1 /* 2 * linux/mm/vmscan.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 * 6 * Swap reorganised 29.12.95, Stephen Tweedie. 7 * kswapd added: 7.1.96 sct 8 * Removed kswapd_ctl limits, and swap out as many pages as needed 9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel. 10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com). 11 * Multiqueue VM started 5.8.00, Rik van Riel. 12 */ 13 14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 15 16 #include <linux/mm.h> 17 #include <linux/sched/mm.h> 18 #include <linux/module.h> 19 #include <linux/gfp.h> 20 #include <linux/kernel_stat.h> 21 #include <linux/swap.h> 22 #include <linux/pagemap.h> 23 #include <linux/init.h> 24 #include <linux/highmem.h> 25 #include <linux/vmpressure.h> 26 #include <linux/vmstat.h> 27 #include <linux/file.h> 28 #include <linux/writeback.h> 29 #include <linux/blkdev.h> 30 #include <linux/buffer_head.h> /* for try_to_release_page(), 31 buffer_heads_over_limit */ 32 #include <linux/mm_inline.h> 33 #include <linux/backing-dev.h> 34 #include <linux/rmap.h> 35 #include <linux/topology.h> 36 #include <linux/cpu.h> 37 #include <linux/cpuset.h> 38 #include <linux/compaction.h> 39 #include <linux/notifier.h> 40 #include <linux/rwsem.h> 41 #include <linux/delay.h> 42 #include <linux/kthread.h> 43 #include <linux/freezer.h> 44 #include <linux/memcontrol.h> 45 #include <linux/delayacct.h> 46 #include <linux/sysctl.h> 47 #include <linux/oom.h> 48 #include <linux/prefetch.h> 49 #include <linux/printk.h> 50 #include <linux/dax.h> 51 52 #include <asm/tlbflush.h> 53 #include <asm/div64.h> 54 55 #include <linux/swapops.h> 56 #include <linux/balloon_compaction.h> 57 58 #include "internal.h" 59 60 #define CREATE_TRACE_POINTS 61 #include <trace/events/vmscan.h> 62 63 struct scan_control { 64 /* How many pages shrink_list() should reclaim */ 65 unsigned long nr_to_reclaim; 66 67 /* This context's GFP mask */ 68 gfp_t gfp_mask; 69 70 /* Allocation order */ 71 int order; 72 73 /* 74 * Nodemask of nodes allowed by the caller. If NULL, all nodes 75 * are scanned. 76 */ 77 nodemask_t *nodemask; 78 79 /* 80 * The memory cgroup that hit its limit and as a result is the 81 * primary target of this reclaim invocation. 82 */ 83 struct mem_cgroup *target_mem_cgroup; 84 85 /* Scan (total_size >> priority) pages at once */ 86 int priority; 87 88 /* The highest zone to isolate pages for reclaim from */ 89 enum zone_type reclaim_idx; 90 91 /* Writepage batching in laptop mode; RECLAIM_WRITE */ 92 unsigned int may_writepage:1; 93 94 /* Can mapped pages be reclaimed? */ 95 unsigned int may_unmap:1; 96 97 /* Can pages be swapped as part of reclaim? */ 98 unsigned int may_swap:1; 99 100 /* 101 * Cgroups are not reclaimed below their configured memory.low, 102 * unless we threaten to OOM. If any cgroups are skipped due to 103 * memory.low and nothing was reclaimed, go back for memory.low. 104 */ 105 unsigned int memcg_low_reclaim:1; 106 unsigned int memcg_low_skipped:1; 107 108 unsigned int hibernation_mode:1; 109 110 /* One of the zones is ready for compaction */ 111 unsigned int compaction_ready:1; 112 113 /* Incremented by the number of inactive pages that were scanned */ 114 unsigned long nr_scanned; 115 116 /* Number of pages freed so far during a call to shrink_zones() */ 117 unsigned long nr_reclaimed; 118 }; 119 120 #ifdef ARCH_HAS_PREFETCH 121 #define prefetch_prev_lru_page(_page, _base, _field) \ 122 do { \ 123 if ((_page)->lru.prev != _base) { \ 124 struct page *prev; \ 125 \ 126 prev = lru_to_page(&(_page->lru)); \ 127 prefetch(&prev->_field); \ 128 } \ 129 } while (0) 130 #else 131 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) 132 #endif 133 134 #ifdef ARCH_HAS_PREFETCHW 135 #define prefetchw_prev_lru_page(_page, _base, _field) \ 136 do { \ 137 if ((_page)->lru.prev != _base) { \ 138 struct page *prev; \ 139 \ 140 prev = lru_to_page(&(_page->lru)); \ 141 prefetchw(&prev->_field); \ 142 } \ 143 } while (0) 144 #else 145 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) 146 #endif 147 148 /* 149 * From 0 .. 100. Higher means more swappy. 150 */ 151 int vm_swappiness = 60; 152 /* 153 * The total number of pages which are beyond the high watermark within all 154 * zones. 155 */ 156 unsigned long vm_total_pages; 157 158 static LIST_HEAD(shrinker_list); 159 static DECLARE_RWSEM(shrinker_rwsem); 160 161 #ifdef CONFIG_MEMCG 162 static bool global_reclaim(struct scan_control *sc) 163 { 164 return !sc->target_mem_cgroup; 165 } 166 167 /** 168 * sane_reclaim - is the usual dirty throttling mechanism operational? 169 * @sc: scan_control in question 170 * 171 * The normal page dirty throttling mechanism in balance_dirty_pages() is 172 * completely broken with the legacy memcg and direct stalling in 173 * shrink_page_list() is used for throttling instead, which lacks all the 174 * niceties such as fairness, adaptive pausing, bandwidth proportional 175 * allocation and configurability. 176 * 177 * This function tests whether the vmscan currently in progress can assume 178 * that the normal dirty throttling mechanism is operational. 179 */ 180 static bool sane_reclaim(struct scan_control *sc) 181 { 182 struct mem_cgroup *memcg = sc->target_mem_cgroup; 183 184 if (!memcg) 185 return true; 186 #ifdef CONFIG_CGROUP_WRITEBACK 187 if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) 188 return true; 189 #endif 190 return false; 191 } 192 #else 193 static bool global_reclaim(struct scan_control *sc) 194 { 195 return true; 196 } 197 198 static bool sane_reclaim(struct scan_control *sc) 199 { 200 return true; 201 } 202 #endif 203 204 /* 205 * This misses isolated pages which are not accounted for to save counters. 206 * As the data only determines if reclaim or compaction continues, it is 207 * not expected that isolated pages will be a dominating factor. 208 */ 209 unsigned long zone_reclaimable_pages(struct zone *zone) 210 { 211 unsigned long nr; 212 213 nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) + 214 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE); 215 if (get_nr_swap_pages() > 0) 216 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) + 217 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON); 218 219 return nr; 220 } 221 222 unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat) 223 { 224 unsigned long nr; 225 226 nr = node_page_state_snapshot(pgdat, NR_ACTIVE_FILE) + 227 node_page_state_snapshot(pgdat, NR_INACTIVE_FILE) + 228 node_page_state_snapshot(pgdat, NR_ISOLATED_FILE); 229 230 if (get_nr_swap_pages() > 0) 231 nr += node_page_state_snapshot(pgdat, NR_ACTIVE_ANON) + 232 node_page_state_snapshot(pgdat, NR_INACTIVE_ANON) + 233 node_page_state_snapshot(pgdat, NR_ISOLATED_ANON); 234 235 return nr; 236 } 237 238 /** 239 * lruvec_lru_size - Returns the number of pages on the given LRU list. 240 * @lruvec: lru vector 241 * @lru: lru to use 242 * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list) 243 */ 244 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx) 245 { 246 unsigned long lru_size; 247 int zid; 248 249 if (!mem_cgroup_disabled()) 250 lru_size = mem_cgroup_get_lru_size(lruvec, lru); 251 else 252 lru_size = node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru); 253 254 for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) { 255 struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid]; 256 unsigned long size; 257 258 if (!managed_zone(zone)) 259 continue; 260 261 if (!mem_cgroup_disabled()) 262 size = mem_cgroup_get_zone_lru_size(lruvec, lru, zid); 263 else 264 size = zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zid], 265 NR_ZONE_LRU_BASE + lru); 266 lru_size -= min(size, lru_size); 267 } 268 269 return lru_size; 270 271 } 272 273 /* 274 * Add a shrinker callback to be called from the vm. 275 */ 276 int register_shrinker(struct shrinker *shrinker) 277 { 278 size_t size = sizeof(*shrinker->nr_deferred); 279 280 if (shrinker->flags & SHRINKER_NUMA_AWARE) 281 size *= nr_node_ids; 282 283 shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); 284 if (!shrinker->nr_deferred) 285 return -ENOMEM; 286 287 down_write(&shrinker_rwsem); 288 list_add_tail(&shrinker->list, &shrinker_list); 289 up_write(&shrinker_rwsem); 290 return 0; 291 } 292 EXPORT_SYMBOL(register_shrinker); 293 294 /* 295 * Remove one 296 */ 297 void unregister_shrinker(struct shrinker *shrinker) 298 { 299 down_write(&shrinker_rwsem); 300 list_del(&shrinker->list); 301 up_write(&shrinker_rwsem); 302 kfree(shrinker->nr_deferred); 303 } 304 EXPORT_SYMBOL(unregister_shrinker); 305 306 #define SHRINK_BATCH 128 307 308 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, 309 struct shrinker *shrinker, 310 unsigned long nr_scanned, 311 unsigned long nr_eligible) 312 { 313 unsigned long freed = 0; 314 unsigned long long delta; 315 long total_scan; 316 long freeable; 317 long nr; 318 long new_nr; 319 int nid = shrinkctl->nid; 320 long batch_size = shrinker->batch ? shrinker->batch 321 : SHRINK_BATCH; 322 long scanned = 0, next_deferred; 323 324 freeable = shrinker->count_objects(shrinker, shrinkctl); 325 if (freeable == 0) 326 return 0; 327 328 /* 329 * copy the current shrinker scan count into a local variable 330 * and zero it so that other concurrent shrinker invocations 331 * don't also do this scanning work. 332 */ 333 nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0); 334 335 total_scan = nr; 336 delta = (4 * nr_scanned) / shrinker->seeks; 337 delta *= freeable; 338 do_div(delta, nr_eligible + 1); 339 total_scan += delta; 340 if (total_scan < 0) { 341 pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n", 342 shrinker->scan_objects, total_scan); 343 total_scan = freeable; 344 next_deferred = nr; 345 } else 346 next_deferred = total_scan; 347 348 /* 349 * We need to avoid excessive windup on filesystem shrinkers 350 * due to large numbers of GFP_NOFS allocations causing the 351 * shrinkers to return -1 all the time. This results in a large 352 * nr being built up so when a shrink that can do some work 353 * comes along it empties the entire cache due to nr >>> 354 * freeable. This is bad for sustaining a working set in 355 * memory. 356 * 357 * Hence only allow the shrinker to scan the entire cache when 358 * a large delta change is calculated directly. 359 */ 360 if (delta < freeable / 4) 361 total_scan = min(total_scan, freeable / 2); 362 363 /* 364 * Avoid risking looping forever due to too large nr value: 365 * never try to free more than twice the estimate number of 366 * freeable entries. 367 */ 368 if (total_scan > freeable * 2) 369 total_scan = freeable * 2; 370 371 trace_mm_shrink_slab_start(shrinker, shrinkctl, nr, 372 nr_scanned, nr_eligible, 373 freeable, delta, total_scan); 374 375 /* 376 * Normally, we should not scan less than batch_size objects in one 377 * pass to avoid too frequent shrinker calls, but if the slab has less 378 * than batch_size objects in total and we are really tight on memory, 379 * we will try to reclaim all available objects, otherwise we can end 380 * up failing allocations although there are plenty of reclaimable 381 * objects spread over several slabs with usage less than the 382 * batch_size. 383 * 384 * We detect the "tight on memory" situations by looking at the total 385 * number of objects we want to scan (total_scan). If it is greater 386 * than the total number of objects on slab (freeable), we must be 387 * scanning at high prio and therefore should try to reclaim as much as 388 * possible. 389 */ 390 while (total_scan >= batch_size || 391 total_scan >= freeable) { 392 unsigned long ret; 393 unsigned long nr_to_scan = min(batch_size, total_scan); 394 395 shrinkctl->nr_to_scan = nr_to_scan; 396 ret = shrinker->scan_objects(shrinker, shrinkctl); 397 if (ret == SHRINK_STOP) 398 break; 399 freed += ret; 400 401 count_vm_events(SLABS_SCANNED, nr_to_scan); 402 total_scan -= nr_to_scan; 403 scanned += nr_to_scan; 404 405 cond_resched(); 406 } 407 408 if (next_deferred >= scanned) 409 next_deferred -= scanned; 410 else 411 next_deferred = 0; 412 /* 413 * move the unused scan count back into the shrinker in a 414 * manner that handles concurrent updates. If we exhausted the 415 * scan, there is no need to do an update. 416 */ 417 if (next_deferred > 0) 418 new_nr = atomic_long_add_return(next_deferred, 419 &shrinker->nr_deferred[nid]); 420 else 421 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]); 422 423 trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan); 424 return freed; 425 } 426 427 /** 428 * shrink_slab - shrink slab caches 429 * @gfp_mask: allocation context 430 * @nid: node whose slab caches to target 431 * @memcg: memory cgroup whose slab caches to target 432 * @nr_scanned: pressure numerator 433 * @nr_eligible: pressure denominator 434 * 435 * Call the shrink functions to age shrinkable caches. 436 * 437 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set, 438 * unaware shrinkers will receive a node id of 0 instead. 439 * 440 * @memcg specifies the memory cgroup to target. If it is not NULL, 441 * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan 442 * objects from the memory cgroup specified. Otherwise, only unaware 443 * shrinkers are called. 444 * 445 * @nr_scanned and @nr_eligible form a ratio that indicate how much of 446 * the available objects should be scanned. Page reclaim for example 447 * passes the number of pages scanned and the number of pages on the 448 * LRU lists that it considered on @nid, plus a bias in @nr_scanned 449 * when it encountered mapped pages. The ratio is further biased by 450 * the ->seeks setting of the shrink function, which indicates the 451 * cost to recreate an object relative to that of an LRU page. 452 * 453 * Returns the number of reclaimed slab objects. 454 */ 455 static unsigned long shrink_slab(gfp_t gfp_mask, int nid, 456 struct mem_cgroup *memcg, 457 unsigned long nr_scanned, 458 unsigned long nr_eligible) 459 { 460 struct shrinker *shrinker; 461 unsigned long freed = 0; 462 463 if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))) 464 return 0; 465 466 if (nr_scanned == 0) 467 nr_scanned = SWAP_CLUSTER_MAX; 468 469 if (!down_read_trylock(&shrinker_rwsem)) { 470 /* 471 * If we would return 0, our callers would understand that we 472 * have nothing else to shrink and give up trying. By returning 473 * 1 we keep it going and assume we'll be able to shrink next 474 * time. 475 */ 476 freed = 1; 477 goto out; 478 } 479 480 list_for_each_entry(shrinker, &shrinker_list, list) { 481 struct shrink_control sc = { 482 .gfp_mask = gfp_mask, 483 .nid = nid, 484 .memcg = memcg, 485 }; 486 487 /* 488 * If kernel memory accounting is disabled, we ignore 489 * SHRINKER_MEMCG_AWARE flag and call all shrinkers 490 * passing NULL for memcg. 491 */ 492 if (memcg_kmem_enabled() && 493 !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE)) 494 continue; 495 496 if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) 497 sc.nid = 0; 498 499 freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible); 500 } 501 502 up_read(&shrinker_rwsem); 503 out: 504 cond_resched(); 505 return freed; 506 } 507 508 void drop_slab_node(int nid) 509 { 510 unsigned long freed; 511 512 do { 513 struct mem_cgroup *memcg = NULL; 514 515 freed = 0; 516 do { 517 freed += shrink_slab(GFP_KERNEL, nid, memcg, 518 1000, 1000); 519 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); 520 } while (freed > 10); 521 } 522 523 void drop_slab(void) 524 { 525 int nid; 526 527 for_each_online_node(nid) 528 drop_slab_node(nid); 529 } 530 531 static inline int is_page_cache_freeable(struct page *page) 532 { 533 /* 534 * A freeable page cache page is referenced only by the caller 535 * that isolated the page, the page cache radix tree and 536 * optional buffer heads at page->private. 