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 #include <trace/events/writeback.h> 38 39 /* 40 * Sleep at most 200ms at a time in balance_dirty_pages(). 41 */ 42 #define MAX_PAUSE max(HZ/5, 1) 43 44 /* 45 * Estimate write bandwidth at 200ms intervals. 46 */ 47 #define BANDWIDTH_INTERVAL max(HZ/5, 1) 48 49 /* 50 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 51 * will look to see if it needs to force writeback or throttling. 52 */ 53 static long ratelimit_pages = 32; 54 55 /* 56 * When balance_dirty_pages decides that the caller needs to perform some 57 * non-background writeback, this is how many pages it will attempt to write. 58 * It should be somewhat larger than dirtied pages to ensure that reasonably 59 * large amounts of I/O are submitted. 60 */ 61 static inline long sync_writeback_pages(unsigned long dirtied) 62 { 63 if (dirtied < ratelimit_pages) 64 dirtied = ratelimit_pages; 65 66 return dirtied + dirtied / 2; 67 } 68 69 /* The following parameters are exported via /proc/sys/vm */ 70 71 /* 72 * Start background writeback (via writeback threads) at this percentage 73 */ 74 int dirty_background_ratio = 10; 75 76 /* 77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of 78 * dirty_background_ratio * the amount of dirtyable memory 79 */ 80 unsigned long dirty_background_bytes; 81 82 /* 83 * free highmem will not be subtracted from the total free memory 84 * for calculating free ratios if vm_highmem_is_dirtyable is true 85 */ 86 int vm_highmem_is_dirtyable; 87 88 /* 89 * The generator of dirty data starts writeback at this percentage 90 */ 91 int vm_dirty_ratio = 20; 92 93 /* 94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of 95 * vm_dirty_ratio * the amount of dirtyable memory 96 */ 97 unsigned long vm_dirty_bytes; 98 99 /* 100 * The interval between `kupdate'-style writebacks 101 */ 102 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ 103 104 /* 105 * The longest time for which data is allowed to remain dirty 106 */ 107 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ 108 109 /* 110 * Flag that makes the machine dump writes/reads and block dirtyings. 111 */ 112 int block_dump; 113 114 /* 115 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 116 * a full sync is triggered after this time elapses without any disk activity. 117 */ 118 int laptop_mode; 119 120 EXPORT_SYMBOL(laptop_mode); 121 122 /* End of sysctl-exported parameters */ 123 124 unsigned long global_dirty_limit; 125 126 /* 127 * Scale the writeback cache size proportional to the relative writeout speeds. 128 * 129 * We do this by keeping a floating proportion between BDIs, based on page 130 * writeback completions [end_page_writeback()]. Those devices that write out 131 * pages fastest will get the larger share, while the slower will get a smaller 132 * share. 133 * 134 * We use page writeout completions because we are interested in getting rid of 135 * dirty pages. Having them written out is the primary goal. 136 * 137 * We introduce a concept of time, a period over which we measure these events, 138 * because demand can/will vary over time. The length of this period itself is 139 * measured in page writeback completions. 140 * 141 */ 142 static struct prop_descriptor vm_completions; 143 static struct prop_descriptor vm_dirties; 144 145 /* 146 * couple the period to the dirty_ratio: 147 * 148 * period/2 ~ roundup_pow_of_two(dirty limit) 149 */ 150 static int calc_period_shift(void) 151 { 152 unsigned long dirty_total; 153 154 if (vm_dirty_bytes) 155 dirty_total = vm_dirty_bytes / PAGE_SIZE; 156 else 157 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 158 100; 159 return 2 + ilog2(dirty_total - 1); 160 } 161 162 /* 163 * update the period when the dirty threshold changes. 164 */ 165 static void update_completion_period(void) 166 { 167 int shift = calc_period_shift(); 168 prop_change_shift(&vm_completions, shift); 169 prop_change_shift(&vm_dirties, shift); 170 } 171 172 int dirty_background_ratio_handler(struct ctl_table *table, int write, 173 void __user *buffer, size_t *lenp, 174 loff_t *ppos) 175 { 176 int ret; 177 178 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 179 if (ret == 0 && write) 180 dirty_background_bytes = 0; 181 return ret; 182 } 183 184 int dirty_background_bytes_handler(struct ctl_table *table, int write, 185 void __user *buffer, size_t *lenp, 186 loff_t *ppos) 187 { 188 int ret; 189 190 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 191 if (ret == 0 && write) 192 dirty_background_ratio = 0; 193 return ret; 194 } 195 196 int dirty_ratio_handler(struct ctl_table *table, int write, 197 void __user *buffer, size_t *lenp, 198 loff_t *ppos) 199 { 200 int old_ratio = vm_dirty_ratio; 201 int ret; 202 203 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 204 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 205 update_completion_period(); 206 vm_dirty_bytes = 0; 207 } 208 return ret; 209 } 210 211 212 int dirty_bytes_handler(struct ctl_table *table, int write, 213 void __user *buffer, size_t *lenp, 214 loff_t *ppos) 215 { 216 unsigned long old_bytes = vm_dirty_bytes; 217 int ret; 218 219 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 220 if (ret == 0 && write && vm_dirty_bytes != old_bytes) { 221 update_completion_period(); 222 vm_dirty_ratio = 0; 223 } 224 return ret; 225 } 226 227 /* 228 * Increment the BDI's writeout completion count and the global writeout 229 * completion count. Called from test_clear_page_writeback(). 230 */ 231 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 232 { 233 __inc_bdi_stat(bdi, BDI_WRITTEN); 234 __prop_inc_percpu_max(&vm_completions, &bdi->completions, 235 bdi->max_prop_frac); 236 } 237 238 void bdi_writeout_inc(struct backing_dev_info *bdi) 239 { 240 unsigned long flags; 241 242 local_irq_save(flags); 243 __bdi_writeout_inc(bdi); 244 local_irq_restore(flags); 245 } 246 EXPORT_SYMBOL_GPL(bdi_writeout_inc); 247 248 void task_dirty_inc(struct task_struct *tsk) 249 { 250 prop_inc_single(&vm_dirties, &tsk->dirties); 251 } 252 253 /* 254 * Obtain an accurate fraction of the BDI's portion. 