                /*
3213                 * If the number of buffer_heads exceeds the maximum allowed
3214                 * then consider reclaiming from all zones. This has a dual
3215                 * purpose -- on 64-bit systems it is expected that
3216                 * buffer_heads are stripped during active rotation. On 32-bit
3217                 * systems, highmem pages can pin lowmem memory and shrinking
3218                 * buffers can relieve lowmem pressure. Reclaim may still not
3219                 * go ahead if all eligible zones for the original allocation
3220                 * request are balanced to avoid excessive reclaim from kswapd.
3221                 */
3222                if (buffer_heads_over_limit) {
3223                        for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
3224                                zone = pgdat->node_zones + i;
3225                                if (!managed_zone(zone))
3226                                        continue;
3227
3228                                sc.reclaim_idx = i;
3229                                break;
3230                        }
3231                }
3232
3233                /*
3234                 * Only reclaim if there are no eligible zones. Check from
3235                 * high to low zone as allocations prefer higher zones.
3236                 * Scanning from low to high zone would allow congestion to be
3237                 * cleared during a very small window when a small low
3238                 * zone was balanced even under extreme pressure when the
3239                 * overall node may be congested. Note that sc.reclaim_idx
3240                 * is not used as buffer_heads_over_limit may have adjusted
3241                 * it.
3242                 */
3243                for (i = classzone_idx; i >= 0; i--) {
3244                        zone = pgdat->node_zones + i;
3245                        if (!managed_zone(zone))
3246                                continue;
3247
3248                        if (zone_balanced(zone, sc.order, classzone_idx))
3249                                goto out;
3250                }
3251
3252                /*
3253                 * Do some background aging of the anon list, to give
3254                 * pages a chance to be referenced before reclaiming. All
3255                 * pages are rotated regardless of classzone as this is
3256                 * about consistent aging.
3257                 */
3258                age_active_anon(pgdat, &sc);
3259
3260                /*
3261                 * If we're getting trouble reclaiming, start doing writepage
3262                 * even in laptop mode.
3263                 */
3264                if (sc.priority < DEF_PRIORITY - 2 || !pgdat_reclaimable(pgdat))
3265                        sc.may_writepage = 1;
3266
3267                /* Call soft limit reclaim before calling shrink_node. */
3268                sc.nr_scanned = 0;
3269                nr_soft_scanned = 0;
3270                nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3271                                                sc.gfp_mask, &nr_soft_scanned);
3272                sc.nr_reclaimed += nr_soft_reclaimed;
3273
3274                /*
3275                 * There should be no need to raise the scanning priority if
3276                 * enough pages are already being scanned that that high
3277                 * watermark would be met at 100% efficiency.
3278                 */
3279                if (kswapd_shrink_node(pgdat, &sc))
3280                        raise_priority = false;
3281
3282                /*
3283                 * If the low watermark is met there is no need for processes
3284                 * to be throttled on pfmemalloc_wait as they should not be
3285                 * able to safely make forward progress. Wake them
3286                 */
3287                if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3288                                pfmemalloc_watermark_ok(pgdat))
3289                        wake_up_all(&pgdat->pfmemalloc_wait);
3290
3291                /* Check if kswapd should be suspending */
3292                if (try_to_freeze() || kthread_should_stop())
3293                        break;
3294
3295                /*
3296                 * Raise priority if scanning rate is too low or there was no
3297                 * progress in reclaiming pages
3298                 */
3299                if (raise_priority || !sc.nr_reclaimed)
3300                        sc.priority--;
3301        } while (sc.priority >= 1);
3302
3303out:
3304        /*
3305         * Return the order kswapd stopped reclaiming at as
3306         * prepare_kswapd_sleep() takes it into account. If another caller
3307         * entered the allocator slow path while kswapd was awake, order will
3308         * remain at the higher level.
3309         */
3310        return sc.order;
3311}
3312
3313static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
3314                                unsigned int classzone_idx)
3315{
3316        long remaining = 0;
3317        DEFINE_WAIT(wait);
3318
3319        if (freezing(current) || kthread_should_stop())
3320                return;
3321
3322        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3323
3324        /* Try to sleep for a short interval */
3325        if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3326                /*
3327                 * Compaction records what page blocks it recently failed to
3328                 * isolate pages from and skips them in the future scanning.
