page-writeback.c revision 05fe478dd04e02fa230c305ab9b5616669821dd3
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 * The maximum number of pages to writeout in a single bdflush/kupdate 40 * operation. We do this so we don't hold I_SYNC against an inode for 41 * enormous amounts of time, which would block a userspace task which has 42 * been forced to throttle against that inode. Also, the code reevaluates 43 * the dirty each time it has written this many pages. 44 */ 45#define MAX_WRITEBACK_PAGES 1024 46 47/* 48 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 49 * will look to see if it needs to force writeback or throttling. 50 */ 51static long ratelimit_pages = 32; 52 53/* 54 * When balance_dirty_pages decides that the caller needs to perform some 55 * non-background writeback, this is how many pages it will attempt to write. 56 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably 57 * large amounts of I/O are submitted. 58 */ 59static inline long sync_writeback_pages(void) 60{ 61 return ratelimit_pages + ratelimit_pages / 2; 62} 63 64/* The following parameters are exported via /proc/sys/vm */ 65 66/* 67 * Start background writeback (via pdflush) at this percentage 68 */ 69int dirty_background_ratio = 5; 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 = 10; 81 82/* 83 * The interval between `kupdate'-style writebacks, in jiffies 84 */ 85int dirty_writeback_interval = 5 * HZ; 86 87/* 88 * The longest number of jiffies for which data is allowed to remain dirty 89 */ 90int dirty_expire_interval = 30 * HZ; 91 92/* 93 * Flag that makes the machine dump writes/reads and block dirtyings. 94 */ 95int block_dump; 96 97/* 98 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 99 * a full sync is triggered after this time elapses without any disk activity. 100 */ 101int laptop_mode; 102 103EXPORT_SYMBOL(laptop_mode); 104 105/* End of sysctl-exported parameters */ 106 107 108static void background_writeout(unsigned long _min_pages); 109 110/* 111 * Scale the writeback cache size proportional to the relative writeout speeds. 112 * 113 * We do this by keeping a floating proportion between BDIs, based on page 114 * writeback completions [end_page_writeback()]. Those devices that write out 115 * pages fastest will get the larger share, while the slower will get a smaller 116 * share. 117 * 118 * We use page writeout completions because we are interested in getting rid of 119 * dirty pages. Having them written out is the primary goal. 120 * 121 * We introduce a concept of time, a period over which we measure these events, 122 * because demand can/will vary over time. The length of this period itself is 123 * measured in page writeback completions. 124 * 125 */ 126static struct prop_descriptor vm_completions; 127static struct prop_descriptor vm_dirties; 128 129/* 130 * couple the period to the dirty_ratio: 131 * 132 * period/2 ~ roundup_pow_of_two(dirty limit) 133 */ 134static int calc_period_shift(void) 135{ 136 unsigned long dirty_total; 137 138 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 100; 139 return 2 + ilog2(dirty_total - 1); 140} 141 142/* 143 * update the period when the dirty ratio changes. 144 */ 145int dirty_ratio_handler(struct ctl_table *table, int write, 146 struct file *filp, void __user *buffer, size_t *lenp, 147 loff_t *ppos) 148{ 149 int old_ratio = vm_dirty_ratio; 150 int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos); 151 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 152 int shift = calc_period_shift(); 153 prop_change_shift(&vm_completions, shift); 154 prop_change_shift(&vm_dirties, shift); 155 } 156 return ret; 157} 158 159/* 160 * Increment the BDI's writeout completion count and the global writeout 161 * completion count. Called from test_clear_page_writeback(). 162 */ 163static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 164{ 165 __prop_inc_percpu_max(&vm_completions, &bdi->completions, 166 bdi->max_prop_frac); 167} 168 169void bdi_writeout_inc(struct backing_dev_info *bdi) 170{ 171 unsigned long flags; 172 173 local_irq_save(flags); 174 __bdi_writeout_inc(bdi); 175 local_irq_restore(flags); 176} 177EXPORT_SYMBOL_GPL(bdi_writeout_inc); 178 179static inline void task_dirty_inc(struct task_struct *tsk) 180{ 181 prop_inc_single(&vm_dirties, &tsk->dirties); 182} 183 184/* 185 * Obtain an accurate fraction of the BDI's portion. 186 */ 187static void bdi_writeout_fraction(struct backing_dev_info *bdi, 188 long *numerator, long *denominator) 189{ 190 if (bdi_cap_writeback_dirty(bdi)) { 191 prop_fraction_percpu(&vm_completions, &bdi->completions, 192 numerator, denominator); 193 } else { 194 *numerator = 0; 195 *denominator = 1; 196 } 197} 198 199/* 200 * Clip the earned share of dirty pages to that which is actually available. 