linux/mm/vmscan.c
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   1/*
   2 *  linux/mm/vmscan.c
   3 *
   4 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5 *
   6 *  Swap reorganised 29.12.95, Stephen Tweedie.
   7 *  kswapd added: 7.1.96  sct
   8 *  Removed kswapd_ctl limits, and swap out as many pages as needed
   9 *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
  10 *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
  11 *  Multiqueue VM started 5.8.00, Rik van Riel.
  12 */
  13
  14#include <linux/mm.h>
  15#include <linux/module.h>
  16#include <linux/gfp.h>
  17#include <linux/kernel_stat.h>
  18#include <linux/swap.h>
  19#include <linux/pagemap.h>
  20#include <linux/init.h>
  21#include <linux/highmem.h>
  22#include <linux/vmpressure.h>
  23#include <linux/vmstat.h>
  24#include <linux/file.h>
  25#include <linux/writeback.h>
  26#include <linux/blkdev.h>
  27#include <linux/buffer_head.h>  /* for try_to_release_page(),
  28                                        buffer_heads_over_limit */
  29#include <linux/mm_inline.h>
  30#include <linux/backing-dev.h>
  31#include <linux/rmap.h>
  32#include <linux/topology.h>
  33#include <linux/cpu.h>
  34#include <linux/cpuset.h>
  35#include <linux/compaction.h>
  36#include <linux/notifier.h>
  37#include <linux/rwsem.h>
  38#include <linux/delay.h>
  39#include <linux/kthread.h>
  40#include <linux/freezer.h>
  41#include <linux/memcontrol.h>
  42#include <linux/delayacct.h>
  43#include <linux/sysctl.h>
  44#include <linux/oom.h>
  45#include <linux/prefetch.h>
  46
  47#include <asm/tlbflush.h>
  48#include <asm/div64.h>
  49
  50#include <linux/swapops.h>
  51
  52#include "internal.h"
  53
  54#define CREATE_TRACE_POINTS
  55#include <trace/events/vmscan.h>
  56
  57struct scan_control {
  58        /* Incremented by the number of inactive pages that were scanned */
  59        unsigned long nr_scanned;
  60
  61        /* Number of pages freed so far during a call to shrink_zones() */
  62        unsigned long nr_reclaimed;
  63
  64        /* How many pages shrink_list() should reclaim */
  65        unsigned long nr_to_reclaim;
  66
  67        unsigned long hibernation_mode;
  68
  69        /* This context's GFP mask */
  70        gfp_t gfp_mask;
  71
  72        int may_writepage;
  73
  74        /* Can mapped pages be reclaimed? */
  75        int may_unmap;
  76
  77        /* Can pages be swapped as part of reclaim? */
  78        int may_swap;
  79
  80        int order;
  81
  82        /* Scan (total_size >> priority) pages at once */
  83        int priority;
  84
  85        /*
  86         * The memory cgroup that hit its limit and as a result is the
  87         * primary target of this reclaim invocation.
  88         */
  89        struct mem_cgroup *target_mem_cgroup;
  90
  91        /*
  92         * Nodemask of nodes allowed by the caller. If NULL, all nodes
  93         * are scanned.
  94         */
  95        nodemask_t      *nodemask;
  96};
  97
  98#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  99
 100#ifdef ARCH_HAS_PREFETCH
 101#define prefetch_prev_lru_page(_page, _base, _field)                    \
 102        do {                                                            \
 103                if ((_page)->lru.prev != _base) {                       \
 104                        struct page *prev;                              \
 105                                                                        \
 106                        prev = lru_to_page(&(_page->lru));              \
 107                        prefetch(&prev->_field);                        \
 108                }                                                       \
 109        } while (0)
 110#else
 111#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
 112#endif
 113
 114#ifdef ARCH_HAS_PREFETCHW
 115#define prefetchw_prev_lru_page(_page, _base, _field)                   \
 116        do {                                                            \
 117                if ((_page)->lru.prev != _base) {                       \
 118                        struct page *prev;                              \
 119                                                                        \
 120                        prev = lru_to_page(&(_page->lru));              \
 121                        prefetchw(&prev->_field);                       \
 122                }                                                       \
 123        } while (0)
 124#else
 125#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 126#endif
 127
 128/*
 129 * From 0 .. 100.  Higher means more swappy.
 130 */
 131int vm_swappiness = 60;
 132unsigned long vm_total_pages;   /* The total number of pages which the VM controls */
 133
 134static LIST_HEAD(shrinker_list);
 135static DECLARE_RWSEM(shrinker_rwsem);
 136
 137#ifdef CONFIG_MEMCG
 138static bool global_reclaim(struct scan_control *sc)
 139{
 140        return !sc->target_mem_cgroup;
 141}
 142#else
 143static bool global_reclaim(struct scan_control *sc)
 144{
 145        return true;
 146}
 147#endif
 148
 149static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
 150{
 151        if (!mem_cgroup_disabled())
 152                return mem_cgroup_get_lru_size(lruvec, lru);
 153
 154        return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
 155}
 156
 157/*
 158 * Add a shrinker callback to be called from the vm
 159 */
 160void register_shrinker(struct shrinker *shrinker)
 161{
 162        atomic_long_set(&shrinker->nr_in_batch, 0);
 163        down_write(&shrinker_rwsem);
 164        list_add_tail(&shrinker->list, &shrinker_list);
 165        up_write(&shrinker_rwsem);
 166}
 167EXPORT_SYMBOL(register_shrinker);
 168
 169/*
 170 * Remove one
 171 */
 172void unregister_shrinker(struct shrinker *shrinker)
 173{
 174        down_write(&shrinker_rwsem);
 175        list_del(&shrinker->list);
 176        up_write(&shrinker_rwsem);
 177}
 178EXPORT_SYMBOL(unregister_shrinker);
 179
 180static inline int do_shrinker_shrink(struct shrinker *shrinker,
 181                                     struct shrink_control *sc,
 182                                     unsigned long nr_to_scan)
 183{
 184        sc->nr_to_scan = nr_to_scan;
 185        return (*shrinker->shrink)(shrinker, sc);
 186}
 187
 188#define SHRINK_BATCH 128
 189/*
 190 * Call the shrink functions to age shrinkable caches
 191 *
 192 * Here we assume it costs one seek to replace a lru page and that it also
 193 * takes a seek to recreate a cache object.  With this in mind we age equal
 194 * percentages of the lru and ageable caches.  This should balance the seeks
 195 * generated by these structures.
 196 *
 197 * If the vm encountered mapped pages on the LRU it increase the pressure on
 198 * slab to avoid swapping.
 199 *
 200 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 201 *
 202 * `lru_pages' represents the number of on-LRU pages in all the zones which
 203 * are eligible for the caller's allocation attempt.  It is used for balancing
 204 * slab reclaim versus page reclaim.
 205 *
 206 * Returns the number of slab objects which we shrunk.
 207 */
 208unsigned long shrink_slab(struct shrink_control *shrink,
 209                          unsigned long nr_pages_scanned,
 210                          unsigned long lru_pages)
 211{
 212        struct shrinker *shrinker;
 213        unsigned long ret = 0;
 214
 215        if (nr_pages_scanned == 0)
 216                nr_pages_scanned = SWAP_CLUSTER_MAX;
 217
 218        if (!down_read_trylock(&shrinker_rwsem)) {
 219                /* Assume we'll be able to shrink next time */
 220                ret = 1;
 221                goto out;
 222        }
 223
 224        list_for_each_entry(shrinker, &shrinker_list, list) {
 225                unsigned long long delta;
 226                long total_scan;
 227                long max_pass;
 228                int shrink_ret = 0;
 229                long nr;
 230                long new_nr;
 231                long batch_size = shrinker->batch ? shrinker->batch
 232                                                  : SHRINK_BATCH;
 233
 234                max_pass = do_shrinker_shrink(shrinker, shrink, 0);
 235                if (max_pass <= 0)
 236                        continue;
 237
 238                /*
 239                 * copy the current shrinker scan count into a local variable
 240                 * and zero it so that other concurrent shrinker invocations
 241                 * don't also do this scanning work.
 242                 */
 243                nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
 244
 245                total_scan = nr;
 246                delta = (4 * nr_pages_scanned) / shrinker->seeks;
 247                delta *= max_pass;
 248                do_div(delta, lru_pages + 1);
 249                total_scan += delta;
 250                if (total_scan < 0) {
 251                        printk(KERN_ERR "shrink_slab: %pF negative objects to "
 252                               "delete nr=%ld\n",
 253                               shrinker->shrink, total_scan);
 254                        total_scan = max_pass;
 255                }
 256
 257                /*
 258                 * We need to avoid excessive windup on filesystem shrinkers
 259                 * due to large numbers of GFP_NOFS allocations causing the
 260                 * shrinkers to return -1 all the time. This results in a large
 261                 * nr being built up so when a shrink that can do some work
 262                 * comes along it empties the entire cache due to nr >>>
 263                 * max_pass.  This is bad for sustaining a working set in
 264                 * memory.
 265                 *
 266                 * Hence only allow the shrinker to scan the entire cache when
 267                 * a large delta change is calculated directly.
 268                 */
 269                if (delta < max_pass / 4)
 270                        total_scan = min(total_scan, max_pass / 2);
 271
 272                /*
 273                 * Avoid risking looping forever due to too large nr value:
 274                 * never try to free more than twice the estimate number of
 275                 * freeable entries.
 276                 */
 277                if (total_scan > max_pass * 2)
 278                        total_scan = max_pass * 2;
 279
 280                trace_mm_shrink_slab_start(shrinker, shrink, nr,
 281                                        nr_pages_scanned, lru_pages,
 282                                        max_pass, delta, total_scan);
 283
 284                while (total_scan >= batch_size) {
 285                        int nr_before;
 286
 287                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
 288                        shrink_ret = do_shrinker_shrink(shrinker, shrink,
 289                                                        batch_size);
 290                        if (shrink_ret == -1)
 291                                break;
 292                        if (shrink_ret < nr_before)
 293                                ret += nr_before - shrink_ret;
 294                        count_vm_events(SLABS_SCANNED, batch_size);
 295                        total_scan -= batch_size;
 296
 297                        cond_resched();
 298                }
 299
 300                /*
 301                 * move the unused scan count back into the shrinker in a
 302                 * manner that handles concurrent updates. If we exhausted the
 303                 * scan, there is no need to do an update.
 304                 */
 305                if (total_scan > 0)
 306                        new_nr = atomic_long_add_return(total_scan,
 307                                        &shrinker->nr_in_batch);
 308                else
 309                        new_nr = atomic_long_read(&shrinker->nr_in_batch);
 310
 311                trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
 312        }
 313        up_read(&shrinker_rwsem);
 314out:
 315        cond_resched();
 316        return ret;
 317}
 318
 319static inline int is_page_cache_freeable(struct page *page)
 320{
 321        /*
 322         * A freeable page cache page is referenced only by the caller
 323         * that isolated the page, the page cache radix tree and
 324         * optional buffer heads at page->private.
 325         */
 326        return page_count(page) - page_has_private(page) == 2;
 327}
 328
 329static int may_write_to_queue(struct backing_dev_info *bdi,
 330                              struct scan_control *sc)
 331{
 332        if (current->flags & PF_SWAPWRITE)
 333                return 1;
 334        if (!bdi_write_congested(bdi))
 335                return 1;
 336        if (bdi == current->backing_dev_info)
 337                return 1;
 338        return 0;
 339}
 340
 341/*
 342 * We detected a synchronous write error writing a page out.  Probably
 343 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 344 * fsync(), msync() or close().
 345 *
 346 * The tricky part is that after writepage we cannot touch the mapping: nothing
 347 * prevents it from being freed up.  But we have a ref on the page and once
 348 * that page is locked, the mapping is pinned.
 349 *
 350 * We're allowed to run sleeping lock_page() here because we know the caller has
 351 * __GFP_FS.
 352 */
 353static void handle_write_error(struct address_space *mapping,
 354                                struct page *page, int error)
 355{
 356        lock_page(page);
 357        if (page_mapping(page) == mapping)
 358                mapping_set_error(mapping, error);
 359        unlock_page(page);
 360}
 361
 362/* possible outcome of pageout() */
 363typedef enum {
 364        /* failed to write page out, page is locked */
 365        PAGE_KEEP,
 366        /* move page to the active list, page is locked */
 367        PAGE_ACTIVATE,
 368        /* page has been sent to the disk successfully, page is unlocked */
 369        PAGE_SUCCESS,
 370        /* page is clean and locked */
 371        PAGE_CLEAN,
 372} pageout_t;
 373
 374/*
 375 * pageout is called by shrink_page_list() for each dirty page.
 376 * Calls ->writepage().
 377 */
 378static pageout_t pageout(struct page *page, struct address_space *mapping,
 379                         struct scan_control *sc)
 380{
 381        /*
 382         * If the page is dirty, only perform writeback if that write
 383         * will be non-blocking.  To prevent this allocation from being
 384         * stalled by pagecache activity.  But note that there may be
 385         * stalls if we need to run get_block().  We could test
 386         * PagePrivate for that.
 387         *
 388         * If this process is currently in __generic_file_aio_write() against
 389         * this page's queue, we can perform writeback even if that
 390         * will block.
 391         *
 392         * If the page is swapcache, write it back even if that would
 393         * block, for some throttling. This happens by accident, because
 394         * swap_backing_dev_info is bust: it doesn't reflect the
 395         * congestion state of the swapdevs.  Easy to fix, if needed.
 396         */
 397        if (!is_page_cache_freeable(page))
 398                return PAGE_KEEP;
 399        if (!mapping) {
 400                /*
 401                 * Some data journaling orphaned pages can have
 402                 * page->mapping == NULL while being dirty with clean buffers.
 403                 */
 404                if (page_has_private(page)) {
 405                        if (try_to_free_buffers(page)) {
 406                                ClearPageDirty(page);
 407                                printk("%s: orphaned page\n", __func__);
 408                                return PAGE_CLEAN;
 409                        }
 410                }
 411                return PAGE_KEEP;
 412        }
 413        if (mapping->a_ops->writepage == NULL)
 414                return PAGE_ACTIVATE;
 415        if (!may_write_to_queue(mapping->backing_dev_info, sc))
 416                return PAGE_KEEP;
 417
 418        if (clear_page_dirty_for_io(page)) {
 419                int res;
 420                struct writeback_control wbc = {
 421                        .sync_mode = WB_SYNC_NONE,
 422                        .nr_to_write = SWAP_CLUSTER_MAX,
 423                        .range_start = 0,
 424                        .range_end = LLONG_MAX,
 425                        .for_reclaim = 1,
 426                };
 427
 428                SetPageReclaim(page);
 429                res = mapping->a_ops->writepage(page, &wbc);
 430                if (res < 0)
 431                        handle_write_error(mapping, page, res);
 432                if (res == AOP_WRITEPAGE_ACTIVATE) {
 433                        ClearPageReclaim(page);
 434                        return PAGE_ACTIVATE;
 435                }
 436
 437                if (!PageWriteback(page)) {
 438                        /* synchronous write or broken a_ops? */
 439                        ClearPageReclaim(page);
 440                }
 441                trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
 442                inc_zone_page_state(page, NR_VMSCAN_WRITE);
 443                return PAGE_SUCCESS;
 444        }
 445
 446        return PAGE_CLEAN;
 447}
 448
 449/*
 450 * Same as remove_mapping, but if the page is removed from the mapping, it
 451 * gets returned with a refcount of 0.
