page-writeback.c revision 22ef37eed673587ac984965dc88ba94c68873291
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 = 10; 70 71/* 72 * dirty_background_bytes starts at 0 (disabled) so that it is a function of 73 * dirty_background_ratio * the amount of dirtyable memory 74 */ 75unsigned long dirty_background_bytes; 76 77/* 78 * free highmem will not be subtracted from the total free memory 79 * for calculating free ratios if vm_highmem_is_dirtyable is true 80 */ 81int vm_highmem_is_dirtyable; 82 83/* 84 * The generator of dirty data starts writeback at this percentage 85 */ 86int vm_dirty_ratio = 20; 87 88/* 89 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of 90 * vm_dirty_ratio * the amount of dirtyable memory 91 */ 92unsigned long vm_dirty_bytes; 93 94/* 95 * The interval between `kupdate'-style writebacks 96 */ 97unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ 98 99/* 100 * The longest time for which data is allowed to remain dirty 101 */ 102unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ 103 104/* 105 * Flag that makes the machine dump writes/reads and block dirtyings. 106 */ 107int block_dump; 108 109/* 110 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 111 * a full sync is triggered after this time elapses without any disk activity. 112 */ 113int laptop_mode; 114 115EXPORT_SYMBOL(laptop_mode); 116 117/* End of sysctl-exported parameters */ 118 119 120static void background_writeout(unsigned long _min_pages); 121 122/* 123 * Scale the writeback cache size proportional to the relative writeout speeds. 124 * 125 * We do this by keeping a floating proportion between BDIs, based on page 126 * writeback completions [end_page_writeback()]. Those devices that write out 127 * pages fastest will get the larger share, while the slower will get a smaller 128 * share. 129 * 130 * We use page writeout completions because we are interested in getting rid of 131 * dirty pages. Having them written out is the primary goal. 132 * 133 * We introduce a concept of time, a period over which we measure these events, 134 * because demand can/will vary over time. The length of this period itself is 135 * measured in page writeback completions. 136 * 137 */ 138static struct prop_descriptor vm_completions; 139static struct prop_descriptor vm_dirties; 140 141/* 142 * couple the period to the dirty_ratio: 143 * 144 * period/2 ~ roundup_pow_of_two(dirty limit) 145 */ 146static int calc_period_shift(void) 147{ 148 unsigned long dirty_total; 149 150 if (vm_dirty_bytes) 151 dirty_total = vm_dirty_bytes / PAGE_SIZE; 152 else 153 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 154 100; 155 return 2 + ilog2(dirty_total - 1); 156} 157 158/* 159 * update the period when the dirty threshold changes. 160 */ 161static void update_completion_period(void) 162{ 163 int shift = calc_period_shift(); 164 prop_change_shift(&vm_completions, shift); 165 prop_change_shift(&vm_dirties, shift); 166} 167 168int dirty_background_ratio_handler(struct ctl_table *table, int write, 169 struct file *filp, void __user *buffer, size_t *lenp, 170 loff_t *ppos) 171{ 172 int ret; 173 174 ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos); 175 if (ret == 0 && write) 176 dirty_background_bytes = 0; 177 return ret; 178} 179 180int dirty_background_bytes_handler(struct ctl_table *table, int write, 181 struct file *filp, void __user *buffer, size_t *lenp, 182 loff_t *ppos) 183{ 184 int ret; 185 186 ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos); 187 if (ret == 0 && write) 188 dirty_background_ratio = 0; 189 return ret; 190} 191 192int dirty_ratio_handler(struct ctl_table *table, int write, 193 struct file *filp, void __user *buffer, size_t *lenp, 194 loff_t *ppos) 195{ 196 int old_ratio = vm_dirty_ratio; 197 int ret; 198 199 ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos); 200 if (ret == 0 && write && vm_dirty_ratio != old_ratio) { 201 update_completion_period(); 202 vm_dirty_bytes = 0; 203 } 204 return ret; 205} 206 207 208int dirty_bytes_handler(struct ctl_table *table, int write, 209 struct file *filp, void __user *buffer, size_t *lenp, 210 loff_t *ppos) 211{ 212 unsigned long old_bytes = vm_dirty_bytes; 213 int ret; 214 215 ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos); 216 if (ret == 0 && write && vm_dirty_bytes != old_bytes) { 217 update_completion_period(); 218 vm_dirty_ratio = 0; 219 } 220 return ret; 221} 222 223/* 224 * Increment the BDI's writeout completion count and the global writeout 225 * completion count. Called from test_clear_page_writeback(). 