page-writeback.c revision 679ceace848e9fd570678396ffe1ef034e00e82d
1/* 2 * mm/page-writeback.c 3 * 4 * Copyright (C) 2002, Linus Torvalds. 5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> 6 * 7 * Contains functions related to writing back dirty pages at the 8 * address_space level. 9 * 10 * 10Apr2002 Andrew Morton 11 * Initial version 12 */ 13 14#include <linux/kernel.h> 15#include <linux/module.h> 16#include <linux/spinlock.h> 17#include <linux/fs.h> 18#include <linux/mm.h> 19#include <linux/swap.h> 20#include <linux/slab.h> 21#include <linux/pagemap.h> 22#include <linux/writeback.h> 23#include <linux/init.h> 24#include <linux/backing-dev.h> 25#include <linux/task_io_accounting_ops.h> 26#include <linux/blkdev.h> 27#include <linux/mpage.h> 28#include <linux/rmap.h> 29#include <linux/percpu.h> 30#include <linux/notifier.h> 31#include <linux/smp.h> 32#include <linux/sysctl.h> 33#include <linux/cpu.h> 34#include <linux/syscalls.h> 35#include <linux/buffer_head.h> 36#include <linux/pagevec.h> 37 38/* 39 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 40 * will look to see if it needs to force writeback or throttling. 41 */ 42static long ratelimit_pages = 32; 43 44/* 45 * When balance_dirty_pages decides that the caller needs to perform some 46 * non-background writeback, this is how many pages it will attempt to write. 47 * It should be somewhat larger than dirtied pages to ensure that reasonably 48 * large amounts of I/O are submitted. 49 */ 50static inline long sync_writeback_pages(unsigned long dirtied) 51{ 52 if (dirtied < ratelimit_pages) 53 dirtied = ratelimit_pages; 54 55 return dirtied + dirtied / 2; 56} 57 58/* The following parameters are exported via /proc/sys/vm */ 59 60/* 61 * Start background writeback (via writeback threads) at this percentage 62 */ 63int dirty_background_ratio = 10; 64 65/* 66 * dirty_background_bytes starts at 0 (disabled) so that it is a function of 67 * dirty_background_ratio * the amount of dirtyable memory 68 */ 69unsigned long dirty_background_bytes; 70 71/* 72 * free highmem will not be subtracted from the total free memory 73 * for calculating free ratios if vm_highmem_is_dirtyable is true 74 */ 75int vm_highmem_is_dirtyable; 76 77/* 78 * The generator of dirty data starts writeback at this percentage 79 */ 80int vm_dirty_ratio = 20; 81 82/* 83 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of 84 * vm_dirty_ratio * the amount of dirtyable memory 85 */ 86unsigned long vm_dirty_bytes; 87 88/* 89 * The interval between `kupdate'-style writebacks 90 */ 91unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ 92 93/* 94 * The longest time for which data is allowed to remain dirty 95 */ 96unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ 97 98/* 99 * Flag that makes the machine dump writes/reads and block dirtyings. 100 */ 101int block_dump; 102 103/* 104 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 105 * a full sync is triggered after this time elapses without any disk activity. 106 */ 107int laptop_mode; 108 109EXPORT_SYMBOL(laptop_mode); 110 111/* End of sysctl-exported parameters */ 112 113 114/* 115 * Scale the writeback cache size proportional to the relative writeout speeds. 116 * 117 * We do this by keeping a floating proportion between BDIs, based on page 118 * writeback completions [end_page_writeback()]. Those devices that write out 119 * pages fastest will get the larger share, while the slower will get a smaller 120 * share. 121 * 122 * We use page writeout completions because we are interested in getting rid of 123 * dirty pages. Having them written out is the primary goal. 124 * 125 * We introduce a concept of time, a period over which we measure these events, 126 * because demand can/will vary over time. The length of this period itself is 127 * measured in page writeback completions. 128 * 129 */ 130static struct prop_descriptor vm_completions; 131static struct prop_descriptor vm_dirties; 132 133/* 134 * couple the period to the dirty_ratio: 135 * 136 * period/2 ~ roundup_pow_of_two(dirty limit) 137 */ 138static int calc_period_shift(void) 139{ 140 unsigned long dirty_total; 141 142 if (vm_dirty_bytes) 143 dirty_total = vm_dirty_bytes / PAGE_SIZE; 144 else 145 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 146 100; 147 return 2 + ilog2(dirty_total - 1); 148} 149 150/* 151 * update the period when the dirty threshold changes. 