page-writeback.c revision 1cf6e7d83bf334cc5916137862c920a97aabc018
1/* 2 * mm/page-writeback.c 3 * 4 * Copyright (C) 2002, Linus Torvalds. 5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> 6 * 7 * Contains functions related to writing back dirty pages at the 8 * address_space level. 9 * 10 * 10Apr2002 Andrew Morton 11 * Initial version 12 */ 13 14#include <linux/kernel.h> 15#include <linux/module.h> 16#include <linux/spinlock.h> 17#include <linux/fs.h> 18#include <linux/mm.h> 19#include <linux/swap.h> 20#include <linux/slab.h> 21#include <linux/pagemap.h> 22#include <linux/writeback.h> 23#include <linux/init.h> 24#include <linux/backing-dev.h> 25#include <linux/task_io_accounting_ops.h> 26#include <linux/blkdev.h> 27#include <linux/mpage.h> 28#include <linux/rmap.h> 29#include <linux/percpu.h> 30#include <linux/notifier.h> 31#include <linux/smp.h> 32#include <linux/sysctl.h> 33#include <linux/cpu.h> 34#include <linux/syscalls.h> 35#include <linux/buffer_head.h> 36#include <linux/pagevec.h> 37 38/* 39 * The maximum number of pages to writeout in a single bdflush/kupdate 40 * operation. We do this so we don't hold I_SYNC against an inode for 41 * enormous amounts of time, which would block a userspace task which has 42 * been forced to throttle against that inode. Also, the code reevaluates 43 * the dirty each time it has written this many pages. 44 */ 45#define MAX_WRITEBACK_PAGES 1024 46 47/* 48 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 49 * will look to see if it needs to force writeback or throttling. 50 */ 51static long ratelimit_pages = 32; 52 53/* 54 * When balance_dirty_pages decides that the caller needs to perform some 55 * non-background writeback, this is how many pages it will attempt to write. 56 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably 57 * large amounts of I/O are submitted. 58 */ 59static inline long sync_writeback_pages(void) 60{ 61 return ratelimit_pages + ratelimit_pages / 2; 62} 63 64/* The following parameters are exported via /proc/sys/vm */ 65 66/* 67 * Start background writeback (via pdflush) at this percentage 68 */ 69int dirty_background_ratio = 5; 70 71/* 72 * dirty_background_bytes starts at 0 (disabled) so that it is a function of 73 * dirty_background_ratio * the amount of dirtyable memory 74 */ 75unsigned long dirty_background_bytes; 76 77/* 78 * free highmem will not be subtracted from the total free memory 79 * for calculating free ratios if vm_highmem_is_dirtyable is true 80 */ 81int vm_highmem_is_dirtyable; 82 83/* 84 * The generator of dirty data starts writeback at this percentage 85 */ 86int vm_dirty_ratio = 10; 87 88/* 89 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of 90 * vm_dirty_ratio * the amount of dirtyable memory 91 */ 92unsigned long vm_dirty_bytes; 93 94/* 95 * The interval between `kupdate'-style writebacks, in jiffies 96 */ 97int dirty_writeback_interval = 5 * HZ; 98 99/* 100 * The longest number of jiffies for which data is allowed to remain dirty 101 */ 102int dirty_expire_interval = 30 * HZ; 103 104/* 105 * Flag that makes the machine dump writes/reads and block dirtyings. 106 */ 107int block_dump; 108 109/* 110 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 111 * a full sync is triggered after this time elapses without any disk activity. 112 */ 113int laptop_mode; 114 115EXPORT_SYMBOL(laptop_mode); 116 117/* End of sysctl-exported parameters */ 118 119 120static void background_writeout(unsigned long _min_pages); 121 122/* 123 * Scale the writeback cache size proportional to the relative writeout speeds. 124 * 125 * We do this by keeping a floating proportion between BDIs, based on page 126 * writeback completions [end_page_writeback()]. Those devices that write out 127 * pages fastest will get the larger share, while the slower will get a smaller 128 * share. 129 * 130 * We use page writeout completions because we are interested in getting rid of 131 * dirty pages. Having them written out is the primary goal. 132 * 133 * We introduce a concept of time, a period over which we measure these events, 134 * because demand can/will vary over time. The length of this period itself is 135 * measured in page writeback completions. 136 * 137 */ 138static struct prop_descriptor vm_completions; 139static struct prop_descriptor vm_dirties; 140 141/* 142 * couple the period to the dirty_ratio: 143 * 144 * period/2 ~ roundup_pow_of_two(dirty limit) 145 */ 146static int calc_period_shift(void) 147{ 148 unsigned long dirty_total; 149 150 if (vm_dirty_bytes) 151 dirty_total = vm_dirty_bytes / PAGE_SIZE; 152 else 153 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 154 100; 155 return 2 + ilog2(dirty_total - 1); 156} 157 158/* 159 * update the period when the dirty threshold changes. 