page-writeback.c revision 687a21cee17000177b1935896b9b475acf136678
1/* 2 * mm/page-writeback.c. 3 * 4 * Copyright (C) 2002, Linus Torvalds. 5 * 6 * Contains functions related to writing back dirty pages at the 7 * address_space level. 8 * 9 * 10Apr2002 akpm@zip.com.au 10 * Initial version 11 */ 12 13#include <linux/kernel.h> 14#include <linux/module.h> 15#include <linux/spinlock.h> 16#include <linux/fs.h> 17#include <linux/mm.h> 18#include <linux/swap.h> 19#include <linux/slab.h> 20#include <linux/pagemap.h> 21#include <linux/writeback.h> 22#include <linux/init.h> 23#include <linux/backing-dev.h> 24#include <linux/blkdev.h> 25#include <linux/mpage.h> 26#include <linux/percpu.h> 27#include <linux/notifier.h> 28#include <linux/smp.h> 29#include <linux/sysctl.h> 30#include <linux/cpu.h> 31#include <linux/syscalls.h> 32 33/* 34 * The maximum number of pages to writeout in a single bdflush/kupdate 35 * operation. We do this so we don't hold I_LOCK against an inode for 36 * enormous amounts of time, which would block a userspace task which has 37 * been forced to throttle against that inode. Also, the code reevaluates 38 * the dirty each time it has written this many pages. 39 */ 40#define MAX_WRITEBACK_PAGES 1024 41 42/* 43 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 44 * will look to see if it needs to force writeback or throttling. 45 */ 46static long ratelimit_pages = 32; 47 48static long total_pages; /* The total number of pages in the machine. */ 49static int dirty_exceeded; /* Dirty mem may be over limit */ 50 51/* 52 * When balance_dirty_pages decides that the caller needs to perform some 53 * non-background writeback, this is how many pages it will attempt to write. 54 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably 55 * large amounts of I/O are submitted. 56 */ 57static inline long sync_writeback_pages(void) 58{ 59 return ratelimit_pages + ratelimit_pages / 2; 60} 61 62/* The following parameters are exported via /proc/sys/vm */ 63 64/* 65 * Start background writeback (via pdflush) at this percentage 66 */ 67int dirty_background_ratio = 10; 68 69/* 70 * The generator of dirty data starts writeback at this percentage 71 */ 72int vm_dirty_ratio = 40; 73 74/* 75 * The interval between `kupdate'-style writebacks, in centiseconds 76 * (hundredths of a second) 77 */ 78int dirty_writeback_centisecs = 5 * 100; 79 80/* 81 * The longest number of centiseconds for which data is allowed to remain dirty 82 */ 83int dirty_expire_centisecs = 30 * 100; 84 85/* 86 * Flag that makes the machine dump writes/reads and block dirtyings. 87 */ 88int block_dump; 89 90/* 91 * Flag that puts the machine in "laptop mode". 92 */ 93int laptop_mode; 94 95EXPORT_SYMBOL(laptop_mode); 96 97/* End of sysctl-exported parameters */ 98 99 100static void background_writeout(unsigned long _min_pages); 101 102struct writeback_state 103{ 104 unsigned long nr_dirty; 105 unsigned long nr_unstable; 106 unsigned long nr_mapped; 107 unsigned long nr_writeback; 108}; 109 110static void get_writeback_state(struct writeback_state *wbs) 111{ 112 wbs->nr_dirty = read_page_state(nr_dirty); 113 wbs->nr_unstable = read_page_state(nr_unstable); 114 wbs->nr_mapped = read_page_state(nr_mapped); 115 wbs->nr_writeback = read_page_state(nr_writeback); 116} 117 118/* 119 * Work out the current dirty-memory clamping and background writeout 120 * thresholds. 121 * 122 * The main aim here is to lower them aggressively if there is a lot of mapped 123 * memory around. To avoid stressing page reclaim with lots of unreclaimable 124 * pages. It is better to clamp down on writers than to start swapping, and 125 * performing lots of scanning. 126 * 127 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 128 * 129 * We don't permit the clamping level to fall below 5% - that is getting rather 130 * excessive. 131 * 132 * We make sure that the background writeout level is below the adjusted 133 * clamping level. 