537 */ 538 return page_count(page) - page_has_private(page) == 2; 539 } 540 541 static int may_write_to_inode(struct inode *inode, struct scan_control *sc) 542 { 543 if (current->flags & PF_SWAPWRITE) 544 return 1; 545 if (!inode_write_congested(inode)) 546 return 1; 547 if (inode_to_bdi(inode) == current->backing_dev_info) 548 return 1; 549 return 0; 550 } 551 552 /* 553 * We detected a synchronous write error writing a page out. Probably 554 * -ENOSPC. We need to propagate that into the address_space for a subsequent 555 * fsync(), msync() or close(). 556 * 557 * The tricky part is that after writepage we cannot touch the mapping: nothing 558 * prevents it from being freed up. But we have a ref on the page and once 559 * that page is locked, the mapping is pinned. 560 * 561 * We're allowed to run sleeping lock_page() here because we know the caller has 562 * __GFP_FS. 563 */ 564 static void handle_write_error(struct address_space *mapping, 565 struct page *page, int error) 566 { 567 lock_page(page); 568 if (page_mapping(page) == mapping) 569 mapping_set_error(mapping, error); 570 unlock_page(page); 571 } 572 573 /* possible outcome of pageout() */ 574 typedef enum { 575 /* failed to write page out, page is locked */ 576 PAGE_KEEP, 577 /* move page to the active list, page is locked */ 578 PAGE_ACTIVATE, 579 /* page has been sent to the disk successfully, page is unlocked */ 580 PAGE_SUCCESS, 581 /* page is clean and locked */ 582 PAGE_CLEAN, 583 } pageout_t; 584 585 /* 586 * pageout is called by shrink_page_list() for each dirty page. 587 * Calls ->writepage(). 588 */ 589 static pageout_t pageout(struct page *page, struct address_space *mapping, 590 struct scan_control *sc) 591 { 592 /* 593 * If the page is dirty, only perform writeback if that write 594 * will be non-blocking. To prevent this allocation from being 595 * stalled by pagecache activity. But note that there may be 596 * stalls if we need to run get_block(). We could test 597 * PagePrivate for that. 598 * 599 * If this process is currently in __generic_file_write_iter() against 600 * this page's queue, we can perform writeback even if that 601 * will block. 602 * 603 * If the page is swapcache, write it back even if that would 604 * block, for some throttling. This happens by accident, because 605 * swap_backing_dev_info is bust: it doesn't reflect the 606 * congestion state of the swapdevs. Easy to fix, if needed. 607 */ 608 if (!is_page_cache_freeable(page)) 609 return PAGE_KEEP; 610 if (!mapping) { 611 /* 612 * Some data journaling orphaned pages can have 613 * page->mapping == NULL while being dirty with clean buffers. 614 */ 615 if (page_has_private(page)) { 616 if (try_to_free_buffers(page)) { 617 ClearPageDirty(page); 618 pr_info("%s: orphaned page\n", __func__); 619 return PAGE_CLEAN; 620 } 621 } 622 return PAGE_KEEP; 623 } 624 if (mapping->a_ops->writepage == NULL) 625 return PAGE_ACTIVATE; 626 if (!may_write_to_inode(mapping->host, sc)) 627 return PAGE_KEEP; 628 629 if (clear_page_dirty_for_io(page)) { 630 int res; 631 struct writeback_control wbc = { 632 .sync_mode = WB_SYNC_NONE, 633 .nr_to_write = SWAP_CLUSTER_MAX, 634 .range_start = 0, 635 .range_end = LLONG_MAX, 636 .for_reclaim = 1, 637 }; 638 639 SetPageReclaim(page); 640 res = mapping->a_ops->writepage(page, &wbc); 641 if (res < 0) 642 handle_write_error(mapping, page, res); 643 if (res == AOP_WRITEPAGE_ACTIVATE) { 644 ClearPageReclaim(page); 645 return PAGE_ACTIVATE; 646 } 647 648 if (!PageWriteback(page)) { 649 /* synchronous write or broken a_ops? */ 650 ClearPageReclaim(page); 651 } 652 trace_mm_vmscan_writepage(page); 653 inc_node_page_state(page, NR_VMSCAN_WRITE); 654 return PAGE_SUCCESS; 655 } 656 657 return PAGE_CLEAN; 658 } 659 660 /* 661 * Same as remove_mapping, but if the page is removed from the mapping, it 662 * gets returned with a refcount of 0. 663 */ 664 static int __remove_mapping(struct address_space *mapping, struct page *page, 665 bool reclaimed) 666 { 667 unsigned long flags; 668 669 BUG_ON(!PageLocked(page)); 670 BUG_ON(mapping != page_mapping(page)); 671 672 spin_lock_irqsave(&mapping->tree_lock, flags); 673 /* 674 * The non racy check for a busy page. 675 * 676 * Must be careful with the order of the tests. When someone has 677 * a ref to the page, it may be possible that they dirty it then 678 * drop the reference. So if PageDirty is tested before page_count 679 * here, then the following race may occur: 680 * 681 * get_user_pages(&page); 682 * [user mapping goes away] 683 * write_to(page); 684 * !PageDirty(page) [good] 685 * SetPageDirty(page); 686 * put_page(page); 687 * !page_count(page) [good, discard it] 688 * 689 * [oops, our write_to data is lost] 690 * 691 * Reversing the order of the tests ensures such a situation cannot 692 * escape unnoticed. The smp_rmb is needed to ensure the page->flags 693 * load is not satisfied before that of page->_refcount. 694 * 695 * Note that if SetPageDirty is always performed via set_page_dirty, 696 * and thus under tree_lock, then this ordering is not required. 697 */ 698 if (!page_ref_freeze(page, 2)) 699 goto cannot_free; 700 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */ 701 if (unlikely(PageDirty(page))) { 702 page_ref_unfreeze(page, 2); 703 goto cannot_free; 704 } 705 706 if (PageSwapCache(page)) { 707 swp_entry_t swap = { .val = page_private(page) }; 708 mem_cgroup_swapout(page, swap); 709 __delete_from_swap_cache(page); 710 spin_unlock_irqrestore(&mapping->tree_lock, flags); 711 put_swap_page(page, swap); 712 } else { 713 void (*freepage)(struct page *); 714 void *shadow = NULL; 715 716 freepage = mapping->a_ops->freepage; 717 /* 718 * Remember a shadow entry for reclaimed file cache in 719 * order to detect refaults, thus thrashing, later on. 720 * 721 * But don't store shadows in an address space that is 722 * already exiting. This is not just an optizimation, 723 * inode reclaim needs to empty out the radix tree or 724 * the nodes are lost. Don't plant shadows behind its 725 * back. 726 * 727 * We also don't store shadows for DAX mappings because the 728 * only page cache pages found in these are zero pages 729 * covering holes, and because we don't want to mix DAX 730 * exceptional entries and shadow exceptional entries in the 731 * same page_tree. 732 */ 733 if (reclaimed && page_is_file_cache(page) && 734 !mapping_exiting(mapping) && !dax_mapping(mapping)) 735 shadow = workingset_eviction(mapping, page); 736 __delete_from_page_cache(page, shadow); 737 spin_unlock_irqrestore(&mapping->tree_lock, flags); 738 739 if (freepage != NULL) 740 freepage(page); 741 } 742 743 return 1; 744 745 cannot_free: 746 spin_unlock_irqrestore(&mapping->tree_lock, flags); 747 return 0; 748 } 749 750 /* 751 * Attempt to detach a locked page from its ->mapping. If it is dirty or if 752 * someone else has a ref on the page, abort and return 0. If it was 753 * successfully detached, return 1. Assumes the caller has a single ref on 754 * this page. 755 */ 756 int remove_mapping(struct address_space *mapping, struct page *page) 757 { 758 if (__remove_mapping(mapping, page, false)) { 759 /* 760 * Unfreezing the refcount with 1 rather than 2 effectively 761 * drops the pagecache ref for us without requiring another 762 * atomic operation. 763 */ 764 page_ref_unfreeze(page, 1); 765 return 1; 766 } 767 return 0; 768 } 769 770 /** 771 * putback_lru_page - put previously isolated page onto appropriate LRU list 772 * @page: page to be put back to appropriate lru list 773 * 774 * Add previously isolated @page to appropriate LRU list. 775 * Page may still be unevictable for other reasons. 776 * 777 * lru_lock must not be held, interrupts must be enabled. 778 */ 779 void putback_lru_page(struct page *page) 780 { 781 bool is_unevictable; 782 int was_unevictable = PageUnevictable(page); 783 784 VM_BUG_ON_PAGE(PageLRU(page), page); 785 786 redo: 787 ClearPageUnevictable(page); 788 789 if (page_evictable(page)) { 790 /* 791 * For evictable pages, we can use the cache. 792 * In event of a race, worst case is we end up with an 793 * unevictable page on [in]active list. 794 * We know how to handle that. 795 */ 796 is_unevictable = false; 797 lru_cache_add(page); 798 } else { 799 /* 800 * Put unevictable pages directly on zone's unevictable 801 * list. 802 */ 803 is_unevictable = true; 804 add_page_to_unevictable_list(page); 805 /* 806 * When racing with an mlock or AS_UNEVICTABLE clearing 807 * (page is unlocked) make sure that if the other thread 808 * does not observe our setting of PG_lru and fails 809 * isolation/check_move_unevictable_pages, 810 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move 811 * the page back to the evictable list. 812 * 813 * The other side is TestClearPageMlocked() or shmem_lock(). 814 */ 815 smp_mb(); 816 } 817 818 /* 819 * page's status can change while we move it among lru. If an evictable 820 * page is on unevictable list, it never be freed. To avoid that, 821 * check after we added it to the list, again. 822 */ 823 if (is_unevictable && page_evictable(page)) { 824 if (!isolate_lru_page(page)) { 825 put_page(page); 826 goto redo; 827 } 828 /* This means someone else dropped this page from LRU 829 * So, it will be freed or putback to LRU again. There is 830 * nothing to do here. 831 */ 832 } 833 834 if (was_unevictable && !is_unevictable) 835 count_vm_event(UNEVICTABLE_PGRESCUED); 836 else if (!was_unevictable && is_unevictable) 837 count_vm_event(UNEVICTABLE_PGCULLED); 838 839 put_page(page); /* drop ref from isolate */ 840 } 841 842 enum page_references { 843 PAGEREF_RECLAIM, 844 PAGEREF_RECLAIM_CLEAN, 845 PAGEREF_KEEP, 846 PAGEREF_ACTIVATE, 847 }; 848 849 static enum page_references page_check_references(struct page *page, 850 struct scan_control *sc) 851 { 852 int referenced_ptes, referenced_page; 853 unsigned long vm_flags; 854 855 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup, 856 &vm_flags); 857 referenced_page = TestClearPageReferenced(page); 858 859 /* 860 * Mlock lost the isolation race with us. Let try_to_unmap() 861 * move the page to the unevictable list. 862 */ 863 if (vm_flags & VM_LOCKED) 864 return PAGEREF_RECLAIM; 865 866 if (referenced_ptes) { 867 if (PageSwapBacked(page)) 868 return PAGEREF_ACTIVATE; 869 /* 870 * All mapped pages start out with page table 871 * references from the instantiating fault, so we need 872 * to look twice if a mapped file page is used more 873 * than once. 874 * 875 * Mark it and spare it for another trip around the 876 * inactive list. Another page table reference will 877 * lead to its activation. 878 * 879 * Note: the mark is set for activated pages as well 880 * so that recently deactivated but used pages are 881 * quickly recovered. 882 */ 883 SetPageReferenced(page); 884 885 if (referenced_page || referenced_ptes > 1) 886 return PAGEREF_ACTIVATE; 887 888 /* 889 * Activate file-backed executable pages after first usage. 890 */ 891 if (vm_flags & VM_EXEC) 892 return PAGEREF_ACTIVATE; 893 894 return PAGEREF_KEEP; 895 } 896 897 /* Reclaim if clean, defer dirty pages to writeback */ 898 if (referenced_page && !PageSwapBacked(page)) 899 return PAGEREF_RECLAIM_CLEAN; 900 901 return PAGEREF_RECLAIM; 902 } 903 904 /* Check if a page is dirty or under writeback */ 905 static void page_check_dirty_writeback(struct page *page, 906 bool *dirty, bool *writeback) 907 { 908 struct address_space *mapping; 909 910 /* 911 * Anonymous pages are not handled by flushers and must be written 912 * from reclaim context. Do not stall reclaim based on them 913 */ 914 if (!page_is_file_cache(page) || 915 (PageAnon(page) && !PageSwapBacked(page))) { 916 *dirty = false; 917 *writeback = false; 918 return; 919 } 920 921 /* By default assume that the page flags are accurate */ 922 *dirty = PageDirty(page); 923 *writeback = PageWriteback(page); 924 925 /* Verify dirty/writeback state if the filesystem supports it */ 926 if (!page_has_private(page)) 927 return; 928 929 mapping = page_mapping(page); 930 if (mapping && mapping->a_ops->is_dirty_writeback) 931 mapping->a_ops->is_dirty_writeback(page, dirty, writeback); 932 } 933 934 struct reclaim_stat { 935 unsigned nr_dirty; 936 unsigned nr_unqueued_dirty; 937 unsigned nr_congested; 938 unsigned nr_writeback; 939 unsigned nr_immediate; 940 unsigned nr_activate; 941 unsigned nr_ref_keep; 942 unsigned nr_unmap_fail; 943 }; 944 945 /* 946 * shrink_page_list() returns the number of reclaimed pages 947 */ 948 static unsigned long shrink_page_list(struct list_head *page_list, 949 struct pglist_data *pgdat, 950 struct scan_control *sc, 951 enum ttu_flags ttu_flags, 952 struct reclaim_stat *stat, 953 bool force_reclaim) 954 { 955 LIST_HEAD(ret_pages); 956 LIST_HEAD(free_pages); 957 int pgactivate = 0; 958 unsigned nr_unqueued_dirty = 0; 959 unsigned nr_dirty = 0; 960 unsigned nr_congested = 0; 961 unsigned nr_reclaimed = 0; 962 unsigned nr_writeback = 0; 963 unsigned nr_immediate = 0; 964 unsigned nr_ref_keep = 0; 965 unsigned nr_unmap_fail = 0; 966 967 cond_resched(); 968 969 while (!list_empty(page_list)) { 970 struct address_space *mapping; 971 struct page *page; 972 int may_enter_fs; 973 enum page_references references = PAGEREF_RECLAIM_CLEAN; 974 bool dirty, writeback; 975 976 cond_resched(); 977 978 page = lru_to_page(page_list); 979 list_del(&page->lru); 980 981 if (!trylock_page(page)) 982 goto keep; 983 984 VM_BUG_ON_PAGE(PageActive(page), page); 985 986 sc->nr_scanned++; 987 988 if (unlikely(!page_evictable(page))) 989 goto activate_locked; 990 991 if (!sc->may_unmap && page_mapped(page)) 992 goto keep_locked; 993 994 /* Double the slab pressure for mapped and swapcache pages */ 995 if ((page_mapped(page) || PageSwapCache(page)) && 996 !(PageAnon(page) && !PageSwapBacked(page))) 997 sc->nr_scanned++; 998 999 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 1000 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 1001 1002 /* 1003 * The number of dirty pages determines if a zone is marked 1004 * reclaim_congested which affects wait_iff_congested. kswapd 1005 * will stall and start writing pages if the tail of the LRU 1006 * is all dirty unqueued pages. 1007 */ 1008 page_check_dirty_writeback(page, &dirty, &writeback); 1009 if (dirty || writeback) 1010 nr_dirty++; 1011 1012 if (dirty && !writeback) 1013 nr_unqueued_dirty++; 1014 1015 /* 1016 * Treat this page as congested if the underlying BDI is or if 1017 * pages are cycling through the LRU so quickly that the 1018 * pages marked for immediate reclaim are making it to the 1019 * end of the LRU a second time. 1020 */ 1021 mapping = page_mapping(page); 1022 if (((dirty || writeback) && mapping && 1023 inode_write_congested(mapping->host)) || 1024 (writeback && PageReclaim(page))) 1025 nr_congested++; 1026 1027 /* 1028 * If a page at the tail of the LRU is under writeback, there 1029 * are three cases to consider. 1030 * 1031 * 1) If reclaim is encountering an excessive number of pages 1032 * under writeback and this page is both under writeback and 1033 * PageReclaim then it indicates that pages are being queued 1034 * for IO but are being recycled through the LRU before the 1035 * IO can complete. Waiting on the page itself risks an 1036 * indefinite stall if it is impossible to writeback the 1037 * page due to IO error or disconnected storage so instead 1038 * note that the LRU is being scanned too quickly and the 1039 * caller can stall after page list has been processed. 1040 * 1041 * 2) Global or new memcg reclaim encounters a page that is 1042 * not marked for immediate reclaim, or the caller does not 1043 * have __GFP_FS (or __GFP_IO if it's simply going to swap, 1044 * not to fs). In this case mark the page for immediate 1045 * reclaim and continue scanning. 1046 * 1047 * Require may_enter_fs because we would wait on fs, which 1048 * may not have submitted IO yet. And the loop driver might 1049 * enter reclaim, and deadlock if it waits on a page for 1050 * which it is needed to do the write (loop masks off 1051 * __GFP_IO|__GFP_FS for this reason); but more thought 1052 * would probably show more reasons. 1053 * 1054 * 3) Legacy memcg encounters a page that is already marked 1055 * PageReclaim. memcg does not have any dirty pages 1056 * throttling so we could easily OOM just because too many 1057 * pages are in writeback and there is nothing else to 1058 * reclaim. Wait for the writeback to complete. 