page-writeback.c revision 54848d73f9f254631303d6eab9b976855988b266
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/export.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#define RATELIMIT_CALC_SHIFT 10 50 51/* 52 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 53 * will look to see if it needs to force writeback or throttling. 54 */ 55static long ratelimit_pages = 32; 56 57/* The following parameters are exported via /proc/sys/vm */ 58 59/* 60 * Start background writeback (via writeback threads) at this percentage 61 */ 62int dirty_background_ratio = 10; 63 64/* 65 * dirty_background_bytes starts at 0 (disabled) so that it is a function of 66 * dirty_background_ratio * the amount of dirtyable memory 67 */ 68unsigned long dirty_background_bytes; 69 70/* 71 * free highmem will not be subtracted from the total free memory 72 * for calculating free ratios if vm_highmem_is_dirtyable is true 73 */ 74int vm_highmem_is_dirtyable; 75 76/* 77 * The generator of dirty data starts writeback at this percentage 78 */ 79int vm_dirty_ratio = 20; 80 81/* 82 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of 83 * vm_dirty_ratio * the amount of dirtyable memory 84 */ 85unsigned long vm_dirty_bytes; 86 87/* 88 * The interval between `kupdate'-style writebacks 89 */ 90unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ 91 92/* 93 * The longest time for which data is allowed to remain dirty 94 */ 95unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ 96 97/* 98 * Flag that makes the machine dump writes/reads and block dirtyings. 99 */ 100int block_dump; 101 102/* 103 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 104 * a full sync is triggered after this time elapses without any disk activity. 105 */ 106int laptop_mode; 107 108EXPORT_SYMBOL(laptop_mode); 109 110/* End of sysctl-exported parameters */ 111 112unsigned long global_dirty_limit; 113 114/* 115 * Scale the writeback cache size proportional to the relative writeout speeds. 116 * 117 * We do this by keeping a floating proportion between BDIs, based on page 118 * writeback completions [end_page_writeback()]. Those devices that write out 119 * pages fastest will get the larger share, while the slower will get a smaller 120 * share. 121 * 122 * We use page writeout completions because we are interested in getting rid of 123 * dirty pages. Having them written out is the primary goal. 124 * 125 * We introduce a concept of time, a period over which we measure these events, 126 * because demand can/will vary over time. The length of this period itself is 127 * measured in page writeback completions. 128 * 129 */ 130static struct prop_descriptor vm_completions; 131 132/* 133 * couple the period to the dirty_ratio: 134 * 135 * period/2 ~ roundup_pow_of_two(dirty limit) 136 */ 137static int calc_period_shift(void) 138{ 139 unsigned long dirty_total; 140 141 if (vm_dirty_bytes) 142 dirty_total = vm_dirty_bytes / PAGE_SIZE; 143 else 144 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 145 100; 146 return 2 + ilog2(dirty_total - 1); 147} 148 149/* 150 * update the period when the dirty threshold changes. 151 */ 152static void update_completion_period(void) 153{ 154 int shift = calc_period_shift(); 155 prop_change_shift(&vm_completions, shift); 156 157 writeback_set_ratelimit(); 158} 159 160int dirty_background_ratio_handler(struct ctl_table *table, int write, 161 void __user *buffer, size_t *lenp, 162 loff_t *ppos) 163{ 164 int ret; 165 166 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 167 if (ret == 0 && write) 168 dirty_background_bytes = 0; 169 return ret; 170} 171 172int dirty_background_bytes_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_doulongvec_minmax(table, write, buffer, lenp, ppos); 179 if (ret == 0 && write) 180 dirty_background_ratio = 0; 181 return ret; 182} 183 184int dirty_ratio_handler(struct ctl_table *table, int write, 185 void __user *buffer, size_t *lenp, 186 loff_t *ppos) 187{ 188 int old_ratio = vm_dirty_ratio; 189 int ret; 190 191 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 192 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 193 update_completion_period(); 194 vm_dirty_bytes = 0; 195 } 196 return ret; 197} 198 199 200int dirty_bytes_handler(struct ctl_table *table, int write, 201 void __user *buffer, size_t *lenp, 202 loff_t *ppos) 203{ 204 unsigned long old_bytes = vm_dirty_bytes; 205 int ret; 206 207 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 208 if (ret == 0 && write && vm_dirty_bytes != old_bytes) { 209 update_completion_period(); 210 vm_dirty_ratio = 0; 211 } 212 return ret; 213} 214 215/* 216 * Increment the BDI's writeout completion count and the global writeout 217 * completion count. Called from test_clear_page_writeback(). 218 */ 219static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 220{ 221 __inc_bdi_stat(bdi, BDI_WRITTEN); 222 __prop_inc_percpu_max(&vm_completions, &bdi->completions, 223 bdi->max_prop_frac); 224} 225 226void bdi_writeout_inc(struct backing_dev_info *bdi) 227{ 228 unsigned long flags; 229 230 local_irq_save(flags); 231 __bdi_writeout_inc(bdi); 232 local_irq_restore(flags); 233} 234EXPORT_SYMBOL_GPL(bdi_writeout_inc); 235 236/* 237 * Obtain an accurate fraction of the BDI's portion. 238 */ 239static void bdi_writeout_fraction(struct backing_dev_info *bdi, 240 long *numerator, long *denominator) 241{ 242 prop_fraction_percpu(&vm_completions, &bdi->completions, 243 numerator, denominator); 244} 245 246/* 247 * bdi_min_ratio keeps the sum of the minimum dirty shares of all 248 * registered backing devices, which, for obvious reasons, can not 249 * exceed 100%. 250 */ 251static unsigned int bdi_min_ratio; 252 253int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 254{ 255 int ret = 0; 256 257 spin_lock_bh(&bdi_lock); 258 if (min_ratio > bdi->max_ratio) { 259 ret = -EINVAL; 260 } else { 261 min_ratio -= bdi->min_ratio; 262 if (bdi_min_ratio + min_ratio < 100) { 263 bdi_min_ratio += min_ratio; 264 bdi->min_ratio += min_ratio; 265 } else { 266 ret = -EINVAL; 267 } 268 } 269 spin_unlock_bh(&bdi_lock); 270 271 return ret; 272} 273 274int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 275{ 276 int ret = 0; 277 278 if (max_ratio > 100) 279 return -EINVAL; 280 281 spin_lock_bh(&bdi_lock); 282 if (bdi->min_ratio > max_ratio) { 283 ret = -EINVAL; 284 } else { 285 bdi->max_ratio = max_ratio; 286 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; 287 } 288 spin_unlock_bh(&bdi_lock); 289 290 return ret; 291} 292EXPORT_SYMBOL(bdi_set_max_ratio); 293 294/* 295 * Work out the current dirty-memory clamping and background writeout 296 * thresholds. 297 * 298 * The main aim here is to lower them aggressively if there is a lot of mapped 299 * memory around. To avoid stressing page reclaim with lots of unreclaimable 300 * pages. It is better to clamp down on writers than to start swapping, and 301 * performing lots of scanning. 302 * 303 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 304 * 305 * We don't permit the clamping level to fall below 5% - that is getting rather 306 * excessive. 307 * 308 * We make sure that the background writeout level is below the adjusted 309 * clamping level. 310 */ 311 312static unsigned long highmem_dirtyable_memory(unsigned long total) 313{ 314#ifdef CONFIG_HIGHMEM 315 int node; 316 unsigned long x = 0; 317 318 for_each_node_state(node, N_HIGH_MEMORY) { 319 struct zone *z = 320 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 321 322 x += zone_page_state(z, NR_FREE_PAGES) + 323 zone_reclaimable_pages(z); 324 } 325 /* 326 * Make sure that the number of highmem pages is never larger 327 * than the number of the total dirtyable memory. This can only 328 * occur in very strange VM situations but we want to make sure 329 * that this does not occur. 330 */ 331 return min(x, total); 332#else 333 return 0; 334#endif 335} 336 337/** 338 * determine_dirtyable_memory - amount of memory that may be used 339 * 340 * Returns the numebr of pages that can currently be freed and used 341 * by the kernel for direct mappings. 