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/slab.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/notifier.h> 36 #include <linux/rwsem.h> 37 #include <linux/delay.h> 38 #include <linux/kthread.h> 39 #include <linux/freezer.h> 40 #include <linux/memcontrol.h> 41 42 #include <asm/tlbflush.h> 43 #include <asm/div64.h> 44 45 #include <linux/swapops.h> 46 47 #include "internal.h" 48 49 struct scan_control { 50 /* Incremented by the number of inactive pages that were scanned */ 51 unsigned long nr_scanned; 52 53 /* This context's GFP mask */ 54 gfp_t gfp_mask; 55 56 int may_writepage; 57 58 /* Can pages be swapped as part of reclaim? */ 59 int may_swap; 60 61 /* This context's SWAP_CLUSTER_MAX. If freeing memory for 62 * suspend, we effectively ignore SWAP_CLUSTER_MAX. 63 * In this context, it doesn't matter that we scan the 64 * whole list at once. */ 65 int swap_cluster_max; 66 67 int swappiness; 68 69 int all_unreclaimable; 70 71 int order; 72 73 /* Which cgroup do we reclaim from */ 74 struct mem_cgroup *mem_cgroup; 75 76 /* Pluggable isolate pages callback */ 77 unsigned long (*isolate_pages)(unsigned long nr, struct list_head *dst, 78 unsigned long *scanned, int order, int mode, 79 struct zone *z, struct mem_cgroup *mem_cont, 80 int active); 81 }; 82 83 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) 84 85 #ifdef ARCH_HAS_PREFETCH 86 #define prefetch_prev_lru_page(_page, _base, _field) \ 87 do { \ 88 if ((_page)->lru.prev != _base) { \ 89 struct page *prev; \ 90 \ 91 prev = lru_to_page(&(_page->lru)); \ 92 prefetch(&prev->_field); \ 93 } \ 94 } while (0) 95 #else 96 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) 97 #endif 98 99 #ifdef ARCH_HAS_PREFETCHW 100 #define prefetchw_prev_lru_page(_page, _base, _field) \ 101 do { \ 102 if ((_page)->lru.prev != _base) { \ 103 struct page *prev; \ 104 \ 105 prev = lru_to_page(&(_page->lru)); \ 106 prefetchw(&prev->_field); \ 107 } \ 108 } while (0) 109 #else 110 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) 111 #endif 112 113 /* 114 * From 0 .. 100. Higher means more swappy. 115 */ 116 int vm_swappiness = 60; 117 long vm_total_pages; /* The total number of pages which the VM controls */ 118 119 static LIST_HEAD(shrinker_list); 120 static DECLARE_RWSEM(shrinker_rwsem); 121 122 #ifdef CONFIG_CGROUP_MEM_RES_CTLR 123 #define scan_global_lru(sc) (!(sc)->mem_cgroup) 124 #else 125 #define scan_global_lru(sc) (1) 126 #endif 127 128 /* 129 * Add a shrinker callback to be called from the vm 130 */ 131 void register_shrinker(struct shrinker *shrinker) 132 { 133 shrinker->nr = 0; 134 down_write(&shrinker_rwsem); 135 list_add_tail(&shrinker->list, &shrinker_list); 136 up_write(&shrinker_rwsem); 137 } 138 EXPORT_SYMBOL(register_shrinker); 139 140 /* 141 * Remove one 142 */ 143 void unregister_shrinker(struct shrinker *shrinker) 144 { 145 down_write(&shrinker_rwsem); 146 list_del(&shrinker->list); 147 up_write(&shrinker_rwsem); 148 } 149 EXPORT_SYMBOL(unregister_shrinker); 150 151 #define SHRINK_BATCH 128 152 /* 153 * Call the shrink functions to age shrinkable caches 154 * 155 * Here we assume it costs one seek to replace a lru page and that it also 156 * takes a seek to recreate a cache object. With this in mind we age equal 157 * percentages of the lru and ageable caches. This should balance the seeks 158 * generated by these structures. 159 * 160 * If the vm encountered mapped pages on the LRU it increase the pressure on 161 * slab to avoid swapping. 162 * 163 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. 164 * 165 * `lru_pages' represents the number of on-LRU pages in all the zones which 166 * are eligible for the caller's allocation attempt. It is used for balancing 167 * slab reclaim versus page reclaim. 168 * 169 * Returns the number of slab objects which we shrunk. 170 */ 171 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, 172 unsigned long lru_pages) 173 { 174 struct shrinker *shrinker; 175 unsigned long ret = 0; 176 177 if (scanned == 0) 178 scanned = SWAP_CLUSTER_MAX; 179 180 if (!down_read_trylock(&shrinker_rwsem)) 181 return 1; /* Assume we'll be able to shrink next time */ 182 183 list_for_each_entry(shrinker, &shrinker_list, list) { 184 unsigned long long delta; 185 unsigned long total_scan; 186 unsigned long max_pass = (*shrinker->shrink)(0, gfp_mask); 187 188 delta = (4 * scanned) / shrinker->seeks; 189 delta *= max_pass; 190 do_div(delta, lru_pages + 1); 191 shrinker->nr += delta; 192 if (shrinker->nr < 0) { 193 printk(KERN_ERR "%s: nr=%ld\n", 194 __func__, shrinker->nr); 195 shrinker->nr = max_pass; 196 } 197 198 /* 199 * Avoid risking looping forever due to too large nr value: 200 * never try to free more than twice the estimate number of 201 * freeable entries. 202 */ 203 if (shrinker->nr > max_pass * 2) 204 shrinker->nr = max_pass * 2; 205 206 total_scan = shrinker->nr; 207 shrinker->nr = 0; 208 209 while (total_scan >= SHRINK_BATCH) { 210 long this_scan = SHRINK_BATCH; 211 int shrink_ret; 212 int nr_before; 213 214 nr_before = (*shrinker->shrink)(0, gfp_mask); 215 shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask); 216 if (shrink_ret == -1) 217 break; 218 if (shrink_ret < nr_before) 219 ret += nr_before - shrink_ret; 220 count_vm_events(SLABS_SCANNED, this_scan); 221 total_scan -= this_scan; 222 223 cond_resched(); 224 } 225 226 shrinker->nr += total_scan; 227 } 228 up_read(&shrinker_rwsem); 229 return ret; 230 } 231 232 /* Called without lock on whether page is mapped, so answer is unstable */ 233 static inline int page_mapping_inuse(struct page *page) 234 { 235 struct address_space *mapping; 236 237 /* Page is in somebody's page tables. */ 238 if (page_mapped(page)) 239 return 1; 240 241 /* Be more reluctant to reclaim swapcache than pagecache */ 242 if (PageSwapCache(page)) 243 return 1; 244 245 mapping = page_mapping(page); 246 if (!mapping) 247 return 0; 248 249 /* File is mmap'd by somebody? */ 250 return mapping_mapped(mapping); 251 } 252 253 static inline int is_page_cache_freeable(struct page *page) 254 { 255 return page_count(page) - !!PagePrivate(page) == 2; 256 } 257 258 static int may_write_to_queue(struct backing_dev_info *bdi) 259 { 260 if (current->flags & PF_SWAPWRITE) 261 return 1; 262 if (!bdi_write_congested(bdi)) 263 return 1; 264 if (bdi == current->backing_dev_info) 265 return 1; 266 return 0; 267 } 268 269 /* 270 * We detected a synchronous write error writing a page out. Probably 271 * -ENOSPC. We need to propagate that into the address_space for a subsequent 272 * fsync(), msync() or close(). 273 * 274 * The tricky part is that after writepage we cannot touch the mapping: nothing 275 * prevents it from being freed up. But we have a ref on the page and once 276 * that page is locked, the mapping is pinned. 277 * 278 * We're allowed to run sleeping lock_page() here because we know the caller has 279 * __GFP_FS. 280 */ 281 static void handle_write_error(struct address_space *mapping, 282 struct page *page, int error) 283 { 284 lock_page(page); 285 if (page_mapping(page) == mapping) 286 mapping_set_error(mapping, error); 287 unlock_page(page); 288 } 289 290 /* Request for sync pageout. */ 291 enum pageout_io { 292 PAGEOUT_IO_ASYNC, 293 PAGEOUT_IO_SYNC, 294 }; 295 296 /* possible outcome of pageout() */ 297 typedef enum { 298 /* failed to write page out, page is locked */ 299 PAGE_KEEP, 300 /* move page to the active list, page is locked */ 301 PAGE_ACTIVATE, 302 /* page has been sent to the disk successfully, page is unlocked */ 303 PAGE_SUCCESS, 304 /* page is clean and locked */ 305 PAGE_CLEAN, 306 } pageout_t; 307 308 /* 309 * pageout is called by shrink_page_list() for each dirty page. 310 * Calls ->writepage(). 