226 */ 227static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) 228{ 229 __prop_inc_percpu_max(&vm_completions, &bdi->completions, 230 bdi->max_prop_frac); 231} 232 233void bdi_writeout_inc(struct backing_dev_info *bdi) 234{ 235 unsigned long flags; 236 237 local_irq_save(flags); 238 __bdi_writeout_inc(bdi); 239 local_irq_restore(flags); 240} 241EXPORT_SYMBOL_GPL(bdi_writeout_inc); 242 243void task_dirty_inc(struct task_struct *tsk) 244{ 245 prop_inc_single(&vm_dirties, &tsk->dirties); 246} 247 248/* 249 * Obtain an accurate fraction of the BDI's portion. 250 */ 251static void bdi_writeout_fraction(struct backing_dev_info *bdi, 252 long *numerator, long *denominator) 253{ 254 if (bdi_cap_writeback_dirty(bdi)) { 255 prop_fraction_percpu(&vm_completions, &bdi->completions, 256 numerator, denominator); 257 } else { 258 *numerator = 0; 259 *denominator = 1; 260 } 261} 262 263/* 264 * Clip the earned share of dirty pages to that which is actually available. 265 * This avoids exceeding the total dirty_limit when the floating averages 266 * fluctuate too quickly. 267 */ 268static void 269clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty) 270{ 271 long avail_dirty; 272 273 avail_dirty = dirty - 274 (global_page_state(NR_FILE_DIRTY) + 275 global_page_state(NR_WRITEBACK) + 276 global_page_state(NR_UNSTABLE_NFS) + 277 global_page_state(NR_WRITEBACK_TEMP)); 278 279 if (avail_dirty < 0) 280 avail_dirty = 0; 281 282 avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) + 283 bdi_stat(bdi, BDI_WRITEBACK); 284 285 *pbdi_dirty = min(*pbdi_dirty, avail_dirty); 286} 287 288static inline void task_dirties_fraction(struct task_struct *tsk, 289 long *numerator, long *denominator) 290{ 291 prop_fraction_single(&vm_dirties, &tsk->dirties, 292 numerator, denominator); 293} 294 295/* 296 * scale the dirty limit 297 * 298 * task specific dirty limit: 299 * 300 * dirty -= (dirty/8) * p_{t} 301 */ 302static void task_dirty_limit(struct task_struct *tsk, long *pdirty) 303{ 304 long numerator, denominator; 305 long dirty = *pdirty; 306 u64 inv = dirty >> 3; 307 308 task_dirties_fraction(tsk, &numerator, &denominator); 309 inv *= numerator; 310 do_div(inv, denominator); 311 312 dirty -= inv; 313 if (dirty < *pdirty/2) 314 dirty = *pdirty/2; 315 316 *pdirty = dirty; 317} 318 319/* 320 * 321 */ 322static DEFINE_SPINLOCK(bdi_lock); 323static unsigned int bdi_min_ratio; 324 325int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 326{ 327 int ret = 0; 328 unsigned long flags; 329 330 spin_lock_irqsave(&bdi_lock, flags); 331 if (min_ratio > bdi->max_ratio) { 332 ret = -EINVAL; 333 } else { 334 min_ratio -= bdi->min_ratio; 335 if (bdi_min_ratio + min_ratio < 100) { 336 bdi_min_ratio += min_ratio; 337 bdi->min_ratio += min_ratio; 338 } else { 339 ret = -EINVAL; 340 } 341 } 342 spin_unlock_irqrestore(&bdi_lock, flags); 343 344 return ret; 345} 346 347int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 348{ 349 unsigned long flags; 350 int ret = 0; 351 352 if (max_ratio > 100) 353 return -EINVAL; 354 355 spin_lock_irqsave(&bdi_lock, flags); 356 if (bdi->min_ratio > max_ratio) { 357 ret = -EINVAL; 358 } else { 359 bdi->max_ratio = max_ratio; 360 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; 361 } 362 spin_unlock_irqrestore(&bdi_lock, flags); 363 364 return ret; 365} 366EXPORT_SYMBOL(bdi_set_max_ratio); 367 368/* 369 * Work out the current dirty-memory clamping and background writeout 370 * thresholds. 371 * 372 * The main aim here is to lower them aggressively if there is a lot of mapped 373 * memory around. To avoid stressing page reclaim with lots of unreclaimable 374 * pages. It is better to clamp down on writers than to start swapping, and 375 * performing lots of scanning. 376 * 377 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 378 * 379 * We don't permit the clamping level to fall below 5% - that is getting rather 380 * excessive. 381 * 382 * We make sure that the background writeout level is below the adjusted 383 * clamping level. 