1059 * 1060 * In cases 1) and 2) we activate the pages to get them out of 1061 * the way while we continue scanning for clean pages on the 1062 * inactive list and refilling from the active list. The 1063 * observation here is that waiting for disk writes is more 1064 * expensive than potentially causing reloads down the line. 1065 * Since they're marked for immediate reclaim, they won't put 1066 * memory pressure on the cache working set any longer than it 1067 * takes to write them to disk. 1068 */ 1069 if (PageWriteback(page)) { 1070 /* Case 1 above */ 1071 if (current_is_kswapd() && 1072 PageReclaim(page) && 1073 test_bit(PGDAT_WRITEBACK, &pgdat->flags)) { 1074 nr_immediate++; 1075 goto activate_locked; 1076 1077 /* Case 2 above */ 1078 } else if (sane_reclaim(sc) || 1079 !PageReclaim(page) || !may_enter_fs) { 1080 /* 1081 * This is slightly racy - end_page_writeback() 1082 * might have just cleared PageReclaim, then 1083 * setting PageReclaim here end up interpreted 1084 * as PageReadahead - but that does not matter 1085 * enough to care. What we do want is for this 1086 * page to have PageReclaim set next time memcg 1087 * reclaim reaches the tests above, so it will 1088 * then wait_on_page_writeback() to avoid OOM; 1089 * and it's also appropriate in global reclaim. 1090 */ 1091 SetPageReclaim(page); 1092 nr_writeback++; 1093 goto activate_locked; 1094 1095 /* Case 3 above */ 1096 } else { 1097 unlock_page(page); 1098 wait_on_page_writeback(page); 1099 /* then go back and try same page again */ 1100 list_add_tail(&page->lru, page_list); 1101 continue; 1102 } 1103 } 1104 1105 if (!force_reclaim) 1106 references = page_check_references(page, sc); 1107 1108 switch (references) { 1109 case PAGEREF_ACTIVATE: 1110 goto activate_locked; 1111 case PAGEREF_KEEP: 1112 nr_ref_keep++; 1113 goto keep_locked; 1114 case PAGEREF_RECLAIM: 1115 case PAGEREF_RECLAIM_CLEAN: 1116 ; /* try to reclaim the page below */ 1117 } 1118 1119 /* 1120 * Anonymous process memory has backing store? 1121 * Try to allocate it some swap space here. 1122 * Lazyfree page could be freed directly 1123 */ 1124 if (PageAnon(page) && PageSwapBacked(page) && 1125 !PageSwapCache(page)) { 1126 if (!(sc->gfp_mask & __GFP_IO)) 1127 goto keep_locked; 1128 if (PageTransHuge(page)) { 1129 /* cannot split THP, skip it */ 1130 if (!can_split_huge_page(page, NULL)) 1131 goto activate_locked; 1132 /* 1133 * Split pages without a PMD map right 1134 * away. Chances are some or all of the 1135 * tail pages can be freed without IO. 1136 */ 1137 if (!compound_mapcount(page) && 1138 split_huge_page_to_list(page, page_list)) 1139 goto activate_locked; 1140 } 1141 if (!add_to_swap(page)) { 1142 if (!PageTransHuge(page)) 1143 goto activate_locked; 1144 /* Split THP and swap individual base pages */ 1145 if (split_huge_page_to_list(page, page_list)) 1146 goto activate_locked; 1147 if (!add_to_swap(page)) 1148 goto activate_locked; 1149 } 1150 1151 /* XXX: We don't support THP writes */ 1152 if (PageTransHuge(page) && 1153 split_huge_page_to_list(page, page_list)) { 1154 delete_from_swap_cache(page); 1155 goto activate_locked; 1156 } 1157 1158 may_enter_fs = 1; 1159 1160 /* Adding to swap updated mapping */ 1161 mapping = page_mapping(page); 1162 } else if (unlikely(PageTransHuge(page))) { 1163 /* Split file THP */ 1164 if (split_huge_page_to_list(page, page_list)) 1165 goto keep_locked; 1166 } 1167 1168 VM_BUG_ON_PAGE(PageTransHuge(page), page); 1169 1170 /* 1171 * The page is mapped into the page tables of one or more 1172 * processes. Try to unmap it here. 1173 */ 1174 if (page_mapped(page)) { 1175 if (!try_to_unmap(page, ttu_flags | TTU_BATCH_FLUSH)) { 1176 nr_unmap_fail++; 1177 goto activate_locked; 1178 } 1179 } 1180 1181 if (PageDirty(page)) { 1182 /* 1183 * Only kswapd can writeback filesystem pages 1184 * to avoid risk of stack overflow. But avoid 1185 * injecting inefficient single-page IO into 1186 * flusher writeback as much as possible: only 1187 * write pages when we've encountered many 1188 * dirty pages, and when we've already scanned 1189 * the rest of the LRU for clean pages and see 1190 * the same dirty pages again (PageReclaim). 1191 */ 1192 if (page_is_file_cache(page) && 1193 (!current_is_kswapd() || !PageReclaim(page) || 1194 !test_bit(PGDAT_DIRTY, &pgdat->flags))) { 1195 /* 1196 * Immediately reclaim when written back. 1197 * Similar in principal to deactivate_page() 1198 * except we already have the page isolated 1199 * and know it's dirty 1200 */ 1201 inc_node_page_state(page, NR_VMSCAN_IMMEDIATE); 1202 SetPageReclaim(page); 1203 1204 goto activate_locked; 1205 } 1206 1207 if (references == PAGEREF_RECLAIM_CLEAN) 1208 goto keep_locked; 1209 if (!may_enter_fs) 1210 goto keep_locked; 1211 if (!sc->may_writepage) 1212 goto keep_locked; 1213 1214 /* 1215 * Page is dirty. Flush the TLB if a writable entry 1216 * potentially exists to avoid CPU writes after IO 1217 * starts and then write it out here. 1218 */ 1219 try_to_unmap_flush_dirty(); 1220 switch (pageout(page, mapping, sc)) { 1221 case PAGE_KEEP: 1222 goto keep_locked; 1223 case PAGE_ACTIVATE: 1224 goto activate_locked; 1225 case PAGE_SUCCESS: 1226 if (PageWriteback(page)) 1227 goto keep; 1228 if (PageDirty(page)) 1229 goto keep; 1230 1231 /* 1232 * A synchronous write - probably a ramdisk. Go 1233 * ahead and try to reclaim the page. 1234 */ 1235 if (!trylock_page(page)) 1236 goto keep; 1237 if (PageDirty(page) || PageWriteback(page)) 1238 goto keep_locked; 1239 mapping = page_mapping(page); 1240 case PAGE_CLEAN: 1241 ; /* try to free the page below */ 1242 } 1243 } 1244 1245 /* 1246 * If the page has buffers, try to free the buffer mappings 1247 * associated with this page. If we succeed we try to free 1248 * the page as well. 1249 * 1250 * We do this even if the page is PageDirty(). 1251 * try_to_release_page() does not perform I/O, but it is 1252 * possible for a page to have PageDirty set, but it is actually 1253 * clean (all its buffers are clean). This happens if the 1254 * buffers were written out directly, with submit_bh(). ext3 1255 * will do this, as well as the blockdev mapping. 1256 * try_to_release_page() will discover that cleanness and will 1257 * drop the buffers and mark the page clean - it can be freed. 1258 * 1259 * Rarely, pages can have buffers and no ->mapping. These are 1260 * the pages which were not successfully invalidated in 1261 * truncate_complete_page(). We try to drop those buffers here 1262 * and if that worked, and the page is no longer mapped into 1263 * process address space (page_count == 1) it can be freed. 1264 * Otherwise, leave the page on the LRU so it is swappable. 1265 */ 1266 if (page_has_private(page)) { 1267 if (!try_to_release_page(page, sc->gfp_mask)) 1268 goto activate_locked; 1269 if (!mapping && page_count(page) == 1) { 1270 unlock_page(page); 1271 if (put_page_testzero(page)) 1272 goto free_it; 1273 else { 1274 /* 1275 * rare race with speculative reference. 1276 * the speculative reference will free 1277 * this page shortly, so we may 1278 * increment nr_reclaimed here (and 1279 * leave it off the LRU). 1280 */ 1281 nr_reclaimed++; 1282 continue; 1283 } 1284 } 1285 } 1286 1287 if (PageAnon(page) && !PageSwapBacked(page)) { 1288 /* follow __remove_mapping for reference */ 1289 if (!page_ref_freeze(page, 1)) 1290 goto keep_locked; 1291 if (PageDirty(page)) { 1292 page_ref_unfreeze(page, 1); 1293 goto keep_locked; 1294 } 1295 1296 count_vm_event(PGLAZYFREED); 1297 count_memcg_page_event(page, PGLAZYFREED); 1298 } else if (!mapping || !__remove_mapping(mapping, page, true)) 1299 goto keep_locked; 1300 /* 1301 * At this point, we have no other references and there is 1302 * no way to pick any more up (removed from LRU, removed 1303 * from pagecache). Can use non-atomic bitops now (and 1304 * we obviously don't have to worry about waking up a process 1305 * waiting on the page lock, because there are no references. 1306 */ 1307 __ClearPageLocked(page); 1308 free_it: 1309 nr_reclaimed++; 1310 1311 /* 1312 * Is there need to periodically free_page_list? It would 1313 * appear not as the counts should be low 1314 */ 1315 list_add(&page->lru, &free_pages); 1316 continue; 1317 1318 activate_locked: 1319 /* Not a candidate for swapping, so reclaim swap space. */ 1320 if (PageSwapCache(page) && (mem_cgroup_swap_full(page) || 1321 PageMlocked(page))) 1322 try_to_free_swap(page); 1323 VM_BUG_ON_PAGE(PageActive(page), page); 1324 if (!PageMlocked(page)) { 1325 SetPageActive(page); 1326 pgactivate++; 1327 count_memcg_page_event(page, PGACTIVATE); 1328 } 1329 keep_locked: 1330 unlock_page(page); 1331 keep: 1332 list_add(&page->lru, &ret_pages); 1333 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page); 1334 } 1335 1336 mem_cgroup_uncharge_list(&free_pages); 1337 try_to_unmap_flush(); 1338 free_hot_cold_page_list(&free_pages, true); 1339 1340 list_splice(&ret_pages, page_list); 1341 count_vm_events(PGACTIVATE, pgactivate); 1342 1343 if (stat) { 1344 stat->nr_dirty = nr_dirty; 1345 stat->nr_congested = nr_congested; 1346 stat->nr_unqueued_dirty = nr_unqueued_dirty; 1347 stat->nr_writeback = nr_writeback; 1348 stat->nr_immediate = nr_immediate; 1349 stat->nr_activate = pgactivate; 1350 stat->nr_ref_keep = nr_ref_keep; 1351 stat->nr_unmap_fail = nr_unmap_fail; 1352 } 1353 return nr_reclaimed; 1354 } 1355 1356 unsigned long reclaim_clean_pages_from_list(struct zone *zone, 1357 struct list_head *page_list) 1358 { 1359 struct scan_control sc = { 1360 .gfp_mask = GFP_KERNEL, 1361 .priority = DEF_PRIORITY, 1362 .may_unmap = 1, 1363 }; 1364 unsigned long ret; 1365 struct page *page, *next; 1366 LIST_HEAD(clean_pages); 1367 1368 list_for_each_entry_safe(page, next, page_list, lru) { 1369 if (page_is_file_cache(page) && !PageDirty(page) && 1370 !__PageMovable(page)) { 1371 ClearPageActive(page); 1372 list_move(&page->lru, &clean_pages); 1373 } 1374 } 1375 1376 ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc, 1377 TTU_IGNORE_ACCESS, NULL, true); 1378 list_splice(&clean_pages, page_list); 1379 mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret); 1380 return ret; 1381 } 1382 1383 /* 1384 * Attempt to remove the specified page from its LRU. Only take this page 1385 * if it is of the appropriate PageActive status. Pages which are being 1386 * freed elsewhere are also ignored. 1387 * 1388 * page: page to consider 1389 * mode: one of the LRU isolation modes defined above 1390 * 1391 * returns 0 on success, -ve errno on failure. 1392 */ 1393 int __isolate_lru_page(struct page *page, isolate_mode_t mode) 1394 { 1395 int ret = -EINVAL; 1396 1397 /* Only take pages on the LRU. */ 1398 if (!PageLRU(page)) 1399 return ret; 1400 1401 /* Compaction should not handle unevictable pages but CMA can do so */ 1402 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE)) 1403 return ret; 1404 1405 ret = -EBUSY; 1406 1407 /* 1408 * To minimise LRU disruption, the caller can indicate that it only 1409 * wants to isolate pages it will be able to operate on without 1410 * blocking - clean pages for the most part. 1411 * 1412 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages 1413 * that it is possible to migrate without blocking 1414 */ 1415 if (mode & ISOLATE_ASYNC_MIGRATE) { 1416 /* All the caller can do on PageWriteback is block */ 1417 if (PageWriteback(page)) 1418 return ret; 1419 1420 if (PageDirty(page)) { 1421 struct address_space *mapping; 1422 1423 /* 1424 * Only pages without mappings or that have a 1425 * ->migratepage callback are possible to migrate 1426 * without blocking 1427 */ 1428 mapping = page_mapping(page); 1429 if (mapping && !mapping->a_ops->migratepage) 1430 return ret; 1431 } 1432 } 1433 1434 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) 1435 return ret; 1436 1437 if (likely(get_page_unless_zero(page))) { 1438 /* 1439 * Be careful not to clear PageLRU until after we're 1440 * sure the page is not being freed elsewhere -- the 1441 * page release code relies on it. 1442 */ 1443 ClearPageLRU(page); 1444 ret = 0; 1445 } 1446 1447 return ret; 1448 } 1449 1450 1451 /* 1452 * Update LRU sizes after isolating pages. The LRU size updates must 1453 * be complete before mem_cgroup_update_lru_size due to a santity check. 1454 */ 1455 static __always_inline void update_lru_sizes(struct lruvec *lruvec, 1456 enum lru_list lru, unsigned long *nr_zone_taken) 1457 { 1458 int zid; 1459 1460 for (zid = 0; zid < MAX_NR_ZONES; zid++) { 1461 if (!nr_zone_taken[zid]) 1462 continue; 1463 1464 __update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]); 1465 #ifdef CONFIG_MEMCG 1466 mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]); 1467 #endif 1468 } 1469 1470 } 1471 1472 /* 1473 * zone_lru_lock is heavily contended. Some of the functions that 1474 * shrink the lists perform better by taking out a batch of pages 1475 * and working on them outside the LRU lock. 1476 * 1477 * For pagecache intensive workloads, this function is the hottest 1478 * spot in the kernel (apart from copy_*_user functions). 1479 * 1480 * Appropriate locks must be held before calling this function. 1481 * 1482 * @nr_to_scan: The number of eligible pages to look through on the list. 1483 * @lruvec: The LRU vector to pull pages from. 1484 * @dst: The temp list to put pages on to. 1485 * @nr_scanned: The number of pages that were scanned. 1486 * @sc: The scan_control struct for this reclaim session 1487 * @mode: One of the LRU isolation modes 1488 * @lru: LRU list id for isolating 1489 * 1490 * returns how many pages were moved onto *@dst. 1491 */ 1492 static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 1493 struct lruvec *lruvec, struct list_head *dst, 1494 unsigned long *nr_scanned, struct scan_control *sc, 1495 isolate_mode_t mode, enum lru_list lru) 1496 { 1497 struct list_head *src = &lruvec->lists[lru]; 1498 unsigned long nr_taken = 0; 1499 unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 }; 1500 unsigned long nr_skipped[MAX_NR_ZONES] = { 0, }; 1501 unsigned long skipped = 0; 1502 unsigned long scan, total_scan, nr_pages; 1503 LIST_HEAD(pages_skipped); 1504 1505 scan = 0; 1506 for (total_scan = 0; 1507 scan < nr_to_scan && nr_taken < nr_to_scan && !list_empty(src); 1508 total_scan++) { 1509 struct page *page; 1510 1511 page = lru_to_page(src); 1512 prefetchw_prev_lru_page(page, src, flags); 1513 1514 VM_BUG_ON_PAGE(!PageLRU(page), page); 1515 1516 if (page_zonenum(page) > sc->reclaim_idx) { 1517 list_move(&page->lru, &pages_skipped); 1518 nr_skipped[page_zonenum(page)]++; 1519 continue; 1520 } 1521 1522 /* 1523 * Do not count skipped pages because that makes the function 1524 * return with no isolated pages if the LRU mostly contains 1525 * ineligible pages. This causes the VM to not reclaim any 1526 * pages, triggering a premature OOM. 1527 */ 1528 scan++; 1529 switch (__isolate_lru_page(page, mode)) { 1530 case 0: 1531 nr_pages = hpage_nr_pages(page); 1532 nr_taken += nr_pages; 1533 nr_zone_taken[page_zonenum(page)] += nr_pages; 1534 list_move(&page->lru, dst); 1535 break; 1536 1537 case -EBUSY: 1538 /* else it is being freed elsewhere */ 1539 list_move(&page->lru, src); 1540 continue; 1541 1542 default: 1543 BUG(); 1544 } 1545 } 1546 1547 /* 1548 * Splice any skipped pages to the start of the LRU list. Note that 1549 * this disrupts the LRU order when reclaiming for lower zones but 1550 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX 1551 * scanning would soon rescan the same pages to skip and put the 1552 * system at risk of premature OOM. 1553 */ 1554 if (!list_empty(&pages_skipped)) { 1555 int zid; 1556 1557 list_splice(&pages_skipped, src); 1558 for (zid = 0; zid < MAX_NR_ZONES; zid++) { 1559 if (!nr_skipped[zid]) 1560 continue; 1561 1562 __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]); 1563 skipped += nr_skipped[zid]; 1564 } 1565 } 1566 *nr_scanned = total_scan; 1567 trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, 1568 total_scan, skipped, nr_taken, mode, lru); 1569 update_lru_sizes(lruvec, lru, nr_zone_taken); 1570 return nr_taken; 1571 } 1572 1573 /** 1574 * isolate_lru_page - tries to isolate a page from its LRU list 1575 * @page: page to isolate from its LRU list 1576 * 1577 * Isolates a @page from an LRU list, clears PageLRU and adjusts the 1578 * vmstat statistic corresponding to whatever LRU list the page was on. 1579 * 1580 * Returns 0 if the page was removed from an LRU list. 1581 * Returns -EBUSY if the page was not on an LRU list. 1582 * 1583 * The returned page will have PageLRU() cleared. If it was found on 1584 * the active list, it will have PageActive set. If it was found on 1585 * the unevictable list, it will have the PageUnevictable bit set. That flag 1586 * may need to be cleared by the caller before letting the page go. 1587 * 1588 * The vmstat statistic corresponding to the list on which the page was 1589 * found will be decremented. 