311 */ 312 static pageout_t pageout(struct page *page, struct address_space *mapping, 313 enum pageout_io sync_writeback) 314 { 315 /* 316 * If the page is dirty, only perform writeback if that write 317 * will be non-blocking. To prevent this allocation from being 318 * stalled by pagecache activity. But note that there may be 319 * stalls if we need to run get_block(). We could test 320 * PagePrivate for that. 321 * 322 * If this process is currently in generic_file_write() against 323 * this page's queue, we can perform writeback even if that 324 * will block. 325 * 326 * If the page is swapcache, write it back even if that would 327 * block, for some throttling. This happens by accident, because 328 * swap_backing_dev_info is bust: it doesn't reflect the 329 * congestion state of the swapdevs. Easy to fix, if needed. 330 * See swapfile.c:page_queue_congested(). 331 */ 332 if (!is_page_cache_freeable(page)) 333 return PAGE_KEEP; 334 if (!mapping) { 335 /* 336 * Some data journaling orphaned pages can have 337 * page->mapping == NULL while being dirty with clean buffers. 338 */ 339 if (PagePrivate(page)) { 340 if (try_to_free_buffers(page)) { 341 ClearPageDirty(page); 342 printk("%s: orphaned page\n", __func__); 343 return PAGE_CLEAN; 344 } 345 } 346 return PAGE_KEEP; 347 } 348 if (mapping->a_ops->writepage == NULL) 349 return PAGE_ACTIVATE; 350 if (!may_write_to_queue(mapping->backing_dev_info)) 351 return PAGE_KEEP; 352 353 if (clear_page_dirty_for_io(page)) { 354 int res; 355 struct writeback_control wbc = { 356 .sync_mode = WB_SYNC_NONE, 357 .nr_to_write = SWAP_CLUSTER_MAX, 358 .range_start = 0, 359 .range_end = LLONG_MAX, 360 .nonblocking = 1, 361 .for_reclaim = 1, 362 }; 363 364 SetPageReclaim(page); 365 res = mapping->a_ops->writepage(page, &wbc); 366 if (res < 0) 367 handle_write_error(mapping, page, res); 368 if (res == AOP_WRITEPAGE_ACTIVATE) { 369 ClearPageReclaim(page); 370 return PAGE_ACTIVATE; 371 } 372 373 /* 374 * Wait on writeback if requested to. This happens when 375 * direct reclaiming a large contiguous area and the 376 * first attempt to free a range of pages fails. 377 */ 378 if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC) 379 wait_on_page_writeback(page); 380 381 if (!PageWriteback(page)) { 382 /* synchronous write or broken a_ops? */ 383 ClearPageReclaim(page); 384 } 385 inc_zone_page_state(page, NR_VMSCAN_WRITE); 386 return PAGE_SUCCESS; 387 } 388 389 return PAGE_CLEAN; 390 } 391 392 /* 393 * Attempt to detach a locked page from its ->mapping. If it is dirty or if 394 * someone else has a ref on the page, abort and return 0. If it was 395 * successfully detached, return 1. Assumes the caller has a single ref on 396 * this page. 397 */ 398 int remove_mapping(struct address_space *mapping, struct page *page) 399 { 400 BUG_ON(!PageLocked(page)); 401 BUG_ON(mapping != page_mapping(page)); 402 403 write_lock_irq(&mapping->tree_lock); 404 /* 405 * The non racy check for a busy page. 406 * 407 * Must be careful with the order of the tests. When someone has 408 * a ref to the page, it may be possible that they dirty it then 409 * drop the reference. So if PageDirty is tested before page_count 410 * here, then the following race may occur: 411 * 412 * get_user_pages(&page); 413 * [user mapping goes away] 414 * write_to(page); 415 * !PageDirty(page) [good] 416 * SetPageDirty(page); 417 * put_page(page); 418 * !page_count(page) [good, discard it] 419 * 420 * [oops, our write_to data is lost] 421 * 422 * Reversing the order of the tests ensures such a situation cannot 423 * escape unnoticed. The smp_rmb is needed to ensure the page->flags 424 * load is not satisfied before that of page->_count. 425 * 426 * Note that if SetPageDirty is always performed via set_page_dirty, 427 * and thus under tree_lock, then this ordering is not required. 428 */ 429 if (unlikely(page_count(page) != 2)) 430 goto cannot_free; 431 smp_rmb(); 432 if (unlikely(PageDirty(page))) 433 goto cannot_free; 434 435 if (PageSwapCache(page)) { 436 swp_entry_t swap = { .val = page_private(page) }; 437 __delete_from_swap_cache(page); 438 write_unlock_irq(&mapping->tree_lock); 439 swap_free(swap); 440 __put_page(page); /* The pagecache ref */ 441 return 1; 442 } 443 444 __remove_from_page_cache(page); 445 write_unlock_irq(&mapping->tree_lock); 446 __put_page(page); 447 return 1; 448 449 cannot_free: 450 write_unlock_irq(&mapping->tree_lock); 451 return 0; 452 } 453 454 /* 455 * shrink_page_list() returns the number of reclaimed pages 456 */ 457 static unsigned long shrink_page_list(struct list_head *page_list, 458 struct scan_control *sc, 459 enum pageout_io sync_writeback) 460 { 461 LIST_HEAD(ret_pages); 462 struct pagevec freed_pvec; 463 int pgactivate = 0; 464 unsigned long nr_reclaimed = 0; 465 466 cond_resched(); 467 468 pagevec_init(&freed_pvec, 1); 469 while (!list_empty(page_list)) { 470 struct address_space *mapping; 471 struct page *page; 472 int may_enter_fs; 473 int referenced; 474 475 cond_resched(); 476 477 page = lru_to_page(page_list); 478 list_del(&page->lru); 479 480 if (TestSetPageLocked(page)) 481 goto keep; 482 483 VM_BUG_ON(PageActive(page)); 484 485 sc->nr_scanned++; 486 487 if (!sc->may_swap && page_mapped(page)) 488 goto keep_locked; 489 490 /* Double the slab pressure for mapped and swapcache pages */ 491 if (page_mapped(page) || PageSwapCache(page)) 492 sc->nr_scanned++; 493 494 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 495 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 496 497 if (PageWriteback(page)) { 498 /* 499 * Synchronous reclaim is performed in two passes, 500 * first an asynchronous pass over the list to 501 * start parallel writeback, and a second synchronous 502 * pass to wait for the IO to complete. Wait here 503 * for any page for which writeback has already 504 * started. 505 */ 506 if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs) 507 wait_on_page_writeback(page); 508 else 509 goto keep_locked; 510 } 511 512 referenced = page_referenced(page, 1, sc->mem_cgroup); 513 /* In active use or really unfreeable? Activate it. */ 514 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && 515 referenced && page_mapping_inuse(page)) 516 goto activate_locked; 517 518 #ifdef CONFIG_SWAP 519 /* 520 * Anonymous process memory has backing store? 521 * Try to allocate it some swap space here. 522 */ 523 if (PageAnon(page) && !PageSwapCache(page)) 524 if (!add_to_swap(page, GFP_ATOMIC)) 525 goto activate_locked; 526 #endif /* CONFIG_SWAP */ 527 528 mapping = page_mapping(page); 529 530 /* 531 * The page is mapped into the page tables of one or more 532 * processes. Try to unmap it here. 533 */ 534 if (page_mapped(page) && mapping) { 535 switch (try_to_unmap(page, 0)) { 536 case SWAP_FAIL: 537 goto activate_locked; 538 case SWAP_AGAIN: 539 goto keep_locked; 540 case SWAP_SUCCESS: 541 ; /* try to free the page below */ 542 } 543 } 544 545 if (PageDirty(page)) { 546 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced) 547 goto keep_locked; 548 if (!may_enter_fs) 549 goto keep_locked; 550 if (!sc->may_writepage) 551 goto keep_locked; 552 553 /* Page is dirty, try to write it out here */ 554 switch (pageout(page, mapping, sync_writeback)) { 555 case PAGE_KEEP: 556 goto keep_locked; 557 case PAGE_ACTIVATE: 558 goto activate_locked; 559 case PAGE_SUCCESS: 560 if (PageWriteback(page) || PageDirty(page)) 561 goto keep; 562 /* 563 * A synchronous write - probably a ramdisk. Go 564 * ahead and try to reclaim the page. 565 */ 566 if (TestSetPageLocked(page)) 567 goto keep; 568 if (PageDirty(page) || PageWriteback(page)) 569 goto keep_locked; 570 mapping = page_mapping(page); 571 case PAGE_CLEAN: 572 ; /* try to free the page below */ 573 } 574 } 575 576 /* 577 * If the page has buffers, try to free the buffer mappings 578 * associated with this page. If we succeed we try to free 579 * the page as well. 580 * 581 * We do this even if the page is PageDirty(). 