384 */ 385 386static unsigned long highmem_dirtyable_memory(unsigned long total) 387{ 388#ifdef CONFIG_HIGHMEM 389 int node; 390 unsigned long x = 0; 391 392 for_each_node_state(node, N_HIGH_MEMORY) { 393 struct zone *z = 394 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 395 396 x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z); 397 } 398 /* 399 * Make sure that the number of highmem pages is never larger 400 * than the number of the total dirtyable memory. This can only 401 * occur in very strange VM situations but we want to make sure 402 * that this does not occur. 403 */ 404 return min(x, total); 405#else 406 return 0; 407#endif 408} 409 410/** 411 * determine_dirtyable_memory - amount of memory that may be used 412 * 413 * Returns the numebr of pages that can currently be freed and used 414 * by the kernel for direct mappings. 415 */ 416unsigned long determine_dirtyable_memory(void) 417{ 418 unsigned long x; 419 420 x = global_page_state(NR_FREE_PAGES) + global_lru_pages(); 421 422 if (!vm_highmem_is_dirtyable) 423 x -= highmem_dirtyable_memory(x); 424 425 return x + 1; /* Ensure that we never return 0 */ 426} 427 428void 429get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty, 430 unsigned long *pbdi_dirty, struct backing_dev_info *bdi) 431{ 432 unsigned long background; 433 unsigned long dirty; 434 unsigned long available_memory = determine_dirtyable_memory(); 435 struct task_struct *tsk; 436 437 if (vm_dirty_bytes) 438 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); 439 else { 440 int dirty_ratio; 441 442 dirty_ratio = vm_dirty_ratio; 443 if (dirty_ratio < 5) 444 dirty_ratio = 5; 445 dirty = (dirty_ratio * available_memory) / 100; 446 } 447 448 if (dirty_background_bytes) 449 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); 450 else 451 background = (dirty_background_ratio * available_memory) / 100; 452 453 if (background >= dirty) 454 background = dirty / 2; 455 tsk = current; 456 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 457 background += background / 4; 458 dirty += dirty / 4; 459 } 460 *pbackground = background; 461 *pdirty = dirty; 462 463 if (bdi) { 464 u64 bdi_dirty; 465 long numerator, denominator; 466 467 /* 468 * Calculate this BDI's share of the dirty ratio. 469 */ 470 bdi_writeout_fraction(bdi, &numerator, &denominator); 471 472 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; 473 bdi_dirty *= numerator; 474 do_div(bdi_dirty, denominator); 475 bdi_dirty += (dirty * bdi->min_ratio) / 100; 476 if (bdi_dirty > (dirty * bdi->max_ratio) / 100) 477 bdi_dirty = dirty * bdi->max_ratio / 100; 478 479 *pbdi_dirty = bdi_dirty; 480 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty); 481 task_dirty_limit(current, pbdi_dirty); 482 } 483} 484 485/* 486 * balance_dirty_pages() must be called by processes which are generating dirty 487 * data. It looks at the number of dirty pages in the machine and will force 488 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 489 * If we're over `background_thresh' then pdflush is woken to perform some 490 * writeout. 491 */ 492static void balance_dirty_pages(struct address_space *mapping) 493{ 494 long nr_reclaimable, bdi_nr_reclaimable; 495 long nr_writeback, bdi_nr_writeback; 496 unsigned long background_thresh; 497 unsigned long dirty_thresh; 498 unsigned long bdi_thresh; 499 unsigned long pages_written = 0; 500 unsigned long write_chunk = sync_writeback_pages(); 501 502 struct backing_dev_info *bdi = mapping->backing_dev_info; 503 504 for (;;) { 505 struct writeback_control wbc = { 506 .bdi = bdi, 507 .sync_mode = WB_SYNC_NONE, 508 .older_than_this = NULL, 509 .nr_to_write = write_chunk, 510 .range_cyclic = 1, 511 }; 512 513 get_dirty_limits(&background_thresh, &dirty_thresh, 514 &bdi_thresh, bdi); 515 516 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 517 global_page_state(NR_UNSTABLE_NFS); 518 nr_writeback = global_page_state(NR_WRITEBACK); 519 520 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 521 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 522 523 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 524 break; 525 526 /* 527 * Throttle it only when the background writeback cannot 528 * catch-up. This avoids (excessively) small writeouts 529 * when the bdi limits are ramping up. 530 */ 531 if (nr_reclaimable + nr_writeback < 532 (background_thresh + dirty_thresh) / 2) 533 break; 534 535 if (!bdi->dirty_exceeded) 536 bdi->dirty_exceeded = 1; 537 538 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 539 * Unstable writes are a feature of certain networked 540 * filesystems (i.e. NFS) in which data may have been 541 * written to the server's write cache, but has not yet 542 * been flushed to permanent storage. 