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 */ 46 static long ratelimit_pages = 32; 47 48 static long total_pages; /* The total number of pages in the machine. */ 49 static int dirty_exceeded __cacheline_aligned_in_smp; /* 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 */ 57 static 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 */ 67 int dirty_background_ratio = 10; 68 69 /* 70 * The generator of dirty data starts writeback at this percentage 71 */ 72 int vm_dirty_ratio = 40; 73 74 /* 75 * The interval between `kupdate'-style writebacks, in jiffies 76 */ 77 int dirty_writeback_interval = 5 * HZ; 78 79 /* 80 * The longest number of jiffies for which data is allowed to remain dirty 81 */ 82 int dirty_expire_interval = 30 * HZ; 83 84 /* 85 * Flag that makes the machine dump writes/reads and block dirtyings. 86 */ 87 int block_dump; 88 89 /* 90 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 91 * a full sync is triggered after this time elapses without any disk activity. 92 */ 93 int laptop_mode; 94 95 EXPORT_SYMBOL(laptop_mode); 96 97 /* End of sysctl-exported parameters */ 98 99 100 static void background_writeout(unsigned long _min_pages); 101 102 struct writeback_state 103 { 104 unsigned long nr_dirty; 105 unsigned long nr_unstable; 106 unsigned long nr_mapped; 107 unsigned long nr_writeback; 108 }; 109 110 static 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 */ 135 static void 136 get_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 */ 190 static 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 if (!dirty_exceeded) 216 dirty_exceeded = 1; 217 218 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 219 * Unstable writes are a feature of certain networked 220 * filesystems (i.e. NFS) in which data may have been 221 * written to the server's write cache, but has not yet 222 * been flushed to permanent storage. 223 */ 224 if (nr_reclaimable) { 225 writeback_inodes(&wbc); 226 get_dirty_limits(&wbs, &background_thresh, 227 &dirty_thresh, mapping); 228 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable; 229 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh) 230 break; 231 pages_written += write_chunk - wbc.nr_to_write; 232 if (pages_written >= write_chunk) 233 break; /* We've done our duty */ 234 } 235 blk_congestion_wait(WRITE, HZ/10); 236 } 237 238 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh && dirty_exceeded) 239 dirty_exceeded = 0; 240 241 if (writeback_in_progress(bdi)) 242 return; /* pdflush is already working this queue */ 243 244 /* 245 * In laptop mode, we wait until hitting the higher threshold before 246 * starting background writeout, and then write out all the way down 247 * to the lower threshold. So slow writers cause minimal disk activity. 248 * 249 * In normal mode, we start background writeout at the lower 250 * background_thresh, to keep the amount of dirty memory low. 251 */ 252 if ((laptop_mode && pages_written) || 253 (!laptop_mode && (nr_reclaimable > background_thresh))) 254 pdflush_operation(background_writeout, 0); 255 } 256 257 /** 258 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 259 * @mapping: address_space which was dirtied 260 * @nr_pages_dirtied: number of pages which the caller has just dirtied 261 * 262 * Processes which are dirtying memory should call in here once for each page 263 * which was newly dirtied. The function will periodically check the system's 264 * dirty state and will initiate writeback if needed. 265 * 266 * On really big machines, get_writeback_state is expensive, so try to avoid 267 * calling it too often (ratelimiting). But once we're over the dirty memory 268 * limit we decrease the ratelimiting by a lot, to prevent individual processes 269 * from overshooting the limit by (ratelimit_pages) each. 270 */ 271 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 272 unsigned long nr_pages_dirtied) 273 { 274 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 275 unsigned long ratelimit; 276 unsigned long *p; 277 278 ratelimit = ratelimit_pages; 279 if (dirty_exceeded) 280 ratelimit = 8; 281 282 /* 283 * Check the rate limiting. Also, we do not want to throttle real-time 284 * tasks in balance_dirty_pages(). Period. 