342 */ 343unsigned long determine_dirtyable_memory(void) 344{ 345 unsigned long x; 346 347 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); 348 349 if (!vm_highmem_is_dirtyable) 350 x -= highmem_dirtyable_memory(x); 351 352 return x + 1; /* Ensure that we never return 0 */ 353} 354 355static unsigned long dirty_freerun_ceiling(unsigned long thresh, 356 unsigned long bg_thresh) 357{ 358 return (thresh + bg_thresh) / 2; 359} 360 361static unsigned long hard_dirty_limit(unsigned long thresh) 362{ 363 return max(thresh, global_dirty_limit); 364} 365 366/* 367 * global_dirty_limits - background-writeback and dirty-throttling thresholds 368 * 369 * Calculate the dirty thresholds based on sysctl parameters 370 * - vm.dirty_background_ratio or vm.dirty_background_bytes 371 * - vm.dirty_ratio or vm.dirty_bytes 372 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and 373 * real-time tasks. 374 */ 375void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) 376{ 377 unsigned long background; 378 unsigned long dirty; 379 unsigned long uninitialized_var(available_memory); 380 struct task_struct *tsk; 381 382 if (!vm_dirty_bytes || !dirty_background_bytes) 383 available_memory = determine_dirtyable_memory(); 384 385 if (vm_dirty_bytes) 386 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); 387 else 388 dirty = (vm_dirty_ratio * available_memory) / 100; 389 390 if (dirty_background_bytes) 391 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); 392 else 393 background = (dirty_background_ratio * available_memory) / 100; 394 395 if (background >= dirty) 396 background = dirty / 2; 397 tsk = current; 398 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 399 background += background / 4; 400 dirty += dirty / 4; 401 } 402 *pbackground = background; 403 *pdirty = dirty; 404 trace_global_dirty_state(background, dirty); 405} 406 407/** 408 * bdi_dirty_limit - @bdi's share of dirty throttling threshold 409 * @bdi: the backing_dev_info to query 410 * @dirty: global dirty limit in pages 411 * 412 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of 413 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. 414 * 415 * Note that balance_dirty_pages() will only seriously take it as a hard limit 416 * when sleeping max_pause per page is not enough to keep the dirty pages under 417 * control. For example, when the device is completely stalled due to some error 418 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. 419 * In the other normal situations, it acts more gently by throttling the tasks 420 * more (rather than completely block them) when the bdi dirty pages go high. 421 * 422 * It allocates high/low dirty limits to fast/slow devices, in order to prevent 423 * - starving fast devices 424 * - piling up dirty pages (that will take long time to sync) on slow devices 425 * 426 * The bdi's share of dirty limit will be adapting to its throughput and 427 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. 428 */ 429unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) 430{ 431 u64 bdi_dirty; 432 long numerator, denominator; 433 434 /* 435 * Calculate this BDI's share of the dirty ratio. 436 */ 437 bdi_writeout_fraction(bdi, &numerator, &denominator); 438 439 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 440 bdi_dirty *= numerator; 441 do_div(bdi_dirty, denominator); 442 443 bdi_dirty += (dirty * bdi->min_ratio) / 100; 444 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 445 bdi_dirty = dirty * bdi->max_ratio / 100; 446 447 return bdi_dirty; 448} 449 450/* 451 * Dirty position control. 452 * 453 * (o) global/bdi setpoints 454 * 455 * We want the dirty pages be balanced around the global/bdi setpoints. 456 * When the number of dirty pages is higher/lower than the setpoint, the 457 * dirty position control ratio (and hence task dirty ratelimit) will be 458 * decreased/increased to bring the dirty pages back to the setpoint. 459 * 460 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT 461 * 462 * if (dirty < setpoint) scale up pos_ratio 463 * if (dirty > setpoint) scale down pos_ratio 464 * 465 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio 466 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio 467 * 468 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT 469 * 470 * (o) global control line 471 * 472 * ^ pos_ratio 473 * | 474 * | |<===== global dirty control scope ======>| 475 * 2.0 .............* 476 * | .* 477 * | . * 478 * | . * 479 * | . * 480 * | . * 481 * | . * 482 * 1.0 ................................* 483 * | . . * 484 * | . . * 485 * | . . * 486 * | . . * 487 * | . . * 488 * 0 +------------.------------------.----------------------*-------------> 489 * freerun^ setpoint^ limit^ dirty pages 490 * 491 * (o) bdi control line 492 * 493 * ^ pos_ratio 494 * | 495 * | * 496 * | * 497 * | * 498 * | * 499 * | * |<=========== span ============>| 500 * 1.0 .......................* 501 * | . * 502 * | . * 503 * | . * 504 * | . * 505 * | . * 506 * | . * 507 * | . * 508 * | . * 509 * | . * 510 * | . * 511 * | . * 512 * 1/4 ...............................................* * * * * * * * * * * * 513 * | . . 514 * | . . 515 * | . . 516 * 0 +----------------------.-------------------------------.-------------> 517 * bdi_setpoint^ x_intercept^ 518 * 519 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can 520 * be smoothly throttled down to normal if it starts high in situations like 521 * - start writing to a slow SD card and a fast disk at the same time. The SD 522 * card's bdi_dirty may rush to many times higher than bdi_setpoint. 523 * - the bdi dirty thresh drops quickly due to change of JBOD workload 524 */ 525static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, 526 unsigned long thresh, 527 unsigned long bg_thresh, 528 unsigned long dirty, 529 unsigned long bdi_thresh, 530 unsigned long bdi_dirty) 531{ 532 unsigned long write_bw = bdi->avg_write_bandwidth; 533 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); 534 unsigned long limit = hard_dirty_limit(thresh); 535 unsigned long x_intercept; 536 unsigned long setpoint; /* dirty pages' target balance point */ 537 unsigned long bdi_setpoint; 538 unsigned long span; 539 long long pos_ratio; /* for scaling up/down the rate limit */ 540 long x; 541 542 if (unlikely(dirty >= limit)) 543 return 0; 544 545 /* 546 * global setpoint 547 * 548 * setpoint - dirty 3 549 * f(dirty) := 1.0 + (----------------) 550 * limit - setpoint 551 * 552 * it's a 3rd order polynomial that subjects to 553 * 554 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast 555 * (2) f(setpoint) = 1.0 => the balance point 556 * (3) f(limit) = 0 => the hard limit 557 * (4) df/dx <= 0 => negative feedback control 558 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) 559 * => fast response on large errors; small oscillation near setpoint 560 */ 561 setpoint = (freerun + limit) / 2; 562 x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT, 563 limit - setpoint + 1); 564 pos_ratio = x; 565 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; 566 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; 567 pos_ratio += 1 << RATELIMIT_CALC_SHIFT; 568 569 /* 570 * We have computed basic pos_ratio above based on global situation. If 571 * the bdi is over/under its share of dirty pages, we want to scale 572 * pos_ratio further down/up. That is done by the following mechanism. 573 */ 574 575 /* 576 * bdi setpoint 577 * 578 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint) 579 * 580 * x_intercept - bdi_dirty 581 * := -------------------------- 582 * x_intercept - bdi_setpoint 583 * 584 * The main bdi control line is a linear function that subjects to 585 * 586 * (1) f(bdi_setpoint) = 1.0 587 * (2) k = - 1 / (8 * write_bw) (in single bdi case) 588 * or equally: x_intercept = bdi_setpoint + 8 * write_bw 589 * 590 * For single bdi case, the dirty pages are observed to fluctuate 591 * regularly within range 592 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2] 593 * for various filesystems, where (2) can yield in a reasonable 12.5% 594 * fluctuation range for pos_ratio. 