543 */ 544 if (bdi_nr_reclaimable) { 545 writeback_inodes(&wbc); 546 pages_written += write_chunk - wbc.nr_to_write; 547 get_dirty_limits(&background_thresh, &dirty_thresh, 548 &bdi_thresh, bdi); 549 } 550 551 /* 552 * In order to avoid the stacked BDI deadlock we need 553 * to ensure we accurately count the 'dirty' pages when 554 * the threshold is low. 555 * 556 * Otherwise it would be possible to get thresh+n pages 557 * reported dirty, even though there are thresh-m pages 558 * actually dirty; with m+n sitting in the percpu 559 * deltas. 560 */ 561 if (bdi_thresh < 2*bdi_stat_error(bdi)) { 562 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); 563 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); 564 } else if (bdi_nr_reclaimable) { 565 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); 566 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); 567 } 568 569 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) 570 break; 571 if (pages_written >= write_chunk) 572 break; /* We've done our duty */ 573 574 congestion_wait(WRITE, HZ/10); 575 } 576 577 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh && 578 bdi->dirty_exceeded) 579 bdi->dirty_exceeded = 0; 580 581 if (writeback_in_progress(bdi)) 582 return; /* pdflush is already working this queue */ 583 584 /* 585 * In laptop mode, we wait until hitting the higher threshold before 586 * starting background writeout, and then write out all the way down 587 * to the lower threshold. So slow writers cause minimal disk activity. 588 * 589 * In normal mode, we start background writeout at the lower 590 * background_thresh, to keep the amount of dirty memory low. 591 */ 592 if ((laptop_mode && pages_written) || 593 (!laptop_mode && (global_page_state(NR_FILE_DIRTY) 594 + global_page_state(NR_UNSTABLE_NFS) 595 > background_thresh))) 596 pdflush_operation(background_writeout, 0); 597} 598 599void set_page_dirty_balance(struct page *page, int page_mkwrite) 600{ 601 if (set_page_dirty(page) || page_mkwrite) { 602 struct address_space *mapping = page_mapping(page); 603 604 if (mapping) 605 balance_dirty_pages_ratelimited(mapping); 606 } 607} 608 609/** 610 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 611 * @mapping: address_space which was dirtied 612 * @nr_pages_dirtied: number of pages which the caller has just dirtied 613 * 614 * Processes which are dirtying memory should call in here once for each page 615 * which was newly dirtied. The function will periodically check the system's 616 * dirty state and will initiate writeback if needed. 617 * 618 * On really big machines, get_writeback_state is expensive, so try to avoid 619 * calling it too often (ratelimiting). But once we're over the dirty memory 620 * limit we decrease the ratelimiting by a lot, to prevent individual processes 621 * from overshooting the limit by (ratelimit_pages) each. 622 */ 623void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 624 unsigned long nr_pages_dirtied) 625{ 626 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 627 unsigned long ratelimit; 628 unsigned long *p; 629 630 ratelimit = ratelimit_pages; 631 if (mapping->backing_dev_info->dirty_exceeded) 632 ratelimit = 8; 633 634 /* 635 * Check the rate limiting. Also, we do not want to throttle real-time 636 * tasks in balance_dirty_pages(). Period. 637 */ 638 preempt_disable(); 639 p = &__get_cpu_var(ratelimits); 640 *p += nr_pages_dirtied; 641 if (unlikely(*p >= ratelimit)) { 642 *p = 0; 643 preempt_enable(); 644 balance_dirty_pages(mapping); 645 return; 646 } 647 preempt_enable(); 648} 649EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 650 651void throttle_vm_writeout(gfp_t gfp_mask) 652{ 653 unsigned long background_thresh; 654 unsigned long dirty_thresh; 655 656 for ( ; ; ) { 657 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 658 659 /* 660 * Boost the allowable dirty threshold a bit for page 661 * allocators so they don't get DoS'ed by heavy writers 662 */ 663 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 664 665 if (global_page_state(NR_UNSTABLE_NFS) + 666 global_page_state(NR_WRITEBACK) <= dirty_thresh) 667 break; 668 congestion_wait(WRITE, HZ/10); 669 670 /* 671 * The caller might hold locks which can prevent IO completion 672 * or progress in the filesystem. So we cannot just sit here 673 * waiting for IO to complete. 