582 * try_to_release_page() does not perform I/O, but it is 583 * possible for a page to have PageDirty set, but it is actually 584 * clean (all its buffers are clean). This happens if the 585 * buffers were written out directly, with submit_bh(). ext3 586 * will do this, as well as the blockdev mapping. 587 * try_to_release_page() will discover that cleanness and will 588 * drop the buffers and mark the page clean - it can be freed. 589 * 590 * Rarely, pages can have buffers and no ->mapping. These are 591 * the pages which were not successfully invalidated in 592 * truncate_complete_page(). We try to drop those buffers here 593 * and if that worked, and the page is no longer mapped into 594 * process address space (page_count == 1) it can be freed. 595 * Otherwise, leave the page on the LRU so it is swappable. 596 */ 597 if (PagePrivate(page)) { 598 if (!try_to_release_page(page, sc->gfp_mask)) 599 goto activate_locked; 600 if (!mapping && page_count(page) == 1) 601 goto free_it; 602 } 603 604 if (!mapping || !remove_mapping(mapping, page)) 605 goto keep_locked; 606 607 free_it: 608 unlock_page(page); 609 nr_reclaimed++; 610 if (!pagevec_add(&freed_pvec, page)) 611 __pagevec_release_nonlru(&freed_pvec); 612 continue; 613 614 activate_locked: 615 SetPageActive(page); 616 pgactivate++; 617 keep_locked: 618 unlock_page(page); 619 keep: 620 list_add(&page->lru, &ret_pages); 621 VM_BUG_ON(PageLRU(page)); 622 } 623 list_splice(&ret_pages, page_list); 624 if (pagevec_count(&freed_pvec)) 625 __pagevec_release_nonlru(&freed_pvec); 626 count_vm_events(PGACTIVATE, pgactivate); 627 return nr_reclaimed; 628 } 629 630 /* LRU Isolation modes. */ 631 #define ISOLATE_INACTIVE 0 /* Isolate inactive pages. */ 632 #define ISOLATE_ACTIVE 1 /* Isolate active pages. */ 633 #define ISOLATE_BOTH 2 /* Isolate both active and inactive pages. */ 634 635 /* 636 * Attempt to remove the specified page from its LRU. Only take this page 637 * if it is of the appropriate PageActive status. Pages which are being 638 * freed elsewhere are also ignored. 639 * 640 * page: page to consider 641 * mode: one of the LRU isolation modes defined above 642 * 643 * returns 0 on success, -ve errno on failure. 644 */ 645 int __isolate_lru_page(struct page *page, int mode) 646 { 647 int ret = -EINVAL; 648 649 /* Only take pages on the LRU. */ 650 if (!PageLRU(page)) 651 return ret; 652 653 /* 654 * When checking the active state, we need to be sure we are 655 * dealing with comparible boolean values. Take the logical not 656 * of each. 657 */ 658 if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode)) 659 return ret; 660 661 ret = -EBUSY; 662 if (likely(get_page_unless_zero(page))) { 663 /* 664 * Be careful not to clear PageLRU until after we're 665 * sure the page is not being freed elsewhere -- the 666 * page release code relies on it. 667 */ 668 ClearPageLRU(page); 669 ret = 0; 670 } 671 672 return ret; 673 } 674 675 /* 676 * zone->lru_lock is heavily contended. Some of the functions that 677 * shrink the lists perform better by taking out a batch of pages 678 * and working on them outside the LRU lock. 679 * 680 * For pagecache intensive workloads, this function is the hottest 681 * spot in the kernel (apart from copy_*_user functions). 682 * 683 * Appropriate locks must be held before calling this function. 684 * 685 * @nr_to_scan: The number of pages to look through on the list. 686 * @src: The LRU list to pull pages off. 687 * @dst: The temp list to put pages on to. 688 * @scanned: The number of pages that were scanned. 689 * @order: The caller's attempted allocation order 690 * @mode: One of the LRU isolation modes 691 * 692 * returns how many pages were moved onto *@dst. 693 */ 694 static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 695 struct list_head *src, struct list_head *dst, 696 unsigned long *scanned, int order, int mode) 697 { 698 unsigned long nr_taken = 0; 699 unsigned long scan; 700 701 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { 702 struct page *page; 703 unsigned long pfn; 704 unsigned long end_pfn; 705 unsigned long page_pfn; 706 int zone_id; 707 708 page = lru_to_page(src); 709 prefetchw_prev_lru_page(page, src, flags); 710 711 VM_BUG_ON(!PageLRU(page)); 712 713 switch (__isolate_lru_page(page, mode)) { 714 case 0: 715 list_move(&page->lru, dst); 716 nr_taken++; 717 break; 718 719 case -EBUSY: 720 /* else it is being freed elsewhere */ 721 list_move(&page->lru, src); 722 continue; 723 724 default: 725 BUG(); 726 } 727 728 if (!order) 729 continue; 730 731 /* 732 * Attempt to take all pages in the order aligned region 733 * surrounding the tag page. Only take those pages of 734 * the same active state as that tag page. We may safely 735 * round the target page pfn down to the requested order 736 * as the mem_map is guarenteed valid out to MAX_ORDER, 737 * where that page is in a different zone we will detect 738 * it from its zone id and abort this block scan. 739 */ 740 zone_id = page_zone_id(page); 741 page_pfn = page_to_pfn(page); 742 pfn = page_pfn & ~((1 << order) - 1); 743 end_pfn = pfn + (1 << order); 744 for (; pfn < end_pfn; pfn++) { 745 struct page *cursor_page; 746 747 /* The target page is in the block, ignore it. */ 748 if (unlikely(pfn == page_pfn)) 749 continue; 750 751 /* Avoid holes within the zone. */ 752 if (unlikely(!pfn_valid_within(pfn))) 753 break; 754 755 cursor_page = pfn_to_page(pfn); 756 /* Check that we have not crossed a zone boundary. */ 757 if (unlikely(page_zone_id(cursor_page) != zone_id)) 758 continue; 759 switch (__isolate_lru_page(cursor_page, mode)) { 760 case 0: 761 list_move(&cursor_page->lru, dst); 762 nr_taken++; 763 scan++; 764 break; 765 766 case -EBUSY: 767 /* else it is being freed elsewhere */ 768 list_move(&cursor_page->lru, src); 769 default: 770 break; 771 } 772 } 773 } 774 775 *scanned = scan; 776 return nr_taken; 777 } 778 779 static unsigned long isolate_pages_global(unsigned long nr, 780 struct list_head *dst, 781 unsigned long *scanned, int order, 782 int mode, struct zone *z, 783 struct mem_cgroup *mem_cont, 784 int active) 785 { 786 if (active) 787 return isolate_lru_pages(nr, &z->active_list, dst, 788 scanned, order, mode); 789 else 790 return isolate_lru_pages(nr, &z->inactive_list, dst, 791 scanned, order, mode); 792 } 793 794 /* 795 * clear_active_flags() is a helper for shrink_active_list(), clearing 796 * any active bits from the pages in the list. 797 */ 798 static unsigned long clear_active_flags(struct list_head *page_list) 799 { 800 int nr_active = 0; 801 struct page *page; 802 803 list_for_each_entry(page, page_list, lru) 804 if (PageActive(page)) { 805 ClearPageActive(page); 806 nr_active++; 807 } 808 809 return nr_active; 810 } 811 812 /* 813 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number 814 * of reclaimed pages 815 */ 816 static unsigned long shrink_inactive_list(unsigned long max_scan, 817 struct zone *zone, struct scan_control *sc) 818 { 819 LIST_HEAD(page_list); 820 struct pagevec pvec; 821 unsigned long nr_scanned = 0; 822 unsigned long nr_reclaimed = 0; 823 824 pagevec_init(&pvec, 1); 825 826 lru_add_drain(); 827 spin_lock_irq(&zone->lru_lock); 828 do { 829 struct page *page; 830 unsigned long nr_taken; 831 unsigned long nr_scan; 832 unsigned long nr_freed; 833 unsigned long nr_active; 834 835 nr_taken = sc->isolate_pages(sc->swap_cluster_max, 836 &page_list, &nr_scan, sc->order, 837 (sc->order > PAGE_ALLOC_COSTLY_ORDER)? 