page-writeback.c revision f61eaf9fc58f3b2d9e3ad424496620f3381ccd1e
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 akpm@zip.com.au 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 * The generator of dirty data starts writeback at this percentage 73 */ 74int vm_dirty_ratio = 10; 75 76/* 77 * The interval between `kupdate'-style writebacks, in jiffies 78 */ 79int dirty_writeback_interval = 5 * HZ; 80 81/* 82 * The longest number of jiffies for which data is allowed to remain dirty 83 */ 84int dirty_expire_interval = 30 * HZ; 85 86/* 87 * Flag that makes the machine dump writes/reads and block dirtyings. 88 */ 89int block_dump; 90 91/* 92 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 93 * a full sync is triggered after this time elapses without any disk activity. 94 */ 95int laptop_mode; 96 97EXPORT_SYMBOL(laptop_mode); 98 99/* End of sysctl-exported parameters */ 100 101 102static void background_writeout(unsigned long _min_pages); 103 104/* 105 * Scale the writeback cache size proportional to the relative writeout speeds. 106 * 107 * We do this by keeping a floating proportion between BDIs, based on page 108 * writeback completions [end_page_writeback()]. Those devices that write out 109 * pages fastest will get the larger share, while the slower will get a smaller 110 * share. 111 * 112 * We use page writeout completions because we are interested in getting rid of 113 * dirty pages. Having them written out is the primary goal. 114 * 115 * We introduce a concept of time, a period over which we measure these events, 116 * because demand can/will vary over time. The length of this period itself is 117 * measured in page writeback completions. 118 * 119 */ 120static struct prop_descriptor vm_completions; 121static struct prop_descriptor vm_dirties; 122 123static unsigned long determine_dirtyable_memory(void); 124 125/* 126 * couple the period to the dirty_ratio: 127 * 128 * period/2 ~ roundup_pow_of_two(dirty limit) 129 */ 130static int calc_period_shift(void) 131{ 132 unsigned long dirty_total; 133 134 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 100; 135 return 2 + ilog2(dirty_total - 1); 136} 137 138/* 139 * update the period when the dirty ratio changes. 140 */ 141int dirty_ratio_handler(struct ctl_table *table, int write, 142 struct file *filp, void __user *buffer, size_t *lenp, 143 loff_t *ppos) 144{ 145 int old_ratio = vm_dirty_ratio; 146 int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos); 147 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 148 int shift = calc_period_shift(); 149 prop_change_shift(&vm_completions, shift); 150 prop_change_shift(&vm_dirties, shift); 151 } 152 return ret; 153} 154 155/* 156 * Increment the BDI's writeout completion count and the global writeout 157 * completion count. Called from test_clear_page_writeback(). 158 */ 159static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 160{ 161 __prop_inc_percpu(&vm_completions, &bdi->completions); 162} 163 164static inline void task_dirty_inc(struct task_struct *tsk) 165{ 166 prop_inc_single(&vm_dirties, &tsk->dirties); 167} 168 169/* 170 * Obtain an accurate fraction of the BDI's portion. 171 */ 172static void bdi_writeout_fraction(struct backing_dev_info *bdi, 173 long *numerator, long *denominator) 174{ 175 if (bdi_cap_writeback_dirty(bdi)) { 176 prop_fraction_percpu(&vm_completions, &bdi->completions, 177 numerator, denominator); 178 } else { 179 *numerator = 0; 180 *denominator = 1; 181 } 182} 183 184/* 185 * Clip the earned share of dirty pages to that which is actually available. 186 * This avoids exceeding the total dirty_limit when the floating averages 187 * fluctuate too quickly. 188 */ 189static void 190clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty) 191{ 192 long avail_dirty; 193 194 avail_dirty = dirty - 195 (global_page_state(NR_FILE_DIRTY) + 196 global_page_state(NR_WRITEBACK) + 197 global_page_state(NR_UNSTABLE_NFS)); 198 199 if (avail_dirty < 0) 200 avail_dirty = 0; 201 202 avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) + 203 bdi_stat(bdi, BDI_WRITEBACK); 204 205 *pbdi_dirty = min(*pbdi_dirty, avail_dirty); 206} 207 208static inline void task_dirties_fraction(struct task_struct *tsk, 209 long *numerator, long *denominator) 210{ 211 prop_fraction_single(&vm_dirties, &tsk->dirties, 212 numerator, denominator); 213} 214 215/* 216 * scale the dirty limit 217 * 218 * task specific dirty limit: 219 * 220 * dirty -= (dirty/8) * p_{t} 221 */ 222static void task_dirty_limit(struct task_struct *tsk, long *pdirty) 223{ 224 long numerator, denominator; 225 long dirty = *pdirty; 226 u64 inv = dirty >> 3; 227 228 task_dirties_fraction(tsk, &numerator, &denominator); 229 inv *= numerator; 230 do_div(inv, denominator); 231 232 dirty -= inv; 233 if (dirty < *pdirty/2) 234 dirty = *pdirty/2; 235 236 *pdirty = dirty; 237} 238 239/* 240 * Work out the current dirty-memory clamping and background writeout 241 * thresholds. 