285 */ 286 preempt_disable(); 287 p = &__get_cpu_var(ratelimits); 288 *p += nr_pages_dirtied; 289 if (unlikely(*p >= ratelimit)) { 290 *p = 0; 291 preempt_enable(); 292 balance_dirty_pages(mapping); 293 return; 294 } 295 preempt_enable(); 296 } 297 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 298 299 void throttle_vm_writeout(void) 300 { 301 struct writeback_state wbs; 302 long background_thresh; 303 long dirty_thresh; 304 305 for ( ; ; ) { 306 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL); 307 308 /* 309 * Boost the allowable dirty threshold a bit for page 310 * allocators so they don't get DoS'ed by heavy writers 311 */ 312 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 313 314 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh) 315 break; 316 blk_congestion_wait(WRITE, HZ/10); 317 } 318 } 319 320 321 /* 322 * writeback at least _min_pages, and keep writing until the amount of dirty 323 * memory is less than the background threshold, or until we're all clean. 324 */ 325 static void background_writeout(unsigned long _min_pages) 326 { 327 long min_pages = _min_pages; 328 struct writeback_control wbc = { 329 .bdi = NULL, 330 .sync_mode = WB_SYNC_NONE, 331 .older_than_this = NULL, 332 .nr_to_write = 0, 333 .nonblocking = 1, 334 }; 335 336 for ( ; ; ) { 337 struct writeback_state wbs; 338 long background_thresh; 339 long dirty_thresh; 340 341 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL); 342 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh 343 && min_pages <= 0) 344 break; 345 wbc.encountered_congestion = 0; 346 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 347 wbc.pages_skipped = 0; 348 writeback_inodes(&wbc); 349 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 350 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 351 /* Wrote less than expected */ 352 blk_congestion_wait(WRITE, HZ/10); 353 if (!wbc.encountered_congestion) 354 break; 355 } 356 } 357 } 358 359 /* 360 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 361 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 362 * -1 if all pdflush threads were busy. 363 */ 364 int wakeup_pdflush(long nr_pages) 365 { 366 if (nr_pages == 0) { 367 struct writeback_state wbs; 368 369 get_writeback_state(&wbs); 370 nr_pages = wbs.nr_dirty + wbs.nr_unstable; 371 } 372 return pdflush_operation(background_writeout, nr_pages); 373 } 374 375 static void wb_timer_fn(unsigned long unused); 376 static void laptop_timer_fn(unsigned long unused); 377 378 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 379 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 380 381 /* 382 * Periodic writeback of "old" data. 383 * 384 * Define "old": the first time one of an inode's pages is dirtied, we mark the 385 * dirtying-time in the inode's address_space. So this periodic writeback code 386 * just walks the superblock inode list, writing back any inodes which are 387 * older than a specific point in time. 388 * 389 * Try to run once per dirty_writeback_interval. But if a writeback event 390 * takes longer than a dirty_writeback_interval interval, then leave a 391 * one-second gap. 392 * 393 * older_than_this takes precedence over nr_to_write. So we'll only write back 394 * all dirty pages if they are all attached to "old" mappings. 395 */ 396 static void wb_kupdate(unsigned long arg) 397 { 398 unsigned long oldest_jif; 399 unsigned long start_jif; 400 unsigned long next_jif; 401 long nr_to_write; 402 struct writeback_state wbs; 403 struct writeback_control wbc = { 404 .bdi = NULL, 405 .sync_mode = WB_SYNC_NONE, 406 .older_than_this = &oldest_jif, 407 .nr_to_write = 0, 408 .nonblocking = 1, 409 .for_kupdate = 1, 410 }; 411 412 sync_supers(); 413 414 get_writeback_state(&wbs); 415 oldest_jif = jiffies - dirty_expire_interval; 416 start_jif = jiffies; 417 next_jif = start_jif + dirty_writeback_interval; 418 nr_to_write = wbs.nr_dirty + wbs.nr_unstable + 419 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 