page-writeback.c revision 17bc6c30cf6bfffd816bdc53682dd46fc34a2cf4
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) 333 + zone_page_state(z, NR_INACTIVE) 334 + zone_page_state(z, NR_ACTIVE); 335 } 336 /* 337 * Make sure that the number of highmem pages is never larger 338 * than the number of the total dirtyable memory. This can only 339 * occur in very strange VM situations but we want to make sure 340 * that this does not occur. 341 */ 342 return min(x, total); 343#else 344 return 0; 345#endif 346} 347 348/** 349 * determine_dirtyable_memory - amount of memory that may be used 350 * 351 * Returns the numebr of pages that can currently be freed and used 352 * by the kernel for direct mappings. 353 */ 354unsigned long determine_dirtyable_memory(void) 355{ 356 unsigned long x; 357 358 x = global_page_state(NR_FREE_PAGES) 359 + global_page_state(NR_INACTIVE) 360 + global_page_state(NR_ACTIVE); 361 362 if (!vm_highmem_is_dirtyable) 363 x -= highmem_dirtyable_memory(x); 364 365 return x + 1; /* Ensure that we never return 0 */ 366} 367 368void 369get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty, 370 struct backing_dev_info *bdi) 371{ 372 int background_ratio; /* Percentages */ 373 int dirty_ratio; 374 long background; 375 long dirty; 376 unsigned long available_memory = determine_dirtyable_memory(); 377 struct task_struct *tsk; 378 379 dirty_ratio = vm_dirty_ratio; 380 if (dirty_ratio < 5) 381 dirty_ratio = 5; 382 383 background_ratio = dirty_background_ratio; 384 if (background_ratio >= dirty_ratio) 385 background_ratio = dirty_ratio / 2; 386 387 background = (background_ratio * available_memory) / 100; 388 dirty = (dirty_ratio * available_memory) / 100; 389 tsk = current; 390 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 391 background += background / 4; 392 dirty += dirty / 4; 393 } 394 *pbackground = background; 395 *pdirty = dirty; 396 397 if (bdi) { 398 u64 bdi_dirty; 399 long numerator, denominator; 400 401 /* 402 * Calculate this BDI's share of the dirty ratio. 403 */ 404 bdi_writeout_fraction(bdi, &numerator, &denominator); 405 406 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 407 bdi_dirty *= numerator; 408 do_div(bdi_dirty, denominator); 409 bdi_dirty += (dirty * bdi->min_ratio) / 100; 410 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 411 bdi_dirty = dirty * bdi->max_ratio / 100; 412 413 *pbdi_dirty = bdi_dirty; 414 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty); 415 task_dirty_limit(current, pbdi_dirty); 416 } 417} 418 419/* 420 * balance_dirty_pages() must be called by processes which are generating dirty 421 * data. It looks at the number of dirty pages in the machine and will force 422 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 423 * If we're over `background_thresh' then pdflush is woken to perform some 424 * writeout. 425 */ 426static void balance_dirty_pages(struct address_space *mapping) 427{ 428 long nr_reclaimable, bdi_nr_reclaimable; 429 long nr_writeback, bdi_nr_writeback; 430 long background_thresh; 431 long dirty_thresh; 432 long bdi_thresh; 433 unsigned long pages_written = 0; 434 unsigned long write_chunk = sync_writeback_pages(); 435 436 struct backing_dev_info *bdi = mapping->backing_dev_info; 437 438 for (;;) { 439 struct writeback_control wbc = { 440 .bdi = bdi, 441 .sync_mode = WB_SYNC_NONE, 442 .older_than_this = NULL, 443 .nr_to_write = write_chunk, 444 .range_cyclic = 1, 445 }; 446 447 get_dirty_limits(&background_thresh, &dirty_thresh, 448 &bdi_thresh, bdi); 449 450 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 451 global_page_state(NR_UNSTABLE_NFS); 452 nr_writeback = global_page_state(NR_WRITEBACK); 453 454 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 455 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 456 457 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 458 break; 459 460 /* 461 * Throttle it only when the background writeback cannot 462 * catch-up. This avoids (excessively) small writeouts 463 * when the bdi limits are ramping up. 464 */ 465 if (nr_reclaimable + nr_writeback < 466 (background_thresh + dirty_thresh) / 2) 467 break; 468 469 if (!bdi->dirty_exceeded) 470 bdi->dirty_exceeded = 1; 471 472 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 473 * Unstable writes are a feature of certain networked 474 * filesystems (i.e. NFS) in which data may have been 475 * written to the server's write cache, but has not yet 476 * been flushed to permanent storage. 477 */ 478 if (bdi_nr_reclaimable) { 479 writeback_inodes(&wbc); 480 pages_written += write_chunk - wbc.nr_to_write; 481 get_dirty_limits(&background_thresh, &dirty_thresh, 482 &bdi_thresh, bdi); 483 } 484 485 /* 486 * In order to avoid the stacked BDI deadlock we need 487 * to ensure we accurately count the 'dirty' pages when 488 * the threshold is low. 489 * 490 * Otherwise it would be possible to get thresh+n pages 491 * reported dirty, even though there are thresh-m pages 492 * actually dirty; with m+n sitting in the percpu 493 * deltas. 494 */ 495 if (bdi_thresh < 2*bdi_stat_error(bdi)) { 496 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 497 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); 498 } else if (bdi_nr_reclaimable) { 499 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 500 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 501 } 502 503 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 504 break; 505 if (pages_written >= write_chunk) 506 break; /* We've done our duty */ 507 508 congestion_wait(WRITE, HZ/10); 509 } 510 511 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh && 512 bdi->dirty_exceeded) 513 bdi->dirty_exceeded = 0; 514 515 if (writeback_in_progress(bdi)) 516 return; /* pdflush is already working this queue */ 517 518 /* 519 * In laptop mode, we wait until hitting the higher threshold before 520 * starting background writeout, and then write out all the way down 521 * to the lower threshold. So slow writers cause minimal disk activity. 522 * 523 * In normal mode, we start background writeout at the lower 524 * background_thresh, to keep the amount of dirty memory low. 525 */ 526 if ((laptop_mode && pages_written) || 527 (!laptop_mode && (global_page_state(NR_FILE_DIRTY) 528 + global_page_state(NR_UNSTABLE_NFS) 529 > background_thresh))) 530 pdflush_operation(background_writeout, 0); 531} 532 533void set_page_dirty_balance(struct page *page, int page_mkwrite) 534{ 535 if (set_page_dirty(page) || page_mkwrite) { 536 struct address_space *mapping = page_mapping(page); 537 538 if (mapping) 539 balance_dirty_pages_ratelimited(mapping); 540 } 541} 542 543/** 544 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 545 * @mapping: address_space which was dirtied 546 * @nr_pages_dirtied: number of pages which the caller has just dirtied 547 * 548 * Processes which are dirtying memory should call in here once for each page 549 * which was newly dirtied. The function will periodically check the system's 550 * dirty state and will initiate writeback if needed. 551 * 552 * On really big machines, get_writeback_state is expensive, so try to avoid 553 * calling it too often (ratelimiting). But once we're over the dirty memory 554 * limit we decrease the ratelimiting by a lot, to prevent individual processes 555 * from overshooting the limit by (ratelimit_pages) each. 556 */ 557void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 558 unsigned long nr_pages_dirtied) 559{ 560 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 561 unsigned long ratelimit; 562 unsigned long *p; 563 564 ratelimit = ratelimit_pages; 565 if (mapping->backing_dev_info->dirty_exceeded) 566 ratelimit = 8; 567 568 /* 569 * Check the rate limiting. Also, we do not want to throttle real-time 570 * tasks in balance_dirty_pages(). Period. 