242 * 243 * The main aim here is to lower them aggressively if there is a lot of mapped 244 * memory around. To avoid stressing page reclaim with lots of unreclaimable 245 * pages. It is better to clamp down on writers than to start swapping, and 246 * performing lots of scanning. 247 * 248 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 249 * 250 * We don't permit the clamping level to fall below 5% - that is getting rather 251 * excessive. 252 * 253 * We make sure that the background writeout level is below the adjusted 254 * clamping level. 255 */ 256 257static unsigned long highmem_dirtyable_memory(unsigned long total) 258{ 259#ifdef CONFIG_HIGHMEM 260 int node; 261 unsigned long x = 0; 262 263 for_each_node_state(node, N_HIGH_MEMORY) { 264 struct zone *z = 265 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 266 267 x += zone_page_state(z, NR_FREE_PAGES) 268 + zone_page_state(z, NR_INACTIVE) 269 + zone_page_state(z, NR_ACTIVE); 270 } 271 /* 272 * Make sure that the number of highmem pages is never larger 273 * than the number of the total dirtyable memory. This can only 274 * occur in very strange VM situations but we want to make sure 275 * that this does not occur. 276 */ 277 return min(x, total); 278#else 279 return 0; 280#endif 281} 282 283static unsigned long determine_dirtyable_memory(void) 284{ 285 unsigned long x; 286 287 x = global_page_state(NR_FREE_PAGES) 288 + global_page_state(NR_INACTIVE) 289 + global_page_state(NR_ACTIVE); 290 x -= highmem_dirtyable_memory(x); 291 return x + 1; /* Ensure that we never return 0 */ 292} 293 294static void 295get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty, 296 struct backing_dev_info *bdi) 297{ 298 int background_ratio; /* Percentages */ 299 int dirty_ratio; 300 long background; 301 long dirty; 302 unsigned long available_memory = determine_dirtyable_memory(); 303 struct task_struct *tsk; 304 305 dirty_ratio = vm_dirty_ratio; 306 if (dirty_ratio < 5) 307 dirty_ratio = 5; 308 309 background_ratio = dirty_background_ratio; 310 if (background_ratio >= dirty_ratio) 311 background_ratio = dirty_ratio / 2; 312 313 background = (background_ratio * available_memory) / 100; 314 dirty = (dirty_ratio * available_memory) / 100; 315 tsk = current; 316 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 317 background += background / 4; 318 dirty += dirty / 4; 319 } 320 *pbackground = background; 321 *pdirty = dirty; 322 323 if (bdi) { 324 u64 bdi_dirty = dirty; 325 long numerator, denominator; 326 327 /* 328 * Calculate this BDI's share of the dirty ratio. 329 */ 330 bdi_writeout_fraction(bdi, &numerator, &denominator); 331 332 bdi_dirty *= numerator; 333 do_div(bdi_dirty, denominator); 334 335 *pbdi_dirty = bdi_dirty; 336 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty); 337 task_dirty_limit(current, pbdi_dirty); 338 } 339} 340 341/* 342 * balance_dirty_pages() must be called by processes which are generating dirty 343 * data. It looks at the number of dirty pages in the machine and will force 344 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 345 * If we're over `background_thresh' then pdflush is woken to perform some 346 * writeout. 347 */ 348static void balance_dirty_pages(struct address_space *mapping) 349{ 350 long nr_reclaimable, bdi_nr_reclaimable; 351 long nr_writeback, bdi_nr_writeback; 352 long background_thresh; 353 long dirty_thresh; 354 long bdi_thresh; 355 unsigned long pages_written = 0; 356 unsigned long write_chunk = sync_writeback_pages(); 357 358 struct backing_dev_info *bdi = mapping->backing_dev_info; 359 360 for (;;) { 361 struct writeback_control wbc = { 362 .bdi = bdi, 363 .sync_mode = WB_SYNC_NONE, 364 .older_than_this = NULL, 365 .nr_to_write = write_chunk, 366 .range_cyclic = 1, 367 }; 368 369 get_dirty_limits(&background_thresh, &dirty_thresh, 370 &bdi_thresh, bdi); 371 372 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 373 global_page_state(NR_UNSTABLE_NFS); 374 nr_writeback = global_page_state(NR_WRITEBACK); 375 376 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 