255 */ 256 static void bdi_writeout_fraction(struct backing_dev_info *bdi, 257 long *numerator, long *denominator) 258 { 259 prop_fraction_percpu(&vm_completions, &bdi->completions, 260 numerator, denominator); 261 } 262 263 static inline void task_dirties_fraction(struct task_struct *tsk, 264 long *numerator, long *denominator) 265 { 266 prop_fraction_single(&vm_dirties, &tsk->dirties, 267 numerator, denominator); 268 } 269 270 /* 271 * task_dirty_limit - scale down dirty throttling threshold for one task 272 * 273 * task specific dirty limit: 274 * 275 * dirty -= (dirty/8) * p_{t} 276 * 277 * To protect light/slow dirtying tasks from heavier/fast ones, we start 278 * throttling individual tasks before reaching the bdi dirty limit. 279 * Relatively low thresholds will be allocated to heavy dirtiers. So when 280 * dirty pages grow large, heavy dirtiers will be throttled first, which will 281 * effectively curb the growth of dirty pages. Light dirtiers with high enough 282 * dirty threshold may never get throttled. 283 */ 284 #define TASK_LIMIT_FRACTION 8 285 static unsigned long task_dirty_limit(struct task_struct *tsk, 286 unsigned long bdi_dirty) 287 { 288 long numerator, denominator; 289 unsigned long dirty = bdi_dirty; 290 u64 inv = dirty / TASK_LIMIT_FRACTION; 291 292 task_dirties_fraction(tsk, &numerator, &denominator); 293 inv *= numerator; 294 do_div(inv, denominator); 295 296 dirty -= inv; 297 298 return max(dirty, bdi_dirty/2); 299 } 300 301 /* Minimum limit for any task */ 302 static unsigned long task_min_dirty_limit(unsigned long bdi_dirty) 303 { 304 return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION; 305 } 306 307 /* 308 * bdi_min_ratio keeps the sum of the minimum dirty shares of all 309 * registered backing devices, which, for obvious reasons, can not 310 * exceed 100%. 311 */ 312 static unsigned int bdi_min_ratio; 313 314 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 315 { 316 int ret = 0; 317 318 spin_lock_bh(&bdi_lock); 319 if (min_ratio > bdi->max_ratio) { 320 ret = -EINVAL; 321 } else { 322 min_ratio -= bdi->min_ratio; 323 if (bdi_min_ratio + min_ratio < 100) { 324 bdi_min_ratio += min_ratio; 325 bdi->min_ratio += min_ratio; 326 } else { 327 ret = -EINVAL; 328 } 329 } 330 spin_unlock_bh(&bdi_lock); 331 332 return ret; 333 } 334 335 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 336 { 337 int ret = 0; 338 339 if (max_ratio > 100) 340 return -EINVAL; 341 342 spin_lock_bh(&bdi_lock); 343 if (bdi->min_ratio > max_ratio) { 344 ret = -EINVAL; 345 } else { 346 bdi->max_ratio = max_ratio; 347 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; 348 } 349 spin_unlock_bh(&bdi_lock); 350 351 return ret; 352 } 353 EXPORT_SYMBOL(bdi_set_max_ratio); 354 355 /* 356 * Work out the current dirty-memory clamping and background writeout 357 * thresholds. 358 * 359 * The main aim here is to lower them aggressively if there is a lot of mapped 360 * memory around. To avoid stressing page reclaim with lots of unreclaimable 361 * pages. It is better to clamp down on writers than to start swapping, and 362 * performing lots of scanning. 363 * 364 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 365 * 366 * We don't permit the clamping level to fall below 5% - that is getting rather 367 * excessive. 368 * 369 * We make sure that the background writeout level is below the adjusted 370 * clamping level. 371 */ 372 373 static unsigned long highmem_dirtyable_memory(unsigned long total) 374 { 375 #ifdef CONFIG_HIGHMEM 376 int node; 377 unsigned long x = 0; 378 379 for_each_node_state(node, N_HIGH_MEMORY) { 380 struct zone *z = 381 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 382 383 x += zone_page_state(z, NR_FREE_PAGES) + 384 zone_reclaimable_pages(z); 385 } 386 /* 387 * Make sure that the number of highmem pages is never larger 388 * than the number of the total dirtyable memory. This can only 389 * occur in very strange VM situations but we want to make sure 390 * that this does not occur. 391 */ 392 return min(x, total); 393 #else 394 return 0; 395 #endif 396 } 397 398 /** 399 * determine_dirtyable_memory - amount of memory that may be used 400 * 401 * Returns the numebr of pages that can currently be freed and used 402 * by the kernel for direct mappings. 403 */ 404 unsigned long determine_dirtyable_memory(void) 405 { 406 unsigned long x; 407 408 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); 409 410 if (!vm_highmem_is_dirtyable) 411 x -= highmem_dirtyable_memory(x); 412 413 return x + 1; /* Ensure that we never return 0 */ 414 } 415 416 static unsigned long hard_dirty_limit(unsigned long thresh) 417 { 418 return max(thresh, global_dirty_limit); 419 } 420 421 /* 422 * global_dirty_limits - background-writeback and dirty-throttling thresholds 423 * 424 * Calculate the dirty thresholds based on sysctl parameters 425 * - vm.dirty_background_ratio or vm.dirty_background_bytes 426 * - vm.dirty_ratio or vm.dirty_bytes 427 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and 428 * real-time tasks. 429 */ 430 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) 431 { 432 unsigned long background; 433 unsigned long dirty; 434 unsigned long uninitialized_var(available_memory); 435 struct task_struct *tsk; 436 437 if (!vm_dirty_bytes || !dirty_background_bytes) 438 available_memory = determine_dirtyable_memory(); 439 440 if (vm_dirty_bytes) 441 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); 442 else 443 dirty = (vm_dirty_ratio * available_memory) / 100; 444 445 if (dirty_background_bytes) 446 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); 447 else 448 background = (dirty_background_ratio * available_memory) / 100; 449 450 if (background >= dirty) 451 background = dirty / 2; 452 tsk = current; 453 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 454 background += background / 4; 455 dirty += dirty / 4; 456 } 457 *pbackground = background; 458 *pdirty = dirty; 459 trace_global_dirty_state(background, dirty); 460 } 461 462 /** 463 * bdi_dirty_limit - @bdi's share of dirty throttling threshold 464 * @bdi: the backing_dev_info to query 465 * @dirty: global dirty limit in pages 466 * 467 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of 468 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. 