134 */ 135static void 136get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty, 137 struct address_space *mapping) 138{ 139 int background_ratio; /* Percentages */ 140 int dirty_ratio; 141 int unmapped_ratio; 142 long background; 143 long dirty; 144 unsigned long available_memory = total_pages; 145 struct task_struct *tsk; 146 147 get_writeback_state(wbs); 148 149#ifdef CONFIG_HIGHMEM 150 /* 151 * If this mapping can only allocate from low memory, 152 * we exclude high memory from our count. 153 */ 154 if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM)) 155 available_memory -= totalhigh_pages; 156#endif 157 158 159 unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages; 160 161 dirty_ratio = vm_dirty_ratio; 162 if (dirty_ratio > unmapped_ratio / 2) 163 dirty_ratio = unmapped_ratio / 2; 164 165 if (dirty_ratio < 5) 166 dirty_ratio = 5; 167 168 background_ratio = dirty_background_ratio; 169 if (background_ratio >= dirty_ratio) 170 background_ratio = dirty_ratio / 2; 171 172 background = (background_ratio * available_memory) / 100; 173 dirty = (dirty_ratio * available_memory) / 100; 174 tsk = current; 175 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 176 background += background / 4; 177 dirty += dirty / 4; 178 } 179 *pbackground = background; 180 *pdirty = dirty; 181} 182 183/* 184 * balance_dirty_pages() must be called by processes which are generating dirty 185 * data. It looks at the number of dirty pages in the machine and will force 186 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 187 * If we're over `background_thresh' then pdflush is woken to perform some 188 * writeout. 189 */ 190static void balance_dirty_pages(struct address_space *mapping) 191{ 192 struct writeback_state wbs; 193 long nr_reclaimable; 194 long background_thresh; 195 long dirty_thresh; 196 unsigned long pages_written = 0; 197 unsigned long write_chunk = sync_writeback_pages(); 198 199 struct backing_dev_info *bdi = mapping->backing_dev_info; 200 201 for (;;) { 202 struct writeback_control wbc = { 203 .bdi = bdi, 204 .sync_mode = WB_SYNC_NONE, 205 .older_than_this = NULL, 206 .nr_to_write = write_chunk, 207 }; 208 209 get_dirty_limits(&wbs, &background_thresh, 210 &dirty_thresh, mapping); 211 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable; 212 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh) 213 break; 214 215 dirty_exceeded = 1; 216 217 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 218 * Unstable writes are a feature of certain networked 219 * filesystems (i.e. NFS) in which data may have been 220 * written to the server's write cache, but has not yet 221 * been flushed to permanent storage. 222 */ 223 if (nr_reclaimable) { 224 writeback_inodes(&wbc); 225 get_dirty_limits(&wbs, &background_thresh, 226 &dirty_thresh, mapping); 227 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable; 228 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh) 229 break; 230 pages_written += write_chunk - wbc.nr_to_write; 231 if (pages_written >= write_chunk) 232 break; /* We've done our duty */ 233 } 234 blk_congestion_wait(WRITE, HZ/10); 235 } 236 237 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh) 238 dirty_exceeded = 0; 239 240 if (writeback_in_progress(bdi)) 241 return; /* pdflush is already working this queue */ 242 243 /* 244 * In laptop mode, we wait until hitting the higher threshold before 245 * starting background writeout, and then write out all the way down 246 * to the lower threshold. So slow writers cause minimal disk activity. 247 * 248 * In normal mode, we start background writeout at the lower 249 * background_thresh, to keep the amount of dirty memory low. 250 */ 251 if ((laptop_mode && pages_written) || 252 (!laptop_mode && (nr_reclaimable > background_thresh))) 253 pdflush_operation(background_writeout, 0); 254} 255 256/** 257 * balance_dirty_pages_ratelimited - balance dirty memory state 258 * @mapping: address_space which was dirtied 259 * 260 * Processes which are dirtying memory should call in here once for each page 261 * which was newly dirtied. The function will periodically check the system's 262 * dirty state and will initiate writeback if needed. 