160 */ 161static void update_completion_period(void) 162{ 163 int shift = calc_period_shift(); 164 prop_change_shift(&vm_completions, shift); 165 prop_change_shift(&vm_dirties, shift); 166} 167 168int dirty_background_ratio_handler(struct ctl_table *table, int write, 169 struct file *filp, void __user *buffer, size_t *lenp, 170 loff_t *ppos) 171{ 172 int ret; 173 174 ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos); 175 if (ret == 0 && write) 176 dirty_background_bytes = 0; 177 return ret; 178} 179 180int dirty_background_bytes_handler(struct ctl_table *table, int write, 181 struct file *filp, void __user *buffer, size_t *lenp, 182 loff_t *ppos) 183{ 184 int ret; 185 186 ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos); 187 if (ret == 0 && write) 188 dirty_background_ratio = 0; 189 return ret; 190} 191 192int dirty_ratio_handler(struct ctl_table *table, int write, 193 struct file *filp, void __user *buffer, size_t *lenp, 194 loff_t *ppos) 195{ 196 int old_ratio = vm_dirty_ratio; 197 int ret; 198 199 ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos); 200 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 201 update_completion_period(); 202 vm_dirty_bytes = 0; 203 } 204 return ret; 205} 206 207 208int dirty_bytes_handler(struct ctl_table *table, int write, 209 struct file *filp, void __user *buffer, size_t *lenp, 210 loff_t *ppos) 211{ 212 unsigned long old_bytes = vm_dirty_bytes; 213 int ret; 214 215 ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos); 216 if (ret == 0 && write && vm_dirty_bytes != old_bytes) { 217 update_completion_period(); 218 vm_dirty_ratio = 0; 219 } 220 return ret; 221} 222 223/* 224 * Increment the BDI's writeout completion count and the global writeout 225 * completion count. Called from test_clear_page_writeback(). 226 */ 227static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 228{ 229 __prop_inc_percpu_max(&vm_completions, &bdi->completions, 230 bdi->max_prop_frac); 231} 232 233void bdi_writeout_inc(struct backing_dev_info *bdi) 234{ 235 unsigned long flags; 236 237 local_irq_save(flags); 238 __bdi_writeout_inc(bdi); 239 local_irq_restore(flags); 240} 241EXPORT_SYMBOL_GPL(bdi_writeout_inc); 242 243void task_dirty_inc(struct task_struct *tsk) 244{ 245 prop_inc_single(&vm_dirties, &tsk->dirties); 246} 247 248/* 249 * Obtain an accurate fraction of the BDI's portion. 250 */ 251static void bdi_writeout_fraction(struct backing_dev_info *bdi, 252 long *numerator, long *denominator) 253{ 254 if (bdi_cap_writeback_dirty(bdi)) { 255 prop_fraction_percpu(&vm_completions, &bdi->completions, 256 numerator, denominator); 257 } else { 258 *numerator = 0; 259 *denominator = 1; 260 } 261} 262 263/* 264 * Clip the earned share of dirty pages to that which is actually available. 265 * This avoids exceeding the total dirty_limit when the floating averages 266 * fluctuate too quickly. 267 */ 268static void 269clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty) 270{ 271 long avail_dirty; 272 273 avail_dirty = dirty - 274 (global_page_state(NR_FILE_DIRTY) + 275 global_page_state(NR_WRITEBACK) + 276 global_page_state(NR_UNSTABLE_NFS) + 277 global_page_state(NR_WRITEBACK_TEMP)); 278 279 if (avail_dirty < 0) 280 avail_dirty = 0; 281 282 avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) + 283 bdi_stat(bdi, BDI_WRITEBACK); 284 285 *pbdi_dirty = min(*pbdi_dirty, avail_dirty); 286} 287 288static inline void task_dirties_fraction(struct task_struct *tsk, 289 long *numerator, long *denominator) 290{ 291 prop_fraction_single(&vm_dirties, &tsk->dirties, 292 numerator, denominator); 293} 294 295/* 296 * scale the dirty limit 297 * 298 * task specific dirty limit: 299 * 300 * dirty -= (dirty/8) * p_{t} 301 */ 302static void task_dirty_limit(struct task_struct *tsk, long *pdirty) 303{ 304 long numerator, denominator; 305 long dirty = *pdirty; 306 u64 inv = dirty >> 3; 307 308 task_dirties_fraction(tsk, &numerator, &denominator); 309 inv *= numerator; 310 do_div(inv, denominator); 311 312 dirty -= inv; 313 if (dirty < *pdirty/2) 314 dirty = *pdirty/2; 315 316 *pdirty = dirty; 317} 318 319/* 320 * 321 */ 322static DEFINE_SPINLOCK(bdi_lock); 323static unsigned int bdi_min_ratio; 324 325int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 326{ 327 int ret = 0; 328 unsigned long flags; 329 330 spin_lock_irqsave(&bdi_lock, flags); 331 if (min_ratio > bdi->max_ratio) { 332 ret = -EINVAL; 333 } else { 334 min_ratio -= bdi->min_ratio; 335 if (bdi_min_ratio + min_ratio < 100) { 336 bdi_min_ratio += min_ratio; 337 bdi->min_ratio += min_ratio; 338 } else { 339 ret = -EINVAL; 340 } 341 } 342 spin_unlock_irqrestore(&bdi_lock, flags); 343 344 return ret; 345} 346 347int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 348{ 349 unsigned long flags; 350 int ret = 0; 351 352 if (max_ratio > 100) 353 return -EINVAL; 354 355 spin_lock_irqsave(&bdi_lock, flags); 356 if (bdi->min_ratio > max_ratio) { 357 ret = -EINVAL; 358 } else { 359 bdi->max_ratio = max_ratio; 360 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; 361 } 362 spin_unlock_irqrestore(&bdi_lock, flags); 363 364 return ret; 365} 366EXPORT_SYMBOL(bdi_set_max_ratio); 367 368/* 369 * Work out the current dirty-memory clamping and background writeout 370 * thresholds. 371 * 372 * The main aim here is to lower them aggressively if there is a lot of mapped 373 * memory around. To avoid stressing page reclaim with lots of unreclaimable 374 * pages. It is better to clamp down on writers than to start swapping, and 375 * performing lots of scanning. 376 * 377 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 378 * 379 * We don't permit the clamping level to fall below 5% - that is getting rather 380 * excessive. 381 * 382 * We make sure that the background writeout level is below the adjusted 383 * clamping level. 