 452 */
 453static int __remove_mapping(struct address_space *mapping, struct page *page)
 454{
 455        BUG_ON(!PageLocked(page));
 456        BUG_ON(mapping != page_mapping(page));
 457
 458        spin_lock_irq(&mapping->tree_lock);
 459        /*
 460         * The non racy check for a busy page.
 461         *
 462         * Must be careful with the order of the tests. When someone has
 463         * a ref to the page, it may be possible that they dirty it then
 464         * drop the reference. So if PageDirty is tested before page_count
 465         * here, then the following race may occur:
 466         *
 467         * get_user_pages(&page);
 468         * [user mapping goes away]
 469         * write_to(page);
 470         *                              !PageDirty(page)    [good]
 471         * SetPageDirty(page);
 472         * put_page(page);
 473         *                              !page_count(page)   [good, discard it]
 474         *
 475         * [oops, our write_to data is lost]
 476         *
 477         * Reversing the order of the tests ensures such a situation cannot
 478         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 479         * load is not satisfied before that of page->_count.
 480         *
 481         * Note that if SetPageDirty is always performed via set_page_dirty,
 482         * and thus under tree_lock, then this ordering is not required.
 483         */
 484        if (!page_freeze_refs(page, 2))
 485                goto cannot_free;
 486        /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
 487        if (unlikely(PageDirty(page))) {
 488                page_unfreeze_refs(page, 2);
 489                goto cannot_free;
 490        }
 491
 492        if (PageSwapCache(page)) {
 493                swp_entry_t swap = { .val = page_private(page) };
 494                __delete_from_swap_cache(page);
 495                spin_unlock_irq(&mapping->tree_lock);
 496                swapcache_free(swap, page);
 497        } else {
 498                void (*freepage)(struct page *);
 499
 500                freepage = mapping->a_ops->freepage;
 501
 502                __delete_from_page_cache(page);
 503                spin_unlock_irq(&mapping->tree_lock);
 504                mem_cgroup_uncharge_cache_page(page);
 505
 506                if (freepage != NULL)
 507                        freepage(page);
 508        }
 509
 510        return 1;
 511
 512cannot_free:
 513        spin_unlock_irq(&mapping->tree_lock);
 514        return 0;
 515}
 516
 517/*
 518 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 519 * someone else has a ref on the page, abort and return 0.  If it was
 520 * successfully detached, return 1.  Assumes the caller has a single ref on
 521 * this page.
 522 */
 523int remove_mapping(struct address_space *mapping, struct page *page)
 524{
 525        if (__remove_mapping(mapping, page)) {
 526                /*
 527                 * Unfreezing the refcount with 1 rather than 2 effectively
 528                 * drops the pagecache ref for us without requiring another
 529                 * atomic operation.
 530                 */
 531                page_unfreeze_refs(page, 1);
 532                return 1;
 533        }
 534        return 0;
 535}
 536
 537/**
 538 * putback_lru_page - put previously isolated page onto appropriate LRU list
 539 * @page: page to be put back to appropriate lru list
 540 *
 541 * Add previously isolated @page to appropriate LRU list.
 542 * Page may still be unevictable for other reasons.
 543 *
 544 * lru_lock must not be held, interrupts must be enabled.
 545 */
 546void putback_lru_page(struct page *page)
 547{
 548        int lru;
 549        int was_unevictable = PageUnevictable(page);
 550
 551        VM_BUG_ON(PageLRU(page));
 552
 553redo:
 554        ClearPageUnevictable(page);
 555
 556        if (page_evictable(page)) {
 557                /*
 558                 * For evictable pages, we can use the cache.
 559                 * In event of a race, worst case is we end up with an
 560                 * unevictable page on [in]active list.
 561                 * We know how to handle that.
 562                 */
 563                lru = page_lru_base_type(page);
 564                lru_cache_add(page);
 565        } else {
 566                /*
 567                 * Put unevictable pages directly on zone's unevictable
 568                 * list.
 569                 */
 570                lru = LRU_UNEVICTABLE;
 571                add_page_to_unevictable_list(page);
 572                /*
 573                 * When racing with an mlock or AS_UNEVICTABLE clearing
 574                 * (page is unlocked) make sure that if the other thread
 575                 * does not observe our setting of PG_lru and fails
 576                 * isolation/check_move_unevictable_pages,
 577                 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
 578                 * the page back to the evictable list.
 579                 *
 580                 * The other side is TestClearPageMlocked() or shmem_lock().
 581                 */
 582                smp_mb();
 583        }
 584
 585        /*
 586         * page's status can change while we move it among lru. If an evictable
 587         * page is on unevictable list, it never be freed. To avoid that,
 588         * check after we added it to the list, again.
 589         */
 590        if (lru == LRU_UNEVICTABLE && page_evictable(page)) {
 591                if (!isolate_lru_page(page)) {
 592                        put_page(page);
 593                        goto redo;
 594                }
 595                /* This means someone else dropped this page from LRU
 596                 * So, it will be freed or putback to LRU again. There is
 597                 * nothing to do here.
 598                 */
 599        }
 600
 601        if (was_unevictable && lru != LRU_UNEVICTABLE)
 602                count_vm_event(UNEVICTABLE_PGRESCUED);
 603        else if (!was_unevictable && lru == LRU_UNEVICTABLE)
 604                count_vm_event(UNEVICTABLE_PGCULLED);
 605
 606        put_page(page);         /* drop ref from isolate */
 607}
 608
 609enum page_references {
 610        PAGEREF_RECLAIM,
 611        PAGEREF_RECLAIM_CLEAN,
 612        PAGEREF_KEEP,
 613        PAGEREF_ACTIVATE,
 614};
 615
 616static enum page_references page_check_references(struct page *page,
 617                                                  struct scan_control *sc)
 618{
 619        int referenced_ptes, referenced_page;
 620        unsigned long vm_flags;
 621
 622        referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
 623                                          &vm_flags);
 624        referenced_page = TestClearPageReferenced(page);
 625
 626        /*
 627         * Mlock lost the isolation race with us.  Let try_to_unmap()
 628         * move the page to the unevictable list.
 629         */
 630        if (vm_flags & VM_LOCKED)
 631                return PAGEREF_RECLAIM;
 632
 633        if (referenced_ptes) {
 634                if (PageSwapBacked(page))
 635                        return PAGEREF_ACTIVATE;
 636                /*
 637                 * All mapped pages start out with page table
 638                 * references from the instantiating fault, so we need
 639                 * to look twice if a mapped file page is used more
 640                 * than once.
 641                 *
 642                 * Mark it and spare it for another trip around the
 643                 * inactive list.  Another page table reference will
 644                 * lead to its activation.
 645                 *
 646                 * Note: the mark is set for activated pages as well
 647                 * so that recently deactivated but used pages are
 648                 * quickly recovered.
 649                 */
 650                SetPageReferenced(page);
 651
 652                if (referenced_page || referenced_ptes > 1)
 653                        return PAGEREF_ACTIVATE;
 654
 655                /*
 656                 * Activate file-backed executable pages after first usage.
 657                 */
 658                if (vm_flags & VM_EXEC)
 659                        return PAGEREF_ACTIVATE;
 660
 661                return PAGEREF_KEEP;
 662        }
 663
 664        /* Reclaim if clean, defer dirty pages to writeback */
 665        if (referenced_page && !PageSwapBacked(page))
 666                return PAGEREF_RECLAIM_CLEAN;
 667
 668        return PAGEREF_RECLAIM;
 669}
 670
 671/* Check if a page is dirty or under writeback */
 672static void page_check_dirty_writeback(struct page *page,
 673                                       bool *dirty, bool *writeback)
 674{
 675        struct address_space *mapping;
 676
 677        /*
 678         * Anonymous pages are not handled by flushers and must be written
 679         * from reclaim context. Do not stall reclaim based on them
 680         */
 681        if (!page_is_file_cache(page)) {
 682                *dirty = false;
 683                *writeback = false;
 684                return;
 685        }
 686
 687        /* By default assume that the page flags are accurate */
 688        *dirty = PageDirty(page);
 689        *writeback = PageWriteback(page);
 690
 691        /* Verify dirty/writeback state if the filesystem supports it */
 692        if (!page_has_private(page))
 693                return;
 694
 695        mapping = page_mapping(page);
 696        if (mapping && mapping->a_ops->is_dirty_writeback)
 697                mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
 698}
 699
 700/*
 701 * shrink_page_list() returns the number of reclaimed pages
 702 */
 703static unsigned long shrink_page_list(struct list_head *page_list,
 704                                      struct zone *zone,
 705                                      struct scan_control *sc,
 706                                      enum ttu_flags ttu_flags,
 707                                      unsigned long *ret_nr_dirty,
 708                                      unsigned long *ret_nr_unqueued_dirty,
 709                                      unsigned long *ret_nr_congested,
 710                                      unsigned long *ret_nr_writeback,
 711                                      unsigned long *ret_nr_immediate,
 712                                      bool force_reclaim)
 713{
 714        LIST_HEAD(ret_pages);
 715        LIST_HEAD(free_pages);
 716        int pgactivate = 0;
 717        unsigned long nr_unqueued_dirty = 0;
 718        unsigned long nr_dirty = 0;
 719        unsigned long nr_congested = 0;
 720        unsigned long nr_reclaimed = 0;
 721        unsigned long nr_writeback = 0;
 722        unsigned long nr_immediate = 0;
 723
 724        cond_resched();
 725
 726        mem_cgroup_uncharge_start();
 727        while (!list_empty(page_list)) {
 728                struct address_space *mapping;
 729                struct page *page;
 730                int may_enter_fs;
 731                enum page_references references = PAGEREF_RECLAIM_CLEAN;
 732                bool dirty, writeback;
 733
 734                cond_resched();
 735
 736                page = lru_to_page(page_list);
 737                list_del(&page->lru);
 738
 739                if (!trylock_page(page))
 740                        goto keep;
 741
 742                VM_BUG_ON(PageActive(page));
 743                VM_BUG_ON(page_zone(page) != zone);
 744
 745                sc->nr_scanned++;
 746
 747                if (unlikely(!page_evictable(page)))
 748                        goto cull_mlocked;
 749
 750                if (!sc->may_unmap && page_mapped(page))
 751                        goto keep_locked;
 752
 753                /* Double the slab pressure for mapped and swapcache pages */
 754                if (page_mapped(page) || PageSwapCache(page))
 755                        sc->nr_scanned++;
 756
 757                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 758                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 759
 760                /*
 761                 * The number of dirty pages determines if a zone is marked
 762                 * reclaim_congested which affects wait_iff_congested. kswapd
 763                 * will stall and start writing pages if the tail of the LRU
 764                 * is all dirty unqueued pages.
 765                 */
 766                page_check_dirty_writeback(page, &dirty, &writeback);
 767                if (dirty || writeback)
 768                        nr_dirty++;
 769
 770                if (dirty && !writeback)
 771                        nr_unqueued_dirty++;
 772
 773                /*
 774                 * Treat this page as congested if the underlying BDI is or if
 775                 * pages are cycling through the LRU so quickly that the
 776                 * pages marked for immediate reclaim are making it to the
 777                 * end of the LRU a second time.
 778                 */
 779                mapping = page_mapping(page);
 780                if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
 781                    (writeback && PageReclaim(page)))
 782                        nr_congested++;
 783
 784                /*
 785                 * If a page at the tail of the LRU is under writeback, there
 786                 * are three cases to consider.
 787                 *
 788                 * 1) If reclaim is encountering an excessive number of pages
 789                 *    under writeback and this page is both under writeback and
 790                 *    PageReclaim then it indicates that pages are being queued
 791                 *    for IO but are being recycled through the LRU before the
 792                 *    IO can complete. Waiting on the page itself risks an
 793                 *    indefinite stall if it is impossible to writeback the
 794                 *    page due to IO error or disconnected storage so instead
 795                 *    note that the LRU is being scanned too quickly and the
 796                 *    caller can stall after page list has been processed.
 797                 *
 798                 * 2) Global reclaim encounters a page, memcg encounters a
 799                 *    page that is not marked for immediate reclaim or
 800                 *    the caller does not have __GFP_IO. In this case mark
 801                 *    the page for immediate reclaim and continue scanning.
 802                 *
 803                 *    __GFP_IO is checked  because a loop driver thread might
 804                 *    enter reclaim, and deadlock if it waits on a page for
 805                 *    which it is needed to do the write (loop masks off
 806                 *    __GFP_IO|__GFP_FS for this reason); but more thought
 807                 *    would probably show more reasons.
 808                 *
 809                 *    Don't require __GFP_FS, since we're not going into the
 810                 *    FS, just waiting on its writeback completion. Worryingly,
 811                 *    ext4 gfs2 and xfs allocate pages with
 812                 *    grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
 813                 *    may_enter_fs here is liable to OOM on them.
 814                 *
 815                 * 3) memcg encounters a page that is not already marked
 816                 *    PageReclaim. memcg does not have any dirty pages
 817                 *    throttling so we could easily OOM just because too many
 818                 *    pages are in writeback and there is nothing else to
 819                 *    reclaim. Wait for the writeback to complete.
 820                 */
 821                if (PageWriteback(page)) {
 822                        /* Case 1 above */
 823                        if (current_is_kswapd() &&
 824                            PageReclaim(page) &&
 825                            zone_is_reclaim_writeback(zone)) {
 826                                nr_immediate++;
 827                                goto keep_locked;
 828
 829                        /* Case 2 above */
 830                        } else if (global_reclaim(sc) ||
 831                            !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
 832                                /*
 833                                 * This is slightly racy - end_page_writeback()
 834                                 * might have just cleared PageReclaim, then
 835                                 * setting PageReclaim here end up interpreted
 836                                 * as PageReadahead - but that does not matter
 837                                 * enough to care.  What we do want is for this
 838                                 * page to have PageReclaim set next time memcg
 839                                 * reclaim reaches the tests above, so it will
 840                                 * then wait_on_page_writeback() to avoid OOM;
 841                                 * and it's also appropriate in global reclaim.
 842                                 */
 843                                SetPageReclaim(page);
 844                                nr_writeback++;
 845
 846                                goto keep_locked;
 847
 848                        /* Case 3 above */
 849                        } else {
 850                                wait_on_page_writeback(page);
 851                        }
 852                }
 853
 854                if (!force_reclaim)
 855                        references = page_check_references(page, sc);
 856
 857                switch (references) {
 858                case PAGEREF_ACTIVATE:
 859                        goto activate_locked;
 860                case PAGEREF_KEEP:
 861                        goto keep_locked;
 862                case PAGEREF_RECLAIM:
 863                case PAGEREF_RECLAIM_CLEAN:
 864                        ; /* try to reclaim the page below */
 865                }
 866
 867                /*
 868                 * Anonymous process memory has backing store?
 869                 * Try to allocate it some swap space here.
 870                 */
 871                if (PageAnon(page) && !PageSwapCache(page)) {
 872                        if (!(sc->gfp_mask & __GFP_IO))
 873                                goto keep_locked;
 874                        if (!add_to_swap(page, page_list))
 875                                goto activate_locked;
 876                        may_enter_fs = 1;
 877
 878                        /* Adding to swap updated mapping */
 879                        mapping = page_mapping(page);
 880                }
 881
 882                /*
 883                 * The page is mapped into the page tables of one or more
 884                 * processes. Try to unmap it here.