469 * And the "limit" in the name is not seriously taken as hard limit in 470 * balance_dirty_pages(). 471 * 472 * It allocates high/low dirty limits to fast/slow devices, in order to prevent 473 * - starving fast devices 474 * - piling up dirty pages (that will take long time to sync) on slow devices 475 * 476 * The bdi's share of dirty limit will be adapting to its throughput and 477 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. 478 */ 479 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) 480 { 481 u64 bdi_dirty; 482 long numerator, denominator; 483 484 /* 485 * Calculate this BDI's share of the dirty ratio. 486 */ 487 bdi_writeout_fraction(bdi, &numerator, &denominator); 488 489 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 490 bdi_dirty *= numerator; 491 do_div(bdi_dirty, denominator); 492 493 bdi_dirty += (dirty * bdi->min_ratio) / 100; 494 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 495 bdi_dirty = dirty * bdi->max_ratio / 100; 496 497 return bdi_dirty; 498 } 499 500 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, 501 unsigned long elapsed, 502 unsigned long written) 503 { 504 const unsigned long period = roundup_pow_of_two(3 * HZ); 505 unsigned long avg = bdi->avg_write_bandwidth; 506 unsigned long old = bdi->write_bandwidth; 507 u64 bw; 508 509 /* 510 * bw = written * HZ / elapsed 511 * 512 * bw * elapsed + write_bandwidth * (period - elapsed) 513 * write_bandwidth = --------------------------------------------------- 514 * period 515 */ 516 bw = written - bdi->written_stamp; 517 bw *= HZ; 518 if (unlikely(elapsed > period)) { 519 do_div(bw, elapsed); 520 avg = bw; 521 goto out; 522 } 523 bw += (u64)bdi->write_bandwidth * (period - elapsed); 524 bw >>= ilog2(period); 525 526 /* 527 * one more level of smoothing, for filtering out sudden spikes 528 */ 529 if (avg > old && old >= (unsigned long)bw) 530 avg -= (avg - old) >> 3; 531 532 if (avg < old && old <= (unsigned long)bw) 533 avg += (old - avg) >> 3; 534 535 out: 536 bdi->write_bandwidth = bw; 537 bdi->avg_write_bandwidth = avg; 538 } 539 540 /* 541 * The global dirtyable memory and dirty threshold could be suddenly knocked 542 * down by a large amount (eg. on the startup of KVM in a swapless system). 543 * This may throw the system into deep dirty exceeded state and throttle 544 * heavy/light dirtiers alike. To retain good responsiveness, maintain 545 * global_dirty_limit for tracking slowly down to the knocked down dirty 546 * threshold. 547 */ 548 static void update_dirty_limit(unsigned long thresh, unsigned long dirty) 549 { 550 unsigned long limit = global_dirty_limit; 551 552 /* 553 * Follow up in one step. 554 */ 555 if (limit < thresh) { 556 limit = thresh; 557 goto update; 558 } 559 560 /* 561 * Follow down slowly. Use the higher one as the target, because thresh 562 * may drop below dirty. This is exactly the reason to introduce 563 * global_dirty_limit which is guaranteed to lie above the dirty pages. 564 */ 565 thresh = max(thresh, dirty); 566 if (limit > thresh) { 567 limit -= (limit - thresh) >> 5; 568 goto update; 569 } 570 return; 571 update: 572 global_dirty_limit = limit; 573 } 574 575 static void global_update_bandwidth(unsigned long thresh, 576 unsigned long dirty, 577 unsigned long now) 578 { 579 static DEFINE_SPINLOCK(dirty_lock); 580 static unsigned long update_time; 581 582 /* 583 * check locklessly first to optimize away locking for the most time 584 */ 585 if (time_before(now, update_time + BANDWIDTH_INTERVAL)) 586 return; 587 588 spin_lock(&dirty_lock); 589 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { 590 update_dirty_limit(thresh, dirty); 591 update_time = now; 592 } 593 spin_unlock(&dirty_lock); 594 } 595 596 void __bdi_update_bandwidth(struct backing_dev_info *bdi, 597 unsigned long thresh, 598 unsigned long dirty, 599 unsigned long bdi_thresh, 600 unsigned long bdi_dirty, 601 unsigned long start_time) 602 { 603 unsigned long now = jiffies; 604 unsigned long elapsed = now - bdi->bw_time_stamp; 605 unsigned long written; 606 607 /* 608 * rate-limit, only update once every 200ms. 609 */ 610 if (elapsed < BANDWIDTH_INTERVAL) 611 return; 612 613 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); 614 615 /* 616 * Skip quiet periods when disk bandwidth is under-utilized. 617 * (at least 1s idle time between two flusher runs) 618 */ 619 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) 620 goto snapshot; 621 622 if (thresh) 623 global_update_bandwidth(thresh, dirty, now); 624 625 bdi_update_write_bandwidth(bdi, elapsed, written); 626 627 snapshot: 628 bdi->written_stamp = written; 629 bdi->bw_time_stamp = now; 630 } 631 632 static void bdi_update_bandwidth(struct backing_dev_info *bdi, 633 unsigned long thresh, 634 unsigned long dirty, 635 unsigned long bdi_thresh, 636 unsigned long bdi_dirty, 637 unsigned long start_time) 638 { 639 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) 640 return; 641 spin_lock(&bdi->wb.list_lock); 642 __bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty, 643 start_time); 644 spin_unlock(&bdi->wb.list_lock); 645 } 646 647 /* 648 * balance_dirty_pages() must be called by processes which are generating dirty 649 * data. It looks at the number of dirty pages in the machine and will force 650 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 651 * If we're over `background_thresh' then the writeback threads are woken to 652 * perform some writeout. 