838 ISOLATE_BOTH : ISOLATE_INACTIVE, 839 zone, sc->mem_cgroup, 0); 840 nr_active = clear_active_flags(&page_list); 841 __count_vm_events(PGDEACTIVATE, nr_active); 842 843 __mod_zone_page_state(zone, NR_ACTIVE, -nr_active); 844 __mod_zone_page_state(zone, NR_INACTIVE, 845 -(nr_taken - nr_active)); 846 if (scan_global_lru(sc)) 847 zone->pages_scanned += nr_scan; 848 spin_unlock_irq(&zone->lru_lock); 849 850 nr_scanned += nr_scan; 851 nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC); 852 853 /* 854 * If we are direct reclaiming for contiguous pages and we do 855 * not reclaim everything in the list, try again and wait 856 * for IO to complete. This will stall high-order allocations 857 * but that should be acceptable to the caller 858 */ 859 if (nr_freed < nr_taken && !current_is_kswapd() && 860 sc->order > PAGE_ALLOC_COSTLY_ORDER) { 861 congestion_wait(WRITE, HZ/10); 862 863 /* 864 * The attempt at page out may have made some 865 * of the pages active, mark them inactive again. 866 */ 867 nr_active = clear_active_flags(&page_list); 868 count_vm_events(PGDEACTIVATE, nr_active); 869 870 nr_freed += shrink_page_list(&page_list, sc, 871 PAGEOUT_IO_SYNC); 872 } 873 874 nr_reclaimed += nr_freed; 875 local_irq_disable(); 876 if (current_is_kswapd()) { 877 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan); 878 __count_vm_events(KSWAPD_STEAL, nr_freed); 879 } else if (scan_global_lru(sc)) 880 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan); 881 882 __count_zone_vm_events(PGSTEAL, zone, nr_freed); 883 884 if (nr_taken == 0) 885 goto done; 886 887 spin_lock(&zone->lru_lock); 888 /* 889 * Put back any unfreeable pages. 890 */ 891 while (!list_empty(&page_list)) { 892 page = lru_to_page(&page_list); 893 VM_BUG_ON(PageLRU(page)); 894 SetPageLRU(page); 895 list_del(&page->lru); 896 if (PageActive(page)) 897 add_page_to_active_list(zone, page); 898 else 899 add_page_to_inactive_list(zone, page); 900 if (!pagevec_add(&pvec, page)) { 901 spin_unlock_irq(&zone->lru_lock); 902 __pagevec_release(&pvec); 903 spin_lock_irq(&zone->lru_lock); 904 } 905 } 906 } while (nr_scanned < max_scan); 907 spin_unlock(&zone->lru_lock); 908 done: 909 local_irq_enable(); 910 pagevec_release(&pvec); 911 return nr_reclaimed; 912 } 913 914 /* 915 * We are about to scan this zone at a certain priority level. If that priority 916 * level is smaller (ie: more urgent) than the previous priority, then note 917 * that priority level within the zone. This is done so that when the next 918 * process comes in to scan this zone, it will immediately start out at this 919 * priority level rather than having to build up its own scanning priority. 920 * Here, this priority affects only the reclaim-mapped threshold. 921 */ 922 static inline void note_zone_scanning_priority(struct zone *zone, int priority) 923 { 924 if (priority < zone->prev_priority) 925 zone->prev_priority = priority; 926 } 927 928 static inline int zone_is_near_oom(struct zone *zone) 929 { 930 return zone->pages_scanned >= (zone_page_state(zone, NR_ACTIVE) 931 + zone_page_state(zone, NR_INACTIVE))*3; 932 } 933 934 /* 935 * Determine we should try to reclaim mapped pages. 936 * This is called only when sc->mem_cgroup is NULL. 937 */ 938 static int calc_reclaim_mapped(struct scan_control *sc, struct zone *zone, 939 int priority) 940 { 941 long mapped_ratio; 942 long distress; 943 long swap_tendency; 944 long imbalance; 945 int reclaim_mapped = 0; 946 int prev_priority; 947 948 if (scan_global_lru(sc) && zone_is_near_oom(zone)) 949 return 1; 950 /* 951 * `distress' is a measure of how much trouble we're having 952 * reclaiming pages. 0 -> no problems. 100 -> great trouble. 953 */ 954 if (scan_global_lru(sc)) 955 prev_priority = zone->prev_priority; 956 else 957 prev_priority = mem_cgroup_get_reclaim_priority(sc->mem_cgroup); 958 959 distress = 100 >> min(prev_priority, priority); 960 961 /* 962 * The point of this algorithm is to decide when to start 963 * reclaiming mapped memory instead of just pagecache. Work out 964 * how much memory 965 * is mapped. 966 */ 967 if (scan_global_lru(sc)) 968 mapped_ratio = ((global_page_state(NR_FILE_MAPPED) + 969 global_page_state(NR_ANON_PAGES)) * 100) / 970 vm_total_pages; 971 else 972 mapped_ratio = mem_cgroup_calc_mapped_ratio(sc->mem_cgroup); 973 974 /* 975 * Now decide how much we really want to unmap some pages. The 976 * mapped ratio is downgraded - just because there's a lot of 977 * mapped memory doesn't necessarily mean that page reclaim 978 * isn't succeeding. 979 * 980 * The distress ratio is important - we don't want to start 981 * going oom. 982 * 983 * A 100% value of vm_swappiness overrides this algorithm 984 * altogether. 985 */ 986 swap_tendency = mapped_ratio / 2 + distress + sc->swappiness; 987 988 /* 989 * If there's huge imbalance between active and inactive 990 * (think active 100 times larger than inactive) we should 991 * become more permissive, or the system will take too much 992 * cpu before it start swapping during memory pressure. 993 * Distress is about avoiding early-oom, this is about 994 * making swappiness graceful despite setting it to low 995 * values. 996 * 997 * Avoid div by zero with nr_inactive+1, and max resulting 998 * value is vm_total_pages. 999 */ 1000 if (scan_global_lru(sc)) { 1001 imbalance = zone_page_state(zone, NR_ACTIVE); 1002 imbalance /= zone_page_state(zone, NR_INACTIVE) + 1; 1003 } else 1004 imbalance = mem_cgroup_reclaim_imbalance(sc->mem_cgroup); 1005 1006 /* 1007 * Reduce the effect of imbalance if swappiness is low, 1008 * this means for a swappiness very low, the imbalance 1009 * must be much higher than 100 for this logic to make 1010 * the difference. 1011 * 1012 * Max temporary value is vm_total_pages*100. 1013 */ 1014 imbalance *= (vm_swappiness + 1); 1015 imbalance /= 100; 1016 1017 /* 1018 * If not much of the ram is mapped, makes the imbalance 1019 * less relevant, it's high priority we refill the inactive 1020 * list with mapped pages only in presence of high ratio of 1021 * mapped pages. 1022 * 1023 * Max temporary value is vm_total_pages*100. 1024 */ 1025 imbalance *= mapped_ratio; 1026 imbalance /= 100; 1027 1028 /* apply imbalance feedback to swap_tendency */ 1029 swap_tendency += imbalance; 1030 1031 /* 1032 * Now use this metric to decide whether to start moving mapped 1033 * memory onto the inactive list. 1034 */ 1035 if (swap_tendency >= 100) 1036 reclaim_mapped = 1; 1037 1038 return reclaim_mapped; 1039 } 1040 1041 /* 1042 * This moves pages from the active list to the inactive list. 1043 * 1044 * We move them the other way if the page is referenced by one or more 1045 * processes, from rmap. 1046 * 1047 * If the pages are mostly unmapped, the processing is fast and it is 1048 * appropriate to hold zone->lru_lock across the whole operation. But if 1049 * the pages are mapped, the processing is slow (page_referenced()) so we 1050 * should drop zone->lru_lock around each page. It's impossible to balance 1051 * this, so instead we remove the pages from the LRU while processing them. 1052 * It is safe to rely on PG_active against the non-LRU pages in here because 1053 * nobody will play with that bit on a non-LRU page. 1054 * 1055 * The downside is that we have to touch page->_count against each page. 1056 * But we had to alter page->flags anyway. 1057 */ 1058 1059 1060 static void shrink_active_list(unsigned long nr_pages, struct zone *zone, 1061 struct scan_control *sc, int priority) 1062 { 1063 unsigned long pgmoved; 1064 int pgdeactivate = 0; 1065 unsigned long pgscanned; 1066 LIST_HEAD(l_hold); /* The pages which were snipped off */ 1067 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */ 1068 LIST_HEAD(l_active); /* Pages to go onto the active_list */ 1069 struct page *page; 1070 struct pagevec pvec; 1071 int reclaim_mapped = 0; 1072 1073 if (sc->may_swap) 1074 reclaim_mapped = calc_reclaim_mapped(sc, zone, priority); 1075 1076 lru_add_drain(); 1077 spin_lock_irq(&zone->lru_lock); 1078 pgmoved = sc->isolate_pages(nr_pages, &l_hold, &pgscanned, sc->order, 1079 ISOLATE_ACTIVE, zone, 1080 sc->mem_cgroup, 1); 1081 /* 1082 * zone->pages_scanned is used for detect zone's oom 1083 * mem_cgroup remembers nr_scan by itself. 