vmscan.c revision f80c0673610e36ae29d63e3297175e22f70dde5f
1/* 2 * linux/mm/vmscan.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 * 6 * Swap reorganised 29.12.95, Stephen Tweedie. 7 * kswapd added: 7.1.96 sct 8 * Removed kswapd_ctl limits, and swap out as many pages as needed 9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel. 10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com). 11 * Multiqueue VM started 5.8.00, Rik van Riel. 12 */ 13 14#include <linux/mm.h> 15#include <linux/module.h> 16#include <linux/gfp.h> 17#include <linux/kernel_stat.h> 18#include <linux/swap.h> 19#include <linux/pagemap.h> 20#include <linux/init.h> 21#include <linux/highmem.h> 22#include <linux/vmstat.h> 23#include <linux/file.h> 24#include <linux/writeback.h> 25#include <linux/blkdev.h> 26#include <linux/buffer_head.h> /* for try_to_release_page(), 27 buffer_heads_over_limit */ 28#include <linux/mm_inline.h> 29#include <linux/pagevec.h> 30#include <linux/backing-dev.h> 31#include <linux/rmap.h> 32#include <linux/topology.h> 33#include <linux/cpu.h> 34#include <linux/cpuset.h> 35#include <linux/compaction.h> 36#include <linux/notifier.h> 37#include <linux/rwsem.h> 38#include <linux/delay.h> 39#include <linux/kthread.h> 40#include <linux/freezer.h> 41#include <linux/memcontrol.h> 42#include <linux/delayacct.h> 43#include <linux/sysctl.h> 44#include <linux/oom.h> 45#include <linux/prefetch.h> 46 47#include <asm/tlbflush.h> 48#include <asm/div64.h> 49 50#include <linux/swapops.h> 51 52#include "internal.h" 53 54#define CREATE_TRACE_POINTS 55#include <trace/events/vmscan.h> 56 57/* 58 * reclaim_mode determines how the inactive list is shrunk 59 * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages 60 * RECLAIM_MODE_ASYNC: Do not block 61 * RECLAIM_MODE_SYNC: Allow blocking e.g. call wait_on_page_writeback 62 * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference 63 * page from the LRU and reclaim all pages within a 64 * naturally aligned range 65 * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of 66 * order-0 pages and then compact the zone 67 */ 68typedef unsigned __bitwise__ reclaim_mode_t; 69#define RECLAIM_MODE_SINGLE ((__force reclaim_mode_t)0x01u) 70#define RECLAIM_MODE_ASYNC ((__force reclaim_mode_t)0x02u) 71#define RECLAIM_MODE_SYNC ((__force reclaim_mode_t)0x04u) 72#define RECLAIM_MODE_LUMPYRECLAIM ((__force reclaim_mode_t)0x08u) 73#define RECLAIM_MODE_COMPACTION ((__force reclaim_mode_t)0x10u) 74 75struct scan_control { 76 /* Incremented by the number of inactive pages that were scanned */ 77 unsigned long nr_scanned; 78 79 /* Number of pages freed so far during a call to shrink_zones() */ 80 unsigned long nr_reclaimed; 81 82 /* How many pages shrink_list() should reclaim */ 83 unsigned long nr_to_reclaim; 84 85 unsigned long hibernation_mode; 86 87 /* This context's GFP mask */ 88 gfp_t gfp_mask; 89 90 int may_writepage; 91 92 /* Can mapped pages be reclaimed? */ 93 int may_unmap; 94 95 /* Can pages be swapped as part of reclaim? */ 96 int may_swap; 97 98 int order; 99 100 /* 101 * Intend to reclaim enough continuous memory rather than reclaim 102 * enough amount of memory. i.e, mode for high order allocation. 103 */ 104 reclaim_mode_t reclaim_mode; 105 106 /* Which cgroup do we reclaim from */ 107 struct mem_cgroup *mem_cgroup; 108 109 /* 110 * Nodemask of nodes allowed by the caller. If NULL, all nodes 111 * are scanned. 112 */ 113 nodemask_t *nodemask; 114}; 115 116#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) 117 118#ifdef ARCH_HAS_PREFETCH 119#define prefetch_prev_lru_page(_page, _base, _field) \ 120 do { \ 121 if ((_page)->lru.prev != _base) { \ 122 struct page *prev; \ 123 \ 124 prev = lru_to_page(&(_page->lru)); \ 125 prefetch(&prev->_field); \ 126 } \ 127 } while (0) 128#else 129#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) 130#endif 131 132#ifdef ARCH_HAS_PREFETCHW 133#define prefetchw_prev_lru_page(_page, _base, _field) \ 134 do { \ 135 if ((_page)->lru.prev != _base) { \ 136 struct page *prev; \ 137 \ 138 prev = lru_to_page(&(_page->lru)); \ 139 prefetchw(&prev->_field); \ 140 } \ 141 } while (0) 142#else 143#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) 144#endif 145 146/* 147 * From 0 .. 100. Higher means more swappy. 148 */ 149int vm_swappiness = 60; 150long vm_total_pages; /* The total number of pages which the VM controls */ 151 152static LIST_HEAD(shrinker_list); 153static DECLARE_RWSEM(shrinker_rwsem); 154 155#ifdef CONFIG_CGROUP_MEM_RES_CTLR 156#define scanning_global_lru(sc) (!(sc)->mem_cgroup) 157#else 158#define scanning_global_lru(sc) (1) 159#endif 160 161static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone, 162 struct scan_control *sc) 163{ 164 if (!scanning_global_lru(sc)) 165 return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone); 166 167 return &zone->reclaim_stat; 168} 169 170static unsigned long zone_nr_lru_pages(struct zone *zone, 171 struct scan_control *sc, enum lru_list lru) 172{ 173 if (!scanning_global_lru(sc)) 174 return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup, 175 zone_to_nid(zone), zone_idx(zone), BIT(lru)); 176 177 return zone_page_state(zone, NR_LRU_BASE + lru); 178} 179 180 181/* 182 * Add a shrinker callback to be called from the vm 183 */ 184void register_shrinker(struct shrinker *shrinker) 185{ 186 shrinker->nr = 0; 187 down_write(&shrinker_rwsem); 188 list_add_tail(&shrinker->list, &shrinker_list); 189 up_write(&shrinker_rwsem); 190} 191EXPORT_SYMBOL(register_shrinker); 192 193/* 194 * Remove one 195 */ 196void unregister_shrinker(struct shrinker *shrinker) 197{ 198 down_write(&shrinker_rwsem); 199 list_del(&shrinker->list); 200 up_write(&shrinker_rwsem); 201} 202EXPORT_SYMBOL(unregister_shrinker); 203 204static inline int do_shrinker_shrink(struct shrinker *shrinker, 205 struct shrink_control *sc, 206 unsigned long nr_to_scan) 207{ 208 sc->nr_to_scan = nr_to_scan; 209 return (*shrinker->shrink)(shrinker, sc); 210} 211 212#define SHRINK_BATCH 128 213/* 214 * Call the shrink functions to age shrinkable caches 215 * 216 * Here we assume it costs one seek to replace a lru page and that it also 217 * takes a seek to recreate a cache object. With this in mind we age equal 218 * percentages of the lru and ageable caches. This should balance the seeks 219 * generated by these structures. 220 * 221 * If the vm encountered mapped pages on the LRU it increase the pressure on 222 * slab to avoid swapping. 223 * 224 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. 225 * 226 * `lru_pages' represents the number of on-LRU pages in all the zones which 227 * are eligible for the caller's allocation attempt. It is used for balancing 228 * slab reclaim versus page reclaim. 229 * 230 * Returns the number of slab objects which we shrunk. 231 */ 232unsigned long shrink_slab(struct shrink_control *shrink, 233 unsigned long nr_pages_scanned, 234 unsigned long lru_pages) 235{ 236 struct shrinker *shrinker; 237 unsigned long ret = 0; 238 239 if (nr_pages_scanned == 0) 240 nr_pages_scanned = SWAP_CLUSTER_MAX; 241 242 if (!down_read_trylock(&shrinker_rwsem)) { 243 /* Assume we'll be able to shrink next time */ 244 ret = 1; 245 goto out; 246 } 247 248 list_for_each_entry(shrinker, &shrinker_list, list) { 249 unsigned long long delta; 250 unsigned long total_scan; 251 unsigned long max_pass; 252 int shrink_ret = 0; 253 long nr; 254 long new_nr; 255 long batch_size = shrinker->batch ? shrinker->batch 256 : SHRINK_BATCH; 257 258 /* 259 * copy the current shrinker scan count into a local variable 260 * and zero it so that other concurrent shrinker invocations 261 * don't also do this scanning work. 262 */ 263 do { 264 nr = shrinker->nr; 265 } while (cmpxchg(&shrinker->nr, nr, 0) != nr); 266 267 total_scan = nr; 268 max_pass = do_shrinker_shrink(shrinker, shrink, 0); 269 delta = (4 * nr_pages_scanned) / shrinker->seeks; 270 delta *= max_pass; 271 do_div(delta, lru_pages + 1); 272 total_scan += delta; 273 if (total_scan < 0) { 274 printk(KERN_ERR "shrink_slab: %pF negative objects to " 275 "delete nr=%ld\n", 276 shrinker->shrink, total_scan); 277 total_scan = max_pass; 278 } 279 280 /* 281 * We need to avoid excessive windup on filesystem shrinkers 282 * due to large numbers of GFP_NOFS allocations causing the 283 * shrinkers to return -1 all the time. This results in a large 284 * nr being built up so when a shrink that can do some work 285 * comes along it empties the entire cache due to nr >>> 286 * max_pass. This is bad for sustaining a working set in 287 * memory. 288 * 289 * Hence only allow the shrinker to scan the entire cache when 290 * a large delta change is calculated directly. 291 */ 292 if (delta < max_pass / 4) 293 total_scan = min(total_scan, max_pass / 2); 294 295 /* 296 * Avoid risking looping forever due to too large nr value: 297 * never try to free more than twice the estimate number of 298 * freeable entries. 299 */ 300 if (total_scan > max_pass * 2) 301 total_scan = max_pass * 2; 302 303 trace_mm_shrink_slab_start(shrinker, shrink, nr, 304 nr_pages_scanned, lru_pages, 305 max_pass, delta, total_scan); 306 307 while (total_scan >= batch_size) { 308 int nr_before; 309 310 nr_before = do_shrinker_shrink(shrinker, shrink, 0); 311 shrink_ret = do_shrinker_shrink(shrinker, shrink, 312 batch_size); 313 if (shrink_ret == -1) 314 break; 315 if (shrink_ret < nr_before) 316 ret += nr_before - shrink_ret; 317 count_vm_events(SLABS_SCANNED, batch_size); 318 total_scan -= batch_size; 319 320 cond_resched(); 321 } 322 323 /* 324 * move the unused scan count back into the shrinker in a 325 * manner that handles concurrent updates. If we exhausted the 326 * scan, there is no need to do an update. 327 */ 328 do { 329 nr = shrinker->nr; 330 new_nr = total_scan + nr; 331 if (total_scan <= 0) 332 break; 333 } while (cmpxchg(&shrinker->nr, nr, new_nr) != nr); 334 335 trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr); 336 } 337 up_read(&shrinker_rwsem); 338out: 339 cond_resched(); 340 return ret; 341} 342 343static void set_reclaim_mode(int priority, struct scan_control *sc, 344 bool sync) 345{ 346 reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC; 347 348 /* 349 * Initially assume we are entering either lumpy reclaim or 350 * reclaim/compaction.Depending on the order, we will either set the 351 * sync mode or just reclaim order-0 pages later. 352 */ 353 if (COMPACTION_BUILD) 354 sc->reclaim_mode = RECLAIM_MODE_COMPACTION; 355 else 356 sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM; 357 358 /* 359 * Avoid using lumpy reclaim or reclaim/compaction if possible by 360 * restricting when its set to either costly allocations or when 361 * under memory pressure 362 */ 363 if (sc->order > PAGE_ALLOC_COSTLY_ORDER) 364 sc->reclaim_mode |= syncmode; 365 else if (sc->order && priority < DEF_PRIORITY - 2) 366 sc->reclaim_mode |= syncmode; 367 else 368 sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC; 369} 370 371static void reset_reclaim_mode(struct scan_control *sc) 372{ 373 sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC; 374} 375 376static inline int is_page_cache_freeable(struct page *page) 377{ 378 /* 379 * A freeable page cache page is referenced only by the caller 380 * that isolated the page, the page cache radix tree and 381 * optional buffer heads at page->private. 382 */ 383 return page_count(page) - page_has_private(page) == 2; 384} 385 386static int may_write_to_queue(struct backing_dev_info *bdi, 387 struct scan_control *sc) 388{ 389 if (current->flags & PF_SWAPWRITE) 390 return 1; 391 if (!bdi_write_congested(bdi)) 392 return 1; 393 if (bdi == current->backing_dev_info) 394 return 1; 395 396 /* lumpy reclaim for hugepage often need a lot of write */ 397 if (sc->order > PAGE_ALLOC_COSTLY_ORDER) 398 return 1; 399 return 0; 400} 401 402/* 403 * We detected a synchronous write error writing a page out. Probably 404 * -ENOSPC. We need to propagate that into the address_space for a subsequent 405 * fsync(), msync() or close(). 406 * 407 * The tricky part is that after writepage we cannot touch the mapping: nothing 408 * prevents it from being freed up. But we have a ref on the page and once 409 * that page is locked, the mapping is pinned. 410 * 411 * We're allowed to run sleeping lock_page() here because we know the caller has 412 * __GFP_FS. 413 */ 414static void handle_write_error(struct address_space *mapping, 415 struct page *page, int error) 416{ 417 lock_page(page); 418 if (page_mapping(page) == mapping) 419 mapping_set_error(mapping, error); 420 unlock_page(page); 421} 422 423/* possible outcome of pageout() */ 424typedef enum { 425 /* failed to write page out, page is locked */ 426 PAGE_KEEP, 427 /* move page to the active list, page is locked */ 428 PAGE_ACTIVATE, 429 /* page has been sent to the disk successfully, page is unlocked */ 430 PAGE_SUCCESS, 431 /* page is clean and locked */ 432 PAGE_CLEAN, 433} pageout_t; 434 435/* 436 * pageout is called by shrink_page_list() for each dirty page. 437 * Calls ->writepage(). 438 */ 439static pageout_t pageout(struct page *page, struct address_space *mapping, 440 struct scan_control *sc) 441{ 442 /* 443 * If the page is dirty, only perform writeback if that write 444 * will be non-blocking. To prevent this allocation from being 445 * stalled by pagecache activity. But note that there may be 446 * stalls if we need to run get_block(). We could test 447 * PagePrivate for that. 448 * 449 * If this process is currently in __generic_file_aio_write() against 450 * this page's queue, we can perform writeback even if that 451 * will block. 