653 */ 654 static void balance_dirty_pages(struct address_space *mapping, 655 unsigned long write_chunk) 656 { 657 unsigned long nr_reclaimable, bdi_nr_reclaimable; 658 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ 659 unsigned long bdi_dirty; 660 unsigned long background_thresh; 661 unsigned long dirty_thresh; 662 unsigned long bdi_thresh; 663 unsigned long task_bdi_thresh; 664 unsigned long min_task_bdi_thresh; 665 unsigned long pages_written = 0; 666 unsigned long pause = 1; 667 bool dirty_exceeded = false; 668 bool clear_dirty_exceeded = true; 669 struct backing_dev_info *bdi = mapping->backing_dev_info; 670 unsigned long start_time = jiffies; 671 672 for (;;) { 673 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 674 global_page_state(NR_UNSTABLE_NFS); 675 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); 676 677 global_dirty_limits(&background_thresh, &dirty_thresh); 678 679 /* 680 * Throttle it only when the background writeback cannot 681 * catch-up. This avoids (excessively) small writeouts 682 * when the bdi limits are ramping up. 683 */ 684 if (nr_dirty <= (background_thresh + dirty_thresh) / 2) 685 break; 686 687 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); 688 min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh); 689 task_bdi_thresh = task_dirty_limit(current, bdi_thresh); 690 691 /* 692 * In order to avoid the stacked BDI deadlock we need 693 * to ensure we accurately count the 'dirty' pages when 694 * the threshold is low. 695 * 696 * Otherwise it would be possible to get thresh+n pages 697 * reported dirty, even though there are thresh-m pages 698 * actually dirty; with m+n sitting in the percpu 699 * deltas. 700 */ 701 if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) { 702 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 703 bdi_dirty = bdi_nr_reclaimable + 704 bdi_stat_sum(bdi, BDI_WRITEBACK); 705 } else { 706 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 707 bdi_dirty = bdi_nr_reclaimable + 708 bdi_stat(bdi, BDI_WRITEBACK); 709 } 710 711 /* 712 * The bdi thresh is somehow "soft" limit derived from the 713 * global "hard" limit. The former helps to prevent heavy IO 714 * bdi or process from holding back light ones; The latter is 715 * the last resort safeguard. 716 */ 717 dirty_exceeded = (bdi_dirty > task_bdi_thresh) || 718 (nr_dirty > dirty_thresh); 719 clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) && 720 (nr_dirty <= dirty_thresh); 721 722 if (!dirty_exceeded) 723 break; 724 725 if (!bdi->dirty_exceeded) 726 bdi->dirty_exceeded = 1; 727 728 bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty, 729 bdi_thresh, bdi_dirty, start_time); 730 731 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 732 * Unstable writes are a feature of certain networked 733 * filesystems (i.e. NFS) in which data may have been 734 * written to the server's write cache, but has not yet 735 * been flushed to permanent storage. 736 * Only move pages to writeback if this bdi is over its 737 * threshold otherwise wait until the disk writes catch 738 * up. 739 */ 740 trace_balance_dirty_start(bdi); 741 if (bdi_nr_reclaimable > task_bdi_thresh) { 742 pages_written += writeback_inodes_wb(&bdi->wb, 743 write_chunk); 744 trace_balance_dirty_written(bdi, pages_written); 745 if (pages_written >= write_chunk) 746 break; /* We've done our duty */ 747 } 748 __set_current_state(TASK_UNINTERRUPTIBLE); 749 io_schedule_timeout(pause); 750 trace_balance_dirty_wait(bdi); 751 752 dirty_thresh = hard_dirty_limit(dirty_thresh); 753 /* 754 * max-pause area. If dirty exceeded but still within this 755 * area, no need to sleep for more than 200ms: (a) 8 pages per 756 * 200ms is typically more than enough to curb heavy dirtiers; 757 * (b) the pause time limit makes the dirtiers more responsive. 758 */ 759 if (nr_dirty < dirty_thresh && 760 bdi_dirty < (task_bdi_thresh + bdi_thresh) / 2 && 761 time_after(jiffies, start_time + MAX_PAUSE)) 762 break; 763 764 /* 765 * Increase the delay for each loop, up to our previous 766 * default of taking a 100ms nap. 767 */ 768 pause <<= 1; 769 if (pause > HZ / 10) 770 pause = HZ / 10; 771 } 772 773 /* Clear dirty_exceeded flag only when no task can exceed the limit */ 774 if (clear_dirty_exceeded && bdi->dirty_exceeded) 775 bdi->dirty_exceeded = 0; 776 777 if (writeback_in_progress(bdi)) 778 return; 779 780 /* 781 * In laptop mode, we wait until hitting the higher threshold before 782 * starting background writeout, and then write out all the way down 783 * to the lower threshold. So slow writers cause minimal disk activity. 784 * 785 * In normal mode, we start background writeout at the lower 786 * background_thresh, to keep the amount of dirty memory low. 787 */ 788 if ((laptop_mode && pages_written) || 789 (!laptop_mode && (nr_reclaimable > background_thresh))) 790 bdi_start_background_writeback(bdi); 791 } 792 793 void set_page_dirty_balance(struct page *page, int page_mkwrite) 794 { 795 if (set_page_dirty(page) || page_mkwrite) { 796 struct address_space *mapping = page_mapping(page); 797 798 if (mapping) 799 balance_dirty_pages_ratelimited(mapping); 800 } 801 } 802 803 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0; 804 805 /** 806 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 807 * @mapping: address_space which was dirtied 808 * @nr_pages_dirtied: number of pages which the caller has just dirtied 809 * 810 * Processes which are dirtying memory should call in here once for each page 811 * which was newly dirtied. The function will periodically check the system's 812 * dirty state and will initiate writeback if needed. 813 * 814 * On really big machines, get_writeback_state is expensive, so try to avoid 815 * calling it too often (ratelimiting). But once we're over the dirty memory 816 * limit we decrease the ratelimiting by a lot, to prevent individual processes 817 * from overshooting the limit by (ratelimit_pages) each. 818 */ 819 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 820 unsigned long nr_pages_dirtied) 821 { 822 struct backing_dev_info *bdi = mapping->backing_dev_info; 823 unsigned long ratelimit; 824 unsigned long *p; 825 826 if (!bdi_cap_account_dirty(bdi)) 827 return; 828 829 ratelimit = ratelimit_pages; 830 if (mapping->backing_dev_info->dirty_exceeded) 831 ratelimit = 8; 832 833 /* 834 * Check the rate limiting. Also, we do not want to throttle real-time 835 * tasks in balance_dirty_pages(). Period. 