420 while (nr_to_write > 0) { 421 wbc.encountered_congestion = 0; 422 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 423 writeback_inodes(&wbc); 424 if (wbc.nr_to_write > 0) { 425 if (wbc.encountered_congestion) 426 blk_congestion_wait(WRITE, HZ/10); 427 else 428 break; /* All the old data is written */ 429 } 430 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 431 } 432 if (time_before(next_jif, jiffies + HZ)) 433 next_jif = jiffies + HZ; 434 if (dirty_writeback_interval) 435 mod_timer(&wb_timer, next_jif); 436 } 437 438 /* 439 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 440 */ 441 int dirty_writeback_centisecs_handler(ctl_table *table, int write, 442 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 443 { 444 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); 445 if (dirty_writeback_interval) { 446 mod_timer(&wb_timer, 447 jiffies + dirty_writeback_interval); 448 } else { 449 del_timer(&wb_timer); 450 } 451 return 0; 452 } 453 454 static void wb_timer_fn(unsigned long unused) 455 { 456 if (pdflush_operation(wb_kupdate, 0) < 0) 457 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 458 } 459 460 static void laptop_flush(unsigned long unused) 461 { 462 sys_sync(); 463 } 464 465 static void laptop_timer_fn(unsigned long unused) 466 { 467 pdflush_operation(laptop_flush, 0); 468 } 469 470 /* 471 * We've spun up the disk and we're in laptop mode: schedule writeback 472 * of all dirty data a few seconds from now. If the flush is already scheduled 473 * then push it back - the user is still using the disk. 474 */ 475 void laptop_io_completion(void) 476 { 477 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 478 } 479 480 /* 481 * We're in laptop mode and we've just synced. The sync's writes will have 482 * caused another writeback to be scheduled by laptop_io_completion. 483 * Nothing needs to be written back anymore, so we unschedule the writeback. 484 */ 485 void laptop_sync_completion(void) 486 { 487 del_timer(&laptop_mode_wb_timer); 488 } 489 490 /* 491 * If ratelimit_pages is too high then we can get into dirty-data overload 492 * if a large number of processes all perform writes at the same time. 493 * If it is too low then SMP machines will call the (expensive) 494 * get_writeback_state too often. 495 * 496 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 497 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 498 * thresholds before writeback cuts in. 499 * 500 * But the limit should not be set too high. Because it also controls the 501 * amount of memory which the balance_dirty_pages() caller has to write back. 502 * If this is too large then the caller will block on the IO queue all the 503 * time. So limit it to four megabytes - the balance_dirty_pages() caller 504 * will write six megabyte chunks, max. 505 */ 506 507 static void set_ratelimit(void) 508 { 509 ratelimit_pages = total_pages / (num_online_cpus() * 32); 510 if (ratelimit_pages < 16) 511 ratelimit_pages = 16; 512 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 513 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 514 } 515 516 static int 517 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 518 { 519 set_ratelimit(); 520 return 0; 521 } 522 523 static struct notifier_block ratelimit_nb = { 524 .notifier_call = ratelimit_handler, 525 .next = NULL, 526 }; 527 528 /* 529 * If the machine has a large highmem:lowmem ratio then scale back the default 530 * dirty memory thresholds: allowing too much dirty highmem pins an excessive 531 * number of buffer_heads. 