595 * 596 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its 597 * own size, so move the slope over accordingly and choose a slope that 598 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh. 599 */ 600 if (unlikely(bdi_thresh > thresh)) 601 bdi_thresh = thresh; 602 /* 603 * It's very possible that bdi_thresh is close to 0 not because the 604 * device is slow, but that it has remained inactive for long time. 605 * Honour such devices a reasonable good (hopefully IO efficient) 606 * threshold, so that the occasional writes won't be blocked and active 607 * writes can rampup the threshold quickly. 608 */ 609 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); 610 /* 611 * scale global setpoint to bdi's: 612 * bdi_setpoint = setpoint * bdi_thresh / thresh 613 */ 614 x = div_u64((u64)bdi_thresh << 16, thresh + 1); 615 bdi_setpoint = setpoint * (u64)x >> 16; 616 /* 617 * Use span=(8*write_bw) in single bdi case as indicated by 618 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case. 619 * 620 * bdi_thresh thresh - bdi_thresh 621 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh 622 * thresh thresh 623 */ 624 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16; 625 x_intercept = bdi_setpoint + span; 626 627 if (bdi_dirty < x_intercept - span / 4) { 628 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), 629 x_intercept - bdi_setpoint + 1); 630 } else 631 pos_ratio /= 4; 632 633 /* 634 * bdi reserve area, safeguard against dirty pool underrun and disk idle 635 * It may push the desired control point of global dirty pages higher 636 * than setpoint. 637 */ 638 x_intercept = bdi_thresh / 2; 639 if (bdi_dirty < x_intercept) { 640 if (bdi_dirty > x_intercept / 8) 641 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty); 642 else 643 pos_ratio *= 8; 644 } 645 646 return pos_ratio; 647} 648 649static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, 650 unsigned long elapsed, 651 unsigned long written) 652{ 653 const unsigned long period = roundup_pow_of_two(3 * HZ); 654 unsigned long avg = bdi->avg_write_bandwidth; 655 unsigned long old = bdi->write_bandwidth; 656 u64 bw; 657 658 /* 659 * bw = written * HZ / elapsed 660 * 661 * bw * elapsed + write_bandwidth * (period - elapsed) 662 * write_bandwidth = --------------------------------------------------- 663 * period 664 */ 665 bw = written - bdi->written_stamp; 666 bw *= HZ; 667 if (unlikely(elapsed > period)) { 668 do_div(bw, elapsed); 669 avg = bw; 670 goto out; 671 } 672 bw += (u64)bdi->write_bandwidth * (period - elapsed); 673 bw >>= ilog2(period); 674 675 /* 676 * one more level of smoothing, for filtering out sudden spikes 677 */ 678 if (avg > old && old >= (unsigned long)bw) 679 avg -= (avg - old) >> 3; 680 681 if (avg < old && old <= (unsigned long)bw) 682 avg += (old - avg) >> 3; 683 684out: 685 bdi->write_bandwidth = bw; 686 bdi->avg_write_bandwidth = avg; 687} 688 689/* 690 * The global dirtyable memory and dirty threshold could be suddenly knocked 691 * down by a large amount (eg. on the startup of KVM in a swapless system). 692 * This may throw the system into deep dirty exceeded state and throttle 693 * heavy/light dirtiers alike. To retain good responsiveness, maintain 694 * global_dirty_limit for tracking slowly down to the knocked down dirty 695 * threshold. 696 */ 697static void update_dirty_limit(unsigned long thresh, unsigned long dirty) 698{ 699 unsigned long limit = global_dirty_limit; 700 701 /* 702 * Follow up in one step. 703 */ 704 if (limit < thresh) { 705 limit = thresh; 706 goto update; 707 } 708 709 /* 710 * Follow down slowly. Use the higher one as the target, because thresh 711 * may drop below dirty. This is exactly the reason to introduce 712 * global_dirty_limit which is guaranteed to lie above the dirty pages. 713 */ 714 thresh = max(thresh, dirty); 715 if (limit > thresh) { 716 limit -= (limit - thresh) >> 5; 717 goto update; 718 } 719 return; 720update: 721 global_dirty_limit = limit; 722} 723 724static void global_update_bandwidth(unsigned long thresh, 725 unsigned long dirty, 726 unsigned long now) 727{ 728 static DEFINE_SPINLOCK(dirty_lock); 729 static unsigned long update_time; 730 731 /* 732 * check locklessly first to optimize away locking for the most time 733 */ 734 if (time_before(now, update_time + BANDWIDTH_INTERVAL)) 735 return; 736 737 spin_lock(&dirty_lock); 738 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { 739 update_dirty_limit(thresh, dirty); 740 update_time = now; 741 } 742 spin_unlock(&dirty_lock); 743} 744 745/* 746 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate. 747 * 748 * Normal bdi tasks will be curbed at or below it in long term. 749 * Obviously it should be around (write_bw / N) when there are N dd tasks. 750 */ 751static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, 752 unsigned long thresh, 753 unsigned long bg_thresh, 754 unsigned long dirty, 755 unsigned long bdi_thresh, 756 unsigned long bdi_dirty, 757 unsigned long dirtied, 758 unsigned long elapsed) 759{ 760 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); 761 unsigned long limit = hard_dirty_limit(thresh); 762 unsigned long setpoint = (freerun + limit) / 2; 763 unsigned long write_bw = bdi->avg_write_bandwidth; 764 unsigned long dirty_ratelimit = bdi->dirty_ratelimit; 765 unsigned long dirty_rate; 766 unsigned long task_ratelimit; 767 unsigned long balanced_dirty_ratelimit; 768 unsigned long pos_ratio; 769 unsigned long step; 770 unsigned long x; 771 772 /* 773 * The dirty rate will match the writeout rate in long term, except 774 * when dirty pages are truncated by userspace or re-dirtied by FS. 775 */ 776 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed; 777 778 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty, 779 bdi_thresh, bdi_dirty); 780 /* 781 * task_ratelimit reflects each dd's dirty rate for the past 200ms. 782 */ 783 task_ratelimit = (u64)dirty_ratelimit * 784 pos_ratio >> RATELIMIT_CALC_SHIFT; 785 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ 786 787 /* 788 * A linear estimation of the "balanced" throttle rate. The theory is, 789 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's 790 * dirty_rate will be measured to be (N * task_ratelimit). So the below 791 * formula will yield the balanced rate limit (write_bw / N). 792 * 793 * Note that the expanded form is not a pure rate feedback: 794 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) 795 * but also takes pos_ratio into account: 796 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) 797 * 798 * (1) is not realistic because pos_ratio also takes part in balancing 799 * the dirty rate. Consider the state 800 * pos_ratio = 0.5 (3) 801 * rate = 2 * (write_bw / N) (4) 802 * If (1) is used, it will stuck in that state! Because each dd will 803 * be throttled at 804 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) 805 * yielding 806 * dirty_rate = N * task_ratelimit = write_bw (6) 807 * put (6) into (1) we get 808 * rate_(i+1) = rate_(i) (7) 809 * 810 * So we end up using (2) to always keep 811 * rate_(i+1) ~= (write_bw / N) (8) 812 * regardless of the value of pos_ratio. As long as (8) is satisfied, 813 * pos_ratio is able to drive itself to 1.0, which is not only where 814 * the dirty count meet the setpoint, but also where the slope of 815 * pos_ratio is most flat and hence task_ratelimit is least fluctuated. 816 */ 817 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, 818 dirty_rate | 1); 819 820 /* 821 * We could safely do this and return immediately: 822 * 823 * bdi->dirty_ratelimit = balanced_dirty_ratelimit; 824 * 825 * However to get a more stable dirty_ratelimit, the below elaborated 826 * code makes use of task_ratelimit to filter out sigular points and 827 * limit the step size. 828 * 829 * The below code essentially only uses the relative value of 830 * 831 * task_ratelimit - dirty_ratelimit 832 * = (pos_ratio - 1) * dirty_ratelimit 833 * 834 * which reflects the direction and size of dirty position error. 