571 */ 572 preempt_disable(); 573 p = &__get_cpu_var(ratelimits); 574 *p += nr_pages_dirtied; 575 if (unlikely(*p >= ratelimit)) { 576 *p = 0; 577 preempt_enable(); 578 balance_dirty_pages(mapping); 579 return; 580 } 581 preempt_enable(); 582} 583EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 584 585void throttle_vm_writeout(gfp_t gfp_mask) 586{ 587 long background_thresh; 588 long dirty_thresh; 589 590 for ( ; ; ) { 591 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 592 593 /* 594 * Boost the allowable dirty threshold a bit for page 595 * allocators so they don't get DoS'ed by heavy writers 596 */ 597 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 598 599 if (global_page_state(NR_UNSTABLE_NFS) + 600 global_page_state(NR_WRITEBACK) <= dirty_thresh) 601 break; 602 congestion_wait(WRITE, HZ/10); 603 604 /* 605 * The caller might hold locks which can prevent IO completion 606 * or progress in the filesystem. So we cannot just sit here 607 * waiting for IO to complete. 608 */ 609 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 610 break; 611 } 612} 613 614/* 615 * writeback at least _min_pages, and keep writing until the amount of dirty 616 * memory is less than the background threshold, or until we're all clean. 617 */ 618static void background_writeout(unsigned long _min_pages) 619{ 620 long min_pages = _min_pages; 621 struct writeback_control wbc = { 622 .bdi = NULL, 623 .sync_mode = WB_SYNC_NONE, 624 .older_than_this = NULL, 625 .nr_to_write = 0, 626 .nonblocking = 1, 627 .range_cyclic = 1, 628 }; 629 630 for ( ; ; ) { 631 long background_thresh; 632 long dirty_thresh; 633 634 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 635 if (global_page_state(NR_FILE_DIRTY) + 636 global_page_state(NR_UNSTABLE_NFS) < background_thresh 637 && min_pages <= 0) 638 break; 639 wbc.more_io = 0; 640 wbc.encountered_congestion = 0; 641 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 642 wbc.pages_skipped = 0; 643 writeback_inodes(&wbc); 644 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 645 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 646 /* Wrote less than expected */ 647 if (wbc.encountered_congestion || wbc.more_io) 648 congestion_wait(WRITE, HZ/10); 649 else 650 break; 651 } 652 } 653} 654 655/* 656 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 657 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 658 * -1 if all pdflush threads were busy. 659 */ 660int wakeup_pdflush(long nr_pages) 661{ 662 if (nr_pages == 0) 663 nr_pages = global_page_state(NR_FILE_DIRTY) + 664 global_page_state(NR_UNSTABLE_NFS); 665 return pdflush_operation(background_writeout, nr_pages); 666} 667 668static void wb_timer_fn(unsigned long unused); 669static void laptop_timer_fn(unsigned long unused); 670 671static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 672static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 673 674/* 675 * Periodic writeback of "old" data. 676 * 677 * Define "old": the first time one of an inode's pages is dirtied, we mark the 678 * dirtying-time in the inode's address_space. So this periodic writeback code 679 * just walks the superblock inode list, writing back any inodes which are 680 * older than a specific point in time. 681 * 682 * Try to run once per dirty_writeback_interval. But if a writeback event 683 * takes longer than a dirty_writeback_interval interval, then leave a 684 * one-second gap. 685 * 686 * older_than_this takes precedence over nr_to_write. So we'll only write back 687 * all dirty pages if they are all attached to "old" mappings. 