152 */ 153static void update_completion_period(void) 154{ 155 int shift = calc_period_shift(); 156 prop_change_shift(&vm_completions, shift); 157 prop_change_shift(&vm_dirties, shift); 158} 159 160int dirty_background_ratio_handler(struct ctl_table *table, int write, 161 void __user *buffer, size_t *lenp, 162 loff_t *ppos) 163{ 164 int ret; 165 166 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 167 if (ret == 0 && write) 168 dirty_background_bytes = 0; 169 return ret; 170} 171 172int dirty_background_bytes_handler(struct ctl_table *table, int write, 173 void __user *buffer, size_t *lenp, 174 loff_t *ppos) 175{ 176 int ret; 177 178 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 179 if (ret == 0 && write) 180 dirty_background_ratio = 0; 181 return ret; 182} 183 184int dirty_ratio_handler(struct ctl_table *table, int write, 185 void __user *buffer, size_t *lenp, 186 loff_t *ppos) 187{ 188 int old_ratio = vm_dirty_ratio; 189 int ret; 190 191 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); 192 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 193 update_completion_period(); 194 vm_dirty_bytes = 0; 195 } 196 return ret; 197} 198 199 200int dirty_bytes_handler(struct ctl_table *table, int write, 201 void __user *buffer, size_t *lenp, 202 loff_t *ppos) 203{ 204 unsigned long old_bytes = vm_dirty_bytes; 205 int ret; 206 207 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 208 if (ret == 0 && write && vm_dirty_bytes != old_bytes) { 209 update_completion_period(); 210 vm_dirty_ratio = 0; 211 } 212 return ret; 213} 214 215/* 216 * Increment the BDI's writeout completion count and the global writeout 217 * completion count. Called from test_clear_page_writeback(). 218 */ 219static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 220{ 221 __prop_inc_percpu_max(&vm_completions, &bdi->completions, 222 bdi->max_prop_frac); 223} 224 225void bdi_writeout_inc(struct backing_dev_info *bdi) 226{ 227 unsigned long flags; 228 229 local_irq_save(flags); 230 __bdi_writeout_inc(bdi); 231 local_irq_restore(flags); 232} 233EXPORT_SYMBOL_GPL(bdi_writeout_inc); 234 235void task_dirty_inc(struct task_struct *tsk) 236{ 237 prop_inc_single(&vm_dirties, &tsk->dirties); 238} 239 240/* 241 * Obtain an accurate fraction of the BDI's portion. 242 */ 243static void bdi_writeout_fraction(struct backing_dev_info *bdi, 244 long *numerator, long *denominator) 245{ 246 if (bdi_cap_writeback_dirty(bdi)) { 247 prop_fraction_percpu(&vm_completions, &bdi->completions, 248 numerator, denominator); 249 } else { 250 *numerator = 0; 251 *denominator = 1; 252 } 253} 254 255/* 256 * Clip the earned share of dirty pages to that which is actually available. 257 * This avoids exceeding the total dirty_limit when the floating averages 258 * fluctuate too quickly. 259 */ 260static void clip_bdi_dirty_limit(struct backing_dev_info *bdi, 261 unsigned long dirty, unsigned long *pbdi_dirty) 262{ 263 unsigned long avail_dirty; 264 265 avail_dirty = global_page_state(NR_FILE_DIRTY) + 266 global_page_state(NR_WRITEBACK) + 267 global_page_state(NR_UNSTABLE_NFS) + 268 global_page_state(NR_WRITEBACK_TEMP); 269 270 if (avail_dirty < dirty) 271 avail_dirty = dirty - avail_dirty; 272 else 273 avail_dirty = 0; 274 275 avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) + 276 bdi_stat(bdi, BDI_WRITEBACK); 277 278 *pbdi_dirty = min(*pbdi_dirty, avail_dirty); 279} 280 281static inline void task_dirties_fraction(struct task_struct *tsk, 282 long *numerator, long *denominator) 283{ 284 prop_fraction_single(&vm_dirties, &tsk->dirties, 285 numerator, denominator); 286} 287 288/* 289 * scale the dirty limit 290 * 291 * task specific dirty limit: 292 * 293 * dirty -= (dirty/8) * p_{t} 294 */ 295static void task_dirty_limit(struct task_struct *tsk, unsigned long *pdirty) 296{ 297 long numerator, denominator; 298 unsigned long dirty = *pdirty; 299 u64 inv = dirty >> 3; 300 301 task_dirties_fraction(tsk, &numerator, &denominator); 302 inv *= numerator; 303 do_div(inv, denominator); 304 305 dirty -= inv; 306 if (dirty < *pdirty/2) 307 dirty = *pdirty/2; 308 309 *pdirty = dirty; 310} 311 312/* 313 * 314 */ 315static unsigned int bdi_min_ratio; 316 317int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 318{ 319 int ret = 0; 320 321 spin_lock_bh(&bdi_lock); 322 if (min_ratio > bdi->max_ratio) { 323 ret = -EINVAL; 324 } else { 325 min_ratio -= bdi->min_ratio; 326 if (bdi_min_ratio + min_ratio < 100) { 327 bdi_min_ratio += min_ratio; 328 bdi->min_ratio += min_ratio; 329 } else { 330 ret = -EINVAL; 331 } 332 } 333 spin_unlock_bh(&bdi_lock); 334 335 return ret; 336} 337 338int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 339{ 340 int ret = 0; 341 342 if (max_ratio > 100) 343 return -EINVAL; 344 345 spin_lock_bh(&bdi_lock); 346 if (bdi->min_ratio > max_ratio) { 347 ret = -EINVAL; 348 } else { 349 bdi->max_ratio = max_ratio; 350 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; 351 } 352 spin_unlock_bh(&bdi_lock); 353 354 return ret; 355} 356EXPORT_SYMBOL(bdi_set_max_ratio); 357 358/* 359 * Work out the current dirty-memory clamping and background writeout 360 * thresholds. 361 * 362 * The main aim here is to lower them aggressively if there is a lot of mapped 363 * memory around. To avoid stressing page reclaim with lots of unreclaimable 364 * pages. It is better to clamp down on writers than to start swapping, and 365 * performing lots of scanning. 366 * 367 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 368 * 369 * We don't permit the clamping level to fall below 5% - that is getting rather 370 * excessive. 