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> /* __set_page_dirty_buffers */ 36 #include <linux/pagevec.h> 37 #include <linux/timer.h> 38 #include <linux/sched/rt.h> 39 #include <linux/mm_inline.h> 40 #include <trace/events/writeback.h> 41 42 #include "internal.h" 43 44 /* 45 * Sleep at most 200ms at a time in balance_dirty_pages(). 46 */ 47 #define MAX_PAUSE max(HZ/5, 1) 48 49 /* 50 * Try to keep balance_dirty_pages() call intervals higher than this many pages 51 * by raising pause time to max_pause when falls below it. 52 */ 53 #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) 54 55 /* 56 * Estimate write bandwidth at 200ms intervals. 57 */ 58 #define BANDWIDTH_INTERVAL max(HZ/5, 1) 59 60 #define RATELIMIT_CALC_SHIFT 10 61 62 /* 63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 64 * will look to see if it needs to force writeback or throttling. 65 */ 66 static long ratelimit_pages = 32; 67 68 /* The following parameters are exported via /proc/sys/vm */ 69 70 /* 71 * Start background writeback (via writeback threads) at this percentage 72 */ 73 int dirty_background_ratio = 10; 74 75 /* 76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of 77 * dirty_background_ratio * the amount of dirtyable memory 78 */ 79 unsigned long dirty_background_bytes; 80 81 /* 82 * free highmem will not be subtracted from the total free memory 83 * for calculating free ratios if vm_highmem_is_dirtyable is true 84 */ 85 int vm_highmem_is_dirtyable; 86 87 /* 88 * The generator of dirty data starts writeback at this percentage 89 */ 90 int vm_dirty_ratio = 20; 91 92 /* 93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of 94 * vm_dirty_ratio * the amount of dirtyable memory 95 */ 96 unsigned long vm_dirty_bytes; 97 98 /* 99 * The interval between `kupdate'-style writebacks 100 */ 101 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ 102 103 EXPORT_SYMBOL_GPL(dirty_writeback_interval); 104 105 /* 106 * The longest time for which data is allowed to remain dirty 107 */ 108 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ 109 110 /* 111 * Flag that makes the machine dump writes/reads and block dirtyings. 112 */ 113 int block_dump; 114 115 /* 116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 117 * a full sync is triggered after this time elapses without any disk activity. 118 */ 119 int laptop_mode; 120 121 EXPORT_SYMBOL(laptop_mode); 122 123 /* End of sysctl-exported parameters */ 124 125 unsigned long global_dirty_limit; 126 127 /* 128 * Scale the writeback cache size proportional to the relative writeout speeds. 129 * 130 * We do this by keeping a floating proportion between BDIs, based on page 131 * writeback completions [end_page_writeback()]. Those devices that write out 132 * pages fastest will get the larger share, while the slower will get a smaller 133 * share. 134 * 135 * We use page writeout completions because we are interested in getting rid of 136 * dirty pages. Having them written out is the primary goal. 137 * 138 * We introduce a concept of time, a period over which we measure these events, 139 * because demand can/will vary over time. The length of this period itself is 140 * measured in page writeback completions. 141 * 142 */ 143 static struct fprop_global writeout_completions; 144 145 static void writeout_period(unsigned long t); 146 /* Timer for aging of writeout_completions */ 147 static struct timer_list writeout_period_timer = 148 TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0); 149 static unsigned long writeout_period_time = 0; 150 151 /* 152 * Length of period for aging writeout fractions of bdis. This is an 153 * arbitrarily chosen number. The longer the period, the slower fractions will 154 * reflect changes in current writeout rate. 155 */ 156 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ) 157 158 /* 159 * Work out the current dirty-memory clamping and background writeout 160 * thresholds. 161 * 162 * The main aim here is to lower them aggressively if there is a lot of mapped 163 * memory around. To avoid stressing page reclaim with lots of unreclaimable 164 * pages. It is better to clamp down on writers than to start swapping, and 165 * performing lots of scanning. 166 * 167 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 168 * 169 * We don't permit the clamping level to fall below 5% - that is getting rather 170 * excessive. 171 * 172 * We make sure that the background writeout level is below the adjusted 173 * clamping level. 174 */ 175 176 /* 177 * In a memory zone, there is a certain amount of pages we consider 178 * available for the page cache, which is essentially the number of 179 * free and reclaimable pages, minus some zone reserves to protect 180 * lowmem and the ability to uphold the zone's watermarks without 181 * requiring writeback. 182 * 183 * This number of dirtyable pages is the base value of which the 184 * user-configurable dirty ratio is the effictive number of pages that 185 * are allowed to be actually dirtied. Per individual zone, or 186 * globally by using the sum of dirtyable pages over all zones. 187 * 188 * Because the user is allowed to specify the dirty limit globally as 189 * absolute number of bytes, calculating the per-zone dirty limit can 190 * require translating the configured limit into a percentage of 191 * global dirtyable memory first. 192 */ 193 194 static unsigned long highmem_dirtyable_memory(unsigned long total) 195 { 196 #ifdef CONFIG_HIGHMEM 197 int node; 198 unsigned long x = 0; 199 200 for_each_node_state(node, N_HIGH_MEMORY) { 201 struct zone *z = 202 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 203 204 x += zone_page_state(z, NR_FREE_PAGES) + 205 zone_reclaimable_pages(z) - z->dirty_balance_reserve; 206 } 207 /* 208 * Unreclaimable memory (kernel memory or anonymous memory 209 * without swap) can bring down the dirtyable pages below 210 * the zone's dirty balance reserve and the above calculation 211 * will underflow. However we still want to add in nodes 212 * which are below threshold (negative values) to get a more 213 * accurate calculation but make sure that the total never 214 * underflows. 215 */ 216 if ((long)x < 0) 217 x = 0; 218 219 /* 220 * Make sure that the number of highmem pages is never larger 221 * than the number of the total dirtyable memory. This can only 222 * occur in very strange VM situations but we want to make sure 223 * that this does not occur. 224 */ 225 return min(x, total); 226 #else 227 return 0; 228 #endif 229 } 230 231 /** 232 * global_dirtyable_memory - number of globally dirtyable pages 233 * 234 * Returns the global number of pages potentially available for dirty 235 * page cache. This is the base value for the global dirty limits. 236 */ 237 static unsigned long global_dirtyable_memory(void) 238 { 239 unsigned long x; 240 241 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); 242 x -= min(x, dirty_balance_reserve); 243 244 if (!vm_highmem_is_dirtyable) 245 x -= highmem_dirtyable_memory(x); 246 247 return x + 1; /* Ensure that we never return 0 */ 248 } 249 250 /* 251 * global_dirty_limits - background-writeback and dirty-throttling thresholds 252 * 253 * Calculate the dirty thresholds based on sysctl parameters 254 * - vm.dirty_background_ratio or vm.dirty_background_bytes 255 * - vm.dirty_ratio or vm.dirty_bytes 256 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and 257 * real-time tasks. 258 */ 259 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) 260 { 261 unsigned long background; 262 unsigned long dirty; 263 unsigned long uninitialized_var(available_memory); 264 struct task_struct *tsk; 265 266 if (!vm_dirty_bytes || !dirty_background_bytes) 267 available_memory = global_dirtyable_memory(); 268 269 if (vm_dirty_bytes) 270 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); 271 else 272 dirty = (vm_dirty_ratio * available_memory) / 100; 273 274 if (dirty_background_bytes) 275 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); 276 else 277 background = (dirty_background_ratio * available_memory) / 100; 278 279 if (background >= dirty) 280 background = dirty / 2; 281 tsk = current; 282 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 283 background += background / 4; 284 dirty += dirty / 4; 285 } 286 *pbackground = background; 287 *pdirty = dirty; 288 trace_global_dirty_state(background, dirty); 289 } 290 291 /** 292 * zone_dirtyable_memory - number of dirtyable pages in a zone 293 * @zone: the zone 294 * 295 * Returns the zone's number of pages potentially available for dirty 296 * page cache. This is the base value for the per-zone dirty limits. 297 */ 298 static unsigned long zone_dirtyable_memory(struct zone *zone) 299 { 300 /* 301 * The effective global number of dirtyable pages may exclude 302 * highmem as a big-picture measure to keep the ratio between 303 * dirty memory and lowmem reasonable. 304 * 305 * But this function is purely about the individual zone and a 306 * highmem zone can hold its share of dirty pages, so we don't 307 * care about vm_highmem_is_dirtyable here. 308 */ 309 unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) + 310 zone_reclaimable_pages(zone); 311 312 /* don't allow this to underflow */ 313 nr_pages -= min(nr_pages, zone->dirty_balance_reserve); 314 return nr_pages; 315 } 316 317 /** 318 * zone_dirty_limit - maximum number of dirty pages allowed in a zone 319 * @zone: the zone 320 * 321 * Returns the maximum number of dirty pages allowed in a zone, based 322 * on the zone's dirtyable memory. 323 */ 324 static unsigned long zone_dirty_limit(struct zone *zone) 325 { 326 unsigned long zone_memory = zone_dirtyable_memory(zone); 327 struct task_struct *tsk = current; 328 unsigned long dirty; 329 330 if (vm_dirty_bytes) 331 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * 332 zone_memory / global_dirtyable_memory(); 333 else 334 dirty = vm_dirty_ratio * zone_memory / 100; 335 336 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) 337 dirty += dirty / 4; 338 339 return dirty; 340 } 341 342 /** 343 * zone_dirty_ok - tells whether a zone is within its dirty limits 344 * @zone: the zone to check 345 * 346 * Returns %true when the dirty pages in @zone are within the zone's 347 * dirty limit, %false if the limit is exceeded. 