1084 */ 1085 if (scan_global_lru(sc)) 1086 zone->pages_scanned += pgscanned; 1087 1088 __mod_zone_page_state(zone, NR_ACTIVE, -pgmoved); 1089 spin_unlock_irq(&zone->lru_lock); 1090 1091 while (!list_empty(&l_hold)) { 1092 cond_resched(); 1093 page = lru_to_page(&l_hold); 1094 list_del(&page->lru); 1095 if (page_mapped(page)) { 1096 if (!reclaim_mapped || 1097 (total_swap_pages == 0 && PageAnon(page)) || 1098 page_referenced(page, 0, sc->mem_cgroup)) { 1099 list_add(&page->lru, &l_active); 1100 continue; 1101 } 1102 } 1103 list_add(&page->lru, &l_inactive); 1104 } 1105 1106 pagevec_init(&pvec, 1); 1107 pgmoved = 0; 1108 spin_lock_irq(&zone->lru_lock); 1109 while (!list_empty(&l_inactive)) { 1110 page = lru_to_page(&l_inactive); 1111 prefetchw_prev_lru_page(page, &l_inactive, flags); 1112 VM_BUG_ON(PageLRU(page)); 1113 SetPageLRU(page); 1114 VM_BUG_ON(!PageActive(page)); 1115 ClearPageActive(page); 1116 1117 list_move(&page->lru, &zone->inactive_list); 1118 mem_cgroup_move_lists(page, false); 1119 pgmoved++; 1120 if (!pagevec_add(&pvec, page)) { 1121 __mod_zone_page_state(zone, NR_INACTIVE, pgmoved); 1122 spin_unlock_irq(&zone->lru_lock); 1123 pgdeactivate += pgmoved; 1124 pgmoved = 0; 1125 if (buffer_heads_over_limit) 1126 pagevec_strip(&pvec); 1127 __pagevec_release(&pvec); 1128 spin_lock_irq(&zone->lru_lock); 1129 } 1130 } 1131 __mod_zone_page_state(zone, NR_INACTIVE, pgmoved); 1132 pgdeactivate += pgmoved; 1133 if (buffer_heads_over_limit) { 1134 spin_unlock_irq(&zone->lru_lock); 1135 pagevec_strip(&pvec); 1136 spin_lock_irq(&zone->lru_lock); 1137 } 1138 1139 pgmoved = 0; 1140 while (!list_empty(&l_active)) { 1141 page = lru_to_page(&l_active); 1142 prefetchw_prev_lru_page(page, &l_active, flags); 1143 VM_BUG_ON(PageLRU(page)); 1144 SetPageLRU(page); 1145 VM_BUG_ON(!PageActive(page)); 1146 1147 list_move(&page->lru, &zone->active_list); 1148 mem_cgroup_move_lists(page, true); 1149 pgmoved++; 1150 if (!pagevec_add(&pvec, page)) { 1151 __mod_zone_page_state(zone, NR_ACTIVE, pgmoved); 1152 pgmoved = 0; 1153 spin_unlock_irq(&zone->lru_lock); 1154 __pagevec_release(&pvec); 1155 spin_lock_irq(&zone->lru_lock); 1156 } 1157 } 1158 __mod_zone_page_state(zone, NR_ACTIVE, pgmoved); 1159 1160 __count_zone_vm_events(PGREFILL, zone, pgscanned); 1161 __count_vm_events(PGDEACTIVATE, pgdeactivate); 1162 spin_unlock_irq(&zone->lru_lock); 1163 1164 pagevec_release(&pvec); 1165 } 1166 1167 /* 1168 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 1169 */ 1170 static unsigned long shrink_zone(int priority, struct zone *zone, 1171 struct scan_control *sc) 1172 { 1173 unsigned long nr_active; 1174 unsigned long nr_inactive; 1175 unsigned long nr_to_scan; 1176 unsigned long nr_reclaimed = 0; 1177 1178 if (scan_global_lru(sc)) { 1179 /* 1180 * Add one to nr_to_scan just to make sure that the kernel 1181 * will slowly sift through the active list. 1182 */ 1183 zone->nr_scan_active += 1184 (zone_page_state(zone, NR_ACTIVE) >> priority) + 1; 1185 nr_active = zone->nr_scan_active; 1186 zone->nr_scan_inactive += 1187 (zone_page_state(zone, NR_INACTIVE) >> priority) + 1; 1188 nr_inactive = zone->nr_scan_inactive; 1189 if (nr_inactive >= sc->swap_cluster_max) 1190 zone->nr_scan_inactive = 0; 1191 else 1192 nr_inactive = 0; 1193 1194 if (nr_active >= sc->swap_cluster_max) 1195 zone->nr_scan_active = 0; 1196 else 1197 nr_active = 0; 1198 } else { 1199 /* 1200 * This reclaim occurs not because zone memory shortage but 1201 * because memory controller hits its limit. 1202 * Then, don't modify zone reclaim related data. 1203 */ 1204 nr_active = mem_cgroup_calc_reclaim_active(sc->mem_cgroup, 1205 zone, priority); 1206 1207 nr_inactive = mem_cgroup_calc_reclaim_inactive(sc->mem_cgroup, 1208 zone, priority); 1209 } 1210 1211 1212 while (nr_active || nr_inactive) { 1213 if (nr_active) { 1214 nr_to_scan = min(nr_active, 1215 (unsigned long)sc->swap_cluster_max); 1216 nr_active -= nr_to_scan; 1217 shrink_active_list(nr_to_scan, zone, sc, priority); 1218 } 1219 1220 if (nr_inactive) { 1221 nr_to_scan = min(nr_inactive, 1222 (unsigned long)sc->swap_cluster_max); 1223 nr_inactive -= nr_to_scan; 1224 nr_reclaimed += shrink_inactive_list(nr_to_scan, zone, 1225 sc); 1226 } 1227 } 1228 1229 throttle_vm_writeout(sc->gfp_mask); 1230 return nr_reclaimed; 1231 } 1232 1233 /* 1234 * This is the direct reclaim path, for page-allocating processes. We only 1235 * try to reclaim pages from zones which will satisfy the caller's allocation 1236 * request. 1237 * 1238 * We reclaim from a zone even if that zone is over pages_high. Because: 1239 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 1240 * allocation or 1241 * b) The zones may be over pages_high but they must go *over* pages_high to 1242 * satisfy the `incremental min' zone defense algorithm. 1243 * 1244 * Returns the number of reclaimed pages. 1245 * 1246 * If a zone is deemed to be full of pinned pages then just give it a light 1247 * scan then give up on it. 1248 */ 1249 static unsigned long shrink_zones(int priority, struct zonelist *zonelist, 1250 struct scan_control *sc) 1251 { 1252 enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask); 1253 unsigned long nr_reclaimed = 0; 1254 struct zoneref *z; 1255 struct zone *zone; 1256 1257 sc->all_unreclaimable = 1; 1258 for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { 1259 if (!populated_zone(zone)) 1260 continue; 1261 /* 1262 * Take care memory controller reclaiming has small influence 1263 * to global LRU. 1264 */ 1265 if (scan_global_lru(sc)) { 1266 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 1267 continue; 1268 note_zone_scanning_priority(zone, priority); 1269 1270 if (zone_is_all_unreclaimable(zone) && 1271 priority != DEF_PRIORITY) 1272 continue; /* Let kswapd poll it */ 1273 sc->all_unreclaimable = 0; 1274 } else { 1275 /* 1276 * Ignore cpuset limitation here. We just want to reduce 1277 * # of used pages by us regardless of memory shortage. 1278 */ 1279 sc->all_unreclaimable = 0; 1280 mem_cgroup_note_reclaim_priority(sc->mem_cgroup, 1281 priority); 1282 } 1283 1284 nr_reclaimed += shrink_zone(priority, zone, sc); 1285 } 1286 1287 return nr_reclaimed; 1288 } 1289 1290 /* 1291 * This is the main entry point to direct page reclaim. 1292 * 1293 * If a full scan of the inactive list fails to free enough memory then we 1294 * are "out of memory" and something needs to be killed. 1295 * 1296 * If the caller is !__GFP_FS then the probability of a failure is reasonably 1297 * high - the zone may be full of dirty or under-writeback pages, which this 1298 * caller can't do much about. We kick pdflush and take explicit naps in the 1299 * hope that some of these pages can be written. But if the allocating task 1300 * holds filesystem locks which prevent writeout this might not work, and the 1301 * allocation attempt will fail. 1302 * 1303 * returns: 0, if no pages reclaimed 1304 * else, the number of pages reclaimed 1305 */ 1306 static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 1307 struct scan_control *sc) 1308 { 1309 int priority; 1310 int ret = 0; 1311 unsigned long total_scanned = 0; 1312 unsigned long nr_reclaimed = 0; 1313 struct reclaim_state *reclaim_state = current->reclaim_state; 1314 unsigned long lru_pages = 0; 1315 struct zoneref *z; 1316 struct zone *zone; 1317 enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask); 1318 1319 if (scan_global_lru(sc)) 1320 count_vm_event(ALLOCSTALL); 1321 /* 1322 * mem_cgroup will not do shrink_slab. 1323 */ 1324 if (scan_global_lru(sc)) { 1325 for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { 1326 1327 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 1328 continue; 1329 1330 lru_pages += zone_page_state(zone, NR_ACTIVE) 1331 + zone_page_state(zone, NR_INACTIVE); 1332 } 1333 } 1334 1335 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 1336 sc->nr_scanned = 0; 1337 if (!priority) 1338 disable_swap_token(); 1339 nr_reclaimed += shrink_zones(priority, zonelist, sc); 1340 /* 1341 * Don't shrink slabs when reclaiming memory from 1342 * over limit cgroups 1343 */ 1344 if (scan_global_lru(sc)) { 1345 shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages); 1346 if (reclaim_state) { 1347 nr_reclaimed += reclaim_state->reclaimed_slab; 1348 reclaim_state->reclaimed_slab = 0; 1349 } 1350 } 1351 total_scanned += sc->nr_scanned; 1352 if (nr_reclaimed >= sc->swap_cluster_max) { 1353 ret = nr_reclaimed; 1354 goto out; 1355 } 1356 1357 /* 1358 * Try to write back as many pages as we just scanned. This 1359 * tends to cause slow streaming writers to write data to the 1360 * disk smoothly, at the dirtying rate, which is nice. But 1361 * that's undesirable in laptop mode, where we *want* lumpy 1362 * writeout. So in laptop mode, write out the whole world. 