835 */ 836 837 /* 838 * dirty_ratelimit will follow balanced_dirty_ratelimit iff 839 * task_ratelimit is on the same side of dirty_ratelimit, too. 840 * For example, when 841 * - dirty_ratelimit > balanced_dirty_ratelimit 842 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) 843 * lowering dirty_ratelimit will help meet both the position and rate 844 * control targets. Otherwise, don't update dirty_ratelimit if it will 845 * only help meet the rate target. After all, what the users ultimately 846 * feel and care are stable dirty rate and small position error. 847 * 848 * |task_ratelimit - dirty_ratelimit| is used to limit the step size 849 * and filter out the sigular points of balanced_dirty_ratelimit. Which 850 * keeps jumping around randomly and can even leap far away at times 851 * due to the small 200ms estimation period of dirty_rate (we want to 852 * keep that period small to reduce time lags). 853 */ 854 step = 0; 855 if (dirty < setpoint) { 856 x = min(bdi->balanced_dirty_ratelimit, 857 min(balanced_dirty_ratelimit, task_ratelimit)); 858 if (dirty_ratelimit < x) 859 step = x - dirty_ratelimit; 860 } else { 861 x = max(bdi->balanced_dirty_ratelimit, 862 max(balanced_dirty_ratelimit, task_ratelimit)); 863 if (dirty_ratelimit > x) 864 step = dirty_ratelimit - x; 865 } 866 867 /* 868 * Don't pursue 100% rate matching. It's impossible since the balanced 869 * rate itself is constantly fluctuating. So decrease the track speed 870 * when it gets close to the target. Helps eliminate pointless tremors. 871 */ 872 step >>= dirty_ratelimit / (2 * step + 1); 873 /* 874 * Limit the tracking speed to avoid overshooting. 875 */ 876 step = (step + 7) / 8; 877 878 if (dirty_ratelimit < balanced_dirty_ratelimit) 879 dirty_ratelimit += step; 880 else 881 dirty_ratelimit -= step; 882 883 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL); 884 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit; 885 886 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit); 887} 888 889void __bdi_update_bandwidth(struct backing_dev_info *bdi, 890 unsigned long thresh, 891 unsigned long bg_thresh, 892 unsigned long dirty, 893 unsigned long bdi_thresh, 894 unsigned long bdi_dirty, 895 unsigned long start_time) 896{ 897 unsigned long now = jiffies; 898 unsigned long elapsed = now - bdi->bw_time_stamp; 899 unsigned long dirtied; 900 unsigned long written; 901 902 /* 903 * rate-limit, only update once every 200ms. 904 */ 905 if (elapsed < BANDWIDTH_INTERVAL) 906 return; 907 908 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]); 909 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); 910 911 /* 912 * Skip quiet periods when disk bandwidth is under-utilized. 913 * (at least 1s idle time between two flusher runs) 914 */ 915 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) 916 goto snapshot; 917 918 if (thresh) { 919 global_update_bandwidth(thresh, dirty, now); 920 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty, 921 bdi_thresh, bdi_dirty, 922 dirtied, elapsed); 923 } 924 bdi_update_write_bandwidth(bdi, elapsed, written); 925 926snapshot: 927 bdi->dirtied_stamp = dirtied; 928 bdi->written_stamp = written; 929 bdi->bw_time_stamp = now; 930} 931 932static void bdi_update_bandwidth(struct backing_dev_info *bdi, 933 unsigned long thresh, 934 unsigned long bg_thresh, 935 unsigned long dirty, 936 unsigned long bdi_thresh, 937 unsigned long bdi_dirty, 938 unsigned long start_time) 939{ 940 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) 941 return; 942 spin_lock(&bdi->wb.list_lock); 943 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty, 944 bdi_thresh, bdi_dirty, start_time); 945 spin_unlock(&bdi->wb.list_lock); 946} 947 948/* 949 * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr() 950 * will look to see if it needs to start dirty throttling. 951 * 952 * If dirty_poll_interval is too low, big NUMA machines will call the expensive 953 * global_page_state() too often. So scale it near-sqrt to the safety margin 954 * (the number of pages we may dirty without exceeding the dirty limits). 955 */ 956static unsigned long dirty_poll_interval(unsigned long dirty, 957 unsigned long thresh) 958{ 959 if (thresh > dirty) 960 return 1UL << (ilog2(thresh - dirty) >> 1); 961 962 return 1; 963} 964 965static unsigned long bdi_max_pause(struct backing_dev_info *bdi, 966 unsigned long bdi_dirty) 967{ 968 unsigned long bw = bdi->avg_write_bandwidth; 969 unsigned long hi = ilog2(bw); 970 unsigned long lo = ilog2(bdi->dirty_ratelimit); 971 unsigned long t; 972 973 /* target for 20ms max pause on 1-dd case */ 974 t = HZ / 50; 975 976 /* 977 * Scale up pause time for concurrent dirtiers in order to reduce CPU 978 * overheads. 979 * 980 * (N * 20ms) on 2^N concurrent tasks. 981 */ 982 if (hi > lo) 983 t += (hi - lo) * (20 * HZ) / 1024; 984 985 /* 986 * Limit pause time for small memory systems. If sleeping for too long 987 * time, a small pool of dirty/writeback pages may go empty and disk go 988 * idle. 989 * 990 * 8 serves as the safety ratio. 991 */ 992 t = min(t, bdi_dirty * HZ / (8 * bw + 1)); 993 994 /* 995 * The pause time will be settled within range (max_pause/4, max_pause). 996 * Apply a minimal value of 4 to get a non-zero max_pause/4. 997 */ 998 return clamp_val(t, 4, MAX_PAUSE); 999} 1000 1001/* 1002 * balance_dirty_pages() must be called by processes which are generating dirty 1003 * data. It looks at the number of dirty pages in the machine and will force 1004 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. 1005 * If we're over `background_thresh' then the writeback threads are woken to 1006 * perform some writeout. 1007 */ 1008static void balance_dirty_pages(struct address_space *mapping, 1009 unsigned long pages_dirtied) 1010{ 1011 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ 1012 unsigned long bdi_reclaimable; 1013 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ 1014 unsigned long bdi_dirty; 1015 unsigned long freerun; 1016 unsigned long background_thresh; 1017 unsigned long dirty_thresh; 1018 unsigned long bdi_thresh; 1019 long pause = 0; 1020 long uninitialized_var(max_pause); 1021 bool dirty_exceeded = false; 1022 unsigned long task_ratelimit; 1023 unsigned long uninitialized_var(dirty_ratelimit); 1024 unsigned long pos_ratio; 1025 struct backing_dev_info *bdi = mapping->backing_dev_info; 1026 unsigned long start_time = jiffies; 1027 1028 for (;;) { 1029 /* 1030 * Unstable writes are a feature of certain networked 1031 * filesystems (i.e. NFS) in which data may have been 1032 * written to the server's write cache, but has not yet 1033 * been flushed to permanent storage. 1034 */ 1035 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 1036 global_page_state(NR_UNSTABLE_NFS); 1037 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); 1038 1039 global_dirty_limits(&background_thresh, &dirty_thresh); 1040 1041 /* 1042 * Throttle it only when the background writeback cannot 1043 * catch-up. This avoids (excessively) small writeouts 1044 * when the bdi limits are ramping up. 1045 */ 1046 freerun = dirty_freerun_ceiling(dirty_thresh, 1047 background_thresh); 1048 if (nr_dirty <= freerun) 1049 break; 1050 1051 if (unlikely(!writeback_in_progress(bdi))) 1052 bdi_start_background_writeback(bdi); 1053 1054 /* 1055 * bdi_thresh is not treated as some limiting factor as 1056 * dirty_thresh, due to reasons 1057 * - in JBOD setup, bdi_thresh can fluctuate a lot 1058 * - in a system with HDD and USB key, the USB key may somehow 1059 * go into state (bdi_dirty >> bdi_thresh) either because 1060 * bdi_dirty starts high, or because bdi_thresh drops low. 1061 * In this case we don't want to hard throttle the USB key 1062 * dirtiers for 100 seconds until bdi_dirty drops under 1063 * bdi_thresh. Instead the auxiliary bdi control line in 1064 * bdi_position_ratio() will let the dirtier task progress 1065 * at some rate <= (write_bw / 2) for bringing down bdi_dirty. 