348 */ 349 bool zone_dirty_ok(struct zone *zone) 350 { 351 unsigned long limit = zone_dirty_limit(zone); 352 353 return zone_page_state(zone, NR_FILE_DIRTY) + 354 zone_page_state(zone, NR_UNSTABLE_NFS) + 355 zone_page_state(zone, NR_WRITEBACK) <= limit; 356 } 357 358 int dirty_background_ratio_handler(struct ctl_table *table, int write, 359 void __user *buffer, size_t *lenp, 360 loff_t *ppos) 361 { 362 int ret; 363 364 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 365 if (ret == 0 && write) 366 dirty_background_bytes = 0; 367 return ret; 368 } 369 370 int dirty_background_bytes_handler(struct ctl_table *table, int write, 371 void __user *buffer, size_t *lenp, 372 loff_t *ppos) 373 { 374 int ret; 375 376 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 377 if (ret == 0 && write) 378 dirty_background_ratio = 0; 379 return ret; 380 } 381 382 int dirty_ratio_handler(struct ctl_table *table, int write, 383 void __user *buffer, size_t *lenp, 384 loff_t *ppos) 385 { 386 int old_ratio = vm_dirty_ratio; 387 int ret; 388 389 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 390 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 391 writeback_set_ratelimit(); 392 vm_dirty_bytes = 0; 393 } 394 return ret; 395 } 396 397 int dirty_bytes_handler(struct ctl_table *table, int write, 398 void __user *buffer, size_t *lenp, 399 loff_t *ppos) 400 { 401 unsigned long old_bytes = vm_dirty_bytes; 402 int ret; 403 404 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 405 if (ret == 0 && write && vm_dirty_bytes != old_bytes) { 406 writeback_set_ratelimit(); 407 vm_dirty_ratio = 0; 408 } 409 return ret; 410 } 411 412 static unsigned long wp_next_time(unsigned long cur_time) 413 { 414 cur_time += VM_COMPLETIONS_PERIOD_LEN; 415 /* 0 has a special meaning... */ 416 if (!cur_time) 417 return 1; 418 return cur_time; 419 } 420 421 /* 422 * Increment the BDI's writeout completion count and the global writeout 423 * completion count. Called from test_clear_page_writeback(). 424 */ 425 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 426 { 427 __inc_bdi_stat(bdi, BDI_WRITTEN); 428 __fprop_inc_percpu_max(&writeout_completions, &bdi->completions, 429 bdi->max_prop_frac); 430 /* First event after period switching was turned off? */ 431 if (!unlikely(writeout_period_time)) { 432 /* 433 * We can race with other __bdi_writeout_inc calls here but 434 * it does not cause any harm since the resulting time when 435 * timer will fire and what is in writeout_period_time will be 436 * roughly the same. 437 */ 438 writeout_period_time = wp_next_time(jiffies); 439 mod_timer(&writeout_period_timer, writeout_period_time); 440 } 441 } 442 443 void bdi_writeout_inc(struct backing_dev_info *bdi) 444 { 445 unsigned long flags; 446 447 local_irq_save(flags); 448 __bdi_writeout_inc(bdi); 449 local_irq_restore(flags); 450 } 451 EXPORT_SYMBOL_GPL(bdi_writeout_inc); 452 453 /* 454 * Obtain an accurate fraction of the BDI's portion. 455 */ 456 static void bdi_writeout_fraction(struct backing_dev_info *bdi, 457 long *numerator, long *denominator) 458 { 459 fprop_fraction_percpu(&writeout_completions, &bdi->completions, 460 numerator, denominator); 461 } 462 463 /* 464 * On idle system, we can be called long after we scheduled because we use 465 * deferred timers so count with missed periods. 466 */ 467 static void writeout_period(unsigned long t) 468 { 469 int miss_periods = (jiffies - writeout_period_time) / 470 VM_COMPLETIONS_PERIOD_LEN; 471 472 if (fprop_new_period(&writeout_completions, miss_periods + 1)) { 473 writeout_period_time = wp_next_time(writeout_period_time + 474 miss_periods * VM_COMPLETIONS_PERIOD_LEN); 475 mod_timer(&writeout_period_timer, writeout_period_time); 476 } else { 477 /* 478 * Aging has zeroed all fractions. Stop wasting CPU on period 479 * updates. 480 */ 481 writeout_period_time = 0; 482 } 483 } 484 485 /* 486 * bdi_min_ratio keeps the sum of the minimum dirty shares of all 487 * registered backing devices, which, for obvious reasons, can not 488 * exceed 100%. 489 */ 490 static unsigned int bdi_min_ratio; 491 492 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 493 { 494 int ret = 0; 495 496 spin_lock_bh(&bdi_lock); 497 if (min_ratio > bdi->max_ratio) { 498 ret = -EINVAL; 499 } else { 500 min_ratio -= bdi->min_ratio; 501 if (bdi_min_ratio + min_ratio < 100) { 502 bdi_min_ratio += min_ratio; 503 bdi->min_ratio += min_ratio; 504 } else { 505 ret = -EINVAL; 506 } 507 } 508 spin_unlock_bh(&bdi_lock); 509 510 return ret; 511 } 512 513 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 514 { 515 int ret = 0; 516 517 if (max_ratio > 100) 518 return -EINVAL; 519 520 spin_lock_bh(&bdi_lock); 521 if (bdi->min_ratio > max_ratio) { 522 ret = -EINVAL; 523 } else { 524 bdi->max_ratio = max_ratio; 525 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; 526 } 527 spin_unlock_bh(&bdi_lock); 528 529 return ret; 530 } 531 EXPORT_SYMBOL(bdi_set_max_ratio); 532 533 static unsigned long dirty_freerun_ceiling(unsigned long thresh, 534 unsigned long bg_thresh) 535 { 536 return (thresh + bg_thresh) / 2; 537 } 538 539 static unsigned long hard_dirty_limit(unsigned long thresh) 540 { 541 return max(thresh, global_dirty_limit); 542 } 543 544 /** 545 * bdi_dirty_limit - @bdi's share of dirty throttling threshold 546 * @bdi: the backing_dev_info to query 547 * @dirty: global dirty limit in pages 548 * 549 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of 550 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. 551 * 552 * Note that balance_dirty_pages() will only seriously take it as a hard limit 553 * when sleeping max_pause per page is not enough to keep the dirty pages under 554 * control. For example, when the device is completely stalled due to some error 555 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. 556 * In the other normal situations, it acts more gently by throttling the tasks 557 * more (rather than completely block them) when the bdi dirty pages go high. 558 * 559 * It allocates high/low dirty limits to fast/slow devices, in order to prevent 560 * - starving fast devices 561 * - piling up dirty pages (that will take long time to sync) on slow devices 562 * 563 * The bdi's share of dirty limit will be adapting to its throughput and 564 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. 565 */ 566 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) 567 { 568 u64 bdi_dirty; 569 long numerator, denominator; 570 571 /* 572 * Calculate this BDI's share of the dirty ratio. 573 */ 574 bdi_writeout_fraction(bdi, &numerator, &denominator); 575 576 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 577 bdi_dirty *= numerator; 578 do_div(bdi_dirty, denominator); 579 580 bdi_dirty += (dirty * bdi->min_ratio) / 100; 581 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 582 bdi_dirty = dirty * bdi->max_ratio / 100; 583 584 return bdi_dirty; 585 } 586 587 /* 588 * setpoint - dirty 3 589 * f(dirty) := 1.0 + (----------------) 590 * limit - setpoint 591 * 592 * it's a 3rd order polynomial that subjects to 593 * 594 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast 595 * (2) f(setpoint) = 1.0 => the balance point 596 * (3) f(limit) = 0 => the hard limit 597 * (4) df/dx <= 0 => negative feedback control 598 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) 599 * => fast response on large errors; small oscillation near setpoint 600 */ 601 static inline long long pos_ratio_polynom(unsigned long setpoint, 602 unsigned long dirty, 603 unsigned long limit) 604 { 605 long long pos_ratio; 606 long x; 607 608 x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, 609 limit - setpoint + 1); 610 pos_ratio = x; 611 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; 612 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; 613 pos_ratio += 1 << RATELIMIT_CALC_SHIFT; 614 615 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT); 616 } 617 618 /* 619 * Dirty position control. 620 * 621 * (o) global/bdi setpoints 622 * 623 * We want the dirty pages be balanced around the global/bdi setpoints. 624 * When the number of dirty pages is higher/lower than the setpoint, the 625 * dirty position control ratio (and hence task dirty ratelimit) will be 626 * decreased/increased to bring the dirty pages back to the setpoint. 627 * 628 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT 629 * 630 * if (dirty < setpoint) scale up pos_ratio 631 * if (dirty > setpoint) scale down pos_ratio 632 * 633 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio 634 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio 635 * 636 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT 637 * 638 * (o) global control line 639 * 640 * ^ pos_ratio 641 * | 642 * | |<===== global dirty control scope ======>| 643 * 2.0 .............* 644 * | .* 645 * | . * 646 * | . * 647 * | . * 648 * | . * 649 * | . * 650 * 1.0 ................................* 651 * | . . * 652 * | . . * 653 * | . . * 654 * | . . * 655 * | . . * 656 * 0 +------------.------------------.----------------------*-------------> 657 * freerun^ setpoint^ limit^ dirty pages 658 * 659 * (o) bdi control line 660 * 661 * ^ pos_ratio 662 * | 663 * | * 664 * | * 665 * | * 666 * | * 667 * | * |<=========== span ============>| 668 * 1.0 .......................* 669 * | . * 670 * | . * 671 * | . * 672 * | . * 673 * | . * 674 * | . * 675 * | . * 676 * | . * 677 * | . * 678 * | . * 679 * | . * 680 * 1/4 ...............................................* * * * * * * * * * * * 681 * | . . 682 * | . . 683 * | . . 684 * 0 +----------------------.-------------------------------.-------------> 685 * bdi_setpoint^ x_intercept^ 686 * 687 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can 688 * be smoothly throttled down to normal if it starts high in situations like 689 * - start writing to a slow SD card and a fast disk at the same time. The SD 690 * card's bdi_dirty may rush to many times higher than bdi_setpoint. 