1363 */ 1364 if (total_scanned > sc->swap_cluster_max + 1365 sc->swap_cluster_max / 2) { 1366 wakeup_pdflush(laptop_mode ? 0 : total_scanned); 1367 sc->may_writepage = 1; 1368 } 1369 1370 /* Take a nap, wait for some writeback to complete */ 1371 if (sc->nr_scanned && priority < DEF_PRIORITY - 2) 1372 congestion_wait(WRITE, HZ/10); 1373 } 1374 /* top priority shrink_caches still had more to do? don't OOM, then */ 1375 if (!sc->all_unreclaimable && scan_global_lru(sc)) 1376 ret = nr_reclaimed; 1377 out: 1378 /* 1379 * Now that we've scanned all the zones at this priority level, note 1380 * that level within the zone so that the next thread which performs 1381 * scanning of this zone will immediately start out at this priority 1382 * level. This affects only the decision whether or not to bring 1383 * mapped pages onto the inactive list. 1384 */ 1385 if (priority < 0) 1386 priority = 0; 1387 1388 if (scan_global_lru(sc)) { 1389 for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { 1390 1391 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 1392 continue; 1393 1394 zone->prev_priority = priority; 1395 } 1396 } else 1397 mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority); 1398 1399 return ret; 1400 } 1401 1402 unsigned long try_to_free_pages(struct zonelist *zonelist, int order, 1403 gfp_t gfp_mask) 1404 { 1405 struct scan_control sc = { 1406 .gfp_mask = gfp_mask, 1407 .may_writepage = !laptop_mode, 1408 .swap_cluster_max = SWAP_CLUSTER_MAX, 1409 .may_swap = 1, 1410 .swappiness = vm_swappiness, 1411 .order = order, 1412 .mem_cgroup = NULL, 1413 .isolate_pages = isolate_pages_global, 1414 }; 1415 1416 return do_try_to_free_pages(zonelist, &sc); 1417 } 1418 1419 #ifdef CONFIG_CGROUP_MEM_RES_CTLR 1420 1421 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, 1422 gfp_t gfp_mask) 1423 { 1424 struct scan_control sc = { 1425 .may_writepage = !laptop_mode, 1426 .may_swap = 1, 1427 .swap_cluster_max = SWAP_CLUSTER_MAX, 1428 .swappiness = vm_swappiness, 1429 .order = 0, 1430 .mem_cgroup = mem_cont, 1431 .isolate_pages = mem_cgroup_isolate_pages, 1432 }; 1433 struct zonelist *zonelist; 1434 1435 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 1436 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); 1437 zonelist = NODE_DATA(numa_node_id())->node_zonelists; 1438 return do_try_to_free_pages(zonelist, &sc); 1439 } 1440 #endif 1441 1442 /* 1443 * For kswapd, balance_pgdat() will work across all this node's zones until 1444 * they are all at pages_high. 1445 * 1446 * Returns the number of pages which were actually freed. 1447 * 1448 * There is special handling here for zones which are full of pinned pages. 1449 * This can happen if the pages are all mlocked, or if they are all used by 1450 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 1451 * What we do is to detect the case where all pages in the zone have been 1452 * scanned twice and there has been zero successful reclaim. Mark the zone as 1453 * dead and from now on, only perform a short scan. Basically we're polling 1454 * the zone for when the problem goes away. 1455 * 1456 * kswapd scans the zones in the highmem->normal->dma direction. It skips 1457 * zones which have free_pages > pages_high, but once a zone is found to have 1458 * free_pages <= pages_high, we scan that zone and the lower zones regardless 1459 * of the number of free pages in the lower zones. This interoperates with 1460 * the page allocator fallback scheme to ensure that aging of pages is balanced 1461 * across the zones. 1462 */ 1463 static unsigned long balance_pgdat(pg_data_t *pgdat, int order) 1464 { 1465 int all_zones_ok; 1466 int priority; 1467 int i; 1468 unsigned long total_scanned; 1469 unsigned long nr_reclaimed; 1470 struct reclaim_state *reclaim_state = current->reclaim_state; 1471 struct scan_control sc = { 1472 .gfp_mask = GFP_KERNEL, 1473 .may_swap = 1, 1474 .swap_cluster_max = SWAP_CLUSTER_MAX, 1475 .swappiness = vm_swappiness, 1476 .order = order, 1477 .mem_cgroup = NULL, 1478 .isolate_pages = isolate_pages_global, 1479 }; 1480 /* 1481 * temp_priority is used to remember the scanning priority at which 1482 * this zone was successfully refilled to free_pages == pages_high. 1483 */ 1484 int temp_priority[MAX_NR_ZONES]; 1485 1486 loop_again: 1487 total_scanned = 0; 1488 nr_reclaimed = 0; 1489 sc.may_writepage = !laptop_mode; 1490 count_vm_event(PAGEOUTRUN); 1491 1492 for (i = 0; i < pgdat->nr_zones; i++) 1493 temp_priority[i] = DEF_PRIORITY; 1494 1495 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 1496 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 1497 unsigned long lru_pages = 0; 1498 1499 /* The swap token gets in the way of swapout... */ 1500 if (!priority) 1501 disable_swap_token(); 1502 1503 all_zones_ok = 1; 1504 1505 /* 1506 * Scan in the highmem->dma direction for the highest 1507 * zone which needs scanning 1508 */ 1509 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 1510 struct zone *zone = pgdat->node_zones + i; 1511 1512 if (!populated_zone(zone)) 1513 continue; 1514 1515 if (zone_is_all_unreclaimable(zone) && 1516 priority != DEF_PRIORITY) 1517 continue; 1518 1519 if (!zone_watermark_ok(zone, order, zone->pages_high, 1520 0, 0)) { 1521 end_zone = i; 1522 break; 1523 } 1524 } 1525 if (i < 0) 1526 goto out; 1527 1528 for (i = 0; i <= end_zone; i++) { 1529 struct zone *zone = pgdat->node_zones + i; 1530 1531 lru_pages += zone_page_state(zone, NR_ACTIVE) 1532 + zone_page_state(zone, NR_INACTIVE); 1533 } 1534 1535 /* 1536 * Now scan the zone in the dma->highmem direction, stopping 1537 * at the last zone which needs scanning. 1538 * 1539 * We do this because the page allocator works in the opposite 1540 * direction. This prevents the page allocator from allocating 1541 * pages behind kswapd's direction of progress, which would 1542 * cause too much scanning of the lower zones. 1543 */ 1544 for (i = 0; i <= end_zone; i++) { 1545 struct zone *zone = pgdat->node_zones + i; 1546 int nr_slab; 1547 1548 if (!populated_zone(zone)) 1549 continue; 1550 1551 if (zone_is_all_unreclaimable(zone) && 1552 priority != DEF_PRIORITY) 1553 continue; 1554 1555 if (!zone_watermark_ok(zone, order, zone->pages_high, 1556 end_zone, 0)) 1557 all_zones_ok = 0; 1558 temp_priority[i] = priority; 1559 sc.nr_scanned = 0; 1560 note_zone_scanning_priority(zone, priority); 1561 /* 1562 * We put equal pressure on every zone, unless one 1563 * zone has way too many pages free already. 