452 * 453 * If the page is swapcache, write it back even if that would 454 * block, for some throttling. This happens by accident, because 455 * swap_backing_dev_info is bust: it doesn't reflect the 456 * congestion state of the swapdevs. Easy to fix, if needed. 457 */ 458 if (!is_page_cache_freeable(page)) 459 return PAGE_KEEP; 460 if (!mapping) { 461 /* 462 * Some data journaling orphaned pages can have 463 * page->mapping == NULL while being dirty with clean buffers. 464 */ 465 if (page_has_private(page)) { 466 if (try_to_free_buffers(page)) { 467 ClearPageDirty(page); 468 printk("%s: orphaned page\n", __func__); 469 return PAGE_CLEAN; 470 } 471 } 472 return PAGE_KEEP; 473 } 474 if (mapping->a_ops->writepage == NULL) 475 return PAGE_ACTIVATE; 476 if (!may_write_to_queue(mapping->backing_dev_info, sc)) 477 return PAGE_KEEP; 478 479 if (clear_page_dirty_for_io(page)) { 480 int res; 481 struct writeback_control wbc = { 482 .sync_mode = WB_SYNC_NONE, 483 .nr_to_write = SWAP_CLUSTER_MAX, 484 .range_start = 0, 485 .range_end = LLONG_MAX, 486 .for_reclaim = 1, 487 }; 488 489 SetPageReclaim(page); 490 res = mapping->a_ops->writepage(page, &wbc); 491 if (res < 0) 492 handle_write_error(mapping, page, res); 493 if (res == AOP_WRITEPAGE_ACTIVATE) { 494 ClearPageReclaim(page); 495 return PAGE_ACTIVATE; 496 } 497 498 /* 499 * Wait on writeback if requested to. This happens when 500 * direct reclaiming a large contiguous area and the 501 * first attempt to free a range of pages fails. 502 */ 503 if (PageWriteback(page) && 504 (sc->reclaim_mode & RECLAIM_MODE_SYNC)) 505 wait_on_page_writeback(page); 506 507 if (!PageWriteback(page)) { 508 /* synchronous write or broken a_ops? */ 509 ClearPageReclaim(page); 510 } 511 trace_mm_vmscan_writepage(page, 512 trace_reclaim_flags(page, sc->reclaim_mode)); 513 inc_zone_page_state(page, NR_VMSCAN_WRITE); 514 return PAGE_SUCCESS; 515 } 516 517 return PAGE_CLEAN; 518} 519 520/* 521 * Same as remove_mapping, but if the page is removed from the mapping, it 522 * gets returned with a refcount of 0. 523 */ 524static int __remove_mapping(struct address_space *mapping, struct page *page) 525{ 526 BUG_ON(!PageLocked(page)); 527 BUG_ON(mapping != page_mapping(page)); 528 529 spin_lock_irq(&mapping->tree_lock); 530 /* 531 * The non racy check for a busy page. 532 * 533 * Must be careful with the order of the tests. When someone has 534 * a ref to the page, it may be possible that they dirty it then 535 * drop the reference. So if PageDirty is tested before page_count 536 * here, then the following race may occur: 537 * 538 * get_user_pages(&page); 539 * [user mapping goes away] 540 * write_to(page); 541 * !PageDirty(page) [good] 542 * SetPageDirty(page); 543 * put_page(page); 544 * !page_count(page) [good, discard it] 545 * 546 * [oops, our write_to data is lost] 547 * 548 * Reversing the order of the tests ensures such a situation cannot 549 * escape unnoticed. The smp_rmb is needed to ensure the page->flags 550 * load is not satisfied before that of page->_count. 551 * 552 * Note that if SetPageDirty is always performed via set_page_dirty, 553 * and thus under tree_lock, then this ordering is not required. 554 */ 555 if (!page_freeze_refs(page, 2)) 556 goto cannot_free; 557 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */ 558 if (unlikely(PageDirty(page))) { 559 page_unfreeze_refs(page, 2); 560 goto cannot_free; 561 } 562 563 if (PageSwapCache(page)) { 564 swp_entry_t swap = { .val = page_private(page) }; 565 __delete_from_swap_cache(page); 566 spin_unlock_irq(&mapping->tree_lock); 567 swapcache_free(swap, page); 568 } else { 569 void (*freepage)(struct page *); 570 571 freepage = mapping->a_ops->freepage; 572 573 __delete_from_page_cache(page); 574 spin_unlock_irq(&mapping->tree_lock); 575 mem_cgroup_uncharge_cache_page(page); 576 577 if (freepage != NULL) 578 freepage(page); 579 } 580 581 return 1; 582 583cannot_free: 584 spin_unlock_irq(&mapping->tree_lock); 585 return 0; 586} 587 588/* 589 * Attempt to detach a locked page from its ->mapping. If it is dirty or if 590 * someone else has a ref on the page, abort and return 0. If it was 591 * successfully detached, return 1. Assumes the caller has a single ref on 592 * this page. 593 */ 594int remove_mapping(struct address_space *mapping, struct page *page) 595{ 596 if (__remove_mapping(mapping, page)) { 597 /* 598 * Unfreezing the refcount with 1 rather than 2 effectively 599 * drops the pagecache ref for us without requiring another 600 * atomic operation. 601 */ 602 page_unfreeze_refs(page, 1); 603 return 1; 604 } 605 return 0; 606} 607 608/** 609 * putback_lru_page - put previously isolated page onto appropriate LRU list 610 * @page: page to be put back to appropriate lru list 611 * 612 * Add previously isolated @page to appropriate LRU list. 613 * Page may still be unevictable for other reasons. 614 * 615 * lru_lock must not be held, interrupts must be enabled. 616 */ 617void putback_lru_page(struct page *page) 618{ 619 int lru; 620 int active = !!TestClearPageActive(page); 621 int was_unevictable = PageUnevictable(page); 622 623 VM_BUG_ON(PageLRU(page)); 624 625redo: 626 ClearPageUnevictable(page); 627 628 if (page_evictable(page, NULL)) { 629 /* 630 * For evictable pages, we can use the cache. 631 * In event of a race, worst case is we end up with an 632 * unevictable page on [in]active list. 633 * We know how to handle that. 634 */ 635 lru = active + page_lru_base_type(page); 636 lru_cache_add_lru(page, lru); 637 } else { 638 /* 639 * Put unevictable pages directly on zone's unevictable 640 * list. 641 */ 642 lru = LRU_UNEVICTABLE; 643 add_page_to_unevictable_list(page); 644 /* 645 * When racing with an mlock clearing (page is 646 * unlocked), make sure that if the other thread does 647 * not observe our setting of PG_lru and fails 648 * isolation, we see PG_mlocked cleared below and move 649 * the page back to the evictable list. 650 * 651 * The other side is TestClearPageMlocked(). 652 */ 653 smp_mb(); 654 } 655 656 /* 657 * page's status can change while we move it among lru. If an evictable 658 * page is on unevictable list, it never be freed. To avoid that, 659 * check after we added it to the list, again. 660 */ 661 if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) { 662 if (!isolate_lru_page(page)) { 663 put_page(page); 664 goto redo; 665 } 666 /* This means someone else dropped this page from LRU 667 * So, it will be freed or putback to LRU again. There is 668 * nothing to do here. 669 */ 670 } 671 672 if (was_unevictable && lru != LRU_UNEVICTABLE) 673 count_vm_event(UNEVICTABLE_PGRESCUED); 674 else if (!was_unevictable && lru == LRU_UNEVICTABLE) 675 count_vm_event(UNEVICTABLE_PGCULLED); 676 677 put_page(page); /* drop ref from isolate */ 678} 679 680enum page_references { 681 PAGEREF_RECLAIM, 682 PAGEREF_RECLAIM_CLEAN, 683 PAGEREF_KEEP, 684 PAGEREF_ACTIVATE, 685}; 686 687static enum page_references page_check_references(struct page *page, 688 struct scan_control *sc) 689{ 690 int referenced_ptes, referenced_page; 691 unsigned long vm_flags; 692 693 referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags); 694 referenced_page = TestClearPageReferenced(page); 695 696 /* Lumpy reclaim - ignore references */ 697 if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM) 698 return PAGEREF_RECLAIM; 699 700 /* 701 * Mlock lost the isolation race with us. Let try_to_unmap() 702 * move the page to the unevictable list. 703 */ 704 if (vm_flags & VM_LOCKED) 705 return PAGEREF_RECLAIM; 706 707 if (referenced_ptes) { 708 if (PageAnon(page)) 709 return PAGEREF_ACTIVATE; 710 /* 711 * All mapped pages start out with page table 712 * references from the instantiating fault, so we need 713 * to look twice if a mapped file page is used more 714 * than once. 715 * 716 * Mark it and spare it for another trip around the 717 * inactive list. Another page table reference will 718 * lead to its activation. 719 * 720 * Note: the mark is set for activated pages as well 721 * so that recently deactivated but used pages are 722 * quickly recovered. 723 */ 724 SetPageReferenced(page); 725 726 if (referenced_page) 727 return PAGEREF_ACTIVATE; 728 729 return PAGEREF_KEEP; 730 } 731 732 /* Reclaim if clean, defer dirty pages to writeback */ 733 if (referenced_page && !PageSwapBacked(page)) 734 return PAGEREF_RECLAIM_CLEAN; 735 736 return PAGEREF_RECLAIM; 737} 738 739static noinline_for_stack void free_page_list(struct list_head *free_pages) 740{ 741 struct pagevec freed_pvec; 742 struct page *page, *tmp; 743 744 pagevec_init(&freed_pvec, 1); 745 746 list_for_each_entry_safe(page, tmp, free_pages, lru) { 747 list_del(&page->lru); 748 if (!pagevec_add(&freed_pvec, page)) { 749 __pagevec_free(&freed_pvec); 750 pagevec_reinit(&freed_pvec); 751 } 752 } 753 754 pagevec_free(&freed_pvec); 755} 756 757/* 758 * shrink_page_list() returns the number of reclaimed pages 759 */ 760static unsigned long shrink_page_list(struct list_head *page_list, 761 struct zone *zone, 762 struct scan_control *sc) 763{ 764 LIST_HEAD(ret_pages); 765 LIST_HEAD(free_pages); 766 int pgactivate = 0; 767 unsigned long nr_dirty = 0; 768 unsigned long nr_congested = 0; 769 unsigned long nr_reclaimed = 0; 770 771 cond_resched(); 772 773 while (!list_empty(page_list)) { 774 enum page_references references; 775 struct address_space *mapping; 776 struct page *page; 777 int may_enter_fs; 778 779 cond_resched(); 780 781 page = lru_to_page(page_list); 782 list_del(&page->lru); 783 784 if (!trylock_page(page)) 785 goto keep; 786 787 VM_BUG_ON(PageActive(page)); 788 VM_BUG_ON(page_zone(page) != zone); 789 790 sc->nr_scanned++; 791 792 if (unlikely(!page_evictable(page, NULL))) 793 goto cull_mlocked; 794 795 if (!sc->may_unmap && page_mapped(page)) 796 goto keep_locked; 797 798 /* Double the slab pressure for mapped and swapcache pages */ 799 if (page_mapped(page) || PageSwapCache(page)) 800 sc->nr_scanned++; 801 802 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 803 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 804 805 if (PageWriteback(page)) { 806 /* 807 * Synchronous reclaim is performed in two passes, 808 * first an asynchronous pass over the list to 809 * start parallel writeback, and a second synchronous 810 * pass to wait for the IO to complete. Wait here 811 * for any page for which writeback has already 812 * started. 813 */ 814 if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) && 815 may_enter_fs) 816 wait_on_page_writeback(page); 817 else { 818 unlock_page(page); 819 goto keep_lumpy; 820 } 821 } 822 823 references = page_check_references(page, sc); 824 switch (references) { 825 case PAGEREF_ACTIVATE: 826 goto activate_locked; 827 case PAGEREF_KEEP: 828 goto keep_locked; 829 case PAGEREF_RECLAIM: 830 case PAGEREF_RECLAIM_CLEAN: 831 ; /* try to reclaim the page below */ 832 } 833 834 /* 835 * Anonymous process memory has backing store? 836 * Try to allocate it some swap space here. 837 */ 838 if (PageAnon(page) && !PageSwapCache(page)) { 839 if (!(sc->gfp_mask & __GFP_IO)) 840 goto keep_locked; 841 if (!add_to_swap(page)) 842 goto activate_locked; 843 may_enter_fs = 1; 844 } 845 846 mapping = page_mapping(page); 847 848 /* 849 * The page is mapped into the page tables of one or more 850 * processes. Try to unmap it here. 851 */ 852 if (page_mapped(page) && mapping) { 853 switch (try_to_unmap(page, TTU_UNMAP)) { 854 case SWAP_FAIL: 855 goto activate_locked; 856 case SWAP_AGAIN: 857 goto keep_locked; 858 case SWAP_MLOCK: 859 goto cull_mlocked; 860 case SWAP_SUCCESS: 861 ; /* try to free the page below */ 862 } 863 } 864 865 if (PageDirty(page)) { 866 nr_dirty++; 867 868 if (references == PAGEREF_RECLAIM_CLEAN) 869 goto keep_locked; 870 if (!may_enter_fs) 871 goto keep_locked; 872 if (!sc->may_writepage) 873 goto keep_locked; 874 875 /* Page is dirty, try to write it out here */ 876 switch (pageout(page, mapping, sc)) { 877 case PAGE_KEEP: 878 nr_congested++; 879 goto keep_locked; 880 case PAGE_ACTIVATE: 881 goto activate_locked; 882 case PAGE_SUCCESS: 883 if (PageWriteback(page)) 884 goto keep_lumpy; 885 if (PageDirty(page)) 886 goto keep; 887 888 /* 889 * A synchronous write - probably a ramdisk. Go 890 * ahead and try to reclaim the page. 891 */ 892 if (!trylock_page(page)) 893 goto keep; 894 if (PageDirty(page) || PageWriteback(page)) 895 goto keep_locked; 896 mapping = page_mapping(page); 897 case PAGE_CLEAN: 898 ; /* try to free the page below */ 899 } 900 } 901 902 /* 903 * If the page has buffers, try to free the buffer mappings 904 * associated with this page. If we succeed we try to free 905 * the page as well. 906 * 907 * We do this even if the page is PageDirty(). 908 * try_to_release_page() does not perform I/O, but it is 909 * possible for a page to have PageDirty set, but it is actually 910 * clean (all its buffers are clean). This happens if the 911 * buffers were written out directly, with submit_bh(). ext3 912 * will do this, as well as the blockdev mapping. 913 * try_to_release_page() will discover that cleanness and will 914 * drop the buffers and mark the page clean - it can be freed. 915 * 916 * Rarely, pages can have buffers and no ->mapping. These are 917 * the pages which were not successfully invalidated in 918 * truncate_complete_page(). We try to drop those buffers here 919 * and if that worked, and the page is no longer mapped into 920 * process address space (page_count == 1) it can be freed. 921 * Otherwise, leave the page on the LRU so it is swappable. 