3329                 * When kswapd is going to sleep, it is reasonable to assume
3330                 * that pages and compaction may succeed so reset the cache.
3331                 */
3332                reset_isolation_suitable(pgdat);
3333
3334                /*
3335                 * We have freed the memory, now we should compact it to make
3336                 * allocation of the requested order possible.
3337                 */
3338                wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3339
3340                remaining = schedule_timeout(HZ/10);
3341
3342                /*
3343                 * If woken prematurely then reset kswapd_classzone_idx and
3344                 * order. The values will either be from a wakeup request or
3345                 * the previous request that slept prematurely.
3346                 */
3347                if (remaining) {
3348                        pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, classzone_idx);
3349                        pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
3350                }
3351
3352                finish_wait(&pgdat->kswapd_wait, &wait);
3353                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3354        }
3355
3356        /*
3357         * After a short sleep, check if it was a premature sleep. If not, then
3358         * go fully to sleep until explicitly woken up.
3359         */
3360        if (!remaining &&
3361            prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3362                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3363
3364                /*
3365                 * vmstat counters are not perfectly accurate and the estimated
3366                 * value for counters such as NR_FREE_PAGES can deviate from the
3367                 * true value by nr_online_cpus * threshold. To avoid the zone
3368                 * watermarks being breached while under pressure, we reduce the
3369                 * per-cpu vmstat threshold while kswapd is awake and restore
3370                 * them before going back to sleep.
3371                 */
3372                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3373
3374                if (!kthread_should_stop())
3375                        schedule();
3376
3377                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3378        } else {
3379                if (remaining)
3380                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3381                else
3382                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3383        }
3384        finish_wait(&pgdat->kswapd_wait, &wait);
3385}
3386
3387/*
3388 * The background pageout daemon, started as a kernel thread
3389 * from the init process.
3390 *
3391 * This basically trickles out pages so that we have _some_
3392 * free memory available even if there is no other activity
3393 * that frees anything up. This is needed for things like routing
3394 * etc, where we otherwise might have all activity going on in
3395 * asynchronous contexts that cannot page things out.
3396 *
3397 * If there are applications that are active memory-allocators
3398 * (most normal use), this basically shouldn't matter.
3399 */
3400static int kswapd(void *p)
3401{
3402        unsigned int alloc_order, reclaim_order, classzone_idx;
3403        pg_data_t *pgdat = (pg_data_t*)p;
3404        struct task_struct *tsk = current;
3405
3406        struct reclaim_state reclaim_state = {
3407                .reclaimed_slab = 0,
3408        };
3409        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3410
3411        lockdep_set_current_reclaim_state(GFP_KERNEL);
3412
3413        if (!cpumask_empty(cpumask))
3414                set_cpus_allowed_ptr(tsk, cpumask);
3415        current->reclaim_state = &reclaim_state;
3416
3417        /*
3418         * Tell the memory management that we're a "memory allocator",
3419         * and that if we need more memory we should get access to it
3420         * regardless (see "__alloc_pages()"). "kswapd" should
3421         * never get caught in the normal page freeing logic.
3422         *
3423         * (Kswapd normally doesn't need memory anyway, but sometimes
3424         * you need a small amount of memory in order to be able to
3425         * page out something else, and this flag essentially protects
3426         * us from recursively trying to free more memory as we're
3427         * trying to free the first piece of memory in the first place).
3428         */
3429        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3430        set_freezable();
3431
3432        pgdat->kswapd_order = alloc_order = reclaim_order = 0;
3433        pgdat->kswapd_classzone_idx = classzone_idx = 0;
3434        for ( ; ; ) {
3435                bool ret;
3436
3437kswapd_try_sleep:
3438                kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
3439                                        classzone_idx);
3440
3441                /* Read the new order and classzone_idx */
3442                alloc_order = reclaim_order = pgdat->kswapd_order;
3443                classzone_idx = pgdat->kswapd_classzone_idx;
3444                pgdat->kswapd_order = 0;
3445                pgdat->kswapd_classzone_idx = 0;
3446
3447                ret = try_to_freeze();
3448                if (kthread_should_stop())
3449                        break;
3450
3451                /*
3452                 * We can speed up thawing tasks if we don't call balance_pgdat
3453                 * after returning from the refrigerator
3454                 */
3455                if (ret)
3456                        continue;
3457
3458                /*
3459                 * Reclaim begins at the requested order but if a high-order
3460                 * reclaim fails then kswapd falls back to reclaiming for
3461                 * order-0. If that happens, kswapd will consider sleeping
3462                 * for the order it finished reclaiming at (reclaim_order)
3463                 * but kcompactd is woken to compact for the original
3464                 * request (alloc_order).