 885                 */
 886                if (page_mapped(page) && mapping) {
 887                        switch (try_to_unmap(page, ttu_flags)) {
 888                        case SWAP_FAIL:
 889                                goto activate_locked;
 890                        case SWAP_AGAIN:
 891                                goto keep_locked;
 892                        case SWAP_MLOCK:
 893                                goto cull_mlocked;
 894                        case SWAP_SUCCESS:
 895                                ; /* try to free the page below */
 896                        }
 897                }
 898
 899                if (PageDirty(page)) {
 900                        /*
 901                         * Only kswapd can writeback filesystem pages to
 902                         * avoid risk of stack overflow but only writeback
 903                         * if many dirty pages have been encountered.
 904                         */
 905                        if (page_is_file_cache(page) &&
 906                                        (!current_is_kswapd() ||
 907                                         !zone_is_reclaim_dirty(zone))) {
 908                                /*
 909                                 * Immediately reclaim when written back.
 910                                 * Similar in principal to deactivate_page()
 911                                 * except we already have the page isolated
 912                                 * and know it's dirty
 913                                 */
 914                                inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
 915                                SetPageReclaim(page);
 916
 917                                goto keep_locked;
 918                        }
 919
 920                        if (references == PAGEREF_RECLAIM_CLEAN)
 921                                goto keep_locked;
 922                        if (!may_enter_fs)
 923                                goto keep_locked;
 924                        if (!sc->may_writepage)
 925                                goto keep_locked;
 926
 927                        /* Page is dirty, try to write it out here */
 928                        switch (pageout(page, mapping, sc)) {
 929                        case PAGE_KEEP:
 930                                goto keep_locked;
 931                        case PAGE_ACTIVATE:
 932                                goto activate_locked;
 933                        case PAGE_SUCCESS:
 934                                if (PageWriteback(page))
 935                                        goto keep;
 936                                if (PageDirty(page))
 937                                        goto keep;
 938
 939                                /*
 940                                 * A synchronous write - probably a ramdisk.  Go
 941                                 * ahead and try to reclaim the page.
 942                                 */
 943                                if (!trylock_page(page))
 944                                        goto keep;
 945                                if (PageDirty(page) || PageWriteback(page))
 946                                        goto keep_locked;
 947                                mapping = page_mapping(page);
 948                        case PAGE_CLEAN:
 949                                ; /* try to free the page below */
 950                        }
 951                }
 952
 953                /*
 954                 * If the page has buffers, try to free the buffer mappings
 955                 * associated with this page. If we succeed we try to free
 956                 * the page as well.
 957                 *
 958                 * We do this even if the page is PageDirty().
 959                 * try_to_release_page() does not perform I/O, but it is
 960                 * possible for a page to have PageDirty set, but it is actually
 961                 * clean (all its buffers are clean).  This happens if the
 962                 * buffers were written out directly, with submit_bh(). ext3
 963                 * will do this, as well as the blockdev mapping.
 964                 * try_to_release_page() will discover that cleanness and will
 965                 * drop the buffers and mark the page clean - it can be freed.
 966                 *
 967                 * Rarely, pages can have buffers and no ->mapping.  These are
 968                 * the pages which were not successfully invalidated in
 969                 * truncate_complete_page().  We try to drop those buffers here
 970                 * and if that worked, and the page is no longer mapped into
 971                 * process address space (page_count == 1) it can be freed.
 972                 * Otherwise, leave the page on the LRU so it is swappable.
 973                 */
 974                if (page_has_private(page)) {
 975                        if (!try_to_release_page(page, sc->gfp_mask))
 976                                goto activate_locked;
 977                        if (!mapping && page_count(page) == 1) {
 978                                unlock_page(page);
 979                                if (put_page_testzero(page))
 980                                        goto free_it;
 981                                else {
 982                                        /*
 983                                         * rare race with speculative reference.
 984                                         * the speculative reference will free
 985                                         * this page shortly, so we may
 986                                         * increment nr_reclaimed here (and
 987                                         * leave it off the LRU).
 988                                         */
 989                                        nr_reclaimed++;
 990                                        continue;
 991                                }
 992                        }
 993                }
 994
 995                if (!mapping || !__remove_mapping(mapping, page))
 996                        goto keep_locked;
 997
 998                /*
 999                 * At this point, we have no other references and there is
1000                 * no way to pick any more up (removed from LRU, removed
1001                 * from pagecache). Can use non-atomic bitops now (and
1002                 * we obviously don't have to worry about waking up a process
1003                 * waiting on the page lock, because there are no references.
1004                 */
1005                __clear_page_locked(page);
1006free_it:
1007                nr_reclaimed++;
1008
1009                /*
1010                 * Is there need to periodically free_page_list? It would
1011                 * appear not as the counts should be low
1012                 */
1013                list_add(&page->lru, &free_pages);
1014                continue;
1015
1016cull_mlocked:
1017                if (PageSwapCache(page))
1018                        try_to_free_swap(page);
1019                unlock_page(page);
1020                putback_lru_page(page);
1021                continue;
1022
1023activate_locked:
1024                /* Not a candidate for swapping, so reclaim swap space. */
1025                if (PageSwapCache(page) && vm_swap_full())
1026                        try_to_free_swap(page);
1027                VM_BUG_ON(PageActive(page));
1028                SetPageActive(page);
1029                pgactivate++;
1030keep_locked:
1031                unlock_page(page);
1032keep:
1033                list_add(&page->lru, &ret_pages);
1034                VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
1035        }
1036
1037        free_hot_cold_page_list(&free_pages, 1);
1038
1039        list_splice(&ret_pages, page_list);
1040        count_vm_events(PGACTIVATE, pgactivate);
1041        mem_cgroup_uncharge_end();
1042        *ret_nr_dirty += nr_dirty;
1043        *ret_nr_congested += nr_congested;
1044        *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1045        *ret_nr_writeback += nr_writeback;
1046        *ret_nr_immediate += nr_immediate;
1047        return nr_reclaimed;
1048}
1049
1050unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1051                                            struct list_head *page_list)
1052{
1053        struct scan_control sc = {
1054                .gfp_mask = GFP_KERNEL,
1055                .priority = DEF_PRIORITY,
1056                .may_unmap = 1,
1057        };
1058        unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1059        struct page *page, *next;
1060        LIST_HEAD(clean_pages);
1061
1062        list_for_each_entry_safe(page, next, page_list, lru) {
1063                if (page_is_file_cache(page) && !PageDirty(page)) {
1064                        ClearPageActive(page);
1065                        list_move(&page->lru, &clean_pages);
1066                }
1067        }
1068
1069        ret = shrink_page_list(&clean_pages, zone, &sc,
1070                        TTU_UNMAP|TTU_IGNORE_ACCESS,
1071                        &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1072        list_splice(&clean_pages, page_list);
1073        __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
1074        return ret;
1075}
1076
1077/*
1078 * Attempt to remove the specified page from its LRU.  Only take this page
1079 * if it is of the appropriate PageActive status.  Pages which are being
1080 * freed elsewhere are also ignored.
1081 *
1082 * page:        page to consider
1083 * mode:        one of the LRU isolation modes defined above
1084 *
1085 * returns 0 on success, -ve errno on failure.
1086 */
1087int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1088{
1089        int ret = -EINVAL;
1090
1091        /* Only take pages on the LRU. */
1092        if (!PageLRU(page))
1093                return ret;
1094
1095        /* Compaction should not handle unevictable pages but CMA can do so */
1096        if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1097                return ret;
1098
1099        ret = -EBUSY;
1100
1101        /*
1102         * To minimise LRU disruption, the caller can indicate that it only
1103         * wants to isolate pages it will be able to operate on without
1104         * blocking - clean pages for the most part.
1105         *
1106         * ISOLATE_CLEAN means that only clean pages should be isolated. This
1107         * is used by reclaim when it is cannot write to backing storage
1108         *
1109         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1110         * that it is possible to migrate without blocking
1111         */
1112        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1113                /* All the caller can do on PageWriteback is block */
1114                if (PageWriteback(page))
1115                        return ret;
1116
1117                if (PageDirty(page)) {
1118                        struct address_space *mapping;
1119
1120                        /* ISOLATE_CLEAN means only clean pages */
1121                        if (mode & ISOLATE_CLEAN)
1122                                return ret;
1123
1124                        /*
1125                         * Only pages without mappings or that have a
1126                         * ->migratepage callback are possible to migrate
1127                         * without blocking
1128                         */
1129                        mapping = page_mapping(page);
1130                        if (mapping && !mapping->a_ops->migratepage)
1131                                return ret;
1132                }
1133        }
1134
1135        if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1136                return ret;
1137
1138        if (likely(get_page_unless_zero(page))) {
1139                /*
1140                 * Be careful not to clear PageLRU until after we're
1141                 * sure the page is not being freed elsewhere -- the
1142                 * page release code relies on it.
1143                 */
1144                ClearPageLRU(page);
1145                ret = 0;
1146        }
1147
1148        return ret;
1149}
1150
1151/*
1152 * zone->lru_lock is heavily contended.  Some of the functions that
1153 * shrink the lists perform better by taking out a batch of pages
1154 * and working on them outside the LRU lock.
1155 *
1156 * For pagecache intensive workloads, this function is the hottest
1157 * spot in the kernel (apart from copy_*_user functions).
1158 *
1159 * Appropriate locks must be held before calling this function.
1160 *
1161 * @nr_to_scan: The number of pages to look through on the list.
1162 * @lruvec:     The LRU vector to pull pages from.
1163 * @dst:        The temp list to put pages on to.
1164 * @nr_scanned: The number of pages that were scanned.
1165 * @sc:         The scan_control struct for this reclaim session
1166 * @mode:       One of the LRU isolation modes
1167 * @lru:        LRU list id for isolating
1168 *
1169 * returns how many pages were moved onto *@dst.
1170 */
1171static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1172                struct lruvec *lruvec, struct list_head *dst,
1173                unsigned long *nr_scanned, struct scan_control *sc,
1174                isolate_mode_t mode, enum lru_list lru)
1175{
1176        struct list_head *src = &lruvec->lists[lru];
1177        unsigned long nr_taken = 0;
1178        unsigned long scan;
1179
1180        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1181                struct page *page;
1182                int nr_pages;
1183
1184                page = lru_to_page(src);
1185                prefetchw_prev_lru_page(page, src, flags);
1186
1187                VM_BUG_ON(!PageLRU(page));
1188
1189                switch (__isolate_lru_page(page, mode)) {
1190                case 0:
1191                        nr_pages = hpage_nr_pages(page);
1192                        mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1193                        list_move(&page->lru, dst);
1194                        nr_taken += nr_pages;
1195                        break;
1196
1197                case -EBUSY:
1198                        /* else it is being freed elsewhere */
1199                        list_move(&page->lru, src);
1200                        continue;
1201
1202                default:
1203                        BUG();
1204                }
1205        }
1206
1207        *nr_scanned = scan;
1208        trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1209                                    nr_taken, mode, is_file_lru(lru));
1210        return nr_taken;
1211}
1212
1213/**
1214 * isolate_lru_page - tries to isolate a page from its LRU list
1215 * @page: page to isolate from its LRU list
1216 *
1217 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1218 * vmstat statistic corresponding to whatever LRU list the page was on.
1219 *
1220 * Returns 0 if the page was removed from an LRU list.
1221 * Returns -EBUSY if the page was not on an LRU list.
1222 *
1223 * The returned page will have PageLRU() cleared.  If it was found on
1224 * the active list, it will have PageActive set.  If it was found on
1225 * the unevictable list, it will have the PageUnevictable bit set. That flag
1226 * may need to be cleared by the caller before letting the page go.
1227 *
1228 * The vmstat statistic corresponding to the list on which the page was
1229 * found will be decremented.
1230 *
1231 * Restrictions:
1232 * (1) Must be called with an elevated refcount on the page. This is a
1233 *     fundamentnal difference from isolate_lru_pages (which is called
1234 *     without a stable reference).
1235 * (2) the lru_lock must not be held.
1236 * (3) interrupts must be enabled.
1237 */
1238int isolate_lru_page(struct page *page)
1239{
1240        int ret = -EBUSY;
1241
1242        VM_BUG_ON(!page_count(page));
1243
1244        if (PageLRU(page)) {
1245                struct zone *zone = page_zone(page);
1246                struct lruvec *lruvec;
1247
1248                spin_lock_irq(&zone->lru_lock);
1249                lruvec = mem_cgroup_page_lruvec(page, zone);
1250                if (PageLRU(page)) {
1251                        int lru = page_lru(page);
1252                        get_page(page);
1253                        ClearPageLRU(page);
1254                        del_page_from_lru_list(page, lruvec, lru);
1255                        ret = 0;
1256                }
1257                spin_unlock_irq(&zone->lru_lock);
1258        }
1259        return ret;
1260}
1261
1262/*
1263 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1264 * then get resheduled. When there are massive number of tasks doing page
1265 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1266 * the LRU list will go small and be scanned faster than necessary, leading to
1267 * unnecessary swapping, thrashing and OOM.
1268 */
1269static int too_many_isolated(struct zone *zone, int file,
1270                struct scan_control *sc)
1271{
1272        unsigned long inactive, isolated;
1273
1274        if (current_is_kswapd())
1275                return 0;
1276
1277        if (!global_reclaim(sc))
1278                return 0;
1279
1280        if (file) {
1281                inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1282                isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1283        } else {
1284                inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1285                isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1286        }
1287
1288        /*
1289         * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1290         * won't get blocked by normal direct-reclaimers, forming a circular
1291         * deadlock.
1292         */
1293        if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1294                inactive >>= 3;
1295
1296        return isolated > inactive;
1297}
1298
1299static noinline_for_stack void
1300putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1301{
1302        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1303        struct zone *zone = lruvec_zone(lruvec);
1304        LIST_HEAD(pages_to_free);
1305
1306        /*
1307         * Put back any unfreeable pages.
1308         */
1309        while (!list_empty(page_list)) {
1310                struct page *page = lru_to_page(page_list);
1311                int lru;
1312
1313                VM_BUG_ON(PageLRU(page));
1314                list_del(&page->lru);
1315                if (unlikely(!page_evictable(page))) {
1316                        spin_unlock_irq(&zone->lru_lock);
1317                        putback_lru_page(page);
1318                        spin_lock_irq(&zone->lru_lock);
1319                        continue;
1320                }
1321
1322                lruvec = mem_cgroup_page_lruvec(page, zone);
1323
1324                SetPageLRU(page);
1325                lru = page_lru(page);
1326                add_page_to_lru_list(page, lruvec, lru);
1327
1328                if (is_active_lru(lru)) {
1329                        int file = is_file_lru(lru);
1330                        int numpages = hpage_nr_pages(page);
1331                        reclaim_stat->recent_rotated[file] += numpages;
1332                }
1333                if (put_page_testzero(page)) {
1334                        __ClearPageLRU(page);
1335                        __ClearPageActive(page);
1336                        del_page_from_lru_list(page, lruvec, lru);
1337
1338                        if (unlikely(PageCompound(page))) {
1339                                spin_unlock_irq(&zone->lru_lock);
1340                                (*get_compound_page_dtor(page))(page);
1341                                spin_lock_irq(&zone->lru_lock);
1342                        } else
1343                                list_add(&page->lru, &pages_to_free);
1344                }
1345        }
1346
1347        /*
1348         * To save our caller's stack, now use input list for pages to free.