688 */ 689static void wb_kupdate(unsigned long arg) 690{ 691 unsigned long oldest_jif; 692 unsigned long start_jif; 693 unsigned long next_jif; 694 long nr_to_write; 695 struct writeback_control wbc = { 696 .bdi = NULL, 697 .sync_mode = WB_SYNC_NONE, 698 .older_than_this = &oldest_jif, 699 .nr_to_write = 0, 700 .nonblocking = 1, 701 .for_kupdate = 1, 702 .range_cyclic = 1, 703 }; 704 705 sync_supers(); 706 707 oldest_jif = jiffies - dirty_expire_interval; 708 start_jif = jiffies; 709 next_jif = start_jif + dirty_writeback_interval; 710 nr_to_write = global_page_state(NR_FILE_DIRTY) + 711 global_page_state(NR_UNSTABLE_NFS) + 712 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 713 while (nr_to_write > 0) { 714 wbc.more_io = 0; 715 wbc.encountered_congestion = 0; 716 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 717 writeback_inodes(&wbc); 718 if (wbc.nr_to_write > 0) { 719 if (wbc.encountered_congestion || wbc.more_io) 720 congestion_wait(WRITE, HZ/10); 721 else 722 break; /* All the old data is written */ 723 } 724 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 725 } 726 if (time_before(next_jif, jiffies + HZ)) 727 next_jif = jiffies + HZ; 728 if (dirty_writeback_interval) 729 mod_timer(&wb_timer, next_jif); 730} 731 732/* 733 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 734 */ 735int dirty_writeback_centisecs_handler(ctl_table *table, int write, 736 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 737{ 738 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); 739 if (dirty_writeback_interval) 740 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 741 else 742 del_timer(&wb_timer); 743 return 0; 744} 745 746static void wb_timer_fn(unsigned long unused) 747{ 748 if (pdflush_operation(wb_kupdate, 0) < 0) 749 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 750} 751 752static void laptop_flush(unsigned long unused) 753{ 754 sys_sync(); 755} 756 757static void laptop_timer_fn(unsigned long unused) 758{ 759 pdflush_operation(laptop_flush, 0); 760} 761 762/* 763 * We've spun up the disk and we're in laptop mode: schedule writeback 764 * of all dirty data a few seconds from now. If the flush is already scheduled 765 * then push it back - the user is still using the disk. 766 */ 767void laptop_io_completion(void) 768{ 769 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 770} 771 772/* 773 * We're in laptop mode and we've just synced. The sync's writes will have 774 * caused another writeback to be scheduled by laptop_io_completion. 775 * Nothing needs to be written back anymore, so we unschedule the writeback. 776 */ 777void laptop_sync_completion(void) 778{ 779 del_timer(&laptop_mode_wb_timer); 780} 781 782/* 783 * If ratelimit_pages is too high then we can get into dirty-data overload 784 * if a large number of processes all perform writes at the same time. 785 * If it is too low then SMP machines will call the (expensive) 786 * get_writeback_state too often. 787 * 788 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 789 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 790 * thresholds before writeback cuts in. 791 * 792 * But the limit should not be set too high. Because it also controls the 793 * amount of memory which the balance_dirty_pages() caller has to write back. 794 * If this is too large then the caller will block on the IO queue all the 795 * time. So limit it to four megabytes - the balance_dirty_pages() caller 796 * will write six megabyte chunks, max. 797 */ 798 799void writeback_set_ratelimit(void) 800{ 801 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 802 if (ratelimit_pages < 16) 803 ratelimit_pages = 16; 804 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 805 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 806} 807 808static int __cpuinit 809ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 810{ 811 writeback_set_ratelimit(); 812 return NOTIFY_DONE; 813} 814 815static struct notifier_block __cpuinitdata ratelimit_nb = { 816 .notifier_call = ratelimit_handler, 817 .next = NULL, 818}; 819 820/* 821 * Called early on to tune the page writeback dirty limits. 