263 * 264 * On really big machines, get_writeback_state is expensive, so try to avoid 265 * calling it too often (ratelimiting). But once we're over the dirty memory 266 * limit we decrease the ratelimiting by a lot, to prevent individual processes 267 * from overshooting the limit by (ratelimit_pages) each. 268 */ 269void balance_dirty_pages_ratelimited(struct address_space *mapping) 270{ 271 static DEFINE_PER_CPU(int, ratelimits) = 0; 272 long ratelimit; 273 274 ratelimit = ratelimit_pages; 275 if (dirty_exceeded) 276 ratelimit = 8; 277 278 /* 279 * Check the rate limiting. Also, we do not want to throttle real-time 280 * tasks in balance_dirty_pages(). Period. 281 */ 282 if (get_cpu_var(ratelimits)++ >= ratelimit) { 283 __get_cpu_var(ratelimits) = 0; 284 put_cpu_var(ratelimits); 285 balance_dirty_pages(mapping); 286 return; 287 } 288 put_cpu_var(ratelimits); 289} 290EXPORT_SYMBOL(balance_dirty_pages_ratelimited); 291 292void throttle_vm_writeout(void) 293{ 294 struct writeback_state wbs; 295 long background_thresh; 296 long dirty_thresh; 297 298 for ( ; ; ) { 299 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL); 300 301 /* 302 * Boost the allowable dirty threshold a bit for page 303 * allocators so they don't get DoS'ed by heavy writers 304 */ 305 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 306 307 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh) 308 break; 309 blk_congestion_wait(WRITE, HZ/10); 310 } 311} 312 313 314/* 315 * writeback at least _min_pages, and keep writing until the amount of dirty 316 * memory is less than the background threshold, or until we're all clean. 317 */ 318static void background_writeout(unsigned long _min_pages) 319{ 320 long min_pages = _min_pages; 321 struct writeback_control wbc = { 322 .bdi = NULL, 323 .sync_mode = WB_SYNC_NONE, 324 .older_than_this = NULL, 325 .nr_to_write = 0, 326 .nonblocking = 1, 327 }; 328 329 for ( ; ; ) { 330 struct writeback_state wbs; 331 long background_thresh; 332 long dirty_thresh; 333 334 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL); 335 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh 336 && min_pages <= 0) 337 break; 338 wbc.encountered_congestion = 0; 339 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 340 wbc.pages_skipped = 0; 341 writeback_inodes(&wbc); 342 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 343 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 344 /* Wrote less than expected */ 345 blk_congestion_wait(WRITE, HZ/10); 346 if (!wbc.encountered_congestion) 347 break; 348 } 349 } 350} 351 352/* 353 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 354 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 355 * -1 if all pdflush threads were busy. 356 */ 357int wakeup_pdflush(long nr_pages) 358{ 359 if (nr_pages == 0) { 360 struct writeback_state wbs; 361 362 get_writeback_state(&wbs); 363 nr_pages = wbs.nr_dirty + wbs.nr_unstable; 364 } 365 return pdflush_operation(background_writeout, nr_pages); 366} 367 368static void wb_timer_fn(unsigned long unused); 369static void laptop_timer_fn(unsigned long unused); 370 371static struct timer_list wb_timer = 372 TIMER_INITIALIZER(wb_timer_fn, 0, 0); 373static struct timer_list laptop_mode_wb_timer = 374 TIMER_INITIALIZER(laptop_timer_fn, 0, 0); 375 376/* 377 * Periodic writeback of "old" data. 378 * 379 * Define "old": the first time one of an inode's pages is dirtied, we mark the 380 * dirtying-time in the inode's address_space. So this periodic writeback code 381 * just walks the superblock inode list, writing back any inodes which are 382 * older than a specific point in time. 383 * 384 * Try to run once per dirty_writeback_centisecs. But if a writeback event 385 * takes longer than a dirty_writeback_centisecs interval, then leave a 386 * one-second gap. 387 * 388 * older_than_this takes precedence over nr_to_write. So we'll only write back 389 * all dirty pages if they are all attached to "old" mappings. 