371 * 372 * We make sure that the background writeout level is below the adjusted 373 * clamping level. 374 */ 375 376static unsigned long highmem_dirtyable_memory(unsigned long total) 377{ 378#ifdef CONFIG_HIGHMEM 379 int node; 380 unsigned long x = 0; 381 382 for_each_node_state(node, N_HIGH_MEMORY) { 383 struct zone *z = 384 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 385 386 x += zone_page_state(z, NR_FREE_PAGES) + 387 zone_reclaimable_pages(z); 388 } 389 /* 390 * Make sure that the number of highmem pages is never larger 391 * than the number of the total dirtyable memory. This can only 392 * occur in very strange VM situations but we want to make sure 393 * that this does not occur. 394 */ 395 return min(x, total); 396#else 397 return 0; 398#endif 399} 400 401/** 402 * determine_dirtyable_memory - amount of memory that may be used 403 * 404 * Returns the numebr of pages that can currently be freed and used 405 * by the kernel for direct mappings. 406 */ 407unsigned long determine_dirtyable_memory(void) 408{ 409 unsigned long x; 410 411 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); 412 413 if (!vm_highmem_is_dirtyable) 414 x -= highmem_dirtyable_memory(x); 415 416 return x + 1; /* Ensure that we never return 0 */ 417} 418 419void 420get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty, 421 unsigned long *pbdi_dirty, struct backing_dev_info *bdi) 422{ 423 unsigned long background; 424 unsigned long dirty; 425 unsigned long available_memory = determine_dirtyable_memory(); 426 struct task_struct *tsk; 427 428 if (vm_dirty_bytes) 429 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); 430 else { 431 int dirty_ratio; 432 433 dirty_ratio = vm_dirty_ratio; 434 if (dirty_ratio < 5) 435 dirty_ratio = 5; 436 dirty = (dirty_ratio * available_memory) / 100; 437 } 438 439 if (dirty_background_bytes) 440 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); 441 else 442 background = (dirty_background_ratio * available_memory) / 100; 443 444 if (background >= dirty) 445 background = dirty / 2; 446 tsk = current; 447 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 448 background += background / 4; 449 dirty += dirty / 4; 450 } 451 *pbackground = background; 452 *pdirty = dirty; 453 454 if (bdi) { 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 bdi_dirty += (dirty * bdi->min_ratio) / 100; 467 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 468 bdi_dirty = dirty * bdi->max_ratio / 100; 469 470 *pbdi_dirty = bdi_dirty; 471 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty); 472 task_dirty_limit(current, pbdi_dirty); 473 } 474} 475 476/* 477 * balance_dirty_pages() must be called by processes which are generating dirty 478 * data. It looks at the number of dirty pages in the machine and will force 479 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 480 * If we're over `background_thresh' then the writeback threads are woken to 481 * perform some writeout. 482 */ 483static void balance_dirty_pages(struct address_space *mapping, 484 unsigned long write_chunk) 485{ 486 long nr_reclaimable, bdi_nr_reclaimable; 487 long nr_writeback, bdi_nr_writeback; 488 unsigned long background_thresh; 489 unsigned long dirty_thresh; 490 unsigned long bdi_thresh; 491 unsigned long pages_written = 0; 492 unsigned long pause = 1; 493 494 struct backing_dev_info *bdi = mapping->backing_dev_info; 495 496 for (;;) { 497 struct writeback_control wbc = { 498 .sync_mode = WB_SYNC_NONE, 499 .older_than_this = NULL, 500 .nr_to_write = write_chunk, 501 .range_cyclic = 1, 502 }; 503 504 get_dirty_limits(&background_thresh, &dirty_thresh, 505 &bdi_thresh, bdi); 506 507 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 508 global_page_state(NR_UNSTABLE_NFS); 509 nr_writeback = global_page_state(NR_WRITEBACK); 510 511 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 512 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 513 514 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 515 break; 516 517 /* 518 * Throttle it only when the background writeback cannot 519 * catch-up. This avoids (excessively) small writeouts 520 * when the bdi limits are ramping up. 521 */ 522 if (nr_reclaimable + nr_writeback < 523 (background_thresh + dirty_thresh) / 2) 524 break; 525 526 if (!bdi->dirty_exceeded) 527 bdi->dirty_exceeded = 1; 528 529 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 530 * Unstable writes are a feature of certain networked 531 * filesystems (i.e. NFS) in which data may have been 532 * written to the server's write cache, but has not yet 533 * been flushed to permanent storage. 534 * Only move pages to writeback if this bdi is over its 535 * threshold otherwise wait until the disk writes catch 536 * up. 537 */ 538 if (bdi_nr_reclaimable > bdi_thresh) { 539 writeback_inodes_wb(&bdi->wb, &wbc); 540 pages_written += write_chunk - wbc.nr_to_write; 541 get_dirty_limits(&background_thresh, &dirty_thresh, 542 &bdi_thresh, bdi); 543 } 544 545 /* 546 * In order to avoid the stacked BDI deadlock we need 547 * to ensure we accurately count the 'dirty' pages when 548 * the threshold is low. 549 * 550 * Otherwise it would be possible to get thresh+n pages 551 * reported dirty, even though there are thresh-m pages 552 * actually dirty; with m+n sitting in the percpu 553 * deltas. 