1349         */
1350        list_splice(&pages_to_free, page_list);
1351}
1352
1353/*
1354 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1355 * of reclaimed pages
1356 */
1357static noinline_for_stack unsigned long
1358shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1359                     struct scan_control *sc, enum lru_list lru)
1360{
1361        LIST_HEAD(page_list);
1362        unsigned long nr_scanned;
1363        unsigned long nr_reclaimed = 0;
1364        unsigned long nr_taken;
1365        unsigned long nr_dirty = 0;
1366        unsigned long nr_congested = 0;
1367        unsigned long nr_unqueued_dirty = 0;
1368        unsigned long nr_writeback = 0;
1369        unsigned long nr_immediate = 0;
1370        isolate_mode_t isolate_mode = 0;
1371        int file = is_file_lru(lru);
1372        struct zone *zone = lruvec_zone(lruvec);
1373        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1374
1375        while (unlikely(too_many_isolated(zone, file, sc))) {
1376                congestion_wait(BLK_RW_ASYNC, HZ/10);
1377
1378                /* We are about to die and free our memory. Return now. */
1379                if (fatal_signal_pending(current))
1380                        return SWAP_CLUSTER_MAX;
1381        }
1382
1383        lru_add_drain();
1384
1385        if (!sc->may_unmap)
1386                isolate_mode |= ISOLATE_UNMAPPED;
1387        if (!sc->may_writepage)
1388                isolate_mode |= ISOLATE_CLEAN;
1389
1390        spin_lock_irq(&zone->lru_lock);
1391
1392        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1393                                     &nr_scanned, sc, isolate_mode, lru);
1394
1395        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1396        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1397
1398        if (global_reclaim(sc)) {
1399                zone->pages_scanned += nr_scanned;
1400                if (current_is_kswapd())
1401                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1402                else
1403                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1404        }
1405        spin_unlock_irq(&zone->lru_lock);
1406
1407        if (nr_taken == 0)
1408                return 0;
1409
1410        nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1411                                &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1412                                &nr_writeback, &nr_immediate,
1413                                false);
1414
1415        spin_lock_irq(&zone->lru_lock);
1416
1417        reclaim_stat->recent_scanned[file] += nr_taken;
1418
1419        if (global_reclaim(sc)) {
1420                if (current_is_kswapd())
1421                        __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1422                                               nr_reclaimed);
1423                else
1424                        __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1425                                               nr_reclaimed);
1426        }
1427
1428        putback_inactive_pages(lruvec, &page_list);
1429
1430        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1431
1432        spin_unlock_irq(&zone->lru_lock);
1433
1434        free_hot_cold_page_list(&page_list, 1);
1435
1436        /*
1437         * If reclaim is isolating dirty pages under writeback, it implies
1438         * that the long-lived page allocation rate is exceeding the page
1439         * laundering rate. Either the global limits are not being effective
1440         * at throttling processes due to the page distribution throughout
1441         * zones or there is heavy usage of a slow backing device. The
1442         * only option is to throttle from reclaim context which is not ideal
1443         * as there is no guarantee the dirtying process is throttled in the
1444         * same way balance_dirty_pages() manages.
1445         *
1446         * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1447         * of pages under pages flagged for immediate reclaim and stall if any
1448         * are encountered in the nr_immediate check below.
1449         */
1450        if (nr_writeback && nr_writeback == nr_taken)
1451                zone_set_flag(zone, ZONE_WRITEBACK);
1452
1453        /*
1454         * memcg will stall in page writeback so only consider forcibly
1455         * stalling for global reclaim
1456         */
1457        if (global_reclaim(sc)) {
1458                /*
1459                 * Tag a zone as congested if all the dirty pages scanned were
1460                 * backed by a congested BDI and wait_iff_congested will stall.
1461                 */
1462                if (nr_dirty && nr_dirty == nr_congested)
1463                        zone_set_flag(zone, ZONE_CONGESTED);
1464
1465                /*
1466                 * If dirty pages are scanned that are not queued for IO, it
1467                 * implies that flushers are not keeping up. In this case, flag
1468                 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
1469                 * pages from reclaim context. It will forcibly stall in the
1470                 * next check.
1471                 */
1472                if (nr_unqueued_dirty == nr_taken)
1473                        zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
1474
1475                /*
1476                 * In addition, if kswapd scans pages marked marked for
1477                 * immediate reclaim and under writeback (nr_immediate), it
1478                 * implies that pages are cycling through the LRU faster than
1479                 * they are written so also forcibly stall.
1480                 */
1481                if (nr_unqueued_dirty == nr_taken || nr_immediate)
1482                        congestion_wait(BLK_RW_ASYNC, HZ/10);
1483        }
1484
1485        /*
1486         * Stall direct reclaim for IO completions if underlying BDIs or zone
1487         * is congested. Allow kswapd to continue until it starts encountering
1488         * unqueued dirty pages or cycling through the LRU too quickly.
1489         */
1490        if (!sc->hibernation_mode && !current_is_kswapd())
1491                wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1492
1493        trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1494                zone_idx(zone),
1495                nr_scanned, nr_reclaimed,
1496                sc->priority,
1497                trace_shrink_flags(file));
1498        return nr_reclaimed;
1499}
1500
1501/*
1502 * This moves pages from the active list to the inactive list.
1503 *
1504 * We move them the other way if the page is referenced by one or more
1505 * processes, from rmap.
1506 *
1507 * If the pages are mostly unmapped, the processing is fast and it is
1508 * appropriate to hold zone->lru_lock across the whole operation.  But if
1509 * the pages are mapped, the processing is slow (page_referenced()) so we
1510 * should drop zone->lru_lock around each page.  It's impossible to balance
1511 * this, so instead we remove the pages from the LRU while processing them.
1512 * It is safe to rely on PG_active against the non-LRU pages in here because
1513 * nobody will play with that bit on a non-LRU page.
1514 *
1515 * The downside is that we have to touch page->_count against each page.
1516 * But we had to alter page->flags anyway.
1517 */
1518
1519static void move_active_pages_to_lru(struct lruvec *lruvec,
1520                                     struct list_head *list,
1521                                     struct list_head *pages_to_free,
1522                                     enum lru_list lru)
1523{
1524        struct zone *zone = lruvec_zone(lruvec);
1525        unsigned long pgmoved = 0;
1526        struct page *page;
1527        int nr_pages;
1528
1529        while (!list_empty(list)) {
1530                page = lru_to_page(list);
1531                lruvec = mem_cgroup_page_lruvec(page, zone);
1532
1533                VM_BUG_ON(PageLRU(page));
1534                SetPageLRU(page);
1535
1536                nr_pages = hpage_nr_pages(page);
1537                mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1538                list_move(&page->lru, &lruvec->lists[lru]);
1539                pgmoved += nr_pages;
1540
1541                if (put_page_testzero(page)) {
1542                        __ClearPageLRU(page);
1543                        __ClearPageActive(page);
1544                        del_page_from_lru_list(page, lruvec, lru);
1545
1546                        if (unlikely(PageCompound(page))) {
1547                                spin_unlock_irq(&zone->lru_lock);
1548                                (*get_compound_page_dtor(page))(page);
1549                                spin_lock_irq(&zone->lru_lock);
1550                        } else
1551                                list_add(&page->lru, pages_to_free);
1552                }
1553        }
1554        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1555        if (!is_active_lru(lru))
1556                __count_vm_events(PGDEACTIVATE, pgmoved);
1557}
1558
1559static void shrink_active_list(unsigned long nr_to_scan,
1560                               struct lruvec *lruvec,
1561                               struct scan_control *sc,
1562                               enum lru_list lru)
1563{
1564        unsigned long nr_taken;
1565        unsigned long nr_scanned;
1566        unsigned long vm_flags;
1567        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1568        LIST_HEAD(l_active);
1569        LIST_HEAD(l_inactive);
1570        struct page *page;
1571        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1572        unsigned long nr_rotated = 0;
1573        isolate_mode_t isolate_mode = 0;
1574        int file = is_file_lru(lru);
1575        struct zone *zone = lruvec_zone(lruvec);
1576
1577        lru_add_drain();
1578
1579        if (!sc->may_unmap)
1580                isolate_mode |= ISOLATE_UNMAPPED;
1581        if (!sc->may_writepage)
1582                isolate_mode |= ISOLATE_CLEAN;
1583
1584        spin_lock_irq(&zone->lru_lock);
1585
1586        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1587                                     &nr_scanned, sc, isolate_mode, lru);
1588        if (global_reclaim(sc))
1589                zone->pages_scanned += nr_scanned;
1590
1591        reclaim_stat->recent_scanned[file] += nr_taken;
1592
1593        __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1594        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1595        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1596        spin_unlock_irq(&zone->lru_lock);
1597
1598        while (!list_empty(&l_hold)) {
1599                cond_resched();
1600                page = lru_to_page(&l_hold);
1601                list_del(&page->lru);
1602
1603                if (unlikely(!page_evictable(page))) {
1604                        putback_lru_page(page);
1605                        continue;
1606                }
1607
1608                if (unlikely(buffer_heads_over_limit)) {
1609                        if (page_has_private(page) && trylock_page(page)) {
1610                                if (page_has_private(page))
1611                                        try_to_release_page(page, 0);
1612                                unlock_page(page);
1613                        }
1614                }
1615
1616                if (page_referenced(page, 0, sc->target_mem_cgroup,
1617                                    &vm_flags)) {
1618                        nr_rotated += hpage_nr_pages(page);
1619                        /*
1620                         * Identify referenced, file-backed active pages and
1621                         * give them one more trip around the active list. So
1622                         * that executable code get better chances to stay in
1623                         * memory under moderate memory pressure.  Anon pages
1624                         * are not likely to be evicted by use-once streaming
1625                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1626                         * so we ignore them here.
1627                         */
1628                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1629                                list_add(&page->lru, &l_active);
1630                                continue;
1631                        }
1632                }
1633
1634                ClearPageActive(page);  /* we are de-activating */
1635                list_add(&page->lru, &l_inactive);
1636        }
1637
1638        /*
1639         * Move pages back to the lru list.
1640         */
1641        spin_lock_irq(&zone->lru_lock);
1642        /*
1643         * Count referenced pages from currently used mappings as rotated,
1644         * even though only some of them are actually re-activated.  This
1645         * helps balance scan pressure between file and anonymous pages in
1646         * get_scan_ratio.
1647         */
1648        reclaim_stat->recent_rotated[file] += nr_rotated;
1649
1650        move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1651        move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1652        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1653        spin_unlock_irq(&zone->lru_lock);
1654
1655        free_hot_cold_page_list(&l_hold, 1);
1656}
1657
1658#ifdef CONFIG_SWAP
1659static int inactive_anon_is_low_global(struct zone *zone)
1660{
1661        unsigned long active, inactive;
1662
1663        active = zone_page_state(zone, NR_ACTIVE_ANON);
1664        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1665
1666        if (inactive * zone->inactive_ratio < active)
1667                return 1;
1668
1669        return 0;
1670}
1671
1672/**
1673 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1674 * @lruvec: LRU vector to check
1675 *
1676 * Returns true if the zone does not have enough inactive anon pages,
1677 * meaning some active anon pages need to be deactivated.
1678 */
1679static int inactive_anon_is_low(struct lruvec *lruvec)
1680{
1681        /*
1682         * If we don't have swap space, anonymous page deactivation
1683         * is pointless.
1684         */
1685        if (!total_swap_pages)
1686                return 0;
1687
1688        if (!mem_cgroup_disabled())
1689                return mem_cgroup_inactive_anon_is_low(lruvec);
1690
1691        return inactive_anon_is_low_global(lruvec_zone(lruvec));
1692}
1693#else
1694static inline int inactive_anon_is_low(struct lruvec *lruvec)
1695{
1696        return 0;
1697}
1698#endif
1699
1700/**
1701 * inactive_file_is_low - check if file pages need to be deactivated
1702 * @lruvec: LRU vector to check
1703 *
1704 * When the system is doing streaming IO, memory pressure here
1705 * ensures that active file pages get deactivated, until more
1706 * than half of the file pages are on the inactive list.
1707 *
1708 * Once we get to that situation, protect the system's working
1709 * set from being evicted by disabling active file page aging.
1710 *
1711 * This uses a different ratio than the anonymous pages, because
1712 * the page cache uses a use-once replacement algorithm.
1713 */
1714static int inactive_file_is_low(struct lruvec *lruvec)
1715{
1716        unsigned long inactive;
1717        unsigned long active;
1718
1719        inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1720        active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1721
1722        return active > inactive;
1723}
1724
1725static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1726{
1727        if (is_file_lru(lru))
1728                return inactive_file_is_low(lruvec);
1729        else
1730                return inactive_anon_is_low(lruvec);
1731}
1732
1733static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1734                                 struct lruvec *lruvec, struct scan_control *sc)
1735{
1736        if (is_active_lru(lru)) {
1737                if (inactive_list_is_low(lruvec, lru))
1738                        shrink_active_list(nr_to_scan, lruvec, sc, lru);
1739                return 0;
1740        }
1741
1742        return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1743}
1744
1745static int vmscan_swappiness(struct scan_control *sc)
1746{
1747        if (global_reclaim(sc))
1748                return vm_swappiness;
1749        return mem_cgroup_swappiness(sc->target_mem_cgroup);
1750}
1751
1752enum scan_balance {
1753        SCAN_EQUAL,
1754        SCAN_FRACT,
1755        SCAN_ANON,
1756        SCAN_FILE,
1757};
1758
1759/*
1760 * Determine how aggressively the anon and file LRU lists should be
1761 * scanned.  The relative value of each set of LRU lists is determined
1762 * by looking at the fraction of the pages scanned we did rotate back
1763 * onto the active list instead of evict.
1764 *
1765 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1766 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1767 */
1768static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1769                           unsigned long *nr)
1770{
1771        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1772        u64 fraction[2];
1773        u64 denominator = 0;    /* gcc */
1774        struct zone *zone = lruvec_zone(lruvec);
1775        unsigned long anon_prio, file_prio;
1776        enum scan_balance scan_balance;
1777        unsigned long anon, file, free;
1778        bool force_scan = false;
1779        unsigned long ap, fp;
1780        enum lru_list lru;
1781
1782        /*
1783         * If the zone or memcg is small, nr[l] can be 0.  This
1784         * results in no scanning on this priority and a potential
1785         * priority drop.  Global direct reclaim can go to the next
1786         * zone and tends to have no problems. Global kswapd is for
1787         * zone balancing and it needs to scan a minimum amount. When
1788         * reclaiming for a memcg, a priority drop can cause high
1789         * latencies, so it's better to scan a minimum amount there as
1790         * well.
1791         */
1792        if (current_is_kswapd() && zone->all_unreclaimable)
1793                force_scan = true;
1794        if (!global_reclaim(sc))
1795                force_scan = true;
1796
1797        /* If we have no swap space, do not bother scanning anon pages. */
1798        if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1799                scan_balance = SCAN_FILE;
1800                goto out;
1801        }
1802
1803        /*
1804         * Global reclaim will swap to prevent OOM even with no
1805         * swappiness, but memcg users want to use this knob to
1806         * disable swapping for individual groups completely when
1807         * using the memory controller's swap limit feature would be
1808         * too expensive.
1809         */
1810        if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1811                scan_balance = SCAN_FILE;
1812                goto out;
1813        }
1814
1815        /*
1816         * Do not apply any pressure balancing cleverness when the
1817         * system is close to OOM, scan both anon and file equally
1818         * (unless the swappiness setting disagrees with swapping).