691 * - the bdi dirty thresh drops quickly due to change of JBOD workload 692 */ 693 static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, 694 unsigned long thresh, 695 unsigned long bg_thresh, 696 unsigned long dirty, 697 unsigned long bdi_thresh, 698 unsigned long bdi_dirty) 699 { 700 unsigned long write_bw = bdi->avg_write_bandwidth; 701 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); 702 unsigned long limit = hard_dirty_limit(thresh); 703 unsigned long x_intercept; 704 unsigned long setpoint; /* dirty pages' target balance point */ 705 unsigned long bdi_setpoint; 706 unsigned long span; 707 long long pos_ratio; /* for scaling up/down the rate limit */ 708 long x; 709 710 if (unlikely(dirty >= limit)) 711 return 0; 712 713 /* 714 * global setpoint 715 * 716 * See comment for pos_ratio_polynom(). 717 */ 718 setpoint = (freerun + limit) / 2; 719 pos_ratio = pos_ratio_polynom(setpoint, dirty, limit); 720 721 /* 722 * The strictlimit feature is a tool preventing mistrusted filesystems 723 * from growing a large number of dirty pages before throttling. For 724 * such filesystems balance_dirty_pages always checks bdi counters 725 * against bdi limits. Even if global "nr_dirty" is under "freerun". 726 * This is especially important for fuse which sets bdi->max_ratio to 727 * 1% by default. Without strictlimit feature, fuse writeback may 728 * consume arbitrary amount of RAM because it is accounted in 729 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty". 730 * 731 * Here, in bdi_position_ratio(), we calculate pos_ratio based on 732 * two values: bdi_dirty and bdi_thresh. Let's consider an example: 733 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global 734 * limits are set by default to 10% and 20% (background and throttle). 735 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages. 736 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is 737 * about ~6K pages (as the average of background and throttle bdi 738 * limits). The 3rd order polynomial will provide positive feedback if 739 * bdi_dirty is under bdi_setpoint and vice versa. 740 * 741 * Note, that we cannot use global counters in these calculations 742 * because we want to throttle process writing to a strictlimit BDI 743 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB 744 * in the example above). 745 */ 746 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) { 747 long long bdi_pos_ratio; 748 unsigned long bdi_bg_thresh; 749 750 if (bdi_dirty < 8) 751 return min_t(long long, pos_ratio * 2, 752 2 << RATELIMIT_CALC_SHIFT); 753 754 if (bdi_dirty >= bdi_thresh) 755 return 0; 756 757 bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh); 758 bdi_setpoint = dirty_freerun_ceiling(bdi_thresh, 759 bdi_bg_thresh); 760 761 if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh) 762 return 0; 763 764 bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty, 765 bdi_thresh); 766 767 /* 768 * Typically, for strictlimit case, bdi_setpoint << setpoint 769 * and pos_ratio >> bdi_pos_ratio. In the other words global 770 * state ("dirty") is not limiting factor and we have to 771 * make decision based on bdi counters. But there is an 772 * important case when global pos_ratio should get precedence: 773 * global limits are exceeded (e.g. due to activities on other 774 * BDIs) while given strictlimit BDI is below limit. 775 * 776 * "pos_ratio * bdi_pos_ratio" would work for the case above, 777 * but it would look too non-natural for the case of all 778 * activity in the system coming from a single strictlimit BDI 779 * with bdi->max_ratio == 100%. 780 * 781 * Note that min() below somewhat changes the dynamics of the 782 * control system. Normally, pos_ratio value can be well over 3 783 * (when globally we are at freerun and bdi is well below bdi 784 * setpoint). Now the maximum pos_ratio in the same situation 785 * is 2. We might want to tweak this if we observe the control 786 * system is too slow to adapt. 787 */ 788 return min(pos_ratio, bdi_pos_ratio); 789 } 790 791 /* 792 * We have computed basic pos_ratio above based on global situation. If 793 * the bdi is over/under its share of dirty pages, we want to scale 794 * pos_ratio further down/up. That is done by the following mechanism. 795 */ 796 797 /* 798 * bdi setpoint 799 * 800 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint) 801 * 802 * x_intercept - bdi_dirty 803 * := -------------------------- 804 * x_intercept - bdi_setpoint 805 * 806 * The main bdi control line is a linear function that subjects to 807 * 808 * (1) f(bdi_setpoint) = 1.0 809 * (2) k = - 1 / (8 * write_bw) (in single bdi case) 810 * or equally: x_intercept = bdi_setpoint + 8 * write_bw 811 * 812 * For single bdi case, the dirty pages are observed to fluctuate 813 * regularly within range 814 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2] 815 * for various filesystems, where (2) can yield in a reasonable 12.5% 816 * fluctuation range for pos_ratio. 817 * 818 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its 819 * own size, so move the slope over accordingly and choose a slope that 820 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh. 821 */ 822 if (unlikely(bdi_thresh > thresh)) 823 bdi_thresh = thresh; 824 /* 825 * It's very possible that bdi_thresh is close to 0 not because the 826 * device is slow, but that it has remained inactive for long time. 827 * Honour such devices a reasonable good (hopefully IO efficient) 828 * threshold, so that the occasional writes won't be blocked and active 829 * writes can rampup the threshold quickly. 830 */ 831 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); 832 /* 833 * scale global setpoint to bdi's: 834 * bdi_setpoint = setpoint * bdi_thresh / thresh 835 */ 836 x = div_u64((u64)bdi_thresh << 16, thresh + 1); 837 bdi_setpoint = setpoint * (u64)x >> 16; 838 /* 839 * Use span=(8*write_bw) in single bdi case as indicated by 840 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case. 841 * 842 * bdi_thresh thresh - bdi_thresh 843 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh 844 * thresh thresh 845 */ 846 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16; 847 x_intercept = bdi_setpoint + span; 848 849 if (bdi_dirty < x_intercept - span / 4) { 850 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), 851 x_intercept - bdi_setpoint + 1); 852 } else 853 pos_ratio /= 4; 854 855 /* 856 * bdi reserve area, safeguard against dirty pool underrun and disk idle 857 * It may push the desired control point of global dirty pages higher 858 * than setpoint. 859 */ 860 x_intercept = bdi_thresh / 2; 861 if (bdi_dirty < x_intercept) { 862 if (bdi_dirty > x_intercept / 8) 863 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty); 864 else 865 pos_ratio *= 8; 866 } 867 868 return pos_ratio; 869 } 870 871 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, 872 unsigned long elapsed, 873 unsigned long written) 874 { 875 const unsigned long period = roundup_pow_of_two(3 * HZ); 876 unsigned long avg = bdi->avg_write_bandwidth; 877 unsigned long old = bdi->write_bandwidth; 878 u64 bw; 879 880 /* 881 * bw = written * HZ / elapsed 882 * 883 * bw * elapsed + write_bandwidth * (period - elapsed) 884 * write_bandwidth = --------------------------------------------------- 885 * period 886 */ 887 bw = written - bdi->written_stamp; 888 bw *= HZ; 889 if (unlikely(elapsed > period)) { 890 do_div(bw, elapsed); 891 avg = bw; 892 goto out; 893 } 894 bw += (u64)bdi->write_bandwidth * (period - elapsed); 895 bw >>= ilog2(period); 896 897 /* 898 * one more level of smoothing, for filtering out sudden spikes 899 */ 900 if (avg > old && old >= (unsigned long)bw) 901 avg -= (avg - old) >> 3; 902 903 if (avg < old && old <= (unsigned long)bw) 904 avg += (old - avg) >> 3; 905 906 out: 907 bdi->write_bandwidth = bw; 908 bdi->avg_write_bandwidth = avg; 909 } 910 911 /* 912 * The global dirtyable memory and dirty threshold could be suddenly knocked 913 * down by a large amount (eg. on the startup of KVM in a swapless system). 914 * This may throw the system into deep dirty exceeded state and throttle 915 * heavy/light dirtiers alike. To retain good responsiveness, maintain 916 * global_dirty_limit for tracking slowly down to the knocked down dirty 917 * threshold. 918 */ 919 static void update_dirty_limit(unsigned long thresh, unsigned long dirty) 920 { 921 unsigned long limit = global_dirty_limit; 922 923 /* 924 * Follow up in one step. 925 */ 926 if (limit < thresh) { 927 limit = thresh; 928 goto update; 929 } 930 931 /* 932 * Follow down slowly. Use the higher one as the target, because thresh 933 * may drop below dirty. This is exactly the reason to introduce 934 * global_dirty_limit which is guaranteed to lie above the dirty pages. 935 */ 936 thresh = max(thresh, dirty); 937 if (limit > thresh) { 938 limit -= (limit - thresh) >> 5; 939 goto update; 940 } 941 return; 942 update: 943 global_dirty_limit = limit; 944 } 945 946 static void global_update_bandwidth(unsigned long thresh, 947 unsigned long dirty, 948 unsigned long now) 949 { 950 static DEFINE_SPINLOCK(dirty_lock); 951 static unsigned long update_time; 952 953 /* 954 * check locklessly first to optimize away locking for the most time 955 */ 956 if (time_before(now, update_time + BANDWIDTH_INTERVAL)) 957 return; 958 959 spin_lock(&dirty_lock); 960 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { 961 update_dirty_limit(thresh, dirty); 962 update_time = now; 963 } 964 spin_unlock(&dirty_lock); 965 } 966 967 /* 968 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate. 969 * 970 * Normal bdi tasks will be curbed at or below it in long term. 971 * Obviously it should be around (write_bw / N) when there are N dd tasks. 