554 */ 555 if (bdi_thresh < 2*bdi_stat_error(bdi)) { 556 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 557 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); 558 } else if (bdi_nr_reclaimable) { 559 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 560 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 561 } 562 563 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 564 break; 565 if (pages_written >= write_chunk) 566 break; /* We've done our duty */ 567 568 __set_current_state(TASK_INTERRUPTIBLE); 569 io_schedule_timeout(pause); 570 571 /* 572 * Increase the delay for each loop, up to our previous 573 * default of taking a 100ms nap. 574 */ 575 pause <<= 1; 576 if (pause > HZ / 10) 577 pause = HZ / 10; 578 } 579 580 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh && 581 bdi->dirty_exceeded) 582 bdi->dirty_exceeded = 0; 583 584 if (writeback_in_progress(bdi)) 585 return; 586 587 /* 588 * In laptop mode, we wait until hitting the higher threshold before 589 * starting background writeout, and then write out all the way down 590 * to the lower threshold. So slow writers cause minimal disk activity. 591 * 592 * In normal mode, we start background writeout at the lower 593 * background_thresh, to keep the amount of dirty memory low. 594 */ 595 if ((laptop_mode && pages_written) || 596 (!laptop_mode && ((global_page_state(NR_FILE_DIRTY) 597 + global_page_state(NR_UNSTABLE_NFS)) 598 > background_thresh))) 599 bdi_start_background_writeback(bdi); 600} 601 602void set_page_dirty_balance(struct page *page, int page_mkwrite) 603{ 604 if (set_page_dirty(page) || page_mkwrite) { 605 struct address_space *mapping = page_mapping(page); 606 607 if (mapping) 608 balance_dirty_pages_ratelimited(mapping); 609 } 610} 611 612static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0; 613 614/** 615 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 616 * @mapping: address_space which was dirtied 617 * @nr_pages_dirtied: number of pages which the caller has just dirtied 618 * 619 * Processes which are dirtying memory should call in here once for each page 620 * which was newly dirtied. The function will periodically check the system's 621 * dirty state and will initiate writeback if needed. 622 * 623 * On really big machines, get_writeback_state is expensive, so try to avoid 624 * calling it too often (ratelimiting). But once we're over the dirty memory 625 * limit we decrease the ratelimiting by a lot, to prevent individual processes 626 * from overshooting the limit by (ratelimit_pages) each. 627 */ 628void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 629 unsigned long nr_pages_dirtied) 630{ 631 unsigned long ratelimit; 632 unsigned long *p; 633 634 ratelimit = ratelimit_pages; 635 if (mapping->backing_dev_info->dirty_exceeded) 636 ratelimit = 8; 637 638 /* 639 * Check the rate limiting. Also, we do not want to throttle real-time 640 * tasks in balance_dirty_pages(). Period. 641 */ 642 preempt_disable(); 643 p = &__get_cpu_var(bdp_ratelimits); 644 *p += nr_pages_dirtied; 645 if (unlikely(*p >= ratelimit)) { 646 ratelimit = sync_writeback_pages(*p); 647 *p = 0; 648 preempt_enable(); 649 balance_dirty_pages(mapping, ratelimit); 650 return; 651 } 652 preempt_enable(); 653} 654EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 655 656void throttle_vm_writeout(gfp_t gfp_mask) 657{ 658 unsigned long background_thresh; 659 unsigned long dirty_thresh; 660 661 for ( ; ; ) { 662 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 663 664 /* 665 * Boost the allowable dirty threshold a bit for page 666 * allocators so they don't get DoS'ed by heavy writers 667 */ 668 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 669 670 if (global_page_state(NR_UNSTABLE_NFS) + 671 global_page_state(NR_WRITEBACK) <= dirty_thresh) 672 break; 673 congestion_wait(BLK_RW_ASYNC, HZ/10); 674 675 /* 676 * The caller might hold locks which can prevent IO completion 677 * or progress in the filesystem. So we cannot just sit here 678 * waiting for IO to complete. 679 */ 680 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 681 break; 682 } 683} 684 685/* 686 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 687 */ 688int dirty_writeback_centisecs_handler(ctl_table *table, int write, 689 void __user *buffer, size_t *length, loff_t *ppos) 690{ 691 proc_dointvec(table, write, buffer, length, ppos); 692 bdi_arm_supers_timer(); 693 return 0; 694} 695 696#ifdef CONFIG_BLOCK 697void laptop_mode_timer_fn(unsigned long data) 698{ 699 struct request_queue *q = (struct request_queue *)data; 700 int nr_pages = global_page_state(NR_FILE_DIRTY) + 701 global_page_state(NR_UNSTABLE_NFS); 702 703 /* 704 * We want to write everything out, not just down to the dirty 705 * threshold 706 */ 707 if (bdi_has_dirty_io(&q->backing_dev_info)) 708 bdi_start_writeback(&q->backing_dev_info, nr_pages); 709} 710 711/* 712 * We've spun up the disk and we're in laptop mode: schedule writeback 713 * of all dirty data a few seconds from now. If the flush is already scheduled 714 * then push it back - the user is still using the disk. 715 */ 716void laptop_io_completion(struct backing_dev_info *info) 717{ 718 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); 719} 720 721/* 722 * We're in laptop mode and we've just synced. The sync's writes will have 723 * caused another writeback to be scheduled by laptop_io_completion. 