922 */ 923 if (page_has_private(page)) { 924 if (!try_to_release_page(page, sc->gfp_mask)) 925 goto activate_locked; 926 if (!mapping && page_count(page) == 1) { 927 unlock_page(page); 928 if (put_page_testzero(page)) 929 goto free_it; 930 else { 931 /* 932 * rare race with speculative reference. 933 * the speculative reference will free 934 * this page shortly, so we may 935 * increment nr_reclaimed here (and 936 * leave it off the LRU). 937 */ 938 nr_reclaimed++; 939 continue; 940 } 941 } 942 } 943 944 if (!mapping || !__remove_mapping(mapping, page)) 945 goto keep_locked; 946 947 /* 948 * At this point, we have no other references and there is 949 * no way to pick any more up (removed from LRU, removed 950 * from pagecache). Can use non-atomic bitops now (and 951 * we obviously don't have to worry about waking up a process 952 * waiting on the page lock, because there are no references. 953 */ 954 __clear_page_locked(page); 955free_it: 956 nr_reclaimed++; 957 958 /* 959 * Is there need to periodically free_page_list? It would 960 * appear not as the counts should be low 961 */ 962 list_add(&page->lru, &free_pages); 963 continue; 964 965cull_mlocked: 966 if (PageSwapCache(page)) 967 try_to_free_swap(page); 968 unlock_page(page); 969 putback_lru_page(page); 970 reset_reclaim_mode(sc); 971 continue; 972 973activate_locked: 974 /* Not a candidate for swapping, so reclaim swap space. */ 975 if (PageSwapCache(page) && vm_swap_full()) 976 try_to_free_swap(page); 977 VM_BUG_ON(PageActive(page)); 978 SetPageActive(page); 979 pgactivate++; 980keep_locked: 981 unlock_page(page); 982keep: 983 reset_reclaim_mode(sc); 984keep_lumpy: 985 list_add(&page->lru, &ret_pages); 986 VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); 987 } 988 989 /* 990 * Tag a zone as congested if all the dirty pages encountered were 991 * backed by a congested BDI. In this case, reclaimers should just 992 * back off and wait for congestion to clear because further reclaim 993 * will encounter the same problem 994 */ 995 if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc)) 996 zone_set_flag(zone, ZONE_CONGESTED); 997 998 free_page_list(&free_pages); 999 1000 list_splice(&ret_pages, page_list); 1001 count_vm_events(PGACTIVATE, pgactivate); 1002 return nr_reclaimed; 1003} 1004 1005/* 1006 * Attempt to remove the specified page from its LRU. Only take this page 1007 * if it is of the appropriate PageActive status. Pages which are being 1008 * freed elsewhere are also ignored. 1009 * 1010 * page: page to consider 1011 * mode: one of the LRU isolation modes defined above 1012 * 1013 * returns 0 on success, -ve errno on failure. 1014 */ 1015int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file) 1016{ 1017 bool all_lru_mode; 1018 int ret = -EINVAL; 1019 1020 /* Only take pages on the LRU. */ 1021 if (!PageLRU(page)) 1022 return ret; 1023 1024 all_lru_mode = (mode & (ISOLATE_ACTIVE|ISOLATE_INACTIVE)) == 1025 (ISOLATE_ACTIVE|ISOLATE_INACTIVE); 1026 1027 /* 1028 * When checking the active state, we need to be sure we are 1029 * dealing with comparible boolean values. Take the logical not 1030 * of each. 1031 */ 1032 if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE)) 1033 return ret; 1034 1035 if (!all_lru_mode && !!page_is_file_cache(page) != file) 1036 return ret; 1037 1038 /* 1039 * When this function is being called for lumpy reclaim, we 1040 * initially look into all LRU pages, active, inactive and 1041 * unevictable; only give shrink_page_list evictable pages. 1042 */ 1043 if (PageUnevictable(page)) 1044 return ret; 1045 1046 ret = -EBUSY; 1047 1048 if ((mode & ISOLATE_CLEAN) && (PageDirty(page) || PageWriteback(page))) 1049 return ret; 1050 1051 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) 1052 return ret; 1053 1054 if (likely(get_page_unless_zero(page))) { 1055 /* 1056 * Be careful not to clear PageLRU until after we're 1057 * sure the page is not being freed elsewhere -- the 1058 * page release code relies on it. 1059 */ 1060 ClearPageLRU(page); 1061 ret = 0; 1062 } 1063 1064 return ret; 1065} 1066 1067/* 1068 * zone->lru_lock is heavily contended. Some of the functions that 1069 * shrink the lists perform better by taking out a batch of pages 1070 * and working on them outside the LRU lock. 1071 * 1072 * For pagecache intensive workloads, this function is the hottest 1073 * spot in the kernel (apart from copy_*_user functions). 1074 * 1075 * Appropriate locks must be held before calling this function. 1076 * 1077 * @nr_to_scan: The number of pages to look through on the list. 1078 * @src: The LRU list to pull pages off. 1079 * @dst: The temp list to put pages on to. 1080 * @scanned: The number of pages that were scanned. 1081 * @order: The caller's attempted allocation order 1082 * @mode: One of the LRU isolation modes 1083 * @file: True [1] if isolating file [!anon] pages 1084 * 1085 * returns how many pages were moved onto *@dst. 1086 */ 1087static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 1088 struct list_head *src, struct list_head *dst, 1089 unsigned long *scanned, int order, isolate_mode_t mode, 1090 int file) 1091{ 1092 unsigned long nr_taken = 0; 1093 unsigned long nr_lumpy_taken = 0; 1094 unsigned long nr_lumpy_dirty = 0; 1095 unsigned long nr_lumpy_failed = 0; 1096 unsigned long scan; 1097 1098 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { 1099 struct page *page; 1100 unsigned long pfn; 1101 unsigned long end_pfn; 1102 unsigned long page_pfn; 1103 int zone_id; 1104 1105 page = lru_to_page(src); 1106 prefetchw_prev_lru_page(page, src, flags); 1107 1108 VM_BUG_ON(!PageLRU(page)); 1109 1110 switch (__isolate_lru_page(page, mode, file)) { 1111 case 0: 1112 list_move(&page->lru, dst); 1113 mem_cgroup_del_lru(page); 1114 nr_taken += hpage_nr_pages(page); 1115 break; 1116 1117 case -EBUSY: 1118 /* else it is being freed elsewhere */ 1119 list_move(&page->lru, src); 1120 mem_cgroup_rotate_lru_list(page, page_lru(page)); 1121 continue; 1122 1123 default: 1124 BUG(); 1125 } 1126 1127 if (!order) 1128 continue; 1129 1130 /* 1131 * Attempt to take all pages in the order aligned region 1132 * surrounding the tag page. Only take those pages of 1133 * the same active state as that tag page. We may safely 1134 * round the target page pfn down to the requested order 1135 * as the mem_map is guaranteed valid out to MAX_ORDER, 1136 * where that page is in a different zone we will detect 1137 * it from its zone id and abort this block scan. 1138 */ 1139 zone_id = page_zone_id(page); 1140 page_pfn = page_to_pfn(page); 1141 pfn = page_pfn & ~((1 << order) - 1); 1142 end_pfn = pfn + (1 << order); 1143 for (; pfn < end_pfn; pfn++) { 1144 struct page *cursor_page; 1145 1146 /* The target page is in the block, ignore it. */ 1147 if (unlikely(pfn == page_pfn)) 1148 continue; 1149 1150 /* Avoid holes within the zone. */ 1151 if (unlikely(!pfn_valid_within(pfn))) 1152 break; 1153 1154 cursor_page = pfn_to_page(pfn); 1155 1156 /* Check that we have not crossed a zone boundary. */ 1157 if (unlikely(page_zone_id(cursor_page) != zone_id)) 1158 break; 1159 1160 /* 1161 * If we don't have enough swap space, reclaiming of 1162 * anon page which don't already have a swap slot is 1163 * pointless. 1164 */ 1165 if (nr_swap_pages <= 0 && PageAnon(cursor_page) && 1166 !PageSwapCache(cursor_page)) 1167 break; 1168 1169 if (__isolate_lru_page(cursor_page, mode, file) == 0) { 1170 list_move(&cursor_page->lru, dst); 1171 mem_cgroup_del_lru(cursor_page); 1172 nr_taken += hpage_nr_pages(page); 1173 nr_lumpy_taken++; 1174 if (PageDirty(cursor_page)) 1175 nr_lumpy_dirty++; 1176 scan++; 1177 } else { 1178 /* 1179 * Check if the page is freed already. 1180 * 1181 * We can't use page_count() as that 1182 * requires compound_head and we don't 1183 * have a pin on the page here. If a 1184 * page is tail, we may or may not 1185 * have isolated the head, so assume 1186 * it's not free, it'd be tricky to 1187 * track the head status without a 1188 * page pin. 1189 */ 1190 if (!PageTail(cursor_page) && 1191 !atomic_read(&cursor_page->_count)) 1192 continue; 1193 break; 1194 } 1195 } 1196 1197 /* If we break out of the loop above, lumpy reclaim failed */ 1198 if (pfn < end_pfn) 1199 nr_lumpy_failed++; 1200 } 1201 1202 *scanned = scan; 1203 1204 trace_mm_vmscan_lru_isolate(order, 1205 nr_to_scan, scan, 1206 nr_taken, 1207 nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed, 1208 mode); 1209 return nr_taken; 1210} 1211 1212static unsigned long isolate_pages_global(unsigned long nr, 1213 struct list_head *dst, 1214 unsigned long *scanned, int order, 1215 isolate_mode_t mode, 1216 struct zone *z, int active, int file) 1217{ 1218 int lru = LRU_BASE; 1219 if (active) 1220 lru += LRU_ACTIVE; 1221 if (file) 1222 lru += LRU_FILE; 1223 return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order, 1224 mode, file); 1225} 1226 1227/* 1228 * clear_active_flags() is a helper for shrink_active_list(), clearing 1229 * any active bits from the pages in the list. 1230 */ 1231static unsigned long clear_active_flags(struct list_head *page_list, 1232 unsigned int *count) 1233{ 1234 int nr_active = 0; 1235 int lru; 1236 struct page *page; 1237 1238 list_for_each_entry(page, page_list, lru) { 1239 int numpages = hpage_nr_pages(page); 1240 lru = page_lru_base_type(page); 1241 if (PageActive(page)) { 1242 lru += LRU_ACTIVE; 1243 ClearPageActive(page); 1244 nr_active += numpages; 1245 } 1246 if (count) 1247 count[lru] += numpages; 1248 } 1249 1250 return nr_active; 1251} 1252 1253/** 1254 * isolate_lru_page - tries to isolate a page from its LRU list 1255 * @page: page to isolate from its LRU list 1256 * 1257 * Isolates a @page from an LRU list, clears PageLRU and adjusts the 1258 * vmstat statistic corresponding to whatever LRU list the page was on. 1259 * 1260 * Returns 0 if the page was removed from an LRU list. 1261 * Returns -EBUSY if the page was not on an LRU list. 1262 * 1263 * The returned page will have PageLRU() cleared. If it was found on 1264 * the active list, it will have PageActive set. If it was found on 1265 * the unevictable list, it will have the PageUnevictable bit set. That flag 1266 * may need to be cleared by the caller before letting the page go. 1267 * 1268 * The vmstat statistic corresponding to the list on which the page was 1269 * found will be decremented. 1270 * 1271 * Restrictions: 1272 * (1) Must be called with an elevated refcount on the page. This is a 1273 * fundamentnal difference from isolate_lru_pages (which is called 1274 * without a stable reference). 1275 * (2) the lru_lock must not be held. 1276 * (3) interrupts must be enabled. 1277 */ 1278int isolate_lru_page(struct page *page) 1279{ 1280 int ret = -EBUSY; 1281 1282 VM_BUG_ON(!page_count(page)); 1283 1284 if (PageLRU(page)) { 1285 struct zone *zone = page_zone(page); 1286 1287 spin_lock_irq(&zone->lru_lock); 1288 if (PageLRU(page)) { 1289 int lru = page_lru(page); 1290 ret = 0; 1291 get_page(page); 1292 ClearPageLRU(page); 1293 1294 del_page_from_lru_list(zone, page, lru); 1295 } 1296 spin_unlock_irq(&zone->lru_lock); 1297 } 1298 return ret; 1299} 1300 1301/* 1302 * Are there way too many processes in the direct reclaim path already? 1303 */ 1304static int too_many_isolated(struct zone *zone, int file, 1305 struct scan_control *sc) 1306{ 1307 unsigned long inactive, isolated; 1308 1309 if (current_is_kswapd()) 1310 return 0; 1311 1312 if (!scanning_global_lru(sc)) 1313 return 0; 1314 1315 if (file) { 1316 inactive = zone_page_state(zone, NR_INACTIVE_FILE); 1317 isolated = zone_page_state(zone, NR_ISOLATED_FILE); 1318 } else { 1319 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1320 isolated = zone_page_state(zone, NR_ISOLATED_ANON); 1321 } 1322 1323 return isolated > inactive; 1324} 1325 1326/* 1327 * TODO: Try merging with migrations version of putback_lru_pages 1328 */ 1329static noinline_for_stack void 1330putback_lru_pages(struct zone *zone, struct scan_control *sc, 1331 unsigned long nr_anon, unsigned long nr_file, 1332 struct list_head *page_list) 1333{ 1334 struct page *page; 1335 struct pagevec pvec; 1336 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1337 1338 pagevec_init(&pvec, 1); 1339 1340 /* 1341 * Put back any unfreeable pages. 1342 */ 1343 spin_lock(&zone->lru_lock); 1344 while (!list_empty(page_list)) { 1345 int lru; 1346 page = lru_to_page(page_list); 1347 VM_BUG_ON(PageLRU(page)); 1348 list_del(&page->lru); 1349 if (unlikely(!page_evictable(page, NULL))) { 1350 spin_unlock_irq(&zone->lru_lock); 1351 putback_lru_page(page); 1352 spin_lock_irq(&zone->lru_lock); 1353 continue; 1354 } 1355 SetPageLRU(page); 1356 lru = page_lru(page); 1357 add_page_to_lru_list(zone, page, lru); 1358 if (is_active_lru(lru)) { 1359 int file = is_file_lru(lru); 1360 int numpages = hpage_nr_pages(page); 1361 reclaim_stat->recent_rotated[file] += numpages; 1362 } 1363 if (!pagevec_add(&pvec, page)) { 1364 spin_unlock_irq(&zone->lru_lock); 1365 __pagevec_release(&pvec); 1366 spin_lock_irq(&zone->lru_lock); 1367 } 1368 } 1369 __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon); 1370 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file); 1371 1372 spin_unlock_irq(&zone->lru_lock); 1373 pagevec_release(&pvec); 1374} 1375 1376static noinline_for_stack void update_isolated_counts(struct zone *zone, 1377 struct scan_control *sc, 1378 unsigned long *nr_anon, 1379 unsigned long *nr_file, 1380 struct list_head *isolated_list) 1381{ 1382 unsigned long nr_active; 1383 unsigned int count[NR_LRU_LISTS] = { 0, }; 1384 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1385 1386 nr_active = clear_active_flags(isolated_list, count); 1387 __count_vm_events(PGDEACTIVATE, nr_active); 1388 1389 __mod_zone_page_state(zone, NR_ACTIVE_FILE, 1390 -count[LRU_ACTIVE_FILE]); 1391 __mod_zone_page_state(zone, NR_INACTIVE_FILE, 1392 -count[LRU_INACTIVE_FILE]); 1393 __mod_zone_page_state(zone, NR_ACTIVE_ANON, 1394 -count[LRU_ACTIVE_ANON]); 1395 __mod_zone_page_state(zone, NR_INACTIVE_ANON, 1396 -count[LRU_INACTIVE_ANON]); 1397 1398 *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON]; 1399 *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE]; 1400 __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon); 1401 __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file); 1402 1403 reclaim_stat->recent_scanned[0] += *nr_anon; 1404 reclaim_stat->recent_scanned[1] += *nr_file; 1405} 1406 1407/* 1408 * Returns true if the caller should wait to clean dirty/writeback pages. 