3465                 */
3466                trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
3467                                                alloc_order);
3468                reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
3469                if (reclaim_order < alloc_order)
3470                        goto kswapd_try_sleep;
3471
3472                alloc_order = reclaim_order = pgdat->kswapd_order;
3473                classzone_idx = pgdat->kswapd_classzone_idx;
3474        }
3475
3476        tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3477        current->reclaim_state = NULL;
3478        lockdep_clear_current_reclaim_state();
3479
3480        return 0;
3481}
3482
3483/*
3484 * A zone is low on free memory, so wake its kswapd task to service it.
3485 */
3486void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3487{
3488        pg_data_t *pgdat;
3489        int z;
3490
3491        if (!managed_zone(zone))
3492                return;
3493
3494        if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
3495                return;
3496        pgdat = zone->zone_pgdat;
3497        pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, classzone_idx);
3498        pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3499        if (!waitqueue_active(&pgdat->kswapd_wait))
3500                return;
3501
3502        /* Only wake kswapd if all zones are unbalanced */
3503        for (z = 0; z <= classzone_idx; z++) {
3504                zone = pgdat->node_zones + z;
3505                if (!managed_zone(zone))
3506                        continue;
3507
3508                if (zone_balanced(zone, order, classzone_idx))
3509                        return;
3510        }
3511
3512        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3513        wake_up_interruptible(&pgdat->kswapd_wait);
3514}
3515
3516#ifdef CONFIG_HIBERNATION
3517/*
3518 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3519 * freed pages.
3520 *
3521 * Rather than trying to age LRUs the aim is to preserve the overall
3522 * LRU order by reclaiming preferentially
3523 * inactive > active > active referenced > active mapped
3524 */
3525unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3526{
3527        struct reclaim_state reclaim_state;
3528        struct scan_control sc = {
3529                .nr_to_reclaim = nr_to_reclaim,
3530                .gfp_mask = GFP_HIGHUSER_MOVABLE,
3531                .reclaim_idx = MAX_NR_ZONES - 1,
3532                .priority = DEF_PRIORITY,
3533                .may_writepage = 1,
3534                .may_unmap = 1,
3535                .may_swap = 1,
3536                .hibernation_mode = 1,
3537        };
3538        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3539        struct task_struct *p = current;
3540        unsigned long nr_reclaimed;
3541
3542        p->flags |= PF_MEMALLOC;
3543        lockdep_set_current_reclaim_state(sc.gfp_mask);
3544        reclaim_state.reclaimed_slab = 0;
3545        p->reclaim_state = &reclaim_state;
3546
3547        nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3548
3549        p->reclaim_state = NULL;
3550        lockdep_clear_current_reclaim_state();
3551        p->flags &= ~PF_MEMALLOC;
3552
3553        return nr_reclaimed;
3554}
3555#endif /* CONFIG_HIBERNATION */
3556
3557/* It's optimal to keep kswapds on the same CPUs as their memory, but
3558   not required for correctness.  So if the last cpu in a node goes
3559   away, we get changed to run anywhere: as the first one comes back,
3560   restore their cpu bindings. */
3561static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3562                        void *hcpu)
3563{
3564        int nid;
3565
3566        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3567                for_each_node_state(nid, N_MEMORY) {
3568                        pg_data_t *pgdat = NODE_DATA(nid);
3569                        const struct cpumask *mask;
3570
3571                        mask = cpumask_of_node(pgdat->node_id);
3572
3573                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3574                                /* One of our CPUs online: restore mask */
3575                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
3576                }
3577        }
3578        return NOTIFY_OK;
3579}
3580
3581/*
3582 * This kswapd start function will be called by init and node-hot-add.