1590 * 1591 * Restrictions: 1592 * (1) Must be called with an elevated refcount on the page. This is a 1593 * fundamentnal difference from isolate_lru_pages (which is called 1594 * without a stable reference). 1595 * (2) the lru_lock must not be held. 1596 * (3) interrupts must be enabled. 1597 */ 1598 int isolate_lru_page(struct page *page) 1599 { 1600 int ret = -EBUSY; 1601 1602 VM_BUG_ON_PAGE(!page_count(page), page); 1603 WARN_RATELIMIT(PageTail(page), "trying to isolate tail page"); 1604 1605 if (PageLRU(page)) { 1606 struct zone *zone = page_zone(page); 1607 struct lruvec *lruvec; 1608 1609 spin_lock_irq(zone_lru_lock(zone)); 1610 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat); 1611 if (PageLRU(page)) { 1612 int lru = page_lru(page); 1613 get_page(page); 1614 ClearPageLRU(page); 1615 del_page_from_lru_list(page, lruvec, lru); 1616 ret = 0; 1617 } 1618 spin_unlock_irq(zone_lru_lock(zone)); 1619 } 1620 return ret; 1621 } 1622 1623 /* 1624 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and 1625 * then get resheduled. When there are massive number of tasks doing page 1626 * allocation, such sleeping direct reclaimers may keep piling up on each CPU, 1627 * the LRU list will go small and be scanned faster than necessary, leading to 1628 * unnecessary swapping, thrashing and OOM. 1629 */ 1630 static int too_many_isolated(struct pglist_data *pgdat, int file, 1631 struct scan_control *sc) 1632 { 1633 unsigned long inactive, isolated; 1634 1635 if (current_is_kswapd()) 1636 return 0; 1637 1638 if (!sane_reclaim(sc)) 1639 return 0; 1640 1641 if (file) { 1642 inactive = node_page_state(pgdat, NR_INACTIVE_FILE); 1643 isolated = node_page_state(pgdat, NR_ISOLATED_FILE); 1644 } else { 1645 inactive = node_page_state(pgdat, NR_INACTIVE_ANON); 1646 isolated = node_page_state(pgdat, NR_ISOLATED_ANON); 1647 } 1648 1649 /* 1650 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they 1651 * won't get blocked by normal direct-reclaimers, forming a circular 1652 * deadlock. 1653 */ 1654 if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS)) 1655 inactive >>= 3; 1656 1657 return isolated > inactive; 1658 } 1659 1660 static noinline_for_stack void 1661 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list) 1662 { 1663 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1664 struct pglist_data *pgdat = lruvec_pgdat(lruvec); 1665 LIST_HEAD(pages_to_free); 1666 1667 /* 1668 * Put back any unfreeable pages. 1669 */ 1670 while (!list_empty(page_list)) { 1671 struct page *page = lru_to_page(page_list); 1672 int lru; 1673 1674 VM_BUG_ON_PAGE(PageLRU(page), page); 1675 list_del(&page->lru); 1676 if (unlikely(!page_evictable(page))) { 1677 spin_unlock_irq(&pgdat->lru_lock); 1678 putback_lru_page(page); 1679 spin_lock_irq(&pgdat->lru_lock); 1680 continue; 1681 } 1682 1683 lruvec = mem_cgroup_page_lruvec(page, pgdat); 1684 1685 SetPageLRU(page); 1686 lru = page_lru(page); 1687 add_page_to_lru_list(page, lruvec, lru); 1688 1689 if (is_active_lru(lru)) { 1690 int file = is_file_lru(lru); 1691 int numpages = hpage_nr_pages(page); 1692 reclaim_stat->recent_rotated[file] += numpages; 1693 } 1694 if (put_page_testzero(page)) { 1695 __ClearPageLRU(page); 1696 __ClearPageActive(page); 1697 del_page_from_lru_list(page, lruvec, lru); 1698 1699 if (unlikely(PageCompound(page))) { 1700 spin_unlock_irq(&pgdat->lru_lock); 1701 mem_cgroup_uncharge(page); 1702 (*get_compound_page_dtor(page))(page); 1703 spin_lock_irq(&pgdat->lru_lock); 1704 } else 1705 list_add(&page->lru, &pages_to_free); 1706 } 1707 } 1708 1709 /* 1710 * To save our caller's stack, now use input list for pages to free. 1711 */ 1712 list_splice(&pages_to_free, page_list); 1713 } 1714 1715 /* 1716 * If a kernel thread (such as nfsd for loop-back mounts) services 1717 * a backing device by writing to the page cache it sets PF_LESS_THROTTLE. 1718 * In that case we should only throttle if the backing device it is 1719 * writing to is congested. In other cases it is safe to throttle. 1720 */ 1721 static int current_may_throttle(void) 1722 { 1723 return !(current->flags & PF_LESS_THROTTLE) || 1724 current->backing_dev_info == NULL || 1725 bdi_write_congested(current->backing_dev_info); 1726 } 1727 1728 /* 1729 * shrink_inactive_list() is a helper for shrink_node(). It returns the number 1730 * of reclaimed pages 1731 */ 1732 static noinline_for_stack unsigned long 1733 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, 1734 struct scan_control *sc, enum lru_list lru) 1735 { 1736 LIST_HEAD(page_list); 1737 unsigned long nr_scanned; 1738 unsigned long nr_reclaimed = 0; 1739 unsigned long nr_taken; 1740 struct reclaim_stat stat = {}; 1741 isolate_mode_t isolate_mode = 0; 1742 int file = is_file_lru(lru); 1743 struct pglist_data *pgdat = lruvec_pgdat(lruvec); 1744 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1745 1746 while (unlikely(too_many_isolated(pgdat, file, sc))) { 1747 congestion_wait(BLK_RW_ASYNC, HZ/10); 1748 1749 /* We are about to die and free our memory. Return now. */ 1750 if (fatal_signal_pending(current)) 1751 return SWAP_CLUSTER_MAX; 1752 } 1753 1754 lru_add_drain(); 1755 1756 if (!sc->may_unmap) 1757 isolate_mode |= ISOLATE_UNMAPPED; 1758 1759 spin_lock_irq(&pgdat->lru_lock); 1760 1761 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list, 1762 &nr_scanned, sc, isolate_mode, lru); 1763 1764 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken); 1765 reclaim_stat->recent_scanned[file] += nr_taken; 1766 1767 if (current_is_kswapd()) { 1768 if (global_reclaim(sc)) 1769 __count_vm_events(PGSCAN_KSWAPD, nr_scanned); 1770 count_memcg_events(lruvec_memcg(lruvec), PGSCAN_KSWAPD, 1771 nr_scanned); 1772 } else { 1773 if (global_reclaim(sc)) 1774 __count_vm_events(PGSCAN_DIRECT, nr_scanned); 1775 count_memcg_events(lruvec_memcg(lruvec), PGSCAN_DIRECT, 1776 nr_scanned); 1777 } 1778 spin_unlock_irq(&pgdat->lru_lock); 1779 1780 if (nr_taken == 0) 1781 return 0; 1782 1783 nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, 0, 1784 &stat, false); 1785 1786 spin_lock_irq(&pgdat->lru_lock); 1787 1788 if (current_is_kswapd()) { 1789 if (global_reclaim(sc)) 1790 __count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed); 1791 count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_KSWAPD, 1792 nr_reclaimed); 1793 } else { 1794 if (global_reclaim(sc)) 1795 __count_vm_events(PGSTEAL_DIRECT, nr_reclaimed); 1796 count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_DIRECT, 1797 nr_reclaimed); 1798 } 1799 1800 putback_inactive_pages(lruvec, &page_list); 1801 1802 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken); 1803 1804 spin_unlock_irq(&pgdat->lru_lock); 1805 1806 mem_cgroup_uncharge_list(&page_list); 1807 free_hot_cold_page_list(&page_list, true); 1808 1809 /* 1810 * If reclaim is isolating dirty pages under writeback, it implies 1811 * that the long-lived page allocation rate is exceeding the page 1812 * laundering rate. Either the global limits are not being effective 1813 * at throttling processes due to the page distribution throughout 1814 * zones or there is heavy usage of a slow backing device. The 1815 * only option is to throttle from reclaim context which is not ideal 1816 * as there is no guarantee the dirtying process is throttled in the 1817 * same way balance_dirty_pages() manages. 1818 * 1819 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number 1820 * of pages under pages flagged for immediate reclaim and stall if any 1821 * are encountered in the nr_immediate check below. 1822 */ 1823 if (stat.nr_writeback && stat.nr_writeback == nr_taken) 1824 set_bit(PGDAT_WRITEBACK, &pgdat->flags); 1825 1826 /* 1827 * Legacy memcg will stall in page writeback so avoid forcibly 1828 * stalling here. 1829 */ 1830 if (sane_reclaim(sc)) { 1831 /* 1832 * Tag a zone as congested if all the dirty pages scanned were 1833 * backed by a congested BDI and wait_iff_congested will stall. 1834 */ 1835 if (stat.nr_dirty && stat.nr_dirty == stat.nr_congested) 1836 set_bit(PGDAT_CONGESTED, &pgdat->flags); 1837 1838 /* 1839 * If dirty pages are scanned that are not queued for IO, it 1840 * implies that flushers are not doing their job. This can 1841 * happen when memory pressure pushes dirty pages to the end of 1842 * the LRU before the dirty limits are breached and the dirty 1843 * data has expired. It can also happen when the proportion of 1844 * dirty pages grows not through writes but through memory 1845 * pressure reclaiming all the clean cache. And in some cases, 1846 * the flushers simply cannot keep up with the allocation 1847 * rate. Nudge the flusher threads in case they are asleep, but 1848 * also allow kswapd to start writing pages during reclaim. 1849 */ 1850 if (stat.nr_unqueued_dirty == nr_taken) { 1851 wakeup_flusher_threads(0, WB_REASON_VMSCAN); 1852 set_bit(PGDAT_DIRTY, &pgdat->flags); 1853 } 1854 1855 /* 1856 * If kswapd scans pages marked marked for immediate 1857 * reclaim and under writeback (nr_immediate), it implies 1858 * that pages are cycling through the LRU faster than 1859 * they are written so also forcibly stall. 1860 */ 1861 if (stat.nr_immediate && current_may_throttle()) 1862 congestion_wait(BLK_RW_ASYNC, HZ/10); 1863 } 1864 1865 /* 1866 * Stall direct reclaim for IO completions if underlying BDIs or zone 1867 * is congested. Allow kswapd to continue until it starts encountering 1868 * unqueued dirty pages or cycling through the LRU too quickly. 1869 */ 1870 if (!sc->hibernation_mode && !current_is_kswapd() && 1871 current_may_throttle()) 1872 wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10); 1873 1874 trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id, 1875 nr_scanned, nr_reclaimed, 1876 stat.nr_dirty, stat.nr_writeback, 1877 stat.nr_congested, stat.nr_immediate, 1878 stat.nr_activate, stat.nr_ref_keep, 1879 stat.nr_unmap_fail, 1880 sc->priority, file); 1881 return nr_reclaimed; 1882 } 1883 1884 /* 1885 * This moves pages from the active list to the inactive list. 1886 * 1887 * We move them the other way if the page is referenced by one or more 1888 * processes, from rmap. 1889 * 1890 * If the pages are mostly unmapped, the processing is fast and it is 1891 * appropriate to hold zone_lru_lock across the whole operation. But if 1892 * the pages are mapped, the processing is slow (page_referenced()) so we 1893 * should drop zone_lru_lock around each page. It's impossible to balance 1894 * this, so instead we remove the pages from the LRU while processing them. 1895 * It is safe to rely on PG_active against the non-LRU pages in here because 1896 * nobody will play with that bit on a non-LRU page. 1897 * 1898 * The downside is that we have to touch page->_refcount against each page. 1899 * But we had to alter page->flags anyway. 1900 * 1901 * Returns the number of pages moved to the given lru. 1902 */ 1903 1904 static unsigned move_active_pages_to_lru(struct lruvec *lruvec, 1905 struct list_head *list, 1906 struct list_head *pages_to_free, 1907 enum lru_list lru) 1908 { 1909 struct pglist_data *pgdat = lruvec_pgdat(lruvec); 1910 struct page *page; 1911 int nr_pages; 1912 int nr_moved = 0; 1913 1914 while (!list_empty(list)) { 1915 page = lru_to_page(list); 1916 lruvec = mem_cgroup_page_lruvec(page, pgdat); 1917 1918 VM_BUG_ON_PAGE(PageLRU(page), page); 1919 SetPageLRU(page); 1920 1921 nr_pages = hpage_nr_pages(page); 1922 update_lru_size(lruvec, lru, page_zonenum(page), nr_pages); 1923 list_move(&page->lru, &lruvec->lists[lru]); 1924 1925 if (put_page_testzero(page)) { 1926 __ClearPageLRU(page); 1927 __ClearPageActive(page); 1928 del_page_from_lru_list(page, lruvec, lru); 1929 1930 if (unlikely(PageCompound(page))) { 1931 spin_unlock_irq(&pgdat->lru_lock); 1932 mem_cgroup_uncharge(page); 1933 (*get_compound_page_dtor(page))(page); 1934 spin_lock_irq(&pgdat->lru_lock); 1935 } else 1936 list_add(&page->lru, pages_to_free); 1937 } else { 1938 nr_moved += nr_pages; 1939 } 1940 } 1941 1942 if (!is_active_lru(lru)) { 1943 __count_vm_events(PGDEACTIVATE, nr_moved); 1944 count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, 1945 nr_moved); 1946 } 1947 1948 return nr_moved; 1949 } 1950 1951 static void shrink_active_list(unsigned long nr_to_scan, 1952 struct lruvec *lruvec, 1953 struct scan_control *sc, 1954 enum lru_list lru) 1955 { 1956 unsigned long nr_taken; 1957 unsigned long nr_scanned; 1958 unsigned long vm_flags; 1959 LIST_HEAD(l_hold); /* The pages which were snipped off */ 1960 LIST_HEAD(l_active); 1961 LIST_HEAD(l_inactive); 1962 struct page *page; 1963 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1964 unsigned nr_deactivate, nr_activate; 1965 unsigned nr_rotated = 0; 1966 isolate_mode_t isolate_mode = 0; 1967 int file = is_file_lru(lru); 1968 struct pglist_data *pgdat = lruvec_pgdat(lruvec); 1969 1970 lru_add_drain(); 1971 1972 if (!sc->may_unmap) 1973 isolate_mode |= ISOLATE_UNMAPPED; 1974 1975 spin_lock_irq(&pgdat->lru_lock); 1976 1977 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold, 1978 &nr_scanned, sc, isolate_mode, lru); 1979 1980 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken); 1981 reclaim_stat->recent_scanned[file] += nr_taken; 1982 1983 __count_vm_events(PGREFILL, nr_scanned); 1984 count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned); 1985 1986 spin_unlock_irq(&pgdat->lru_lock); 1987 1988 while (!list_empty(&l_hold)) { 1989 cond_resched(); 1990 page = lru_to_page(&l_hold); 1991 list_del(&page->lru); 1992 1993 if (unlikely(!page_evictable(page))) { 1994 putback_lru_page(page); 1995 continue; 1996 } 1997 1998 if (unlikely(buffer_heads_over_limit)) { 1999 if (page_has_private(page) && trylock_page(page)) { 2000 if (page_has_private(page)) 2001 try_to_release_page(page, 0); 2002 unlock_page(page); 2003 } 2004 } 2005 2006 if (page_referenced(page, 0, sc->target_mem_cgroup, 2007 &vm_flags)) { 2008 nr_rotated += hpage_nr_pages(page); 2009 /* 2010 * Identify referenced, file-backed active pages and 2011 * give them one more trip around the active list. So 2012 * that executable code get better chances to stay in 2013 * memory under moderate memory pressure. Anon pages 2014 * are not likely to be evicted by use-once streaming 2015 * IO, plus JVM can create lots of anon VM_EXEC pages, 2016 * so we ignore them here. 2017 */ 2018 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) { 2019 list_add(&page->lru, &l_active); 2020 continue; 2021 } 2022 } 2023 2024 ClearPageActive(page); /* we are de-activating */ 2025 list_add(&page->lru, &l_inactive); 2026 } 2027 2028 /* 2029 * Move pages back to the lru list. 2030 */ 2031 spin_lock_irq(&pgdat->lru_lock); 2032 /* 2033 * Count referenced pages from currently used mappings as rotated, 2034 * even though only some of them are actually re-activated. This 2035 * helps balance scan pressure between file and anonymous pages in 2036 * get_scan_count. 