1409 * 1410 * If we are direct reclaiming for contiguous pages and we do not reclaim 1411 * everything in the list, try again and wait for writeback IO to complete. 1412 * This will stall high-order allocations noticeably. Only do that when really 1413 * need to free the pages under high memory pressure. 1414 */ 1415static inline bool should_reclaim_stall(unsigned long nr_taken, 1416 unsigned long nr_freed, 1417 int priority, 1418 struct scan_control *sc) 1419{ 1420 int lumpy_stall_priority; 1421 1422 /* kswapd should not stall on sync IO */ 1423 if (current_is_kswapd()) 1424 return false; 1425 1426 /* Only stall on lumpy reclaim */ 1427 if (sc->reclaim_mode & RECLAIM_MODE_SINGLE) 1428 return false; 1429 1430 /* If we have reclaimed everything on the isolated list, no stall */ 1431 if (nr_freed == nr_taken) 1432 return false; 1433 1434 /* 1435 * For high-order allocations, there are two stall thresholds. 1436 * High-cost allocations stall immediately where as lower 1437 * order allocations such as stacks require the scanning 1438 * priority to be much higher before stalling. 1439 */ 1440 if (sc->order > PAGE_ALLOC_COSTLY_ORDER) 1441 lumpy_stall_priority = DEF_PRIORITY; 1442 else 1443 lumpy_stall_priority = DEF_PRIORITY / 3; 1444 1445 return priority <= lumpy_stall_priority; 1446} 1447 1448/* 1449 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number 1450 * of reclaimed pages 1451 */ 1452static noinline_for_stack unsigned long 1453shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone, 1454 struct scan_control *sc, int priority, int file) 1455{ 1456 LIST_HEAD(page_list); 1457 unsigned long nr_scanned; 1458 unsigned long nr_reclaimed = 0; 1459 unsigned long nr_taken; 1460 unsigned long nr_anon; 1461 unsigned long nr_file; 1462 isolate_mode_t reclaim_mode = ISOLATE_INACTIVE; 1463 1464 while (unlikely(too_many_isolated(zone, file, sc))) { 1465 congestion_wait(BLK_RW_ASYNC, HZ/10); 1466 1467 /* We are about to die and free our memory. Return now. */ 1468 if (fatal_signal_pending(current)) 1469 return SWAP_CLUSTER_MAX; 1470 } 1471 1472 set_reclaim_mode(priority, sc, false); 1473 if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM) 1474 reclaim_mode |= ISOLATE_ACTIVE; 1475 1476 lru_add_drain(); 1477 1478 if (!sc->may_unmap) 1479 reclaim_mode |= ISOLATE_UNMAPPED; 1480 if (!sc->may_writepage) 1481 reclaim_mode |= ISOLATE_CLEAN; 1482 1483 spin_lock_irq(&zone->lru_lock); 1484 1485 if (scanning_global_lru(sc)) { 1486 nr_taken = isolate_pages_global(nr_to_scan, &page_list, 1487 &nr_scanned, sc->order, reclaim_mode, zone, 0, file); 1488 zone->pages_scanned += nr_scanned; 1489 if (current_is_kswapd()) 1490 __count_zone_vm_events(PGSCAN_KSWAPD, zone, 1491 nr_scanned); 1492 else 1493 __count_zone_vm_events(PGSCAN_DIRECT, zone, 1494 nr_scanned); 1495 } else { 1496 nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list, 1497 &nr_scanned, sc->order, reclaim_mode, zone, 1498 sc->mem_cgroup, 0, file); 1499 /* 1500 * mem_cgroup_isolate_pages() keeps track of 1501 * scanned pages on its own. 1502 */ 1503 } 1504 1505 if (nr_taken == 0) { 1506 spin_unlock_irq(&zone->lru_lock); 1507 return 0; 1508 } 1509 1510 update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list); 1511 1512 spin_unlock_irq(&zone->lru_lock); 1513 1514 nr_reclaimed = shrink_page_list(&page_list, zone, sc); 1515 1516 /* Check if we should syncronously wait for writeback */ 1517 if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) { 1518 set_reclaim_mode(priority, sc, true); 1519 nr_reclaimed += shrink_page_list(&page_list, zone, sc); 1520 } 1521 1522 local_irq_disable(); 1523 if (current_is_kswapd()) 1524 __count_vm_events(KSWAPD_STEAL, nr_reclaimed); 1525 __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed); 1526 1527 putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list); 1528 1529 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, 1530 zone_idx(zone), 1531 nr_scanned, nr_reclaimed, 1532 priority, 1533 trace_shrink_flags(file, sc->reclaim_mode)); 1534 return nr_reclaimed; 1535} 1536 1537/* 1538 * This moves pages from the active list to the inactive list. 1539 * 1540 * We move them the other way if the page is referenced by one or more 1541 * processes, from rmap. 1542 * 1543 * If the pages are mostly unmapped, the processing is fast and it is 1544 * appropriate to hold zone->lru_lock across the whole operation. But if 1545 * the pages are mapped, the processing is slow (page_referenced()) so we 1546 * should drop zone->lru_lock around each page. It's impossible to balance 1547 * this, so instead we remove the pages from the LRU while processing them. 1548 * It is safe to rely on PG_active against the non-LRU pages in here because 1549 * nobody will play with that bit on a non-LRU page. 1550 * 1551 * The downside is that we have to touch page->_count against each page. 1552 * But we had to alter page->flags anyway. 1553 */ 1554 1555static void move_active_pages_to_lru(struct zone *zone, 1556 struct list_head *list, 1557 enum lru_list lru) 1558{ 1559 unsigned long pgmoved = 0; 1560 struct pagevec pvec; 1561 struct page *page; 1562 1563 pagevec_init(&pvec, 1); 1564 1565 while (!list_empty(list)) { 1566 page = lru_to_page(list); 1567 1568 VM_BUG_ON(PageLRU(page)); 1569 SetPageLRU(page); 1570 1571 list_move(&page->lru, &zone->lru[lru].list); 1572 mem_cgroup_add_lru_list(page, lru); 1573 pgmoved += hpage_nr_pages(page); 1574 1575 if (!pagevec_add(&pvec, page) || list_empty(list)) { 1576 spin_unlock_irq(&zone->lru_lock); 1577 if (buffer_heads_over_limit) 1578 pagevec_strip(&pvec); 1579 __pagevec_release(&pvec); 1580 spin_lock_irq(&zone->lru_lock); 1581 } 1582 } 1583 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); 1584 if (!is_active_lru(lru)) 1585 __count_vm_events(PGDEACTIVATE, pgmoved); 1586} 1587 1588static void shrink_active_list(unsigned long nr_pages, struct zone *zone, 1589 struct scan_control *sc, int priority, int file) 1590{ 1591 unsigned long nr_taken; 1592 unsigned long pgscanned; 1593 unsigned long vm_flags; 1594 LIST_HEAD(l_hold); /* The pages which were snipped off */ 1595 LIST_HEAD(l_active); 1596 LIST_HEAD(l_inactive); 1597 struct page *page; 1598 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1599 unsigned long nr_rotated = 0; 1600 isolate_mode_t reclaim_mode = ISOLATE_ACTIVE; 1601 1602 lru_add_drain(); 1603 1604 if (!sc->may_unmap) 1605 reclaim_mode |= ISOLATE_UNMAPPED; 1606 if (!sc->may_writepage) 1607 reclaim_mode |= ISOLATE_CLEAN; 1608 1609 spin_lock_irq(&zone->lru_lock); 1610 if (scanning_global_lru(sc)) { 1611 nr_taken = isolate_pages_global(nr_pages, &l_hold, 1612 &pgscanned, sc->order, 1613 reclaim_mode, zone, 1614 1, file); 1615 zone->pages_scanned += pgscanned; 1616 } else { 1617 nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold, 1618 &pgscanned, sc->order, 1619 reclaim_mode, zone, 1620 sc->mem_cgroup, 1, file); 1621 /* 1622 * mem_cgroup_isolate_pages() keeps track of 1623 * scanned pages on its own. 1624 */ 1625 } 1626 1627 reclaim_stat->recent_scanned[file] += nr_taken; 1628 1629 __count_zone_vm_events(PGREFILL, zone, pgscanned); 1630 if (file) 1631 __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken); 1632 else 1633 __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken); 1634 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); 1635 spin_unlock_irq(&zone->lru_lock); 1636 1637 while (!list_empty(&l_hold)) { 1638 cond_resched(); 1639 page = lru_to_page(&l_hold); 1640 list_del(&page->lru); 1641 1642 if (unlikely(!page_evictable(page, NULL))) { 1643 putback_lru_page(page); 1644 continue; 1645 } 1646 1647 if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) { 1648 nr_rotated += hpage_nr_pages(page); 1649 /* 1650 * Identify referenced, file-backed active pages and 1651 * give them one more trip around the active list. So 1652 * that executable code get better chances to stay in 1653 * memory under moderate memory pressure. Anon pages 1654 * are not likely to be evicted by use-once streaming 1655 * IO, plus JVM can create lots of anon VM_EXEC pages, 1656 * so we ignore them here. 1657 */ 1658 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) { 1659 list_add(&page->lru, &l_active); 1660 continue; 1661 } 1662 } 1663 1664 ClearPageActive(page); /* we are de-activating */ 1665 list_add(&page->lru, &l_inactive); 1666 } 1667 1668 /* 1669 * Move pages back to the lru list. 1670 */ 1671 spin_lock_irq(&zone->lru_lock); 1672 /* 1673 * Count referenced pages from currently used mappings as rotated, 1674 * even though only some of them are actually re-activated. This 1675 * helps balance scan pressure between file and anonymous pages in 1676 * get_scan_ratio. 1677 */ 1678 reclaim_stat->recent_rotated[file] += nr_rotated; 1679 1680 move_active_pages_to_lru(zone, &l_active, 1681 LRU_ACTIVE + file * LRU_FILE); 1682 move_active_pages_to_lru(zone, &l_inactive, 1683 LRU_BASE + file * LRU_FILE); 1684 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); 1685 spin_unlock_irq(&zone->lru_lock); 1686} 1687 1688#ifdef CONFIG_SWAP 1689static int inactive_anon_is_low_global(struct zone *zone) 1690{ 1691 unsigned long active, inactive; 1692 1693 active = zone_page_state(zone, NR_ACTIVE_ANON); 1694 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1695 1696 if (inactive * zone->inactive_ratio < active) 1697 return 1; 1698 1699 return 0; 1700} 1701 1702/** 1703 * inactive_anon_is_low - check if anonymous pages need to be deactivated 1704 * @zone: zone to check 1705 * @sc: scan control of this context 1706 * 1707 * Returns true if the zone does not have enough inactive anon pages, 1708 * meaning some active anon pages need to be deactivated. 1709 */ 1710static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc) 1711{ 1712 int low; 1713 1714 /* 1715 * If we don't have swap space, anonymous page deactivation 1716 * is pointless. 1717 */ 1718 if (!total_swap_pages) 1719 return 0; 1720 1721 if (scanning_global_lru(sc)) 1722 low = inactive_anon_is_low_global(zone); 1723 else 1724 low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup); 1725 return low; 1726} 1727#else 1728static inline int inactive_anon_is_low(struct zone *zone, 1729 struct scan_control *sc) 1730{ 1731 return 0; 1732} 1733#endif 1734 1735static int inactive_file_is_low_global(struct zone *zone) 1736{ 1737 unsigned long active, inactive; 1738 1739 active = zone_page_state(zone, NR_ACTIVE_FILE); 1740 inactive = zone_page_state(zone, NR_INACTIVE_FILE); 1741 1742 return (active > inactive); 1743} 1744 1745/** 1746 * inactive_file_is_low - check if file pages need to be deactivated 1747 * @zone: zone to check 1748 * @sc: scan control of this context 1749 * 1750 * When the system is doing streaming IO, memory pressure here 1751 * ensures that active file pages get deactivated, until more 1752 * than half of the file pages are on the inactive list. 1753 * 1754 * Once we get to that situation, protect the system's working 1755 * set from being evicted by disabling active file page aging. 1756 * 1757 * This uses a different ratio than the anonymous pages, because 1758 * the page cache uses a use-once replacement algorithm. 1759 */ 1760static int inactive_file_is_low(struct zone *zone, struct scan_control *sc) 1761{ 1762 int low; 1763 1764 if (scanning_global_lru(sc)) 1765 low = inactive_file_is_low_global(zone); 1766 else 1767 low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup); 1768 return low; 1769} 1770 1771static int inactive_list_is_low(struct zone *zone, struct scan_control *sc, 1772 int file) 1773{ 1774 if (file) 1775 return inactive_file_is_low(zone, sc); 1776 else 1777 return inactive_anon_is_low(zone, sc); 1778} 1779 1780static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, 1781 struct zone *zone, struct scan_control *sc, int priority) 1782{ 1783 int file = is_file_lru(lru); 1784 1785 if (is_active_lru(lru)) { 1786 if (inactive_list_is_low(zone, sc, file)) 1787 shrink_active_list(nr_to_scan, zone, sc, priority, file); 1788 return 0; 1789 } 1790 1791 return shrink_inactive_list(nr_to_scan, zone, sc, priority, file); 1792} 1793 1794static int vmscan_swappiness(struct scan_control *sc) 1795{ 1796 if (scanning_global_lru(sc)) 1797 return vm_swappiness; 1798 return mem_cgroup_swappiness(sc->mem_cgroup); 1799} 1800 1801/* 1802 * Determine how aggressively the anon and file LRU lists should be 1803 * scanned. The relative value of each set of LRU lists is determined 1804 * by looking at the fraction of the pages scanned we did rotate back 1805 * onto the active list instead of evict. 