201 * This avoids exceeding the total dirty_limit when the floating averages 202 * fluctuate too quickly. 203 */ 204static void 205clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty) 206{ 207 long avail_dirty; 208 209 avail_dirty = dirty - 210 (global_page_state(NR_FILE_DIRTY) + 211 global_page_state(NR_WRITEBACK) + 212 global_page_state(NR_UNSTABLE_NFS) + 213 global_page_state(NR_WRITEBACK_TEMP)); 214 215 if (avail_dirty < 0) 216 avail_dirty = 0; 217 218 avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) + 219 bdi_stat(bdi, BDI_WRITEBACK); 220 221 *pbdi_dirty = min(*pbdi_dirty, avail_dirty); 222} 223 224static inline void task_dirties_fraction(struct task_struct *tsk, 225 long *numerator, long *denominator) 226{ 227 prop_fraction_single(&vm_dirties, &tsk->dirties, 228 numerator, denominator); 229} 230 231/* 232 * scale the dirty limit 233 * 234 * task specific dirty limit: 235 * 236 * dirty -= (dirty/8) * p_{t} 237 */ 238static void task_dirty_limit(struct task_struct *tsk, long *pdirty) 239{ 240 long numerator, denominator; 241 long dirty = *pdirty; 242 u64 inv = dirty >> 3; 243 244 task_dirties_fraction(tsk, &numerator, &denominator); 245 inv *= numerator; 246 do_div(inv, denominator); 247 248 dirty -= inv; 249 if (dirty < *pdirty/2) 250 dirty = *pdirty/2; 251 252 *pdirty = dirty; 253} 254 255/* 256 * 257 */ 258static DEFINE_SPINLOCK(bdi_lock); 259static unsigned int bdi_min_ratio; 260 261int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 262{ 263 int ret = 0; 264 unsigned long flags; 265 266 spin_lock_irqsave(&bdi_lock, flags); 267 if (min_ratio > bdi->max_ratio) { 268 ret = -EINVAL; 269 } else { 270 min_ratio -= bdi->min_ratio; 271 if (bdi_min_ratio + min_ratio < 100) { 272 bdi_min_ratio += min_ratio; 273 bdi->min_ratio += min_ratio; 274 } else { 275 ret = -EINVAL; 276 } 277 } 278 spin_unlock_irqrestore(&bdi_lock, flags); 279 280 return ret; 281} 282 283int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 284{ 285 unsigned long flags; 286 int ret = 0; 287 288 if (max_ratio > 100) 289 return -EINVAL; 290 291 spin_lock_irqsave(&bdi_lock, flags); 292 if (bdi->min_ratio > max_ratio) { 293 ret = -EINVAL; 294 } else { 295 bdi->max_ratio = max_ratio; 296 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; 297 } 298 spin_unlock_irqrestore(&bdi_lock, flags); 299 300 return ret; 301} 302EXPORT_SYMBOL(bdi_set_max_ratio); 303 304/* 305 * Work out the current dirty-memory clamping and background writeout 306 * thresholds. 307 * 308 * The main aim here is to lower them aggressively if there is a lot of mapped 309 * memory around. To avoid stressing page reclaim with lots of unreclaimable 310 * pages. It is better to clamp down on writers than to start swapping, and 311 * performing lots of scanning. 312 * 313 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 314 * 315 * We don't permit the clamping level to fall below 5% - that is getting rather 316 * excessive. 317 * 318 * We make sure that the background writeout level is below the adjusted 319 * clamping level. 320 */ 321 322static unsigned long highmem_dirtyable_memory(unsigned long total) 323{ 324#ifdef CONFIG_HIGHMEM 325 int node; 326 unsigned long x = 0; 327 328 for_each_node_state(node, N_HIGH_MEMORY) { 329 struct zone *z = 330 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 331 332 x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z); 333 } 334 /* 335 * Make sure that the number of highmem pages is never larger 336 * than the number of the total dirtyable memory. This can only 337 * occur in very strange VM situations but we want to make sure 338 * that this does not occur. 339 */ 340 return min(x, total); 341#else 342 return 0; 343#endif 344} 345 346/** 347 * determine_dirtyable_memory - amount of memory that may be used 348 * 349 * Returns the numebr of pages that can currently be freed and used 350 * by the kernel for direct mappings. 351 */ 352unsigned long determine_dirtyable_memory(void) 353{ 354 unsigned long x; 355 356 x = global_page_state(NR_FREE_PAGES) + global_lru_pages(); 357 358 if (!vm_highmem_is_dirtyable) 359 x -= highmem_dirtyable_memory(x); 360 361 return x + 1; /* Ensure that we never return 0 */ 362} 363 364void 365get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty, 366 struct backing_dev_info *bdi) 367{ 368 int background_ratio; /* Percentages */ 369 int dirty_ratio; 370 long background; 371 long dirty; 372 unsigned long available_memory = determine_dirtyable_memory(); 373 struct task_struct *tsk; 374 375 dirty_ratio = vm_dirty_ratio; 376 if (dirty_ratio < 5) 377 dirty_ratio = 5; 378 379 background_ratio = dirty_background_ratio; 380 if (background_ratio >= dirty_ratio) 381 background_ratio = dirty_ratio / 2; 382 383 background = (background_ratio * available_memory) / 100; 384 dirty = (dirty_ratio * available_memory) / 100; 385 tsk = current; 386 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 387 background += background / 4; 388 dirty += dirty / 4; 389 } 390 *pbackground = background; 391 *pdirty = dirty; 392 393 if (bdi) { 394 u64 bdi_dirty; 395 long numerator, denominator; 396 397 /* 398 * Calculate this BDI's share of the dirty ratio. 