724 * Nothing needs to be written back anymore, so we unschedule the writeback. 725 */ 726void laptop_sync_completion(void) 727{ 728 struct backing_dev_info *bdi; 729 730 rcu_read_lock(); 731 732 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) 733 del_timer(&bdi->laptop_mode_wb_timer); 734 735 rcu_read_unlock(); 736} 737#endif 738 739/* 740 * If ratelimit_pages is too high then we can get into dirty-data overload 741 * if a large number of processes all perform writes at the same time. 742 * If it is too low then SMP machines will call the (expensive) 743 * get_writeback_state too often. 744 * 745 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 746 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 747 * thresholds before writeback cuts in. 748 * 749 * But the limit should not be set too high. Because it also controls the 750 * amount of memory which the balance_dirty_pages() caller has to write back. 751 * If this is too large then the caller will block on the IO queue all the 752 * time. So limit it to four megabytes - the balance_dirty_pages() caller 753 * will write six megabyte chunks, max. 754 */ 755 756void writeback_set_ratelimit(void) 757{ 758 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 759 if (ratelimit_pages < 16) 760 ratelimit_pages = 16; 761 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 762 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 763} 764 765static int __cpuinit 766ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 767{ 768 writeback_set_ratelimit(); 769 return NOTIFY_DONE; 770} 771 772static struct notifier_block __cpuinitdata ratelimit_nb = { 773 .notifier_call = ratelimit_handler, 774 .next = NULL, 775}; 776 777/* 778 * Called early on to tune the page writeback dirty limits. 779 * 780 * We used to scale dirty pages according to how total memory 781 * related to pages that could be allocated for buffers (by 782 * comparing nr_free_buffer_pages() to vm_total_pages. 783 * 784 * However, that was when we used "dirty_ratio" to scale with 785 * all memory, and we don't do that any more. "dirty_ratio" 786 * is now applied to total non-HIGHPAGE memory (by subtracting 787 * totalhigh_pages from vm_total_pages), and as such we can't 788 * get into the old insane situation any more where we had 789 * large amounts of dirty pages compared to a small amount of 790 * non-HIGHMEM memory. 791 * 792 * But we might still want to scale the dirty_ratio by how 793 * much memory the box has.. 794 */ 795void __init page_writeback_init(void) 796{ 797 int shift; 798 799 writeback_set_ratelimit(); 800 register_cpu_notifier(&ratelimit_nb); 801 802 shift = calc_period_shift(); 803 prop_descriptor_init(&vm_completions, shift); 804 prop_descriptor_init(&vm_dirties, shift); 805} 806 807/** 808 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 809 * @mapping: address space structure to write 810 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 811 * @writepage: function called for each page 812 * @data: data passed to writepage function 813 * 814 * If a page is already under I/O, write_cache_pages() skips it, even 815 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 816 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 817 * and msync() need to guarantee that all the data which was dirty at the time 818 * the call was made get new I/O started against them. If wbc->sync_mode is 819 * WB_SYNC_ALL then we were called for data integrity and we must wait for 820 * existing IO to complete. 821 */ 822int write_cache_pages(struct address_space *mapping, 823 struct writeback_control *wbc, writepage_t writepage, 824 void *data) 825{ 826 int ret = 0; 827 int done = 0; 828 struct pagevec pvec; 829 int nr_pages; 830 pgoff_t uninitialized_var(writeback_index); 831 pgoff_t index; 832 pgoff_t end; /* Inclusive */ 833 pgoff_t done_index; 834 int cycled; 835 int range_whole = 0; 836 837 pagevec_init(&pvec, 0); 838 if (wbc->range_cyclic) { 839 writeback_index = mapping->writeback_index; /* prev offset */ 840 index = writeback_index; 841 if (index == 0) 842 cycled = 1; 843 else 844 cycled = 0; 845 end = -1; 846 } else { 847 index = wbc->range_start >> PAGE_CACHE_SHIFT; 848 end = wbc->range_end >> PAGE_CACHE_SHIFT; 849 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 850 range_whole = 1; 851 cycled = 