377 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 378 379 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 380 break; 381 382 /* 383 * Throttle it only when the background writeback cannot 384 * catch-up. This avoids (excessively) small writeouts 385 * when the bdi limits are ramping up. 386 */ 387 if (nr_reclaimable + nr_writeback < 388 (background_thresh + dirty_thresh) / 2) 389 break; 390 391 if (!bdi->dirty_exceeded) 392 bdi->dirty_exceeded = 1; 393 394 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 395 * Unstable writes are a feature of certain networked 396 * filesystems (i.e. NFS) in which data may have been 397 * written to the server's write cache, but has not yet 398 * been flushed to permanent storage. 399 */ 400 if (bdi_nr_reclaimable) { 401 writeback_inodes(&wbc); 402 pages_written += write_chunk - wbc.nr_to_write; 403 get_dirty_limits(&background_thresh, &dirty_thresh, 404 &bdi_thresh, bdi); 405 } 406 407 /* 408 * In order to avoid the stacked BDI deadlock we need 409 * to ensure we accurately count the 'dirty' pages when 410 * the threshold is low. 411 * 412 * Otherwise it would be possible to get thresh+n pages 413 * reported dirty, even though there are thresh-m pages 414 * actually dirty; with m+n sitting in the percpu 415 * deltas. 416 */ 417 if (bdi_thresh < 2*bdi_stat_error(bdi)) { 418 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 419 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); 420 } else if (bdi_nr_reclaimable) { 421 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 422 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 423 } 424 425 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 426 break; 427 if (pages_written >= write_chunk) 428 break; /* We've done our duty */ 429 430 congestion_wait(WRITE, HZ/10); 431 } 432 433 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh && 434 bdi->dirty_exceeded) 435 bdi->dirty_exceeded = 0; 436 437 if (writeback_in_progress(bdi)) 438 return; /* pdflush is already working this queue */ 439 440 /* 441 * In laptop mode, we wait until hitting the higher threshold before 442 * starting background writeout, and then write out all the way down 443 * to the lower threshold. So slow writers cause minimal disk activity. 444 * 445 * In normal mode, we start background writeout at the lower 446 * background_thresh, to keep the amount of dirty memory low. 447 */ 448 if ((laptop_mode && pages_written) || 449 (!laptop_mode && (global_page_state(NR_FILE_DIRTY) 450 + global_page_state(NR_UNSTABLE_NFS) 451 > background_thresh))) 452 pdflush_operation(background_writeout, 0); 453} 454 455void set_page_dirty_balance(struct page *page, int page_mkwrite) 456{ 457 if (set_page_dirty(page) || page_mkwrite) { 458 struct address_space *mapping = page_mapping(page); 459 460 if (mapping) 461 balance_dirty_pages_ratelimited(mapping); 462 } 463} 464 465/** 466 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 467 * @mapping: address_space which was dirtied 468 * @nr_pages_dirtied: number of pages which the caller has just dirtied 469 * 470 * Processes which are dirtying memory should call in here once for each page 471 * which was newly dirtied. The function will periodically check the system's 472 * dirty state and will initiate writeback if needed. 473 * 474 * On really big machines, get_writeback_state is expensive, so try to avoid 475 * calling it too often (ratelimiting). But once we're over the dirty memory 476 * limit we decrease the ratelimiting by a lot, to prevent individual processes 477 * from overshooting the limit by (ratelimit_pages) each. 478 */ 479void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 480 unsigned long nr_pages_dirtied) 481{ 482 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 483 unsigned long ratelimit; 484 unsigned long *p; 485 486 ratelimit = ratelimit_pages; 487 if (mapping->backing_dev_info->dirty_exceeded) 488 ratelimit = 8; 489 490 /* 491 * Check the rate limiting. Also, we do not want to throttle real-time 492 * tasks in balance_dirty_pages(). Period. 