399 */ 400 bdi_writeout_fraction(bdi, &numerator, &denominator); 401 402 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 403 bdi_dirty *= numerator; 404 do_div(bdi_dirty, denominator); 405 bdi_dirty += (dirty * bdi->min_ratio) / 100; 406 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 407 bdi_dirty = dirty * bdi->max_ratio / 100; 408 409 *pbdi_dirty = bdi_dirty; 410 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty); 411 task_dirty_limit(current, pbdi_dirty); 412 } 413} 414 415/* 416 * balance_dirty_pages() must be called by processes which are generating dirty 417 * data. It looks at the number of dirty pages in the machine and will force 418 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 419 * If we're over `background_thresh' then pdflush is woken to perform some 420 * writeout. 421 */ 422static void balance_dirty_pages(struct address_space *mapping) 423{ 424 long nr_reclaimable, bdi_nr_reclaimable; 425 long nr_writeback, bdi_nr_writeback; 426 long background_thresh; 427 long dirty_thresh; 428 long bdi_thresh; 429 unsigned long pages_written = 0; 430 unsigned long write_chunk = sync_writeback_pages(); 431 432 struct backing_dev_info *bdi = mapping->backing_dev_info; 433 434 for (;;) { 435 struct writeback_control wbc = { 436 .bdi = bdi, 437 .sync_mode = WB_SYNC_NONE, 438 .older_than_this = NULL, 439 .nr_to_write = write_chunk, 440 .range_cyclic = 1, 441 }; 442 443 get_dirty_limits(&background_thresh, &dirty_thresh, 444 &bdi_thresh, bdi); 445 446 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 447 global_page_state(NR_UNSTABLE_NFS); 448 nr_writeback = global_page_state(NR_WRITEBACK); 449 450 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 451 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 452 453 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 454 break; 455 456 /* 457 * Throttle it only when the background writeback cannot 458 * catch-up. This avoids (excessively) small writeouts 459 * when the bdi limits are ramping up. 460 */ 461 if (nr_reclaimable + nr_writeback < 462 (background_thresh + dirty_thresh) / 2) 463 break; 464 465 if (!bdi->dirty_exceeded) 466 bdi->dirty_exceeded = 1; 467 468 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 469 * Unstable writes are a feature of certain networked 470 * filesystems (i.e. NFS) in which data may have been 471 * written to the server's write cache, but has not yet 472 * been flushed to permanent storage. 473 */ 474 if (bdi_nr_reclaimable) { 475 writeback_inodes(&wbc); 476 pages_written += write_chunk - wbc.nr_to_write; 477 get_dirty_limits(&background_thresh, &dirty_thresh, 478 &bdi_thresh, bdi); 479 } 480 481 /* 482 * In order to avoid the stacked BDI deadlock we need 483 * to ensure we accurately count the 'dirty' pages when 484 * the threshold is low. 485 * 486 * Otherwise it would be possible to get thresh+n pages 487 * reported dirty, even though there are thresh-m pages 488 * actually dirty; with m+n sitting in the percpu 489 * deltas. 490 */ 491 if (bdi_thresh < 2*bdi_stat_error(bdi)) { 492 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 493 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); 494 } else if (bdi_nr_reclaimable) { 495 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 496 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 497 } 498 499 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 500 break; 501 if (pages_written >= write_chunk) 502 break; /* We've done our duty */ 503 504 congestion_wait(WRITE, HZ/10); 505 } 506 507 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh && 508 bdi->dirty_exceeded) 509 bdi->dirty_exceeded = 0; 510 511 if (writeback_in_progress(bdi)) 512 return; /* pdflush is already working this queue */ 513 514 /* 515 * In laptop mode, we wait until hitting the higher threshold before 516 * starting background writeout, and then write out all the way down 517 * to the lower threshold. So slow writers cause minimal disk activity. 518 * 519 * In normal mode, we start background writeout at the lower 520 * background_thresh, to keep the amount of dirty memory low. 521 */ 522 if ((laptop_mode && pages_written) || 523 (!laptop_mode && (global_page_state(NR_FILE_DIRTY) 524 + global_page_state(NR_UNSTABLE_NFS) 525 > background_thresh))) 526 pdflush_operation(background_writeout, 0); 527} 528 529void set_page_dirty_balance(struct page *page, int page_mkwrite) 530{ 531 if (set_page_dirty(page) || page_mkwrite) { 532 struct address_space *mapping = page_mapping(page); 533 534 if (mapping) 535 balance_dirty_pages_ratelimited(mapping); 536 } 537} 538 539/** 540 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 541 * @mapping: address_space which was dirtied 542 * @nr_pages_dirtied: number of pages which the caller has just dirtied 543 * 544 * Processes which are dirtying memory should call in here once for each page 545 * which was newly dirtied. The function will periodically check the system's 546 * dirty state and will initiate writeback if needed. 