822 * 823 * We used to scale dirty pages according to how total memory 824 * related to pages that could be allocated for buffers (by 825 * comparing nr_free_buffer_pages() to vm_total_pages. 826 * 827 * However, that was when we used "dirty_ratio" to scale with 828 * all memory, and we don't do that any more. "dirty_ratio" 829 * is now applied to total non-HIGHPAGE memory (by subtracting 830 * totalhigh_pages from vm_total_pages), and as such we can't 831 * get into the old insane situation any more where we had 832 * large amounts of dirty pages compared to a small amount of 833 * non-HIGHMEM memory. 834 * 835 * But we might still want to scale the dirty_ratio by how 836 * much memory the box has.. 837 */ 838void __init page_writeback_init(void) 839{ 840 int shift; 841 842 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 843 writeback_set_ratelimit(); 844 register_cpu_notifier(&ratelimit_nb); 845 846 shift = calc_period_shift(); 847 prop_descriptor_init(&vm_completions, shift); 848 prop_descriptor_init(&vm_dirties, shift); 849} 850 851/** 852 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 853 * @mapping: address space structure to write 854 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 855 * @writepage: function called for each page 856 * @data: data passed to writepage function 857 * 858 * If a page is already under I/O, write_cache_pages() skips it, even 859 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 860 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 861 * and msync() need to guarantee that all the data which was dirty at the time 862 * the call was made get new I/O started against them. If wbc->sync_mode is 863 * WB_SYNC_ALL then we were called for data integrity and we must wait for 864 * existing IO to complete. 865 */ 866int write_cache_pages(struct address_space *mapping, 867 struct writeback_control *wbc, writepage_t writepage, 868 void *data) 869{ 870 struct backing_dev_info *bdi = mapping->backing_dev_info; 871 int ret = 0; 872 int done = 0; 873 struct pagevec pvec; 874 int nr_pages; 875 pgoff_t index; 876 pgoff_t end; /* Inclusive */ 877 int scanned = 0; 878 int range_whole = 0; 879 long nr_to_write = wbc->nr_to_write; 880 881 if (wbc->nonblocking && bdi_write_congested(bdi)) { 882 wbc->encountered_congestion = 1; 883 return 0; 884 } 885 886 pagevec_init(&pvec, 0); 887 if (wbc->range_cyclic) { 888 index = mapping->writeback_index; /* Start from prev offset */ 889 end = -1; 890 } else { 891 index = wbc->range_start >> PAGE_CACHE_SHIFT; 892 end = wbc->range_end >> PAGE_CACHE_SHIFT; 893 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 894 range_whole = 1; 895 scanned = 1; 896 } 897retry: 898 while (!done && (index <= end) && 899 (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 900 PAGECACHE_TAG_DIRTY, 901 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) { 902 unsigned i; 903 904 scanned = 1; 905 for (i = 0; i < nr_pages; i++) { 906 struct page *page = pvec.pages[i]; 907 908 /* 909 * At this point we hold neither mapping->tree_lock nor 910 * lock on the page itself: the page may be truncated or 911 * invalidated (changing page->mapping to NULL), or even 912 * swizzled back from swapper_space to tmpfs file 913 * mapping 914 */ 915 lock_page(page); 916 917 if (unlikely(page->mapping != mapping)) { 918 unlock_page(page); 919 continue; 920 } 921 922 if (!wbc->range_cyclic && page->index > end) { 923 done = 1; 924 unlock_page(page); 925 continue; 926 } 927 928 if (wbc->sync_mode != WB_SYNC_NONE) 929 wait_on_page_writeback(page); 930 931 if (PageWriteback(page) || 932 !clear_page_dirty_for_io(page)) { 933 unlock_page(page); 934 continue; 935 } 936 937 ret = (*writepage)(page, wbc, data); 938 939 if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) { 940 unlock_page(page); 941 ret = 0; 942 } 943 if (ret || (--nr_to_write <= 0)) 944 done = 1; 945 if (wbc->nonblocking && bdi_write_congested(bdi)) { 946 wbc->encountered_congestion = 1; 947 done = 1; 948 } 949 } 950 pagevec_release(&pvec); 951 cond_resched(); 952 } 953 if (!scanned && !done) { 954 /* 955 * We hit the last page and there is more work to be done: wrap 956 * back to the start of the file 957 */ 958 scanned = 1; 959 index = 0; 960 goto retry; 961 } 962 if (!wbc->no_nrwrite_index_update) { 963 if (wbc->range_cyclic || (range_whole && nr_to_write > 0)) 964 mapping->writeback_index = index; 965 wbc->nr_to_write = nr_to_write; 966 } 967 968 return ret; 969} 970EXPORT_SYMBOL(write_cache_pages); 971 972/* 973 * Function used by generic_writepages to call the real writepage 974 * function and set the mapping flags on error 975 */ 976static int __writepage(struct page *page, struct writeback_control *wbc, 977 void *data) 978{ 979 struct address_space *mapping = data; 980 int ret = mapping->a_ops->writepage(page, wbc); 981 mapping_set_error(mapping, ret); 982 return ret; 983} 984 985/** 986 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 987 * @mapping: address space structure to write 988 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 989 * 990 * This is a library function, which implements the writepages() 991 * address_space_operation. 992 */ 993int generic_writepages(struct address_space *mapping, 994 struct writeback_control *wbc) 995{ 996 /* deal with chardevs and other special file */ 997 if (!mapping->a_ops->writepage) 998 return 0; 999 1000 return write_cache_pages(mapping, wbc, __writepage, mapping); 1001} 1002 1003EXPORT_SYMBOL(generic_writepages); 1004 1005int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1006{ 1007 int ret; 1008 1009 if (wbc->nr_to_write <= 0) 1010 return 0; 1011 wbc->for_writepages = 1; 1012 if (mapping->a_ops->writepages) 1013 ret = mapping->a_ops->writepages(mapping, wbc); 1014 else 1015 ret = generic_writepages(mapping, wbc); 1016 wbc->for_writepages = 0; 1017 return ret; 1018} 1019 1020/** 1021 * write_one_page - write out a single page and optionally wait on I/O 1022 * @page: the page to write 1023 * @wait: if true, wait on writeout 1024 * 1025 * The page must be locked by the caller and will be unlocked upon return. 1026 * 1027 * write_one_page() returns a negative error code if I/O failed. 1028 */ 1029int write_one_page(struct page *page, int wait) 1030{ 1031 struct address_space *mapping = page->mapping; 1032 int ret = 0; 1033 struct writeback_control wbc = { 1034 .sync_mode = WB_SYNC_ALL, 1035 .nr_to_write = 1, 1036 }; 1037 1038 BUG_ON(!PageLocked(page)); 1039 1040 if (wait) 1041 wait_on_page_writeback(page); 1042 1043 if (clear_page_dirty_for_io(page)) { 1044 page_cache_get(page); 1045 ret = mapping->a_ops->writepage(page, &wbc); 1046 if (ret == 0 && wait) { 1047 wait_on_page_writeback(page); 1048 if (PageError(page)) 1049 ret = -EIO; 1050 } 1051 page_cache_release(page); 1052 } else { 1053 unlock_page(page); 1054 } 1055 return ret; 1056} 1057EXPORT_SYMBOL(write_one_page); 1058 1059/* 1060 * For address_spaces which do not use buffers nor write back. 1061 */ 1062int __set_page_dirty_no_writeback(struct page *page) 1063{ 1064 if (!PageDirty(page)) 1065 SetPageDirty(page); 1066 return 0; 1067} 1068 1069/* 1070 * For address_spaces which do not use buffers. Just tag the page as dirty in 1071 * its radix tree. 1072 * 1073 * This is also used when a single buffer is being dirtied: we want to set the 1074 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1075 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1076 * 1077 * Most callers have locked the page, which pins the address_space in memory. 1078 * But zap_pte_range() does not lock the page, however in that case the 1079 * mapping is pinned by the vma's ->vm_file reference. 