384 */ 385 386static unsigned long highmem_dirtyable_memory(unsigned long total) 387{ 388#ifdef CONFIG_HIGHMEM 389 int node; 390 unsigned long x = 0; 391 392 for_each_node_state(node, N_HIGH_MEMORY) { 393 struct zone *z = 394 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 395 396 x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z); 397 } 398 /* 399 * Make sure that the number of highmem pages is never larger 400 * than the number of the total dirtyable memory. This can only 401 * occur in very strange VM situations but we want to make sure 402 * that this does not occur. 403 */ 404 return min(x, total); 405#else 406 return 0; 407#endif 408} 409 410/** 411 * determine_dirtyable_memory - amount of memory that may be used 412 * 413 * Returns the numebr of pages that can currently be freed and used 414 * by the kernel for direct mappings. 415 */ 416unsigned long determine_dirtyable_memory(void) 417{ 418 unsigned long x; 419 420 x = global_page_state(NR_FREE_PAGES) + global_lru_pages(); 421 422 if (!vm_highmem_is_dirtyable) 423 x -= highmem_dirtyable_memory(x); 424 425 return x + 1; /* Ensure that we never return 0 */ 426} 427 428void 429get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty, 430 unsigned long *pbdi_dirty, struct backing_dev_info *bdi) 431{ 432 unsigned long background; 433 unsigned long dirty; 434 unsigned long available_memory = determine_dirtyable_memory(); 435 struct task_struct *tsk; 436 437 if (vm_dirty_bytes) 438 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); 439 else { 440 int dirty_ratio; 441 442 dirty_ratio = vm_dirty_ratio; 443 if (dirty_ratio < 5) 444 dirty_ratio = 5; 445 dirty = (dirty_ratio * available_memory) / 100; 446 } 447 448 if (dirty_background_bytes) 449 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); 450 else 451 background = (dirty_background_ratio * available_memory) / 100; 452 453 if (background >= dirty) 454 background = dirty / 2; 455 tsk = current; 456 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 457 background += background / 4; 458 dirty += dirty / 4; 459 } 460 *pbackground = background; 461 *pdirty = dirty; 462 463 if (bdi) { 464 u64 bdi_dirty; 465 long numerator, denominator; 466 467 /* 468 * Calculate this BDI's share of the dirty ratio. 469 */ 470 bdi_writeout_fraction(bdi, &numerator, &denominator); 471 472 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 473 bdi_dirty *= numerator; 474 do_div(bdi_dirty, denominator); 475 bdi_dirty += (dirty * bdi->min_ratio) / 100; 476 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 477 bdi_dirty = dirty * bdi->max_ratio / 100; 478 479 *pbdi_dirty = bdi_dirty; 480 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty); 481 task_dirty_limit(current, pbdi_dirty); 482 } 483} 484 485/* 486 * balance_dirty_pages() must be called by processes which are generating dirty 487 * data. It looks at the number of dirty pages in the machine and will force 488 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 489 * If we're over `background_thresh' then pdflush is woken to perform some 490 * writeout. 491 */ 492static void balance_dirty_pages(struct address_space *mapping) 493{ 494 long nr_reclaimable, bdi_nr_reclaimable; 495 long nr_writeback, bdi_nr_writeback; 496 unsigned long background_thresh; 497 unsigned long dirty_thresh; 498 unsigned long bdi_thresh; 499 unsigned long pages_written = 0; 500 unsigned long write_chunk = sync_writeback_pages(); 501 502 struct backing_dev_info *bdi = mapping->backing_dev_info; 503 504 for (;;) { 505 struct writeback_control wbc = { 506 .bdi = bdi, 507 .sync_mode = WB_SYNC_NONE, 508 .older_than_this = NULL, 509 .nr_to_write = write_chunk, 510 .range_cyclic = 1, 511 }; 512 513 get_dirty_limits(&background_thresh, &dirty_thresh, 514 &bdi_thresh, bdi); 515 516 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 517 global_page_state(NR_UNSTABLE_NFS); 518 nr_writeback = global_page_state(NR_WRITEBACK); 519 520 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 521 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 522 523 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 524 break; 525 526 /* 527 * Throttle it only when the background writeback cannot 528 * catch-up. This avoids (excessively) small writeouts 529 * when the bdi limits are ramping up. 530 */ 531 if (nr_reclaimable + nr_writeback < 532 (background_thresh + dirty_thresh) / 2) 533 break; 534 535 if (!bdi->dirty_exceeded) 536 bdi->dirty_exceeded = 1; 537 538 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 539 * Unstable writes are a feature of certain networked 540 * filesystems (i.e. NFS) in which data may have been 541 * written to the server's write cache, but has not yet 542 * been flushed to permanent storage. 543 */ 544 if (bdi_nr_reclaimable) { 545 writeback_inodes(&wbc); 546 pages_written += write_chunk - wbc.nr_to_write; 547 get_dirty_limits(&background_thresh, &dirty_thresh, 548 &bdi_thresh, bdi); 549 } 550 551 /* 552 * In order to avoid the stacked BDI deadlock we need 553 * to ensure we accurately count the 'dirty' pages when 554 * the threshold is low. 555 * 556 * Otherwise it would be possible to get thresh+n pages 557 * reported dirty, even though there are thresh-m pages 558 * actually dirty; with m+n sitting in the percpu 559 * deltas. 