1819         */
1820        if (!sc->priority && vmscan_swappiness(sc)) {
1821                scan_balance = SCAN_EQUAL;
1822                goto out;
1823        }
1824
1825        anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1826                get_lru_size(lruvec, LRU_INACTIVE_ANON);
1827        file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1828                get_lru_size(lruvec, LRU_INACTIVE_FILE);
1829
1830        /*
1831         * If it's foreseeable that reclaiming the file cache won't be
1832         * enough to get the zone back into a desirable shape, we have
1833         * to swap.  Better start now and leave the - probably heavily
1834         * thrashing - remaining file pages alone.
1835         */
1836        if (global_reclaim(sc)) {
1837                free = zone_page_state(zone, NR_FREE_PAGES);
1838                if (unlikely(file + free <= high_wmark_pages(zone))) {
1839                        scan_balance = SCAN_ANON;
1840                        goto out;
1841                }
1842        }
1843
1844        /*
1845         * There is enough inactive page cache, do not reclaim
1846         * anything from the anonymous working set right now.
1847         */
1848        if (!inactive_file_is_low(lruvec)) {
1849                scan_balance = SCAN_FILE;
1850                goto out;
1851        }
1852
1853        scan_balance = SCAN_FRACT;
1854
1855        /*
1856         * With swappiness at 100, anonymous and file have the same priority.
1857         * This scanning priority is essentially the inverse of IO cost.
1858         */
1859        anon_prio = vmscan_swappiness(sc);
1860        file_prio = 200 - anon_prio;
1861
1862        /*
1863         * OK, so we have swap space and a fair amount of page cache
1864         * pages.  We use the recently rotated / recently scanned
1865         * ratios to determine how valuable each cache is.
1866         *
1867         * Because workloads change over time (and to avoid overflow)
1868         * we keep these statistics as a floating average, which ends
1869         * up weighing recent references more than old ones.
1870         *
1871         * anon in [0], file in [1]
1872         */
1873        spin_lock_irq(&zone->lru_lock);
1874        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1875                reclaim_stat->recent_scanned[0] /= 2;
1876                reclaim_stat->recent_rotated[0] /= 2;
1877        }
1878
1879        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1880                reclaim_stat->recent_scanned[1] /= 2;
1881                reclaim_stat->recent_rotated[1] /= 2;
1882        }
1883
1884        /*
1885         * The amount of pressure on anon vs file pages is inversely
1886         * proportional to the fraction of recently scanned pages on
1887         * each list that were recently referenced and in active use.
1888         */
1889        ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1890        ap /= reclaim_stat->recent_rotated[0] + 1;
1891
1892        fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1893        fp /= reclaim_stat->recent_rotated[1] + 1;
1894        spin_unlock_irq(&zone->lru_lock);
1895
1896        fraction[0] = ap;
1897        fraction[1] = fp;
1898        denominator = ap + fp + 1;
1899out:
1900        for_each_evictable_lru(lru) {
1901                int file = is_file_lru(lru);
1902                unsigned long size;
1903                unsigned long scan;
1904
1905                size = get_lru_size(lruvec, lru);
1906                scan = size >> sc->priority;
1907
1908                if (!scan && force_scan)
1909                        scan = min(size, SWAP_CLUSTER_MAX);
1910
1911                switch (scan_balance) {
1912                case SCAN_EQUAL:
1913                        /* Scan lists relative to size */
1914                        break;
1915                case SCAN_FRACT:
1916                        /*
1917                         * Scan types proportional to swappiness and
1918                         * their relative recent reclaim efficiency.
1919                         */
1920                        scan = div64_u64(scan * fraction[file], denominator);
1921                        break;
1922                case SCAN_FILE:
1923                case SCAN_ANON:
1924                        /* Scan one type exclusively */
1925                        if ((scan_balance == SCAN_FILE) != file)
1926                                scan = 0;
1927                        break;
1928                default:
1929                        /* Look ma, no brain */
1930                        BUG();
1931                }
1932                nr[lru] = scan;
1933        }
1934}
1935
1936/*
1937 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1938 */
1939static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1940{
1941        unsigned long nr[NR_LRU_LISTS];
1942        unsigned long targets[NR_LRU_LISTS];
1943        unsigned long nr_to_scan;
1944        enum lru_list lru;
1945        unsigned long nr_reclaimed = 0;
1946        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1947        struct blk_plug plug;
1948        bool scan_adjusted = false;
1949
1950        get_scan_count(lruvec, sc, nr);
1951
1952        /* Record the original scan target for proportional adjustments later */
1953        memcpy(targets, nr, sizeof(nr));
1954
1955        blk_start_plug(&plug);
1956        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1957                                        nr[LRU_INACTIVE_FILE]) {
1958                unsigned long nr_anon, nr_file, percentage;
1959                unsigned long nr_scanned;
1960
1961                for_each_evictable_lru(lru) {
1962                        if (nr[lru]) {
1963                                nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
1964                                nr[lru] -= nr_to_scan;
1965
1966                                nr_reclaimed += shrink_list(lru, nr_to_scan,
1967                                                            lruvec, sc);
1968                        }
1969                }
1970
1971                if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
1972                        continue;
1973
1974                /*
1975                 * For global direct reclaim, reclaim only the number of pages
1976                 * requested. Less care is taken to scan proportionally as it
1977                 * is more important to minimise direct reclaim stall latency
1978                 * than it is to properly age the LRU lists.
1979                 */
1980                if (global_reclaim(sc) && !current_is_kswapd())
1981                        break;
1982
1983                /*
1984                 * For kswapd and memcg, reclaim at least the number of pages
1985                 * requested. Ensure that the anon and file LRUs shrink
1986                 * proportionally what was requested by get_scan_count(). We
1987                 * stop reclaiming one LRU and reduce the amount scanning
1988                 * proportional to the original scan target.
1989                 */
1990                nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
1991                nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
1992
1993                if (nr_file > nr_anon) {
1994                        unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
1995                                                targets[LRU_ACTIVE_ANON] + 1;
1996                        lru = LRU_BASE;
1997                        percentage = nr_anon * 100 / scan_target;
1998                } else {
1999                        unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2000                                                targets[LRU_ACTIVE_FILE] + 1;
2001                        lru = LRU_FILE;
2002                        percentage = nr_file * 100 / scan_target;
2003                }
2004
2005                /* Stop scanning the smaller of the LRU */
2006                nr[lru] = 0;
2007                nr[lru + LRU_ACTIVE] = 0;
2008
2009                /*
2010                 * Recalculate the other LRU scan count based on its original
2011                 * scan target and the percentage scanning already complete
2012                 */
2013                lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2014                nr_scanned = targets[lru] - nr[lru];
2015                nr[lru] = targets[lru] * (100 - percentage) / 100;
2016                nr[lru] -= min(nr[lru], nr_scanned);
2017
2018                lru += LRU_ACTIVE;
2019                nr_scanned = targets[lru] - nr[lru];
2020                nr[lru] = targets[lru] * (100 - percentage) / 100;
2021                nr[lru] -= min(nr[lru], nr_scanned);
2022
2023                scan_adjusted = true;
2024        }
2025        blk_finish_plug(&plug);
2026        sc->nr_reclaimed += nr_reclaimed;
2027
2028        /*
2029         * Even if we did not try to evict anon pages at all, we want to
2030         * rebalance the anon lru active/inactive ratio.
2031         */
2032        if (inactive_anon_is_low(lruvec))
2033                shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2034                                   sc, LRU_ACTIVE_ANON);
2035
2036        throttle_vm_writeout(sc->gfp_mask);
2037}
2038
2039/* Use reclaim/compaction for costly allocs or under memory pressure */
2040static bool in_reclaim_compaction(struct scan_control *sc)
2041{
2042        if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2043                        (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2044                         sc->priority < DEF_PRIORITY - 2))
2045                return true;
2046
2047        return false;
2048}
2049
2050/*
2051 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2052 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2053 * true if more pages should be reclaimed such that when the page allocator
2054 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2055 * It will give up earlier than that if there is difficulty reclaiming pages.
2056 */
2057static inline bool should_continue_reclaim(struct zone *zone,
2058                                        unsigned long nr_reclaimed,
2059                                        unsigned long nr_scanned,
2060                                        struct scan_control *sc)
2061{
2062        unsigned long pages_for_compaction;
2063        unsigned long inactive_lru_pages;
2064
2065        /* If not in reclaim/compaction mode, stop */
2066        if (!in_reclaim_compaction(sc))
2067                return false;
2068
2069        /* Consider stopping depending on scan and reclaim activity */
2070        if (sc->gfp_mask & __GFP_REPEAT) {
2071                /*
2072                 * For __GFP_REPEAT allocations, stop reclaiming if the
2073                 * full LRU list has been scanned and we are still failing
2074                 * to reclaim pages. This full LRU scan is potentially
2075                 * expensive but a __GFP_REPEAT caller really wants to succeed
2076                 */
2077                if (!nr_reclaimed && !nr_scanned)
2078                        return false;
2079        } else {
2080                /*
2081                 * For non-__GFP_REPEAT allocations which can presumably
2082                 * fail without consequence, stop if we failed to reclaim
2083                 * any pages from the last SWAP_CLUSTER_MAX number of
2084                 * pages that were scanned. This will return to the
2085                 * caller faster at the risk reclaim/compaction and
2086                 * the resulting allocation attempt fails
2087                 */
2088                if (!nr_reclaimed)
2089                        return false;
2090        }
2091
2092        /*
2093         * If we have not reclaimed enough pages for compaction and the
2094         * inactive lists are large enough, continue reclaiming
2095         */
2096        pages_for_compaction = (2UL << sc->order);
2097        inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
2098        if (get_nr_swap_pages() > 0)
2099                inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
2100        if (sc->nr_reclaimed < pages_for_compaction &&
2101                        inactive_lru_pages > pages_for_compaction)
2102                return true;
2103
2104        /* If compaction would go ahead or the allocation would succeed, stop */
2105        switch (compaction_suitable(zone, sc->order)) {
2106        case COMPACT_PARTIAL:
2107        case COMPACT_CONTINUE:
2108                return false;
2109        default:
2110                return true;
2111        }
2112}
2113
2114static void shrink_zone(struct zone *zone, struct scan_control *sc)
2115{
2116        unsigned long nr_reclaimed, nr_scanned;
2117
2118        do {
2119                struct mem_cgroup *root = sc->target_mem_cgroup;
2120                struct mem_cgroup_reclaim_cookie reclaim = {
2121                        .zone = zone,
2122                        .priority = sc->priority,
2123                };
2124                struct mem_cgroup *memcg;
2125
2126                nr_reclaimed = sc->nr_reclaimed;
2127                nr_scanned = sc->nr_scanned;
2128
2129                memcg = mem_cgroup_iter(root, NULL, &reclaim);
2130                do {
2131                        struct lruvec *lruvec;
2132
2133                        lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2134
2135                        shrink_lruvec(lruvec, sc);
2136
2137                        /*
2138                         * Direct reclaim and kswapd have to scan all memory
2139                         * cgroups to fulfill the overall scan target for the
2140                         * zone.
2141                         *
2142                         * Limit reclaim, on the other hand, only cares about
2143                         * nr_to_reclaim pages to be reclaimed and it will
2144                         * retry with decreasing priority if one round over the
2145                         * whole hierarchy is not sufficient.
2146                         */
2147                        if (!global_reclaim(sc) &&
2148                                        sc->nr_reclaimed >= sc->nr_to_reclaim) {
2149                                mem_cgroup_iter_break(root, memcg);
2150                                break;
2151                        }
2152                        memcg = mem_cgroup_iter(root, memcg, &reclaim);
2153                } while (memcg);
2154
2155                vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
2156                           sc->nr_scanned - nr_scanned,
2157                           sc->nr_reclaimed - nr_reclaimed);
2158
2159        } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
2160                                         sc->nr_scanned - nr_scanned, sc));
2161}
2162
2163/* Returns true if compaction should go ahead for a high-order request */
2164static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2165{
2166        unsigned long balance_gap, watermark;
2167        bool watermark_ok;
2168
2169        /* Do not consider compaction for orders reclaim is meant to satisfy */
2170        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
2171                return false;
2172
2173        /*
2174         * Compaction takes time to run and there are potentially other
2175         * callers using the pages just freed. Continue reclaiming until
2176         * there is a buffer of free pages available to give compaction
2177         * a reasonable chance of completing and allocating the page
2178         */
2179        balance_gap = min(low_wmark_pages(zone),
2180                (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2181                        KSWAPD_ZONE_BALANCE_GAP_RATIO);
2182        watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
2183        watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2184
2185        /*
2186         * If compaction is deferred, reclaim up to a point where
2187         * compaction will have a chance of success when re-enabled
2188         */
2189        if (compaction_deferred(zone, sc->order))
2190                return watermark_ok;
2191
2192        /* If compaction is not ready to start, keep reclaiming */
2193        if (!compaction_suitable(zone, sc->order))
2194                return false;
2195
2196        return watermark_ok;
2197}
2198
2199/*
2200 * This is the direct reclaim path, for page-allocating processes.  We only
2201 * try to reclaim pages from zones which will satisfy the caller's allocation
2202 * request.
2203 *
2204 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2205 * Because:
2206 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2207 *    allocation or
2208 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2209 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2210 *    zone defense algorithm.
2211 *
2212 * If a zone is deemed to be full of pinned pages then just give it a light
2213 * scan then give up on it.
2214 *
2215 * This function returns true if a zone is being reclaimed for a costly
2216 * high-order allocation and compaction is ready to begin. This indicates to
2217 * the caller that it should consider retrying the allocation instead of
2218 * further reclaim.
2219 */
2220static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2221{
2222        struct zoneref *z;
2223        struct zone *zone;
2224        unsigned long nr_soft_reclaimed;
2225        unsigned long nr_soft_scanned;
2226        bool aborted_reclaim = false;
2227
2228        /*
2229         * If the number of buffer_heads in the machine exceeds the maximum
2230         * allowed level, force direct reclaim to scan the highmem zone as
2231         * highmem pages could be pinning lowmem pages storing buffer_heads
2232         */
2233        if (buffer_heads_over_limit)
2234                sc->gfp_mask |= __GFP_HIGHMEM;
2235
2236        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2237                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2238                if (!populated_zone(zone))
2239                        continue;
2240                /*
2241                 * Take care memory controller reclaiming has small influence
2242                 * to global LRU.
2243                 */
2244                if (global_reclaim(sc)) {
2245                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2246                                continue;
2247                        if (zone->all_unreclaimable &&
2248                                        sc->priority != DEF_PRIORITY)
2249                                continue;       /* Let kswapd poll it */
2250                        if (IS_ENABLED(CONFIG_COMPACTION)) {
2251                                /*
2252                                 * If we already have plenty of memory free for
2253                                 * compaction in this zone, don't free any more.
2254                                 * Even though compaction is invoked for any
2255                                 * non-zero order, only frequent costly order
2256                                 * reclamation is disruptive enough to become a
2257                                 * noticeable problem, like transparent huge
2258                                 * page allocations.
2259                                 */
2260                                if (compaction_ready(zone, sc)) {
2261                                        aborted_reclaim = true;
2262                                        continue;
2263                                }
2264                        }
2265                        /*
2266                         * This steals pages from memory cgroups over softlimit
2267                         * and returns the number of reclaimed pages and
2268                         * scanned pages. This works for global memory pressure
2269                         * and balancing, not for a memcg's limit.