836 */ 837 preempt_disable(); 838 p = &__get_cpu_var(bdp_ratelimits); 839 *p += nr_pages_dirtied; 840 if (unlikely(*p >= ratelimit)) { 841 ratelimit = sync_writeback_pages(*p); 842 *p = 0; 843 preempt_enable(); 844 balance_dirty_pages(mapping, ratelimit); 845 return; 846 } 847 preempt_enable(); 848 } 849 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 850 851 void throttle_vm_writeout(gfp_t gfp_mask) 852 { 853 unsigned long background_thresh; 854 unsigned long dirty_thresh; 855 856 for ( ; ; ) { 857 global_dirty_limits(&background_thresh, &dirty_thresh); 858 859 /* 860 * Boost the allowable dirty threshold a bit for page 861 * allocators so they don't get DoS'ed by heavy writers 862 */ 863 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 864 865 if (global_page_state(NR_UNSTABLE_NFS) + 866 global_page_state(NR_WRITEBACK) <= dirty_thresh) 867 break; 868 congestion_wait(BLK_RW_ASYNC, HZ/10); 869 870 /* 871 * The caller might hold locks which can prevent IO completion 872 * or progress in the filesystem. So we cannot just sit here 873 * waiting for IO to complete. 874 */ 875 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 876 break; 877 } 878 } 879 880 /* 881 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 882 */ 883 int dirty_writeback_centisecs_handler(ctl_table *table, int write, 884 void __user *buffer, size_t *length, loff_t *ppos) 885 { 886 proc_dointvec(table, write, buffer, length, ppos); 887 bdi_arm_supers_timer(); 888 return 0; 889 } 890 891 #ifdef CONFIG_BLOCK 892 void laptop_mode_timer_fn(unsigned long data) 893 { 894 struct request_queue *q = (struct request_queue *)data; 895 int nr_pages = global_page_state(NR_FILE_DIRTY) + 896 global_page_state(NR_UNSTABLE_NFS); 897 898 /* 899 * We want to write everything out, not just down to the dirty 900 * threshold 901 */ 902 if (bdi_has_dirty_io(&q->backing_dev_info)) 903 bdi_start_writeback(&q->backing_dev_info, nr_pages); 904 } 905 906 /* 907 * We've spun up the disk and we're in laptop mode: schedule writeback 908 * of all dirty data a few seconds from now. If the flush is already scheduled 909 * then push it back - the user is still using the disk. 910 */ 911 void laptop_io_completion(struct backing_dev_info *info) 912 { 913 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); 914 } 915 916 /* 917 * We're in laptop mode and we've just synced. The sync's writes will have 918 * caused another writeback to be scheduled by laptop_io_completion. 919 * Nothing needs to be written back anymore, so we unschedule the writeback. 920 */ 921 void laptop_sync_completion(void) 922 { 923 struct backing_dev_info *bdi; 924 925 rcu_read_lock(); 926 927 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) 928 del_timer(&bdi->laptop_mode_wb_timer); 929 930 rcu_read_unlock(); 931 } 932 #endif 933 934 /* 935 * If ratelimit_pages is too high then we can get into dirty-data overload 936 * if a large number of processes all perform writes at the same time. 937 * If it is too low then SMP machines will call the (expensive) 938 * get_writeback_state too often. 939 * 940 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 941 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 942 * thresholds before writeback cuts in. 943 * 944 * But the limit should not be set too high. Because it also controls the 945 * amount of memory which the balance_dirty_pages() caller has to write back. 946 * If this is too large then the caller will block on the IO queue all the 947 * time. So limit it to four megabytes - the balance_dirty_pages() caller 948 * will write six megabyte chunks, max. 949 */ 950 951 void writeback_set_ratelimit(void) 952 { 953 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 954 if (ratelimit_pages < 16) 955 ratelimit_pages = 16; 956 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 957 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 958 } 959 960 static int __cpuinit 961 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 962 { 963 writeback_set_ratelimit(); 964 return NOTIFY_DONE; 965 } 966 967 static struct notifier_block __cpuinitdata ratelimit_nb = { 968 .notifier_call = ratelimit_handler, 969 .next = NULL, 970 }; 971 972 /* 973 * Called early on to tune the page writeback dirty limits. 974 * 975 * We used to scale dirty pages according to how total memory 976 * related to pages that could be allocated for buffers (by 977 * comparing nr_free_buffer_pages() to vm_total_pages. 978 * 979 * However, that was when we used "dirty_ratio" to scale with 980 * all memory, and we don't do that any more. "dirty_ratio" 981 * is now applied to total non-HIGHPAGE memory (by subtracting 982 * totalhigh_pages from vm_total_pages), and as such we can't 983 * get into the old insane situation any more where we had 984 * large amounts of dirty pages compared to a small amount of 985 * non-HIGHMEM memory. 986 * 987 * But we might still want to scale the dirty_ratio by how 988 * much memory the box has.. 989 */ 990 void __init page_writeback_init(void) 991 { 992 int shift; 993 994 writeback_set_ratelimit(); 995 register_cpu_notifier(&ratelimit_nb); 996 997 shift = calc_period_shift(); 998 prop_descriptor_init(&vm_completions, shift); 999 prop_descriptor_init(&vm_dirties, shift); 1000 } 1001 1002 /** 1003 * tag_pages_for_writeback - tag pages to be written by write_cache_pages 1004 * @mapping: address space structure to write 1005 * @start: starting page index 1006 * @end: ending page index (inclusive) 1007 * 1008 * This function scans the page range from @start to @end (inclusive) and tags 1009 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is 1010 * that write_cache_pages (or whoever calls this function) will then use 1011 * TOWRITE tag to identify pages eligible for writeback. This mechanism is 1012 * used to avoid livelocking of writeback by a process steadily creating new 1013 * dirty pages in the file (thus it is important for this function to be quick 1014 * so that it can tag pages faster than a dirtying process can create them). 1015 */ 1016 /* 1017 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. 