1; /* ignore range_cyclic tests */ 852 853 /* 854 * If this is a data integrity sync, cap the writeback to the 855 * current end of file. Any extension to the file that occurs 856 * after this is a new write and we don't need to write those 857 * pages out to fulfil our data integrity requirements. If we 858 * try to write them out, we can get stuck in this scan until 859 * the concurrent writer stops adding dirty pages and extending 860 * EOF. 861 */ 862 if (wbc->sync_mode == WB_SYNC_ALL && 863 wbc->range_end == LLONG_MAX) { 864 end = i_size_read(mapping->host) >> PAGE_CACHE_SHIFT; 865 } 866 } 867 868retry: 869 done_index = index; 870 while (!done && (index <= end)) { 871 int i; 872 873 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 874 PAGECACHE_TAG_DIRTY, 875 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); 876 if (nr_pages == 0) 877 break; 878 879 for (i = 0; i < nr_pages; i++) { 880 struct page *page = pvec.pages[i]; 881 882 /* 883 * At this point, the page may be truncated or 884 * invalidated (changing page->mapping to NULL), or 885 * even swizzled back from swapper_space to tmpfs file 886 * mapping. However, page->index will not change 887 * because we have a reference on the page. 888 */ 889 if (page->index > end) { 890 /* 891 * can't be range_cyclic (1st pass) because 892 * end == -1 in that case. 893 */ 894 done = 1; 895 break; 896 } 897 898 done_index = page->index + 1; 899 900 lock_page(page); 901 902 /* 903 * Page truncated or invalidated. We can freely skip it 904 * then, even for data integrity operations: the page 905 * has disappeared concurrently, so there could be no 906 * real expectation of this data interity operation 907 * even if there is now a new, dirty page at the same 908 * pagecache address. 909 */ 910 if (unlikely(page->mapping != mapping)) { 911continue_unlock: 912 unlock_page(page); 913 continue; 914 } 915 916 if (!PageDirty(page)) { 917 /* someone wrote it for us */ 918 goto continue_unlock; 919 } 920 921 if (PageWriteback(page)) { 922 if (wbc->sync_mode != WB_SYNC_NONE) 923 wait_on_page_writeback(page); 924 else 925 goto continue_unlock; 926 } 927 928 BUG_ON(PageWriteback(page)); 929 if (!clear_page_dirty_for_io(page)) 930 goto continue_unlock; 931 932 ret = (*writepage)(page, wbc, data); 933 if (unlikely(ret)) { 934 if (ret == AOP_WRITEPAGE_ACTIVATE) { 935 unlock_page(page); 936 ret = 0; 937 } else { 938 /* 939 * done_index is set past this page, 940 * so media errors will not choke 941 * background writeout for the entire 942 * file. This has consequences for 943 * range_cyclic semantics (ie. it may 944 * not be suitable for data integrity 945 * writeout). 946 */ 947 done = 1; 948 break; 949 } 950 } 951 952 if (wbc->nr_to_write > 0) { 953 if (--wbc->nr_to_write == 0 && 954 wbc->sync_mode == WB_SYNC_NONE) { 955 /* 956 * We stop writing back only if we are 957 * not doing integrity sync. In case of 958 * integrity sync we have to keep going 959 * because someone may be concurrently 960 * dirtying pages, and we might have 961 * synced a lot of newly appeared dirty 962 * pages, but have not synced all of the 963 * old dirty pages. 964 */ 965 done = 1; 966 break; 967 } 968 } 969 } 970 pagevec_release(&pvec); 971 cond_resched(); 972 } 973 if (!cycled && !done) { 974 /* 975 * range_cyclic: 976 * We hit the last page and there is more work to be done: wrap 977 * back to the start of the file 978 */ 979 cycled = 1; 980 index = 0; 981 end = writeback_index - 1; 982 goto retry; 983 } 984 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) 985 mapping->writeback_index = done_index; 986 987 return ret; 988} 989EXPORT_SYMBOL(write_cache_pages); 990 991/* 992 * Function used by generic_writepages to call the real writepage 993 * function and set the mapping flags on error 994 */ 995static int __writepage(struct page *page, struct writeback_control *wbc, 996 void *data) 997{ 998 struct address_space *mapping = data; 999 int ret = mapping->a_ops->writepage(page, wbc); 1000 mapping_set_error(mapping, ret); 1001 return ret; 1002} 1003 1004/** 1005 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 1006 * @mapping: address space structure to write 1007 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1008 * 1009 * This is a library function, which implements the writepages() 1010 * address_space_operation. 1011 */ 1012int generic_writepages(struct address_space *mapping, 1013 struct writeback_control *wbc) 1014{ 1015 /* deal with chardevs and other special file */ 1016 if (!mapping->a_ops->writepage) 1017 return 0; 1018 1019 return write_cache_pages(mapping, wbc, __writepage, mapping); 1020} 1021 1022EXPORT_SYMBOL(generic_writepages); 1023 1024int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1025{ 1026 int ret; 1027 1028 if (wbc->nr_to_write <= 0) 1029 return 0; 1030 if (mapping->a_ops->writepages) 1031 ret = mapping->a_ops->writepages(mapping, wbc); 1032 else 1033 ret = generic_writepages(mapping, wbc); 1034 return ret; 1035} 1036 1037/** 1038 * write_one_page - write out a single page and optionally wait on I/O 1039 * @page: the page to write 1040 * @wait: if true, wait on writeout 1041 * 1042 * The page must be locked by the caller and will be unlocked upon return. 