1080 * 1081 * We take care to handle the case where the page was truncated from the 1082 * mapping by re-checking page_mapping() inside tree_lock. 1083 */ 1084int __set_page_dirty_nobuffers(struct page *page) 1085{ 1086 if (!TestSetPageDirty(page)) { 1087 struct address_space *mapping = page_mapping(page); 1088 struct address_space *mapping2; 1089 1090 if (!mapping) 1091 return 1; 1092 1093 spin_lock_irq(&mapping->tree_lock); 1094 mapping2 = page_mapping(page); 1095 if (mapping2) { /* Race with truncate? */ 1096 BUG_ON(mapping2 != mapping); 1097 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1098 if (mapping_cap_account_dirty(mapping)) { 1099 __inc_zone_page_state(page, NR_FILE_DIRTY); 1100 __inc_bdi_stat(mapping->backing_dev_info, 1101 BDI_RECLAIMABLE); 1102 task_io_account_write(PAGE_CACHE_SIZE); 1103 } 1104 radix_tree_tag_set(&mapping->page_tree, 1105 page_index(page), PAGECACHE_TAG_DIRTY); 1106 } 1107 spin_unlock_irq(&mapping->tree_lock); 1108 if (mapping->host) { 1109 /* !PageAnon && !swapper_space */ 1110 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1111 } 1112 return 1; 1113 } 1114 return 0; 1115} 1116EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1117 1118/* 1119 * When a writepage implementation decides that it doesn't want to write this 1120 * page for some reason, it should redirty the locked page via 1121 * redirty_page_for_writepage() and it should then unlock the page and return 0 1122 */ 1123int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1124{ 1125 wbc->pages_skipped++; 1126 return __set_page_dirty_nobuffers(page); 1127} 1128EXPORT_SYMBOL(redirty_page_for_writepage); 1129 1130/* 1131 * If the mapping doesn't provide a set_page_dirty a_op, then 1132 * just fall through and assume that it wants buffer_heads. 1133 */ 1134static int __set_page_dirty(struct page *page) 1135{ 1136 struct address_space *mapping = page_mapping(page); 1137 1138 if (likely(mapping)) { 1139 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1140#ifdef CONFIG_BLOCK 1141 if (!spd) 1142 spd = __set_page_dirty_buffers; 1143#endif 1144 return (*spd)(page); 1145 } 1146 if (!PageDirty(page)) { 1147 if (!TestSetPageDirty(page)) 1148 return 1; 1149 } 1150 return 0; 1151} 1152 1153int set_page_dirty(struct page *page) 1154{ 1155 int ret = __set_page_dirty(page); 1156 if (ret) 1157 task_dirty_inc(current); 1158 return ret; 1159} 1160EXPORT_SYMBOL(set_page_dirty); 1161 1162/* 1163 * set_page_dirty() is racy if the caller has no reference against 1164 * page->mapping->host, and if the page is unlocked. This is because another 1165 * CPU could truncate the page off the mapping and then free the mapping. 1166 * 1167 * Usually, the page _is_ locked, or the caller is a user-space process which 1168 * holds a reference on the inode by having an open file. 1169 * 1170 * In other cases, the page should be locked before running set_page_dirty(). 1171 */ 1172int set_page_dirty_lock(struct page *page) 1173{ 1174 int ret; 1175 1176 lock_page_nosync(page); 1177 ret = set_page_dirty(page); 1178 unlock_page(page); 1179 return ret; 1180} 1181EXPORT_SYMBOL(set_page_dirty_lock); 1182 1183/* 1184 * Clear a page's dirty flag, while caring for dirty memory accounting. 1185 * Returns true if the page was previously dirty. 1186 * 1187 * This is for preparing to put the page under writeout. We leave the page 1188 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1189 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1190 * implementation will run either set_page_writeback() or set_page_dirty(), 1191 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1192 * back into sync. 1193 * 1194 * This incoherency between the page's dirty flag and radix-tree tag is 1195 * unfortunate, but it only exists while the page is locked. 1196 */ 1197int clear_page_dirty_for_io(struct page *page) 1198{ 1199 struct address_space *mapping = page_mapping(page); 1200 1201 BUG_ON(!PageLocked(page)); 1202 1203 ClearPageReclaim(page); 1204 if (mapping && mapping_cap_account_dirty(mapping)) { 1205 /* 1206 * Yes, Virginia, this is indeed insane. 