972 */ 973 static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, 974 unsigned long thresh, 975 unsigned long bg_thresh, 976 unsigned long dirty, 977 unsigned long bdi_thresh, 978 unsigned long bdi_dirty, 979 unsigned long dirtied, 980 unsigned long elapsed) 981 { 982 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); 983 unsigned long limit = hard_dirty_limit(thresh); 984 unsigned long setpoint = (freerun + limit) / 2; 985 unsigned long write_bw = bdi->avg_write_bandwidth; 986 unsigned long dirty_ratelimit = bdi->dirty_ratelimit; 987 unsigned long dirty_rate; 988 unsigned long task_ratelimit; 989 unsigned long balanced_dirty_ratelimit; 990 unsigned long pos_ratio; 991 unsigned long step; 992 unsigned long x; 993 994 /* 995 * The dirty rate will match the writeout rate in long term, except 996 * when dirty pages are truncated by userspace or re-dirtied by FS. 997 */ 998 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed; 999 1000 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty, 1001 bdi_thresh, bdi_dirty); 1002 /* 1003 * task_ratelimit reflects each dd's dirty rate for the past 200ms. 1004 */ 1005 task_ratelimit = (u64)dirty_ratelimit * 1006 pos_ratio >> RATELIMIT_CALC_SHIFT; 1007 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ 1008 1009 /* 1010 * A linear estimation of the "balanced" throttle rate. The theory is, 1011 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's 1012 * dirty_rate will be measured to be (N * task_ratelimit). So the below 1013 * formula will yield the balanced rate limit (write_bw / N). 1014 * 1015 * Note that the expanded form is not a pure rate feedback: 1016 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) 1017 * but also takes pos_ratio into account: 1018 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) 1019 * 1020 * (1) is not realistic because pos_ratio also takes part in balancing 1021 * the dirty rate. Consider the state 1022 * pos_ratio = 0.5 (3) 1023 * rate = 2 * (write_bw / N) (4) 1024 * If (1) is used, it will stuck in that state! Because each dd will 1025 * be throttled at 1026 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) 1027 * yielding 1028 * dirty_rate = N * task_ratelimit = write_bw (6) 1029 * put (6) into (1) we get 1030 * rate_(i+1) = rate_(i) (7) 1031 * 1032 * So we end up using (2) to always keep 1033 * rate_(i+1) ~= (write_bw / N) (8) 1034 * regardless of the value of pos_ratio. As long as (8) is satisfied, 1035 * pos_ratio is able to drive itself to 1.0, which is not only where 1036 * the dirty count meet the setpoint, but also where the slope of 1037 * pos_ratio is most flat and hence task_ratelimit is least fluctuated. 1038 */ 1039 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, 1040 dirty_rate | 1); 1041 /* 1042 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw 1043 */ 1044 if (unlikely(balanced_dirty_ratelimit > write_bw)) 1045 balanced_dirty_ratelimit = write_bw; 1046 1047 /* 1048 * We could safely do this and return immediately: 1049 * 1050 * bdi->dirty_ratelimit = balanced_dirty_ratelimit; 1051 * 1052 * However to get a more stable dirty_ratelimit, the below elaborated 1053 * code makes use of task_ratelimit to filter out singular points and 1054 * limit the step size. 1055 * 1056 * The below code essentially only uses the relative value of 1057 * 1058 * task_ratelimit - dirty_ratelimit 1059 * = (pos_ratio - 1) * dirty_ratelimit 1060 * 1061 * which reflects the direction and size of dirty position error. 1062 */ 1063 1064 /* 1065 * dirty_ratelimit will follow balanced_dirty_ratelimit iff 1066 * task_ratelimit is on the same side of dirty_ratelimit, too. 1067 * For example, when 1068 * - dirty_ratelimit > balanced_dirty_ratelimit 1069 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) 1070 * lowering dirty_ratelimit will help meet both the position and rate 1071 * control targets. Otherwise, don't update dirty_ratelimit if it will 1072 * only help meet the rate target. After all, what the users ultimately 1073 * feel and care are stable dirty rate and small position error. 1074 * 1075 * |task_ratelimit - dirty_ratelimit| is used to limit the step size 1076 * and filter out the singular points of balanced_dirty_ratelimit. Which 1077 * keeps jumping around randomly and can even leap far away at times 1078 * due to the small 200ms estimation period of dirty_rate (we want to 1079 * keep that period small to reduce time lags). 1080 */ 1081 step = 0; 1082 1083 /* 1084 * For strictlimit case, calculations above were based on bdi counters 1085 * and limits (starting from pos_ratio = bdi_position_ratio() and up to 1086 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). 1087 * Hence, to calculate "step" properly, we have to use bdi_dirty as 1088 * "dirty" and bdi_setpoint as "setpoint". 1089 * 1090 * We rampup dirty_ratelimit forcibly if bdi_dirty is low because 1091 * it's possible that bdi_thresh is close to zero due to inactivity 1092 * of backing device (see the implementation of bdi_dirty_limit()). 1093 */ 1094 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) { 1095 dirty = bdi_dirty; 1096 if (bdi_dirty < 8) 1097 setpoint = bdi_dirty + 1; 1098 else 1099 setpoint = (bdi_thresh + 1100 bdi_dirty_limit(bdi, bg_thresh)) / 2; 1101 } 1102 1103 if (dirty < setpoint) { 1104 x = min(bdi->balanced_dirty_ratelimit, 1105 min(balanced_dirty_ratelimit, task_ratelimit)); 1106 if (dirty_ratelimit < x) 1107 step = x - dirty_ratelimit; 1108 } else { 1109 x = max(bdi->balanced_dirty_ratelimit, 1110 max(balanced_dirty_ratelimit, task_ratelimit)); 1111 if (dirty_ratelimit > x) 1112 step = dirty_ratelimit - x; 1113 } 1114 1115 /* 1116 * Don't pursue 100% rate matching. It's impossible since the balanced 1117 * rate itself is constantly fluctuating. So decrease the track speed 1118 * when it gets close to the target. Helps eliminate pointless tremors. 1119 */ 1120 step >>= dirty_ratelimit / (2 * step + 1); 1121 /* 1122 * Limit the tracking speed to avoid overshooting. 1123 */ 1124 step = (step + 7) / 8; 1125 1126 if (dirty_ratelimit < balanced_dirty_ratelimit) 1127 dirty_ratelimit += step; 1128 else 1129 dirty_ratelimit -= step; 1130 1131 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL); 1132 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit; 1133 1134 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit); 1135 } 1136 1137 void __bdi_update_bandwidth(struct backing_dev_info *bdi, 1138 unsigned long thresh, 1139 unsigned long bg_thresh, 1140 unsigned long dirty, 1141 unsigned long bdi_thresh, 1142 unsigned long bdi_dirty, 1143 unsigned long start_time) 1144 { 1145 unsigned long now = jiffies; 1146 unsigned long elapsed = now - bdi->bw_time_stamp; 1147 unsigned long dirtied; 1148 unsigned long written; 1149 1150 /* 1151 * rate-limit, only update once every 200ms. 1152 */ 1153 if (elapsed < BANDWIDTH_INTERVAL) 1154 return; 1155 1156 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]); 1157 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); 1158 1159 /* 1160 * Skip quiet periods when disk bandwidth is under-utilized. 1161 * (at least 1s idle time between two flusher runs) 1162 */ 1163 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) 1164 goto snapshot; 1165 1166 if (thresh) { 1167 global_update_bandwidth(thresh, dirty, now); 1168 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty, 1169 bdi_thresh, bdi_dirty, 1170 dirtied, elapsed); 1171 } 1172 bdi_update_write_bandwidth(bdi, elapsed, written); 1173 1174 snapshot: 1175 bdi->dirtied_stamp = dirtied; 1176 bdi->written_stamp = written; 1177 bdi->bw_time_stamp = now; 1178 } 1179 1180 static void bdi_update_bandwidth(struct backing_dev_info *bdi, 1181 unsigned long thresh, 1182 unsigned long bg_thresh, 1183 unsigned long dirty, 1184 unsigned long bdi_thresh, 1185 unsigned long bdi_dirty, 1186 unsigned long start_time) 1187 { 1188 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) 1189 return; 1190 spin_lock(&bdi->wb.list_lock); 1191 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty, 1192 bdi_thresh, bdi_dirty, start_time); 1193 spin_unlock(&bdi->wb.list_lock); 1194 } 1195 1196 /* 1197 * After a task dirtied this many pages, balance_dirty_pages_ratelimited() 1198 * will look to see if it needs to start dirty throttling. 1199 * 1200 * If dirty_poll_interval is too low, big NUMA machines will call the expensive 1201 * global_page_state() too often. So scale it near-sqrt to the safety margin 1202 * (the number of pages we may dirty without exceeding the dirty limits). 1203 */ 1204 static unsigned long dirty_poll_interval(unsigned long dirty, 1205 unsigned long thresh) 1206 { 1207 if (thresh > dirty) 1208 return 1UL << (ilog2(thresh - dirty) >> 1); 1209 1210 return 1; 1211 } 1212 1213 static long bdi_max_pause(struct backing_dev_info *bdi, 1214 unsigned long bdi_dirty) 1215 { 1216 long bw = bdi->avg_write_bandwidth; 1217 long t; 1218 1219 /* 1220 * Limit pause time for small memory systems. If sleeping for too long 1221 * time, a small pool of dirty/writeback pages may go empty and disk go 1222 * idle. 1223 * 1224 * 8 serves as the safety ratio. 1225 */ 1226 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); 1227 t++; 1228 1229 return min_t(long, t, MAX_PAUSE); 1230 } 1231 1232 static long bdi_min_pause(struct backing_dev_info *bdi, 1233 long max_pause, 1234 unsigned long task_ratelimit, 1235 unsigned long dirty_ratelimit, 1236 int *nr_dirtied_pause) 1237 { 1238 long hi = ilog2(bdi->avg_write_bandwidth); 1239 long lo = ilog2(bdi->dirty_ratelimit); 1240 long t; /* target pause */ 1241 long pause; /* estimated next pause */ 1242 int pages; /* target nr_dirtied_pause */ 1243 1244 /* target for 10ms pause on 1-dd case */ 1245 t = max(1, HZ / 100); 1246 1247 /* 1248 * Scale up pause time for concurrent dirtiers in order to reduce CPU 1249 * overheads. 1250 * 1251 * (N * 10ms) on 2^N concurrent tasks. 1252 */ 1253 if (hi > lo) 1254 t += (hi - lo) * (10 * HZ) / 1024; 1255 1256 /* 1257 * This is a bit convoluted. We try to base the next nr_dirtied_pause 1258 * on the much more stable dirty_ratelimit. However the next pause time 1259 * will be computed based on task_ratelimit and the two rate limits may 1260 * depart considerably at some time. Especially if task_ratelimit goes 1261 * below dirty_ratelimit/2 and the target pause is max_pause, the next 1262 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a 1263 * result task_ratelimit won't be executed faithfully, which could 1264 * eventually bring down dirty_ratelimit. 