1018 */ 1019 void tag_pages_for_writeback(struct address_space *mapping, 1020 pgoff_t start, pgoff_t end) 1021 { 1022 #define WRITEBACK_TAG_BATCH 4096 1023 unsigned long tagged; 1024 1025 do { 1026 spin_lock_irq(&mapping->tree_lock); 1027 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, 1028 &start, end, WRITEBACK_TAG_BATCH, 1029 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); 1030 spin_unlock_irq(&mapping->tree_lock); 1031 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); 1032 cond_resched(); 1033 /* We check 'start' to handle wrapping when end == ~0UL */ 1034 } while (tagged >= WRITEBACK_TAG_BATCH && start); 1035 } 1036 EXPORT_SYMBOL(tag_pages_for_writeback); 1037 1038 /** 1039 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 1040 * @mapping: address space structure to write 1041 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1042 * @writepage: function called for each page 1043 * @data: data passed to writepage function 1044 * 1045 * If a page is already under I/O, write_cache_pages() skips it, even 1046 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 1047 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 1048 * and msync() need to guarantee that all the data which was dirty at the time 1049 * the call was made get new I/O started against them. If wbc->sync_mode is 1050 * WB_SYNC_ALL then we were called for data integrity and we must wait for 1051 * existing IO to complete. 1052 * 1053 * To avoid livelocks (when other process dirties new pages), we first tag 1054 * pages which should be written back with TOWRITE tag and only then start 1055 * writing them. For data-integrity sync we have to be careful so that we do 1056 * not miss some pages (e.g., because some other process has cleared TOWRITE 1057 * tag we set). The rule we follow is that TOWRITE tag can be cleared only 1058 * by the process clearing the DIRTY tag (and submitting the page for IO). 1059 */ 1060 int write_cache_pages(struct address_space *mapping, 1061 struct writeback_control *wbc, writepage_t writepage, 1062 void *data) 1063 { 1064 int ret = 0; 1065 int done = 0; 1066 struct pagevec pvec; 1067 int nr_pages; 1068 pgoff_t uninitialized_var(writeback_index); 1069 pgoff_t index; 1070 pgoff_t end; /* Inclusive */ 1071 pgoff_t done_index; 1072 int cycled; 1073 int range_whole = 0; 1074 int tag; 1075 1076 pagevec_init(&pvec, 0); 1077 if (wbc->range_cyclic) { 1078 writeback_index = mapping->writeback_index; /* prev offset */ 1079 index = writeback_index; 1080 if (index == 0) 1081 cycled = 1; 1082 else 1083 cycled = 0; 1084 end = -1; 1085 } else { 1086 index = wbc->range_start >> PAGE_CACHE_SHIFT; 1087 end = wbc->range_end >> PAGE_CACHE_SHIFT; 1088 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 1089 range_whole = 1; 1090 cycled = 1; /* ignore range_cyclic tests */ 1091 } 1092 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) 1093 tag = PAGECACHE_TAG_TOWRITE; 1094 else 1095 tag = PAGECACHE_TAG_DIRTY; 1096 retry: 1097 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) 1098 tag_pages_for_writeback(mapping, index, end); 1099 done_index = index; 1100 while (!done && (index <= end)) { 1101 int i; 1102 1103 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, 1104 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); 1105 if (nr_pages == 0) 1106 break; 1107 1108 for (i = 0; i < nr_pages; i++) { 1109 struct page *page = pvec.pages[i]; 1110 1111 /* 1112 * At this point, the page may be truncated or 1113 * invalidated (changing page->mapping to NULL), or 1114 * even swizzled back from swapper_space to tmpfs file 1115 * mapping. However, page->index will not change 1116 * because we have a reference on the page. 1117 */ 1118 if (page->index > end) { 1119 /* 1120 * can't be range_cyclic (1st pass) because 1121 * end == -1 in that case. 1122 */ 1123 done = 1; 1124 break; 1125 } 1126 1127 done_index = page->index; 1128 1129 lock_page(page); 1130 1131 /* 1132 * Page truncated or invalidated. We can freely skip it 1133 * then, even for data integrity operations: the page 1134 * has disappeared concurrently, so there could be no 1135 * real expectation of this data interity operation 1136 * even if there is now a new, dirty page at the same 1137 * pagecache address. 1138 */ 1139 if (unlikely(page->mapping != mapping)) { 1140 continue_unlock: 1141 unlock_page(page); 1142 continue; 1143 } 1144 1145 if (!PageDirty(page)) { 1146 /* someone wrote it for us */ 1147 goto continue_unlock; 1148 } 1149 1150 if (PageWriteback(page)) { 1151 if (wbc->sync_mode != WB_SYNC_NONE) 1152 wait_on_page_writeback(page); 1153 else 1154 goto continue_unlock; 1155 } 1156 1157 BUG_ON(PageWriteback(page)); 1158 if (!clear_page_dirty_for_io(page)) 1159 goto continue_unlock; 1160 1161 trace_wbc_writepage(wbc, mapping->backing_dev_info); 1162 ret = (*writepage)(page, wbc, data); 1163 if (unlikely(ret)) { 1164 if (ret == AOP_WRITEPAGE_ACTIVATE) { 1165 unlock_page(page); 1166 ret = 0; 1167 } else { 1168 /* 1169 * done_index is set past this page, 1170 * so media errors will not choke 1171 * background writeout for the entire 1172 * file. This has consequences for 1173 * range_cyclic semantics (ie. it may 1174 * not be suitable for data integrity 1175 * writeout). 1176 */ 1177 done_index = page->index + 1; 1178 done = 1; 1179 break; 1180 } 1181 } 1182 1183 /* 1184 * We stop writing back only if we are not doing 1185 * integrity sync. In case of integrity sync we have to 1186 * keep going until we have written all the pages 1187 * we tagged for writeback prior to entering this loop. 1188 */ 1189 if (--wbc->nr_to_write <= 0 && 1190 wbc->sync_mode == WB_SYNC_NONE) { 1191 done = 1; 1192 break; 1193 } 1194 } 1195 pagevec_release(&pvec); 1196 cond_resched(); 1197 } 1198 if (!cycled && !done) { 1199 /* 1200 * range_cyclic: 1201 * We hit the last page and there is more work to be done: wrap 1202 * back to the start of the file 1203 */ 1204 cycled = 1; 1205 index = 0; 1206 end = writeback_index - 1; 1207 goto retry; 1208 } 1209 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) 1210 mapping->writeback_index = done_index; 1211 1212 return ret; 1213 } 1214 EXPORT_SYMBOL(write_cache_pages); 1215 1216 /* 1217 * Function used by generic_writepages to call the real writepage 1218 * function and set the mapping flags on error 1219 */ 1220 static int __writepage(struct page *page, struct writeback_control *wbc, 1221 void *data) 1222 { 1223 struct address_space *mapping = data; 1224 int ret = mapping->a_ops->writepage(page, wbc); 1225 mapping_set_error(mapping, ret); 1226 return ret; 1227 } 1228 1229 /** 1230 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 1231 * @mapping: address space structure to write 1232 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1233 * 1234 * This is a library function, which implements the writepages() 1235 * address_space_operation. 