493 */ 494 preempt_disable(); 495 p = &__get_cpu_var(ratelimits); 496 *p += nr_pages_dirtied; 497 if (unlikely(*p >= ratelimit)) { 498 *p = 0; 499 preempt_enable(); 500 balance_dirty_pages(mapping); 501 return; 502 } 503 preempt_enable(); 504} 505EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 506 507void throttle_vm_writeout(gfp_t gfp_mask) 508{ 509 long background_thresh; 510 long dirty_thresh; 511 512 for ( ; ; ) { 513 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 514 515 /* 516 * Boost the allowable dirty threshold a bit for page 517 * allocators so they don't get DoS'ed by heavy writers 518 */ 519 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 520 521 if (global_page_state(NR_UNSTABLE_NFS) + 522 global_page_state(NR_WRITEBACK) <= dirty_thresh) 523 break; 524 congestion_wait(WRITE, HZ/10); 525 526 /* 527 * The caller might hold locks which can prevent IO completion 528 * or progress in the filesystem. So we cannot just sit here 529 * waiting for IO to complete. 530 */ 531 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 532 break; 533 } 534} 535 536/* 537 * writeback at least _min_pages, and keep writing until the amount of dirty 538 * memory is less than the background threshold, or until we're all clean. 539 */ 540static void background_writeout(unsigned long _min_pages) 541{ 542 long min_pages = _min_pages; 543 struct writeback_control wbc = { 544 .bdi = NULL, 545 .sync_mode = WB_SYNC_NONE, 546 .older_than_this = NULL, 547 .nr_to_write = 0, 548 .nonblocking = 1, 549 .range_cyclic = 1, 550 }; 551 552 for ( ; ; ) { 553 long background_thresh; 554 long dirty_thresh; 555 556 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 557 if (global_page_state(NR_FILE_DIRTY) + 558 global_page_state(NR_UNSTABLE_NFS) < background_thresh 559 && min_pages <= 0) 560 break; 561 wbc.encountered_congestion = 0; 562 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 563 wbc.pages_skipped = 0; 564 writeback_inodes(&wbc); 565 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 566 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 567 /* Wrote less than expected */ 568 congestion_wait(WRITE, HZ/10); 569 if (!wbc.encountered_congestion) 570 break; 571 } 572 } 573} 574 575/* 576 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 577 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 578 * -1 if all pdflush threads were busy. 579 */ 580int wakeup_pdflush(long nr_pages) 581{ 582 if (nr_pages == 0) 583 nr_pages = global_page_state(NR_FILE_DIRTY) + 584 global_page_state(NR_UNSTABLE_NFS); 585 return pdflush_operation(background_writeout, nr_pages); 586} 587 588static void wb_timer_fn(unsigned long unused); 589static void laptop_timer_fn(unsigned long unused); 590 591static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 592static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 593 594/* 595 * Periodic writeback of "old" data. 596 * 597 * Define "old": the first time one of an inode's pages is dirtied, we mark the 598 * dirtying-time in the inode's address_space. So this periodic writeback code 599 * just walks the superblock inode list, writing back any inodes which are 600 * older than a specific point in time. 601 * 602 * Try to run once per dirty_writeback_interval. But if a writeback event 603 * takes longer than a dirty_writeback_interval interval, then leave a 604 * one-second gap. 605 * 606 * older_than_this takes precedence over nr_to_write. So we'll only write back 607 * all dirty pages if they are all attached to "old" mappings. 608 */ 609static void wb_kupdate(unsigned long arg) 610{ 611 unsigned long oldest_jif; 612 unsigned long start_jif; 613 unsigned long next_jif; 614 long nr_to_write; 615 struct writeback_control wbc = { 616 .bdi = NULL, 617 .sync_mode = WB_SYNC_NONE, 618 .older_than_this = &oldest_jif, 619 .nr_to_write = 0, 620 .nonblocking = 1, 621 .for_kupdate = 1, 622 .range_cyclic = 1, 623 }; 624 625 sync_supers(); 626 627 oldest_jif = jiffies - dirty_expire_interval; 628 start_jif = jiffies; 629 next_jif = start_jif + dirty_writeback_interval; 630 nr_to_write = global_page_state(NR_FILE_DIRTY) + 631 global_page_state(NR_UNSTABLE_NFS) + 632 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 633 while (nr_to_write > 0) { 634 wbc.encountered_congestion = 0; 635 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 636 writeback_inodes(&wbc); 637 if (wbc.nr_to_write > 0) { 638 if (wbc.encountered_congestion) 639 congestion_wait(WRITE, HZ/10); 640 else 641 break; /* All the old data is written */ 642 } 643 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 644 } 645 if (time_before(next_jif, jiffies + HZ)) 646 next_jif = jiffies + HZ; 647 if (dirty_writeback_interval) 648 mod_timer(&wb_timer, next_jif); 649} 650 651/* 652 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 653 */ 654int dirty_writeback_centisecs_handler(ctl_table *table, int write, 655 