1265 * 1266 * We apply two rules to fix it up: 1267 * 1) try to estimate the next pause time and if necessary, use a lower 1268 * nr_dirtied_pause so as not to exceed max_pause. When this happens, 1269 * nr_dirtied_pause will be "dancing" with task_ratelimit. 1270 * 2) limit the target pause time to max_pause/2, so that the normal 1271 * small fluctuations of task_ratelimit won't trigger rule (1) and 1272 * nr_dirtied_pause will remain as stable as dirty_ratelimit. 1273 */ 1274 t = min(t, 1 + max_pause / 2); 1275 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); 1276 1277 /* 1278 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test 1279 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. 1280 * When the 16 consecutive reads are often interrupted by some dirty 1281 * throttling pause during the async writes, cfq will go into idles 1282 * (deadline is fine). So push nr_dirtied_pause as high as possible 1283 * until reaches DIRTY_POLL_THRESH=32 pages. 1284 */ 1285 if (pages < DIRTY_POLL_THRESH) { 1286 t = max_pause; 1287 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); 1288 if (pages > DIRTY_POLL_THRESH) { 1289 pages = DIRTY_POLL_THRESH; 1290 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; 1291 } 1292 } 1293 1294 pause = HZ * pages / (task_ratelimit + 1); 1295 if (pause > max_pause) { 1296 t = max_pause; 1297 pages = task_ratelimit * t / roundup_pow_of_two(HZ); 1298 } 1299 1300 *nr_dirtied_pause = pages; 1301 /* 1302 * The minimal pause time will normally be half the target pause time. 1303 */ 1304 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; 1305 } 1306 1307 static inline void bdi_dirty_limits(struct backing_dev_info *bdi, 1308 unsigned long dirty_thresh, 1309 unsigned long background_thresh, 1310 unsigned long *bdi_dirty, 1311 unsigned long *bdi_thresh, 1312 unsigned long *bdi_bg_thresh) 1313 { 1314 unsigned long bdi_reclaimable; 1315 1316 /* 1317 * bdi_thresh is not treated as some limiting factor as 1318 * dirty_thresh, due to reasons 1319 * - in JBOD setup, bdi_thresh can fluctuate a lot 1320 * - in a system with HDD and USB key, the USB key may somehow 1321 * go into state (bdi_dirty >> bdi_thresh) either because 1322 * bdi_dirty starts high, or because bdi_thresh drops low. 1323 * In this case we don't want to hard throttle the USB key 1324 * dirtiers for 100 seconds until bdi_dirty drops under 1325 * bdi_thresh. Instead the auxiliary bdi control line in 1326 * bdi_position_ratio() will let the dirtier task progress 1327 * at some rate <= (write_bw / 2) for bringing down bdi_dirty. 1328 */ 1329 *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); 1330 1331 if (bdi_bg_thresh) 1332 *bdi_bg_thresh = div_u64((u64)*bdi_thresh * 1333 background_thresh, 1334 dirty_thresh); 1335 1336 /* 1337 * In order to avoid the stacked BDI deadlock we need 1338 * to ensure we accurately count the 'dirty' pages when 1339 * the threshold is low. 1340 * 1341 * Otherwise it would be possible to get thresh+n pages 1342 * reported dirty, even though there are thresh-m pages 1343 * actually dirty; with m+n sitting in the percpu 1344 * deltas. 1345 */ 1346 if (*bdi_thresh < 2 * bdi_stat_error(bdi)) { 1347 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 1348 *bdi_dirty = bdi_reclaimable + 1349 bdi_stat_sum(bdi, BDI_WRITEBACK); 1350 } else { 1351 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 1352 *bdi_dirty = bdi_reclaimable + 1353 bdi_stat(bdi, BDI_WRITEBACK); 1354 } 1355 } 1356 1357 /* 1358 * balance_dirty_pages() must be called by processes which are generating dirty 1359 * data. It looks at the number of dirty pages in the machine and will force 1360 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. 1361 * If we're over `background_thresh' then the writeback threads are woken to 1362 * perform some writeout. 1363 */ 1364 static void balance_dirty_pages(struct address_space *mapping, 1365 unsigned long pages_dirtied) 1366 { 1367 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ 1368 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ 1369 unsigned long background_thresh; 1370 unsigned long dirty_thresh; 1371 long period; 1372 long pause; 1373 long max_pause; 1374 long min_pause; 1375 int nr_dirtied_pause; 1376 bool dirty_exceeded = false; 1377 unsigned long task_ratelimit; 1378 unsigned long dirty_ratelimit; 1379 unsigned long pos_ratio; 1380 struct backing_dev_info *bdi = mapping->backing_dev_info; 1381 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT; 1382 unsigned long start_time = jiffies; 1383 1384 for (;;) { 1385 unsigned long now = jiffies; 1386 unsigned long uninitialized_var(bdi_thresh); 1387 unsigned long thresh; 1388 unsigned long uninitialized_var(bdi_dirty); 1389 unsigned long dirty; 1390 unsigned long bg_thresh; 1391 1392 /* 1393 * Unstable writes are a feature of certain networked 1394 * filesystems (i.e. NFS) in which data may have been 1395 * written to the server's write cache, but has not yet 1396 * been flushed to permanent storage. 1397 */ 1398 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 1399 global_page_state(NR_UNSTABLE_NFS); 1400 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); 1401 1402 global_dirty_limits(&background_thresh, &dirty_thresh); 1403 1404 if (unlikely(strictlimit)) { 1405 bdi_dirty_limits(bdi, dirty_thresh, background_thresh, 1406 &bdi_dirty, &bdi_thresh, &bg_thresh); 1407 1408 dirty = bdi_dirty; 1409 thresh = bdi_thresh; 1410 } else { 1411 dirty = nr_dirty; 1412 thresh = dirty_thresh; 1413 bg_thresh = background_thresh; 1414 } 1415 1416 /* 1417 * Throttle it only when the background writeback cannot 1418 * catch-up. This avoids (excessively) small writeouts 1419 * when the bdi limits are ramping up in case of !strictlimit. 1420 * 1421 * In strictlimit case make decision based on the bdi counters 1422 * and limits. Small writeouts when the bdi limits are ramping 1423 * up are the price we consciously pay for strictlimit-ing. 1424 */ 1425 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) { 1426 current->dirty_paused_when = now; 1427 current->nr_dirtied = 0; 1428 current->nr_dirtied_pause = 1429 dirty_poll_interval(dirty, thresh); 1430 break; 1431 } 1432 1433 if (unlikely(!writeback_in_progress(bdi))) 1434 bdi_start_background_writeback(bdi); 1435 1436 if (!strictlimit) 1437 bdi_dirty_limits(bdi, dirty_thresh, background_thresh, 1438 &bdi_dirty, &bdi_thresh, NULL); 1439 1440 dirty_exceeded = (bdi_dirty > bdi_thresh) && 1441 ((nr_dirty > dirty_thresh) || strictlimit); 1442 if (dirty_exceeded && !bdi->dirty_exceeded) 1443 bdi->dirty_exceeded = 1; 1444 1445 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, 1446 nr_dirty, bdi_thresh, bdi_dirty, 1447 start_time); 1448 1449 dirty_ratelimit = bdi->dirty_ratelimit; 1450 pos_ratio = bdi_position_ratio(bdi, dirty_thresh, 1451 background_thresh, nr_dirty, 1452 bdi_thresh, bdi_dirty); 1453 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >> 1454 RATELIMIT_CALC_SHIFT; 1455 max_pause = bdi_max_pause(bdi, bdi_dirty); 1456 min_pause = bdi_min_pause(bdi, max_pause, 1457 task_ratelimit, dirty_ratelimit, 1458 &nr_dirtied_pause); 1459 1460 if (unlikely(task_ratelimit == 0)) { 1461 period = max_pause; 1462 pause = max_pause; 1463 goto pause; 1464 } 1465 period = HZ * pages_dirtied / task_ratelimit; 1466 pause = period; 1467 if (current->dirty_paused_when) 1468 pause -= now - current->dirty_paused_when; 1469 /* 1470 * For less than 1s think time (ext3/4 may block the dirtier 1471 * for up to 800ms from time to time on 1-HDD; so does xfs, 1472 * however at much less frequency), try to compensate it in 1473 * future periods by updating the virtual time; otherwise just 1474 * do a reset, as it may be a light dirtier. 1475 */ 1476 if (pause < min_pause) { 1477 trace_balance_dirty_pages(bdi, 1478 dirty_thresh, 1479 background_thresh, 1480 nr_dirty, 1481 bdi_thresh, 1482 bdi_dirty, 1483 dirty_ratelimit, 1484 task_ratelimit, 1485 pages_dirtied, 1486 period, 1487 min(pause, 0L), 1488 start_time); 1489 if (pause < -HZ) { 1490 current->dirty_paused_when = now; 1491 current->nr_dirtied = 0; 1492 } else if (period) { 1493 current->dirty_paused_when += period; 1494 current->nr_dirtied = 0; 1495 } else if (current->nr_dirtied_pause <= pages_dirtied) 1496 current->nr_dirtied_pause += pages_dirtied; 1497 break; 1498 } 1499 if (unlikely(pause > max_pause)) { 1500 /* for occasional dropped task_ratelimit */ 1501 now += min(pause - max_pause, max_pause); 1502 pause = max_pause; 1503 } 1504 1505 pause: 1506 trace_balance_dirty_pages(bdi, 1507 dirty_thresh, 1508 background_thresh, 1509 nr_dirty, 1510 bdi_thresh, 1511 bdi_dirty, 1512 dirty_ratelimit, 1513 task_ratelimit, 1514 pages_dirtied, 1515 period, 1516 pause, 1517 start_time); 1518 __set_current_state(TASK_KILLABLE); 1519 io_schedule_timeout(pause); 1520 1521 current->dirty_paused_when = now + pause; 1522 current->nr_dirtied = 0; 1523 current->nr_dirtied_pause = nr_dirtied_pause; 1524 1525 /* 1526 * This is typically equal to (nr_dirty < dirty_thresh) and can 1527 * also keep "1000+ dd on a slow USB stick" under control. 1528 */ 1529 if (task_ratelimit) 1530 break; 1531 1532 /* 1533 * In the case of an unresponding NFS server and the NFS dirty 1534 * pages exceeds dirty_thresh, give the other good bdi's a pipe 1535 * to go through, so that tasks on them still remain responsive. 1536 * 1537 * In theory 1 page is enough to keep the comsumer-producer 1538 * pipe going: the flusher cleans 1 page => the task dirties 1 1539 * more page. However bdi_dirty has accounting errors. So use 1540 * the larger and more IO friendly bdi_stat_error. 1541 */ 1542 if (bdi_dirty <= bdi_stat_error(bdi)) 1543 break; 1544 1545 if (fatal_signal_pending(current)) 1546 break; 1547 } 1548 1549 if (!dirty_exceeded && bdi->dirty_exceeded) 1550 bdi->dirty_exceeded = 0; 1551 1552 if (writeback_in_progress(bdi)) 1553 return; 1554 1555 /* 1556 * In laptop mode, we wait until hitting the higher threshold before 1557 * starting background writeout, and then write out all the way down 1558 * to the lower threshold. So slow writers cause minimal disk activity. 