390 */ 391static void wb_kupdate(unsigned long arg) 392{ 393 unsigned long oldest_jif; 394 unsigned long start_jif; 395 unsigned long next_jif; 396 long nr_to_write; 397 struct writeback_state wbs; 398 struct writeback_control wbc = { 399 .bdi = NULL, 400 .sync_mode = WB_SYNC_NONE, 401 .older_than_this = &oldest_jif, 402 .nr_to_write = 0, 403 .nonblocking = 1, 404 .for_kupdate = 1, 405 }; 406 407 sync_supers(); 408 409 get_writeback_state(&wbs); 410 oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100; 411 start_jif = jiffies; 412 next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100; 413 nr_to_write = wbs.nr_dirty + wbs.nr_unstable + 414 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 415 while (nr_to_write > 0) { 416 wbc.encountered_congestion = 0; 417 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 418 writeback_inodes(&wbc); 419 if (wbc.nr_to_write > 0) { 420 if (wbc.encountered_congestion) 421 blk_congestion_wait(WRITE, HZ/10); 422 else 423 break; /* All the old data is written */ 424 } 425 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 426 } 427 if (time_before(next_jif, jiffies + HZ)) 428 next_jif = jiffies + HZ; 429 if (dirty_writeback_centisecs) 430 mod_timer(&wb_timer, next_jif); 431} 432 433/* 434 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 435 */ 436int dirty_writeback_centisecs_handler(ctl_table *table, int write, 437 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 438{ 439 proc_dointvec(table, write, file, buffer, length, ppos); 440 if (dirty_writeback_centisecs) { 441 mod_timer(&wb_timer, 442 jiffies + (dirty_writeback_centisecs * HZ) / 100); 443 } else { 444 del_timer(&wb_timer); 445 } 446 return 0; 447} 448 449static void wb_timer_fn(unsigned long unused) 450{ 451 if (pdflush_operation(wb_kupdate, 0) < 0) 452 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 453} 454 455static void laptop_flush(unsigned long unused) 456{ 457 sys_sync(); 458} 459 460static void laptop_timer_fn(unsigned long unused) 461{ 462 pdflush_operation(laptop_flush, 0); 463} 464 465/* 466 * We've spun up the disk and we're in laptop mode: schedule writeback 467 * of all dirty data a few seconds from now. If the flush is already scheduled 468 * then push it back - the user is still using the disk. 469 */ 470void laptop_io_completion(void) 471{ 472 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ); 473} 474 475/* 476 * We're in laptop mode and we've just synced. The sync's writes will have 477 * caused another writeback to be scheduled by laptop_io_completion. 478 * Nothing needs to be written back anymore, so we unschedule the writeback. 479 */ 480void laptop_sync_completion(void) 481{ 482 del_timer(&laptop_mode_wb_timer); 483} 484 485/* 486 * If ratelimit_pages is too high then we can get into dirty-data overload 487 * if a large number of processes all perform writes at the same time. 488 * If it is too low then SMP machines will call the (expensive) 489 * get_writeback_state too often. 490 * 491 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 492 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 493 * thresholds before writeback cuts in. 494 * 495 * But the limit should not be set too high. Because it also controls the 496 * amount of memory which the balance_dirty_pages() caller has to write back. 497 * If this is too large then the caller will block on the IO queue all the 498 * time. So limit it to four megabytes - the balance_dirty_pages() caller 499 * will write six megabyte chunks, max. 500 */ 501 502static void set_ratelimit(void) 503{ 504 ratelimit_pages = total_pages / (num_online_cpus() * 32); 505 if (ratelimit_pages < 16) 506 ratelimit_pages = 16; 507 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 508 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 509} 510 511static int 512ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 513{ 514 set_ratelimit(); 515 return 0; 516} 517 518static struct notifier_block ratelimit_nb = { 519 .notifier_call = ratelimit_handler, 520 .next = NULL, 521}; 522 523/* 524 * If the machine has a large highmem:lowmem ratio then scale back the default 525 * dirty memory thresholds: allowing too much dirty highmem pins an excessive 526 * number of buffer_heads. 