1043 * 1044 * write_one_page() returns a negative error code if I/O failed. 1045 */ 1046int write_one_page(struct page *page, int wait) 1047{ 1048 struct address_space *mapping = page->mapping; 1049 int ret = 0; 1050 struct writeback_control wbc = { 1051 .sync_mode = WB_SYNC_ALL, 1052 .nr_to_write = 1, 1053 }; 1054 1055 BUG_ON(!PageLocked(page)); 1056 1057 if (wait) 1058 wait_on_page_writeback(page); 1059 1060 if (clear_page_dirty_for_io(page)) { 1061 page_cache_get(page); 1062 ret = mapping->a_ops->writepage(page, &wbc); 1063 if (ret == 0 && wait) { 1064 wait_on_page_writeback(page); 1065 if (PageError(page)) 1066 ret = -EIO; 1067 } 1068 page_cache_release(page); 1069 } else { 1070 unlock_page(page); 1071 } 1072 return ret; 1073} 1074EXPORT_SYMBOL(write_one_page); 1075 1076/* 1077 * For address_spaces which do not use buffers nor write back. 1078 */ 1079int __set_page_dirty_no_writeback(struct page *page) 1080{ 1081 if (!PageDirty(page)) 1082 SetPageDirty(page); 1083 return 0; 1084} 1085 1086/* 1087 * Helper function for set_page_dirty family. 1088 * NOTE: This relies on being atomic wrt interrupts. 1089 */ 1090void account_page_dirtied(struct page *page, struct address_space *mapping) 1091{ 1092 if (mapping_cap_account_dirty(mapping)) { 1093 __inc_zone_page_state(page, NR_FILE_DIRTY); 1094 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); 1095 task_dirty_inc(current); 1096 task_io_account_write(PAGE_CACHE_SIZE); 1097 } 1098} 1099EXPORT_SYMBOL(account_page_dirtied); 1100 1101/* 1102 * For address_spaces which do not use buffers. Just tag the page as dirty in 1103 * its radix tree. 1104 * 1105 * This is also used when a single buffer is being dirtied: we want to set the 1106 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1107 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1108 * 1109 * Most callers have locked the page, which pins the address_space in memory. 1110 * But zap_pte_range() does not lock the page, however in that case the 1111 * mapping is pinned by the vma's ->vm_file reference. 1112 * 1113 * We take care to handle the case where the page was truncated from the 1114 * mapping by re-checking page_mapping() inside tree_lock. 1115 */ 1116int __set_page_dirty_nobuffers(struct page *page) 1117{ 1118 if (!TestSetPageDirty(page)) { 1119 struct address_space *mapping = page_mapping(page); 1120 struct address_space *mapping2; 1121 1122 if (!mapping) 1123 return 1; 1124 1125 spin_lock_irq(&mapping->tree_lock); 1126 mapping2 = page_mapping(page); 1127 if (mapping2) { /* Race with truncate? */ 1128 BUG_ON(mapping2 != mapping); 1129 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1130 account_page_dirtied(page, mapping); 1131 radix_tree_tag_set(&mapping->page_tree, 1132 page_index(page), PAGECACHE_TAG_DIRTY); 1133 } 1134 spin_unlock_irq(&mapping->tree_lock); 1135 if (mapping->host) { 1136 /* !PageAnon && !swapper_space */ 1137 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1138 } 1139 return 1; 1140 } 1141 return 0; 1142} 1143EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1144 1145/* 1146 * When a writepage implementation decides that it doesn't want to write this 1147 * page for some reason, it should redirty the locked page via 1148 * redirty_page_for_writepage() and it should then unlock the page and return 0 1149 */ 1150int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1151{ 1152 wbc->pages_skipped++; 1153 return __set_page_dirty_nobuffers(page); 1154} 1155EXPORT_SYMBOL(redirty_page_for_writepage); 1156 1157/* 1158 * Dirty a page. 1159 * 1160 * For pages with a mapping this should be done under the page lock 1161 * for the benefit of asynchronous memory errors who prefer a consistent 1162 * dirty state. This rule can be broken in some special cases, 1163 * but should be better not to. 1164 * 1165 * If the mapping doesn't provide a set_page_dirty a_op, then 1166 * just fall through and assume that it wants buffer_heads. 1167 */ 1168int set_page_dirty(struct page *page) 1169{ 1170 struct address_space *mapping = page_mapping(page); 1171 1172 if (likely(mapping)) { 1173 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1174#ifdef CONFIG_BLOCK 1175 if (!spd) 1176 spd = __set_page_dirty_buffers; 1177#endif 1178 return (*spd)(page); 1179 } 1180 if (!PageDirty(page)) { 1181 if (!TestSetPageDirty(page)) 1182 return 1; 1183 } 1184 return 0; 1185} 1186EXPORT_SYMBOL(set_page_dirty); 1187 1188/* 1189 * set_page_dirty() is racy if the caller has no reference against 1190 * page->mapping->host, and if the page is unlocked. This is because another 1191 * CPU could truncate the page off the mapping and then free the mapping. 1192 * 1193 * Usually, the page _is_ locked, or the caller is a user-space process which 1194 * holds a reference on the inode by having an open file. 1195 * 1196 * In other cases, the page should be locked before running set_page_dirty(). 