560 */ 561 if (bdi_thresh < 2*bdi_stat_error(bdi)) { 562 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 563 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); 564 } else if (bdi_nr_reclaimable) { 565 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 566 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 567 } 568 569 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 570 break; 571 if (pages_written >= write_chunk) 572 break; /* We've done our duty */ 573 574 congestion_wait(WRITE, HZ/10); 575 } 576 577 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh && 578 bdi->dirty_exceeded) 579 bdi->dirty_exceeded = 0; 580 581 if (writeback_in_progress(bdi)) 582 return; /* pdflush is already working this queue */ 583 584 /* 585 * In laptop mode, we wait until hitting the higher threshold before 586 * starting background writeout, and then write out all the way down 587 * to the lower threshold. So slow writers cause minimal disk activity. 588 * 589 * In normal mode, we start background writeout at the lower 590 * background_thresh, to keep the amount of dirty memory low. 591 */ 592 if ((laptop_mode && pages_written) || 593 (!laptop_mode && (global_page_state(NR_FILE_DIRTY) 594 + global_page_state(NR_UNSTABLE_NFS) 595 > background_thresh))) 596 pdflush_operation(background_writeout, 0); 597} 598 599void set_page_dirty_balance(struct page *page, int page_mkwrite) 600{ 601 if (set_page_dirty(page) || page_mkwrite) { 602 struct address_space *mapping = page_mapping(page); 603 604 if (mapping) 605 balance_dirty_pages_ratelimited(mapping); 606 } 607} 608 609/** 610 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 611 * @mapping: address_space which was dirtied 612 * @nr_pages_dirtied: number of pages which the caller has just dirtied 613 * 614 * Processes which are dirtying memory should call in here once for each page 615 * which was newly dirtied. The function will periodically check the system's 616 * dirty state and will initiate writeback if needed. 617 * 618 * On really big machines, get_writeback_state is expensive, so try to avoid 619 * calling it too often (ratelimiting). But once we're over the dirty memory 620 * limit we decrease the ratelimiting by a lot, to prevent individual processes 621 * from overshooting the limit by (ratelimit_pages) each. 622 */ 623void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 624 unsigned long nr_pages_dirtied) 625{ 626 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 627 unsigned long ratelimit; 628 unsigned long *p; 629 630 ratelimit = ratelimit_pages; 631 if (mapping->backing_dev_info->dirty_exceeded) 632 ratelimit = 8; 633 634 /* 635 * Check the rate limiting. Also, we do not want to throttle real-time 636 * tasks in balance_dirty_pages(). Period. 637 */ 638 preempt_disable(); 639 p = &__get_cpu_var(ratelimits); 640 *p += nr_pages_dirtied; 641 if (unlikely(*p >= ratelimit)) { 642 *p = 0; 643 preempt_enable(); 644 balance_dirty_pages(mapping); 645 return; 646 } 647 preempt_enable(); 648} 649EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 650 651void throttle_vm_writeout(gfp_t gfp_mask) 652{ 653 unsigned long background_thresh; 654 unsigned long dirty_thresh; 655 656 for ( ; ; ) { 657 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 658 659 /* 660 * Boost the allowable dirty threshold a bit for page 661 * allocators so they don't get DoS'ed by heavy writers 662 */ 663 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 664 665 if (global_page_state(NR_UNSTABLE_NFS) + 666 global_page_state(NR_WRITEBACK) <= dirty_thresh) 667 break; 668 congestion_wait(WRITE, HZ/10); 669 670 /* 671 * The caller might hold locks which can prevent IO completion 672 * or progress in the filesystem. So we cannot just sit here 673 * waiting for IO to complete. 674 */ 675 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 676 break; 677 } 678} 679 680/* 681 * writeback at least _min_pages, and keep writing until the amount of dirty 682 * memory is less than the background threshold, or until we're all clean. 683 */ 684static void background_writeout(unsigned long _min_pages) 685{ 686 long min_pages = _min_pages; 687 struct writeback_control wbc = { 688 .bdi = NULL, 689 .sync_mode = WB_SYNC_NONE, 690 .older_than_this = NULL, 691 .nr_to_write = 0, 692 .nonblocking = 1, 693 .range_cyclic = 1, 694 }; 695 696 for ( ; ; ) { 697 unsigned long background_thresh; 698 unsigned long dirty_thresh; 699 700 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 701 if (global_page_state(NR_FILE_DIRTY) + 702 global_page_state(NR_UNSTABLE_NFS) < background_thresh 703 && min_pages <= 0) 704 break; 705 wbc.more_io = 0; 706 wbc.encountered_congestion = 0; 707 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 708 wbc.pages_skipped = 0; 709 writeback_inodes(&wbc); 710 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 711 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 712 /* Wrote less than expected */ 713 if (wbc.encountered_congestion || wbc.more_io) 714 congestion_wait(WRITE, HZ/10); 715 else 716 break; 717 } 718 } 719} 720 721/* 722 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 723 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 724 * -1 if all pdflush threads were busy. 725 */ 726int wakeup_pdflush(long nr_pages) 727{ 728 if (nr_pages == 0) 729 nr_pages = global_page_state(NR_FILE_DIRTY) + 730 global_page_state(NR_UNSTABLE_NFS); 731 return pdflush_operation(background_writeout, nr_pages); 732} 733 734static void wb_timer_fn(unsigned long unused); 735static void laptop_timer_fn(unsigned long unused); 736 737static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 738static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 739 740/* 741 * Periodic writeback of "old" data. 742 * 743 * Define "old": the first time one of an inode's pages is dirtied, we mark the 744 * dirtying-time in the inode's address_space. So this periodic writeback code 745 * just walks the superblock inode list, writing back any inodes which are 746 * older than a specific point in time. 747 * 748 * Try to run once per dirty_writeback_interval. But if a writeback event 749 * takes longer than a dirty_writeback_interval interval, then leave a 750 * one-second gap. 751 * 752 * older_than_this takes precedence over nr_to_write. So we'll only write back 753 * all dirty pages if they are all attached to "old" mappings. 