2037 */ 2038 reclaim_stat->recent_rotated[file] += nr_rotated; 2039 2040 nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru); 2041 nr_deactivate = move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE); 2042 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken); 2043 spin_unlock_irq(&pgdat->lru_lock); 2044 2045 mem_cgroup_uncharge_list(&l_hold); 2046 free_hot_cold_page_list(&l_hold, true); 2047 trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate, 2048 nr_deactivate, nr_rotated, sc->priority, file); 2049 } 2050 2051 /* 2052 * The inactive anon list should be small enough that the VM never has 2053 * to do too much work. 2054 * 2055 * The inactive file list should be small enough to leave most memory 2056 * to the established workingset on the scan-resistant active list, 2057 * but large enough to avoid thrashing the aggregate readahead window. 2058 * 2059 * Both inactive lists should also be large enough that each inactive 2060 * page has a chance to be referenced again before it is reclaimed. 2061 * 2062 * If that fails and refaulting is observed, the inactive list grows. 2063 * 2064 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages 2065 * on this LRU, maintained by the pageout code. A zone->inactive_ratio 2066 * of 3 means 3:1 or 25% of the pages are kept on the inactive list. 2067 * 2068 * total target max 2069 * memory ratio inactive 2070 * ------------------------------------- 2071 * 10MB 1 5MB 2072 * 100MB 1 50MB 2073 * 1GB 3 250MB 2074 * 10GB 10 0.9GB 2075 * 100GB 31 3GB 2076 * 1TB 101 10GB 2077 * 10TB 320 32GB 2078 */ 2079 static bool inactive_list_is_low(struct lruvec *lruvec, bool file, 2080 struct mem_cgroup *memcg, 2081 struct scan_control *sc, bool actual_reclaim) 2082 { 2083 enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE; 2084 struct pglist_data *pgdat = lruvec_pgdat(lruvec); 2085 enum lru_list inactive_lru = file * LRU_FILE; 2086 unsigned long inactive, active; 2087 unsigned long inactive_ratio; 2088 unsigned long refaults; 2089 unsigned long gb; 2090 2091 /* 2092 * If we don't have swap space, anonymous page deactivation 2093 * is pointless. 2094 */ 2095 if (!file && !total_swap_pages) 2096 return false; 2097 2098 inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx); 2099 active = lruvec_lru_size(lruvec, active_lru, sc->reclaim_idx); 2100 2101 if (memcg) 2102 refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE); 2103 else 2104 refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE); 2105 2106 /* 2107 * When refaults are being observed, it means a new workingset 2108 * is being established. Disable active list protection to get 2109 * rid of the stale workingset quickly. 2110 */ 2111 if (file && actual_reclaim && lruvec->refaults != refaults) { 2112 inactive_ratio = 0; 2113 } else { 2114 gb = (inactive + active) >> (30 - PAGE_SHIFT); 2115 if (gb) 2116 inactive_ratio = int_sqrt(10 * gb); 2117 else 2118 inactive_ratio = 1; 2119 } 2120 2121 if (actual_reclaim) 2122 trace_mm_vmscan_inactive_list_is_low(pgdat->node_id, sc->reclaim_idx, 2123 lruvec_lru_size(lruvec, inactive_lru, MAX_NR_ZONES), inactive, 2124 lruvec_lru_size(lruvec, active_lru, MAX_NR_ZONES), active, 2125 inactive_ratio, file); 2126 2127 return inactive * inactive_ratio < active; 2128 } 2129 2130 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, 2131 struct lruvec *lruvec, struct mem_cgroup *memcg, 2132 struct scan_control *sc) 2133 { 2134 if (is_active_lru(lru)) { 2135 if (inactive_list_is_low(lruvec, is_file_lru(lru), 2136 memcg, sc, true)) 2137 shrink_active_list(nr_to_scan, lruvec, sc, lru); 2138 return 0; 2139 } 2140 2141 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru); 2142 } 2143 2144 enum scan_balance { 2145 SCAN_EQUAL, 2146 SCAN_FRACT, 2147 SCAN_ANON, 2148 SCAN_FILE, 2149 }; 2150 2151 /* 2152 * Determine how aggressively the anon and file LRU lists should be 2153 * scanned. The relative value of each set of LRU lists is determined 2154 * by looking at the fraction of the pages scanned we did rotate back 2155 * onto the active list instead of evict. 2156 * 2157 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan 2158 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan 2159 */ 2160 static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, 2161 struct scan_control *sc, unsigned long *nr, 2162 unsigned long *lru_pages) 2163 { 2164 int swappiness = mem_cgroup_swappiness(memcg); 2165 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 2166 u64 fraction[2]; 2167 u64 denominator = 0; /* gcc */ 2168 struct pglist_data *pgdat = lruvec_pgdat(lruvec); 2169 unsigned long anon_prio, file_prio; 2170 enum scan_balance scan_balance; 2171 unsigned long anon, file; 2172 unsigned long ap, fp; 2173 enum lru_list lru; 2174 2175 /* If we have no swap space, do not bother scanning anon pages. */ 2176 if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) { 2177 scan_balance = SCAN_FILE; 2178 goto out; 2179 } 2180 2181 /* 2182 * Global reclaim will swap to prevent OOM even with no 2183 * swappiness, but memcg users want to use this knob to 2184 * disable swapping for individual groups completely when 2185 * using the memory controller's swap limit feature would be 2186 * too expensive. 2187 */ 2188 if (!global_reclaim(sc) && !swappiness) { 2189 scan_balance = SCAN_FILE; 2190 goto out; 2191 } 2192 2193 /* 2194 * Do not apply any pressure balancing cleverness when the 2195 * system is close to OOM, scan both anon and file equally 2196 * (unless the swappiness setting disagrees with swapping). 2197 */ 2198 if (!sc->priority && swappiness) { 2199 scan_balance = SCAN_EQUAL; 2200 goto out; 2201 } 2202 2203 /* 2204 * Prevent the reclaimer from falling into the cache trap: as 2205 * cache pages start out inactive, every cache fault will tip 2206 * the scan balance towards the file LRU. And as the file LRU 2207 * shrinks, so does the window for rotation from references. 2208 * This means we have a runaway feedback loop where a tiny 2209 * thrashing file LRU becomes infinitely more attractive than 2210 * anon pages. Try to detect this based on file LRU size. 2211 */ 2212 if (global_reclaim(sc)) { 2213 unsigned long pgdatfile; 2214 unsigned long pgdatfree; 2215 int z; 2216 unsigned long total_high_wmark = 0; 2217 2218 pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES); 2219 pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) + 2220 node_page_state(pgdat, NR_INACTIVE_FILE); 2221 2222 for (z = 0; z < MAX_NR_ZONES; z++) { 2223 struct zone *zone = &pgdat->node_zones[z]; 2224 if (!managed_zone(zone)) 2225 continue; 2226 2227 total_high_wmark += high_wmark_pages(zone); 2228 } 2229 2230 if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) { 2231 /* 2232 * Force SCAN_ANON if there are enough inactive 2233 * anonymous pages on the LRU in eligible zones. 2234 * Otherwise, the small LRU gets thrashed. 2235 */ 2236 if (!inactive_list_is_low(lruvec, false, memcg, sc, false) && 2237 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx) 2238 >> sc->priority) { 2239 scan_balance = SCAN_ANON; 2240 goto out; 2241 } 2242 } 2243 } 2244 2245 /* 2246 * If there is enough inactive page cache, i.e. if the size of the 2247 * inactive list is greater than that of the active list *and* the 2248 * inactive list actually has some pages to scan on this priority, we 2249 * do not reclaim anything from the anonymous working set right now. 2250 * Without the second condition we could end up never scanning an 2251 * lruvec even if it has plenty of old anonymous pages unless the 2252 * system is under heavy pressure. 2253 */ 2254 if (!inactive_list_is_low(lruvec, true, memcg, sc, false) && 2255 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) { 2256 scan_balance = SCAN_FILE; 2257 goto out; 2258 } 2259 2260 scan_balance = SCAN_FRACT; 2261 2262 /* 2263 * With swappiness at 100, anonymous and file have the same priority. 2264 * This scanning priority is essentially the inverse of IO cost. 2265 */ 2266 anon_prio = swappiness; 2267 file_prio = 200 - anon_prio; 2268 2269 /* 2270 * OK, so we have swap space and a fair amount of page cache 2271 * pages. We use the recently rotated / recently scanned 2272 * ratios to determine how valuable each cache is. 2273 * 2274 * Because workloads change over time (and to avoid overflow) 2275 * we keep these statistics as a floating average, which ends 2276 * up weighing recent references more than old ones. 2277 * 2278 * anon in [0], file in [1] 2279 */ 2280 2281 anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) + 2282 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES); 2283 file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) + 2284 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES); 2285 2286 spin_lock_irq(&pgdat->lru_lock); 2287 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { 2288 reclaim_stat->recent_scanned[0] /= 2; 2289 reclaim_stat->recent_rotated[0] /= 2; 2290 } 2291 2292 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { 2293 reclaim_stat->recent_scanned[1] /= 2; 2294 reclaim_stat->recent_rotated[1] /= 2; 2295 } 2296 2297 /* 2298 * The amount of pressure on anon vs file pages is inversely 2299 * proportional to the fraction of recently scanned pages on 2300 * each list that were recently referenced and in active use. 2301 */ 2302 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1); 2303 ap /= reclaim_stat->recent_rotated[0] + 1; 2304 2305 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1); 2306 fp /= reclaim_stat->recent_rotated[1] + 1; 2307 spin_unlock_irq(&pgdat->lru_lock); 2308 2309 fraction[0] = ap; 2310 fraction[1] = fp; 2311 denominator = ap + fp + 1; 2312 out: 2313 *lru_pages = 0; 2314 for_each_evictable_lru(lru) { 2315 int file = is_file_lru(lru); 2316 unsigned long size; 2317 unsigned long scan; 2318 2319 size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx); 2320 scan = size >> sc->priority; 2321 /* 2322 * If the cgroup's already been deleted, make sure to 2323 * scrape out the remaining cache. 2324 */ 2325 if (!scan && !mem_cgroup_online(memcg)) 2326 scan = min(size, SWAP_CLUSTER_MAX); 2327 2328 switch (scan_balance) { 2329 case SCAN_EQUAL: 2330 /* Scan lists relative to size */ 2331 break; 2332 case SCAN_FRACT: 2333 /* 2334 * Scan types proportional to swappiness and 2335 * their relative recent reclaim efficiency. 2336 */ 2337 scan = div64_u64(scan * fraction[file], 2338 denominator); 2339 break; 2340 case SCAN_FILE: 2341 case SCAN_ANON: 2342 /* Scan one type exclusively */ 2343 if ((scan_balance == SCAN_FILE) != file) { 2344 size = 0; 2345 scan = 0; 2346 } 2347 break; 2348 default: 2349 /* Look ma, no brain */ 2350 BUG(); 2351 } 2352 2353 *lru_pages += size; 2354 nr[lru] = scan; 2355 } 2356 } 2357 2358 /* 2359 * This is a basic per-node page freer. Used by both kswapd and direct reclaim. 2360 */ 2361 static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg, 2362 struct scan_control *sc, unsigned long *lru_pages) 2363 { 2364 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg); 2365 unsigned long nr[NR_LRU_LISTS]; 2366 unsigned long targets[NR_LRU_LISTS]; 2367 unsigned long nr_to_scan; 2368 enum lru_list lru; 2369 unsigned long nr_reclaimed = 0; 2370 unsigned long nr_to_reclaim = sc->nr_to_reclaim; 2371 struct blk_plug plug; 2372 bool scan_adjusted; 2373 2374 get_scan_count(lruvec, memcg, sc, nr, lru_pages); 2375 2376 /* Record the original scan target for proportional adjustments later */ 2377 memcpy(targets, nr, sizeof(nr)); 2378 2379 /* 2380 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal 2381 * event that can occur when there is little memory pressure e.g. 2382 * multiple streaming readers/writers. Hence, we do not abort scanning 2383 * when the requested number of pages are reclaimed when scanning at 2384 * DEF_PRIORITY on the assumption that the fact we are direct 2385 * reclaiming implies that kswapd is not keeping up and it is best to 2386 * do a batch of work at once. For memcg reclaim one check is made to 2387 * abort proportional reclaim if either the file or anon lru has already 2388 * dropped to zero at the first pass. 2389 */ 2390 scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() && 2391 sc->priority == DEF_PRIORITY); 2392 2393 blk_start_plug(&plug); 2394 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || 2395 nr[LRU_INACTIVE_FILE]) { 2396 unsigned long nr_anon, nr_file, percentage; 2397 unsigned long nr_scanned; 2398 2399 for_each_evictable_lru(lru) { 2400 if (nr[lru]) { 2401 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX); 2402 nr[lru] -= nr_to_scan; 2403 2404 nr_reclaimed += shrink_list(lru, nr_to_scan, 2405 lruvec, memcg, sc); 2406 } 2407 } 2408 2409 cond_resched(); 2410 2411 if (nr_reclaimed < nr_to_reclaim || scan_adjusted) 2412 continue; 2413 2414 /* 2415 * For kswapd and memcg, reclaim at least the number of pages 2416 * requested. Ensure that the anon and file LRUs are scanned 2417 * proportionally what was requested by get_scan_count(). We 2418 * stop reclaiming one LRU and reduce the amount scanning 2419 * proportional to the original scan target. 2420 */ 2421 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE]; 2422 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON]; 2423 2424 /* 2425 * It's just vindictive to attack the larger once the smaller 2426 * has gone to zero. And given the way we stop scanning the 2427 * smaller below, this makes sure that we only make one nudge 2428 * towards proportionality once we've got nr_to_reclaim. 2429 */ 2430 if (!nr_file || !nr_anon) 2431 break; 2432 2433 if (nr_file > nr_anon) { 2434 unsigned long scan_target = targets[LRU_INACTIVE_ANON] + 2435 targets[LRU_ACTIVE_ANON] + 1; 2436 lru = LRU_BASE; 2437 percentage = nr_anon * 100 / scan_target; 2438 } else { 2439 unsigned long scan_target = targets[LRU_INACTIVE_FILE] + 2440 targets[LRU_ACTIVE_FILE] + 1; 2441 lru = LRU_FILE; 2442 percentage = nr_file * 100 / scan_target; 2443 } 2444 2445 /* Stop scanning the smaller of the LRU */ 2446 nr[lru] = 0; 2447 nr[lru + LRU_ACTIVE] = 0; 2448 2449 /* 2450 * Recalculate the other LRU scan count based on its original 2451 * scan target and the percentage scanning already complete 2452 */ 2453 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE; 2454 nr_scanned = targets[lru] - nr[lru]; 2455 nr[lru] = targets[lru] * (100 - percentage) / 100; 2456 nr[lru] -= min(nr[lru], nr_scanned); 2457 2458 lru += LRU_ACTIVE; 2459 nr_scanned = targets[lru] - nr[lru]; 2460 nr[lru] = targets[lru] * (100 - percentage) / 100; 2461 nr[lru] -= min(nr[lru], nr_scanned); 2462 2463 scan_adjusted = true; 2464 } 2465 blk_finish_plug(&plug); 2466 sc->nr_reclaimed += nr_reclaimed; 2467 2468 /* 2469 * Even if we did not try to evict anon pages at all, we want to 2470 * rebalance the anon lru active/inactive ratio. 2471 */ 2472 if (inactive_list_is_low(lruvec, false, memcg, sc, true)) 2473 shrink_active_list(SWAP_CLUSTER_MAX, lruvec, 2474 sc, LRU_ACTIVE_ANON); 2475 } 2476 2477 /* Use reclaim/compaction for costly allocs or under memory pressure */ 2478 static bool in_reclaim_compaction(struct scan_control *sc) 2479 { 2480 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order && 2481 (sc->order > PAGE_ALLOC_COSTLY_ORDER || 2482 sc->priority < DEF_PRIORITY - 2)) 2483 return true; 2484 2485 return false; 2486 } 2487 2488 /* 2489 * Reclaim/compaction is used for high-order allocation requests. It reclaims 2490 * order-0 pages before compacting the zone. should_continue_reclaim() returns 2491 * true if more pages should be reclaimed such that when the page allocator 2492 * calls try_to_compact_zone() that it will have enough free pages to succeed. 2493 * It will give up earlier than that if there is difficulty reclaiming pages. 