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