754 */ 755static void wb_kupdate(unsigned long arg) 756{ 757 unsigned long oldest_jif; 758 unsigned long start_jif; 759 unsigned long next_jif; 760 long nr_to_write; 761 struct writeback_control wbc = { 762 .bdi = NULL, 763 .sync_mode = WB_SYNC_NONE, 764 .older_than_this = &oldest_jif, 765 .nr_to_write = 0, 766 .nonblocking = 1, 767 .for_kupdate = 1, 768 .range_cyclic = 1, 769 }; 770 771 sync_supers(); 772 773 oldest_jif = jiffies - dirty_expire_interval; 774 start_jif = jiffies; 775 next_jif = start_jif + dirty_writeback_interval; 776 nr_to_write = global_page_state(NR_FILE_DIRTY) + 777 global_page_state(NR_UNSTABLE_NFS) + 778 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 779 while (nr_to_write > 0) { 780 wbc.more_io = 0; 781 wbc.encountered_congestion = 0; 782 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 783 writeback_inodes(&wbc); 784 if (wbc.nr_to_write > 0) { 785 if (wbc.encountered_congestion || wbc.more_io) 786 congestion_wait(WRITE, HZ/10); 787 else 788 break; /* All the old data is written */ 789 } 790 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 791 } 792 if (time_before(next_jif, jiffies + HZ)) 793 next_jif = jiffies + HZ; 794 if (dirty_writeback_interval) 795 mod_timer(&wb_timer, next_jif); 796} 797 798/* 799 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 800 */ 801int dirty_writeback_centisecs_handler(ctl_table *table, int write, 802 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 803{ 804 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); 805 if (dirty_writeback_interval) 806 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 807 else 808 del_timer(&wb_timer); 809 return 0; 810} 811 812static void wb_timer_fn(unsigned long unused) 813{ 814 if (pdflush_operation(wb_kupdate, 0) < 0) 815 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 816} 817 818static void laptop_flush(unsigned long unused) 819{ 820 sys_sync(); 821} 822 823static void laptop_timer_fn(unsigned long unused) 824{ 825 pdflush_operation(laptop_flush, 0); 826} 827 828/* 829 * We've spun up the disk and we're in laptop mode: schedule writeback 830 * of all dirty data a few seconds from now. If the flush is already scheduled 831 * then push it back - the user is still using the disk. 832 */ 833void laptop_io_completion(void) 834{ 835 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 836} 837 838/* 839 * We're in laptop mode and we've just synced. The sync's writes will have 840 * caused another writeback to be scheduled by laptop_io_completion. 841 * Nothing needs to be written back anymore, so we unschedule the writeback. 842 */ 843void laptop_sync_completion(void) 844{ 845 del_timer(&laptop_mode_wb_timer); 846} 847 848/* 849 * If ratelimit_pages is too high then we can get into dirty-data overload 850 * if a large number of processes all perform writes at the same time. 851 * If it is too low then SMP machines will call the (expensive) 852 * get_writeback_state too often. 853 * 854 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 855 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 856 * thresholds before writeback cuts in. 857 * 858 * But the limit should not be set too high. Because it also controls the 859 * amount of memory which the balance_dirty_pages() caller has to write back. 860 * If this is too large then the caller will block on the IO queue all the 861 * time. So limit it to four megabytes - the balance_dirty_pages() caller 862 * will write six megabyte chunks, max. 863 */ 864 865void writeback_set_ratelimit(void) 866{ 867 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 868 if (ratelimit_pages < 16) 869 ratelimit_pages = 16; 870 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 871 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 872} 873 874static int __cpuinit 875ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 876{ 877 writeback_set_ratelimit(); 878 return NOTIFY_DONE; 879} 880 881static struct notifier_block __cpuinitdata ratelimit_nb = { 882 .notifier_call = ratelimit_handler, 883 .next = NULL, 884}; 885 886/* 887 * Called early on to tune the page writeback dirty limits. 888 * 889 * We used to scale dirty pages according to how total memory 890 * related to pages that could be allocated for buffers (by 891 * comparing nr_free_buffer_pages() to vm_total_pages. 892 * 893 * However, that was when we used "dirty_ratio" to scale with 894 * all memory, and we don't do that any more. "dirty_ratio" 895 * is now applied to total non-HIGHPAGE memory (by subtracting 896 * totalhigh_pages from vm_total_pages), and as such we can't 897 * get into the old insane situation any more where we had 898 * large amounts of dirty pages compared to a small amount of 899 * non-HIGHMEM memory. 