1559 * 1560 * In normal mode, we start background writeout at the lower 1561 * background_thresh, to keep the amount of dirty memory low. 1562 */ 1563 if (laptop_mode) 1564 return; 1565 1566 if (nr_reclaimable > background_thresh) 1567 bdi_start_background_writeback(bdi); 1568 } 1569 1570 void set_page_dirty_balance(struct page *page, int page_mkwrite) 1571 { 1572 if (set_page_dirty(page) || page_mkwrite) { 1573 struct address_space *mapping = page_mapping(page); 1574 1575 if (mapping) 1576 balance_dirty_pages_ratelimited(mapping); 1577 } 1578 } 1579 1580 static DEFINE_PER_CPU(int, bdp_ratelimits); 1581 1582 /* 1583 * Normal tasks are throttled by 1584 * loop { 1585 * dirty tsk->nr_dirtied_pause pages; 1586 * take a snap in balance_dirty_pages(); 1587 * } 1588 * However there is a worst case. If every task exit immediately when dirtied 1589 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be 1590 * called to throttle the page dirties. The solution is to save the not yet 1591 * throttled page dirties in dirty_throttle_leaks on task exit and charge them 1592 * randomly into the running tasks. This works well for the above worst case, 1593 * as the new task will pick up and accumulate the old task's leaked dirty 1594 * count and eventually get throttled. 1595 */ 1596 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; 1597 1598 /** 1599 * balance_dirty_pages_ratelimited - balance dirty memory state 1600 * @mapping: address_space which was dirtied 1601 * 1602 * Processes which are dirtying memory should call in here once for each page 1603 * which was newly dirtied. The function will periodically check the system's 1604 * dirty state and will initiate writeback if needed. 1605 * 1606 * On really big machines, get_writeback_state is expensive, so try to avoid 1607 * calling it too often (ratelimiting). But once we're over the dirty memory 1608 * limit we decrease the ratelimiting by a lot, to prevent individual processes 1609 * from overshooting the limit by (ratelimit_pages) each. 1610 */ 1611 void balance_dirty_pages_ratelimited(struct address_space *mapping) 1612 { 1613 struct backing_dev_info *bdi = mapping->backing_dev_info; 1614 int ratelimit; 1615 int *p; 1616 1617 if (!bdi_cap_account_dirty(bdi)) 1618 return; 1619 1620 ratelimit = current->nr_dirtied_pause; 1621 if (bdi->dirty_exceeded) 1622 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); 1623 1624 preempt_disable(); 1625 /* 1626 * This prevents one CPU to accumulate too many dirtied pages without 1627 * calling into balance_dirty_pages(), which can happen when there are 1628 * 1000+ tasks, all of them start dirtying pages at exactly the same 1629 * time, hence all honoured too large initial task->nr_dirtied_pause. 1630 */ 1631 p = &__get_cpu_var(bdp_ratelimits); 1632 if (unlikely(current->nr_dirtied >= ratelimit)) 1633 *p = 0; 1634 else if (unlikely(*p >= ratelimit_pages)) { 1635 *p = 0; 1636 ratelimit = 0; 1637 } 1638 /* 1639 * Pick up the dirtied pages by the exited tasks. This avoids lots of 1640 * short-lived tasks (eg. gcc invocations in a kernel build) escaping 1641 * the dirty throttling and livelock other long-run dirtiers. 1642 */ 1643 p = &__get_cpu_var(dirty_throttle_leaks); 1644 if (*p > 0 && current->nr_dirtied < ratelimit) { 1645 unsigned long nr_pages_dirtied; 1646 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); 1647 *p -= nr_pages_dirtied; 1648 current->nr_dirtied += nr_pages_dirtied; 1649 } 1650 preempt_enable(); 1651 1652 if (unlikely(current->nr_dirtied >= ratelimit)) 1653 balance_dirty_pages(mapping, current->nr_dirtied); 1654 } 1655 EXPORT_SYMBOL(balance_dirty_pages_ratelimited); 1656 1657 void throttle_vm_writeout(gfp_t gfp_mask) 1658 { 1659 unsigned long background_thresh; 1660 unsigned long dirty_thresh; 1661 1662 for ( ; ; ) { 1663 global_dirty_limits(&background_thresh, &dirty_thresh); 1664 dirty_thresh = hard_dirty_limit(dirty_thresh); 1665 1666 /* 1667 * Boost the allowable dirty threshold a bit for page 1668 * allocators so they don't get DoS'ed by heavy writers 1669 */ 1670 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 1671 1672 if (global_page_state(NR_UNSTABLE_NFS) + 1673 global_page_state(NR_WRITEBACK) <= dirty_thresh) 1674 break; 1675 congestion_wait(BLK_RW_ASYNC, HZ/10); 1676 1677 /* 1678 * The caller might hold locks which can prevent IO completion 1679 * or progress in the filesystem. So we cannot just sit here 1680 * waiting for IO to complete. 1681 */ 1682 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 1683 break; 1684 } 1685 } 1686 1687 /* 1688 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 1689 */ 1690 int dirty_writeback_centisecs_handler(ctl_table *table, int write, 1691 void __user *buffer, size_t *length, loff_t *ppos) 1692 { 1693 proc_dointvec(table, write, buffer, length, ppos); 1694 return 0; 1695 } 1696 1697 #ifdef CONFIG_BLOCK 1698 void laptop_mode_timer_fn(unsigned long data) 1699 { 1700 struct request_queue *q = (struct request_queue *)data; 1701 int nr_pages = global_page_state(NR_FILE_DIRTY) + 1702 global_page_state(NR_UNSTABLE_NFS); 1703 1704 /* 1705 * We want to write everything out, not just down to the dirty 1706 * threshold 1707 */ 1708 if (bdi_has_dirty_io(&q->backing_dev_info)) 1709 bdi_start_writeback(&q->backing_dev_info, nr_pages, 1710 WB_REASON_LAPTOP_TIMER); 1711 } 1712 1713 /* 1714 * We've spun up the disk and we're in laptop mode: schedule writeback 1715 * of all dirty data a few seconds from now. If the flush is already scheduled 1716 * then push it back - the user is still using the disk. 1717 */ 1718 void laptop_io_completion(struct backing_dev_info *info) 1719 { 1720 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); 1721 } 1722 1723 /* 1724 * We're in laptop mode and we've just synced. The sync's writes will have 1725 * caused another writeback to be scheduled by laptop_io_completion. 1726 * Nothing needs to be written back anymore, so we unschedule the writeback. 1727 */ 1728 void laptop_sync_completion(void) 1729 { 1730 struct backing_dev_info *bdi; 1731 1732 rcu_read_lock(); 1733 1734 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) 1735 del_timer(&bdi->laptop_mode_wb_timer); 1736 1737 rcu_read_unlock(); 1738 } 1739 #endif 1740 1741 /* 1742 * If ratelimit_pages is too high then we can get into dirty-data overload 1743 * if a large number of processes all perform writes at the same time. 1744 * If it is too low then SMP machines will call the (expensive) 1745 * get_writeback_state too often. 1746 * 1747 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 1748 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 1749 * thresholds. 1750 */ 1751 1752 void writeback_set_ratelimit(void) 1753 { 1754 unsigned long background_thresh; 1755 unsigned long dirty_thresh; 1756 global_dirty_limits(&background_thresh, &dirty_thresh); 1757 global_dirty_limit = dirty_thresh; 1758 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); 1759 if (ratelimit_pages < 16) 1760 ratelimit_pages = 16; 1761 } 1762 1763 static int 1764 ratelimit_handler(struct notifier_block *self, unsigned long action, 1765 void *hcpu) 1766 { 1767 1768 switch (action & ~CPU_TASKS_FROZEN) { 1769 case CPU_ONLINE: 1770 case CPU_DEAD: 1771 writeback_set_ratelimit(); 1772 return NOTIFY_OK; 1773 default: 1774 return NOTIFY_DONE; 1775 } 1776 } 1777 1778 static struct notifier_block ratelimit_nb = { 1779 .notifier_call = ratelimit_handler, 1780 .next = NULL, 1781 }; 1782 1783 /* 1784 * Called early on to tune the page writeback dirty limits. 1785 * 1786 * We used to scale dirty pages according to how total memory 1787 * related to pages that could be allocated for buffers (by 1788 * comparing nr_free_buffer_pages() to vm_total_pages. 1789 * 1790 * However, that was when we used "dirty_ratio" to scale with 1791 * all memory, and we don't do that any more. "dirty_ratio" 1792 * is now applied to total non-HIGHPAGE memory (by subtracting 1793 * totalhigh_pages from vm_total_pages), and as such we can't 1794 * get into the old insane situation any more where we had 1795 * large amounts of dirty pages compared to a small amount of 1796 * non-HIGHMEM memory. 1797 * 1798 * But we might still want to scale the dirty_ratio by how 1799 * much memory the box has.. 1800 */ 1801 void __init page_writeback_init(void) 1802 { 1803 writeback_set_ratelimit(); 1804 register_cpu_notifier(&ratelimit_nb); 1805 1806 fprop_global_init(&writeout_completions); 1807 } 1808 1809 /** 1810 * tag_pages_for_writeback - tag pages to be written by write_cache_pages 1811 * @mapping: address space structure to write 1812 * @start: starting page index 1813 * @end: ending page index (inclusive) 1814 * 1815 * This function scans the page range from @start to @end (inclusive) and tags 1816 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is 1817 * that write_cache_pages (or whoever calls this function) will then use 1818 * TOWRITE tag to identify pages eligible for writeback. This mechanism is 1819 * used to avoid livelocking of writeback by a process steadily creating new 1820 * dirty pages in the file (thus it is important for this function to be quick 1821 * so that it can tag pages faster than a dirtying process can create them). 1822 */ 1823 /* 1824 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. 