1806 * 1807 * nr[0] = anon pages to scan; nr[1] = file pages to scan 1808 */ 1809static void get_scan_count(struct zone *zone, struct scan_control *sc, 1810 unsigned long *nr, int priority) 1811{ 1812 unsigned long anon, file, free; 1813 unsigned long anon_prio, file_prio; 1814 unsigned long ap, fp; 1815 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1816 u64 fraction[2], denominator; 1817 enum lru_list l; 1818 int noswap = 0; 1819 bool force_scan = false; 1820 unsigned long nr_force_scan[2]; 1821 1822 /* kswapd does zone balancing and needs to scan this zone */ 1823 if (scanning_global_lru(sc) && current_is_kswapd()) 1824 force_scan = true; 1825 /* memcg may have small limit and need to avoid priority drop */ 1826 if (!scanning_global_lru(sc)) 1827 force_scan = true; 1828 1829 /* If we have no swap space, do not bother scanning anon pages. */ 1830 if (!sc->may_swap || (nr_swap_pages <= 0)) { 1831 noswap = 1; 1832 fraction[0] = 0; 1833 fraction[1] = 1; 1834 denominator = 1; 1835 nr_force_scan[0] = 0; 1836 nr_force_scan[1] = SWAP_CLUSTER_MAX; 1837 goto out; 1838 } 1839 1840 anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) + 1841 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON); 1842 file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) + 1843 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); 1844 1845 if (scanning_global_lru(sc)) { 1846 free = zone_page_state(zone, NR_FREE_PAGES); 1847 /* If we have very few page cache pages, 1848 force-scan anon pages. */ 1849 if (unlikely(file + free <= high_wmark_pages(zone))) { 1850 fraction[0] = 1; 1851 fraction[1] = 0; 1852 denominator = 1; 1853 nr_force_scan[0] = SWAP_CLUSTER_MAX; 1854 nr_force_scan[1] = 0; 1855 goto out; 1856 } 1857 } 1858 1859 /* 1860 * With swappiness at 100, anonymous and file have the same priority. 1861 * This scanning priority is essentially the inverse of IO cost. 1862 */ 1863 anon_prio = vmscan_swappiness(sc); 1864 file_prio = 200 - vmscan_swappiness(sc); 1865 1866 /* 1867 * OK, so we have swap space and a fair amount of page cache 1868 * pages. We use the recently rotated / recently scanned 1869 * ratios to determine how valuable each cache is. 1870 * 1871 * Because workloads change over time (and to avoid overflow) 1872 * we keep these statistics as a floating average, which ends 1873 * up weighing recent references more than old ones. 1874 * 1875 * anon in [0], file in [1] 1876 */ 1877 spin_lock_irq(&zone->lru_lock); 1878 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { 1879 reclaim_stat->recent_scanned[0] /= 2; 1880 reclaim_stat->recent_rotated[0] /= 2; 1881 } 1882 1883 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { 1884 reclaim_stat->recent_scanned[1] /= 2; 1885 reclaim_stat->recent_rotated[1] /= 2; 1886 } 1887 1888 /* 1889 * The amount of pressure on anon vs file pages is inversely 1890 * proportional to the fraction of recently scanned pages on 1891 * each list that were recently referenced and in active use. 1892 */ 1893 ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1); 1894 ap /= reclaim_stat->recent_rotated[0] + 1; 1895 1896 fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1); 1897 fp /= reclaim_stat->recent_rotated[1] + 1; 1898 spin_unlock_irq(&zone->lru_lock); 1899 1900 fraction[0] = ap; 1901 fraction[1] = fp; 1902 denominator = ap + fp + 1; 1903 if (force_scan) { 1904 unsigned long scan = SWAP_CLUSTER_MAX; 1905 nr_force_scan[0] = div64_u64(scan * ap, denominator); 1906 nr_force_scan[1] = div64_u64(scan * fp, denominator); 1907 } 1908out: 1909 for_each_evictable_lru(l) { 1910 int file = is_file_lru(l); 1911 unsigned long scan; 1912 1913 scan = zone_nr_lru_pages(zone, sc, l); 1914 if (priority || noswap) { 1915 scan >>= priority; 1916 scan = div64_u64(scan * fraction[file], denominator); 1917 } 1918 1919 /* 1920 * If zone is small or memcg is small, nr[l] can be 0. 1921 * This results no-scan on this priority and priority drop down. 1922 * For global direct reclaim, it can visit next zone and tend 1923 * not to have problems. For global kswapd, it's for zone 1924 * balancing and it need to scan a small amounts. When using 1925 * memcg, priority drop can cause big latency. So, it's better 1926 * to scan small amount. See may_noscan above. 1927 */ 1928 if (!scan && force_scan) 1929 scan = nr_force_scan[file]; 1930 nr[l] = scan; 1931 } 1932} 1933 1934/* 1935 * Reclaim/compaction depends on a number of pages being freed. To avoid 1936 * disruption to the system, a small number of order-0 pages continue to be 1937 * rotated and reclaimed in the normal fashion. However, by the time we get 1938 * back to the allocator and call try_to_compact_zone(), we ensure that 1939 * there are enough free pages for it to be likely successful 1940 */ 1941static inline bool should_continue_reclaim(struct zone *zone, 1942 unsigned long nr_reclaimed, 1943 unsigned long nr_scanned, 1944 struct scan_control *sc) 1945{ 1946 unsigned long pages_for_compaction; 1947 unsigned long inactive_lru_pages; 1948 1949 /* If not in reclaim/compaction mode, stop */ 1950 if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION)) 1951 return false; 1952 1953 /* Consider stopping depending on scan and reclaim activity */ 1954 if (sc->gfp_mask & __GFP_REPEAT) { 1955 /* 1956 * For __GFP_REPEAT allocations, stop reclaiming if the 1957 * full LRU list has been scanned and we are still failing 1958 * to reclaim pages. This full LRU scan is potentially 1959 * expensive but a __GFP_REPEAT caller really wants to succeed 1960 */ 1961 if (!nr_reclaimed && !nr_scanned) 1962 return false; 1963 } else { 1964 /* 1965 * For non-__GFP_REPEAT allocations which can presumably 1966 * fail without consequence, stop if we failed to reclaim 1967 * any pages from the last SWAP_CLUSTER_MAX number of 1968 * pages that were scanned. This will return to the 1969 * caller faster at the risk reclaim/compaction and 1970 * the resulting allocation attempt fails 1971 */ 1972 if (!nr_reclaimed) 1973 return false; 1974 } 1975 1976 /* 1977 * If we have not reclaimed enough pages for compaction and the 1978 * inactive lists are large enough, continue reclaiming 1979 */ 1980 pages_for_compaction = (2UL << sc->order); 1981 inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON) + 1982 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); 1983 if (sc->nr_reclaimed < pages_for_compaction && 1984 inactive_lru_pages > pages_for_compaction) 1985 return true; 1986 1987 /* If compaction would go ahead or the allocation would succeed, stop */ 1988 switch (compaction_suitable(zone, sc->order)) { 1989 case COMPACT_PARTIAL: 1990 case COMPACT_CONTINUE: 1991 return false; 1992 default: 1993 return true; 1994 } 1995} 1996 1997/* 1998 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 1999 */ 2000static void shrink_zone(int priority, struct zone *zone, 2001 struct scan_control *sc) 2002{ 2003 unsigned long nr[NR_LRU_LISTS]; 2004 unsigned long nr_to_scan; 2005 enum lru_list l; 2006 unsigned long nr_reclaimed, nr_scanned; 2007 unsigned long nr_to_reclaim = sc->nr_to_reclaim; 2008 2009restart: 2010 nr_reclaimed = 0; 2011 nr_scanned = sc->nr_scanned; 2012 get_scan_count(zone, sc, nr, priority); 2013 2014 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || 2015 nr[LRU_INACTIVE_FILE]) { 2016 for_each_evictable_lru(l) { 2017 if (nr[l]) { 2018 nr_to_scan = min_t(unsigned long, 2019 nr[l], SWAP_CLUSTER_MAX); 2020 nr[l] -= nr_to_scan; 2021 2022 nr_reclaimed += shrink_list(l, nr_to_scan, 2023 zone, sc, priority); 2024 } 2025 } 2026 /* 2027 * On large memory systems, scan >> priority can become 2028 * really large. This is fine for the starting priority; 2029 * we want to put equal scanning pressure on each zone. 2030 * However, if the VM has a harder time of freeing pages, 2031 * with multiple processes reclaiming pages, the total 2032 * freeing target can get unreasonably large. 2033 */ 2034 if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY) 2035 break; 2036 } 2037 sc->nr_reclaimed += nr_reclaimed; 2038 2039 /* 2040 * Even if we did not try to evict anon pages at all, we want to 2041 * rebalance the anon lru active/inactive ratio. 2042 */ 2043 if (inactive_anon_is_low(zone, sc)) 2044 shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); 2045 2046 /* reclaim/compaction might need reclaim to continue */ 2047 if (should_continue_reclaim(zone, nr_reclaimed, 2048 sc->nr_scanned - nr_scanned, sc)) 2049 goto restart; 2050 2051 throttle_vm_writeout(sc->gfp_mask); 2052} 2053 2054/* 2055 * This is the direct reclaim path, for page-allocating processes. We only 2056 * try to reclaim pages from zones which will satisfy the caller's allocation 2057 * request. 2058 * 2059 * We reclaim from a zone even if that zone is over high_wmark_pages(zone). 2060 * Because: 2061 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 2062 * allocation or 2063 * b) The target zone may be at high_wmark_pages(zone) but the lower zones 2064 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min' 2065 * zone defense algorithm. 2066 * 2067 * If a zone is deemed to be full of pinned pages then just give it a light 2068 * scan then give up on it. 2069 */ 2070static void shrink_zones(int priority, struct zonelist *zonelist, 2071 struct scan_control *sc) 2072{ 2073 struct zoneref *z; 2074 struct zone *zone; 2075 unsigned long nr_soft_reclaimed; 2076 unsigned long nr_soft_scanned; 2077 2078 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2079 gfp_zone(sc->gfp_mask), sc->nodemask) { 2080 if (!populated_zone(zone)) 2081 continue; 2082 /* 2083 * Take care memory controller reclaiming has small influence 2084 * to global LRU. 2085 */ 2086 if (scanning_global_lru(sc)) { 2087 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2088 continue; 2089 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2090 continue; /* Let kswapd poll it */ 2091 /* 2092 * This steals pages from memory cgroups over softlimit 2093 * and returns the number of reclaimed pages and 2094 * scanned pages. This works for global memory pressure 2095 * and balancing, not for a memcg's limit. 2096 */ 2097 nr_soft_scanned = 0; 2098 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2099 sc->order, sc->gfp_mask, 2100 &nr_soft_scanned); 2101 sc->nr_reclaimed += nr_soft_reclaimed; 2102 sc->nr_scanned += nr_soft_scanned; 2103 /* need some check for avoid more shrink_zone() */ 2104 } 2105 2106 shrink_zone(priority, zone, sc); 2107 } 2108} 2109 2110static bool zone_reclaimable(struct zone *zone) 2111{ 2112 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; 2113} 2114 2115/* All zones in zonelist are unreclaimable? */ 2116static bool all_unreclaimable(struct zonelist *zonelist, 2117 struct scan_control *sc) 2118{ 2119 struct zoneref *z; 2120 struct zone *zone; 2121 2122 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2123 gfp_zone(sc->gfp_mask), sc->nodemask) { 2124 if (!populated_zone(zone)) 2125 continue; 2126 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2127 continue; 2128 if (!zone->all_unreclaimable) 2129 return false; 2130 } 2131 2132 return true; 2133} 2134 2135/* 2136 * This is the main entry point to direct page reclaim. 2137 * 2138 * If a full scan of the inactive list fails to free enough memory then we 2139 * are "out of memory" and something needs to be killed. 2140 * 2141 * If the caller is !__GFP_FS then the probability of a failure is reasonably 2142 * high - the zone may be full of dirty or under-writeback pages, which this 2143 * caller can't do much about. We kick the writeback threads and take explicit 2144 * naps in the hope that some of these pages can be written. But if the 2145 * allocating task holds filesystem locks which prevent writeout this might not 2146 * work, and the allocation attempt will fail. 2147 * 2148 * returns: 0, if no pages reclaimed 2149 * else, the number of pages reclaimed 2150 */ 2151static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 2152 struct scan_control *sc, 2153 struct shrink_control *shrink) 2154{ 2155 int priority; 2156 unsigned long total_scanned = 0; 2157 struct reclaim_state *reclaim_state = current->reclaim_state; 2158 struct zoneref *z; 2159 struct zone *zone; 2160 unsigned long writeback_threshold; 2161 2162 get_mems_allowed(); 2163 delayacct_freepages_start(); 2164 2165 if (scanning_global_lru(sc)) 2166 count_vm_event(ALLOCSTALL); 2167 2168 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 2169 sc->nr_scanned = 0; 2170 if (!priority) 2171 disable_swap_token(sc->mem_cgroup); 2172 shrink_zones(priority, zonelist, sc); 2173 /* 2174 * Don't shrink slabs when reclaiming memory from 2175 * over limit cgroups 2176 */ 2177 if (scanning_global_lru(sc)) { 2178 unsigned long lru_pages = 0; 2179 for_each_zone_zonelist(zone, z, zonelist, 2180 gfp_zone(sc->gfp_mask)) { 2181 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2182 continue; 2183 2184 lru_pages += zone_reclaimable_pages(zone); 2185 } 2186 2187 shrink_slab(shrink, sc->nr_scanned, lru_pages); 2188 if (reclaim_state) { 2189 sc->nr_reclaimed += reclaim_state->reclaimed_slab; 2190 reclaim_state->reclaimed_slab = 0; 2191 } 2192 } 2193 total_scanned += sc->nr_scanned; 2194 if (sc->nr_reclaimed >= sc->nr_to_reclaim) 2195 goto out; 2196 2197 /* 2198 * Try to write back as many pages as we just scanned. This 2199 * tends to cause slow streaming writers to write data to the 2200 * disk smoothly, at the dirtying rate, which is nice. But 2201 * that's undesirable in laptop mode, where we *want* lumpy 2202 * writeout. So in laptop mode, write out the whole world. 