900 * 901 * But we might still want to scale the dirty_ratio by how 902 * much memory the box has.. 903 */ 904void __init page_writeback_init(void) 905{ 906 int shift; 907 908 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 909 writeback_set_ratelimit(); 910 register_cpu_notifier(&ratelimit_nb); 911 912 shift = calc_period_shift(); 913 prop_descriptor_init(&vm_completions, shift); 914 prop_descriptor_init(&vm_dirties, shift); 915} 916 917/** 918 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 919 * @mapping: address space structure to write 920 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 921 * @writepage: function called for each page 922 * @data: data passed to writepage function 923 * 924 * If a page is already under I/O, write_cache_pages() skips it, even 925 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 926 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 927 * and msync() need to guarantee that all the data which was dirty at the time 928 * the call was made get new I/O started against them. If wbc->sync_mode is 929 * WB_SYNC_ALL then we were called for data integrity and we must wait for 930 * existing IO to complete. 931 */ 932int write_cache_pages(struct address_space *mapping, 933 struct writeback_control *wbc, writepage_t writepage, 934 void *data) 935{ 936 struct backing_dev_info *bdi = mapping->backing_dev_info; 937 int ret = 0; 938 int done = 0; 939 struct pagevec pvec; 940 int nr_pages; 941 pgoff_t uninitialized_var(writeback_index); 942 pgoff_t index; 943 pgoff_t end; /* Inclusive */ 944 pgoff_t done_index; 945 int cycled; 946 int range_whole = 0; 947 long nr_to_write = wbc->nr_to_write; 948 949 if (wbc->nonblocking && bdi_write_congested(bdi)) { 950 wbc->encountered_congestion = 1; 951 return 0; 952 } 953 954 pagevec_init(&pvec, 0); 955 if (wbc->range_cyclic) { 956 writeback_index = mapping->writeback_index; /* prev offset */ 957 index = writeback_index; 958 if (index == 0) 959 cycled = 1; 960 else 961 cycled = 0; 962 end = -1; 963 } else { 964 index = wbc->range_start >> PAGE_CACHE_SHIFT; 965 end = wbc->range_end >> PAGE_CACHE_SHIFT; 966 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 967 range_whole = 1; 968 cycled = 1; /* ignore range_cyclic tests */ 969 } 970retry: 971 done_index = index; 972 while (!done && (index <= end)) { 973 int i; 974 975 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 976 PAGECACHE_TAG_DIRTY, 977 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); 978 if (nr_pages == 0) 979 break; 980 981 for (i = 0; i < nr_pages; i++) { 982 struct page *page = pvec.pages[i]; 983 984 /* 985 * At this point, the page may be truncated or 986 * invalidated (changing page->mapping to NULL), or 987 * even swizzled back from swapper_space to tmpfs file 988 * mapping. However, page->index will not change 989 * because we have a reference on the page. 990 */ 991 if (page->index > end) { 992 /* 993 * can't be range_cyclic (1st pass) because 994 * end == -1 in that case. 995 */ 996 done = 1; 997 break; 998 } 999 1000 done_index = page->index + 1; 1001 1002 lock_page(page); 1003 1004 /* 1005 * Page truncated or invalidated. We can freely skip it 1006 * then, even for data integrity operations: the page 1007 * has disappeared concurrently, so there could be no 1008 * real expectation of this data interity operation 1009 * even if there is now a new, dirty page at the same 1010 * pagecache address. 1011 */ 1012 if (unlikely(page->mapping != mapping)) { 1013continue_unlock: 1014 unlock_page(page); 1015 continue; 1016 } 1017 1018 if (!PageDirty(page)) { 1019 /* someone wrote it for us */ 1020 goto continue_unlock; 1021 } 1022 1023 if (PageWriteback(page)) { 1024 if (wbc->sync_mode != WB_SYNC_NONE) 1025 wait_on_page_writeback(page); 1026 else 1027 goto continue_unlock; 1028 } 1029 1030 BUG_ON(PageWriteback(page)); 1031 if (!clear_page_dirty_for_io(page)) 1032 goto continue_unlock; 1033 1034 ret = (*writepage)(page, wbc, data); 1035 if (unlikely(ret)) { 1036 if (ret == AOP_WRITEPAGE_ACTIVATE) { 1037 unlock_page(page); 1038 ret = 0; 1039 } else { 1040 /* 1041 * done_index is set past this page, 1042 * so media errors will not choke 1043 * background writeout for the entire 1044 * file. This has consequences for 1045 * range_cyclic semantics (ie. it may 1046 * not be suitable for data integrity 1047 * writeout). 1048 */ 1049 done = 1; 1050 break; 1051 } 1052 } 1053 1054 if (nr_to_write > 0) { 1055 nr_to_write--; 1056 if (nr_to_write == 0 && 1057 wbc->sync_mode == WB_SYNC_NONE) { 1058 /* 1059 * We stop writing back only if we are 1060 * not doing integrity sync. In case of 1061 * integrity sync we have to keep going 1062 * because someone may be concurrently 1063 * dirtying pages, and we might have 1064 * synced a lot of newly appeared dirty 1065 * pages, but have not synced all of the 1066 * old dirty pages. 1067 */ 1068 done = 1; 1069 break; 1070 } 1071 } 1072 1073 if (wbc->nonblocking && bdi_write_congested(bdi)) { 1074 wbc->encountered_congestion = 1; 1075 done = 1; 1076 break; 1077 } 1078 } 1079 pagevec_release(&pvec); 1080 cond_resched(); 1081 } 1082 if (!cycled && !done) { 1083 /* 1084 * range_cyclic: 1085 * We hit the last page and there is more work to be done: wrap 1086 * back to the start of the file 1087 */ 1088 cycled = 1; 1089 index = 0; 1090 end = writeback_index - 1; 1091 goto retry; 1092 } 1093 if (!wbc->no_nrwrite_index_update) { 1094 if (wbc->range_cyclic || (range_whole && nr_to_write > 0)) 1095 mapping->writeback_index = done_index; 1096 wbc->nr_to_write = nr_to_write; 1097 } 1098 1099 return ret; 1100} 1101EXPORT_SYMBOL(write_cache_pages); 1102 1103/* 1104 * Function used by generic_writepages to call the real writepage 1105 * function and set the mapping flags on error 1106 */ 1107static int __writepage(struct page *page, struct writeback_control *wbc, 1108 void *data) 1109{ 1110 struct address_space *mapping = data; 1111 int ret = mapping->a_ops->writepage(page, wbc); 1112 mapping_set_error(mapping, ret); 1113 return ret; 1114} 1115 1116/** 1117 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 1118 * @mapping: address space structure to write 1119 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1120 * 1121 * This is a library function, which implements the writepages() 1122 * address_space_operation. 