532 */ 533 void __init page_writeback_init(void) 534 { 535 long buffer_pages = nr_free_buffer_pages(); 536 long correction; 537 538 total_pages = nr_free_pagecache_pages(); 539 540 correction = (100 * 4 * buffer_pages) / total_pages; 541 542 if (correction < 100) { 543 dirty_background_ratio *= correction; 544 dirty_background_ratio /= 100; 545 vm_dirty_ratio *= correction; 546 vm_dirty_ratio /= 100; 547 548 if (dirty_background_ratio <= 0) 549 dirty_background_ratio = 1; 550 if (vm_dirty_ratio <= 0) 551 vm_dirty_ratio = 1; 552 } 553 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 554 set_ratelimit(); 555 register_cpu_notifier(&ratelimit_nb); 556 } 557 558 int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 559 { 560 int ret; 561 562 if (wbc->nr_to_write <= 0) 563 return 0; 564 wbc->for_writepages = 1; 565 if (mapping->a_ops->writepages) 566 ret = mapping->a_ops->writepages(mapping, wbc); 567 else 568 ret = generic_writepages(mapping, wbc); 569 wbc->for_writepages = 0; 570 return ret; 571 } 572 573 /** 574 * write_one_page - write out a single page and optionally wait on I/O 575 * 576 * @page: the page to write 577 * @wait: if true, wait on writeout 578 * 579 * The page must be locked by the caller and will be unlocked upon return. 580 * 581 * write_one_page() returns a negative error code if I/O failed. 582 */ 583 int write_one_page(struct page *page, int wait) 584 { 585 struct address_space *mapping = page->mapping; 586 int ret = 0; 587 struct writeback_control wbc = { 588 .sync_mode = WB_SYNC_ALL, 589 .nr_to_write = 1, 590 }; 591 592 BUG_ON(!PageLocked(page)); 593 594 if (wait) 595 wait_on_page_writeback(page); 596 597 if (clear_page_dirty_for_io(page)) { 598 page_cache_get(page); 599 ret = mapping->a_ops->writepage(page, &wbc); 600 if (ret == 0 && wait) { 601 wait_on_page_writeback(page); 602 if (PageError(page)) 603 ret = -EIO; 604 } 605 page_cache_release(page); 606 } else { 607 unlock_page(page); 608 } 609 return ret; 610 } 611 EXPORT_SYMBOL(write_one_page); 612 613 /* 614 * For address_spaces which do not use buffers. Just tag the page as dirty in 615 * its radix tree. 616 * 617 * This is also used when a single buffer is being dirtied: we want to set the 618 * page dirty in that case, but not all the buffers. This is a "bottom-up" 619 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 620 * 621 * Most callers have locked the page, which pins the address_space in memory. 622 * But zap_pte_range() does not lock the page, however in that case the 623 * mapping is pinned by the vma's ->vm_file reference. 624 * 625 * We take care to handle the case where the page was truncated from the 626 * mapping by re-checking page_mapping() insode tree_lock. 627 */ 628 int __set_page_dirty_nobuffers(struct page *page) 629 { 630 if (!TestSetPageDirty(page)) { 631 struct address_space *mapping = page_mapping(page); 632 struct address_space *mapping2; 633 634 if (mapping) { 635 write_lock_irq(&mapping->tree_lock); 636 mapping2 = page_mapping(page); 637 if (mapping2) { /* Race with truncate? */ 638 BUG_ON(mapping2 != mapping); 639 if (mapping_cap_account_dirty(mapping)) 640 inc_page_state(nr_dirty); 641 radix_tree_tag_set(&mapping->page_tree, 642 page_index(page), PAGECACHE_TAG_DIRTY); 643 } 644 write_unlock_irq(&mapping->tree_lock); 645 if (mapping->host) { 646 /* !PageAnon && !swapper_space */ 647 __mark_inode_dirty(mapping->host, 648 I_DIRTY_PAGES); 649 } 650 } 651 return 1; 652 } 653 return 0; 654 } 655 EXPORT_SYMBOL(__set_page_dirty_nobuffers); 656 657 /* 658 * When a writepage implementation decides that it doesn't want to write this 659 * page for some reason, it should redirty the locked page via 660 * redirty_page_for_writepage() and it should then unlock the page and return 0 661 */ 662 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 663 { 664 wbc->pages_skipped++; 665 return __set_page_dirty_nobuffers(page); 666 } 667 EXPORT_SYMBOL(redirty_page_for_writepage); 668 669 /* 670 * If the mapping doesn't provide a set_page_dirty a_op, then 671 * just fall through and assume that it wants buffer_heads. 672 */ 673 int fastcall set_page_dirty(struct page *page) 674 { 675 struct address_space *mapping = page_mapping(page); 676 677 if (likely(mapping)) { 678 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 679 if (spd) 680 return (*spd)(page); 681 return __set_page_dirty_buffers(page); 682 } 683 if (!PageDirty(page)) { 684 if (!TestSetPageDirty(page)) 685 return 1; 686 } 687 return 0; 688 } 689 EXPORT_SYMBOL(set_page_dirty); 690 691 /* 692 * set_page_dirty() is racy if the caller has no reference against 693 * page->mapping->host, and if the page is unlocked. This is because another 694 * CPU could truncate the page off the mapping and then free the mapping. 