1066 */ 1067 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); 1068 1069 /* 1070 * In order to avoid the stacked BDI deadlock we need 1071 * to ensure we accurately count the 'dirty' pages when 1072 * the threshold is low. 1073 * 1074 * Otherwise it would be possible to get thresh+n pages 1075 * reported dirty, even though there are thresh-m pages 1076 * actually dirty; with m+n sitting in the percpu 1077 * deltas. 1078 */ 1079 if (bdi_thresh < 2 * bdi_stat_error(bdi)) { 1080 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 1081 bdi_dirty = bdi_reclaimable + 1082 bdi_stat_sum(bdi, BDI_WRITEBACK); 1083 } else { 1084 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 1085 bdi_dirty = bdi_reclaimable + 1086 bdi_stat(bdi, BDI_WRITEBACK); 1087 } 1088 1089 dirty_exceeded = (bdi_dirty > bdi_thresh) || 1090 (nr_dirty > dirty_thresh); 1091 if (dirty_exceeded && !bdi->dirty_exceeded) 1092 bdi->dirty_exceeded = 1; 1093 1094 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, 1095 nr_dirty, bdi_thresh, bdi_dirty, 1096 start_time); 1097 1098 max_pause = bdi_max_pause(bdi, bdi_dirty); 1099 1100 dirty_ratelimit = bdi->dirty_ratelimit; 1101 pos_ratio = bdi_position_ratio(bdi, dirty_thresh, 1102 background_thresh, nr_dirty, 1103 bdi_thresh, bdi_dirty); 1104 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >> 1105 RATELIMIT_CALC_SHIFT; 1106 if (unlikely(task_ratelimit == 0)) { 1107 pause = max_pause; 1108 goto pause; 1109 } 1110 pause = HZ * pages_dirtied / task_ratelimit; 1111 if (unlikely(pause <= 0)) { 1112 trace_balance_dirty_pages(bdi, 1113 dirty_thresh, 1114 background_thresh, 1115 nr_dirty, 1116 bdi_thresh, 1117 bdi_dirty, 1118 dirty_ratelimit, 1119 task_ratelimit, 1120 pages_dirtied, 1121 pause, 1122 start_time); 1123 pause = 1; /* avoid resetting nr_dirtied_pause below */ 1124 break; 1125 } 1126 pause = min(pause, max_pause); 1127 1128pause: 1129 trace_balance_dirty_pages(bdi, 1130 dirty_thresh, 1131 background_thresh, 1132 nr_dirty, 1133 bdi_thresh, 1134 bdi_dirty, 1135 dirty_ratelimit, 1136 task_ratelimit, 1137 pages_dirtied, 1138 pause, 1139 start_time); 1140 __set_current_state(TASK_KILLABLE); 1141 io_schedule_timeout(pause); 1142 1143 /* 1144 * This is typically equal to (nr_dirty < dirty_thresh) and can 1145 * also keep "1000+ dd on a slow USB stick" under control. 1146 */ 1147 if (task_ratelimit) 1148 break; 1149 1150 /* 1151 * In the case of an unresponding NFS server and the NFS dirty 1152 * pages exceeds dirty_thresh, give the other good bdi's a pipe 1153 * to go through, so that tasks on them still remain responsive. 1154 * 1155 * In theory 1 page is enough to keep the comsumer-producer 1156 * pipe going: the flusher cleans 1 page => the task dirties 1 1157 * more page. However bdi_dirty has accounting errors. So use 1158 * the larger and more IO friendly bdi_stat_error. 1159 */ 1160 if (bdi_dirty <= bdi_stat_error(bdi)) 1161 break; 1162 1163 if (fatal_signal_pending(current)) 1164 break; 1165 } 1166 1167 if (!dirty_exceeded && bdi->dirty_exceeded) 1168 bdi->dirty_exceeded = 0; 1169 1170 current->nr_dirtied = 0; 1171 if (pause == 0) { /* in freerun area */ 1172 current->nr_dirtied_pause = 1173 dirty_poll_interval(nr_dirty, dirty_thresh); 1174 } else if (pause <= max_pause / 4 && 1175 pages_dirtied >= current->nr_dirtied_pause) { 1176 current->nr_dirtied_pause = clamp_val( 1177 dirty_ratelimit * (max_pause / 2) / HZ, 1178 pages_dirtied + pages_dirtied / 8, 1179 pages_dirtied * 4); 1180 } else if (pause >= max_pause) { 1181 current->nr_dirtied_pause = 1 | clamp_val( 1182 dirty_ratelimit * (max_pause / 2) / HZ, 1183 pages_dirtied / 4, 1184 pages_dirtied - pages_dirtied / 8); 1185 } 1186 1187 if (writeback_in_progress(bdi)) 1188 return; 1189 1190 /* 1191 * In laptop mode, we wait until hitting the higher threshold before 1192 * starting background writeout, and then write out all the way down 1193 * to the lower threshold. So slow writers cause minimal disk activity. 1194 * 1195 * In normal mode, we start background writeout at the lower 1196 * background_thresh, to keep the amount of dirty memory low. 1197 */ 1198 if (laptop_mode) 1199 return; 1200 1201 if (nr_reclaimable > background_thresh) 1202 bdi_start_background_writeback(bdi); 1203} 1204 1205void set_page_dirty_balance(struct page *page, int page_mkwrite) 1206{ 1207 if (set_page_dirty(page) || page_mkwrite) { 1208 struct address_space *mapping = page_mapping(page); 1209 1210 if (mapping) 1211 balance_dirty_pages_ratelimited(mapping); 1212 } 1213} 1214 1215static DEFINE_PER_CPU(int, bdp_ratelimits); 1216 1217/* 1218 * Normal tasks are throttled by 1219 * loop { 1220 * dirty tsk->nr_dirtied_pause pages; 1221 * take a snap in balance_dirty_pages(); 1222 * } 1223 * However there is a worst case. If every task exit immediately when dirtied 1224 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be 1225 * called to throttle the page dirties. The solution is to save the not yet 1226 * throttled page dirties in dirty_throttle_leaks on task exit and charge them 1227 * randomly into the running tasks. This works well for the above worst case, 1228 * as the new task will pick up and accumulate the old task's leaked dirty 1229 * count and eventually get throttled. 1230 */ 1231DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; 1232 1233/** 1234 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 1235 * @mapping: address_space which was dirtied 1236 * @nr_pages_dirtied: number of pages which the caller has just dirtied 1237 * 1238 * Processes which are dirtying memory should call in here once for each page 1239 * which was newly dirtied. The function will periodically check the system's 1240 * dirty state and will initiate writeback if needed. 1241 * 1242 * On really big machines, get_writeback_state is expensive, so try to avoid 1243 * calling it too often (ratelimiting). But once we're over the dirty memory 1244 * limit we decrease the ratelimiting by a lot, to prevent individual processes 1245 * from overshooting the limit by (ratelimit_pages) each. 1246 */ 1247void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 1248 unsigned long nr_pages_dirtied) 1249{ 1250 struct backing_dev_info *bdi = mapping->backing_dev_info; 1251 int ratelimit; 1252 int *p; 1253 1254 if (!bdi_cap_account_dirty(bdi)) 1255 return; 1256 1257 ratelimit = current->nr_dirtied_pause; 1258 if (bdi->dirty_exceeded) 1259 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); 1260 1261 current->nr_dirtied += nr_pages_dirtied; 1262 1263 preempt_disable(); 1264 /* 1265 * This prevents one CPU to accumulate too many dirtied pages without 1266 * calling into balance_dirty_pages(), which can happen when there are 1267 * 1000+ tasks, all of them start dirtying pages at exactly the same 1268 * time, hence all honoured too large initial task->nr_dirtied_pause. 1269 */ 1270 p = &__get_cpu_var(bdp_ratelimits); 1271 if (unlikely(current->nr_dirtied >= ratelimit)) 1272 *p = 0; 1273 else { 1274 *p += nr_pages_dirtied; 1275 if (unlikely(*p >= ratelimit_pages)) { 1276 *p = 0; 1277 ratelimit = 0; 1278 } 1279 } 1280 /* 1281 * Pick up the dirtied pages by the exited tasks. This avoids lots of 1282 * short-lived tasks (eg. gcc invocations in a kernel build) escaping 1283 * the dirty throttling and livelock other long-run dirtiers. 