2494 */ 2495 static inline bool should_continue_reclaim(struct pglist_data *pgdat, 2496 unsigned long nr_reclaimed, 2497 unsigned long nr_scanned, 2498 struct scan_control *sc) 2499 { 2500 unsigned long pages_for_compaction; 2501 unsigned long inactive_lru_pages; 2502 int z; 2503 2504 /* If not in reclaim/compaction mode, stop */ 2505 if (!in_reclaim_compaction(sc)) 2506 return false; 2507 2508 /* Consider stopping depending on scan and reclaim activity */ 2509 if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) { 2510 /* 2511 * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the 2512 * full LRU list has been scanned and we are still failing 2513 * to reclaim pages. This full LRU scan is potentially 2514 * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed 2515 */ 2516 if (!nr_reclaimed && !nr_scanned) 2517 return false; 2518 } else { 2519 /* 2520 * For non-__GFP_RETRY_MAYFAIL allocations which can presumably 2521 * fail without consequence, stop if we failed to reclaim 2522 * any pages from the last SWAP_CLUSTER_MAX number of 2523 * pages that were scanned. This will return to the 2524 * caller faster at the risk reclaim/compaction and 2525 * the resulting allocation attempt fails 2526 */ 2527 if (!nr_reclaimed) 2528 return false; 2529 } 2530 2531 /* 2532 * If we have not reclaimed enough pages for compaction and the 2533 * inactive lists are large enough, continue reclaiming 2534 */ 2535 pages_for_compaction = compact_gap(sc->order); 2536 inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE); 2537 if (get_nr_swap_pages() > 0) 2538 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON); 2539 if (sc->nr_reclaimed < pages_for_compaction && 2540 inactive_lru_pages > pages_for_compaction) 2541 return true; 2542 2543 /* If compaction would go ahead or the allocation would succeed, stop */ 2544 for (z = 0; z <= sc->reclaim_idx; z++) { 2545 struct zone *zone = &pgdat->node_zones[z]; 2546 if (!managed_zone(zone)) 2547 continue; 2548 2549 switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) { 2550 case COMPACT_SUCCESS: 2551 case COMPACT_CONTINUE: 2552 return false; 2553 default: 2554 /* check next zone */ 2555 ; 2556 } 2557 } 2558 return true; 2559 } 2560 2561 static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) 2562 { 2563 struct reclaim_state *reclaim_state = current->reclaim_state; 2564 unsigned long nr_reclaimed, nr_scanned; 2565 bool reclaimable = false; 2566 2567 do { 2568 struct mem_cgroup *root = sc->target_mem_cgroup; 2569 struct mem_cgroup_reclaim_cookie reclaim = { 2570 .pgdat = pgdat, 2571 .priority = sc->priority, 2572 }; 2573 unsigned long node_lru_pages = 0; 2574 struct mem_cgroup *memcg; 2575 2576 nr_reclaimed = sc->nr_reclaimed; 2577 nr_scanned = sc->nr_scanned; 2578 2579 memcg = mem_cgroup_iter(root, NULL, &reclaim); 2580 do { 2581 unsigned long lru_pages; 2582 unsigned long reclaimed; 2583 unsigned long scanned; 2584 2585 if (mem_cgroup_low(root, memcg)) { 2586 if (!sc->memcg_low_reclaim) { 2587 sc->memcg_low_skipped = 1; 2588 continue; 2589 } 2590 mem_cgroup_event(memcg, MEMCG_LOW); 2591 } 2592 2593 reclaimed = sc->nr_reclaimed; 2594 scanned = sc->nr_scanned; 2595 2596 shrink_node_memcg(pgdat, memcg, sc, &lru_pages); 2597 node_lru_pages += lru_pages; 2598 2599 if (memcg) 2600 shrink_slab(sc->gfp_mask, pgdat->node_id, 2601 memcg, sc->nr_scanned - scanned, 2602 lru_pages); 2603 2604 /* Record the group's reclaim efficiency */ 2605 vmpressure(sc->gfp_mask, memcg, false, 2606 sc->nr_scanned - scanned, 2607 sc->nr_reclaimed - reclaimed); 2608 2609 /* 2610 * Direct reclaim and kswapd have to scan all memory 2611 * cgroups to fulfill the overall scan target for the 2612 * node. 2613 * 2614 * Limit reclaim, on the other hand, only cares about 2615 * nr_to_reclaim pages to be reclaimed and it will 2616 * retry with decreasing priority if one round over the 2617 * whole hierarchy is not sufficient. 2618 */ 2619 if (!global_reclaim(sc) && 2620 sc->nr_reclaimed >= sc->nr_to_reclaim) { 2621 mem_cgroup_iter_break(root, memcg); 2622 break; 2623 } 2624 } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim))); 2625 2626 /* 2627 * Shrink the slab caches in the same proportion that 2628 * the eligible LRU pages were scanned. 2629 */ 2630 if (global_reclaim(sc)) 2631 shrink_slab(sc->gfp_mask, pgdat->node_id, NULL, 2632 sc->nr_scanned - nr_scanned, 2633 node_lru_pages); 2634 2635 if (reclaim_state) { 2636 sc->nr_reclaimed += reclaim_state->reclaimed_slab; 2637 reclaim_state->reclaimed_slab = 0; 2638 } 2639 2640 /* Record the subtree's reclaim efficiency */ 2641 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true, 2642 sc->nr_scanned - nr_scanned, 2643 sc->nr_reclaimed - nr_reclaimed); 2644 2645 if (sc->nr_reclaimed - nr_reclaimed) 2646 reclaimable = true; 2647 2648 } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed, 2649 sc->nr_scanned - nr_scanned, sc)); 2650 2651 /* 2652 * Kswapd gives up on balancing particular nodes after too 2653 * many failures to reclaim anything from them and goes to 2654 * sleep. On reclaim progress, reset the failure counter. A 2655 * successful direct reclaim run will revive a dormant kswapd. 2656 */ 2657 if (reclaimable) 2658 pgdat->kswapd_failures = 0; 2659 2660 return reclaimable; 2661 } 2662 2663 /* 2664 * Returns true if compaction should go ahead for a costly-order request, or 2665 * the allocation would already succeed without compaction. Return false if we 2666 * should reclaim first. 2667 */ 2668 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc) 2669 { 2670 unsigned long watermark; 2671 enum compact_result suitable; 2672 2673 suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx); 2674 if (suitable == COMPACT_SUCCESS) 2675 /* Allocation should succeed already. Don't reclaim. */ 2676 return true; 2677 if (suitable == COMPACT_SKIPPED) 2678 /* Compaction cannot yet proceed. Do reclaim. */ 2679 return false; 2680 2681 /* 2682 * Compaction is already possible, but it takes time to run and there 2683 * are potentially other callers using the pages just freed. So proceed 2684 * with reclaim to make a buffer of free pages available to give 2685 * compaction a reasonable chance of completing and allocating the page. 2686 * Note that we won't actually reclaim the whole buffer in one attempt 2687 * as the target watermark in should_continue_reclaim() is lower. But if 2688 * we are already above the high+gap watermark, don't reclaim at all. 2689 */ 2690 watermark = high_wmark_pages(zone) + compact_gap(sc->order); 2691 2692 return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx); 2693 } 2694 2695 /* 2696 * This is the direct reclaim path, for page-allocating processes. We only 2697 * try to reclaim pages from zones which will satisfy the caller's allocation 2698 * request. 2699 * 2700 * If a zone is deemed to be full of pinned pages then just give it a light 2701 * scan then give up on it. 2702 */ 2703 static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc) 2704 { 2705 struct zoneref *z; 2706 struct zone *zone; 2707 unsigned long nr_soft_reclaimed; 2708 unsigned long nr_soft_scanned; 2709 gfp_t orig_mask; 2710 pg_data_t *last_pgdat = NULL; 2711 2712 /* 2713 * If the number of buffer_heads in the machine exceeds the maximum 2714 * allowed level, force direct reclaim to scan the highmem zone as 2715 * highmem pages could be pinning lowmem pages storing buffer_heads 2716 */ 2717 orig_mask = sc->gfp_mask; 2718 if (buffer_heads_over_limit) { 2719 sc->gfp_mask |= __GFP_HIGHMEM; 2720 sc->reclaim_idx = gfp_zone(sc->gfp_mask); 2721 } 2722 2723 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2724 sc->reclaim_idx, sc->nodemask) { 2725 /* 2726 * Take care memory controller reclaiming has small influence 2727 * to global LRU. 2728 */ 2729 if (global_reclaim(sc)) { 2730 if (!cpuset_zone_allowed(zone, 2731 GFP_KERNEL | __GFP_HARDWALL)) 2732 continue; 2733 2734 /* 2735 * If we already have plenty of memory free for 2736 * compaction in this zone, don't free any more. 2737 * Even though compaction is invoked for any 2738 * non-zero order, only frequent costly order 2739 * reclamation is disruptive enough to become a 2740 * noticeable problem, like transparent huge 2741 * page allocations. 2742 */ 2743 if (IS_ENABLED(CONFIG_COMPACTION) && 2744 sc->order > PAGE_ALLOC_COSTLY_ORDER && 2745 compaction_ready(zone, sc)) { 2746 sc->compaction_ready = true; 2747 continue; 2748 } 2749 2750 /* 2751 * Shrink each node in the zonelist once. If the 2752 * zonelist is ordered by zone (not the default) then a 2753 * node may be shrunk multiple times but in that case 2754 * the user prefers lower zones being preserved. 2755 */ 2756 if (zone->zone_pgdat == last_pgdat) 2757 continue; 2758 2759 /* 2760 * This steals pages from memory cgroups over softlimit 2761 * and returns the number of reclaimed pages and 2762 * scanned pages. This works for global memory pressure 2763 * and balancing, not for a memcg's limit. 2764 */ 2765 nr_soft_scanned = 0; 2766 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat, 2767 sc->order, sc->gfp_mask, 2768 &nr_soft_scanned); 2769 sc->nr_reclaimed += nr_soft_reclaimed; 2770 sc->nr_scanned += nr_soft_scanned; 2771 /* need some check for avoid more shrink_zone() */ 2772 } 2773 2774 /* See comment about same check for global reclaim above */ 2775 if (zone->zone_pgdat == last_pgdat) 2776 continue; 2777 last_pgdat = zone->zone_pgdat; 2778 shrink_node(zone->zone_pgdat, sc); 2779 } 2780 2781 /* 2782 * Restore to original mask to avoid the impact on the caller if we 2783 * promoted it to __GFP_HIGHMEM. 2784 */ 2785 sc->gfp_mask = orig_mask; 2786 } 2787 2788 static void snapshot_refaults(struct mem_cgroup *root_memcg, pg_data_t *pgdat) 2789 { 2790 struct mem_cgroup *memcg; 2791 2792 memcg = mem_cgroup_iter(root_memcg, NULL, NULL); 2793 do { 2794 unsigned long refaults; 2795 struct lruvec *lruvec; 2796 2797 if (memcg) 2798 refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE); 2799 else 2800 refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE); 2801 2802 lruvec = mem_cgroup_lruvec(pgdat, memcg); 2803 lruvec->refaults = refaults; 2804 } while ((memcg = mem_cgroup_iter(root_memcg, memcg, NULL))); 2805 } 2806 2807 /* 2808 * This is the main entry point to direct page reclaim. 2809 * 2810 * If a full scan of the inactive list fails to free enough memory then we 2811 * are "out of memory" and something needs to be killed. 2812 * 2813 * If the caller is !__GFP_FS then the probability of a failure is reasonably 2814 * high - the zone may be full of dirty or under-writeback pages, which this 2815 * caller can't do much about. We kick the writeback threads and take explicit 2816 * naps in the hope that some of these pages can be written. But if the 2817 * allocating task holds filesystem locks which prevent writeout this might not 2818 * work, and the allocation attempt will fail. 2819 * 2820 * returns: 0, if no pages reclaimed 2821 * else, the number of pages reclaimed 2822 */ 2823 static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 2824 struct scan_control *sc) 2825 { 2826 int initial_priority = sc->priority; 2827 pg_data_t *last_pgdat; 2828 struct zoneref *z; 2829 struct zone *zone; 2830 retry: 2831 delayacct_freepages_start(); 2832 2833 if (global_reclaim(sc)) 2834 __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1); 2835 2836 do { 2837 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup, 2838 sc->priority); 2839 sc->nr_scanned = 0; 2840 shrink_zones(zonelist, sc); 2841 2842 if (sc->nr_reclaimed >= sc->nr_to_reclaim) 2843 break; 2844 2845 if (sc->compaction_ready) 2846 break; 2847 2848 /* 2849 * If we're getting trouble reclaiming, start doing 2850 * writepage even in laptop mode. 2851 */ 2852 if (sc->priority < DEF_PRIORITY - 2) 2853 sc->may_writepage = 1; 2854 } while (--sc->priority >= 0); 2855 2856 last_pgdat = NULL; 2857 for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx, 2858 sc->nodemask) { 2859 if (zone->zone_pgdat == last_pgdat) 2860 continue; 2861 last_pgdat = zone->zone_pgdat; 2862 snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat); 2863 } 2864 2865 delayacct_freepages_end(); 2866 2867 if (sc->nr_reclaimed) 2868 return sc->nr_reclaimed; 2869 2870 /* Aborted reclaim to try compaction? don't OOM, then */ 2871 if (sc->compaction_ready) 2872 return 1; 2873 2874 /* Untapped cgroup reserves? Don't OOM, retry. */ 2875 if (sc->memcg_low_skipped) { 2876 sc->priority = initial_priority; 2877 sc->memcg_low_reclaim = 1; 2878 sc->memcg_low_skipped = 0; 2879 goto retry; 2880 } 2881 2882 return 0; 2883 } 2884 2885 static bool allow_direct_reclaim(pg_data_t *pgdat) 2886 { 2887 struct zone *zone; 2888 unsigned long pfmemalloc_reserve = 0; 2889 unsigned long free_pages = 0; 2890 int i; 2891 bool wmark_ok; 2892 2893 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES) 2894 return true; 2895 2896 for (i = 0; i <= ZONE_NORMAL; i++) { 2897 zone = &pgdat->node_zones[i]; 2898 if (!managed_zone(zone)) 2899 continue; 2900 2901 if (!zone_reclaimable_pages(zone)) 2902 continue; 2903 2904 pfmemalloc_reserve += min_wmark_pages(zone); 2905 free_pages += zone_page_state(zone, NR_FREE_PAGES); 2906 } 2907 2908 /* If there are no reserves (unexpected config) then do not throttle */ 2909 if (!pfmemalloc_reserve) 2910 return true; 2911 2912 wmark_ok = free_pages > pfmemalloc_reserve / 2; 2913 2914 /* kswapd must be awake if processes are being throttled */ 2915 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) { 2916 pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx, 2917 (enum zone_type)ZONE_NORMAL); 2918 wake_up_interruptible(&pgdat->kswapd_wait); 2919 } 2920 2921 return wmark_ok; 2922 } 2923 2924 /* 2925 * Throttle direct reclaimers if backing storage is backed by the network 2926 * and the PFMEMALLOC reserve for the preferred node is getting dangerously 2927 * depleted. kswapd will continue to make progress and wake the processes 2928 * when the low watermark is reached. 2929 * 2930 * Returns true if a fatal signal was delivered during throttling. If this 2931 * happens, the page allocator should not consider triggering the OOM killer. 2932 */ 2933 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist, 2934 nodemask_t *nodemask) 2935 { 2936 struct zoneref *z; 2937 struct zone *zone; 2938 pg_data_t *pgdat = NULL; 2939 2940 /* 2941 * Kernel threads should not be throttled as they may be indirectly 2942 * responsible for cleaning pages necessary for reclaim to make forward 2943 * progress. kjournald for example may enter direct reclaim while 2944 * committing a transaction where throttling it could forcing other 2945 * processes to block on log_wait_commit(). 2946 */ 2947 if (current->flags & PF_KTHREAD) 2948 goto out; 2949 2950 /* 2951 * If a fatal signal is pending, this process should not throttle. 2952 * It should return quickly so it can exit and free its memory 2953 */ 2954 if (fatal_signal_pending(current)) 2955 goto out; 2956 2957 /* 2958 * Check if the pfmemalloc reserves are ok by finding the first node 2959 * with a usable ZONE_NORMAL or lower zone. The expectation is that 2960 * GFP_KERNEL will be required for allocating network buffers when 2961 * swapping over the network so ZONE_HIGHMEM is unusable. 2962 * 2963 * Throttling is based on the first usable node and throttled processes 2964 * wait on a queue until kswapd makes progress and wakes them. There 2965 * is an affinity then between processes waking up and where reclaim 2966 * progress has been made assuming the process wakes on the same node. 2967 * More importantly, processes running on remote nodes will not compete 2968 * for remote pfmemalloc reserves and processes on different nodes 2969 * should make reasonable progress. 2970 */ 2971 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2972 gfp_zone(gfp_mask), nodemask) { 2973 if (zone_idx(zone) > ZONE_NORMAL) 2974 continue; 2975 2976 /* Throttle based on the first usable node */ 2977 pgdat = zone->zone_pgdat; 2978 if (allow_direct_reclaim(pgdat)) 2979 goto out; 2980 break; 2981 } 2982 2983 /* If no zone was usable by the allocation flags then do not throttle */ 2984 if (!pgdat) 2985 goto out; 2986 2987 /* Account for the throttling */ 2988 count_vm_event(PGSCAN_DIRECT_THROTTLE); 2989 2990 /* 2991 * If the caller cannot enter the filesystem, it's possible that it 2992 * is due to the caller holding an FS lock or performing a journal 2993 * transaction in the case of a filesystem like ext[3|4]. In this case, 2994 * it is not safe to block on pfmemalloc_wait as kswapd could be 2995 * blocked waiting on the same lock. Instead, throttle for up to a 2996 * second before continuing. 