1123 */ 1124int generic_writepages(struct address_space *mapping, 1125 struct writeback_control *wbc) 1126{ 1127 /* deal with chardevs and other special file */ 1128 if (!mapping->a_ops->writepage) 1129 return 0; 1130 1131 return write_cache_pages(mapping, wbc, __writepage, mapping); 1132} 1133 1134EXPORT_SYMBOL(generic_writepages); 1135 1136int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1137{ 1138 int ret; 1139 1140 if (wbc->nr_to_write <= 0) 1141 return 0; 1142 wbc->for_writepages = 1; 1143 if (mapping->a_ops->writepages) 1144 ret = mapping->a_ops->writepages(mapping, wbc); 1145 else 1146 ret = generic_writepages(mapping, wbc); 1147 wbc->for_writepages = 0; 1148 return ret; 1149} 1150 1151/** 1152 * write_one_page - write out a single page and optionally wait on I/O 1153 * @page: the page to write 1154 * @wait: if true, wait on writeout 1155 * 1156 * The page must be locked by the caller and will be unlocked upon return. 1157 * 1158 * write_one_page() returns a negative error code if I/O failed. 1159 */ 1160int write_one_page(struct page *page, int wait) 1161{ 1162 struct address_space *mapping = page->mapping; 1163 int ret = 0; 1164 struct writeback_control wbc = { 1165 .sync_mode = WB_SYNC_ALL, 1166 .nr_to_write = 1, 1167 }; 1168 1169 BUG_ON(!PageLocked(page)); 1170 1171 if (wait) 1172 wait_on_page_writeback(page); 1173 1174 if (clear_page_dirty_for_io(page)) { 1175 page_cache_get(page); 1176 ret = mapping->a_ops->writepage(page, &wbc); 1177 if (ret == 0 && wait) { 1178 wait_on_page_writeback(page); 1179 if (PageError(page)) 1180 ret = -EIO; 1181 } 1182 page_cache_release(page); 1183 } else { 1184 unlock_page(page); 1185 } 1186 return ret; 1187} 1188EXPORT_SYMBOL(write_one_page); 1189 1190/* 1191 * For address_spaces which do not use buffers nor write back. 1192 */ 1193int __set_page_dirty_no_writeback(struct page *page) 1194{ 1195 if (!PageDirty(page)) 1196 SetPageDirty(page); 1197 return 0; 1198} 1199 1200/* 1201 * For address_spaces which do not use buffers. Just tag the page as dirty in 1202 * its radix tree. 1203 * 1204 * This is also used when a single buffer is being dirtied: we want to set the 1205 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1206 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1207 * 1208 * Most callers have locked the page, which pins the address_space in memory. 1209 * But zap_pte_range() does not lock the page, however in that case the 1210 * mapping is pinned by the vma's ->vm_file reference. 1211 * 1212 * We take care to handle the case where the page was truncated from the 1213 * mapping by re-checking page_mapping() inside tree_lock. 1214 */ 1215int __set_page_dirty_nobuffers(struct page *page) 1216{ 1217 if (!TestSetPageDirty(page)) { 1218 struct address_space *mapping = page_mapping(page); 1219 struct address_space *mapping2; 1220 1221 if (!mapping) 1222 return 1; 1223 1224 spin_lock_irq(&mapping->tree_lock); 1225 mapping2 = page_mapping(page); 1226 if (mapping2) { /* Race with truncate? */ 1227 BUG_ON(mapping2 != mapping); 1228 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1229 if (mapping_cap_account_dirty(mapping)) { 1230 __inc_zone_page_state(page, NR_FILE_DIRTY); 1231 __inc_bdi_stat(mapping->backing_dev_info, 1232 BDI_RECLAIMABLE); 1233 task_dirty_inc(current); 1234 task_io_account_write(PAGE_CACHE_SIZE); 1235 } 1236 radix_tree_tag_set(&mapping->page_tree, 1237 page_index(page), PAGECACHE_TAG_DIRTY); 1238 } 1239 spin_unlock_irq(&mapping->tree_lock); 1240 if (mapping->host) { 1241 /* !PageAnon && !swapper_space */ 1242 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1243 } 1244 return 1; 1245 } 1246 return 0; 1247} 1248EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1249 1250/* 1251 * When a writepage implementation decides that it doesn't want to write this 1252 * page for some reason, it should redirty the locked page via 1253 * redirty_page_for_writepage() and it should then unlock the page and return 0 1254 */ 1255int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1256{ 1257 wbc->pages_skipped++; 1258 return __set_page_dirty_nobuffers(page); 1259} 1260EXPORT_SYMBOL(redirty_page_for_writepage); 1261 1262/* 1263 * If the mapping doesn't provide a set_page_dirty a_op, then 1264 * just fall through and assume that it wants buffer_heads. 1265 */ 1266int set_page_dirty(struct page *page) 1267{ 1268 struct address_space *mapping = page_mapping(page); 1269 1270 if (likely(mapping)) { 1271 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1272#ifdef CONFIG_BLOCK 1273 if (!spd) 1274 spd = __set_page_dirty_buffers; 1275#endif 1276 return (*spd)(page); 1277 } 1278 if (!PageDirty(page)) { 1279 if (!TestSetPageDirty(page)) 1280 return 1; 1281 } 1282 return 0; 1283} 1284EXPORT_SYMBOL(set_page_dirty); 1285 1286/* 1287 * set_page_dirty() is racy if the caller has no reference against 1288 * page->mapping->host, and if the page is unlocked. This is because another 1289 * CPU could truncate the page off the mapping and then free the mapping. 