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 656{ 657 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); 658 if (dirty_writeback_interval) 659 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 660 else 661 del_timer(&wb_timer); 662 return 0; 663} 664 665static void wb_timer_fn(unsigned long unused) 666{ 667 if (pdflush_operation(wb_kupdate, 0) < 0) 668 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 669} 670 671static void laptop_flush(unsigned long unused) 672{ 673 sys_sync(); 674} 675 676static void laptop_timer_fn(unsigned long unused) 677{ 678 pdflush_operation(laptop_flush, 0); 679} 680 681/* 682 * We've spun up the disk and we're in laptop mode: schedule writeback 683 * of all dirty data a few seconds from now. If the flush is already scheduled 684 * then push it back - the user is still using the disk. 685 */ 686void laptop_io_completion(void) 687{ 688 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 689} 690 691/* 692 * We're in laptop mode and we've just synced. The sync's writes will have 693 * caused another writeback to be scheduled by laptop_io_completion. 694 * Nothing needs to be written back anymore, so we unschedule the writeback. 695 */ 696void laptop_sync_completion(void) 697{ 698 del_timer(&laptop_mode_wb_timer); 699} 700 701/* 702 * If ratelimit_pages is too high then we can get into dirty-data overload 703 * if a large number of processes all perform writes at the same time. 704 * If it is too low then SMP machines will call the (expensive) 705 * get_writeback_state too often. 706 * 707 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 708 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 709 * thresholds before writeback cuts in. 710 * 711 * But the limit should not be set too high. Because it also controls the 712 * amount of memory which the balance_dirty_pages() caller has to write back. 713 * If this is too large then the caller will block on the IO queue all the 714 * time. So limit it to four megabytes - the balance_dirty_pages() caller 715 * will write six megabyte chunks, max. 716 */ 717 718void writeback_set_ratelimit(void) 719{ 720 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 721 if (ratelimit_pages < 16) 722 ratelimit_pages = 16; 723 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 724 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 725} 726 727static int __cpuinit 728ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 729{ 730 writeback_set_ratelimit(); 731 return NOTIFY_DONE; 732} 733 734static struct notifier_block __cpuinitdata ratelimit_nb = { 735 .notifier_call = ratelimit_handler, 736 .next = NULL, 737}; 738 739/* 740 * Called early on to tune the page writeback dirty limits. 741 * 742 * We used to scale dirty pages according to how total memory 743 * related to pages that could be allocated for buffers (by 744 * comparing nr_free_buffer_pages() to vm_total_pages. 745 * 746 * However, that was when we used "dirty_ratio" to scale with 747 * all memory, and we don't do that any more. "dirty_ratio" 748 * is now applied to total non-HIGHPAGE memory (by subtracting 749 * totalhigh_pages from vm_total_pages), and as such we can't 750 * get into the old insane situation any more where we had 751 * large amounts of dirty pages compared to a small amount of 752 * non-HIGHMEM memory. 753 * 754 * But we might still want to scale the dirty_ratio by how 755 * much memory the box has.. 756 */ 757void __init page_writeback_init(void) 758{ 759 int shift; 760 761 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 762 writeback_set_ratelimit(); 763 register_cpu_notifier(&ratelimit_nb); 764 765 shift = calc_period_shift(); 766 prop_descriptor_init(&vm_completions, shift); 767 prop_descriptor_init(&vm_dirties, shift); 768} 769 770/** 771 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 772 * @mapping: address space structure to write 773 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 774 * @writepage: function called for each page 775 * @data: data passed to writepage function 776 * 777 * If a page is already under I/O, write_cache_pages() skips it, even 778 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 779 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 780 * and msync() need to guarantee that all the data which was dirty at the time 781 * the call was made get new I/O started against them. If wbc->sync_mode is 782 * WB_SYNC_ALL then we were called for data integrity and we must wait for 783 * existing IO to complete. 