2997 */ 2998 if (!(gfp_mask & __GFP_FS)) { 2999 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait, 3000 allow_direct_reclaim(pgdat), HZ); 3001 3002 goto check_pending; 3003 } 3004 3005 /* Throttle until kswapd wakes the process */ 3006 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait, 3007 allow_direct_reclaim(pgdat)); 3008 3009 check_pending: 3010 if (fatal_signal_pending(current)) 3011 return true; 3012 3013 out: 3014 return false; 3015 } 3016 3017 unsigned long try_to_free_pages(struct zonelist *zonelist, int order, 3018 gfp_t gfp_mask, nodemask_t *nodemask) 3019 { 3020 unsigned long nr_reclaimed; 3021 struct scan_control sc = { 3022 .nr_to_reclaim = SWAP_CLUSTER_MAX, 3023 .gfp_mask = current_gfp_context(gfp_mask), 3024 .reclaim_idx = gfp_zone(gfp_mask), 3025 .order = order, 3026 .nodemask = nodemask, 3027 .priority = DEF_PRIORITY, 3028 .may_writepage = !laptop_mode, 3029 .may_unmap = 1, 3030 .may_swap = 1, 3031 }; 3032 3033 /* 3034 * Do not enter reclaim if fatal signal was delivered while throttled. 3035 * 1 is returned so that the page allocator does not OOM kill at this 3036 * point. 3037 */ 3038 if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask)) 3039 return 1; 3040 3041 trace_mm_vmscan_direct_reclaim_begin(order, 3042 sc.may_writepage, 3043 sc.gfp_mask, 3044 sc.reclaim_idx); 3045 3046 nr_reclaimed = do_try_to_free_pages(zonelist, &sc); 3047 3048 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); 3049 3050 return nr_reclaimed; 3051 } 3052 3053 #ifdef CONFIG_MEMCG 3054 3055 unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg, 3056 gfp_t gfp_mask, bool noswap, 3057 pg_data_t *pgdat, 3058 unsigned long *nr_scanned) 3059 { 3060 struct scan_control sc = { 3061 .nr_to_reclaim = SWAP_CLUSTER_MAX, 3062 .target_mem_cgroup = memcg, 3063 .may_writepage = !laptop_mode, 3064 .may_unmap = 1, 3065 .reclaim_idx = MAX_NR_ZONES - 1, 3066 .may_swap = !noswap, 3067 }; 3068 unsigned long lru_pages; 3069 3070 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 3071 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); 3072 3073 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order, 3074 sc.may_writepage, 3075 sc.gfp_mask, 3076 sc.reclaim_idx); 3077 3078 /* 3079 * NOTE: Although we can get the priority field, using it 3080 * here is not a good idea, since it limits the pages we can scan. 3081 * if we don't reclaim here, the shrink_node from balance_pgdat 3082 * will pick up pages from other mem cgroup's as well. We hack 3083 * the priority and make it zero. 3084 */ 3085 shrink_node_memcg(pgdat, memcg, &sc, &lru_pages); 3086 3087 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); 3088 3089 *nr_scanned = sc.nr_scanned; 3090 return sc.nr_reclaimed; 3091 } 3092 3093 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, 3094 unsigned long nr_pages, 3095 gfp_t gfp_mask, 3096 bool may_swap) 3097 { 3098 struct zonelist *zonelist; 3099 unsigned long nr_reclaimed; 3100 int nid; 3101 unsigned int noreclaim_flag; 3102 struct scan_control sc = { 3103 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), 3104 .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) | 3105 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), 3106 .reclaim_idx = MAX_NR_ZONES - 1, 3107 .target_mem_cgroup = memcg, 3108 .priority = DEF_PRIORITY, 3109 .may_writepage = !laptop_mode, 3110 .may_unmap = 1, 3111 .may_swap = may_swap, 3112 }; 3113 3114 /* 3115 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't 3116 * take care of from where we get pages. So the node where we start the 3117 * scan does not need to be the current node. 3118 */ 3119 nid = mem_cgroup_select_victim_node(memcg); 3120 3121 zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK]; 3122 3123 trace_mm_vmscan_memcg_reclaim_begin(0, 3124 sc.may_writepage, 3125 sc.gfp_mask, 3126 sc.reclaim_idx); 3127 3128 noreclaim_flag = memalloc_noreclaim_save(); 3129 nr_reclaimed = do_try_to_free_pages(zonelist, &sc); 3130 memalloc_noreclaim_restore(noreclaim_flag); 3131 3132 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); 3133 3134 return nr_reclaimed; 3135 } 3136 #endif 3137 3138 static void age_active_anon(struct pglist_data *pgdat, 3139 struct scan_control *sc) 3140 { 3141 struct mem_cgroup *memcg; 3142 3143 if (!total_swap_pages) 3144 return; 3145 3146 memcg = mem_cgroup_iter(NULL, NULL, NULL); 3147 do { 3148 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg); 3149 3150 if (inactive_list_is_low(lruvec, false, memcg, sc, true)) 3151 shrink_active_list(SWAP_CLUSTER_MAX, lruvec, 3152 sc, LRU_ACTIVE_ANON); 3153 3154 memcg = mem_cgroup_iter(NULL, memcg, NULL); 3155 } while (memcg); 3156 } 3157 3158 /* 3159 * Returns true if there is an eligible zone balanced for the request order 3160 * and classzone_idx 3161 */ 3162 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx) 3163 { 3164 int i; 3165 unsigned long mark = -1; 3166 struct zone *zone; 3167 3168 for (i = 0; i <= classzone_idx; i++) { 3169 zone = pgdat->node_zones + i; 3170 3171 if (!managed_zone(zone)) 3172 continue; 3173 3174 mark = high_wmark_pages(zone); 3175 if (zone_watermark_ok_safe(zone, order, mark, classzone_idx)) 3176 return true; 3177 } 3178 3179 /* 3180 * If a node has no populated zone within classzone_idx, it does not 3181 * need balancing by definition. This can happen if a zone-restricted 3182 * allocation tries to wake a remote kswapd. 3183 */ 3184 if (mark == -1) 3185 return true; 3186 3187 return false; 3188 } 3189 3190 /* Clear pgdat state for congested, dirty or under writeback. */ 3191 static void clear_pgdat_congested(pg_data_t *pgdat) 3192 { 3193 clear_bit(PGDAT_CONGESTED, &pgdat->flags); 3194 clear_bit(PGDAT_DIRTY, &pgdat->flags); 3195 clear_bit(PGDAT_WRITEBACK, &pgdat->flags); 3196 } 3197 3198 /* 3199 * Prepare kswapd for sleeping. This verifies that there are no processes 3200 * waiting in throttle_direct_reclaim() and that watermarks have been met. 3201 * 3202 * Returns true if kswapd is ready to sleep 3203 */ 3204 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx) 3205 { 3206 /* 3207 * The throttled processes are normally woken up in balance_pgdat() as 3208 * soon as allow_direct_reclaim() is true. But there is a potential 3209 * race between when kswapd checks the watermarks and a process gets 3210 * throttled. There is also a potential race if processes get 3211 * throttled, kswapd wakes, a large process exits thereby balancing the 3212 * zones, which causes kswapd to exit balance_pgdat() before reaching 3213 * the wake up checks. If kswapd is going to sleep, no process should 3214 * be sleeping on pfmemalloc_wait, so wake them now if necessary. If 3215 * the wake up is premature, processes will wake kswapd and get 3216 * throttled again. The difference from wake ups in balance_pgdat() is 3217 * that here we are under prepare_to_wait(). 3218 */ 3219 if (waitqueue_active(&pgdat->pfmemalloc_wait)) 3220 wake_up_all(&pgdat->pfmemalloc_wait); 3221 3222 /* Hopeless node, leave it to direct reclaim */ 3223 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES) 3224 return true; 3225 3226 if (pgdat_balanced(pgdat, order, classzone_idx)) { 3227 clear_pgdat_congested(pgdat); 3228 return true; 3229 } 3230 3231 return false; 3232 } 3233 3234 /* 3235 * kswapd shrinks a node of pages that are at or below the highest usable 3236 * zone that is currently unbalanced. 3237 * 3238 * Returns true if kswapd scanned at least the requested number of pages to 3239 * reclaim or if the lack of progress was due to pages under writeback. 3240 * This is used to determine if the scanning priority needs to be raised. 3241 */ 3242 static bool kswapd_shrink_node(pg_data_t *pgdat, 3243 struct scan_control *sc) 3244 { 3245 struct zone *zone; 3246 int z; 3247 3248 /* Reclaim a number of pages proportional to the number of zones */ 3249 sc->nr_to_reclaim = 0; 3250 for (z = 0; z <= sc->reclaim_idx; z++) { 3251 zone = pgdat->node_zones + z; 3252 if (!managed_zone(zone)) 3253 continue; 3254 3255 sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX); 3256 } 3257 3258 /* 3259 * Historically care was taken to put equal pressure on all zones but 3260 * now pressure is applied based on node LRU order. 3261 */ 3262 shrink_node(pgdat, sc); 3263 3264 /* 3265 * Fragmentation may mean that the system cannot be rebalanced for 3266 * high-order allocations. If twice the allocation size has been 3267 * reclaimed then recheck watermarks only at order-0 to prevent 3268 * excessive reclaim. Assume that a process requested a high-order 3269 * can direct reclaim/compact. 3270 */ 3271 if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order)) 3272 sc->order = 0; 3273 3274 return sc->nr_scanned >= sc->nr_to_reclaim; 3275 } 3276 3277 /* 3278 * For kswapd, balance_pgdat() will reclaim pages across a node from zones 3279 * that are eligible for use by the caller until at least one zone is 3280 * balanced. 3281 * 3282 * Returns the order kswapd finished reclaiming at. 3283 * 3284 * kswapd scans the zones in the highmem->normal->dma direction. It skips 3285 * zones which have free_pages > high_wmark_pages(zone), but once a zone is 3286 * found to have free_pages <= high_wmark_pages(zone), any page is that zone 3287 * or lower is eligible for reclaim until at least one usable zone is 3288 * balanced. 3289 */ 3290 static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) 3291 { 3292 int i; 3293 unsigned long nr_soft_reclaimed; 3294 unsigned long nr_soft_scanned; 3295 struct zone *zone; 3296 struct scan_control sc = { 3297 .gfp_mask = GFP_KERNEL, 3298 .order = order, 3299 .priority = DEF_PRIORITY, 3300 .may_writepage = !laptop_mode, 3301 .may_unmap = 1, 3302 .may_swap = 1, 3303 }; 3304 count_vm_event(PAGEOUTRUN); 3305 3306 do { 3307 unsigned long nr_reclaimed = sc.nr_reclaimed; 3308 bool raise_priority = true; 3309 3310 sc.reclaim_idx = classzone_idx; 3311 3312 /* 3313 * If the number of buffer_heads exceeds the maximum allowed 3314 * then consider reclaiming from all zones. This has a dual 3315 * purpose -- on 64-bit systems it is expected that 3316 * buffer_heads are stripped during active rotation. On 32-bit 3317 * systems, highmem pages can pin lowmem memory and shrinking 3318 * buffers can relieve lowmem pressure. Reclaim may still not 3319 * go ahead if all eligible zones for the original allocation 3320 * request are balanced to avoid excessive reclaim from kswapd. 3321 */ 3322 if (buffer_heads_over_limit) { 3323 for (i = MAX_NR_ZONES - 1; i >= 0; i--) { 3324 zone = pgdat->node_zones + i; 3325 if (!managed_zone(zone)) 3326 continue; 3327 3328 sc.reclaim_idx = i; 3329 break; 3330 } 3331 } 3332 3333 /* 3334 * Only reclaim if there are no eligible zones. Note that 3335 * sc.reclaim_idx is not used as buffer_heads_over_limit may 3336 * have adjusted it. 3337 */ 3338 if (pgdat_balanced(pgdat, sc.order, classzone_idx)) 3339 goto out; 3340 3341 /* 3342 * Do some background aging of the anon list, to give 3343 * pages a chance to be referenced before reclaiming. All 3344 * pages are rotated regardless of classzone as this is 3345 * about consistent aging. 3346 */ 3347 age_active_anon(pgdat, &sc); 3348 3349 /* 3350 * If we're getting trouble reclaiming, start doing writepage 3351 * even in laptop mode. 3352 */ 3353 if (sc.priority < DEF_PRIORITY - 2) 3354 sc.may_writepage = 1; 3355 3356 /* Call soft limit reclaim before calling shrink_node. */ 3357 sc.nr_scanned = 0; 3358 nr_soft_scanned = 0; 3359 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order, 3360 sc.gfp_mask, &nr_soft_scanned); 3361 sc.nr_reclaimed += nr_soft_reclaimed; 3362 3363 /* 3364 * There should be no need to raise the scanning priority if 3365 * enough pages are already being scanned that that high 3366 * watermark would be met at 100% efficiency. 3367 */ 3368 if (kswapd_shrink_node(pgdat, &sc)) 3369 raise_priority = false; 3370 3371 /* 3372 * If the low watermark is met there is no need for processes 3373 * to be throttled on pfmemalloc_wait as they should not be 3374 * able to safely make forward progress. Wake them 3375 */ 3376 if (waitqueue_active(&pgdat->pfmemalloc_wait) && 3377 allow_direct_reclaim(pgdat)) 3378 wake_up_all(&pgdat->pfmemalloc_wait); 3379 3380 /* Check if kswapd should be suspending */ 3381 if (try_to_freeze() || kthread_should_stop()) 3382 break; 3383 3384 /* 3385 * Raise priority if scanning rate is too low or there was no 3386 * progress in reclaiming pages 3387 */ 3388 nr_reclaimed = sc.nr_reclaimed - nr_reclaimed; 3389 if (raise_priority || !nr_reclaimed) 3390 sc.priority--; 3391 } while (sc.priority >= 1); 3392 3393 if (!sc.nr_reclaimed) 3394 pgdat->kswapd_failures++; 3395 3396 out: 3397 snapshot_refaults(NULL, pgdat); 3398 /* 3399 * Return the order kswapd stopped reclaiming at as 3400 * prepare_kswapd_sleep() takes it into account. If another caller 3401 * entered the allocator slow path while kswapd was awake, order will 3402 * remain at the higher level. 3403 */ 3404 return sc.order; 3405 } 3406 3407 /* 3408 * pgdat->kswapd_classzone_idx is the highest zone index that a recent 3409 * allocation request woke kswapd for. When kswapd has not woken recently, 3410 * the value is MAX_NR_ZONES which is not a valid index. This compares a 3411 * given classzone and returns it or the highest classzone index kswapd 3412 * was recently woke for. 3413 */ 3414 static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat, 3415 enum zone_type classzone_idx) 3416 { 3417 if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES) 3418 return classzone_idx; 3419 3420 return max(pgdat->kswapd_classzone_idx, classzone_idx); 3421 } 3422 3423 static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order, 3424 unsigned int classzone_idx) 3425 { 3426 long remaining = 0; 3427 DEFINE_WAIT(wait); 3428 3429 if (freezing(current) || kthread_should_stop()) 3430 return; 3431 3432 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 3433 3434 /* 3435 * Try to sleep for a short interval. Note that kcompactd will only be 3436 * woken if it is possible to sleep for a short interval. This is 3437 * deliberate on the assumption that if reclaim cannot keep an 3438 * eligible zone balanced that it's also unlikely that compaction will 3439 * succeed. 3440 */ 3441 if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) { 3442 /* 3443 * Compaction records what page blocks it recently failed to 3444 * isolate pages from and skips them in the future scanning. 3445 * When kswapd is going to sleep, it is reasonable to assume 3446 * that pages and compaction may succeed so reset the cache. 3447 */ 3448 reset_isolation_suitable(pgdat); 3449 3450 /* 3451 * We have freed the memory, now we should compact it to make 3452 * allocation of the requested order possible. 3453 */ 3454 wakeup_kcompactd(pgdat, alloc_order, classzone_idx); 3455 3456 remaining = schedule_timeout(HZ/10); 3457 3458 /* 3459 * If woken prematurely then reset kswapd_classzone_idx and 3460 * order. The values will either be from a wakeup request or 3461 * the previous request that slept prematurely. 3462 */ 3463 if (remaining) { 3464 pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx); 3465 pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order); 3466 } 3467 3468 finish_wait(&pgdat->kswapd_wait, &wait); 3469 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 3470 } 3471 3472 /* 3473 * After a short sleep, check if it was a premature sleep. If not, then 3474 * go fully to sleep until explicitly woken up. 3475 */ 3476 if (!remaining && 3477 prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) { 3478 trace_mm_vmscan_kswapd_sleep(pgdat->node_id); 3479 3480 /* 3481 * vmstat counters are not perfectly accurate and the estimated 3482 * value for counters such as NR_FREE_PAGES can deviate from the 3483 * true value by nr_online_cpus * threshold. To avoid the zone 3484 * watermarks being breached while under pressure, we reduce the 3485 * per-cpu vmstat threshold while kswapd is awake and restore 3486 * them before going back to sleep. 