2203 */ 2204 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2; 2205 if (total_scanned > writeback_threshold) { 2206 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned); 2207 sc->may_writepage = 1; 2208 } 2209 2210 /* Take a nap, wait for some writeback to complete */ 2211 if (!sc->hibernation_mode && sc->nr_scanned && 2212 priority < DEF_PRIORITY - 2) { 2213 struct zone *preferred_zone; 2214 2215 first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask), 2216 &cpuset_current_mems_allowed, 2217 &preferred_zone); 2218 wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10); 2219 } 2220 } 2221 2222out: 2223 delayacct_freepages_end(); 2224 put_mems_allowed(); 2225 2226 if (sc->nr_reclaimed) 2227 return sc->nr_reclaimed; 2228 2229 /* 2230 * As hibernation is going on, kswapd is freezed so that it can't mark 2231 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable 2232 * check. 2233 */ 2234 if (oom_killer_disabled) 2235 return 0; 2236 2237 /* top priority shrink_zones still had more to do? don't OOM, then */ 2238 if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc)) 2239 return 1; 2240 2241 return 0; 2242} 2243 2244unsigned long try_to_free_pages(struct zonelist *zonelist, int order, 2245 gfp_t gfp_mask, nodemask_t *nodemask) 2246{ 2247 unsigned long nr_reclaimed; 2248 struct scan_control sc = { 2249 .gfp_mask = gfp_mask, 2250 .may_writepage = !laptop_mode, 2251 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2252 .may_unmap = 1, 2253 .may_swap = 1, 2254 .order = order, 2255 .mem_cgroup = NULL, 2256 .nodemask = nodemask, 2257 }; 2258 struct shrink_control shrink = { 2259 .gfp_mask = sc.gfp_mask, 2260 }; 2261 2262 trace_mm_vmscan_direct_reclaim_begin(order, 2263 sc.may_writepage, 2264 gfp_mask); 2265 2266 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2267 2268 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); 2269 2270 return nr_reclaimed; 2271} 2272 2273#ifdef CONFIG_CGROUP_MEM_RES_CTLR 2274 2275unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem, 2276 gfp_t gfp_mask, bool noswap, 2277 struct zone *zone, 2278 unsigned long *nr_scanned) 2279{ 2280 struct scan_control sc = { 2281 .nr_scanned = 0, 2282 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2283 .may_writepage = !laptop_mode, 2284 .may_unmap = 1, 2285 .may_swap = !noswap, 2286 .order = 0, 2287 .mem_cgroup = mem, 2288 }; 2289 2290 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2291 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); 2292 2293 trace_mm_vmscan_memcg_softlimit_reclaim_begin(0, 2294 sc.may_writepage, 2295 sc.gfp_mask); 2296 2297 /* 2298 * NOTE: Although we can get the priority field, using it 2299 * here is not a good idea, since it limits the pages we can scan. 2300 * if we don't reclaim here, the shrink_zone from balance_pgdat 2301 * will pick up pages from other mem cgroup's as well. We hack 2302 * the priority and make it zero. 2303 */ 2304 shrink_zone(0, zone, &sc); 2305 2306 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); 2307 2308 *nr_scanned = sc.nr_scanned; 2309 return sc.nr_reclaimed; 2310} 2311 2312unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, 2313 gfp_t gfp_mask, 2314 bool noswap) 2315{ 2316 struct zonelist *zonelist; 2317 unsigned long nr_reclaimed; 2318 int nid; 2319 struct scan_control sc = { 2320 .may_writepage = !laptop_mode, 2321 .may_unmap = 1, 2322 .may_swap = !noswap, 2323 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2324 .order = 0, 2325 .mem_cgroup = mem_cont, 2326 .nodemask = NULL, /* we don't care the placement */ 2327 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2328 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), 2329 }; 2330 struct shrink_control shrink = { 2331 .gfp_mask = sc.gfp_mask, 2332 }; 2333 2334 /* 2335 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't 2336 * take care of from where we get pages. So the node where we start the 2337 * scan does not need to be the current node. 2338 */ 2339 nid = mem_cgroup_select_victim_node(mem_cont); 2340 2341 zonelist = NODE_DATA(nid)->node_zonelists; 2342 2343 trace_mm_vmscan_memcg_reclaim_begin(0, 2344 sc.may_writepage, 2345 sc.gfp_mask); 2346 2347 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2348 2349 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); 2350 2351 return nr_reclaimed; 2352} 2353#endif 2354 2355/* 2356 * pgdat_balanced is used when checking if a node is balanced for high-order 2357 * allocations. Only zones that meet watermarks and are in a zone allowed 2358 * by the callers classzone_idx are added to balanced_pages. The total of 2359 * balanced pages must be at least 25% of the zones allowed by classzone_idx 2360 * for the node to be considered balanced. Forcing all zones to be balanced 2361 * for high orders can cause excessive reclaim when there are imbalanced zones. 2362 * The choice of 25% is due to 2363 * o a 16M DMA zone that is balanced will not balance a zone on any 2364 * reasonable sized machine 2365 * o On all other machines, the top zone must be at least a reasonable 2366 * percentage of the middle zones. For example, on 32-bit x86, highmem 2367 * would need to be at least 256M for it to be balance a whole node. 2368 * Similarly, on x86-64 the Normal zone would need to be at least 1G 2369 * to balance a node on its own. These seemed like reasonable ratios. 2370 */ 2371static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages, 2372 int classzone_idx) 2373{ 2374 unsigned long present_pages = 0; 2375 int i; 2376 2377 for (i = 0; i <= classzone_idx; i++) 2378 present_pages += pgdat->node_zones[i].present_pages; 2379 2380 /* A special case here: if zone has no page, we think it's balanced */ 2381 return balanced_pages >= (present_pages >> 2); 2382} 2383 2384/* is kswapd sleeping prematurely? */ 2385static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, 2386 int classzone_idx) 2387{ 2388 int i; 2389 unsigned long balanced = 0; 2390 bool all_zones_ok = true; 2391 2392 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ 2393 if (remaining) 2394 return true; 2395 2396 /* Check the watermark levels */ 2397 for (i = 0; i <= classzone_idx; i++) { 2398 struct zone *zone = pgdat->node_zones + i; 2399 2400 if (!populated_zone(zone)) 2401 continue; 2402 2403 /* 2404 * balance_pgdat() skips over all_unreclaimable after 2405 * DEF_PRIORITY. Effectively, it considers them balanced so 2406 * they must be considered balanced here as well if kswapd 2407 * is to sleep 2408 */ 2409 if (zone->all_unreclaimable) { 2410 balanced += zone->present_pages; 2411 continue; 2412 } 2413 2414 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone), 2415 i, 0)) 2416 all_zones_ok = false; 2417 else 2418 balanced += zone->present_pages; 2419 } 2420 2421 /* 2422 * For high-order requests, the balanced zones must contain at least 2423 * 25% of the nodes pages for kswapd to sleep. For order-0, all zones 2424 * must be balanced 2425 */ 2426 if (order) 2427 return !pgdat_balanced(pgdat, balanced, classzone_idx); 2428 else 2429 return !all_zones_ok; 2430} 2431 2432/* 2433 * For kswapd, balance_pgdat() will work across all this node's zones until 2434 * they are all at high_wmark_pages(zone). 2435 * 2436 * Returns the final order kswapd was reclaiming at 2437 * 2438 * There is special handling here for zones which are full of pinned pages. 2439 * This can happen if the pages are all mlocked, or if they are all used by 2440 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 2441 * What we do is to detect the case where all pages in the zone have been 2442 * scanned twice and there has been zero successful reclaim. Mark the zone as 2443 * dead and from now on, only perform a short scan. Basically we're polling 2444 * the zone for when the problem goes away. 2445 * 2446 * kswapd scans the zones in the highmem->normal->dma direction. It skips 2447 * zones which have free_pages > high_wmark_pages(zone), but once a zone is 2448 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the 2449 * lower zones regardless of the number of free pages in the lower zones. This 2450 * interoperates with the page allocator fallback scheme to ensure that aging 2451 * of pages is balanced across the zones. 2452 */ 2453static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 2454 int *classzone_idx) 2455{ 2456 int all_zones_ok; 2457 unsigned long balanced; 2458 int priority; 2459 int i; 2460 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 2461 unsigned long total_scanned; 2462 struct reclaim_state *reclaim_state = current->reclaim_state; 2463 unsigned long nr_soft_reclaimed; 2464 unsigned long nr_soft_scanned; 2465 struct scan_control sc = { 2466 .gfp_mask = GFP_KERNEL, 2467 .may_unmap = 1, 2468 .may_swap = 1, 2469 /* 2470 * kswapd doesn't want to be bailed out while reclaim. because 2471 * we want to put equal scanning pressure on each zone. 2472 */ 2473 .nr_to_reclaim = ULONG_MAX, 2474 .order = order, 2475 .mem_cgroup = NULL, 2476 }; 2477 struct shrink_control shrink = { 2478 .gfp_mask = sc.gfp_mask, 2479 }; 2480loop_again: 2481 total_scanned = 0; 2482 sc.nr_reclaimed = 0; 2483 sc.may_writepage = !laptop_mode; 2484 count_vm_event(PAGEOUTRUN); 2485 2486 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 2487 unsigned long lru_pages = 0; 2488 int has_under_min_watermark_zone = 0; 2489 2490 /* The swap token gets in the way of swapout... */ 2491 if (!priority) 2492 disable_swap_token(NULL); 2493 2494 all_zones_ok = 1; 2495 balanced = 0; 2496 2497 /* 2498 * Scan in the highmem->dma direction for the highest 2499 * zone which needs scanning 2500 */ 2501 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 2502 struct zone *zone = pgdat->node_zones + i; 2503 2504 if (!populated_zone(zone)) 2505 continue; 2506 2507 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2508 continue; 2509 2510 /* 2511 * Do some background aging of the anon list, to give 2512 * pages a chance to be referenced before reclaiming. 2513 */ 2514 if (inactive_anon_is_low(zone, &sc)) 2515 shrink_active_list(SWAP_CLUSTER_MAX, zone, 2516 &sc, priority, 0); 2517 2518 if (!zone_watermark_ok_safe(zone, order, 2519 high_wmark_pages(zone), 0, 0)) { 2520 end_zone = i; 2521 break; 2522 } else { 2523 /* If balanced, clear the congested flag */ 2524 zone_clear_flag(zone, ZONE_CONGESTED); 2525 } 2526 } 2527 if (i < 0) 2528 goto out; 2529 2530 for (i = 0; i <= end_zone; i++) { 2531 struct zone *zone = pgdat->node_zones + i; 2532 2533 lru_pages += zone_reclaimable_pages(zone); 2534 } 2535 2536 /* 2537 * Now scan the zone in the dma->highmem direction, stopping 2538 * at the last zone which needs scanning. 2539 * 2540 * We do this because the page allocator works in the opposite 2541 * direction. This prevents the page allocator from allocating 2542 * pages behind kswapd's direction of progress, which would 2543 * cause too much scanning of the lower zones. 2544 */ 2545 for (i = 0; i <= end_zone; i++) { 2546 struct zone *zone = pgdat->node_zones + i; 2547 int nr_slab; 2548 unsigned long balance_gap; 2549 2550 if (!populated_zone(zone)) 2551 continue; 2552 2553 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2554 continue; 2555 2556 sc.nr_scanned = 0; 2557 2558 nr_soft_scanned = 0; 2559 /* 2560 * Call soft limit reclaim before calling shrink_zone. 2561 */ 2562 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2563 order, sc.gfp_mask, 2564 &nr_soft_scanned); 2565 sc.nr_reclaimed += nr_soft_reclaimed; 2566 total_scanned += nr_soft_scanned; 2567 2568 /* 2569 * We put equal pressure on every zone, unless 2570 * one zone has way too many pages free 2571 * already. The "too many pages" is defined 2572 * as the high wmark plus a "gap" where the 2573 * gap is either the low watermark or 1% 2574 * of the zone, whichever is smaller. 2575 */ 2576 balance_gap = min(low_wmark_pages(zone), 2577 (zone->present_pages + 2578 KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / 2579 KSWAPD_ZONE_BALANCE_GAP_RATIO); 2580 if (!zone_watermark_ok_safe(zone, order, 2581 high_wmark_pages(zone) + balance_gap, 2582 end_zone, 0)) { 2583 shrink_zone(priority, zone, &sc); 2584 2585 reclaim_state->reclaimed_slab = 0; 2586 nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages); 2587 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 2588 total_scanned += sc.nr_scanned; 2589 2590 if (nr_slab == 0 && !zone_reclaimable(zone)) 2591 zone->all_unreclaimable = 1; 2592 } 2593 2594 /* 2595 * If we've done a decent amount of scanning and 2596 * the reclaim ratio is low, start doing writepage 2597 * even in laptop mode 2598 */ 2599 if (total_scanned > SWAP_CLUSTER_MAX * 2 && 2600 total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2) 2601 sc.may_writepage = 1; 2602 2603 if (zone->all_unreclaimable) { 2604 if (end_zone && end_zone == i) 2605 end_zone--; 2606 continue; 2607 } 2608 2609 if (!zone_watermark_ok_safe(zone, order, 2610 high_wmark_pages(zone), end_zone, 0)) { 2611 all_zones_ok = 0; 2612 /* 2613 * We are still under min water mark. This 2614 * means that we have a GFP_ATOMIC allocation 2615 * failure risk. Hurry up! 2616 */ 2617 if (!zone_watermark_ok_safe(zone, order, 2618 min_wmark_pages(zone), end_zone, 0)) 2619 has_under_min_watermark_zone = 1; 2620 } else { 2621 /* 2622 * If a zone reaches its high watermark, 2623 * consider it to be no longer congested. It's 2624 * possible there are dirty pages backed by 2625 * congested BDIs but as pressure is relieved, 2626 * spectulatively avoid congestion waits 2627 */ 2628 zone_clear_flag(zone, ZONE_CONGESTED); 2629 if (i <= *classzone_idx) 2630 balanced += zone->present_pages; 2631 } 2632 2633 } 2634 if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx))) 2635 break; /* kswapd: all done */ 2636 /* 2637 * OK, kswapd is getting into trouble. Take a nap, then take 2638 * another pass across the zones. 