784 */ 785int write_cache_pages(struct address_space *mapping, 786 struct writeback_control *wbc, writepage_t writepage, 787 void *data) 788{ 789 struct backing_dev_info *bdi = mapping->backing_dev_info; 790 int ret = 0; 791 int done = 0; 792 struct pagevec pvec; 793 int nr_pages; 794 pgoff_t index; 795 pgoff_t end; /* Inclusive */ 796 int scanned = 0; 797 int range_whole = 0; 798 799 if (wbc->nonblocking && bdi_write_congested(bdi)) { 800 wbc->encountered_congestion = 1; 801 return 0; 802 } 803 804 pagevec_init(&pvec, 0); 805 if (wbc->range_cyclic) { 806 index = mapping->writeback_index; /* Start from prev offset */ 807 end = -1; 808 } else { 809 index = wbc->range_start >> PAGE_CACHE_SHIFT; 810 end = wbc->range_end >> PAGE_CACHE_SHIFT; 811 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 812 range_whole = 1; 813 scanned = 1; 814 } 815retry: 816 while (!done && (index <= end) && 817 (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 818 PAGECACHE_TAG_DIRTY, 819 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) { 820 unsigned i; 821 822 scanned = 1; 823 for (i = 0; i < nr_pages; i++) { 824 struct page *page = pvec.pages[i]; 825 826 /* 827 * At this point we hold neither mapping->tree_lock nor 828 * lock on the page itself: the page may be truncated or 829 * invalidated (changing page->mapping to NULL), or even 830 * swizzled back from swapper_space to tmpfs file 831 * mapping 832 */ 833 lock_page(page); 834 835 if (unlikely(page->mapping != mapping)) { 836 unlock_page(page); 837 continue; 838 } 839 840 if (!wbc->range_cyclic && page->index > end) { 841 done = 1; 842 unlock_page(page); 843 continue; 844 } 845 846 if (wbc->sync_mode != WB_SYNC_NONE) 847 wait_on_page_writeback(page); 848 849 if (PageWriteback(page) || 850 !clear_page_dirty_for_io(page)) { 851 unlock_page(page); 852 continue; 853 } 854 855 ret = (*writepage)(page, wbc, data); 856 857 if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) { 858 unlock_page(page); 859 ret = 0; 860 } 861 if (ret || (--(wbc->nr_to_write) <= 0)) 862 done = 1; 863 if (wbc->nonblocking && bdi_write_congested(bdi)) { 864 wbc->encountered_congestion = 1; 865 done = 1; 866 } 867 } 868 pagevec_release(&pvec); 869 cond_resched(); 870 } 871 if (!scanned && !done) { 872 /* 873 * We hit the last page and there is more work to be done: wrap 874 * back to the start of the file 875 */ 876 scanned = 1; 877 index = 0; 878 goto retry; 879 } 880 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) 881 mapping->writeback_index = index; 882 return ret; 883} 884EXPORT_SYMBOL(write_cache_pages); 885 886/* 887 * Function used by generic_writepages to call the real writepage 888 * function and set the mapping flags on error 889 */ 890static int __writepage(struct page *page, struct writeback_control *wbc, 891 void *data) 892{ 893 struct address_space *mapping = data; 894 int ret = mapping->a_ops->writepage(page, wbc); 895 mapping_set_error(mapping, ret); 896 return ret; 897} 898 899/** 900 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 901 * @mapping: address space structure to write 902 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 903 * 904 * This is a library function, which implements the writepages() 905 * address_space_operation. 906 */ 907int generic_writepages(struct address_space *mapping, 908 struct writeback_control *wbc) 909{ 910 /* deal with chardevs and other special file */ 911 if (!mapping->a_ops->writepage) 912 return 0; 913 914 return write_cache_pages(mapping, wbc, __writepage, mapping); 915} 916 917EXPORT_SYMBOL(generic_writepages); 918 919int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 920{ 921 int ret; 922 923 if (wbc->nr_to_write <= 0) 924 return 0; 925 wbc->for_writepages = 1; 926 if (mapping->a_ops->writepages) 927 ret = mapping->a_ops->writepages(mapping, wbc); 928 else 929 ret = generic_writepages(mapping, wbc); 930 wbc->for_writepages = 0; 931 return ret; 932} 933 934/** 935 * write_one_page - write out a single page and optionally wait on I/O 936 * @page: the page to write 937 * @wait: if true, wait on writeout 938 * 939 * The page must be locked by the caller and will be unlocked upon return. 940 * 941 * write_one_page() returns a negative error code if I/O failed. 