2270                         */
2271                        nr_soft_scanned = 0;
2272                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2273                                                sc->order, sc->gfp_mask,
2274                                                &nr_soft_scanned);
2275                        sc->nr_reclaimed += nr_soft_reclaimed;
2276                        sc->nr_scanned += nr_soft_scanned;
2277                        /* need some check for avoid more shrink_zone() */
2278                }
2279
2280                shrink_zone(zone, sc);
2281        }
2282
2283        return aborted_reclaim;
2284}
2285
2286static bool zone_reclaimable(struct zone *zone)
2287{
2288        return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2289}
2290
2291/* All zones in zonelist are unreclaimable? */
2292static bool all_unreclaimable(struct zonelist *zonelist,
2293                struct scan_control *sc)
2294{
2295        struct zoneref *z;
2296        struct zone *zone;
2297
2298        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2299                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2300                if (!populated_zone(zone))
2301                        continue;
2302                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2303                        continue;
2304                if (!zone->all_unreclaimable)
2305                        return false;
2306        }
2307
2308        return true;
2309}
2310
2311/*
2312 * This is the main entry point to direct page reclaim.
2313 *
2314 * If a full scan of the inactive list fails to free enough memory then we
2315 * are "out of memory" and something needs to be killed.
2316 *
2317 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2318 * high - the zone may be full of dirty or under-writeback pages, which this
2319 * caller can't do much about.  We kick the writeback threads and take explicit
2320 * naps in the hope that some of these pages can be written.  But if the
2321 * allocating task holds filesystem locks which prevent writeout this might not
2322 * work, and the allocation attempt will fail.
2323 *
2324 * returns:     0, if no pages reclaimed
2325 *              else, the number of pages reclaimed
2326 */
2327static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2328                                        struct scan_control *sc,
2329                                        struct shrink_control *shrink)
2330{
2331        unsigned long total_scanned = 0;
2332        struct reclaim_state *reclaim_state = current->reclaim_state;
2333        struct zoneref *z;
2334        struct zone *zone;
2335        unsigned long writeback_threshold;
2336        bool aborted_reclaim;
2337
2338        delayacct_freepages_start();
2339
2340        if (global_reclaim(sc))
2341                count_vm_event(ALLOCSTALL);
2342
2343        do {
2344                vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2345                                sc->priority);
2346                sc->nr_scanned = 0;
2347                aborted_reclaim = shrink_zones(zonelist, sc);
2348
2349                /*
2350                 * Don't shrink slabs when reclaiming memory from over limit
2351                 * cgroups but do shrink slab at least once when aborting
2352                 * reclaim for compaction to avoid unevenly scanning file/anon
2353                 * LRU pages over slab pages.
2354                 */
2355                if (global_reclaim(sc)) {
2356                        unsigned long lru_pages = 0;
2357                        for_each_zone_zonelist(zone, z, zonelist,
2358                                        gfp_zone(sc->gfp_mask)) {
2359                                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2360                                        continue;
2361
2362                                lru_pages += zone_reclaimable_pages(zone);
2363                        }
2364
2365                        shrink_slab(shrink, sc->nr_scanned, lru_pages);
2366                        if (reclaim_state) {
2367                                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2368                                reclaim_state->reclaimed_slab = 0;
2369                        }
2370                }
2371                total_scanned += sc->nr_scanned;
2372                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2373                        goto out;
2374
2375                /*
2376                 * If we're getting trouble reclaiming, start doing
2377                 * writepage even in laptop mode.
2378                 */
2379                if (sc->priority < DEF_PRIORITY - 2)
2380                        sc->may_writepage = 1;
2381
2382                /*
2383                 * Try to write back as many pages as we just scanned.  This
2384                 * tends to cause slow streaming writers to write data to the
2385                 * disk smoothly, at the dirtying rate, which is nice.   But
2386                 * that's undesirable in laptop mode, where we *want* lumpy
2387                 * writeout.  So in laptop mode, write out the whole world.
2388                 */
2389                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2390                if (total_scanned > writeback_threshold) {
2391                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2392                                                WB_REASON_TRY_TO_FREE_PAGES);
2393                        sc->may_writepage = 1;
2394                }
2395        } while (--sc->priority >= 0 && !aborted_reclaim);
2396
2397out:
2398        delayacct_freepages_end();
2399
2400        if (sc->nr_reclaimed)
2401                return sc->nr_reclaimed;
2402
2403        /*
2404         * As hibernation is going on, kswapd is freezed so that it can't mark
2405         * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2406         * check.
2407         */
2408        if (oom_killer_disabled)
2409                return 0;
2410
2411        /* Aborted reclaim to try compaction? don't OOM, then */
2412        if (aborted_reclaim)
2413                return 1;
2414
2415        /* top priority shrink_zones still had more to do? don't OOM, then */
2416        if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2417                return 1;
2418
2419        return 0;
2420}
2421
2422static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2423{
2424        struct zone *zone;
2425        unsigned long pfmemalloc_reserve = 0;
2426        unsigned long free_pages = 0;
2427        int i;
2428        bool wmark_ok;
2429
2430        for (i = 0; i <= ZONE_NORMAL; i++) {
2431                zone = &pgdat->node_zones[i];
2432                pfmemalloc_reserve += min_wmark_pages(zone);
2433                free_pages += zone_page_state(zone, NR_FREE_PAGES);
2434        }
2435
2436        wmark_ok = free_pages > pfmemalloc_reserve / 2;
2437
2438        /* kswapd must be awake if processes are being throttled */
2439        if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2440                pgdat->classzone_idx = min(pgdat->classzone_idx,
2441                                                (enum zone_type)ZONE_NORMAL);
2442                wake_up_interruptible(&pgdat->kswapd_wait);
2443        }
2444
2445        return wmark_ok;
2446}
2447
2448/*
2449 * Throttle direct reclaimers if backing storage is backed by the network
2450 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2451 * depleted. kswapd will continue to make progress and wake the processes
2452 * when the low watermark is reached.
2453 *
2454 * Returns true if a fatal signal was delivered during throttling. If this
2455 * happens, the page allocator should not consider triggering the OOM killer.
2456 */
2457static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2458                                        nodemask_t *nodemask)
2459{
2460        struct zone *zone;
2461        int high_zoneidx = gfp_zone(gfp_mask);
2462        pg_data_t *pgdat;
2463
2464        /*
2465         * Kernel threads should not be throttled as they may be indirectly
2466         * responsible for cleaning pages necessary for reclaim to make forward
2467         * progress. kjournald for example may enter direct reclaim while
2468         * committing a transaction where throttling it could forcing other
2469         * processes to block on log_wait_commit().
2470         */
2471        if (current->flags & PF_KTHREAD)
2472                goto out;
2473
2474        /*
2475         * If a fatal signal is pending, this process should not throttle.
2476         * It should return quickly so it can exit and free its memory
2477         */
2478        if (fatal_signal_pending(current))
2479                goto out;
2480
2481        /* Check if the pfmemalloc reserves are ok */
2482        first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2483        pgdat = zone->zone_pgdat;
2484        if (pfmemalloc_watermark_ok(pgdat))
2485                goto out;
2486
2487        /* Account for the throttling */
2488        count_vm_event(PGSCAN_DIRECT_THROTTLE);
2489
2490        /*
2491         * If the caller cannot enter the filesystem, it's possible that it
2492         * is due to the caller holding an FS lock or performing a journal
2493         * transaction in the case of a filesystem like ext[3|4]. In this case,
2494         * it is not safe to block on pfmemalloc_wait as kswapd could be
2495         * blocked waiting on the same lock. Instead, throttle for up to a
2496         * second before continuing.
2497         */
2498        if (!(gfp_mask & __GFP_FS)) {
2499                wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2500                        pfmemalloc_watermark_ok(pgdat), HZ);
2501
2502                goto check_pending;
2503        }
2504
2505        /* Throttle until kswapd wakes the process */
2506        wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2507                pfmemalloc_watermark_ok(pgdat));
2508
2509check_pending:
2510        if (fatal_signal_pending(current))
2511                return true;
2512
2513out:
2514        return false;
2515}
2516
2517unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2518                                gfp_t gfp_mask, nodemask_t *nodemask)
2519{
2520        unsigned long nr_reclaimed;
2521        struct scan_control sc = {
2522                .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2523                .may_writepage = !laptop_mode,
2524                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2525                .may_unmap = 1,
2526                .may_swap = 1,
2527                .order = order,
2528                .priority = DEF_PRIORITY,
2529                .target_mem_cgroup = NULL,
2530                .nodemask = nodemask,
2531        };
2532        struct shrink_control shrink = {
2533                .gfp_mask = sc.gfp_mask,
2534        };
2535
2536        /*
2537         * Do not enter reclaim if fatal signal was delivered while throttled.
2538         * 1 is returned so that the page allocator does not OOM kill at this
2539         * point.
2540         */
2541        if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2542                return 1;
2543
2544        trace_mm_vmscan_direct_reclaim_begin(order,
2545                                sc.may_writepage,
2546                                gfp_mask);
2547
2548        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2549
2550        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2551
2552        return nr_reclaimed;
2553}
2554
2555#ifdef CONFIG_MEMCG
2556
2557unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2558                                                gfp_t gfp_mask, bool noswap,
2559                                                struct zone *zone,
2560                                                unsigned long *nr_scanned)
2561{
2562        struct scan_control sc = {
2563                .nr_scanned = 0,
2564                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2565                .may_writepage = !laptop_mode,
2566                .may_unmap = 1,
2567                .may_swap = !noswap,
2568                .order = 0,
2569                .priority = 0,
2570                .target_mem_cgroup = memcg,
2571        };
2572        struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2573
2574        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2575                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2576
2577        trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2578                                                      sc.may_writepage,
2579                                                      sc.gfp_mask);
2580
2581        /*
2582         * NOTE: Although we can get the priority field, using it
2583         * here is not a good idea, since it limits the pages we can scan.
2584         * if we don't reclaim here, the shrink_zone from balance_pgdat
2585         * will pick up pages from other mem cgroup's as well. We hack
2586         * the priority and make it zero.
2587         */
2588        shrink_lruvec(lruvec, &sc);
2589
2590        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2591
2592        *nr_scanned = sc.nr_scanned;
2593        return sc.nr_reclaimed;
2594}
2595
2596unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2597                                           gfp_t gfp_mask,
2598                                           bool noswap)
2599{
2600        struct zonelist *zonelist;
2601        unsigned long nr_reclaimed;
2602        int nid;
2603        struct scan_control sc = {
2604                .may_writepage = !laptop_mode,
2605                .may_unmap = 1,
2606                .may_swap = !noswap,
2607                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2608                .order = 0,
2609                .priority = DEF_PRIORITY,
2610                .target_mem_cgroup = memcg,
2611                .nodemask = NULL, /* we don't care the placement */
2612                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2613                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2614        };
2615        struct shrink_control shrink = {
2616                .gfp_mask = sc.gfp_mask,
2617        };
2618
2619        /*
2620         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2621         * take care of from where we get pages. So the node where we start the
2622         * scan does not need to be the current node.
2623         */
2624        nid = mem_cgroup_select_victim_node(memcg);
2625
2626        zonelist = NODE_DATA(nid)->node_zonelists;
2627
2628        trace_mm_vmscan_memcg_reclaim_begin(0,
2629                                            sc.may_writepage,
2630                                            sc.gfp_mask);
2631
2632        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2633
2634        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2635
2636        return nr_reclaimed;
2637}
2638#endif
2639
2640static void age_active_anon(struct zone *zone, struct scan_control *sc)
2641{
2642        struct mem_cgroup *memcg;
2643
2644        if (!total_swap_pages)
2645                return;
2646
2647        memcg = mem_cgroup_iter(NULL, NULL, NULL);
2648        do {
2649                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2650
2651                if (inactive_anon_is_low(lruvec))
2652                        shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2653                                           sc, LRU_ACTIVE_ANON);
2654
2655                memcg = mem_cgroup_iter(NULL, memcg, NULL);
2656        } while (memcg);
2657}
2658
2659static bool zone_balanced(struct zone *zone, int order,
2660                          unsigned long balance_gap, int classzone_idx)
2661{
2662        if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2663                                    balance_gap, classzone_idx, 0))
2664                return false;
2665
2666        if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2667            !compaction_suitable(zone, order))
2668                return false;
2669
2670        return true;
2671}
2672
2673/*
2674 * pgdat_balanced() is used when checking if a node is balanced.
2675 *
2676 * For order-0, all zones must be balanced!
2677 *
2678 * For high-order allocations only zones that meet watermarks and are in a
2679 * zone allowed by the callers classzone_idx are added to balanced_pages. The
2680 * total of balanced pages must be at least 25% of the zones allowed by
2681 * classzone_idx for the node to be considered balanced. Forcing all zones to
2682 * be balanced for high orders can cause excessive reclaim when there are
2683 * imbalanced zones.
2684 * The choice of 25% is due to
2685 *   o a 16M DMA zone that is balanced will not balance a zone on any
2686 *     reasonable sized machine
2687 *   o On all other machines, the top zone must be at least a reasonable
2688 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2689 *     would need to be at least 256M for it to be balance a whole node.
2690 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2691 *     to balance a node on its own. These seemed like reasonable ratios.
2692 */
2693static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2694{
2695        unsigned long managed_pages = 0;
2696        unsigned long balanced_pages = 0;
2697        int i;
2698
2699        /* Check the watermark levels */
2700        for (i = 0; i <= classzone_idx; i++) {
2701                struct zone *zone = pgdat->node_zones + i;
2702
2703                if (!populated_zone(zone))
2704                        continue;
2705
2706                managed_pages += zone->managed_pages;
2707
2708                /*
2709                 * A special case here:
2710                 *
2711                 * balance_pgdat() skips over all_unreclaimable after
2712                 * DEF_PRIORITY. Effectively, it considers them balanced so
2713                 * they must be considered balanced here as well!
2714                 */
2715                if (zone->all_unreclaimable) {
2716                        balanced_pages += zone->managed_pages;
2717                        continue;
2718                }
2719
2720                if (zone_balanced(zone, order, 0, i))
2721                        balanced_pages += zone->managed_pages;
2722                else if (!order)
2723                        return false;
2724        }
2725
2726        if (order)
2727                return balanced_pages >= (managed_pages >> 2);
2728        else
2729                return true;
2730}
2731
2732/*
2733 * Prepare kswapd for sleeping. This verifies that there are no processes
2734 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2735 *
2736 * Returns true if kswapd is ready to sleep
2737 */
2738static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2739                                        int classzone_idx)
2740{
2741        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2742        if (remaining)
2743                return false;
2744
2745        /*
2746         * There is a potential race between when kswapd checks its watermarks
2747         * and a process gets throttled. There is also a potential race if
2748         * processes get throttled, kswapd wakes, a large process exits therby
2749         * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2750         * is going to sleep, no process should be sleeping on pfmemalloc_wait
2751         * so wake them now if necessary. If necessary, processes will wake
2752         * kswapd and get throttled again
2753         */
2754        if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2755                wake_up(&pgdat->pfmemalloc_wait);
2756                return false;
2757        }
2758
2759        return pgdat_balanced(pgdat, order, classzone_idx);
2760}
2761
2762/*
2763 * kswapd shrinks the zone by the number of pages required to reach
2764 * the high watermark.
2765 *
2766 * Returns true if kswapd scanned at least the requested number of pages to
2767 * reclaim or if the lack of progress was due to pages under writeback.
2768 * This is used to determine if the scanning priority needs to be raised.