3583 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3584 */
3585int kswapd_run(int nid)
3586{
3587        pg_data_t *pgdat = NODE_DATA(nid);
3588        int ret = 0;
3589
3590        if (pgdat->kswapd)
3591                return 0;
3592
3593        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3594        if (IS_ERR(pgdat->kswapd)) {
3595                /* failure at boot is fatal */
3596                BUG_ON(system_state == SYSTEM_BOOTING);
3597                pr_err("Failed to start kswapd on node %d\n", nid);
3598                ret = PTR_ERR(pgdat->kswapd);
3599                pgdat->kswapd = NULL;
3600        }
3601        return ret;
3602}
3603
3604/*
3605 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3606 * hold mem_hotplug_begin/end().
3607 */
3608void kswapd_stop(int nid)
3609{
3610        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3611
3612        if (kswapd) {
3613                kthread_stop(kswapd);
3614                NODE_DATA(nid)->kswapd = NULL;
3615        }
3616}
3617
3618static int __init kswapd_init(void)
3619{
3620        int nid;
3621
3622        swap_setup();
3623        for_each_node_state(nid, N_MEMORY)
3624                kswapd_run(nid);
3625        hotcpu_notifier(cpu_callback, 0);
3626        return 0;
3627}
3628
3629module_init(kswapd_init)
3630
3631#ifdef CONFIG_NUMA
3632/*
3633 * Node reclaim mode
3634 *
3635 * If non-zero call node_reclaim when the number of free pages falls below
3636 * the watermarks.
3637 */
3638int node_reclaim_mode __read_mostly;
3639
3640#define RECLAIM_OFF 0
3641#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3642#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3643#define RECLAIM_UNMAP (1<<2)    /* Unmap pages during reclaim */
3644
3645/*
3646 * Priority for NODE_RECLAIM. This determines the fraction of pages
3647 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3648 * a zone.
3649 */
3650#define NODE_RECLAIM_PRIORITY 4
3651
3652/*
3653 * Percentage of pages in a zone that must be unmapped for node_reclaim to
3654 * occur.
3655 */
3656int sysctl_min_unmapped_ratio = 1;
3657
3658/*
3659 * If the number of slab pages in a zone grows beyond this percentage then
3660 * slab reclaim needs to occur.
3661 */
3662int sysctl_min_slab_ratio = 5;
3663
3664static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
3665{
3666        unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
3667        unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
3668                node_page_state(pgdat, NR_ACTIVE_FILE);
3669
3670        /*
3671         * It's possible for there to be more file mapped pages than
3672         * accounted for by the pages on the file LRU lists because
3673         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3674         */
3675        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3676}
3677
3678/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3679static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
3680{
3681        unsigned long nr_pagecache_reclaimable;
3682        unsigned long delta = 0;
3683
3684        /*
3685         * If RECLAIM_UNMAP is set, then all file pages are considered
3686         * potentially reclaimable. Otherwise, we have to worry about
3687         * pages like swapcache and node_unmapped_file_pages() provides
3688         * a better estimate
3689         */
3690        if (node_reclaim_mode & RECLAIM_UNMAP)
3691                nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
3692        else
3693                nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
3694
3695        /* If we can't clean pages, remove dirty pages from consideration */
3696        if (!(node_reclaim_mode & RECLAIM_WRITE))
3697                delta += node_page_state(pgdat, NR_FILE_DIRTY);
3698
3699        /* Watch for any possible underflows due to delta */
3700        if (unlikely(delta > nr_pagecache_reclaimable))
3701                delta = nr_pagecache_reclaimable;
3702
3703        return nr_pagecache_reclaimable - delta;
3704}
3705
3706/*
3707 * Try to free up some pages from this node through reclaim.
3708 */
3709static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3710{
3711        /* Minimum pages needed in order to stay on node */
3712        const unsigned long nr_pages = 1 << order;
3713        struct task_struct *p = current;
3714        struct reclaim_state reclaim_state;
3715        int classzone_idx = gfp_zone(gfp_mask);
3716        struct scan_control sc = {
3717                .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3718                .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3719                .order = order,
3720                .priority = NODE_RECLAIM_PRIORITY,
3721                .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
3722                .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
3723                .may_swap = 1,
3724                .reclaim_idx = classzone_idx,
3725        };
3726
3727        cond_resched();
3728        /*
3729         * We need to be able to allocate from the reserves for RECLAIM_UNMAP
3730         * and we also need to be able to write out pages for RECLAIM_WRITE
3731         * and RECLAIM_UNMAP.