942 */ 943int write_one_page(struct page *page, int wait) 944{ 945 struct address_space *mapping = page->mapping; 946 int ret = 0; 947 struct writeback_control wbc = { 948 .sync_mode = WB_SYNC_ALL, 949 .nr_to_write = 1, 950 }; 951 952 BUG_ON(!PageLocked(page)); 953 954 if (wait) 955 wait_on_page_writeback(page); 956 957 if (clear_page_dirty_for_io(page)) { 958 page_cache_get(page); 959 ret = mapping->a_ops->writepage(page, &wbc); 960 if (ret == 0 && wait) { 961 wait_on_page_writeback(page); 962 if (PageError(page)) 963 ret = -EIO; 964 } 965 page_cache_release(page); 966 } else { 967 unlock_page(page); 968 } 969 return ret; 970} 971EXPORT_SYMBOL(write_one_page); 972 973/* 974 * For address_spaces which do not use buffers nor write back. 975 */ 976int __set_page_dirty_no_writeback(struct page *page) 977{ 978 if (!PageDirty(page)) 979 SetPageDirty(page); 980 return 0; 981} 982 983/* 984 * For address_spaces which do not use buffers. Just tag the page as dirty in 985 * its radix tree. 986 * 987 * This is also used when a single buffer is being dirtied: we want to set the 988 * page dirty in that case, but not all the buffers. This is a "bottom-up" 989 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 990 * 991 * Most callers have locked the page, which pins the address_space in memory. 992 * But zap_pte_range() does not lock the page, however in that case the 993 * mapping is pinned by the vma's ->vm_file reference. 994 * 995 * We take care to handle the case where the page was truncated from the 996 * mapping by re-checking page_mapping() inside tree_lock. 997 */ 998int __set_page_dirty_nobuffers(struct page *page) 999{ 1000 if (!TestSetPageDirty(page)) { 1001 struct address_space *mapping = page_mapping(page); 1002 struct address_space *mapping2; 1003 1004 if (!mapping) 1005 return 1; 1006 1007 write_lock_irq(&mapping->tree_lock); 1008 mapping2 = page_mapping(page); 1009 if (mapping2) { /* Race with truncate? */ 1010 BUG_ON(mapping2 != mapping); 1011 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1012 if (mapping_cap_account_dirty(mapping)) { 1013 __inc_zone_page_state(page, NR_FILE_DIRTY); 1014 __inc_bdi_stat(mapping->backing_dev_info, 1015 BDI_RECLAIMABLE); 1016 task_io_account_write(PAGE_CACHE_SIZE); 1017 } 1018 radix_tree_tag_set(&mapping->page_tree, 1019 page_index(page), PAGECACHE_TAG_DIRTY); 1020 } 1021 write_unlock_irq(&mapping->tree_lock); 1022 if (mapping->host) { 1023 /* !PageAnon && !swapper_space */ 1024 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1025 } 1026 return 1; 1027 } 1028 return 0; 1029} 1030EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1031 1032/* 1033 * When a writepage implementation decides that it doesn't want to write this 1034 * page for some reason, it should redirty the locked page via 1035 * redirty_page_for_writepage() and it should then unlock the page and return 0 1036 */ 1037int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1038{ 1039 wbc->pages_skipped++; 1040 return __set_page_dirty_nobuffers(page); 1041} 1042EXPORT_SYMBOL(redirty_page_for_writepage); 1043 1044/* 1045 * If the mapping doesn't provide a set_page_dirty a_op, then 1046 * just fall through and assume that it wants buffer_heads. 1047 */ 1048static int __set_page_dirty(struct page *page) 1049{ 1050 struct address_space *mapping = page_mapping(page); 1051 1052 if (likely(mapping)) { 1053 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1054#ifdef CONFIG_BLOCK 1055 if (!spd) 1056 spd = __set_page_dirty_buffers; 1057#endif 1058 return (*spd)(page); 1059 } 1060 if (!PageDirty(page)) { 1061 if (!TestSetPageDirty(page)) 1062 return 1; 1063 } 1064 return 0; 1065} 1066 1067int fastcall set_page_dirty(struct page *page) 1068{ 1069 int ret = __set_page_dirty(page); 1070 if (ret) 1071 task_dirty_inc(current); 1072 return ret; 1073} 1074EXPORT_SYMBOL(set_page_dirty); 1075 1076/* 1077 * set_page_dirty() is racy if the caller has no reference against 1078 * page->mapping->host, and if the page is unlocked. This is because another 1079 * CPU could truncate the page off the mapping and then free the mapping. 1080 * 1081 * Usually, the page _is_ locked, or the caller is a user-space process which 1082 * holds a reference on the inode by having an open file. 1083 * 1084 * In other cases, the page should be locked before running set_page_dirty(). 1085 */ 1086int set_page_dirty_lock(struct page *page) 1087{ 1088 int ret; 1089 1090 lock_page_nosync(page); 1091 ret = set_page_dirty(page); 1092 unlock_page(page); 1093 return ret; 1094} 1095EXPORT_SYMBOL(set_page_dirty_lock); 1096 1097/* 1098 * Clear a page's dirty flag, while caring for dirty memory accounting. 1099 * Returns true if the page was previously dirty. 