1236 */ 1237 int generic_writepages(struct address_space *mapping, 1238 struct writeback_control *wbc) 1239 { 1240 struct blk_plug plug; 1241 int ret; 1242 1243 /* deal with chardevs and other special file */ 1244 if (!mapping->a_ops->writepage) 1245 return 0; 1246 1247 blk_start_plug(&plug); 1248 ret = write_cache_pages(mapping, wbc, __writepage, mapping); 1249 blk_finish_plug(&plug); 1250 return ret; 1251 } 1252 1253 EXPORT_SYMBOL(generic_writepages); 1254 1255 int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1256 { 1257 int ret; 1258 1259 if (wbc->nr_to_write <= 0) 1260 return 0; 1261 if (mapping->a_ops->writepages) 1262 ret = mapping->a_ops->writepages(mapping, wbc); 1263 else 1264 ret = generic_writepages(mapping, wbc); 1265 return ret; 1266 } 1267 1268 /** 1269 * write_one_page - write out a single page and optionally wait on I/O 1270 * @page: the page to write 1271 * @wait: if true, wait on writeout 1272 * 1273 * The page must be locked by the caller and will be unlocked upon return. 1274 * 1275 * write_one_page() returns a negative error code if I/O failed. 1276 */ 1277 int write_one_page(struct page *page, int wait) 1278 { 1279 struct address_space *mapping = page->mapping; 1280 int ret = 0; 1281 struct writeback_control wbc = { 1282 .sync_mode = WB_SYNC_ALL, 1283 .nr_to_write = 1, 1284 }; 1285 1286 BUG_ON(!PageLocked(page)); 1287 1288 if (wait) 1289 wait_on_page_writeback(page); 1290 1291 if (clear_page_dirty_for_io(page)) { 1292 page_cache_get(page); 1293 ret = mapping->a_ops->writepage(page, &wbc); 1294 if (ret == 0 && wait) { 1295 wait_on_page_writeback(page); 1296 if (PageError(page)) 1297 ret = -EIO; 1298 } 1299 page_cache_release(page); 1300 } else { 1301 unlock_page(page); 1302 } 1303 return ret; 1304 } 1305 EXPORT_SYMBOL(write_one_page); 1306 1307 /* 1308 * For address_spaces which do not use buffers nor write back. 1309 */ 1310 int __set_page_dirty_no_writeback(struct page *page) 1311 { 1312 if (!PageDirty(page)) 1313 return !TestSetPageDirty(page); 1314 return 0; 1315 } 1316 1317 /* 1318 * Helper function for set_page_dirty family. 1319 * NOTE: This relies on being atomic wrt interrupts. 1320 */ 1321 void account_page_dirtied(struct page *page, struct address_space *mapping) 1322 { 1323 if (mapping_cap_account_dirty(mapping)) { 1324 __inc_zone_page_state(page, NR_FILE_DIRTY); 1325 __inc_zone_page_state(page, NR_DIRTIED); 1326 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); 1327 task_dirty_inc(current); 1328 task_io_account_write(PAGE_CACHE_SIZE); 1329 } 1330 } 1331 EXPORT_SYMBOL(account_page_dirtied); 1332 1333 /* 1334 * Helper function for set_page_writeback family. 1335 * NOTE: Unlike account_page_dirtied this does not rely on being atomic 1336 * wrt interrupts. 1337 */ 1338 void account_page_writeback(struct page *page) 1339 { 1340 inc_zone_page_state(page, NR_WRITEBACK); 1341 } 1342 EXPORT_SYMBOL(account_page_writeback); 1343 1344 /* 1345 * For address_spaces which do not use buffers. Just tag the page as dirty in 1346 * its radix tree. 1347 * 1348 * This is also used when a single buffer is being dirtied: we want to set the 1349 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1350 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1351 * 1352 * Most callers have locked the page, which pins the address_space in memory. 1353 * But zap_pte_range() does not lock the page, however in that case the 1354 * mapping is pinned by the vma's ->vm_file reference. 1355 * 1356 * We take care to handle the case where the page was truncated from the 1357 * mapping by re-checking page_mapping() inside tree_lock. 1358 */ 1359 int __set_page_dirty_nobuffers(struct page *page) 1360 { 1361 if (!TestSetPageDirty(page)) { 1362 struct address_space *mapping = page_mapping(page); 1363 struct address_space *mapping2; 1364 1365 if (!mapping) 1366 return 1; 1367 1368 spin_lock_irq(&mapping->tree_lock); 1369 mapping2 = page_mapping(page); 1370 if (mapping2) { /* Race with truncate? */ 1371 BUG_ON(mapping2 != mapping); 1372 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1373 account_page_dirtied(page, mapping); 1374 radix_tree_tag_set(&mapping->page_tree, 1375 page_index(page), PAGECACHE_TAG_DIRTY); 1376 } 1377 spin_unlock_irq(&mapping->tree_lock); 1378 if (mapping->host) { 1379 /* !PageAnon && !swapper_space */ 1380 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1381 } 1382 return 1; 1383 } 1384 return 0; 1385 } 1386 EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1387 1388 /* 1389 * When a writepage implementation decides that it doesn't want to write this 1390 * page for some reason, it should redirty the locked page via 1391 * redirty_page_for_writepage() and it should then unlock the page and return 0 1392 */ 1393 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1394 { 1395 wbc->pages_skipped++; 1396 return __set_page_dirty_nobuffers(page); 1397 } 1398 EXPORT_SYMBOL(redirty_page_for_writepage); 1399 1400 /* 1401 * Dirty a page. 1402 * 1403 * For pages with a mapping this should be done under the page lock 1404 * for the benefit of asynchronous memory errors who prefer a consistent 1405 * dirty state. This rule can be broken in some special cases, 1406 * but should be better not to. 1407 * 1408 * If the mapping doesn't provide a set_page_dirty a_op, then 1409 * just fall through and assume that it wants buffer_heads. 1410 */ 1411 int set_page_dirty(struct page *page) 1412 { 1413 struct address_space *mapping = page_mapping(page); 1414 1415 if (likely(mapping)) { 1416 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1417 /* 1418 * readahead/lru_deactivate_page could remain 1419 * PG_readahead/PG_reclaim due to race with end_page_writeback 1420 * About readahead, if the page is written, the flags would be 1421 * reset. So no problem. 