2769 */
2770static bool kswapd_shrink_zone(struct zone *zone,
2771                               int classzone_idx,
2772                               struct scan_control *sc,
2773                               unsigned long lru_pages,
2774                               unsigned long *nr_attempted)
2775{
2776        unsigned long nr_slab;
2777        int testorder = sc->order;
2778        unsigned long balance_gap;
2779        struct reclaim_state *reclaim_state = current->reclaim_state;
2780        struct shrink_control shrink = {
2781                .gfp_mask = sc->gfp_mask,
2782        };
2783        bool lowmem_pressure;
2784
2785        /* Reclaim above the high watermark. */
2786        sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
2787
2788        /*
2789         * Kswapd reclaims only single pages with compaction enabled. Trying
2790         * too hard to reclaim until contiguous free pages have become
2791         * available can hurt performance by evicting too much useful data
2792         * from memory. Do not reclaim more than needed for compaction.
2793         */
2794        if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2795                        compaction_suitable(zone, sc->order) !=
2796                                COMPACT_SKIPPED)
2797                testorder = 0;
2798
2799        /*
2800         * We put equal pressure on every zone, unless one zone has way too
2801         * many pages free already. The "too many pages" is defined as the
2802         * high wmark plus a "gap" where the gap is either the low
2803         * watermark or 1% of the zone, whichever is smaller.
2804         */
2805        balance_gap = min(low_wmark_pages(zone),
2806                (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2807                KSWAPD_ZONE_BALANCE_GAP_RATIO);
2808
2809        /*
2810         * If there is no low memory pressure or the zone is balanced then no
2811         * reclaim is necessary
2812         */
2813        lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
2814        if (!lowmem_pressure && zone_balanced(zone, testorder,
2815                                                balance_gap, classzone_idx))
2816                return true;
2817
2818        shrink_zone(zone, sc);
2819
2820        reclaim_state->reclaimed_slab = 0;
2821        nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2822        sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2823
2824        /* Account for the number of pages attempted to reclaim */
2825        *nr_attempted += sc->nr_to_reclaim;
2826
2827        if (nr_slab == 0 && !zone_reclaimable(zone))
2828                zone->all_unreclaimable = 1;
2829
2830        zone_clear_flag(zone, ZONE_WRITEBACK);
2831
2832        /*
2833         * If a zone reaches its high watermark, consider it to be no longer
2834         * congested. It's possible there are dirty pages backed by congested
2835         * BDIs but as pressure is relieved, speculatively avoid congestion
2836         * waits.
2837         */
2838        if (!zone->all_unreclaimable &&
2839            zone_balanced(zone, testorder, 0, classzone_idx)) {
2840                zone_clear_flag(zone, ZONE_CONGESTED);
2841                zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2842        }
2843
2844        return sc->nr_scanned >= sc->nr_to_reclaim;
2845}
2846
2847/*
2848 * For kswapd, balance_pgdat() will work across all this node's zones until
2849 * they are all at high_wmark_pages(zone).
2850 *
2851 * Returns the final order kswapd was reclaiming at
2852 *
2853 * There is special handling here for zones which are full of pinned pages.
2854 * This can happen if the pages are all mlocked, or if they are all used by
2855 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2856 * What we do is to detect the case where all pages in the zone have been
2857 * scanned twice and there has been zero successful reclaim.  Mark the zone as
2858 * dead and from now on, only perform a short scan.  Basically we're polling
2859 * the zone for when the problem goes away.
2860 *
2861 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2862 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2863 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2864 * lower zones regardless of the number of free pages in the lower zones. This
2865 * interoperates with the page allocator fallback scheme to ensure that aging
2866 * of pages is balanced across the zones.
2867 */
2868static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2869                                                        int *classzone_idx)
2870{
2871        int i;
2872        int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2873        unsigned long nr_soft_reclaimed;
2874        unsigned long nr_soft_scanned;
2875        struct scan_control sc = {
2876                .gfp_mask = GFP_KERNEL,
2877                .priority = DEF_PRIORITY,
2878                .may_unmap = 1,
2879                .may_swap = 1,
2880                .may_writepage = !laptop_mode,
2881                .order = order,
2882                .target_mem_cgroup = NULL,
2883        };
2884        count_vm_event(PAGEOUTRUN);
2885
2886        do {
2887                unsigned long lru_pages = 0;
2888                unsigned long nr_attempted = 0;
2889                bool raise_priority = true;
2890                bool pgdat_needs_compaction = (order > 0);
2891
2892                sc.nr_reclaimed = 0;
2893
2894                /*
2895                 * Scan in the highmem->dma direction for the highest
2896                 * zone which needs scanning
2897                 */
2898                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2899                        struct zone *zone = pgdat->node_zones + i;
2900
2901                        if (!populated_zone(zone))
2902                                continue;
2903
2904                        if (zone->all_unreclaimable &&
2905                            sc.priority != DEF_PRIORITY)
2906                                continue;
2907
2908                        /*
2909                         * Do some background aging of the anon list, to give
2910                         * pages a chance to be referenced before reclaiming.
2911                         */
2912                        age_active_anon(zone, &sc);
2913
2914                        /*
2915                         * If the number of buffer_heads in the machine
2916                         * exceeds the maximum allowed level and this node
2917                         * has a highmem zone, force kswapd to reclaim from
2918                         * it to relieve lowmem pressure.
2919                         */
2920                        if (buffer_heads_over_limit && is_highmem_idx(i)) {
2921                                end_zone = i;
2922                                break;
2923                        }
2924
2925                        if (!zone_balanced(zone, order, 0, 0)) {
2926                                end_zone = i;
2927                                break;
2928                        } else {
2929                                /*
2930                                 * If balanced, clear the dirty and congested
2931                                 * flags
2932                                 */
2933                                zone_clear_flag(zone, ZONE_CONGESTED);
2934                                zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2935                        }
2936                }
2937
2938                if (i < 0)
2939                        goto out;
2940
2941                for (i = 0; i <= end_zone; i++) {
2942                        struct zone *zone = pgdat->node_zones + i;
2943
2944                        if (!populated_zone(zone))
2945                                continue;
2946
2947                        lru_pages += zone_reclaimable_pages(zone);
2948
2949                        /*
2950                         * If any zone is currently balanced then kswapd will
2951                         * not call compaction as it is expected that the
2952                         * necessary pages are already available.
2953                         */
2954                        if (pgdat_needs_compaction &&
2955                                        zone_watermark_ok(zone, order,
2956                                                low_wmark_pages(zone),
2957                                                *classzone_idx, 0))
2958                                pgdat_needs_compaction = false;
2959                }
2960
2961                /*
2962                 * If we're getting trouble reclaiming, start doing writepage
2963                 * even in laptop mode.
2964                 */
2965                if (sc.priority < DEF_PRIORITY - 2)
2966                        sc.may_writepage = 1;
2967
2968                /*
2969                 * Now scan the zone in the dma->highmem direction, stopping
2970                 * at the last zone which needs scanning.
2971                 *
2972                 * We do this because the page allocator works in the opposite
2973                 * direction.  This prevents the page allocator from allocating
2974                 * pages behind kswapd's direction of progress, which would
2975                 * cause too much scanning of the lower zones.
2976                 */
2977                for (i = 0; i <= end_zone; i++) {
2978                        struct zone *zone = pgdat->node_zones + i;
2979
2980                        if (!populated_zone(zone))
2981                                continue;
2982
2983                        if (zone->all_unreclaimable &&
2984                            sc.priority != DEF_PRIORITY)
2985                                continue;
2986
2987                        sc.nr_scanned = 0;
2988
2989                        nr_soft_scanned = 0;
2990                        /*
2991                         * Call soft limit reclaim before calling shrink_zone.
2992                         */
2993                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2994                                                        order, sc.gfp_mask,
2995                                                        &nr_soft_scanned);
2996                        sc.nr_reclaimed += nr_soft_reclaimed;
2997
2998                        /*
2999                         * There should be no need to raise the scanning
3000                         * priority if enough pages are already being scanned
3001                         * that that high watermark would be met at 100%
3002                         * efficiency.
3003                         */
3004                        if (kswapd_shrink_zone(zone, end_zone, &sc,
3005                                        lru_pages, &nr_attempted))
3006                                raise_priority = false;
3007                }
3008
3009                /*
3010                 * If the low watermark is met there is no need for processes
3011                 * to be throttled on pfmemalloc_wait as they should not be
3012                 * able to safely make forward progress. Wake them
3013                 */
3014                if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3015                                pfmemalloc_watermark_ok(pgdat))
3016                        wake_up(&pgdat->pfmemalloc_wait);
3017
3018                /*
3019                 * Fragmentation may mean that the system cannot be rebalanced
3020                 * for high-order allocations in all zones. If twice the
3021                 * allocation size has been reclaimed and the zones are still
3022                 * not balanced then recheck the watermarks at order-0 to
3023                 * prevent kswapd reclaiming excessively. Assume that a
3024                 * process requested a high-order can direct reclaim/compact.
3025                 */
3026                if (order && sc.nr_reclaimed >= 2UL << order)
3027                        order = sc.order = 0;
3028
3029                /* Check if kswapd should be suspending */
3030                if (try_to_freeze() || kthread_should_stop())
3031                        break;
3032
3033                /*
3034                 * Compact if necessary and kswapd is reclaiming at least the
3035                 * high watermark number of pages as requsted
3036                 */
3037                if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
3038                        compact_pgdat(pgdat, order);
3039
3040                /*
3041                 * Raise priority if scanning rate is too low or there was no
3042                 * progress in reclaiming pages
3043                 */
3044                if (raise_priority || !sc.nr_reclaimed)
3045                        sc.priority--;
3046        } while (sc.priority >= 1 &&
3047                 !pgdat_balanced(pgdat, order, *classzone_idx));
3048
3049out:
3050        /*
3051         * Return the order we were reclaiming at so prepare_kswapd_sleep()
3052         * makes a decision on the order we were last reclaiming at. However,
3053         * if another caller entered the allocator slow path while kswapd
3054         * was awake, order will remain at the higher level
3055         */
3056        *classzone_idx = end_zone;
3057        return order;
3058}
3059
3060static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3061{
3062        long remaining = 0;
3063        DEFINE_WAIT(wait);
3064
3065        if (freezing(current) || kthread_should_stop())
3066                return;
3067
3068        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3069
3070        /* Try to sleep for a short interval */
3071        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3072                remaining = schedule_timeout(HZ/10);
3073                finish_wait(&pgdat->kswapd_wait, &wait);
3074                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3075        }
3076
3077        /*
3078         * After a short sleep, check if it was a premature sleep. If not, then
3079         * go fully to sleep until explicitly woken up.
3080         */
3081        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3082                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3083
3084                /*
3085                 * vmstat counters are not perfectly accurate and the estimated
3086                 * value for counters such as NR_FREE_PAGES can deviate from the
3087                 * true value by nr_online_cpus * threshold. To avoid the zone
3088                 * watermarks being breached while under pressure, we reduce the
3089                 * per-cpu vmstat threshold while kswapd is awake and restore
3090                 * them before going back to sleep.
3091                 */
3092                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3093
3094                /*
3095                 * Compaction records what page blocks it recently failed to
3096                 * isolate pages from and skips them in the future scanning.
3097                 * When kswapd is going to sleep, it is reasonable to assume
3098                 * that pages and compaction may succeed so reset the cache.
3099                 */
3100                reset_isolation_suitable(pgdat);
3101
3102                if (!kthread_should_stop())
3103                        schedule();
3104
3105                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3106        } else {
3107                if (remaining)
3108                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3109                else
3110                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3111        }
3112        finish_wait(&pgdat->kswapd_wait, &wait);
3113}
3114
3115/*
3116 * The background pageout daemon, started as a kernel thread
3117 * from the init process.
3118 *
3119 * This basically trickles out pages so that we have _some_
3120 * free memory available even if there is no other activity
3121 * that frees anything up. This is needed for things like routing
3122 * etc, where we otherwise might have all activity going on in
3123 * asynchronous contexts that cannot page things out.
3124 *
3125 * If there are applications that are active memory-allocators
3126 * (most normal use), this basically shouldn't matter.
3127 */
3128static int kswapd(void *p)
3129{
3130        unsigned long order, new_order;
3131        unsigned balanced_order;
3132        int classzone_idx, new_classzone_idx;
3133        int balanced_classzone_idx;
3134        pg_data_t *pgdat = (pg_data_t*)p;
3135        struct task_struct *tsk = current;
3136
3137        struct reclaim_state reclaim_state = {
3138                .reclaimed_slab = 0,
3139        };
3140        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3141
3142        lockdep_set_current_reclaim_state(GFP_KERNEL);
3143
3144        if (!cpumask_empty(cpumask))
3145                set_cpus_allowed_ptr(tsk, cpumask);
3146        current->reclaim_state = &reclaim_state;
3147
3148        /*
3149         * Tell the memory management that we're a "memory allocator",
3150         * and that if we need more memory we should get access to it
3151         * regardless (see "__alloc_pages()"). "kswapd" should
3152         * never get caught in the normal page freeing logic.
3153         *
3154         * (Kswapd normally doesn't need memory anyway, but sometimes
3155         * you need a small amount of memory in order to be able to
3156         * page out something else, and this flag essentially protects
3157         * us from recursively trying to free more memory as we're
3158         * trying to free the first piece of memory in the first place).
3159         */
3160        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3161        set_freezable();
3162
3163        order = new_order = 0;
3164        balanced_order = 0;
3165        classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3166        balanced_classzone_idx = classzone_idx;
3167        for ( ; ; ) {
3168                bool ret;
3169
3170                /*
3171                 * If the last balance_pgdat was unsuccessful it's unlikely a
3172                 * new request of a similar or harder type will succeed soon
3173                 * so consider going to sleep on the basis we reclaimed at
3174                 */
3175                if (balanced_classzone_idx >= new_classzone_idx &&
3176                                        balanced_order == new_order) {
3177                        new_order = pgdat->kswapd_max_order;
3178                        new_classzone_idx = pgdat->classzone_idx;
3179                        pgdat->kswapd_max_order =  0;
3180                        pgdat->classzone_idx = pgdat->nr_zones - 1;
3181                }
3182
3183                if (order < new_order || classzone_idx > new_classzone_idx) {
3184                        /*
3185                         * Don't sleep if someone wants a larger 'order'
3186                         * allocation or has tigher zone constraints
3187                         */
3188                        order = new_order;
3189                        classzone_idx = new_classzone_idx;
3190                } else {
3191                        kswapd_try_to_sleep(pgdat, balanced_order,
3192                                                balanced_classzone_idx);
3193                        order = pgdat->kswapd_max_order;
3194                        classzone_idx = pgdat->classzone_idx;
3195                        new_order = order;
3196                        new_classzone_idx = classzone_idx;
3197                        pgdat->kswapd_max_order = 0;
3198                        pgdat->classzone_idx = pgdat->nr_zones - 1;
3199                }
3200
3201                ret = try_to_freeze();
3202                if (kthread_should_stop())
3203                        break;
3204
3205                /*
3206                 * We can speed up thawing tasks if we don't call balance_pgdat
3207                 * after returning from the refrigerator
3208                 */
3209                if (!ret) {
3210                        trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3211                        balanced_classzone_idx = classzone_idx;
3212                        balanced_order = balance_pgdat(pgdat, order,
3213                                                &balanced_classzone_idx);
3214                }
3215        }
3216
3217        current->reclaim_state = NULL;
3218        return 0;
3219}
3220
3221/*
3222 * A zone is low on free memory, so wake its kswapd task to service it.