547 * 548 * On really big machines, get_writeback_state is expensive, so try to avoid 549 * calling it too often (ratelimiting). But once we're over the dirty memory 550 * limit we decrease the ratelimiting by a lot, to prevent individual processes 551 * from overshooting the limit by (ratelimit_pages) each. 552 */ 553void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 554 unsigned long nr_pages_dirtied) 555{ 556 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 557 unsigned long ratelimit; 558 unsigned long *p; 559 560 ratelimit = ratelimit_pages; 561 if (mapping->backing_dev_info->dirty_exceeded) 562 ratelimit = 8; 563 564 /* 565 * Check the rate limiting. Also, we do not want to throttle real-time 566 * tasks in balance_dirty_pages(). Period. 567 */ 568 preempt_disable(); 569 p = &__get_cpu_var(ratelimits); 570 *p += nr_pages_dirtied; 571 if (unlikely(*p >= ratelimit)) { 572 *p = 0; 573 preempt_enable(); 574 balance_dirty_pages(mapping); 575 return; 576 } 577 preempt_enable(); 578} 579EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 580 581void throttle_vm_writeout(gfp_t gfp_mask) 582{ 583 long background_thresh; 584 long dirty_thresh; 585 586 for ( ; ; ) { 587 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 588 589 /* 590 * Boost the allowable dirty threshold a bit for page 591 * allocators so they don't get DoS'ed by heavy writers 592 */ 593 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 594 595 if (global_page_state(NR_UNSTABLE_NFS) + 596 global_page_state(NR_WRITEBACK) <= dirty_thresh) 597 break; 598 congestion_wait(WRITE, HZ/10); 599 600 /* 601 * The caller might hold locks which can prevent IO completion 602 * or progress in the filesystem. So we cannot just sit here 603 * waiting for IO to complete. 604 */ 605 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 606 break; 607 } 608} 609 610/* 611 * writeback at least _min_pages, and keep writing until the amount of dirty 612 * memory is less than the background threshold, or until we're all clean. 613 */ 614static void background_writeout(unsigned long _min_pages) 615{ 616 long min_pages = _min_pages; 617 struct writeback_control wbc = { 618 .bdi = NULL, 619 .sync_mode = WB_SYNC_NONE, 620 .older_than_this = NULL, 621 .nr_to_write = 0, 622 .nonblocking = 1, 623 .range_cyclic = 1, 624 }; 625 626 for ( ; ; ) { 627 long background_thresh; 628 long dirty_thresh; 629 630 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 631 if (global_page_state(NR_FILE_DIRTY) + 632 global_page_state(NR_UNSTABLE_NFS) < background_thresh 633 && min_pages <= 0) 634 break; 635 wbc.more_io = 0; 636 wbc.encountered_congestion = 0; 637 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 638 wbc.pages_skipped = 0; 639 writeback_inodes(&wbc); 640 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 641 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 642 /* Wrote less than expected */ 643 if (wbc.encountered_congestion || wbc.more_io) 644 congestion_wait(WRITE, HZ/10); 645 else 646 break; 647 } 648 } 649} 650 651/* 652 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 653 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 654 * -1 if all pdflush threads were busy. 655 */ 656int wakeup_pdflush(long nr_pages) 657{ 658 if (nr_pages == 0) 659 nr_pages = global_page_state(NR_FILE_DIRTY) + 660 global_page_state(NR_UNSTABLE_NFS); 661 return pdflush_operation(background_writeout, nr_pages); 662} 663 664static void wb_timer_fn(unsigned long unused); 665static void laptop_timer_fn(unsigned long unused); 666 667static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 668static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 669 670/* 671 * Periodic writeback of "old" data. 672 * 673 * Define "old": the first time one of an inode's pages is dirtied, we mark the 674 * dirtying-time in the inode's address_space. So this periodic writeback code 675 * just walks the superblock inode list, writing back any inodes which are 676 * older than a specific point in time. 677 * 678 * Try to run once per dirty_writeback_interval. But if a writeback event 679 * takes longer than a dirty_writeback_interval interval, then leave a 680 * one-second gap. 681 * 682 * older_than_this takes precedence over nr_to_write. So we'll only write back 683 * all dirty pages if they are all attached to "old" mappings. 