527 */ 528void __init page_writeback_init(void) 529{ 530 long buffer_pages = nr_free_buffer_pages(); 531 long correction; 532 533 total_pages = nr_free_pagecache_pages(); 534 535 correction = (100 * 4 * buffer_pages) / total_pages; 536 537 if (correction < 100) { 538 dirty_background_ratio *= correction; 539 dirty_background_ratio /= 100; 540 vm_dirty_ratio *= correction; 541 vm_dirty_ratio /= 100; 542 543 if (dirty_background_ratio <= 0) 544 dirty_background_ratio = 1; 545 if (vm_dirty_ratio <= 0) 546 vm_dirty_ratio = 1; 547 } 548 mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100); 549 set_ratelimit(); 550 register_cpu_notifier(&ratelimit_nb); 551} 552 553int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 554{ 555 if (wbc->nr_to_write <= 0) 556 return 0; 557 if (mapping->a_ops->writepages) 558 return mapping->a_ops->writepages(mapping, wbc); 559 return generic_writepages(mapping, wbc); 560} 561 562/** 563 * write_one_page - write out a single page and optionally wait on I/O 564 * 565 * @page: the page to write 566 * @wait: if true, wait on writeout 567 * 568 * The page must be locked by the caller and will be unlocked upon return. 569 * 570 * write_one_page() returns a negative error code if I/O failed. 571 */ 572int write_one_page(struct page *page, int wait) 573{ 574 struct address_space *mapping = page->mapping; 575 int ret = 0; 576 struct writeback_control wbc = { 577 .sync_mode = WB_SYNC_ALL, 578 .nr_to_write = 1, 579 }; 580 581 BUG_ON(!PageLocked(page)); 582 583 if (wait) 584 wait_on_page_writeback(page); 585 586 if (clear_page_dirty_for_io(page)) { 587 page_cache_get(page); 588 ret = mapping->a_ops->writepage(page, &wbc); 589 if (ret == 0 && wait) { 590 wait_on_page_writeback(page); 591 if (PageError(page)) 592 ret = -EIO; 593 } 594 page_cache_release(page); 595 } else { 596 unlock_page(page); 597 } 598 return ret; 599} 600EXPORT_SYMBOL(write_one_page); 601 602/* 603 * For address_spaces which do not use buffers. Just tag the page as dirty in 604 * its radix tree. 605 * 606 * This is also used when a single buffer is being dirtied: we want to set the 607 * page dirty in that case, but not all the buffers. This is a "bottom-up" 608 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 609 * 610 * Most callers have locked the page, which pins the address_space in memory. 611 * But zap_pte_range() does not lock the page, however in that case the 612 * mapping is pinned by the vma's ->vm_file reference. 613 * 614 * We take care to handle the case where the page was truncated from the 615 * mapping by re-checking page_mapping() insode tree_lock. 616 */ 617int __set_page_dirty_nobuffers(struct page *page) 618{ 619 int ret = 0; 620 621 if (!TestSetPageDirty(page)) { 622 struct address_space *mapping = page_mapping(page); 623 struct address_space *mapping2; 624 625 if (mapping) { 626 write_lock_irq(&mapping->tree_lock); 627 mapping2 = page_mapping(page); 628 if (mapping2) { /* Race with truncate? */ 629 BUG_ON(mapping2 != mapping); 630 if (mapping_cap_account_dirty(mapping)) 631 inc_page_state(nr_dirty); 632 radix_tree_tag_set(&mapping->page_tree, 633 page_index(page), PAGECACHE_TAG_DIRTY); 634 } 635 write_unlock_irq(&mapping->tree_lock); 636 if (mapping->host) { 637 /* !PageAnon && !swapper_space */ 638 __mark_inode_dirty(mapping->host, 639 I_DIRTY_PAGES); 640 } 641 } 642 } 643 return ret; 644} 645EXPORT_SYMBOL(__set_page_dirty_nobuffers); 646 647/* 648 * When a writepage implementation decides that it doesn't want to write this 649 * page for some reason, it should redirty the locked page via 650 * redirty_page_for_writepage() and it should then unlock the page and return 0 651 */ 652int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 653{ 654 wbc->pages_skipped++; 655 return __set_page_dirty_nobuffers(page); 656} 657EXPORT_SYMBOL(redirty_page_for_writepage); 658 659/* 660 * If the mapping doesn't provide a set_page_dirty a_op, then 661 * just fall through and assume that it wants buffer_heads. 662 */ 663int fastcall set_page_dirty(struct page *page) 664{ 665 struct address_space *mapping = page_mapping(page); 666 667 if (likely(mapping)) { 668 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 669 if (spd) 670 return (*spd)(page); 671 return __set_page_dirty_buffers(page); 672 } 673 if (!PageDirty(page)) 674 SetPageDirty(page); 675 return 0; 676} 677EXPORT_SYMBOL(set_page_dirty); 678 679/* 680 * set_page_dirty() is racy if the caller has no reference against 681 * page->mapping->host, and if the page is unlocked. This is because another 682 * CPU could truncate the page off the mapping and then free the mapping. 