3223 */
3224void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3225{
3226        pg_data_t *pgdat;
3227
3228        if (!populated_zone(zone))
3229                return;
3230
3231        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3232                return;
3233        pgdat = zone->zone_pgdat;
3234        if (pgdat->kswapd_max_order < order) {
3235                pgdat->kswapd_max_order = order;
3236                pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3237        }
3238        if (!waitqueue_active(&pgdat->kswapd_wait))
3239                return;
3240        if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
3241                return;
3242
3243        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3244        wake_up_interruptible(&pgdat->kswapd_wait);
3245}
3246
3247/*
3248 * The reclaimable count would be mostly accurate.
3249 * The less reclaimable pages may be
3250 * - mlocked pages, which will be moved to unevictable list when encountered
3251 * - mapped pages, which may require several travels to be reclaimed
3252 * - dirty pages, which is not "instantly" reclaimable
3253 */
3254unsigned long global_reclaimable_pages(void)
3255{
3256        int nr;
3257
3258        nr = global_page_state(NR_ACTIVE_FILE) +
3259             global_page_state(NR_INACTIVE_FILE);
3260
3261        if (get_nr_swap_pages() > 0)
3262                nr += global_page_state(NR_ACTIVE_ANON) +
3263                      global_page_state(NR_INACTIVE_ANON);
3264
3265        return nr;
3266}
3267
3268unsigned long zone_reclaimable_pages(struct zone *zone)
3269{
3270        int nr;
3271
3272        nr = zone_page_state(zone, NR_ACTIVE_FILE) +
3273             zone_page_state(zone, NR_INACTIVE_FILE);
3274
3275        if (get_nr_swap_pages() > 0)
3276                nr += zone_page_state(zone, NR_ACTIVE_ANON) +
3277                      zone_page_state(zone, NR_INACTIVE_ANON);
3278
3279        return nr;
3280}
3281
3282#ifdef CONFIG_HIBERNATION
3283/*
3284 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3285 * freed pages.
3286 *
3287 * Rather than trying to age LRUs the aim is to preserve the overall
3288 * LRU order by reclaiming preferentially
3289 * inactive > active > active referenced > active mapped
3290 */
3291unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3292{
3293        struct reclaim_state reclaim_state;
3294        struct scan_control sc = {
3295                .gfp_mask = GFP_HIGHUSER_MOVABLE,
3296                .may_swap = 1,
3297                .may_unmap = 1,
3298                .may_writepage = 1,
3299                .nr_to_reclaim = nr_to_reclaim,
3300                .hibernation_mode = 1,
3301                .order = 0,
3302                .priority = DEF_PRIORITY,
3303        };
3304        struct shrink_control shrink = {
3305                .gfp_mask = sc.gfp_mask,
3306        };
3307        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3308        struct task_struct *p = current;
3309        unsigned long nr_reclaimed;
3310
3311        p->flags |= PF_MEMALLOC;
3312        lockdep_set_current_reclaim_state(sc.gfp_mask);
3313        reclaim_state.reclaimed_slab = 0;
3314        p->reclaim_state = &reclaim_state;
3315
3316        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3317
3318        p->reclaim_state = NULL;
3319        lockdep_clear_current_reclaim_state();
3320        p->flags &= ~PF_MEMALLOC;
3321
3322        return nr_reclaimed;
3323}
3324#endif /* CONFIG_HIBERNATION */
3325
3326/* It's optimal to keep kswapds on the same CPUs as their memory, but
3327   not required for correctness.  So if the last cpu in a node goes
3328   away, we get changed to run anywhere: as the first one comes back,
3329   restore their cpu bindings. */
3330static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3331                        void *hcpu)
3332{
3333        int nid;
3334
3335        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3336                for_each_node_state(nid, N_MEMORY) {
3337                        pg_data_t *pgdat = NODE_DATA(nid);
3338                        const struct cpumask *mask;
3339
3340                        mask = cpumask_of_node(pgdat->node_id);
3341
3342                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3343                                /* One of our CPUs online: restore mask */
3344                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
3345                }
3346        }
3347        return NOTIFY_OK;
3348}
3349
3350/*
3351 * This kswapd start function will be called by init and node-hot-add.
3352 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3353 */
3354int kswapd_run(int nid)
3355{
3356        pg_data_t *pgdat = NODE_DATA(nid);
3357        int ret = 0;
3358
3359        if (pgdat->kswapd)
3360                return 0;
3361
3362        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3363        if (IS_ERR(pgdat->kswapd)) {
3364                /* failure at boot is fatal */
3365                BUG_ON(system_state == SYSTEM_BOOTING);
3366                pr_err("Failed to start kswapd on node %d\n", nid);
3367                ret = PTR_ERR(pgdat->kswapd);
3368                pgdat->kswapd = NULL;
3369        }
3370        return ret;
3371}
3372
3373/*
3374 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3375 * hold lock_memory_hotplug().
3376 */
3377void kswapd_stop(int nid)
3378{
3379        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3380
3381        if (kswapd) {
3382                kthread_stop(kswapd);
3383                NODE_DATA(nid)->kswapd = NULL;
3384        }
3385}
3386
3387static int __init kswapd_init(void)
3388{
3389        int nid;
3390
3391        swap_setup();
3392        for_each_node_state(nid, N_MEMORY)
3393                kswapd_run(nid);
3394        hotcpu_notifier(cpu_callback, 0);
3395        return 0;
3396}
3397
3398module_init(kswapd_init)
3399
3400#ifdef CONFIG_NUMA
3401/*
3402 * Zone reclaim mode
3403 *
3404 * If non-zero call zone_reclaim when the number of free pages falls below
3405 * the watermarks.
3406 */
3407int zone_reclaim_mode __read_mostly;
3408
3409#define RECLAIM_OFF 0
3410#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3411#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3412#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3413
3414/*
3415 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3416 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3417 * a zone.
3418 */
3419#define ZONE_RECLAIM_PRIORITY 4
3420
3421/*
3422 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3423 * occur.
3424 */
3425int sysctl_min_unmapped_ratio = 1;
3426
3427/*
3428 * If the number of slab pages in a zone grows beyond this percentage then
3429 * slab reclaim needs to occur.
3430 */
3431int sysctl_min_slab_ratio = 5;
3432
3433static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3434{
3435        unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3436        unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3437                zone_page_state(zone, NR_ACTIVE_FILE);
3438
3439        /*
3440         * It's possible for there to be more file mapped pages than
3441         * accounted for by the pages on the file LRU lists because
3442         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3443         */
3444        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3445}
3446
3447/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3448static long zone_pagecache_reclaimable(struct zone *zone)
3449{
3450        long nr_pagecache_reclaimable;
3451        long delta = 0;
3452
3453        /*
3454         * If RECLAIM_SWAP is set, then all file pages are considered
3455         * potentially reclaimable. Otherwise, we have to worry about
3456         * pages like swapcache and zone_unmapped_file_pages() provides
3457         * a better estimate
3458         */
3459        if (zone_reclaim_mode & RECLAIM_SWAP)
3460                nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3461        else
3462                nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3463
3464        /* If we can't clean pages, remove dirty pages from consideration */
3465        if (!(zone_reclaim_mode & RECLAIM_WRITE))
3466                delta += zone_page_state(zone, NR_FILE_DIRTY);
3467
3468        /* Watch for any possible underflows due to delta */
3469        if (unlikely(delta > nr_pagecache_reclaimable))
3470                delta = nr_pagecache_reclaimable;
3471
3472        return nr_pagecache_reclaimable - delta;
3473}
3474
3475/*
3476 * Try to free up some pages from this zone through reclaim.
3477 */
3478static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3479{
3480        /* Minimum pages needed in order to stay on node */
3481        const unsigned long nr_pages = 1 << order;
3482        struct task_struct *p = current;
3483        struct reclaim_state reclaim_state;
3484        struct scan_control sc = {
3485                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3486                .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3487                .may_swap = 1,
3488                .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3489                .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3490                .order = order,
3491                .priority = ZONE_RECLAIM_PRIORITY,
3492        };
3493        struct shrink_control shrink = {
3494                .gfp_mask = sc.gfp_mask,
3495        };
3496        unsigned long nr_slab_pages0, nr_slab_pages1;
3497
3498        cond_resched();
3499        /*
3500         * We need to be able to allocate from the reserves for RECLAIM_SWAP
3501         * and we also need to be able to write out pages for RECLAIM_WRITE
3502         * and RECLAIM_SWAP.
3503         */
3504        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3505        lockdep_set_current_reclaim_state(gfp_mask);
3506        reclaim_state.reclaimed_slab = 0;
3507        p->reclaim_state = &reclaim_state;
3508
3509        if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3510                /*
3511                 * Free memory by calling shrink zone with increasing
3512                 * priorities until we have enough memory freed.
3513                 */
3514                do {
3515                        shrink_zone(zone, &sc);
3516                } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3517        }
3518
3519        nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3520        if (nr_slab_pages0 > zone->min_slab_pages) {
3521                /*
3522                 * shrink_slab() does not currently allow us to determine how
3523                 * many pages were freed in this zone. So we take the current
3524                 * number of slab pages and shake the slab until it is reduced
3525                 * by the same nr_pages that we used for reclaiming unmapped
3526                 * pages.
3527                 *
3528                 * Note that shrink_slab will free memory on all zones and may
3529                 * take a long time.
3530                 */
3531                for (;;) {
3532                        unsigned long lru_pages = zone_reclaimable_pages(zone);
3533
3534                        /* No reclaimable slab or very low memory pressure */
3535                        if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3536                                break;
3537
3538                        /* Freed enough memory */
3539                        nr_slab_pages1 = zone_page_state(zone,
3540                                                        NR_SLAB_RECLAIMABLE);
3541                        if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3542                                break;
3543                }
3544
3545                /*
3546                 * Update nr_reclaimed by the number of slab pages we
3547                 * reclaimed from this zone.
3548                 */
3549                nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3550                if (nr_slab_pages1 < nr_slab_pages0)
3551                        sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3552        }
3553
3554        p->reclaim_state = NULL;
3555        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3556        lockdep_clear_current_reclaim_state();
3557        return sc.nr_reclaimed >= nr_pages;
3558}
3559
3560int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3561{
3562        int node_id;
3563        int ret;
3564
3565        /*
3566         * Zone reclaim reclaims unmapped file backed pages and
3567         * slab pages if we are over the defined limits.
3568         *
3569         * A small portion of unmapped file backed pages is needed for
3570         * file I/O otherwise pages read by file I/O will be immediately
3571         * thrown out if the zone is overallocated. So we do not reclaim
3572         * if less than a specified percentage of the zone is used by
3573         * unmapped file backed pages.
3574         */
3575        if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3576            zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3577                return ZONE_RECLAIM_FULL;
3578
3579        if (zone->all_unreclaimable)
3580                return ZONE_RECLAIM_FULL;
3581
3582        /*
3583         * Do not scan if the allocation should not be delayed.
3584         */
3585        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3586                return ZONE_RECLAIM_NOSCAN;
3587
3588        /*
3589         * Only run zone reclaim on the local zone or on zones that do not
3590         * have associated processors. This will favor the local processor
3591         * over remote processors and spread off node memory allocations
3592         * as wide as possible.
3593         */
3594        node_id = zone_to_nid(zone);
3595        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3596                return ZONE_RECLAIM_NOSCAN;
3597
3598        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3599                return ZONE_RECLAIM_NOSCAN;
3600
3601        ret = __zone_reclaim(zone, gfp_mask, order);
3602        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3603
3604        if (!ret)
3605                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3606
3607        return ret;
3608}
3609#endif
3610
3611/*
3612 * page_evictable - test whether a page is evictable
3613 * @page: the page to test
3614 *
3615 * Test whether page is evictable--i.e., should be placed on active/inactive
3616 * lists vs unevictable list.
3617 *
3618 * Reasons page might not be evictable:
3619 * (1) page's mapping marked unevictable
3620 * (2) page is part of an mlocked VMA
3621 *
3622 */
3623int page_evictable(struct page *page)
3624{
3625        return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3626}
3627
3628#ifdef CONFIG_SHMEM
3629/**
3630 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3631 * @pages:      array of pages to check
3632 * @nr_pages:   number of pages to check
3633 *
3634 * Checks pages for evictability and moves them to the appropriate lru list.
3635 *
3636 * This function is only used for SysV IPC SHM_UNLOCK.
3637 */
3638void check_move_unevictable_pages(struct page **pages, int nr_pages)
3639{
3640        struct lruvec *lruvec;
3641        struct zone *zone = NULL;
3642        int pgscanned = 0;
3643        int pgrescued = 0;
3644        int i;
3645
3646        for (i = 0; i < nr_pages; i++) {
3647                struct page *page = pages[i];
3648                struct zone *pagezone;
3649
3650                pgscanned++;
3651                pagezone = page_zone(page);
3652                if (pagezone != zone) {
3653                        if (zone)
3654                                spin_unlock_irq(&zone->lru_lock);
3655                        zone = pagezone;
3656                        spin_lock_irq(&zone->lru_lock);
3657                }
3658                lruvec = mem_cgroup_page_lruvec(page, zone);
3659
3660                if (!PageLRU(page) || !PageUnevictable(page))
3661                        continue;
3662
3663                if (page_evictable(page)) {
3664                        enum lru_list lru = page_lru_base_type(page);
3665
3666                        VM_BUG_ON(PageActive(page));
3667                        ClearPageUnevictable(page);
3668                        del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3669                        add_page_to_lru_list(page, lruvec, lru);
3670                        pgrescued++;
3671                }
3672        }
3673
3674        if (zone) {
3675                __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3676                __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3677                spin_unlock_irq(&zone->lru_lock);
3678        }
3679}
3680#endif /* CONFIG_SHMEM */
3681
3682static void warn_scan_unevictable_pages(void)
3683{
3684        printk_once(KERN_WARNING
3685                    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3686                    "disabled for lack of a legitimate use case.  If you have "
3687                    "one, please send an email to linux-mm@kvack.org.\n",
3688                    current->comm);
3689}
3690
3691/*
3692 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3693 * all nodes' unevictable lists for evictable pages
3694 */
3695unsigned long scan_unevictable_pages;
3696
3697int scan_unevictable_handler(struct ctl_table *table, int write,
3698                           void __user *buffer,
3699                           size_t *length, loff_t *ppos)
3700{
3701        warn_scan_unevictable_pages();
3702        proc_doulongvec_minmax(table, write, buffer, length, ppos);
3703        scan_unevictable_pages = 0;
3704        return 0;
3705}
3706
3707#ifdef CONFIG_NUMA
3708/*
3709 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3710 * a specified node's per zone unevictable lists for evictable pages.
3711 */
3712
3713static ssize_t read_scan_unevictable_node(struct device *dev,
3714                                          struct device_attribute *attr,
3715                                          char *buf)
3716{
3717        warn_scan_unevictable_pages();
3718        return sprintf(buf, "0\n");     /* always zero; should fit... */
3719}
3720
3721static ssize_t write_scan_unevictable_node(struct device *dev,
3722                                           struct device_attribute *attr,
3723                                        const char *buf, size_t count)
3724{
3725        warn_scan_unevictable_pages();
3726        return 1;
3727}
3728
3729
3730static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3731                        read_scan_unevictable_node,
3732                        write_scan_unevictable_node);
3733
3734int scan_unevictable_register_node(struct node *node)
3735{
3736        return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3737}
3738
3739void scan_unevictable_unregister_node(struct node *node)
3740{
3741        device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3742}
3743#endif
3744
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