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