695 * 696 * Usually, the page _is_ locked, or the caller is a user-space process which 697 * holds a reference on the inode by having an open file. 698 * 699 * In other cases, the page should be locked before running set_page_dirty(). 700 */ 701 int set_page_dirty_lock(struct page *page) 702 { 703 int ret; 704 705 lock_page(page); 706 ret = set_page_dirty(page); 707 unlock_page(page); 708 return ret; 709 } 710 EXPORT_SYMBOL(set_page_dirty_lock); 711 712 /* 713 * Clear a page's dirty flag, while caring for dirty memory accounting. 714 * Returns true if the page was previously dirty. 715 */ 716 int test_clear_page_dirty(struct page *page) 717 { 718 struct address_space *mapping = page_mapping(page); 719 unsigned long flags; 720 721 if (mapping) { 722 write_lock_irqsave(&mapping->tree_lock, flags); 723 if (TestClearPageDirty(page)) { 724 radix_tree_tag_clear(&mapping->page_tree, 725 page_index(page), 726 PAGECACHE_TAG_DIRTY); 727 write_unlock_irqrestore(&mapping->tree_lock, flags); 728 if (mapping_cap_account_dirty(mapping)) 729 dec_page_state(nr_dirty); 730 return 1; 731 } 732 write_unlock_irqrestore(&mapping->tree_lock, flags); 733 return 0; 734 } 735 return TestClearPageDirty(page); 736 } 737 EXPORT_SYMBOL(test_clear_page_dirty); 738 739 /* 740 * Clear a page's dirty flag, while caring for dirty memory accounting. 741 * Returns true if the page was previously dirty. 742 * 743 * This is for preparing to put the page under writeout. We leave the page 744 * tagged as dirty in the radix tree so that a concurrent write-for-sync 745 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 746 * implementation will run either set_page_writeback() or set_page_dirty(), 747 * at which stage we bring the page's dirty flag and radix-tree dirty tag 748 * back into sync. 749 * 750 * This incoherency between the page's dirty flag and radix-tree tag is 751 * unfortunate, but it only exists while the page is locked. 752 */ 753 int clear_page_dirty_for_io(struct page *page) 754 { 755 struct address_space *mapping = page_mapping(page); 756 757 if (mapping) { 758 if (TestClearPageDirty(page)) { 759 if (mapping_cap_account_dirty(mapping)) 760 dec_page_state(nr_dirty); 761 return 1; 762 } 763 return 0; 764 } 765 return TestClearPageDirty(page); 766 } 767 EXPORT_SYMBOL(clear_page_dirty_for_io); 768 769 int test_clear_page_writeback(struct page *page) 770 { 771 struct address_space *mapping = page_mapping(page); 772 int ret; 773 774 if (mapping) { 775 unsigned long flags; 776 777 write_lock_irqsave(&mapping->tree_lock, flags); 778 ret = TestClearPageWriteback(page); 779 if (ret) 780 radix_tree_tag_clear(&mapping->page_tree, 781 page_index(page), 782 PAGECACHE_TAG_WRITEBACK); 783 write_unlock_irqrestore(&mapping->tree_lock, flags); 784 } else { 785 ret = TestClearPageWriteback(page); 786 } 787 return ret; 788 } 789 790 int test_set_page_writeback(struct page *page) 791 { 792 struct address_space *mapping = page_mapping(page); 793 int ret; 794 795 if (mapping) { 796 unsigned long flags; 797 798 write_lock_irqsave(&mapping->tree_lock, flags); 799 ret = TestSetPageWriteback(page); 800 if (!ret) 801 radix_tree_tag_set(&mapping->page_tree, 802 page_index(page), 803 PAGECACHE_TAG_WRITEBACK); 804 if (!PageDirty(page)) 805 radix_tree_tag_clear(&mapping->page_tree, 806 page_index(page), 807 PAGECACHE_TAG_DIRTY); 808 write_unlock_irqrestore(&mapping->tree_lock, flags); 809 } else { 810 ret = TestSetPageWriteback(page); 811 } 812 return ret; 813 814 } 815 EXPORT_SYMBOL(test_set_page_writeback); 816 817 /* 818 * Return true if any of the pages in the mapping are marged with the 819 * passed tag. 820 */ 821 int mapping_tagged(struct address_space *mapping, int tag) 822 { 823 unsigned long flags; 824 int ret; 825 826 read_lock_irqsave(&mapping->tree_lock, flags); 827 ret = radix_tree_tagged(&mapping->page_tree, tag); 828 read_unlock_irqrestore(&mapping->tree_lock, flags); 829 return ret; 830 } 831 EXPORT_SYMBOL(mapping_tagged); 832