1422 * About lru_deactivate_page, if the page is redirty, the flag 1423 * will be reset. So no problem. but if the page is used by readahead 1424 * it will confuse readahead and make it restart the size rampup 1425 * process. But it's a trivial problem. 1426 */ 1427 ClearPageReclaim(page); 1428 #ifdef CONFIG_BLOCK 1429 if (!spd) 1430 spd = __set_page_dirty_buffers; 1431 #endif 1432 return (*spd)(page); 1433 } 1434 if (!PageDirty(page)) { 1435 if (!TestSetPageDirty(page)) 1436 return 1; 1437 } 1438 return 0; 1439 } 1440 EXPORT_SYMBOL(set_page_dirty); 1441 1442 /* 1443 * set_page_dirty() is racy if the caller has no reference against 1444 * page->mapping->host, and if the page is unlocked. This is because another 1445 * CPU could truncate the page off the mapping and then free the mapping. 1446 * 1447 * Usually, the page _is_ locked, or the caller is a user-space process which 1448 * holds a reference on the inode by having an open file. 1449 * 1450 * In other cases, the page should be locked before running set_page_dirty(). 1451 */ 1452 int set_page_dirty_lock(struct page *page) 1453 { 1454 int ret; 1455 1456 lock_page(page); 1457 ret = set_page_dirty(page); 1458 unlock_page(page); 1459 return ret; 1460 } 1461 EXPORT_SYMBOL(set_page_dirty_lock); 1462 1463 /* 1464 * Clear a page's dirty flag, while caring for dirty memory accounting. 1465 * Returns true if the page was previously dirty. 1466 * 1467 * This is for preparing to put the page under writeout. We leave the page 1468 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1469 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1470 * implementation will run either set_page_writeback() or set_page_dirty(), 1471 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1472 * back into sync. 1473 * 1474 * This incoherency between the page's dirty flag and radix-tree tag is 1475 * unfortunate, but it only exists while the page is locked. 1476 */ 1477 int clear_page_dirty_for_io(struct page *page) 1478 { 1479 struct address_space *mapping = page_mapping(page); 1480 1481 BUG_ON(!PageLocked(page)); 1482 1483 if (mapping && mapping_cap_account_dirty(mapping)) { 1484 /* 1485 * Yes, Virginia, this is indeed insane. 1486 * 1487 * We use this sequence to make sure that 1488 * (a) we account for dirty stats properly 1489 * (b) we tell the low-level filesystem to 1490 * mark the whole page dirty if it was 1491 * dirty in a pagetable. Only to then 1492 * (c) clean the page again and return 1 to 1493 * cause the writeback. 1494 * 1495 * This way we avoid all nasty races with the 1496 * dirty bit in multiple places and clearing 1497 * them concurrently from different threads. 1498 * 1499 * Note! Normally the "set_page_dirty(page)" 1500 * has no effect on the actual dirty bit - since 1501 * that will already usually be set. But we 1502 * need the side effects, and it can help us 1503 * avoid races. 1504 * 1505 * We basically use the page "master dirty bit" 1506 * as a serialization point for all the different 1507 * threads doing their things. 1508 */ 1509 if (page_mkclean(page)) 1510 set_page_dirty(page); 1511 /* 1512 * We carefully synchronise fault handlers against 1513 * installing a dirty pte and marking the page dirty 1514 * at this point. We do this by having them hold the 1515 * page lock at some point after installing their 1516 * pte, but before marking the page dirty. 1517 * Pages are always locked coming in here, so we get 1518 * the desired exclusion. See mm/memory.c:do_wp_page() 1519 * for more comments. 1520 */ 1521 if (TestClearPageDirty(page)) { 1522 dec_zone_page_state(page, NR_FILE_DIRTY); 1523 dec_bdi_stat(mapping->backing_dev_info, 1524 BDI_RECLAIMABLE); 1525 return 1; 1526 } 1527 return 0; 1528 } 1529 return TestClearPageDirty(page); 1530 } 1531 EXPORT_SYMBOL(clear_page_dirty_for_io); 1532 1533 int test_clear_page_writeback(struct page *page) 1534 { 1535 struct address_space *mapping = page_mapping(page); 1536 int ret; 1537 1538 if (mapping) { 1539 struct backing_dev_info *bdi = mapping->backing_dev_info; 1540 unsigned long flags; 1541 1542 spin_lock_irqsave(&mapping->tree_lock, flags); 1543 ret = TestClearPageWriteback(page); 1544 if (ret) { 1545 radix_tree_tag_clear(&mapping->page_tree, 1546 page_index(page), 1547 PAGECACHE_TAG_WRITEBACK); 1548 if (bdi_cap_account_writeback(bdi)) { 1549 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1550 __bdi_writeout_inc(bdi); 1551 } 1552 } 1553 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1554 } else { 1555 ret = TestClearPageWriteback(page); 1556 } 1557 if (ret) { 1558 dec_zone_page_state(page, NR_WRITEBACK); 1559 inc_zone_page_state(page, NR_WRITTEN); 1560 } 1561 return ret; 1562 } 1563 1564 int test_set_page_writeback(struct page *page) 1565 { 1566 struct address_space *mapping = page_mapping(page); 1567 int ret; 1568 1569 if (mapping) { 1570 struct backing_dev_info *bdi = mapping->backing_dev_info; 1571 unsigned long flags; 1572 1573 spin_lock_irqsave(&mapping->tree_lock, flags); 1574 ret = TestSetPageWriteback(page); 1575 if (!ret) { 1576 radix_tree_tag_set(&mapping->page_tree, 1577 page_index(page), 1578 PAGECACHE_TAG_WRITEBACK); 1579 if (bdi_cap_account_writeback(bdi)) 1580 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1581 } 1582 if (!PageDirty(page)) 1583 radix_tree_tag_clear(&mapping->page_tree, 1584 page_index(page), 1585 PAGECACHE_TAG_DIRTY); 1586 radix_tree_tag_clear(&mapping->page_tree, 1587 page_index(page), 1588 PAGECACHE_TAG_TOWRITE); 1589 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1590 } else { 1591 ret = TestSetPageWriteback(page); 1592 } 1593 if (!ret) 1594 account_page_writeback(page); 1595 return ret; 1596 1597 } 1598 EXPORT_SYMBOL(test_set_page_writeback); 1599 1600 /* 1601 * Return true if any of the pages in the mapping are marked with the 1602 * passed tag. 1603 */ 1604 int mapping_tagged(struct address_space *mapping, int tag) 1605 { 1606 return radix_tree_tagged(&mapping->page_tree, tag); 1607 } 1608 EXPORT_SYMBOL(mapping_tagged); 1609