3487 */ 3488 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); 3489 3490 if (!kthread_should_stop()) 3491 schedule(); 3492 3493 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); 3494 } else { 3495 if (remaining) 3496 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); 3497 else 3498 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); 3499 } 3500 finish_wait(&pgdat->kswapd_wait, &wait); 3501 } 3502 3503 /* 3504 * The background pageout daemon, started as a kernel thread 3505 * from the init process. 3506 * 3507 * This basically trickles out pages so that we have _some_ 3508 * free memory available even if there is no other activity 3509 * that frees anything up. This is needed for things like routing 3510 * etc, where we otherwise might have all activity going on in 3511 * asynchronous contexts that cannot page things out. 3512 * 3513 * If there are applications that are active memory-allocators 3514 * (most normal use), this basically shouldn't matter. 3515 */ 3516 static int kswapd(void *p) 3517 { 3518 unsigned int alloc_order, reclaim_order; 3519 unsigned int classzone_idx = MAX_NR_ZONES - 1; 3520 pg_data_t *pgdat = (pg_data_t*)p; 3521 struct task_struct *tsk = current; 3522 3523 struct reclaim_state reclaim_state = { 3524 .reclaimed_slab = 0, 3525 }; 3526 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); 3527 3528 lockdep_set_current_reclaim_state(GFP_KERNEL); 3529 3530 if (!cpumask_empty(cpumask)) 3531 set_cpus_allowed_ptr(tsk, cpumask); 3532 current->reclaim_state = &reclaim_state; 3533 3534 /* 3535 * Tell the memory management that we're a "memory allocator", 3536 * and that if we need more memory we should get access to it 3537 * regardless (see "__alloc_pages()"). "kswapd" should 3538 * never get caught in the normal page freeing logic. 3539 * 3540 * (Kswapd normally doesn't need memory anyway, but sometimes 3541 * you need a small amount of memory in order to be able to 3542 * page out something else, and this flag essentially protects 3543 * us from recursively trying to free more memory as we're 3544 * trying to free the first piece of memory in the first place). 3545 */ 3546 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; 3547 set_freezable(); 3548 3549 pgdat->kswapd_order = 0; 3550 pgdat->kswapd_classzone_idx = MAX_NR_ZONES; 3551 for ( ; ; ) { 3552 bool ret; 3553 3554 alloc_order = reclaim_order = pgdat->kswapd_order; 3555 classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx); 3556 3557 kswapd_try_sleep: 3558 kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order, 3559 classzone_idx); 3560 3561 /* Read the new order and classzone_idx */ 3562 alloc_order = reclaim_order = pgdat->kswapd_order; 3563 classzone_idx = kswapd_classzone_idx(pgdat, 0); 3564 pgdat->kswapd_order = 0; 3565 pgdat->kswapd_classzone_idx = MAX_NR_ZONES; 3566 3567 ret = try_to_freeze(); 3568 if (kthread_should_stop()) 3569 break; 3570 3571 /* 3572 * We can speed up thawing tasks if we don't call balance_pgdat 3573 * after returning from the refrigerator 3574 */ 3575 if (ret) 3576 continue; 3577 3578 /* 3579 * Reclaim begins at the requested order but if a high-order 3580 * reclaim fails then kswapd falls back to reclaiming for 3581 * order-0. If that happens, kswapd will consider sleeping 3582 * for the order it finished reclaiming at (reclaim_order) 3583 * but kcompactd is woken to compact for the original 3584 * request (alloc_order). 3585 */ 3586 trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx, 3587 alloc_order); 3588 reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx); 3589 if (reclaim_order < alloc_order) 3590 goto kswapd_try_sleep; 3591 } 3592 3593 tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); 3594 current->reclaim_state = NULL; 3595 lockdep_clear_current_reclaim_state(); 3596 3597 return 0; 3598 } 3599 3600 /* 3601 * A zone is low on free memory, so wake its kswapd task to service it. 3602 */ 3603 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) 3604 { 3605 pg_data_t *pgdat; 3606 3607 if (!managed_zone(zone)) 3608 return; 3609 3610 if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL)) 3611 return; 3612 pgdat = zone->zone_pgdat; 3613 pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, 3614 classzone_idx); 3615 pgdat->kswapd_order = max(pgdat->kswapd_order, order); 3616 if (!waitqueue_active(&pgdat->kswapd_wait)) 3617 return; 3618 3619 /* Hopeless node, leave it to direct reclaim */ 3620 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES) 3621 return; 3622 3623 if (pgdat_balanced(pgdat, order, classzone_idx)) 3624 return; 3625 3626 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, classzone_idx, order); 3627 wake_up_interruptible(&pgdat->kswapd_wait); 3628 } 3629 3630 #ifdef CONFIG_HIBERNATION 3631 /* 3632 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of 3633 * freed pages. 3634 * 3635 * Rather than trying to age LRUs the aim is to preserve the overall 3636 * LRU order by reclaiming preferentially 3637 * inactive > active > active referenced > active mapped 3638 */ 3639 unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 3640 { 3641 struct reclaim_state reclaim_state; 3642 struct scan_control sc = { 3643 .nr_to_reclaim = nr_to_reclaim, 3644 .gfp_mask = GFP_HIGHUSER_MOVABLE, 3645 .reclaim_idx = MAX_NR_ZONES - 1, 3646 .priority = DEF_PRIORITY, 3647 .may_writepage = 1, 3648 .may_unmap = 1, 3649 .may_swap = 1, 3650 .hibernation_mode = 1, 3651 }; 3652 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); 3653 struct task_struct *p = current; 3654 unsigned long nr_reclaimed; 3655 unsigned int noreclaim_flag; 3656 3657 noreclaim_flag = memalloc_noreclaim_save(); 3658 lockdep_set_current_reclaim_state(sc.gfp_mask); 3659 reclaim_state.reclaimed_slab = 0; 3660 p->reclaim_state = &reclaim_state; 3661 3662 nr_reclaimed = do_try_to_free_pages(zonelist, &sc); 3663 3664 p->reclaim_state = NULL; 3665 lockdep_clear_current_reclaim_state(); 3666 memalloc_noreclaim_restore(noreclaim_flag); 3667 3668 return nr_reclaimed; 3669 } 3670 #endif /* CONFIG_HIBERNATION */ 3671 3672 /* It's optimal to keep kswapds on the same CPUs as their memory, but 3673 not required for correctness. So if the last cpu in a node goes 3674 away, we get changed to run anywhere: as the first one comes back, 3675 restore their cpu bindings. */ 3676 static int kswapd_cpu_online(unsigned int cpu) 3677 { 3678 int nid; 3679 3680 for_each_node_state(nid, N_MEMORY) { 3681 pg_data_t *pgdat = NODE_DATA(nid); 3682 const struct cpumask *mask; 3683 3684 mask = cpumask_of_node(pgdat->node_id); 3685 3686 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) 3687 /* One of our CPUs online: restore mask */ 3688 set_cpus_allowed_ptr(pgdat->kswapd, mask); 3689 } 3690 return 0; 3691 } 3692 3693 /* 3694 * This kswapd start function will be called by init and node-hot-add. 3695 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. 3696 */ 3697 int kswapd_run(int nid) 3698 { 3699 pg_data_t *pgdat = NODE_DATA(nid); 3700 int ret = 0; 3701 3702 if (pgdat->kswapd) 3703 return 0; 3704 3705 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); 3706 if (IS_ERR(pgdat->kswapd)) { 3707 /* failure at boot is fatal */ 3708 BUG_ON(system_state < SYSTEM_RUNNING); 3709 pr_err("Failed to start kswapd on node %d\n", nid); 3710 ret = PTR_ERR(pgdat->kswapd); 3711 pgdat->kswapd = NULL; 3712 } 3713 return ret; 3714 } 3715 3716 /* 3717 * Called by memory hotplug when all memory in a node is offlined. Caller must 3718 * hold mem_hotplug_begin/end(). 3719 */ 3720 void kswapd_stop(int nid) 3721 { 3722 struct task_struct *kswapd = NODE_DATA(nid)->kswapd; 3723 3724 if (kswapd) { 3725 kthread_stop(kswapd); 3726 NODE_DATA(nid)->kswapd = NULL; 3727 } 3728 } 3729 3730 static int __init kswapd_init(void) 3731 { 3732 int nid, ret; 3733 3734 swap_setup(); 3735 for_each_node_state(nid, N_MEMORY) 3736 kswapd_run(nid); 3737 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 3738 "mm/vmscan:online", kswapd_cpu_online, 3739 NULL); 3740 WARN_ON(ret < 0); 3741 return 0; 3742 } 3743 3744 module_init(kswapd_init) 3745 3746 #ifdef CONFIG_NUMA 3747 /* 3748 * Node reclaim mode 3749 * 3750 * If non-zero call node_reclaim when the number of free pages falls below 3751 * the watermarks. 3752 */ 3753 int node_reclaim_mode __read_mostly; 3754 3755 #define RECLAIM_OFF 0 3756 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ 3757 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ 3758 #define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ 3759 3760 /* 3761 * Priority for NODE_RECLAIM. This determines the fraction of pages 3762 * of a node considered for each zone_reclaim. 4 scans 1/16th of 3763 * a zone. 3764 */ 3765 #define NODE_RECLAIM_PRIORITY 4 3766 3767 /* 3768 * Percentage of pages in a zone that must be unmapped for node_reclaim to 3769 * occur. 3770 */ 3771 int sysctl_min_unmapped_ratio = 1; 3772 3773 /* 3774 * If the number of slab pages in a zone grows beyond this percentage then 3775 * slab reclaim needs to occur. 3776 */ 3777 int sysctl_min_slab_ratio = 5; 3778 3779 static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat) 3780 { 3781 unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED); 3782 unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) + 3783 node_page_state(pgdat, NR_ACTIVE_FILE); 3784 3785 /* 3786 * It's possible for there to be more file mapped pages than 3787 * accounted for by the pages on the file LRU lists because 3788 * tmpfs pages accounted for as ANON can also be FILE_MAPPED 3789 */ 3790 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; 3791 } 3792 3793 /* Work out how many page cache pages we can reclaim in this reclaim_mode */ 3794 static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat) 3795 { 3796 unsigned long nr_pagecache_reclaimable; 3797 unsigned long delta = 0; 3798 3799 /* 3800 * If RECLAIM_UNMAP is set, then all file pages are considered 3801 * potentially reclaimable. Otherwise, we have to worry about 3802 * pages like swapcache and node_unmapped_file_pages() provides 3803 * a better estimate 3804 */ 3805 if (node_reclaim_mode & RECLAIM_UNMAP) 3806 nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES); 3807 else 3808 nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat); 3809 3810 /* If we can't clean pages, remove dirty pages from consideration */ 3811 if (!(node_reclaim_mode & RECLAIM_WRITE)) 3812 delta += node_page_state(pgdat, NR_FILE_DIRTY); 3813 3814 /* Watch for any possible underflows due to delta */ 3815 if (unlikely(delta > nr_pagecache_reclaimable)) 3816 delta = nr_pagecache_reclaimable; 3817 3818 return nr_pagecache_reclaimable - delta; 3819 } 3820 3821 /* 3822 * Try to free up some pages from this node through reclaim. 3823 */ 3824 static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order) 3825 { 3826 /* Minimum pages needed in order to stay on node */ 3827 const unsigned long nr_pages = 1 << order; 3828 struct task_struct *p = current; 3829 struct reclaim_state reclaim_state; 3830 unsigned int noreclaim_flag; 3831 struct scan_control sc = { 3832 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), 3833 .gfp_mask = current_gfp_context(gfp_mask), 3834 .order = order, 3835 .priority = NODE_RECLAIM_PRIORITY, 3836 .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE), 3837 .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP), 3838 .may_swap = 1, 3839 .reclaim_idx = gfp_zone(gfp_mask), 3840 }; 3841 3842 cond_resched(); 3843 /* 3844 * We need to be able to allocate from the reserves for RECLAIM_UNMAP 3845 * and we also need to be able to write out pages for RECLAIM_WRITE 3846 * and RECLAIM_UNMAP. 3847 */ 3848 noreclaim_flag = memalloc_noreclaim_save(); 3849 p->flags |= PF_SWAPWRITE; 3850 lockdep_set_current_reclaim_state(sc.gfp_mask); 3851 reclaim_state.reclaimed_slab = 0; 3852 p->reclaim_state = &reclaim_state; 3853 3854 if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) { 3855 /* 3856 * Free memory by calling shrink zone with increasing 3857 * priorities until we have enough memory freed. 3858 */ 3859 do { 3860 shrink_node(pgdat, &sc); 3861 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0); 3862 } 3863 3864 p->reclaim_state = NULL; 3865 current->flags &= ~PF_SWAPWRITE; 3866 memalloc_noreclaim_restore(noreclaim_flag); 3867 lockdep_clear_current_reclaim_state(); 3868 return sc.nr_reclaimed >= nr_pages; 3869 } 3870 3871 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order) 3872 { 3873 int ret; 3874 3875 /* 3876 * Node reclaim reclaims unmapped file backed pages and 3877 * slab pages if we are over the defined limits. 3878 * 3879 * A small portion of unmapped file backed pages is needed for 3880 * file I/O otherwise pages read by file I/O will be immediately 3881 * thrown out if the node is overallocated. So we do not reclaim 3882 * if less than a specified percentage of the node is used by 3883 * unmapped file backed pages. 3884 */ 3885 if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages && 3886 node_page_state(pgdat, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages) 3887 return NODE_RECLAIM_FULL; 3888 3889 /* 3890 * Do not scan if the allocation should not be delayed. 3891 */ 3892 if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC)) 3893 return NODE_RECLAIM_NOSCAN; 3894 3895 /* 3896 * Only run node reclaim on the local node or on nodes that do not 3897 * have associated processors. This will favor the local processor 3898 * over remote processors and spread off node memory allocations 3899 * as wide as possible. 3900 */ 3901 if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id()) 3902 return NODE_RECLAIM_NOSCAN; 3903 3904 if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags)) 3905 return NODE_RECLAIM_NOSCAN; 3906 3907 ret = __node_reclaim(pgdat, gfp_mask, order); 3908 clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags); 3909 3910 if (!ret) 3911 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED); 3912 3913 return ret; 3914 } 3915 #endif 3916 3917 /* 3918 * page_evictable - test whether a page is evictable 3919 * @page: the page to test 3920 * 3921 * Test whether page is evictable--i.e., should be placed on active/inactive 3922 * lists vs unevictable list. 3923 * 3924 * Reasons page might not be evictable: 3925 * (1) page's mapping marked unevictable 3926 * (2) page is part of an mlocked VMA 3927 * 3928 */ 3929 int page_evictable(struct page *page) 3930 { 3931 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page); 3932 } 3933 3934 #ifdef CONFIG_SHMEM 3935 /** 3936 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list 3937 * @pages: array of pages to check 3938 * @nr_pages: number of pages to check 3939 * 3940 * Checks pages for evictability and moves them to the appropriate lru list. 3941 * 3942 * This function is only used for SysV IPC SHM_UNLOCK. 3943 */ 3944 void check_move_unevictable_pages(struct page **pages, int nr_pages) 3945 { 3946 struct lruvec *lruvec; 3947 struct pglist_data *pgdat = NULL; 3948 int pgscanned = 0; 3949 int pgrescued = 0; 3950 int i; 3951 3952 for (i = 0; i < nr_pages; i++) { 3953 struct page *page = pages[i]; 3954 struct pglist_data *pagepgdat = page_pgdat(page); 3955 3956 pgscanned++; 3957 if (pagepgdat != pgdat) { 3958 if (pgdat) 3959 spin_unlock_irq(&pgdat->lru_lock); 3960 pgdat = pagepgdat; 3961 spin_lock_irq(&pgdat->lru_lock); 3962 } 3963 lruvec = mem_cgroup_page_lruvec(page, pgdat); 3964 3965 if (!PageLRU(page) || !PageUnevictable(page)) 3966 continue; 3967 3968 if (page_evictable(page)) { 3969 enum lru_list lru = page_lru_base_type(page); 3970 3971 VM_BUG_ON_PAGE(PageActive(page), page); 3972 ClearPageUnevictable(page); 3973 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE); 3974 add_page_to_lru_list(page, lruvec, lru); 3975 pgrescued++; 3976 } 3977 } 3978 3979 if (pgdat) { 3980 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); 3981 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); 3982 spin_unlock_irq(&pgdat->lru_lock); 3983 } 3984 } 3985 #endif /* CONFIG_SHMEM */ 3986