684 */ 685static void wb_kupdate(unsigned long arg) 686{ 687 unsigned long oldest_jif; 688 unsigned long start_jif; 689 unsigned long next_jif; 690 long nr_to_write; 691 struct writeback_control wbc = { 692 .bdi = NULL, 693 .sync_mode = WB_SYNC_NONE, 694 .older_than_this = &oldest_jif, 695 .nr_to_write = 0, 696 .nonblocking = 1, 697 .for_kupdate = 1, 698 .range_cyclic = 1, 699 }; 700 701 sync_supers(); 702 703 oldest_jif = jiffies - dirty_expire_interval; 704 start_jif = jiffies; 705 next_jif = start_jif + dirty_writeback_interval; 706 nr_to_write = global_page_state(NR_FILE_DIRTY) + 707 global_page_state(NR_UNSTABLE_NFS) + 708 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 709 while (nr_to_write > 0) { 710 wbc.more_io = 0; 711 wbc.encountered_congestion = 0; 712 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 713 writeback_inodes(&wbc); 714 if (wbc.nr_to_write > 0) { 715 if (wbc.encountered_congestion || wbc.more_io) 716 congestion_wait(WRITE, HZ/10); 717 else 718 break; /* All the old data is written */ 719 } 720 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 721 } 722 if (time_before(next_jif, jiffies + HZ)) 723 next_jif = jiffies + HZ; 724 if (dirty_writeback_interval) 725 mod_timer(&wb_timer, next_jif); 726} 727 728/* 729 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 730 */ 731int dirty_writeback_centisecs_handler(ctl_table *table, int write, 732 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 733{ 734 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); 735 if (dirty_writeback_interval) 736 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 737 else 738 del_timer(&wb_timer); 739 return 0; 740} 741 742static void wb_timer_fn(unsigned long unused) 743{ 744 if (pdflush_operation(wb_kupdate, 0) < 0) 745 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 746} 747 748static void laptop_flush(unsigned long unused) 749{ 750 sys_sync(); 751} 752 753static void laptop_timer_fn(unsigned long unused) 754{ 755 pdflush_operation(laptop_flush, 0); 756} 757 758/* 759 * We've spun up the disk and we're in laptop mode: schedule writeback 760 * of all dirty data a few seconds from now. If the flush is already scheduled 761 * then push it back - the user is still using the disk. 762 */ 763void laptop_io_completion(void) 764{ 765 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 766} 767 768/* 769 * We're in laptop mode and we've just synced. The sync's writes will have 770 * caused another writeback to be scheduled by laptop_io_completion. 771 * Nothing needs to be written back anymore, so we unschedule the writeback. 772 */ 773void laptop_sync_completion(void) 774{ 775 del_timer(&laptop_mode_wb_timer); 776} 777 778/* 779 * If ratelimit_pages is too high then we can get into dirty-data overload 780 * if a large number of processes all perform writes at the same time. 781 * If it is too low then SMP machines will call the (expensive) 782 * get_writeback_state too often. 783 * 784 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 785 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 786 * thresholds before writeback cuts in. 787 * 788 * But the limit should not be set too high. Because it also controls the 789 * amount of memory which the balance_dirty_pages() caller has to write back. 790 * If this is too large then the caller will block on the IO queue all the 791 * time. So limit it to four megabytes - the balance_dirty_pages() caller 792 * will write six megabyte chunks, max. 793 */ 794 795void writeback_set_ratelimit(void) 796{ 797 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 798 if (ratelimit_pages < 16) 799 ratelimit_pages = 16; 800 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 801 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 802} 803 804static int __cpuinit 805ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 806{ 807 writeback_set_ratelimit(); 808 return NOTIFY_DONE; 809} 810 811static struct notifier_block __cpuinitdata ratelimit_nb = { 812 .notifier_call = ratelimit_handler, 813 .next = NULL, 814}; 815 816/* 817 * Called early on to tune the page writeback dirty limits. 818 * 819 * We used to scale dirty pages according to how total memory 820 * related to pages that could be allocated for buffers (by 821 * comparing nr_free_buffer_pages() to vm_total_pages. 822 * 823 * However, that was when we used "dirty_ratio" to scale with 824 * all memory, and we don't do that any more. "dirty_ratio" 825 * is now applied to total non-HIGHPAGE memory (by subtracting 826 * totalhigh_pages from vm_total_pages), and as such we can't 827 * get into the old insane situation any more where we had 828 * large amounts of dirty pages compared to a small amount of 829 * non-HIGHMEM memory. 