1284 */ 1285 p = &__get_cpu_var(dirty_throttle_leaks); 1286 if (*p > 0 && current->nr_dirtied < ratelimit) { 1287 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); 1288 *p -= nr_pages_dirtied; 1289 current->nr_dirtied += nr_pages_dirtied; 1290 } 1291 preempt_enable(); 1292 1293 if (unlikely(current->nr_dirtied >= ratelimit)) 1294 balance_dirty_pages(mapping, current->nr_dirtied); 1295} 1296EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 1297 1298void throttle_vm_writeout(gfp_t gfp_mask) 1299{ 1300 unsigned long background_thresh; 1301 unsigned long dirty_thresh; 1302 1303 for ( ; ; ) { 1304 global_dirty_limits(&background_thresh, &dirty_thresh); 1305 1306 /* 1307 * Boost the allowable dirty threshold a bit for page 1308 * allocators so they don't get DoS'ed by heavy writers 1309 */ 1310 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 1311 1312 if (global_page_state(NR_UNSTABLE_NFS) + 1313 global_page_state(NR_WRITEBACK) <= dirty_thresh) 1314 break; 1315 congestion_wait(BLK_RW_ASYNC, HZ/10); 1316 1317 /* 1318 * The caller might hold locks which can prevent IO completion 1319 * or progress in the filesystem. So we cannot just sit here 1320 * waiting for IO to complete. 1321 */ 1322 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 1323 break; 1324 } 1325} 1326 1327/* 1328 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 1329 */ 1330int dirty_writeback_centisecs_handler(ctl_table *table, int write, 1331 void __user *buffer, size_t *length, loff_t *ppos) 1332{ 1333 proc_dointvec(table, write, buffer, length, ppos); 1334 bdi_arm_supers_timer(); 1335 return 0; 1336} 1337 1338#ifdef CONFIG_BLOCK 1339void laptop_mode_timer_fn(unsigned long data) 1340{ 1341 struct request_queue *q = (struct request_queue *)data; 1342 int nr_pages = global_page_state(NR_FILE_DIRTY) + 1343 global_page_state(NR_UNSTABLE_NFS); 1344 1345 /* 1346 * We want to write everything out, not just down to the dirty 1347 * threshold 1348 */ 1349 if (bdi_has_dirty_io(&q->backing_dev_info)) 1350 bdi_start_writeback(&q->backing_dev_info, nr_pages, 1351 WB_REASON_LAPTOP_TIMER); 1352} 1353 1354/* 1355 * We've spun up the disk and we're in laptop mode: schedule writeback 1356 * of all dirty data a few seconds from now. If the flush is already scheduled 1357 * then push it back - the user is still using the disk. 1358 */ 1359void laptop_io_completion(struct backing_dev_info *info) 1360{ 1361 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); 1362} 1363 1364/* 1365 * We're in laptop mode and we've just synced. The sync's writes will have 1366 * caused another writeback to be scheduled by laptop_io_completion. 1367 * Nothing needs to be written back anymore, so we unschedule the writeback. 1368 */ 1369void laptop_sync_completion(void) 1370{ 1371 struct backing_dev_info *bdi; 1372 1373 rcu_read_lock(); 1374 1375 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) 1376 del_timer(&bdi->laptop_mode_wb_timer); 1377 1378 rcu_read_unlock(); 1379} 1380#endif 1381 1382/* 1383 * If ratelimit_pages is too high then we can get into dirty-data overload 1384 * if a large number of processes all perform writes at the same time. 1385 * If it is too low then SMP machines will call the (expensive) 1386 * get_writeback_state too often. 1387 * 1388 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 1389 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 1390 * thresholds. 1391 */ 1392 1393void writeback_set_ratelimit(void) 1394{ 1395 unsigned long background_thresh; 1396 unsigned long dirty_thresh; 1397 global_dirty_limits(&background_thresh, &dirty_thresh); 1398 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); 1399 if (ratelimit_pages < 16) 1400 ratelimit_pages = 16; 1401} 1402 1403static int __cpuinit 1404ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 1405{ 1406 writeback_set_ratelimit(); 1407 return NOTIFY_DONE; 1408} 1409 1410static struct notifier_block __cpuinitdata ratelimit_nb = { 1411 .notifier_call = ratelimit_handler, 1412 .next = NULL, 1413}; 1414 1415/* 1416 * Called early on to tune the page writeback dirty limits. 1417 * 1418 * We used to scale dirty pages according to how total memory 1419 * related to pages that could be allocated for buffers (by 1420 * comparing nr_free_buffer_pages() to vm_total_pages. 1421 * 1422 * However, that was when we used "dirty_ratio" to scale with 1423 * all memory, and we don't do that any more. "dirty_ratio" 1424 * is now applied to total non-HIGHPAGE memory (by subtracting 1425 * totalhigh_pages from vm_total_pages), and as such we can't 1426 * get into the old insane situation any more where we had 1427 * large amounts of dirty pages compared to a small amount of 1428 * non-HIGHMEM memory. 1429 * 1430 * But we might still want to scale the dirty_ratio by how 1431 * much memory the box has.. 1432 */ 1433void __init page_writeback_init(void) 1434{ 1435 int shift; 1436 1437 writeback_set_ratelimit(); 1438 register_cpu_notifier(&ratelimit_nb); 1439 1440 shift = calc_period_shift(); 1441 prop_descriptor_init(&vm_completions, shift); 1442} 1443 1444/** 1445 * tag_pages_for_writeback - tag pages to be written by write_cache_pages 1446 * @mapping: address space structure to write 1447 * @start: starting page index 1448 * @end: ending page index (inclusive) 1449 * 1450 * This function scans the page range from @start to @end (inclusive) and tags 1451 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is 1452 * that write_cache_pages (or whoever calls this function) will then use 1453 * TOWRITE tag to identify pages eligible for writeback. This mechanism is 1454 * used to avoid livelocking of writeback by a process steadily creating new 1455 * dirty pages in the file (thus it is important for this function to be quick 1456 * so that it can tag pages faster than a dirtying process can create them). 1457 */ 1458/* 1459 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. 1460 */ 1461void tag_pages_for_writeback(struct address_space *mapping, 1462 pgoff_t start, pgoff_t end) 1463{ 1464#define WRITEBACK_TAG_BATCH 4096 1465 unsigned long tagged; 1466 1467 do { 1468 spin_lock_irq(&mapping->tree_lock); 1469 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, 1470 &start, end, WRITEBACK_TAG_BATCH, 1471 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); 1472 spin_unlock_irq(&mapping->tree_lock); 1473 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); 1474 cond_resched(); 1475 /* We check 'start' to handle wrapping when end == ~0UL */ 1476 } while (tagged >= WRITEBACK_TAG_BATCH && start); 1477} 1478EXPORT_SYMBOL(tag_pages_for_writeback); 1479 1480/** 1481 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 1482 * @mapping: address space structure to write 1483 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1484 * @writepage: function called for each page 1485 * @data: data passed to writepage function 1486 * 1487 * If a page is already under I/O, write_cache_pages() skips it, even 1488 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 1489 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 1490 * and msync() need to guarantee that all the data which was dirty at the time 1491 * the call was made get new I/O started against them. If wbc->sync_mode is 1492 * WB_SYNC_ALL then we were called for data integrity and we must wait for 1493 * existing IO to complete. 1494 * 1495 * To avoid livelocks (when other process dirties new pages), we first tag 1496 * pages which should be written back with TOWRITE tag and only then start 1497 * writing them. For data-integrity sync we have to be careful so that we do 1498 * not miss some pages (e.g., because some other process has cleared TOWRITE 1499 * tag we set). The rule we follow is that TOWRITE tag can be cleared only 1500 * by the process clearing the DIRTY tag (and submitting the page for IO). 