1825 */ 1826 void tag_pages_for_writeback(struct address_space *mapping, 1827 pgoff_t start, pgoff_t end) 1828 { 1829 #define WRITEBACK_TAG_BATCH 4096 1830 unsigned long tagged; 1831 1832 do { 1833 spin_lock_irq(&mapping->tree_lock); 1834 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, 1835 &start, end, WRITEBACK_TAG_BATCH, 1836 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); 1837 spin_unlock_irq(&mapping->tree_lock); 1838 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); 1839 cond_resched(); 1840 /* We check 'start' to handle wrapping when end == ~0UL */ 1841 } while (tagged >= WRITEBACK_TAG_BATCH && start); 1842 } 1843 EXPORT_SYMBOL(tag_pages_for_writeback); 1844 1845 /** 1846 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 1847 * @mapping: address space structure to write 1848 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1849 * @writepage: function called for each page 1850 * @data: data passed to writepage function 1851 * 1852 * If a page is already under I/O, write_cache_pages() skips it, even 1853 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 1854 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 1855 * and msync() need to guarantee that all the data which was dirty at the time 1856 * the call was made get new I/O started against them. If wbc->sync_mode is 1857 * WB_SYNC_ALL then we were called for data integrity and we must wait for 1858 * existing IO to complete. 1859 * 1860 * To avoid livelocks (when other process dirties new pages), we first tag 1861 * pages which should be written back with TOWRITE tag and only then start 1862 * writing them. For data-integrity sync we have to be careful so that we do 1863 * not miss some pages (e.g., because some other process has cleared TOWRITE 1864 * tag we set). The rule we follow is that TOWRITE tag can be cleared only 1865 * by the process clearing the DIRTY tag (and submitting the page for IO). 1866 */ 1867 int write_cache_pages(struct address_space *mapping, 1868 struct writeback_control *wbc, writepage_t writepage, 1869 void *data) 1870 { 1871 int ret = 0; 1872 int done = 0; 1873 struct pagevec pvec; 1874 int nr_pages; 1875 pgoff_t uninitialized_var(writeback_index); 1876 pgoff_t index; 1877 pgoff_t end; /* Inclusive */ 1878 pgoff_t done_index; 1879 int cycled; 1880 int range_whole = 0; 1881 int tag; 1882 1883 pagevec_init(&pvec, 0); 1884 if (wbc->range_cyclic) { 1885 writeback_index = mapping->writeback_index; /* prev offset */ 1886 index = writeback_index; 1887 if (index == 0) 1888 cycled = 1; 1889 else 1890 cycled = 0; 1891 end = -1; 1892 } else { 1893 index = wbc->range_start >> PAGE_CACHE_SHIFT; 1894 end = wbc->range_end >> PAGE_CACHE_SHIFT; 1895 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 1896 range_whole = 1; 1897 cycled = 1; /* ignore range_cyclic tests */ 1898 } 1899 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) 1900 tag = PAGECACHE_TAG_TOWRITE; 1901 else 1902 tag = PAGECACHE_TAG_DIRTY; 1903 retry: 1904 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) 1905 tag_pages_for_writeback(mapping, index, end); 1906 done_index = index; 1907 while (!done && (index <= end)) { 1908 int i; 1909 1910 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, 1911 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); 1912 if (nr_pages == 0) 1913 break; 1914 1915 for (i = 0; i < nr_pages; i++) { 1916 struct page *page = pvec.pages[i]; 1917 1918 /* 1919 * At this point, the page may be truncated or 1920 * invalidated (changing page->mapping to NULL), or 1921 * even swizzled back from swapper_space to tmpfs file 1922 * mapping. However, page->index will not change 1923 * because we have a reference on the page. 1924 */ 1925 if (page->index > end) { 1926 /* 1927 * can't be range_cyclic (1st pass) because 1928 * end == -1 in that case. 1929 */ 1930 done = 1; 1931 break; 1932 } 1933 1934 done_index = page->index; 1935 1936 lock_page(page); 1937 1938 /* 1939 * Page truncated or invalidated. We can freely skip it 1940 * then, even for data integrity operations: the page 1941 * has disappeared concurrently, so there could be no 1942 * real expectation of this data interity operation 1943 * even if there is now a new, dirty page at the same 1944 * pagecache address. 1945 */ 1946 if (unlikely(page->mapping != mapping)) { 1947 continue_unlock: 1948 unlock_page(page); 1949 continue; 1950 } 1951 1952 if (!PageDirty(page)) { 1953 /* someone wrote it for us */ 1954 goto continue_unlock; 1955 } 1956 1957 if (PageWriteback(page)) { 1958 if (wbc->sync_mode != WB_SYNC_NONE) 1959 wait_on_page_writeback(page); 1960 else 1961 goto continue_unlock; 1962 } 1963 1964 BUG_ON(PageWriteback(page)); 1965 if (!clear_page_dirty_for_io(page)) 1966 goto continue_unlock; 1967 1968 trace_wbc_writepage(wbc, mapping->backing_dev_info); 1969 ret = (*writepage)(page, wbc, data); 1970 if (unlikely(ret)) { 1971 if (ret == AOP_WRITEPAGE_ACTIVATE) { 1972 unlock_page(page); 1973 ret = 0; 1974 } else { 1975 /* 1976 * done_index is set past this page, 1977 * so media errors will not choke 1978 * background writeout for the entire 1979 * file. This has consequences for 1980 * range_cyclic semantics (ie. it may 1981 * not be suitable for data integrity 1982 * writeout). 1983 */ 1984 done_index = page->index + 1; 1985 done = 1; 1986 break; 1987 } 1988 } 1989 1990 /* 1991 * We stop writing back only if we are not doing 1992 * integrity sync. In case of integrity sync we have to 1993 * keep going until we have written all the pages 1994 * we tagged for writeback prior to entering this loop. 1995 */ 1996 if (--wbc->nr_to_write <= 0 && 1997 wbc->sync_mode == WB_SYNC_NONE) { 1998 done = 1; 1999 break; 2000 } 2001 } 2002 pagevec_release(&pvec); 2003 cond_resched(); 2004 } 2005 if (!cycled && !done) { 2006 /* 2007 * range_cyclic: 2008 * We hit the last page and there is more work to be done: wrap 2009 * back to the start of the file 2010 */ 2011 cycled = 1; 2012 index = 0; 2013 end = writeback_index - 1; 2014 goto retry; 2015 } 2016 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) 2017 mapping->writeback_index = done_index; 2018 2019 return ret; 2020 } 2021 EXPORT_SYMBOL(write_cache_pages); 2022 2023 /* 2024 * Function used by generic_writepages to call the real writepage 2025 * function and set the mapping flags on error 2026 */ 2027 static int __writepage(struct page *page, struct writeback_control *wbc, 2028 void *data) 2029 { 2030 struct address_space *mapping = data; 2031 int ret = mapping->a_ops->writepage(page, wbc); 2032 mapping_set_error(mapping, ret); 2033 return ret; 2034 } 2035 2036 /** 2037 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 2038 * @mapping: address space structure to write 2039 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 2040 * 2041 * This is a library function, which implements the writepages() 2042 * address_space_operation. 2043 */ 2044 int generic_writepages(struct address_space *mapping, 2045 struct writeback_control *wbc) 2046 { 2047 struct blk_plug plug; 2048 int ret; 2049 2050 /* deal with chardevs and other special file */ 2051 if (!mapping->a_ops->writepage) 2052 return 0; 2053 2054 blk_start_plug(&plug); 2055 ret = write_cache_pages(mapping, wbc, __writepage, mapping); 2056 blk_finish_plug(&plug); 2057 return ret; 2058 } 2059 2060 EXPORT_SYMBOL(generic_writepages); 2061 2062 int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 2063 { 2064 int ret; 2065 2066 if (wbc->nr_to_write <= 0) 2067 return 0; 2068 if (mapping->a_ops->writepages) 2069 ret = mapping->a_ops->writepages(mapping, wbc); 2070 else 2071 ret = generic_writepages(mapping, wbc); 2072 return ret; 2073 } 2074 2075 /** 2076 * write_one_page - write out a single page and optionally wait on I/O 2077 * @page: the page to write 2078 * @wait: if true, wait on writeout 2079 * 2080 * The page must be locked by the caller and will be unlocked upon return. 2081 * 2082 * write_one_page() returns a negative error code if I/O failed. 2083 */ 2084 int write_one_page(struct page *page, int wait) 2085 { 2086 struct address_space *mapping = page->mapping; 2087 int ret = 0; 2088 struct writeback_control wbc = { 2089 .sync_mode = WB_SYNC_ALL, 2090 .nr_to_write = 1, 2091 }; 2092 2093 BUG_ON(!PageLocked(page)); 2094 2095 if (wait) 2096 wait_on_page_writeback(page); 2097 2098 if (clear_page_dirty_for_io(page)) { 2099 page_cache_get(page); 2100 ret = mapping->a_ops->writepage(page, &wbc); 2101 if (ret == 0 && wait) { 2102 wait_on_page_writeback(page); 2103 if (PageError(page)) 2104 ret = -EIO; 2105 } 2106 page_cache_release(page); 2107 } else { 2108 unlock_page(page); 2109 } 2110 return ret; 2111 } 2112 EXPORT_SYMBOL(write_one_page); 2113 2114 /* 2115 * For address_spaces which do not use buffers nor write back. 2116 */ 2117 int __set_page_dirty_no_writeback(struct page *page) 2118 { 2119 if (!PageDirty(page)) 2120 return !TestSetPageDirty(page); 2121 return 0; 2122 } 2123 2124 /* 2125 * Helper function for set_page_dirty family. 2126 * NOTE: This relies on being atomic wrt interrupts. 2127 */ 2128 void account_page_dirtied(struct page *page, struct address_space *mapping) 2129 { 2130 trace_writeback_dirty_page(page, mapping); 2131 2132 if (mapping_cap_account_dirty(mapping)) { 2133 __inc_zone_page_state(page, NR_FILE_DIRTY); 2134 __inc_zone_page_state(page, NR_DIRTIED); 2135 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); 2136 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); 2137 task_io_account_write(PAGE_CACHE_SIZE); 2138 current->nr_dirtied++; 2139 this_cpu_inc(bdp_ratelimits); 2140 } 2141 } 2142 EXPORT_SYMBOL(account_page_dirtied); 2143 2144 /* 2145 * Helper function for set_page_writeback family. 2146 * 2147 * The caller must hold mem_cgroup_begin/end_update_page_stat() lock 2148 * while calling this function. 2149 * See test_set_page_writeback for example. 2150 * 2151 * NOTE: Unlike account_page_dirtied this does not rely on being atomic 2152 * wrt interrupts. 2153 */ 2154 void account_page_writeback(struct page *page) 2155 { 2156 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK); 2157 inc_zone_page_state(page, NR_WRITEBACK); 2158 } 2159 EXPORT_SYMBOL(account_page_writeback); 2160 2161 /* 2162 * For address_spaces which do not use buffers. Just tag the page as dirty in 2163 * its radix tree. 2164 * 2165 * This is also used when a single buffer is being dirtied: we want to set the 2166 * page dirty in that case, but not all the buffers. This is a "bottom-up" 2167 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 2168 * 2169 * Most callers have locked the page, which pins the address_space in memory. 2170 * But zap_pte_range() does not lock the page, however in that case the 2171 * mapping is pinned by the vma's ->vm_file reference. 