830 * 831 * But we might still want to scale the dirty_ratio by how 832 * much memory the box has.. 833 */ 834void __init page_writeback_init(void) 835{ 836 int shift; 837 838 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 839 writeback_set_ratelimit(); 840 register_cpu_notifier(&ratelimit_nb); 841 842 shift = calc_period_shift(); 843 prop_descriptor_init(&vm_completions, shift); 844 prop_descriptor_init(&vm_dirties, shift); 845} 846 847/** 848 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 849 * @mapping: address space structure to write 850 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 851 * @writepage: function called for each page 852 * @data: data passed to writepage function 853 * 854 * If a page is already under I/O, write_cache_pages() skips it, even 855 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 856 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 857 * and msync() need to guarantee that all the data which was dirty at the time 858 * the call was made get new I/O started against them. If wbc->sync_mode is 859 * WB_SYNC_ALL then we were called for data integrity and we must wait for 860 * existing IO to complete. 861 */ 862int write_cache_pages(struct address_space *mapping, 863 struct writeback_control *wbc, writepage_t writepage, 864 void *data) 865{ 866 struct backing_dev_info *bdi = mapping->backing_dev_info; 867 int ret = 0; 868 int done = 0; 869 struct pagevec pvec; 870 int nr_pages; 871 pgoff_t uninitialized_var(writeback_index); 872 pgoff_t index; 873 pgoff_t end; /* Inclusive */ 874 pgoff_t done_index; 875 int cycled; 876 int range_whole = 0; 877 long nr_to_write = wbc->nr_to_write; 878 879 if (wbc->nonblocking && bdi_write_congested(bdi)) { 880 wbc->encountered_congestion = 1; 881 return 0; 882 } 883 884 pagevec_init(&pvec, 0); 885 if (wbc->range_cyclic) { 886 writeback_index = mapping->writeback_index; /* prev offset */ 887 index = writeback_index; 888 if (index == 0) 889 cycled = 1; 890 else 891 cycled = 0; 892 end = -1; 893 } else { 894 index = wbc->range_start >> PAGE_CACHE_SHIFT; 895 end = wbc->range_end >> PAGE_CACHE_SHIFT; 896 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 897 range_whole = 1; 898 cycled = 1; /* ignore range_cyclic tests */ 899 } 900retry: 901 done_index = index; 902 while (!done && (index <= end) && 903 (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 904 PAGECACHE_TAG_DIRTY, 905 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) { 906 unsigned i; 907 908 for (i = 0; i < nr_pages; i++) { 909 struct page *page = pvec.pages[i]; 910 911 done_index = page->index + 1; 912 913 /* 914 * At this point we hold neither mapping->tree_lock nor 915 * lock on the page itself: the page may be truncated or 916 * invalidated (changing page->mapping to NULL), or even 917 * swizzled back from swapper_space to tmpfs file 918 * mapping 919 */ 920 lock_page(page); 921 922 if (unlikely(page->mapping != mapping)) { 923 unlock_page(page); 924 continue; 925 } 926 927 if (page->index > end) { 928 /* 929 * can't be range_cyclic (1st pass) because 930 * end == -1 in that case. 931 */ 932 done = 1; 933 unlock_page(page); 934 continue; 935 } 936 937 if (wbc->sync_mode != WB_SYNC_NONE) 938 wait_on_page_writeback(page); 939 940 if (PageWriteback(page) || 941 !clear_page_dirty_for_io(page)) { 942 unlock_page(page); 943 continue; 944 } 945 946 ret = (*writepage)(page, wbc, data); 947 if (unlikely(ret)) { 948 if (ret == AOP_WRITEPAGE_ACTIVATE) { 949 unlock_page(page); 950 ret = 0; 951 } else { 952 /* 953 * done_index is set past this page, 954 * so media errors will not choke 955 * background writeout for the entire 956 * file. This has consequences for 957 * range_cyclic semantics (ie. it may 958 * not be suitable for data integrity 959 * writeout). 960 */ 961 done = 1; 962 break; 963 } 964 } 965 966 if (wbc->sync_mode == WB_SYNC_NONE) { 967 if (--wbc->nr_to_write <= 0) 968 done = 1; 969 } 970 if (wbc->nonblocking && bdi_write_congested(bdi)) { 971 wbc->encountered_congestion = 1; 972 done = 1; 973 } 974 } 975 pagevec_release(&pvec); 976 cond_resched(); 977 } 978 if (!cycled) { 979 /* 980 * range_cyclic: 981 * We hit the last page and there is more work to be done: wrap 982 * back to the start of the file 983 */ 984 cycled = 1; 985 index = 0; 986 end = writeback_index - 1; 987 goto retry; 988 } 989 if (!wbc->no_nrwrite_index_update) { 990 if (wbc->range_cyclic || (range_whole && nr_to_write > 0)) 991 mapping->writeback_index = done_index; 992 wbc->nr_to_write = nr_to_write; 993 } 994 995 return ret; 996} 997EXPORT_SYMBOL(write_cache_pages); 998 999/* 1000 * Function used by generic_writepages to call the real writepage 1001 * function and set the mapping flags on error 1002 */ 1003static int __writepage(struct page *page, struct writeback_control *wbc, 1004 void *data) 1005{ 1006 struct address_space *mapping = data; 1007 int ret = mapping->a_ops->writepage(page, wbc); 1008 mapping_set_error(mapping, ret); 1009 return ret; 1010} 1011 1012/** 1013 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 1014 * @mapping: address space structure to write 1015 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1016 * 1017 * This is a library function, which implements the writepages() 1018 * address_space_operation. 