1197 */ 1198int set_page_dirty_lock(struct page *page) 1199{ 1200 int ret; 1201 1202 lock_page_nosync(page); 1203 ret = set_page_dirty(page); 1204 unlock_page(page); 1205 return ret; 1206} 1207EXPORT_SYMBOL(set_page_dirty_lock); 1208 1209/* 1210 * Clear a page's dirty flag, while caring for dirty memory accounting. 1211 * Returns true if the page was previously dirty. 1212 * 1213 * This is for preparing to put the page under writeout. We leave the page 1214 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1215 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1216 * implementation will run either set_page_writeback() or set_page_dirty(), 1217 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1218 * back into sync. 1219 * 1220 * This incoherency between the page's dirty flag and radix-tree tag is 1221 * unfortunate, but it only exists while the page is locked. 1222 */ 1223int clear_page_dirty_for_io(struct page *page) 1224{ 1225 struct address_space *mapping = page_mapping(page); 1226 1227 BUG_ON(!PageLocked(page)); 1228 1229 ClearPageReclaim(page); 1230 if (mapping && mapping_cap_account_dirty(mapping)) { 1231 /* 1232 * Yes, Virginia, this is indeed insane. 1233 * 1234 * We use this sequence to make sure that 1235 * (a) we account for dirty stats properly 1236 * (b) we tell the low-level filesystem to 1237 * mark the whole page dirty if it was 1238 * dirty in a pagetable. Only to then 1239 * (c) clean the page again and return 1 to 1240 * cause the writeback. 1241 * 1242 * This way we avoid all nasty races with the 1243 * dirty bit in multiple places and clearing 1244 * them concurrently from different threads. 1245 * 1246 * Note! Normally the "set_page_dirty(page)" 1247 * has no effect on the actual dirty bit - since 1248 * that will already usually be set. But we 1249 * need the side effects, and it can help us 1250 * avoid races. 1251 * 1252 * We basically use the page "master dirty bit" 1253 * as a serialization point for all the different 1254 * threads doing their things. 1255 */ 1256 if (page_mkclean(page)) 1257 set_page_dirty(page); 1258 /* 1259 * We carefully synchronise fault handlers against 1260 * installing a dirty pte and marking the page dirty 1261 * at this point. We do this by having them hold the 1262 * page lock at some point after installing their 1263 * pte, but before marking the page dirty. 1264 * Pages are always locked coming in here, so we get 1265 * the desired exclusion. See mm/memory.c:do_wp_page() 1266 * for more comments. 1267 */ 1268 if (TestClearPageDirty(page)) { 1269 dec_zone_page_state(page, NR_FILE_DIRTY); 1270 dec_bdi_stat(mapping->backing_dev_info, 1271 BDI_RECLAIMABLE); 1272 return 1; 1273 } 1274 return 0; 1275 } 1276 return TestClearPageDirty(page); 1277} 1278EXPORT_SYMBOL(clear_page_dirty_for_io); 1279 1280int test_clear_page_writeback(struct page *page) 1281{ 1282 struct address_space *mapping = page_mapping(page); 1283 int ret; 1284 1285 if (mapping) { 1286 struct backing_dev_info *bdi = mapping->backing_dev_info; 1287 unsigned long flags; 1288 1289 spin_lock_irqsave(&mapping->tree_lock, flags); 1290 ret = TestClearPageWriteback(page); 1291 if (ret) { 1292 radix_tree_tag_clear(&mapping->page_tree, 1293 page_index(page), 1294 PAGECACHE_TAG_WRITEBACK); 1295 if (bdi_cap_account_writeback(bdi)) { 1296 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1297 __bdi_writeout_inc(bdi); 1298 } 1299 } 1300 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1301 } else { 1302 ret = TestClearPageWriteback(page); 1303 } 1304 if (ret) 1305 dec_zone_page_state(page, NR_WRITEBACK); 1306 return ret; 1307} 1308 1309int test_set_page_writeback(struct page *page) 1310{ 1311 struct address_space *mapping = page_mapping(page); 1312 int ret; 1313 1314 if (mapping) { 1315 struct backing_dev_info *bdi = mapping->backing_dev_info; 1316 unsigned long flags; 1317 1318 spin_lock_irqsave(&mapping->tree_lock, flags); 1319 ret = TestSetPageWriteback(page); 1320 if (!ret) { 1321 radix_tree_tag_set(&mapping->page_tree, 1322 page_index(page), 1323 PAGECACHE_TAG_WRITEBACK); 1324 if (bdi_cap_account_writeback(bdi)) 1325 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1326 } 1327 if (!PageDirty(page)) 1328 radix_tree_tag_clear(&mapping->page_tree, 1329 page_index(page), 1330 PAGECACHE_TAG_DIRTY); 1331 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1332 } else { 1333 ret = TestSetPageWriteback(page); 1334 } 1335 if (!ret) 1336 inc_zone_page_state(page, NR_WRITEBACK); 1337 return ret; 1338 1339} 1340EXPORT_SYMBOL(test_set_page_writeback); 1341 1342/* 1343 * Return true if any of the pages in the mapping are marked with the 1344 * passed tag. 1345 */ 1346int mapping_tagged(struct address_space *mapping, int tag) 1347{ 1348 int ret; 1349 rcu_read_lock(); 1350 ret = radix_tree_tagged(&mapping->page_tree, tag); 1351 rcu_read_unlock(); 1352 return ret; 1353} 1354EXPORT_SYMBOL(mapping_tagged); 1355