1100 * 1101 * This is for preparing to put the page under writeout. We leave the page 1102 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1103 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1104 * implementation will run either set_page_writeback() or set_page_dirty(), 1105 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1106 * back into sync. 1107 * 1108 * This incoherency between the page's dirty flag and radix-tree tag is 1109 * unfortunate, but it only exists while the page is locked. 1110 */ 1111int clear_page_dirty_for_io(struct page *page) 1112{ 1113 struct address_space *mapping = page_mapping(page); 1114 1115 BUG_ON(!PageLocked(page)); 1116 1117 ClearPageReclaim(page); 1118 if (mapping && mapping_cap_account_dirty(mapping)) { 1119 /* 1120 * Yes, Virginia, this is indeed insane. 1121 * 1122 * We use this sequence to make sure that 1123 * (a) we account for dirty stats properly 1124 * (b) we tell the low-level filesystem to 1125 * mark the whole page dirty if it was 1126 * dirty in a pagetable. Only to then 1127 * (c) clean the page again and return 1 to 1128 * cause the writeback. 1129 * 1130 * This way we avoid all nasty races with the 1131 * dirty bit in multiple places and clearing 1132 * them concurrently from different threads. 1133 * 1134 * Note! Normally the "set_page_dirty(page)" 1135 * has no effect on the actual dirty bit - since 1136 * that will already usually be set. But we 1137 * need the side effects, and it can help us 1138 * avoid races. 1139 * 1140 * We basically use the page "master dirty bit" 1141 * as a serialization point for all the different 1142 * threads doing their things. 1143 */ 1144 if (page_mkclean(page)) 1145 set_page_dirty(page); 1146 /* 1147 * We carefully synchronise fault handlers against 1148 * installing a dirty pte and marking the page dirty 1149 * at this point. We do this by having them hold the 1150 * page lock at some point after installing their 1151 * pte, but before marking the page dirty. 1152 * Pages are always locked coming in here, so we get 1153 * the desired exclusion. See mm/memory.c:do_wp_page() 1154 * for more comments. 1155 */ 1156 if (TestClearPageDirty(page)) { 1157 dec_zone_page_state(page, NR_FILE_DIRTY); 1158 dec_bdi_stat(mapping->backing_dev_info, 1159 BDI_RECLAIMABLE); 1160 return 1; 1161 } 1162 return 0; 1163 } 1164 return TestClearPageDirty(page); 1165} 1166EXPORT_SYMBOL(clear_page_dirty_for_io); 1167 1168int test_clear_page_writeback(struct page *page) 1169{ 1170 struct address_space *mapping = page_mapping(page); 1171 int ret; 1172 1173 if (mapping) { 1174 struct backing_dev_info *bdi = mapping->backing_dev_info; 1175 unsigned long flags; 1176 1177 write_lock_irqsave(&mapping->tree_lock, flags); 1178 ret = TestClearPageWriteback(page); 1179 if (ret) { 1180 radix_tree_tag_clear(&mapping->page_tree, 1181 page_index(page), 1182 PAGECACHE_TAG_WRITEBACK); 1183 if (bdi_cap_writeback_dirty(bdi)) { 1184 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1185 __bdi_writeout_inc(bdi); 1186 } 1187 } 1188 write_unlock_irqrestore(&mapping->tree_lock, flags); 1189 } else { 1190 ret = TestClearPageWriteback(page); 1191 } 1192 if (ret) 1193 dec_zone_page_state(page, NR_WRITEBACK); 1194 return ret; 1195} 1196 1197int test_set_page_writeback(struct page *page) 1198{ 1199 struct address_space *mapping = page_mapping(page); 1200 int ret; 1201 1202 if (mapping) { 1203 struct backing_dev_info *bdi = mapping->backing_dev_info; 1204 unsigned long flags; 1205 1206 write_lock_irqsave(&mapping->tree_lock, flags); 1207 ret = TestSetPageWriteback(page); 1208 if (!ret) { 1209 radix_tree_tag_set(&mapping->page_tree, 1210 page_index(page), 1211 PAGECACHE_TAG_WRITEBACK); 1212 if (bdi_cap_writeback_dirty(bdi)) 1213 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1214 } 1215 if (!PageDirty(page)) 1216 radix_tree_tag_clear(&mapping->page_tree, 1217 page_index(page), 1218 PAGECACHE_TAG_DIRTY); 1219 write_unlock_irqrestore(&mapping->tree_lock, flags); 1220 } else { 1221 ret = TestSetPageWriteback(page); 1222 } 1223 if (!ret) 1224 inc_zone_page_state(page, NR_WRITEBACK); 1225 return ret; 1226 1227} 1228EXPORT_SYMBOL(test_set_page_writeback); 1229 1230/* 1231 * Return true if any of the pages in the mapping are marked with the 1232 * passed tag. 1233 */ 1234int mapping_tagged(struct address_space *mapping, int tag) 1235{ 1236 int ret; 1237 rcu_read_lock(); 1238 ret = radix_tree_tagged(&mapping->page_tree, tag); 1239 rcu_read_unlock(); 1240 return ret; 1241} 1242EXPORT_SYMBOL(mapping_tagged); 1243