1019 */ 1020int generic_writepages(struct address_space *mapping, 1021 struct writeback_control *wbc) 1022{ 1023 /* deal with chardevs and other special file */ 1024 if (!mapping->a_ops->writepage) 1025 return 0; 1026 1027 return write_cache_pages(mapping, wbc, __writepage, mapping); 1028} 1029 1030EXPORT_SYMBOL(generic_writepages); 1031 1032int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1033{ 1034 int ret; 1035 1036 if (wbc->nr_to_write <= 0) 1037 return 0; 1038 wbc->for_writepages = 1; 1039 if (mapping->a_ops->writepages) 1040 ret = mapping->a_ops->writepages(mapping, wbc); 1041 else 1042 ret = generic_writepages(mapping, wbc); 1043 wbc->for_writepages = 0; 1044 return ret; 1045} 1046 1047/** 1048 * write_one_page - write out a single page and optionally wait on I/O 1049 * @page: the page to write 1050 * @wait: if true, wait on writeout 1051 * 1052 * The page must be locked by the caller and will be unlocked upon return. 1053 * 1054 * write_one_page() returns a negative error code if I/O failed. 1055 */ 1056int write_one_page(struct page *page, int wait) 1057{ 1058 struct address_space *mapping = page->mapping; 1059 int ret = 0; 1060 struct writeback_control wbc = { 1061 .sync_mode = WB_SYNC_ALL, 1062 .nr_to_write = 1, 1063 }; 1064 1065 BUG_ON(!PageLocked(page)); 1066 1067 if (wait) 1068 wait_on_page_writeback(page); 1069 1070 if (clear_page_dirty_for_io(page)) { 1071 page_cache_get(page); 1072 ret = mapping->a_ops->writepage(page, &wbc); 1073 if (ret == 0 && wait) { 1074 wait_on_page_writeback(page); 1075 if (PageError(page)) 1076 ret = -EIO; 1077 } 1078 page_cache_release(page); 1079 } else { 1080 unlock_page(page); 1081 } 1082 return ret; 1083} 1084EXPORT_SYMBOL(write_one_page); 1085 1086/* 1087 * For address_spaces which do not use buffers nor write back. 1088 */ 1089int __set_page_dirty_no_writeback(struct page *page) 1090{ 1091 if (!PageDirty(page)) 1092 SetPageDirty(page); 1093 return 0; 1094} 1095 1096/* 1097 * For address_spaces which do not use buffers. Just tag the page as dirty in 1098 * its radix tree. 1099 * 1100 * This is also used when a single buffer is being dirtied: we want to set the 1101 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1102 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1103 * 1104 * Most callers have locked the page, which pins the address_space in memory. 1105 * But zap_pte_range() does not lock the page, however in that case the 1106 * mapping is pinned by the vma's ->vm_file reference. 1107 * 1108 * We take care to handle the case where the page was truncated from the 1109 * mapping by re-checking page_mapping() inside tree_lock. 1110 */ 1111int __set_page_dirty_nobuffers(struct page *page) 1112{ 1113 if (!TestSetPageDirty(page)) { 1114 struct address_space *mapping = page_mapping(page); 1115 struct address_space *mapping2; 1116 1117 if (!mapping) 1118 return 1; 1119 1120 spin_lock_irq(&mapping->tree_lock); 1121 mapping2 = page_mapping(page); 1122 if (mapping2) { /* Race with truncate? */ 1123 BUG_ON(mapping2 != mapping); 1124 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1125 if (mapping_cap_account_dirty(mapping)) { 1126 __inc_zone_page_state(page, NR_FILE_DIRTY); 1127 __inc_bdi_stat(mapping->backing_dev_info, 1128 BDI_RECLAIMABLE); 1129 task_io_account_write(PAGE_CACHE_SIZE); 1130 } 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 * If the mapping doesn't provide a set_page_dirty a_op, then 1159 * just fall through and assume that it wants buffer_heads. 1160 */ 1161static int __set_page_dirty(struct page *page) 1162{ 1163 struct address_space *mapping = page_mapping(page); 1164 1165 if (likely(mapping)) { 1166 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1167#ifdef CONFIG_BLOCK 1168 if (!spd) 1169 spd = __set_page_dirty_buffers; 1170#endif 1171 return (*spd)(page); 1172 } 1173 if (!PageDirty(page)) { 1174 if (!TestSetPageDirty(page)) 1175 return 1; 1176 } 1177 return 0; 1178} 1179 1180int set_page_dirty(struct page *page) 1181{ 1182 int ret = __set_page_dirty(page); 1183 if (ret) 1184 task_dirty_inc(current); 1185 return ret; 1186} 1187EXPORT_SYMBOL(set_page_dirty); 1188 1189/* 1190 * set_page_dirty() is racy if the caller has no reference against 1191 * page->mapping->host, and if the page is unlocked. This is because another 1192 * CPU could truncate the page off the mapping and then free the mapping. 