1501 */ 1502int write_cache_pages(struct address_space *mapping, 1503 struct writeback_control *wbc, writepage_t writepage, 1504 void *data) 1505{ 1506 int ret = 0; 1507 int done = 0; 1508 struct pagevec pvec; 1509 int nr_pages; 1510 pgoff_t uninitialized_var(writeback_index); 1511 pgoff_t index; 1512 pgoff_t end; /* Inclusive */ 1513 pgoff_t done_index; 1514 int cycled; 1515 int range_whole = 0; 1516 int tag; 1517 1518 pagevec_init(&pvec, 0); 1519 if (wbc->range_cyclic) { 1520 writeback_index = mapping->writeback_index; /* prev offset */ 1521 index = writeback_index; 1522 if (index == 0) 1523 cycled = 1; 1524 else 1525 cycled = 0; 1526 end = -1; 1527 } else { 1528 index = wbc->range_start >> PAGE_CACHE_SHIFT; 1529 end = wbc->range_end >> PAGE_CACHE_SHIFT; 1530 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 1531 range_whole = 1; 1532 cycled = 1; /* ignore range_cyclic tests */ 1533 } 1534 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) 1535 tag = PAGECACHE_TAG_TOWRITE; 1536 else 1537 tag = PAGECACHE_TAG_DIRTY; 1538retry: 1539 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) 1540 tag_pages_for_writeback(mapping, index, end); 1541 done_index = index; 1542 while (!done && (index <= end)) { 1543 int i; 1544 1545 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, 1546 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); 1547 if (nr_pages == 0) 1548 break; 1549 1550 for (i = 0; i < nr_pages; i++) { 1551 struct page *page = pvec.pages[i]; 1552 1553 /* 1554 * At this point, the page may be truncated or 1555 * invalidated (changing page->mapping to NULL), or 1556 * even swizzled back from swapper_space to tmpfs file 1557 * mapping. However, page->index will not change 1558 * because we have a reference on the page. 1559 */ 1560 if (page->index > end) { 1561 /* 1562 * can't be range_cyclic (1st pass) because 1563 * end == -1 in that case. 1564 */ 1565 done = 1; 1566 break; 1567 } 1568 1569 done_index = page->index; 1570 1571 lock_page(page); 1572 1573 /* 1574 * Page truncated or invalidated. We can freely skip it 1575 * then, even for data integrity operations: the page 1576 * has disappeared concurrently, so there could be no 1577 * real expectation of this data interity operation 1578 * even if there is now a new, dirty page at the same 1579 * pagecache address. 1580 */ 1581 if (unlikely(page->mapping != mapping)) { 1582continue_unlock: 1583 unlock_page(page); 1584 continue; 1585 } 1586 1587 if (!PageDirty(page)) { 1588 /* someone wrote it for us */ 1589 goto continue_unlock; 1590 } 1591 1592 if (PageWriteback(page)) { 1593 if (wbc->sync_mode != WB_SYNC_NONE) 1594 wait_on_page_writeback(page); 1595 else 1596 goto continue_unlock; 1597 } 1598 1599 BUG_ON(PageWriteback(page)); 1600 if (!clear_page_dirty_for_io(page)) 1601 goto continue_unlock; 1602 1603 trace_wbc_writepage(wbc, mapping->backing_dev_info); 1604 ret = (*writepage)(page, wbc, data); 1605 if (unlikely(ret)) { 1606 if (ret == AOP_WRITEPAGE_ACTIVATE) { 1607 unlock_page(page); 1608 ret = 0; 1609 } else { 1610 /* 1611 * done_index is set past this page, 1612 * so media errors will not choke 1613 * background writeout for the entire 1614 * file. This has consequences for 1615 * range_cyclic semantics (ie. it may 1616 * not be suitable for data integrity 1617 * writeout). 1618 */ 1619 done_index = page->index + 1; 1620 done = 1; 1621 break; 1622 } 1623 } 1624 1625 /* 1626 * We stop writing back only if we are not doing 1627 * integrity sync. In case of integrity sync we have to 1628 * keep going until we have written all the pages 1629 * we tagged for writeback prior to entering this loop. 1630 */ 1631 if (--wbc->nr_to_write <= 0 && 1632 wbc->sync_mode == WB_SYNC_NONE) { 1633 done = 1; 1634 break; 1635 } 1636 } 1637 pagevec_release(&pvec); 1638 cond_resched(); 1639 } 1640 if (!cycled && !done) { 1641 /* 1642 * range_cyclic: 1643 * We hit the last page and there is more work to be done: wrap 1644 * back to the start of the file 1645 */ 1646 cycled = 1; 1647 index = 0; 1648 end = writeback_index - 1; 1649 goto retry; 1650 } 1651 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) 1652 mapping->writeback_index = done_index; 1653 1654 return ret; 1655} 1656EXPORT_SYMBOL(write_cache_pages); 1657 1658/* 1659 * Function used by generic_writepages to call the real writepage 1660 * function and set the mapping flags on error 1661 */ 1662static int __writepage(struct page *page, struct writeback_control *wbc, 1663 void *data) 1664{ 1665 struct address_space *mapping = data; 1666 int ret = mapping->a_ops->writepage(page, wbc); 1667 mapping_set_error(mapping, ret); 1668 return ret; 1669} 1670 1671/** 1672 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 1673 * @mapping: address space structure to write 1674 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1675 * 1676 * This is a library function, which implements the writepages() 1677 * address_space_operation. 1678 */ 1679int generic_writepages(struct address_space *mapping, 1680 struct writeback_control *wbc) 1681{ 1682 struct blk_plug plug; 1683 int ret; 1684 1685 /* deal with chardevs and other special file */ 1686 if (!mapping->a_ops->writepage) 1687 return 0; 1688 1689 blk_start_plug(&plug); 1690 ret = write_cache_pages(mapping, wbc, __writepage, mapping); 1691 blk_finish_plug(&plug); 1692 return ret; 1693} 1694 1695EXPORT_SYMBOL(generic_writepages); 1696 1697int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1698{ 1699 int ret; 1700 1701 if (wbc->nr_to_write <= 0) 1702 return 0; 1703 if (mapping->a_ops->writepages) 1704 ret = mapping->a_ops->writepages(mapping, wbc); 1705 else 1706 ret = generic_writepages(mapping, wbc); 1707 return ret; 1708} 1709 1710/** 1711 * write_one_page - write out a single page and optionally wait on I/O 1712 * @page: the page to write 1713 * @wait: if true, wait on writeout 1714 * 1715 * The page must be locked by the caller and will be unlocked upon return. 1716 * 1717 * write_one_page() returns a negative error code if I/O failed. 1718 */ 1719int write_one_page(struct page *page, int wait) 1720{ 1721 struct address_space *mapping = page->mapping; 1722 int ret = 0; 1723 struct writeback_control wbc = { 1724 .sync_mode = WB_SYNC_ALL, 1725 .nr_to_write = 1, 1726 }; 1727 1728 BUG_ON(!PageLocked(page)); 1729 1730 if (wait) 1731 wait_on_page_writeback(page); 1732 1733 if (clear_page_dirty_for_io(page)) { 1734 page_cache_get(page); 1735 ret = mapping->a_ops->writepage(page, &wbc); 1736 if (ret == 0 && wait) { 1737 wait_on_page_writeback(page); 1738 if (PageError(page)) 1739 ret = -EIO; 1740 } 1741 page_cache_release(page); 1742 } else { 1743 unlock_page(page); 1744 } 1745 return ret; 1746} 1747EXPORT_SYMBOL(write_one_page); 1748 1749/* 1750 * For address_spaces which do not use buffers nor write back. 1751 */ 1752int __set_page_dirty_no_writeback(struct page *page) 1753{ 1754 if (!PageDirty(page)) 1755 return !TestSetPageDirty(page); 1756 return 0; 1757} 1758 1759/* 1760 * Helper function for set_page_dirty family. 1761 * NOTE: This relies on being atomic wrt interrupts. 1762 */ 1763void account_page_dirtied(struct page *page, struct address_space *mapping) 1764{ 1765 if (mapping_cap_account_dirty(mapping)) { 1766 __inc_zone_page_state(page, NR_FILE_DIRTY); 1767 __inc_zone_page_state(page, NR_DIRTIED); 1768 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); 1769 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); 1770 task_io_account_write(PAGE_CACHE_SIZE); 1771 } 1772} 1773EXPORT_SYMBOL(account_page_dirtied); 1774 1775/* 1776 * Helper function for set_page_writeback family. 1777 * NOTE: Unlike account_page_dirtied this does not rely on being atomic 1778 * wrt interrupts. 1779 */ 1780void account_page_writeback(struct page *page) 1781{ 1782 inc_zone_page_state(page, NR_WRITEBACK); 1783} 1784EXPORT_SYMBOL(account_page_writeback); 1785 1786/* 1787 * For address_spaces which do not use buffers. Just tag the page as dirty in 1788 * its radix tree. 1789 * 1790 * This is also used when a single buffer is being dirtied: we want to set the 1791 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1792 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1793 * 1794 * Most callers have locked the page, which pins the address_space in memory. 1795 * But zap_pte_range() does not lock the page, however in that case the 1796 * mapping is pinned by the vma's ->vm_file reference. 