2639 */ 2640 if (total_scanned && (priority < DEF_PRIORITY - 2)) { 2641 if (has_under_min_watermark_zone) 2642 count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT); 2643 else 2644 congestion_wait(BLK_RW_ASYNC, HZ/10); 2645 } 2646 2647 /* 2648 * We do this so kswapd doesn't build up large priorities for 2649 * example when it is freeing in parallel with allocators. It 2650 * matches the direct reclaim path behaviour in terms of impact 2651 * on zone->*_priority. 2652 */ 2653 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) 2654 break; 2655 } 2656out: 2657 2658 /* 2659 * order-0: All zones must meet high watermark for a balanced node 2660 * high-order: Balanced zones must make up at least 25% of the node 2661 * for the node to be balanced 2662 */ 2663 if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) { 2664 cond_resched(); 2665 2666 try_to_freeze(); 2667 2668 /* 2669 * Fragmentation may mean that the system cannot be 2670 * rebalanced for high-order allocations in all zones. 2671 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX, 2672 * it means the zones have been fully scanned and are still 2673 * not balanced. For high-order allocations, there is 2674 * little point trying all over again as kswapd may 2675 * infinite loop. 2676 * 2677 * Instead, recheck all watermarks at order-0 as they 2678 * are the most important. If watermarks are ok, kswapd will go 2679 * back to sleep. High-order users can still perform direct 2680 * reclaim if they wish. 2681 */ 2682 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX) 2683 order = sc.order = 0; 2684 2685 goto loop_again; 2686 } 2687 2688 /* 2689 * If kswapd was reclaiming at a higher order, it has the option of 2690 * sleeping without all zones being balanced. Before it does, it must 2691 * ensure that the watermarks for order-0 on *all* zones are met and 2692 * that the congestion flags are cleared. The congestion flag must 2693 * be cleared as kswapd is the only mechanism that clears the flag 2694 * and it is potentially going to sleep here. 2695 */ 2696 if (order) { 2697 for (i = 0; i <= end_zone; i++) { 2698 struct zone *zone = pgdat->node_zones + i; 2699 2700 if (!populated_zone(zone)) 2701 continue; 2702 2703 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2704 continue; 2705 2706 /* Confirm the zone is balanced for order-0 */ 2707 if (!zone_watermark_ok(zone, 0, 2708 high_wmark_pages(zone), 0, 0)) { 2709 order = sc.order = 0; 2710 goto loop_again; 2711 } 2712 2713 /* If balanced, clear the congested flag */ 2714 zone_clear_flag(zone, ZONE_CONGESTED); 2715 } 2716 } 2717 2718 /* 2719 * Return the order we were reclaiming at so sleeping_prematurely() 2720 * makes a decision on the order we were last reclaiming at. However, 2721 * if another caller entered the allocator slow path while kswapd 2722 * was awake, order will remain at the higher level 2723 */ 2724 *classzone_idx = end_zone; 2725 return order; 2726} 2727 2728static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx) 2729{ 2730 long remaining = 0; 2731 DEFINE_WAIT(wait); 2732 2733 if (freezing(current) || kthread_should_stop()) 2734 return; 2735 2736 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 2737 2738 /* Try to sleep for a short interval */ 2739 if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { 2740 remaining = schedule_timeout(HZ/10); 2741 finish_wait(&pgdat->kswapd_wait, &wait); 2742 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 2743 } 2744 2745 /* 2746 * After a short sleep, check if it was a premature sleep. If not, then 2747 * go fully to sleep until explicitly woken up. 2748 */ 2749 if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { 2750 trace_mm_vmscan_kswapd_sleep(pgdat->node_id); 2751 2752 /* 2753 * vmstat counters are not perfectly accurate and the estimated 2754 * value for counters such as NR_FREE_PAGES can deviate from the 2755 * true value by nr_online_cpus * threshold. To avoid the zone 2756 * watermarks being breached while under pressure, we reduce the 2757 * per-cpu vmstat threshold while kswapd is awake and restore 2758 * them before going back to sleep. 2759 */ 2760 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); 2761 schedule(); 2762 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); 2763 } else { 2764 if (remaining) 2765 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); 2766 else 2767 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); 2768 } 2769 finish_wait(&pgdat->kswapd_wait, &wait); 2770} 2771 2772/* 2773 * The background pageout daemon, started as a kernel thread 2774 * from the init process. 2775 * 2776 * This basically trickles out pages so that we have _some_ 2777 * free memory available even if there is no other activity 2778 * that frees anything up. This is needed for things like routing 2779 * etc, where we otherwise might have all activity going on in 2780 * asynchronous contexts that cannot page things out. 2781 * 2782 * If there are applications that are active memory-allocators 2783 * (most normal use), this basically shouldn't matter. 2784 */ 2785static int kswapd(void *p) 2786{ 2787 unsigned long order, new_order; 2788 int classzone_idx, new_classzone_idx; 2789 pg_data_t *pgdat = (pg_data_t*)p; 2790 struct task_struct *tsk = current; 2791 2792 struct reclaim_state reclaim_state = { 2793 .reclaimed_slab = 0, 2794 }; 2795 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); 2796 2797 lockdep_set_current_reclaim_state(GFP_KERNEL); 2798 2799 if (!cpumask_empty(cpumask)) 2800 set_cpus_allowed_ptr(tsk, cpumask); 2801 current->reclaim_state = &reclaim_state; 2802 2803 /* 2804 * Tell the memory management that we're a "memory allocator", 2805 * and that if we need more memory we should get access to it 2806 * regardless (see "__alloc_pages()"). "kswapd" should 2807 * never get caught in the normal page freeing logic. 2808 * 2809 * (Kswapd normally doesn't need memory anyway, but sometimes 2810 * you need a small amount of memory in order to be able to 2811 * page out something else, and this flag essentially protects 2812 * us from recursively trying to free more memory as we're 2813 * trying to free the first piece of memory in the first place). 2814 */ 2815 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; 2816 set_freezable(); 2817 2818 order = new_order = 0; 2819 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1; 2820 for ( ; ; ) { 2821 int ret; 2822 2823 /* 2824 * If the last balance_pgdat was unsuccessful it's unlikely a 2825 * new request of a similar or harder type will succeed soon 2826 * so consider going to sleep on the basis we reclaimed at 2827 */ 2828 if (classzone_idx >= new_classzone_idx && order == new_order) { 2829 new_order = pgdat->kswapd_max_order; 2830 new_classzone_idx = pgdat->classzone_idx; 2831 pgdat->kswapd_max_order = 0; 2832 pgdat->classzone_idx = pgdat->nr_zones - 1; 2833 } 2834 2835 if (order < new_order || classzone_idx > new_classzone_idx) { 2836 /* 2837 * Don't sleep if someone wants a larger 'order' 2838 * allocation or has tigher zone constraints 2839 */ 2840 order = new_order; 2841 classzone_idx = new_classzone_idx; 2842 } else { 2843 kswapd_try_to_sleep(pgdat, order, classzone_idx); 2844 order = pgdat->kswapd_max_order; 2845 classzone_idx = pgdat->classzone_idx; 2846 pgdat->kswapd_max_order = 0; 2847 pgdat->classzone_idx = pgdat->nr_zones - 1; 2848 } 2849 2850 ret = try_to_freeze(); 2851 if (kthread_should_stop()) 2852 break; 2853 2854 /* 2855 * We can speed up thawing tasks if we don't call balance_pgdat 2856 * after returning from the refrigerator 2857 */ 2858 if (!ret) { 2859 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order); 2860 order = balance_pgdat(pgdat, order, &classzone_idx); 2861 } 2862 } 2863 return 0; 2864} 2865 2866/* 2867 * A zone is low on free memory, so wake its kswapd task to service it. 2868 */ 2869void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) 2870{ 2871 pg_data_t *pgdat; 2872 2873 if (!populated_zone(zone)) 2874 return; 2875 2876 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2877 return; 2878 pgdat = zone->zone_pgdat; 2879 if (pgdat->kswapd_max_order < order) { 2880 pgdat->kswapd_max_order = order; 2881 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx); 2882 } 2883 if (!waitqueue_active(&pgdat->kswapd_wait)) 2884 return; 2885 if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) 2886 return; 2887 2888 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); 2889 wake_up_interruptible(&pgdat->kswapd_wait); 2890} 2891 2892/* 2893 * The reclaimable count would be mostly accurate. 2894 * The less reclaimable pages may be 2895 * - mlocked pages, which will be moved to unevictable list when encountered 2896 * - mapped pages, which may require several travels to be reclaimed 2897 * - dirty pages, which is not "instantly" reclaimable 2898 */ 2899unsigned long global_reclaimable_pages(void) 2900{ 2901 int nr; 2902 2903 nr = global_page_state(NR_ACTIVE_FILE) + 2904 global_page_state(NR_INACTIVE_FILE); 2905 2906 if (nr_swap_pages > 0) 2907 nr += global_page_state(NR_ACTIVE_ANON) + 2908 global_page_state(NR_INACTIVE_ANON); 2909 2910 return nr; 2911} 2912 2913unsigned long zone_reclaimable_pages(struct zone *zone) 2914{ 2915 int nr; 2916 2917 nr = zone_page_state(zone, NR_ACTIVE_FILE) + 2918 zone_page_state(zone, NR_INACTIVE_FILE); 2919 2920 if (nr_swap_pages > 0) 2921 nr += zone_page_state(zone, NR_ACTIVE_ANON) + 2922 zone_page_state(zone, NR_INACTIVE_ANON); 2923 2924 return nr; 2925} 2926 2927#ifdef CONFIG_HIBERNATION 2928/* 2929 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of 2930 * freed pages. 2931 * 2932 * Rather than trying to age LRUs the aim is to preserve the overall 2933 * LRU order by reclaiming preferentially 2934 * inactive > active > active referenced > active mapped 2935 */ 2936unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 2937{ 2938 struct reclaim_state reclaim_state; 2939 struct scan_control sc = { 2940 .gfp_mask = GFP_HIGHUSER_MOVABLE, 2941 .may_swap = 1, 2942 .may_unmap = 1, 2943 .may_writepage = 1, 2944 .nr_to_reclaim = nr_to_reclaim, 2945 .hibernation_mode = 1, 2946 .order = 0, 2947 }; 2948 struct shrink_control shrink = { 2949 .gfp_mask = sc.gfp_mask, 2950 }; 2951 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); 2952 struct task_struct *p = current; 2953 unsigned long nr_reclaimed; 2954 2955 p->flags |= PF_MEMALLOC; 2956 lockdep_set_current_reclaim_state(sc.gfp_mask); 2957 reclaim_state.reclaimed_slab = 0; 2958 p->reclaim_state = &reclaim_state; 2959 2960 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2961 2962 p->reclaim_state = NULL; 2963 lockdep_clear_current_reclaim_state(); 2964 p->flags &= ~PF_MEMALLOC; 2965 2966 return nr_reclaimed; 2967} 2968#endif /* CONFIG_HIBERNATION */ 2969 2970/* It's optimal to keep kswapds on the same CPUs as their memory, but 2971 not required for correctness. So if the last cpu in a node goes 2972 away, we get changed to run anywhere: as the first one comes back, 2973 restore their cpu bindings. */ 2974static int __devinit cpu_callback(struct notifier_block *nfb, 2975 unsigned long action, void *hcpu) 2976{ 2977 int nid; 2978 2979 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { 2980 for_each_node_state(nid, N_HIGH_MEMORY) { 2981 pg_data_t *pgdat = NODE_DATA(nid); 2982 const struct cpumask *mask; 2983 2984 mask = cpumask_of_node(pgdat->node_id); 2985 2986 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) 2987 /* One of our CPUs online: restore mask */ 2988 set_cpus_allowed_ptr(pgdat->kswapd, mask); 2989 } 2990 } 2991 return NOTIFY_OK; 2992} 2993 2994/* 2995 * This kswapd start function will be called by init and node-hot-add. 2996 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. 2997 */ 2998int kswapd_run(int nid) 2999{ 3000 pg_data_t *pgdat = NODE_DATA(nid); 3001 int ret = 0; 3002 3003 if (pgdat->kswapd) 3004 return 0; 3005 3006 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); 3007 if (IS_ERR(pgdat->kswapd)) { 3008 /* failure at boot is fatal */ 3009 BUG_ON(system_state == SYSTEM_BOOTING); 3010 printk("Failed to start kswapd on node %d\n",nid); 3011 ret = -1; 3012 } 3013 return ret; 3014} 3015 3016/* 3017 * Called by memory hotplug when all memory in a node is offlined. 3018 */ 3019void kswapd_stop(int nid) 3020{ 3021 struct task_struct *kswapd = NODE_DATA(nid)->kswapd; 3022 3023 if (kswapd) 3024 kthread_stop(kswapd); 3025} 3026 3027static int __init kswapd_init(void) 3028{ 3029 int nid; 3030 3031 swap_setup(); 3032 for_each_node_state(nid, N_HIGH_MEMORY) 3033 kswapd_run(nid); 3034 hotcpu_notifier(cpu_callback, 0); 3035 return 0; 3036} 3037 3038module_init(kswapd_init) 3039 3040#ifdef CONFIG_NUMA 3041/* 3042 * Zone reclaim mode 3043 * 3044 * If non-zero call zone_reclaim when the number of free pages falls below 3045 * the watermarks. 3046 */ 3047int zone_reclaim_mode __read_mostly; 3048 3049#define RECLAIM_OFF 0 3050#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ 3051#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ 3052#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ 3053 3054/* 3055 * Priority for ZONE_RECLAIM. This determines the fraction of pages 3056 * of a node considered for each zone_reclaim. 4 scans 1/16th of 3057 * a zone. 3058 */ 3059#define ZONE_RECLAIM_PRIORITY 4 3060 3061/* 3062 * Percentage of pages in a zone that must be unmapped for zone_reclaim to 3063 * occur. 3064 */ 3065int sysctl_min_unmapped_ratio = 1; 3066 3067/* 3068 * If the number of slab pages in a zone grows beyond this percentage then 3069 * slab reclaim needs to occur. 