1193 * 1194 * Usually, the page _is_ locked, or the caller is a user-space process which 1195 * holds a reference on the inode by having an open file. 1196 * 1197 * In other cases, the page should be locked before running set_page_dirty(). 1198 */ 1199int set_page_dirty_lock(struct page *page) 1200{ 1201 int ret; 1202 1203 lock_page_nosync(page); 1204 ret = set_page_dirty(page); 1205 unlock_page(page); 1206 return ret; 1207} 1208EXPORT_SYMBOL(set_page_dirty_lock); 1209 1210/* 1211 * Clear a page's dirty flag, while caring for dirty memory accounting. 1212 * Returns true if the page was previously dirty. 1213 * 1214 * This is for preparing to put the page under writeout. We leave the page 1215 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1216 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1217 * implementation will run either set_page_writeback() or set_page_dirty(), 1218 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1219 * back into sync. 1220 * 1221 * This incoherency between the page's dirty flag and radix-tree tag is 1222 * unfortunate, but it only exists while the page is locked. 1223 */ 1224int clear_page_dirty_for_io(struct page *page) 1225{ 1226 struct address_space *mapping = page_mapping(page); 1227 1228 BUG_ON(!PageLocked(page)); 1229 1230 ClearPageReclaim(page); 1231 if (mapping && mapping_cap_account_dirty(mapping)) { 1232 /* 1233 * Yes, Virginia, this is indeed insane. 1234 * 1235 * We use this sequence to make sure that 1236 * (a) we account for dirty stats properly 1237 * (b) we tell the low-level filesystem to 1238 * mark the whole page dirty if it was 1239 * dirty in a pagetable. Only to then 1240 * (c) clean the page again and return 1 to 1241 * cause the writeback. 1242 * 1243 * This way we avoid all nasty races with the 1244 * dirty bit in multiple places and clearing 1245 * them concurrently from different threads. 1246 * 1247 * Note! Normally the "set_page_dirty(page)" 1248 * has no effect on the actual dirty bit - since 1249 * that will already usually be set. But we 1250 * need the side effects, and it can help us 1251 * avoid races. 1252 * 1253 * We basically use the page "master dirty bit" 1254 * as a serialization point for all the different 1255 * threads doing their things. 1256 */ 1257 if (page_mkclean(page)) 1258 set_page_dirty(page); 1259 /* 1260 * We carefully synchronise fault handlers against 1261 * installing a dirty pte and marking the page dirty 1262 * at this point. We do this by having them hold the 1263 * page lock at some point after installing their 1264 * pte, but before marking the page dirty. 1265 * Pages are always locked coming in here, so we get 1266 * the desired exclusion. See mm/memory.c:do_wp_page() 1267 * for more comments. 1268 */ 1269 if (TestClearPageDirty(page)) { 1270 dec_zone_page_state(page, NR_FILE_DIRTY); 1271 dec_bdi_stat(mapping->backing_dev_info, 1272 BDI_RECLAIMABLE); 1273 return 1; 1274 } 1275 return 0; 1276 } 1277 return TestClearPageDirty(page); 1278} 1279EXPORT_SYMBOL(clear_page_dirty_for_io); 1280 1281int test_clear_page_writeback(struct page *page) 1282{ 1283 struct address_space *mapping = page_mapping(page); 1284 int ret; 1285 1286 if (mapping) { 1287 struct backing_dev_info *bdi = mapping->backing_dev_info; 1288 unsigned long flags; 1289 1290 spin_lock_irqsave(&mapping->tree_lock, flags); 1291 ret = TestClearPageWriteback(page); 1292 if (ret) { 1293 radix_tree_tag_clear(&mapping->page_tree, 1294 page_index(page), 1295 PAGECACHE_TAG_WRITEBACK); 1296 if (bdi_cap_account_writeback(bdi)) { 1297 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1298 __bdi_writeout_inc(bdi); 1299 } 1300 } 1301 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1302 } else { 1303 ret = TestClearPageWriteback(page); 1304 } 1305 if (ret) 1306 dec_zone_page_state(page, NR_WRITEBACK); 1307 return ret; 1308} 1309 1310int test_set_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 = TestSetPageWriteback(page); 1321 if (!ret) { 1322 radix_tree_tag_set(&mapping->page_tree, 1323 page_index(page), 1324 PAGECACHE_TAG_WRITEBACK); 1325 if (bdi_cap_account_writeback(bdi)) 1326 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1327 } 1328 if (!PageDirty(page)) 1329 radix_tree_tag_clear(&mapping->page_tree, 1330 page_index(page), 1331 PAGECACHE_TAG_DIRTY); 1332 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1333 } else { 1334 ret = TestSetPageWriteback(page); 1335 } 1336 if (!ret) 1337 inc_zone_page_state(page, NR_WRITEBACK); 1338 return ret; 1339 1340} 1341EXPORT_SYMBOL(test_set_page_writeback); 1342 1343/* 1344 * Return true if any of the pages in the mapping are marked with the 1345 * passed tag. 1346 */ 1347int mapping_tagged(struct address_space *mapping, int tag) 1348{ 1349 int ret; 1350 rcu_read_lock(); 1351 ret = radix_tree_tagged(&mapping->page_tree, tag); 1352 rcu_read_unlock(); 1353 return ret; 1354} 1355EXPORT_SYMBOL(mapping_tagged); 1356