1564 */ 1565 if (!zone_watermark_ok(zone, order, 8*zone->pages_high, 1566 end_zone, 0)) 1567 nr_reclaimed += shrink_zone(priority, zone, &sc); 1568 reclaim_state->reclaimed_slab = 0; 1569 nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL, 1570 lru_pages); 1571 nr_reclaimed += reclaim_state->reclaimed_slab; 1572 total_scanned += sc.nr_scanned; 1573 if (zone_is_all_unreclaimable(zone)) 1574 continue; 1575 if (nr_slab == 0 && zone->pages_scanned >= 1576 (zone_page_state(zone, NR_ACTIVE) 1577 + zone_page_state(zone, NR_INACTIVE)) * 6) 1578 zone_set_flag(zone, 1579 ZONE_ALL_UNRECLAIMABLE); 1580 /* 1581 * If we've done a decent amount of scanning and 1582 * the reclaim ratio is low, start doing writepage 1583 * even in laptop mode 1584 */ 1585 if (total_scanned > SWAP_CLUSTER_MAX * 2 && 1586 total_scanned > nr_reclaimed + nr_reclaimed / 2) 1587 sc.may_writepage = 1; 1588 } 1589 if (all_zones_ok) 1590 break; /* kswapd: all done */ 1591 /* 1592 * OK, kswapd is getting into trouble. Take a nap, then take 1593 * another pass across the zones. 1594 */ 1595 if (total_scanned && priority < DEF_PRIORITY - 2) 1596 congestion_wait(WRITE, HZ/10); 1597 1598 /* 1599 * We do this so kswapd doesn't build up large priorities for 1600 * example when it is freeing in parallel with allocators. It 1601 * matches the direct reclaim path behaviour in terms of impact 1602 * on zone->*_priority. 1603 */ 1604 if (nr_reclaimed >= SWAP_CLUSTER_MAX) 1605 break; 1606 } 1607 out: 1608 /* 1609 * Note within each zone the priority level at which this zone was 1610 * brought into a happy state. So that the next thread which scans this 1611 * zone will start out at that priority level. 1612 */ 1613 for (i = 0; i < pgdat->nr_zones; i++) { 1614 struct zone *zone = pgdat->node_zones + i; 1615 1616 zone->prev_priority = temp_priority[i]; 1617 } 1618 if (!all_zones_ok) { 1619 cond_resched(); 1620 1621 try_to_freeze(); 1622 1623 goto loop_again; 1624 } 1625 1626 return nr_reclaimed; 1627 } 1628 1629 /* 1630 * The background pageout daemon, started as a kernel thread 1631 * from the init process. 1632 * 1633 * This basically trickles out pages so that we have _some_ 1634 * free memory available even if there is no other activity 1635 * that frees anything up. This is needed for things like routing 1636 * etc, where we otherwise might have all activity going on in 1637 * asynchronous contexts that cannot page things out. 1638 * 1639 * If there are applications that are active memory-allocators 1640 * (most normal use), this basically shouldn't matter. 1641 */ 1642 static int kswapd(void *p) 1643 { 1644 unsigned long order; 1645 pg_data_t *pgdat = (pg_data_t*)p; 1646 struct task_struct *tsk = current; 1647 DEFINE_WAIT(wait); 1648 struct reclaim_state reclaim_state = { 1649 .reclaimed_slab = 0, 1650 }; 1651 node_to_cpumask_ptr(cpumask, pgdat->node_id); 1652 1653 if (!cpus_empty(*cpumask)) 1654 set_cpus_allowed_ptr(tsk, cpumask); 1655 current->reclaim_state = &reclaim_state; 1656 1657 /* 1658 * Tell the memory management that we're a "memory allocator", 1659 * and that if we need more memory we should get access to it 1660 * regardless (see "__alloc_pages()"). "kswapd" should 1661 * never get caught in the normal page freeing logic. 1662 * 1663 * (Kswapd normally doesn't need memory anyway, but sometimes 1664 * you need a small amount of memory in order to be able to 1665 * page out something else, and this flag essentially protects 1666 * us from recursively trying to free more memory as we're 1667 * trying to free the first piece of memory in the first place). 1668 */ 1669 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; 1670 set_freezable(); 1671 1672 order = 0; 1673 for ( ; ; ) { 1674 unsigned long new_order; 1675 1676 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 1677 new_order = pgdat->kswapd_max_order; 1678 pgdat->kswapd_max_order = 0; 1679 if (order < new_order) { 1680 /* 1681 * Don't sleep if someone wants a larger 'order' 1682 * allocation 1683 */ 1684 order = new_order; 1685 } else { 1686 if (!freezing(current)) 1687 schedule(); 1688 1689 order = pgdat->kswapd_max_order; 1690 } 1691 finish_wait(&pgdat->kswapd_wait, &wait); 1692 1693 if (!try_to_freeze()) { 1694 /* We can speed up thawing tasks if we don't call 1695 * balance_pgdat after returning from the refrigerator 1696 */ 1697 balance_pgdat(pgdat, order); 1698 } 1699 } 1700 return 0; 1701 } 1702 1703 /* 1704 * A zone is low on free memory, so wake its kswapd task to service it. 1705 */ 1706 void wakeup_kswapd(struct zone *zone, int order) 1707 { 1708 pg_data_t *pgdat; 1709 1710 if (!populated_zone(zone)) 1711 return; 1712 1713 pgdat = zone->zone_pgdat; 1714 if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0)) 1715 return; 1716 if (pgdat->kswapd_max_order < order) 1717 pgdat->kswapd_max_order = order; 1718 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 1719 return; 1720 if (!waitqueue_active(&pgdat->kswapd_wait)) 1721 return; 1722 wake_up_interruptible(&pgdat->kswapd_wait); 1723 } 1724 1725 #ifdef CONFIG_PM 1726 /* 1727 * Helper function for shrink_all_memory(). Tries to reclaim 'nr_pages' pages 1728 * from LRU lists system-wide, for given pass and priority, and returns the 1729 * number of reclaimed pages 1730 * 1731 * For pass > 3 we also try to shrink the LRU lists that contain a few pages 1732 */ 1733 static unsigned long shrink_all_zones(unsigned long nr_pages, int prio, 1734 int pass, struct scan_control *sc) 1735 { 1736 struct zone *zone; 1737 unsigned long nr_to_scan, ret = 0; 1738 1739 for_each_zone(zone) { 1740 1741 if (!populated_zone(zone)) 1742 continue; 1743 1744 if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY) 1745 continue; 1746 1747 /* For pass = 0 we don't shrink the active list */ 1748 if (pass > 0) { 1749 zone->nr_scan_active += 1750 (zone_page_state(zone, NR_ACTIVE) >> prio) + 1; 1751 if (zone->nr_scan_active >= nr_pages || pass > 3) { 1752 zone->nr_scan_active = 0; 1753 nr_to_scan = min(nr_pages, 1754 zone_page_state(zone, NR_ACTIVE)); 1755 shrink_active_list(nr_to_scan, zone, sc, prio); 1756 } 1757 } 1758 1759 zone->nr_scan_inactive += 1760 (zone_page_state(zone, NR_INACTIVE) >> prio) + 1; 1761 if (zone->nr_scan_inactive >= nr_pages || pass > 3) { 1762 zone->nr_scan_inactive = 0; 1763 nr_to_scan = min(nr_pages, 1764 zone_page_state(zone, NR_INACTIVE)); 1765 ret += shrink_inactive_list(nr_to_scan, zone, sc); 1766 if (ret >= nr_pages) 1767 return ret; 1768 } 1769 } 1770 1771 return ret; 1772 } 1773 1774 static unsigned long count_lru_pages(void) 1775 { 1776 return global_page_state(NR_ACTIVE) + global_page_state(NR_INACTIVE); 1777 } 1778 1779 /* 1780 * Try to free `nr_pages' of memory, system-wide, and return the number of 1781 * freed pages. 1782 * 1783 * Rather than trying to age LRUs the aim is to preserve the overall 1784 * LRU order by reclaiming preferentially 1785 * inactive > active > active referenced > active mapped 1786 */ 1787 unsigned long shrink_all_memory(unsigned long nr_pages) 1788 { 1789 unsigned long lru_pages, nr_slab; 1790 unsigned long ret = 0; 1791 int pass; 1792 struct reclaim_state reclaim_state; 1793 struct scan_control sc = { 1794 .gfp_mask = GFP_KERNEL, 1795 .may_swap = 0, 1796 .swap_cluster_max = nr_pages, 1797 .may_writepage = 1, 1798 .swappiness = vm_swappiness, 1799 .isolate_pages = isolate_pages_global, 1800 }; 1801 1802 current->reclaim_state = &reclaim_state; 1803 1804 lru_pages = count_lru_pages(); 1805 nr_slab = global_page_state(NR_SLAB_RECLAIMABLE); 1806 /* If slab caches are huge, it's better to hit them first */ 1807 while (nr_slab >= lru_pages) { 1808 reclaim_state.reclaimed_slab = 0; 1809 shrink_slab(nr_pages, sc.gfp_mask, lru_pages); 1810 if (!reclaim_state.reclaimed_slab) 1811 break; 1812 1813 ret += reclaim_state.reclaimed_slab; 1814 if (ret >= nr_pages) 1815 goto out; 1816 1817 nr_slab -= reclaim_state.reclaimed_slab; 1818 } 1819 1820 /* 1821 * We try to shrink LRUs in 5 passes: 1822 * 0 = Reclaim from inactive_list only 1823 * 1 = Reclaim from active list but don't reclaim mapped 1824 * 2 = 2nd pass of type 1 1825 * 3 = Reclaim mapped (normal reclaim) 1826 * 4 = 2nd pass of type 3 1827 */ 1828 for (pass = 0; pass < 5; pass++) { 1829 int prio; 1830 1831 /* Force reclaiming mapped pages in the passes #3 and #4 */ 1832 if (pass > 2) { 1833 sc.may_swap = 1; 