3732         */
3733        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3734        lockdep_set_current_reclaim_state(gfp_mask);
3735        reclaim_state.reclaimed_slab = 0;
3736        p->reclaim_state = &reclaim_state;
3737
3738        if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
3739                /*
3740                 * Free memory by calling shrink zone with increasing
3741                 * priorities until we have enough memory freed.
3742                 */
3743                do {
3744                        shrink_node(pgdat, &sc);
3745                } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3746        }
3747
3748        p->reclaim_state = NULL;
3749        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3750        lockdep_clear_current_reclaim_state();
3751        return sc.nr_reclaimed >= nr_pages;
3752}
3753
3754int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3755{
3756        int ret;
3757
3758        /*
3759         * Node reclaim reclaims unmapped file backed pages and
3760         * slab pages if we are over the defined limits.
3761         *
3762         * A small portion of unmapped file backed pages is needed for
3763         * file I/O otherwise pages read by file I/O will be immediately
3764         * thrown out if the node is overallocated. So we do not reclaim
3765         * if less than a specified percentage of the node is used by
3766         * unmapped file backed pages.
3767         */
3768        if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
3769            sum_zone_node_page_state(pgdat->node_id, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
3770                return NODE_RECLAIM_FULL;
3771
3772        if (!pgdat_reclaimable(pgdat))
3773                return NODE_RECLAIM_FULL;
3774
3775        /*
3776         * Do not scan if the allocation should not be delayed.
3777         */
3778        if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
3779                return NODE_RECLAIM_NOSCAN;
3780
3781        /*
3782         * Only run node reclaim on the local node or on nodes that do not
3783         * have associated processors. This will favor the local processor
3784         * over remote processors and spread off node memory allocations
3785         * as wide as possible.
3786         */
3787        if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
3788                return NODE_RECLAIM_NOSCAN;
3789
3790        if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
3791                return NODE_RECLAIM_NOSCAN;
3792
3793        ret = __node_reclaim(pgdat, gfp_mask, order);
3794        clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
3795
3796        if (!ret)
3797                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3798
3799        return ret;
3800}
3801#endif
3802
3803/*
3804 * page_evictable - test whether a page is evictable
3805 * @page: the page to test
3806 *
3807 * Test whether page is evictable--i.e., should be placed on active/inactive
3808 * lists vs unevictable list.
3809 *
3810 * Reasons page might not be evictable:
3811 * (1) page's mapping marked unevictable
3812 * (2) page is part of an mlocked VMA
3813 *
3814 */
3815int page_evictable(struct page *page)
3816{
3817        return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3818}
3819
3820#ifdef CONFIG_SHMEM
3821/**
3822 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3823 * @pages:      array of pages to check
3824 * @nr_pages:   number of pages to check
3825 *
3826 * Checks pages for evictability and moves them to the appropriate lru list.
3827 *
3828 * This function is only used for SysV IPC SHM_UNLOCK.
3829 */
3830void check_move_unevictable_pages(struct page **pages, int nr_pages)
3831{
3832        struct lruvec *lruvec;
3833        struct pglist_data *pgdat = NULL;
3834        int pgscanned = 0;
3835        int pgrescued = 0;
3836        int i;
3837
3838        for (i = 0; i < nr_pages; i++) {
3839                struct page *page = pages[i];
3840                struct pglist_data *pagepgdat = page_pgdat(page);
3841
3842                pgscanned++;
3843                if (pagepgdat != pgdat) {
3844                        if (pgdat)
3845                                spin_unlock_irq(&pgdat->lru_lock);
3846                        pgdat = pagepgdat;
3847                        spin_lock_irq(&pgdat->lru_lock);
3848                }
3849                lruvec = mem_cgroup_page_lruvec(page, pgdat);
3850
3851                if (!PageLRU(page) || !PageUnevictable(page))
3852                        continue;
3853
3854                if (page_evictable(page)) {
3855                        enum lru_list lru = page_lru_base_type(page);
3856
3857                        VM_BUG_ON_PAGE(PageActive(page), page);
3858                        ClearPageUnevictable(page);
3859                        del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3860                        add_page_to_lru_list(page, lruvec, lru);
3861                        pgrescued++;
3862                }
3863        }
3864
3865        if (pgdat) {
3866                __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3867                __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3868                spin_unlock_irq(&pgdat->lru_lock);
3869        }
3870}
3871#endif /* CONFIG_SHMEM */
3872