2172 * 2173 * We take care to handle the case where the page was truncated from the 2174 * mapping by re-checking page_mapping() inside tree_lock. 2175 */ 2176 int __set_page_dirty_nobuffers(struct page *page) 2177 { 2178 if (!TestSetPageDirty(page)) { 2179 struct address_space *mapping = page_mapping(page); 2180 struct address_space *mapping2; 2181 2182 if (!mapping) 2183 return 1; 2184 2185 spin_lock_irq(&mapping->tree_lock); 2186 mapping2 = page_mapping(page); 2187 if (mapping2) { /* Race with truncate? */ 2188 BUG_ON(mapping2 != mapping); 2189 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 2190 account_page_dirtied(page, mapping); 2191 radix_tree_tag_set(&mapping->page_tree, 2192 page_index(page), PAGECACHE_TAG_DIRTY); 2193 } 2194 spin_unlock_irq(&mapping->tree_lock); 2195 if (mapping->host) { 2196 /* !PageAnon && !swapper_space */ 2197 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 2198 } 2199 return 1; 2200 } 2201 return 0; 2202 } 2203 EXPORT_SYMBOL(__set_page_dirty_nobuffers); 2204 2205 /* 2206 * Call this whenever redirtying a page, to de-account the dirty counters 2207 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written 2208 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to 2209 * systematic errors in balanced_dirty_ratelimit and the dirty pages position 2210 * control. 2211 */ 2212 void account_page_redirty(struct page *page) 2213 { 2214 struct address_space *mapping = page->mapping; 2215 if (mapping && mapping_cap_account_dirty(mapping)) { 2216 current->nr_dirtied--; 2217 dec_zone_page_state(page, NR_DIRTIED); 2218 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); 2219 } 2220 } 2221 EXPORT_SYMBOL(account_page_redirty); 2222 2223 /* 2224 * When a writepage implementation decides that it doesn't want to write this 2225 * page for some reason, it should redirty the locked page via 2226 * redirty_page_for_writepage() and it should then unlock the page and return 0 2227 */ 2228 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 2229 { 2230 wbc->pages_skipped++; 2231 account_page_redirty(page); 2232 return __set_page_dirty_nobuffers(page); 2233 } 2234 EXPORT_SYMBOL(redirty_page_for_writepage); 2235 2236 /* 2237 * Dirty a page. 2238 * 2239 * For pages with a mapping this should be done under the page lock 2240 * for the benefit of asynchronous memory errors who prefer a consistent 2241 * dirty state. This rule can be broken in some special cases, 2242 * but should be better not to. 2243 * 2244 * If the mapping doesn't provide a set_page_dirty a_op, then 2245 * just fall through and assume that it wants buffer_heads. 2246 */ 2247 int set_page_dirty(struct page *page) 2248 { 2249 struct address_space *mapping = page_mapping(page); 2250 2251 if (likely(mapping)) { 2252 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 2253 /* 2254 * readahead/lru_deactivate_page could remain 2255 * PG_readahead/PG_reclaim due to race with end_page_writeback 2256 * About readahead, if the page is written, the flags would be 2257 * reset. So no problem. 2258 * About lru_deactivate_page, if the page is redirty, the flag 2259 * will be reset. So no problem. but if the page is used by readahead 2260 * it will confuse readahead and make it restart the size rampup 2261 * process. But it's a trivial problem. 2262 */ 2263 ClearPageReclaim(page); 2264 #ifdef CONFIG_BLOCK 2265 if (!spd) 2266 spd = __set_page_dirty_buffers; 2267 #endif 2268 return (*spd)(page); 2269 } 2270 if (!PageDirty(page)) { 2271 if (!TestSetPageDirty(page)) 2272 return 1; 2273 } 2274 return 0; 2275 } 2276 EXPORT_SYMBOL(set_page_dirty); 2277 2278 /* 2279 * set_page_dirty() is racy if the caller has no reference against 2280 * page->mapping->host, and if the page is unlocked. This is because another 2281 * CPU could truncate the page off the mapping and then free the mapping. 2282 * 2283 * Usually, the page _is_ locked, or the caller is a user-space process which 2284 * holds a reference on the inode by having an open file. 2285 * 2286 * In other cases, the page should be locked before running set_page_dirty(). 2287 */ 2288 int set_page_dirty_lock(struct page *page) 2289 { 2290 int ret; 2291 2292 lock_page(page); 2293 ret = set_page_dirty(page); 2294 unlock_page(page); 2295 return ret; 2296 } 2297 EXPORT_SYMBOL(set_page_dirty_lock); 2298 2299 /* 2300 * Clear a page's dirty flag, while caring for dirty memory accounting. 2301 * Returns true if the page was previously dirty. 2302 * 2303 * This is for preparing to put the page under writeout. We leave the page 2304 * tagged as dirty in the radix tree so that a concurrent write-for-sync 2305 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 2306 * implementation will run either set_page_writeback() or set_page_dirty(), 2307 * at which stage we bring the page's dirty flag and radix-tree dirty tag 2308 * back into sync. 2309 * 2310 * This incoherency between the page's dirty flag and radix-tree tag is 2311 * unfortunate, but it only exists while the page is locked. 2312 */ 2313 int clear_page_dirty_for_io(struct page *page) 2314 { 2315 struct address_space *mapping = page_mapping(page); 2316 2317 BUG_ON(!PageLocked(page)); 2318 2319 if (mapping && mapping_cap_account_dirty(mapping)) { 2320 /* 2321 * Yes, Virginia, this is indeed insane. 2322 * 2323 * We use this sequence to make sure that 2324 * (a) we account for dirty stats properly 2325 * (b) we tell the low-level filesystem to 2326 * mark the whole page dirty if it was 2327 * dirty in a pagetable. Only to then 2328 * (c) clean the page again and return 1 to 2329 * cause the writeback. 2330 * 2331 * This way we avoid all nasty races with the 2332 * dirty bit in multiple places and clearing 2333 * them concurrently from different threads. 2334 * 2335 * Note! Normally the "set_page_dirty(page)" 2336 * has no effect on the actual dirty bit - since 2337 * that will already usually be set. But we 2338 * need the side effects, and it can help us 2339 * avoid races. 2340 * 2341 * We basically use the page "master dirty bit" 2342 * as a serialization point for all the different 2343 * threads doing their things. 2344 */ 2345 if (page_mkclean(page)) 2346 set_page_dirty(page); 2347 /* 2348 * We carefully synchronise fault handlers against 2349 * installing a dirty pte and marking the page dirty 2350 * at this point. We do this by having them hold the 2351 * page lock at some point after installing their 2352 * pte, but before marking the page dirty. 2353 * Pages are always locked coming in here, so we get 2354 * the desired exclusion. See mm/memory.c:do_wp_page() 2355 * for more comments. 2356 */ 2357 if (TestClearPageDirty(page)) { 2358 dec_zone_page_state(page, NR_FILE_DIRTY); 2359 dec_bdi_stat(mapping->backing_dev_info, 2360 BDI_RECLAIMABLE); 2361 return 1; 2362 } 2363 return 0; 2364 } 2365 return TestClearPageDirty(page); 2366 } 2367 EXPORT_SYMBOL(clear_page_dirty_for_io); 2368 2369 int test_clear_page_writeback(struct page *page) 2370 { 2371 struct address_space *mapping = page_mapping(page); 2372 int ret; 2373 bool locked; 2374 unsigned long memcg_flags; 2375 2376 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags); 2377 if (mapping) { 2378 struct backing_dev_info *bdi = mapping->backing_dev_info; 2379 unsigned long flags; 2380 2381 spin_lock_irqsave(&mapping->tree_lock, flags); 2382 ret = TestClearPageWriteback(page); 2383 if (ret) { 2384 radix_tree_tag_clear(&mapping->page_tree, 2385 page_index(page), 2386 PAGECACHE_TAG_WRITEBACK); 2387 if (bdi_cap_account_writeback(bdi)) { 2388 __dec_bdi_stat(bdi, BDI_WRITEBACK); 2389 __bdi_writeout_inc(bdi); 2390 } 2391 } 2392 spin_unlock_irqrestore(&mapping->tree_lock, flags); 2393 } else { 2394 ret = TestClearPageWriteback(page); 2395 } 2396 if (ret) { 2397 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK); 2398 dec_zone_page_state(page, NR_WRITEBACK); 2399 inc_zone_page_state(page, NR_WRITTEN); 2400 } 2401 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags); 2402 return ret; 2403 } 2404 2405 int test_set_page_writeback(struct page *page) 2406 { 2407 struct address_space *mapping = page_mapping(page); 2408 int ret; 2409 bool locked; 2410 unsigned long memcg_flags; 2411 2412 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags); 2413 if (mapping) { 2414 struct backing_dev_info *bdi = mapping->backing_dev_info; 2415 unsigned long flags; 2416 2417 spin_lock_irqsave(&mapping->tree_lock, flags); 2418 ret = TestSetPageWriteback(page); 2419 if (!ret) { 2420 radix_tree_tag_set(&mapping->page_tree, 2421 page_index(page), 2422 PAGECACHE_TAG_WRITEBACK); 2423 if (bdi_cap_account_writeback(bdi)) 2424 __inc_bdi_stat(bdi, BDI_WRITEBACK); 2425 } 2426 if (!PageDirty(page)) 2427 radix_tree_tag_clear(&mapping->page_tree, 2428 page_index(page), 2429 PAGECACHE_TAG_DIRTY); 2430 radix_tree_tag_clear(&mapping->page_tree, 2431 page_index(page), 2432 PAGECACHE_TAG_TOWRITE); 2433 spin_unlock_irqrestore(&mapping->tree_lock, flags); 2434 } else { 2435 ret = TestSetPageWriteback(page); 2436 } 2437 if (!ret) 2438 account_page_writeback(page); 2439 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags); 2440 return ret; 2441 2442 } 2443 EXPORT_SYMBOL(test_set_page_writeback); 2444 2445 /* 2446 * Return true if any of the pages in the mapping are marked with the 2447 * passed tag. 2448 */ 2449 int mapping_tagged(struct address_space *mapping, int tag) 2450 { 2451 return radix_tree_tagged(&mapping->page_tree, tag); 2452 } 2453 EXPORT_SYMBOL(mapping_tagged); 2454 2455 /** 2456 * wait_for_stable_page() - wait for writeback to finish, if necessary. 2457 * @page: The page to wait on. 2458 * 2459 * This function determines if the given page is related to a backing device 2460 * that requires page contents to be held stable during writeback. If so, then 2461 * it will wait for any pending writeback to complete. 2462 */ 2463 void wait_for_stable_page(struct page *page) 2464 { 2465 struct address_space *mapping = page_mapping(page); 2466 struct backing_dev_info *bdi = mapping->backing_dev_info; 2467 2468 if (!bdi_cap_stable_pages_required(bdi)) 2469 return; 2470 2471 wait_on_page_writeback(page); 2472 } 2473 EXPORT_SYMBOL_GPL(wait_for_stable_page); 2474