1834 sc.swappiness = 100; 1835 } 1836 1837 for (prio = DEF_PRIORITY; prio >= 0; prio--) { 1838 unsigned long nr_to_scan = nr_pages - ret; 1839 1840 sc.nr_scanned = 0; 1841 ret += shrink_all_zones(nr_to_scan, prio, pass, &sc); 1842 if (ret >= nr_pages) 1843 goto out; 1844 1845 reclaim_state.reclaimed_slab = 0; 1846 shrink_slab(sc.nr_scanned, sc.gfp_mask, 1847 count_lru_pages()); 1848 ret += reclaim_state.reclaimed_slab; 1849 if (ret >= nr_pages) 1850 goto out; 1851 1852 if (sc.nr_scanned && prio < DEF_PRIORITY - 2) 1853 congestion_wait(WRITE, HZ / 10); 1854 } 1855 } 1856 1857 /* 1858 * If ret = 0, we could not shrink LRUs, but there may be something 1859 * in slab caches 1860 */ 1861 if (!ret) { 1862 do { 1863 reclaim_state.reclaimed_slab = 0; 1864 shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages()); 1865 ret += reclaim_state.reclaimed_slab; 1866 } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0); 1867 } 1868 1869 out: 1870 current->reclaim_state = NULL; 1871 1872 return ret; 1873 } 1874 #endif 1875 1876 /* It's optimal to keep kswapds on the same CPUs as their memory, but 1877 not required for correctness. So if the last cpu in a node goes 1878 away, we get changed to run anywhere: as the first one comes back, 1879 restore their cpu bindings. */ 1880 static int __devinit cpu_callback(struct notifier_block *nfb, 1881 unsigned long action, void *hcpu) 1882 { 1883 int nid; 1884 1885 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { 1886 for_each_node_state(nid, N_HIGH_MEMORY) { 1887 pg_data_t *pgdat = NODE_DATA(nid); 1888 node_to_cpumask_ptr(mask, pgdat->node_id); 1889 1890 if (any_online_cpu(*mask) < nr_cpu_ids) 1891 /* One of our CPUs online: restore mask */ 1892 set_cpus_allowed_ptr(pgdat->kswapd, mask); 1893 } 1894 } 1895 return NOTIFY_OK; 1896 } 1897 1898 /* 1899 * This kswapd start function will be called by init and node-hot-add. 1900 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. 1901 */ 1902 int kswapd_run(int nid) 1903 { 1904 pg_data_t *pgdat = NODE_DATA(nid); 1905 int ret = 0; 1906 1907 if (pgdat->kswapd) 1908 return 0; 1909 1910 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); 1911 if (IS_ERR(pgdat->kswapd)) { 1912 /* failure at boot is fatal */ 1913 BUG_ON(system_state == SYSTEM_BOOTING); 1914 printk("Failed to start kswapd on node %d\n",nid); 1915 ret = -1; 1916 } 1917 return ret; 1918 } 1919 1920 static int __init kswapd_init(void) 1921 { 1922 int nid; 1923 1924 swap_setup(); 1925 for_each_node_state(nid, N_HIGH_MEMORY) 1926 kswapd_run(nid); 1927 hotcpu_notifier(cpu_callback, 0); 1928 return 0; 1929 } 1930 1931 module_init(kswapd_init) 1932 1933 #ifdef CONFIG_NUMA 1934 /* 1935 * Zone reclaim mode 1936 * 1937 * If non-zero call zone_reclaim when the number of free pages falls below 1938 * the watermarks. 1939 */ 1940 int zone_reclaim_mode __read_mostly; 1941 1942 #define RECLAIM_OFF 0 1943 #define RECLAIM_ZONE (1<<0) /* Run shrink_cache on the zone */ 1944 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ 1945 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ 1946 1947 /* 1948 * Priority for ZONE_RECLAIM. This determines the fraction of pages 1949 * of a node considered for each zone_reclaim. 4 scans 1/16th of 1950 * a zone. 1951 */ 1952 #define ZONE_RECLAIM_PRIORITY 4 1953 1954 /* 1955 * Percentage of pages in a zone that must be unmapped for zone_reclaim to 1956 * occur. 1957 */ 1958 int sysctl_min_unmapped_ratio = 1; 1959 1960 /* 1961 * If the number of slab pages in a zone grows beyond this percentage then 1962 * slab reclaim needs to occur. 1963 */ 1964 int sysctl_min_slab_ratio = 5; 1965 1966 /* 1967 * Try to free up some pages from this zone through reclaim. 1968 */ 1969 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 1970 { 1971 /* Minimum pages needed in order to stay on node */ 1972 const unsigned long nr_pages = 1 << order; 1973 struct task_struct *p = current; 1974 struct reclaim_state reclaim_state; 1975 int priority; 1976 unsigned long nr_reclaimed = 0; 1977 struct scan_control sc = { 1978 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), 1979 .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP), 1980 .swap_cluster_max = max_t(unsigned long, nr_pages, 1981 SWAP_CLUSTER_MAX), 1982 .gfp_mask = gfp_mask, 1983 .swappiness = vm_swappiness, 1984 .isolate_pages = isolate_pages_global, 1985 }; 1986 unsigned long slab_reclaimable; 1987 1988 disable_swap_token(); 1989 cond_resched(); 1990 /* 1991 * We need to be able to allocate from the reserves for RECLAIM_SWAP 1992 * and we also need to be able to write out pages for RECLAIM_WRITE 1993 * and RECLAIM_SWAP. 1994 */ 1995 p->flags |= PF_MEMALLOC | PF_SWAPWRITE; 1996 reclaim_state.reclaimed_slab = 0; 1997 p->reclaim_state = &reclaim_state; 1998 1999 if (zone_page_state(zone, NR_FILE_PAGES) - 2000 zone_page_state(zone, NR_FILE_MAPPED) > 2001 zone->min_unmapped_pages) { 2002 /* 2003 * Free memory by calling shrink zone with increasing 2004 * priorities until we have enough memory freed. 2005 */ 2006 priority = ZONE_RECLAIM_PRIORITY; 2007 do { 2008 note_zone_scanning_priority(zone, priority); 2009 nr_reclaimed += shrink_zone(priority, zone, &sc); 2010 priority--; 2011 } while (priority >= 0 && nr_reclaimed < nr_pages); 2012 } 2013 2014 slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 2015 if (slab_reclaimable > zone->min_slab_pages) { 2016 /* 2017 * shrink_slab() does not currently allow us to determine how 2018 * many pages were freed in this zone. So we take the current 2019 * number of slab pages and shake the slab until it is reduced 2020 * by the same nr_pages that we used for reclaiming unmapped 2021 * pages. 2022 * 2023 * Note that shrink_slab will free memory on all zones and may 2024 * take a long time. 2025 */ 2026 while (shrink_slab(sc.nr_scanned, gfp_mask, order) && 2027 zone_page_state(zone, NR_SLAB_RECLAIMABLE) > 2028 slab_reclaimable - nr_pages) 2029 ; 2030 2031 /* 2032 * Update nr_reclaimed by the number of slab pages we 2033 * reclaimed from this zone. 2034 */ 2035 nr_reclaimed += slab_reclaimable - 2036 zone_page_state(zone, NR_SLAB_RECLAIMABLE); 2037 } 2038 2039 p->reclaim_state = NULL; 2040 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); 2041 return nr_reclaimed >= nr_pages; 2042 } 2043 2044 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 2045 { 2046 int node_id; 2047 int ret; 2048 2049 /* 2050 * Zone reclaim reclaims unmapped file backed pages and 2051 * slab pages if we are over the defined limits. 2052 * 2053 * A small portion of unmapped file backed pages is needed for 2054 * file I/O otherwise pages read by file I/O will be immediately 2055 * thrown out if the zone is overallocated. So we do not reclaim 2056 * if less than a specified percentage of the zone is used by 2057 * unmapped file backed pages. 2058 */ 2059 if (zone_page_state(zone, NR_FILE_PAGES) - 2060 zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages 2061 && zone_page_state(zone, NR_SLAB_RECLAIMABLE) 2062 <= zone->min_slab_pages) 2063 return 0; 2064 2065 if (zone_is_all_unreclaimable(zone)) 2066 return 0; 2067 2068 /* 2069 * Do not scan if the allocation should not be delayed. 2070 */ 2071 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) 2072 return 0; 2073 2074 /* 2075 * Only run zone reclaim on the local zone or on zones that do not 2076 * have associated processors. This will favor the local processor 2077 * over remote processors and spread off node memory allocations 2078 * as wide as possible. 2079 */ 2080 node_id = zone_to_nid(zone); 2081 if (node_state(node_id, N_CPU) && node_id != numa_node_id()) 2082 return 0; 2083 2084 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) 2085 return 0; 2086 ret = __zone_reclaim(zone, gfp_mask, order); 2087 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); 2088 2089 return ret; 2090 } 2091 #endif 2092