1207 * 1208 * We use this sequence to make sure that 1209 * (a) we account for dirty stats properly 1210 * (b) we tell the low-level filesystem to 1211 * mark the whole page dirty if it was 1212 * dirty in a pagetable. Only to then 1213 * (c) clean the page again and return 1 to 1214 * cause the writeback. 1215 * 1216 * This way we avoid all nasty races with the 1217 * dirty bit in multiple places and clearing 1218 * them concurrently from different threads. 1219 * 1220 * Note! Normally the "set_page_dirty(page)" 1221 * has no effect on the actual dirty bit - since 1222 * that will already usually be set. But we 1223 * need the side effects, and it can help us 1224 * avoid races. 1225 * 1226 * We basically use the page "master dirty bit" 1227 * as a serialization point for all the different 1228 * threads doing their things. 1229 */ 1230 if (page_mkclean(page)) 1231 set_page_dirty(page); 1232 /* 1233 * We carefully synchronise fault handlers against 1234 * installing a dirty pte and marking the page dirty 1235 * at this point. We do this by having them hold the 1236 * page lock at some point after installing their 1237 * pte, but before marking the page dirty. 1238 * Pages are always locked coming in here, so we get 1239 * the desired exclusion. See mm/memory.c:do_wp_page() 1240 * for more comments. 1241 */ 1242 if (TestClearPageDirty(page)) { 1243 dec_zone_page_state(page, NR_FILE_DIRTY); 1244 dec_bdi_stat(mapping->backing_dev_info, 1245 BDI_RECLAIMABLE); 1246 return 1; 1247 } 1248 return 0; 1249 } 1250 return TestClearPageDirty(page); 1251} 1252EXPORT_SYMBOL(clear_page_dirty_for_io); 1253 1254int test_clear_page_writeback(struct page *page) 1255{ 1256 struct address_space *mapping = page_mapping(page); 1257 int ret; 1258 1259 if (mapping) { 1260 struct backing_dev_info *bdi = mapping->backing_dev_info; 1261 unsigned long flags; 1262 1263 spin_lock_irqsave(&mapping->tree_lock, flags); 1264 ret = TestClearPageWriteback(page); 1265 if (ret) { 1266 radix_tree_tag_clear(&mapping->page_tree, 1267 page_index(page), 1268 PAGECACHE_TAG_WRITEBACK); 1269 if (bdi_cap_account_writeback(bdi)) { 1270 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1271 __bdi_writeout_inc(bdi); 1272 } 1273 } 1274 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1275 } else { 1276 ret = TestClearPageWriteback(page); 1277 } 1278 if (ret) 1279 dec_zone_page_state(page, NR_WRITEBACK); 1280 return ret; 1281} 1282 1283int test_set_page_writeback(struct page *page) 1284{ 1285 struct address_space *mapping = page_mapping(page); 1286 int ret; 1287 1288 if (mapping) { 1289 struct backing_dev_info *bdi = mapping->backing_dev_info; 1290 unsigned long flags; 1291 1292 spin_lock_irqsave(&mapping->tree_lock, flags); 1293 ret = TestSetPageWriteback(page); 1294 if (!ret) { 1295 radix_tree_tag_set(&mapping->page_tree, 1296 page_index(page), 1297 PAGECACHE_TAG_WRITEBACK); 1298 if (bdi_cap_account_writeback(bdi)) 1299 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1300 } 1301 if (!PageDirty(page)) 1302 radix_tree_tag_clear(&mapping->page_tree, 1303 page_index(page), 1304 PAGECACHE_TAG_DIRTY); 1305 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1306 } else { 1307 ret = TestSetPageWriteback(page); 1308 } 1309 if (!ret) 1310 inc_zone_page_state(page, NR_WRITEBACK); 1311 return ret; 1312 1313} 1314EXPORT_SYMBOL(test_set_page_writeback); 1315 1316/* 1317 * Return true if any of the pages in the mapping are marked with the 1318 * passed tag. 1319 */ 1320int mapping_tagged(struct address_space *mapping, int tag) 1321{ 1322 int ret; 1323 rcu_read_lock(); 1324 ret = radix_tree_tagged(&mapping->page_tree, tag); 1325 rcu_read_unlock(); 1326 return ret; 1327} 1328EXPORT_SYMBOL(mapping_tagged); 1329