1290 * 1291 * Usually, the page _is_ locked, or the caller is a user-space process which 1292 * holds a reference on the inode by having an open file. 1293 * 1294 * In other cases, the page should be locked before running set_page_dirty(). 1295 */ 1296int set_page_dirty_lock(struct page *page) 1297{ 1298 int ret; 1299 1300 lock_page_nosync(page); 1301 ret = set_page_dirty(page); 1302 unlock_page(page); 1303 return ret; 1304} 1305EXPORT_SYMBOL(set_page_dirty_lock); 1306 1307/* 1308 * Clear a page's dirty flag, while caring for dirty memory accounting. 1309 * Returns true if the page was previously dirty. 1310 * 1311 * This is for preparing to put the page under writeout. We leave the page 1312 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1313 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1314 * implementation will run either set_page_writeback() or set_page_dirty(), 1315 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1316 * back into sync. 1317 * 1318 * This incoherency between the page's dirty flag and radix-tree tag is 1319 * unfortunate, but it only exists while the page is locked. 1320 */ 1321int clear_page_dirty_for_io(struct page *page) 1322{ 1323 struct address_space *mapping = page_mapping(page); 1324 1325 BUG_ON(!PageLocked(page)); 1326 1327 ClearPageReclaim(page); 1328 if (mapping && mapping_cap_account_dirty(mapping)) { 1329 /* 1330 * Yes, Virginia, this is indeed insane. 1331 * 1332 * We use this sequence to make sure that 1333 * (a) we account for dirty stats properly 1334 * (b) we tell the low-level filesystem to 1335 * mark the whole page dirty if it was 1336 * dirty in a pagetable. Only to then 1337 * (c) clean the page again and return 1 to 1338 * cause the writeback. 1339 * 1340 * This way we avoid all nasty races with the 1341 * dirty bit in multiple places and clearing 1342 * them concurrently from different threads. 1343 * 1344 * Note! Normally the "set_page_dirty(page)" 1345 * has no effect on the actual dirty bit - since 1346 * that will already usually be set. But we 1347 * need the side effects, and it can help us 1348 * avoid races. 1349 * 1350 * We basically use the page "master dirty bit" 1351 * as a serialization point for all the different 1352 * threads doing their things. 1353 */ 1354 if (page_mkclean(page)) 1355 set_page_dirty(page); 1356 /* 1357 * We carefully synchronise fault handlers against 1358 * installing a dirty pte and marking the page dirty 1359 * at this point. We do this by having them hold the 1360 * page lock at some point after installing their 1361 * pte, but before marking the page dirty. 1362 * Pages are always locked coming in here, so we get 1363 * the desired exclusion. See mm/memory.c:do_wp_page() 1364 * for more comments. 1365 */ 1366 if (TestClearPageDirty(page)) { 1367 dec_zone_page_state(page, NR_FILE_DIRTY); 1368 dec_bdi_stat(mapping->backing_dev_info, 1369 BDI_RECLAIMABLE); 1370 return 1; 1371 } 1372 return 0; 1373 } 1374 return TestClearPageDirty(page); 1375} 1376EXPORT_SYMBOL(clear_page_dirty_for_io); 1377 1378int test_clear_page_writeback(struct page *page) 1379{ 1380 struct address_space *mapping = page_mapping(page); 1381 int ret; 1382 1383 if (mapping) { 1384 struct backing_dev_info *bdi = mapping->backing_dev_info; 1385 unsigned long flags; 1386 1387 spin_lock_irqsave(&mapping->tree_lock, flags); 1388 ret = TestClearPageWriteback(page); 1389 if (ret) { 1390 radix_tree_tag_clear(&mapping->page_tree, 1391 page_index(page), 1392 PAGECACHE_TAG_WRITEBACK); 1393 if (bdi_cap_account_writeback(bdi)) { 1394 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1395 __bdi_writeout_inc(bdi); 1396 } 1397 } 1398 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1399 } else { 1400 ret = TestClearPageWriteback(page); 1401 } 1402 if (ret) 1403 dec_zone_page_state(page, NR_WRITEBACK); 1404 return ret; 1405} 1406 1407int test_set_page_writeback(struct page *page) 1408{ 1409 struct address_space *mapping = page_mapping(page); 1410 int ret; 1411 1412 if (mapping) { 1413 struct backing_dev_info *bdi = mapping->backing_dev_info; 1414 unsigned long flags; 1415 1416 spin_lock_irqsave(&mapping->tree_lock, flags); 1417 ret = TestSetPageWriteback(page); 1418 if (!ret) { 1419 radix_tree_tag_set(&mapping->page_tree, 1420 page_index(page), 1421 PAGECACHE_TAG_WRITEBACK); 1422 if (bdi_cap_account_writeback(bdi)) 1423 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1424 } 1425 if (!PageDirty(page)) 1426 radix_tree_tag_clear(&mapping->page_tree, 1427 page_index(page), 1428 PAGECACHE_TAG_DIRTY); 1429 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1430 } else { 1431 ret = TestSetPageWriteback(page); 1432 } 1433 if (!ret) 1434 inc_zone_page_state(page, NR_WRITEBACK); 1435 return ret; 1436 1437} 1438EXPORT_SYMBOL(test_set_page_writeback); 1439 1440/* 1441 * Return true if any of the pages in the mapping are marked with the 1442 * passed tag. 1443 */ 1444int mapping_tagged(struct address_space *mapping, int tag) 1445{ 1446 int ret; 1447 rcu_read_lock(); 1448 ret = radix_tree_tagged(&mapping->page_tree, tag); 1449 rcu_read_unlock(); 1450 return ret; 1451} 1452EXPORT_SYMBOL(mapping_tagged); 1453