1797 * 1798 * We take care to handle the case where the page was truncated from the 1799 * mapping by re-checking page_mapping() inside tree_lock. 1800 */ 1801int __set_page_dirty_nobuffers(struct page *page) 1802{ 1803 if (!TestSetPageDirty(page)) { 1804 struct address_space *mapping = page_mapping(page); 1805 struct address_space *mapping2; 1806 1807 if (!mapping) 1808 return 1; 1809 1810 spin_lock_irq(&mapping->tree_lock); 1811 mapping2 = page_mapping(page); 1812 if (mapping2) { /* Race with truncate? */ 1813 BUG_ON(mapping2 != mapping); 1814 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1815 account_page_dirtied(page, mapping); 1816 radix_tree_tag_set(&mapping->page_tree, 1817 page_index(page), PAGECACHE_TAG_DIRTY); 1818 } 1819 spin_unlock_irq(&mapping->tree_lock); 1820 if (mapping->host) { 1821 /* !PageAnon && !swapper_space */ 1822 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1823 } 1824 return 1; 1825 } 1826 return 0; 1827} 1828EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1829 1830/* 1831 * When a writepage implementation decides that it doesn't want to write this 1832 * page for some reason, it should redirty the locked page via 1833 * redirty_page_for_writepage() and it should then unlock the page and return 0 1834 */ 1835int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1836{ 1837 wbc->pages_skipped++; 1838 return __set_page_dirty_nobuffers(page); 1839} 1840EXPORT_SYMBOL(redirty_page_for_writepage); 1841 1842/* 1843 * Dirty a page. 1844 * 1845 * For pages with a mapping this should be done under the page lock 1846 * for the benefit of asynchronous memory errors who prefer a consistent 1847 * dirty state. This rule can be broken in some special cases, 1848 * but should be better not to. 1849 * 1850 * If the mapping doesn't provide a set_page_dirty a_op, then 1851 * just fall through and assume that it wants buffer_heads. 1852 */ 1853int set_page_dirty(struct page *page) 1854{ 1855 struct address_space *mapping = page_mapping(page); 1856 1857 if (likely(mapping)) { 1858 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1859 /* 1860 * readahead/lru_deactivate_page could remain 1861 * PG_readahead/PG_reclaim due to race with end_page_writeback 1862 * About readahead, if the page is written, the flags would be 1863 * reset. So no problem. 1864 * About lru_deactivate_page, if the page is redirty, the flag 1865 * will be reset. So no problem. but if the page is used by readahead 1866 * it will confuse readahead and make it restart the size rampup 1867 * process. But it's a trivial problem. 1868 */ 1869 ClearPageReclaim(page); 1870#ifdef CONFIG_BLOCK 1871 if (!spd) 1872 spd = __set_page_dirty_buffers; 1873#endif 1874 return (*spd)(page); 1875 } 1876 if (!PageDirty(page)) { 1877 if (!TestSetPageDirty(page)) 1878 return 1; 1879 } 1880 return 0; 1881} 1882EXPORT_SYMBOL(set_page_dirty); 1883 1884/* 1885 * set_page_dirty() is racy if the caller has no reference against 1886 * page->mapping->host, and if the page is unlocked. This is because another 1887 * CPU could truncate the page off the mapping and then free the mapping. 1888 * 1889 * Usually, the page _is_ locked, or the caller is a user-space process which 1890 * holds a reference on the inode by having an open file. 1891 * 1892 * In other cases, the page should be locked before running set_page_dirty(). 1893 */ 1894int set_page_dirty_lock(struct page *page) 1895{ 1896 int ret; 1897 1898 lock_page(page); 1899 ret = set_page_dirty(page); 1900 unlock_page(page); 1901 return ret; 1902} 1903EXPORT_SYMBOL(set_page_dirty_lock); 1904 1905/* 1906 * Clear a page's dirty flag, while caring for dirty memory accounting. 1907 * Returns true if the page was previously dirty. 1908 * 1909 * This is for preparing to put the page under writeout. We leave the page 1910 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1911 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1912 * implementation will run either set_page_writeback() or set_page_dirty(), 1913 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1914 * back into sync. 1915 * 1916 * This incoherency between the page's dirty flag and radix-tree tag is 1917 * unfortunate, but it only exists while the page is locked. 1918 */ 1919int clear_page_dirty_for_io(struct page *page) 1920{ 1921 struct address_space *mapping = page_mapping(page); 1922 1923 BUG_ON(!PageLocked(page)); 1924 1925 if (mapping && mapping_cap_account_dirty(mapping)) { 1926 /* 1927 * Yes, Virginia, this is indeed insane. 1928 * 1929 * We use this sequence to make sure that 1930 * (a) we account for dirty stats properly 1931 * (b) we tell the low-level filesystem to 1932 * mark the whole page dirty if it was 1933 * dirty in a pagetable. Only to then 1934 * (c) clean the page again and return 1 to 1935 * cause the writeback. 1936 * 1937 * This way we avoid all nasty races with the 1938 * dirty bit in multiple places and clearing 1939 * them concurrently from different threads. 1940 * 1941 * Note! Normally the "set_page_dirty(page)" 1942 * has no effect on the actual dirty bit - since 1943 * that will already usually be set. But we 1944 * need the side effects, and it can help us 1945 * avoid races. 1946 * 1947 * We basically use the page "master dirty bit" 1948 * as a serialization point for all the different 1949 * threads doing their things. 1950 */ 1951 if (page_mkclean(page)) 1952 set_page_dirty(page); 1953 /* 1954 * We carefully synchronise fault handlers against 1955 * installing a dirty pte and marking the page dirty 1956 * at this point. We do this by having them hold the 1957 * page lock at some point after installing their 1958 * pte, but before marking the page dirty. 1959 * Pages are always locked coming in here, so we get 1960 * the desired exclusion. See mm/memory.c:do_wp_page() 1961 * for more comments. 1962 */ 1963 if (TestClearPageDirty(page)) { 1964 dec_zone_page_state(page, NR_FILE_DIRTY); 1965 dec_bdi_stat(mapping->backing_dev_info, 1966 BDI_RECLAIMABLE); 1967 return 1; 1968 } 1969 return 0; 1970 } 1971 return TestClearPageDirty(page); 1972} 1973EXPORT_SYMBOL(clear_page_dirty_for_io); 1974 1975int test_clear_page_writeback(struct page *page) 1976{ 1977 struct address_space *mapping = page_mapping(page); 1978 int ret; 1979 1980 if (mapping) { 1981 struct backing_dev_info *bdi = mapping->backing_dev_info; 1982 unsigned long flags; 1983 1984 spin_lock_irqsave(&mapping->tree_lock, flags); 1985 ret = TestClearPageWriteback(page); 1986 if (ret) { 1987 radix_tree_tag_clear(&mapping->page_tree, 1988 page_index(page), 1989 PAGECACHE_TAG_WRITEBACK); 1990 if (bdi_cap_account_writeback(bdi)) { 1991 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1992 __bdi_writeout_inc(bdi); 1993 } 1994 } 1995 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1996 } else { 1997 ret = TestClearPageWriteback(page); 1998 } 1999 if (ret) { 2000 dec_zone_page_state(page, NR_WRITEBACK); 2001 inc_zone_page_state(page, NR_WRITTEN); 2002 } 2003 return ret; 2004} 2005 2006int test_set_page_writeback(struct page *page) 2007{ 2008 struct address_space *mapping = page_mapping(page); 2009 int ret; 2010 2011 if (mapping) { 2012 struct backing_dev_info *bdi = mapping->backing_dev_info; 2013 unsigned long flags; 2014 2015 spin_lock_irqsave(&mapping->tree_lock, flags); 2016 ret = TestSetPageWriteback(page); 2017 if (!ret) { 2018 radix_tree_tag_set(&mapping->page_tree, 2019 page_index(page), 2020 PAGECACHE_TAG_WRITEBACK); 2021 if (bdi_cap_account_writeback(bdi)) 2022 __inc_bdi_stat(bdi, BDI_WRITEBACK); 2023 } 2024 if (!PageDirty(page)) 2025 radix_tree_tag_clear(&mapping->page_tree, 2026 page_index(page), 2027 PAGECACHE_TAG_DIRTY); 2028 radix_tree_tag_clear(&mapping->page_tree, 2029 page_index(page), 2030 PAGECACHE_TAG_TOWRITE); 2031 spin_unlock_irqrestore(&mapping->tree_lock, flags); 2032 } else { 2033 ret = TestSetPageWriteback(page); 2034 } 2035 if (!ret) 2036 account_page_writeback(page); 2037 return ret; 2038 2039} 2040EXPORT_SYMBOL(test_set_page_writeback); 2041 2042/* 2043 * Return true if any of the pages in the mapping are marked with the 2044 * passed tag. 2045 */ 2046int mapping_tagged(struct address_space *mapping, int tag) 2047{ 2048 return radix_tree_tagged(&mapping->page_tree, tag); 2049} 2050EXPORT_SYMBOL(mapping_tagged); 2051