3070 */ 3071int sysctl_min_slab_ratio = 5; 3072 3073static inline unsigned long zone_unmapped_file_pages(struct zone *zone) 3074{ 3075 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED); 3076 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) + 3077 zone_page_state(zone, NR_ACTIVE_FILE); 3078 3079 /* 3080 * It's possible for there to be more file mapped pages than 3081 * accounted for by the pages on the file LRU lists because 3082 * tmpfs pages accounted for as ANON can also be FILE_MAPPED 3083 */ 3084 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; 3085} 3086 3087/* Work out how many page cache pages we can reclaim in this reclaim_mode */ 3088static long zone_pagecache_reclaimable(struct zone *zone) 3089{ 3090 long nr_pagecache_reclaimable; 3091 long delta = 0; 3092 3093 /* 3094 * If RECLAIM_SWAP is set, then all file pages are considered 3095 * potentially reclaimable. Otherwise, we have to worry about 3096 * pages like swapcache and zone_unmapped_file_pages() provides 3097 * a better estimate 3098 */ 3099 if (zone_reclaim_mode & RECLAIM_SWAP) 3100 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); 3101 else 3102 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone); 3103 3104 /* If we can't clean pages, remove dirty pages from consideration */ 3105 if (!(zone_reclaim_mode & RECLAIM_WRITE)) 3106 delta += zone_page_state(zone, NR_FILE_DIRTY); 3107 3108 /* Watch for any possible underflows due to delta */ 3109 if (unlikely(delta > nr_pagecache_reclaimable)) 3110 delta = nr_pagecache_reclaimable; 3111 3112 return nr_pagecache_reclaimable - delta; 3113} 3114 3115/* 3116 * Try to free up some pages from this zone through reclaim. 3117 */ 3118static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3119{ 3120 /* Minimum pages needed in order to stay on node */ 3121 const unsigned long nr_pages = 1 << order; 3122 struct task_struct *p = current; 3123 struct reclaim_state reclaim_state; 3124 int priority; 3125 struct scan_control sc = { 3126 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), 3127 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP), 3128 .may_swap = 1, 3129 .nr_to_reclaim = max_t(unsigned long, nr_pages, 3130 SWAP_CLUSTER_MAX), 3131 .gfp_mask = gfp_mask, 3132 .order = order, 3133 }; 3134 struct shrink_control shrink = { 3135 .gfp_mask = sc.gfp_mask, 3136 }; 3137 unsigned long nr_slab_pages0, nr_slab_pages1; 3138 3139 cond_resched(); 3140 /* 3141 * We need to be able to allocate from the reserves for RECLAIM_SWAP 3142 * and we also need to be able to write out pages for RECLAIM_WRITE 3143 * and RECLAIM_SWAP. 3144 */ 3145 p->flags |= PF_MEMALLOC | PF_SWAPWRITE; 3146 lockdep_set_current_reclaim_state(gfp_mask); 3147 reclaim_state.reclaimed_slab = 0; 3148 p->reclaim_state = &reclaim_state; 3149 3150 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) { 3151 /* 3152 * Free memory by calling shrink zone with increasing 3153 * priorities until we have enough memory freed. 3154 */ 3155 priority = ZONE_RECLAIM_PRIORITY; 3156 do { 3157 shrink_zone(priority, zone, &sc); 3158 priority--; 3159 } while (priority >= 0 && sc.nr_reclaimed < nr_pages); 3160 } 3161 3162 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3163 if (nr_slab_pages0 > zone->min_slab_pages) { 3164 /* 3165 * shrink_slab() does not currently allow us to determine how 3166 * many pages were freed in this zone. So we take the current 3167 * number of slab pages and shake the slab until it is reduced 3168 * by the same nr_pages that we used for reclaiming unmapped 3169 * pages. 3170 * 3171 * Note that shrink_slab will free memory on all zones and may 3172 * take a long time. 3173 */ 3174 for (;;) { 3175 unsigned long lru_pages = zone_reclaimable_pages(zone); 3176 3177 /* No reclaimable slab or very low memory pressure */ 3178 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages)) 3179 break; 3180 3181 /* Freed enough memory */ 3182 nr_slab_pages1 = zone_page_state(zone, 3183 NR_SLAB_RECLAIMABLE); 3184 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0) 3185 break; 3186 } 3187 3188 /* 3189 * Update nr_reclaimed by the number of slab pages we 3190 * reclaimed from this zone. 3191 */ 3192 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3193 if (nr_slab_pages1 < nr_slab_pages0) 3194 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1; 3195 } 3196 3197 p->reclaim_state = NULL; 3198 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); 3199 lockdep_clear_current_reclaim_state(); 3200 return sc.nr_reclaimed >= nr_pages; 3201} 3202 3203int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3204{ 3205 int node_id; 3206 int ret; 3207 3208 /* 3209 * Zone reclaim reclaims unmapped file backed pages and 3210 * slab pages if we are over the defined limits. 3211 * 3212 * A small portion of unmapped file backed pages is needed for 3213 * file I/O otherwise pages read by file I/O will be immediately 3214 * thrown out if the zone is overallocated. So we do not reclaim 3215 * if less than a specified percentage of the zone is used by 3216 * unmapped file backed pages. 3217 */ 3218 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages && 3219 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) 3220 return ZONE_RECLAIM_FULL; 3221 3222 if (zone->all_unreclaimable) 3223 return ZONE_RECLAIM_FULL; 3224 3225 /* 3226 * Do not scan if the allocation should not be delayed. 3227 */ 3228 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) 3229 return ZONE_RECLAIM_NOSCAN; 3230 3231 /* 3232 * Only run zone reclaim on the local zone or on zones that do not 3233 * have associated processors. This will favor the local processor 3234 * over remote processors and spread off node memory allocations 3235 * as wide as possible. 3236 */ 3237 node_id = zone_to_nid(zone); 3238 if (node_state(node_id, N_CPU) && node_id != numa_node_id()) 3239 return ZONE_RECLAIM_NOSCAN; 3240 3241 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) 3242 return ZONE_RECLAIM_NOSCAN; 3243 3244 ret = __zone_reclaim(zone, gfp_mask, order); 3245 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); 3246 3247 if (!ret) 3248 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED); 3249 3250 return ret; 3251} 3252#endif 3253 3254/* 3255 * page_evictable - test whether a page is evictable 3256 * @page: the page to test 3257 * @vma: the VMA in which the page is or will be mapped, may be NULL 3258 * 3259 * Test whether page is evictable--i.e., should be placed on active/inactive 3260 * lists vs unevictable list. The vma argument is !NULL when called from the 3261 * fault path to determine how to instantate a new page. 3262 * 3263 * Reasons page might not be evictable: 3264 * (1) page's mapping marked unevictable 3265 * (2) page is part of an mlocked VMA 3266 * 3267 */ 3268int page_evictable(struct page *page, struct vm_area_struct *vma) 3269{ 3270 3271 if (mapping_unevictable(page_mapping(page))) 3272 return 0; 3273 3274 if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page))) 3275 return 0; 3276 3277 return 1; 3278} 3279 3280/** 3281 * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list 3282 * @page: page to check evictability and move to appropriate lru list 3283 * @zone: zone page is in 3284 * 3285 * Checks a page for evictability and moves the page to the appropriate 3286 * zone lru list. 3287 * 3288 * Restrictions: zone->lru_lock must be held, page must be on LRU and must 3289 * have PageUnevictable set. 3290 */ 3291static void check_move_unevictable_page(struct page *page, struct zone *zone) 3292{ 3293 VM_BUG_ON(PageActive(page)); 3294 3295retry: 3296 ClearPageUnevictable(page); 3297 if (page_evictable(page, NULL)) { 3298 enum lru_list l = page_lru_base_type(page); 3299 3300 __dec_zone_state(zone, NR_UNEVICTABLE); 3301 list_move(&page->lru, &zone->lru[l].list); 3302 mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l); 3303 __inc_zone_state(zone, NR_INACTIVE_ANON + l); 3304 __count_vm_event(UNEVICTABLE_PGRESCUED); 3305 } else { 3306 /* 3307 * rotate unevictable list 3308 */ 3309 SetPageUnevictable(page); 3310 list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list); 3311 mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE); 3312 if (page_evictable(page, NULL)) 3313 goto retry; 3314 } 3315} 3316 3317/** 3318 * scan_mapping_unevictable_pages - scan an address space for evictable pages 3319 * @mapping: struct address_space to scan for evictable pages 3320 * 3321 * Scan all pages in mapping. Check unevictable pages for 3322 * evictability and move them to the appropriate zone lru list. 3323 */ 3324void scan_mapping_unevictable_pages(struct address_space *mapping) 3325{ 3326 pgoff_t next = 0; 3327 pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >> 3328 PAGE_CACHE_SHIFT; 3329 struct zone *zone; 3330 struct pagevec pvec; 3331 3332 if (mapping->nrpages == 0) 3333 return; 3334 3335 pagevec_init(&pvec, 0); 3336 while (next < end && 3337 pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) { 3338 int i; 3339 int pg_scanned = 0; 3340 3341 zone = NULL; 3342 3343 for (i = 0; i < pagevec_count(&pvec); i++) { 3344 struct page *page = pvec.pages[i]; 3345 pgoff_t page_index = page->index; 3346 struct zone *pagezone = page_zone(page); 3347 3348 pg_scanned++; 3349 if (page_index > next) 3350 next = page_index; 3351 next++; 3352 3353 if (pagezone != zone) { 3354 if (zone) 3355 spin_unlock_irq(&zone->lru_lock); 3356 zone = pagezone; 3357 spin_lock_irq(&zone->lru_lock); 3358 } 3359 3360 if (PageLRU(page) && PageUnevictable(page)) 3361 check_move_unevictable_page(page, zone); 3362 } 3363 if (zone) 3364 spin_unlock_irq(&zone->lru_lock); 3365 pagevec_release(&pvec); 3366 3367 count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned); 3368 } 3369 3370} 3371 3372/** 3373 * scan_zone_unevictable_pages - check unevictable list for evictable pages 3374 * @zone - zone of which to scan the unevictable list 3375 * 3376 * Scan @zone's unevictable LRU lists to check for pages that have become 3377 * evictable. Move those that have to @zone's inactive list where they 3378 * become candidates for reclaim, unless shrink_inactive_zone() decides 3379 * to reactivate them. Pages that are still unevictable are rotated 3380 * back onto @zone's unevictable list. 3381 */ 3382#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */ 3383static void scan_zone_unevictable_pages(struct zone *zone) 3384{ 3385 struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list; 3386 unsigned long scan; 3387 unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE); 3388 3389 while (nr_to_scan > 0) { 3390 unsigned long batch_size = min(nr_to_scan, 3391 SCAN_UNEVICTABLE_BATCH_SIZE); 3392 3393 spin_lock_irq(&zone->lru_lock); 3394 for (scan = 0; scan < batch_size; scan++) { 3395 struct page *page = lru_to_page(l_unevictable); 3396 3397 if (!trylock_page(page)) 3398 continue; 3399 3400 prefetchw_prev_lru_page(page, l_unevictable, flags); 3401 3402 if (likely(PageLRU(page) && PageUnevictable(page))) 3403 check_move_unevictable_page(page, zone); 3404 3405 unlock_page(page); 3406 } 3407 spin_unlock_irq(&zone->lru_lock); 3408 3409 nr_to_scan -= batch_size; 3410 } 3411} 3412 3413 3414/** 3415 * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages 3416 * 3417 * A really big hammer: scan all zones' unevictable LRU lists to check for 3418 * pages that have become evictable. Move those back to the zones' 3419 * inactive list where they become candidates for reclaim. 3420 * This occurs when, e.g., we have unswappable pages on the unevictable lists, 3421 * and we add swap to the system. As such, it runs in the context of a task 3422 * that has possibly/probably made some previously unevictable pages 3423 * evictable. 3424 */ 3425static void scan_all_zones_unevictable_pages(void) 3426{ 3427 struct zone *zone; 3428 3429 for_each_zone(zone) { 3430 scan_zone_unevictable_pages(zone); 3431 } 3432} 3433 3434/* 3435 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of 3436 * all nodes' unevictable lists for evictable pages 3437 */ 3438unsigned long scan_unevictable_pages; 3439 3440int scan_unevictable_handler(struct ctl_table *table, int write, 3441 void __user *buffer, 3442 size_t *length, loff_t *ppos) 3443{ 3444 proc_doulongvec_minmax(table, write, buffer, length, ppos); 3445 3446 if (write && *(unsigned long *)table->data) 3447 scan_all_zones_unevictable_pages(); 3448 3449 scan_unevictable_pages = 0; 3450 return 0; 3451} 3452 3453#ifdef CONFIG_NUMA 3454/* 3455 * per node 'scan_unevictable_pages' attribute. On demand re-scan of 3456 * a specified node's per zone unevictable lists for evictable pages. 3457 */ 3458 3459static ssize_t read_scan_unevictable_node(struct sys_device *dev, 3460 struct sysdev_attribute *attr, 3461 char *buf) 3462{ 3463 return sprintf(buf, "0\n"); /* always zero; should fit... */ 3464} 3465 3466static ssize_t write_scan_unevictable_node(struct sys_device *dev, 3467 struct sysdev_attribute *attr, 3468 const char *buf, size_t count) 3469{ 3470 struct zone *node_zones = NODE_DATA(dev->id)->node_zones; 3471 struct zone *zone; 3472 unsigned long res; 3473 unsigned long req = strict_strtoul(buf, 10, &res); 3474 3475 if (!req) 3476 return 1; /* zero is no-op */ 3477 3478 for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) { 3479 if (!populated_zone(zone)) 3480 continue; 3481 scan_zone_unevictable_pages(zone); 3482 } 3483 return 1; 3484} 3485 3486 3487static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR, 3488 read_scan_unevictable_node, 3489 write_scan_unevictable_node); 3490 3491int scan_unevictable_register_node(struct node *node) 3492{ 3493 return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages); 3494} 3495 3496void scan_unevictable_unregister_node(struct node *node) 3497{ 3498 sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages); 3499} 3500#endif 3501