683 * 684 * Usually, the page _is_ locked, or the caller is a user-space process which 685 * holds a reference on the inode by having an open file. 686 * 687 * In other cases, the page should be locked before running set_page_dirty(). 688 */ 689int set_page_dirty_lock(struct page *page) 690{ 691 int ret; 692 693 lock_page(page); 694 ret = set_page_dirty(page); 695 unlock_page(page); 696 return ret; 697} 698EXPORT_SYMBOL(set_page_dirty_lock); 699 700/* 701 * Clear a page's dirty flag, while caring for dirty memory accounting. 702 * Returns true if the page was previously dirty. 703 */ 704int test_clear_page_dirty(struct page *page) 705{ 706 struct address_space *mapping = page_mapping(page); 707 unsigned long flags; 708 709 if (mapping) { 710 write_lock_irqsave(&mapping->tree_lock, flags); 711 if (TestClearPageDirty(page)) { 712 radix_tree_tag_clear(&mapping->page_tree, 713 page_index(page), 714 PAGECACHE_TAG_DIRTY); 715 write_unlock_irqrestore(&mapping->tree_lock, flags); 716 if (mapping_cap_account_dirty(mapping)) 717 dec_page_state(nr_dirty); 718 return 1; 719 } 720 write_unlock_irqrestore(&mapping->tree_lock, flags); 721 return 0; 722 } 723 return TestClearPageDirty(page); 724} 725EXPORT_SYMBOL(test_clear_page_dirty); 726 727/* 728 * Clear a page's dirty flag, while caring for dirty memory accounting. 729 * Returns true if the page was previously dirty. 730 * 731 * This is for preparing to put the page under writeout. We leave the page 732 * tagged as dirty in the radix tree so that a concurrent write-for-sync 733 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 734 * implementation will run either set_page_writeback() or set_page_dirty(), 735 * at which stage we bring the page's dirty flag and radix-tree dirty tag 736 * back into sync. 737 * 738 * This incoherency between the page's dirty flag and radix-tree tag is 739 * unfortunate, but it only exists while the page is locked. 740 */ 741int clear_page_dirty_for_io(struct page *page) 742{ 743 struct address_space *mapping = page_mapping(page); 744 745 if (mapping) { 746 if (TestClearPageDirty(page)) { 747 if (mapping_cap_account_dirty(mapping)) 748 dec_page_state(nr_dirty); 749 return 1; 750 } 751 return 0; 752 } 753 return TestClearPageDirty(page); 754} 755EXPORT_SYMBOL(clear_page_dirty_for_io); 756 757int test_clear_page_writeback(struct page *page) 758{ 759 struct address_space *mapping = page_mapping(page); 760 int ret; 761 762 if (mapping) { 763 unsigned long flags; 764 765 write_lock_irqsave(&mapping->tree_lock, flags); 766 ret = TestClearPageWriteback(page); 767 if (ret) 768 radix_tree_tag_clear(&mapping->page_tree, 769 page_index(page), 770 PAGECACHE_TAG_WRITEBACK); 771 write_unlock_irqrestore(&mapping->tree_lock, flags); 772 } else { 773 ret = TestClearPageWriteback(page); 774 } 775 return ret; 776} 777 778int test_set_page_writeback(struct page *page) 779{ 780 struct address_space *mapping = page_mapping(page); 781 int ret; 782 783 if (mapping) { 784 unsigned long flags; 785 786 write_lock_irqsave(&mapping->tree_lock, flags); 787 ret = TestSetPageWriteback(page); 788 if (!ret) 789 radix_tree_tag_set(&mapping->page_tree, 790 page_index(page), 791 PAGECACHE_TAG_WRITEBACK); 792 if (!PageDirty(page)) 793 radix_tree_tag_clear(&mapping->page_tree, 794 page_index(page), 795 PAGECACHE_TAG_DIRTY); 796 write_unlock_irqrestore(&mapping->tree_lock, flags); 797 } else { 798 ret = TestSetPageWriteback(page); 799 } 800 return ret; 801 802} 803EXPORT_SYMBOL(test_set_page_writeback); 804 805/* 806 * Return true if any of the pages in the mapping are marged with the 807 * passed tag. 808 */ 809int mapping_tagged(struct address_space *mapping, int tag) 810{ 811 unsigned long flags; 812 int ret; 813 814 read_lock_irqsave(&mapping->tree_lock, flags); 815 ret = radix_tree_tagged(&mapping->page_tree, tag); 816 read_unlock_irqrestore(&mapping->tree_lock, flags); 817 return ret; 818} 819EXPORT_SYMBOL(mapping_tagged); 820