674 */ 675 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) 676 break; 677 } 678} 679 680/* 681 * writeback at least _min_pages, and keep writing until the amount of dirty 682 * memory is less than the background threshold, or until we're all clean. 683 */ 684static void background_writeout(unsigned long _min_pages) 685{ 686 long min_pages = _min_pages; 687 struct writeback_control wbc = { 688 .bdi = NULL, 689 .sync_mode = WB_SYNC_NONE, 690 .older_than_this = NULL, 691 .nr_to_write = 0, 692 .nonblocking = 1, 693 .range_cyclic = 1, 694 }; 695 696 for ( ; ; ) { 697 unsigned long background_thresh; 698 unsigned long dirty_thresh; 699 700 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); 701 if (global_page_state(NR_FILE_DIRTY) + 702 global_page_state(NR_UNSTABLE_NFS) < background_thresh 703 && min_pages <= 0) 704 break; 705 wbc.more_io = 0; 706 wbc.encountered_congestion = 0; 707 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 708 wbc.pages_skipped = 0; 709 writeback_inodes(&wbc); 710 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 711 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 712 /* Wrote less than expected */ 713 if (wbc.encountered_congestion || wbc.more_io) 714 congestion_wait(WRITE, HZ/10); 715 else 716 break; 717 } 718 } 719} 720 721/* 722 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 723 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 724 * -1 if all pdflush threads were busy. 725 */ 726int wakeup_pdflush(long nr_pages) 727{ 728 if (nr_pages == 0) 729 nr_pages = global_page_state(NR_FILE_DIRTY) + 730 global_page_state(NR_UNSTABLE_NFS); 731 return pdflush_operation(background_writeout, nr_pages); 732} 733 734static void wb_timer_fn(unsigned long unused); 735static void laptop_timer_fn(unsigned long unused); 736 737static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 738static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 739 740/* 741 * Periodic writeback of "old" data. 742 * 743 * Define "old": the first time one of an inode's pages is dirtied, we mark the 744 * dirtying-time in the inode's address_space. So this periodic writeback code 745 * just walks the superblock inode list, writing back any inodes which are 746 * older than a specific point in time. 747 * 748 * Try to run once per dirty_writeback_interval. But if a writeback event 749 * takes longer than a dirty_writeback_interval interval, then leave a 750 * one-second gap. 751 * 752 * older_than_this takes precedence over nr_to_write. So we'll only write back 753 * all dirty pages if they are all attached to "old" mappings. 754 */ 755static void wb_kupdate(unsigned long arg) 756{ 757 unsigned long oldest_jif; 758 unsigned long start_jif; 759 unsigned long next_jif; 760 long nr_to_write; 761 struct writeback_control wbc = { 762 .bdi = NULL, 763 .sync_mode = WB_SYNC_NONE, 764 .older_than_this = &oldest_jif, 765 .nr_to_write = 0, 766 .nonblocking = 1, 767 .for_kupdate = 1, 768 .range_cyclic = 1, 769 }; 770 771 sync_supers(); 772 773 oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10); 774 start_jif = jiffies; 775 next_jif = start_jif + msecs_to_jiffies(dirty_writeback_interval * 10); 776 nr_to_write = global_page_state(NR_FILE_DIRTY) + 777 global_page_state(NR_UNSTABLE_NFS) + 778 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 779 while (nr_to_write > 0) { 780 wbc.more_io = 0; 781 wbc.encountered_congestion = 0; 782 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 783 writeback_inodes(&wbc); 784 if (wbc.nr_to_write > 0) { 785 if (wbc.encountered_congestion || wbc.more_io) 786 congestion_wait(WRITE, HZ/10); 787 else 788 break; /* All the old data is written */ 789 } 790 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 791 } 792 if (time_before(next_jif, jiffies + HZ)) 793 next_jif = jiffies + HZ; 794 if (dirty_writeback_interval) 795 mod_timer(&wb_timer, next_jif); 796} 797 798/* 799 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 800 */ 801int dirty_writeback_centisecs_handler(ctl_table *table, int write, 802 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 803{ 804 proc_dointvec(table, write, file, buffer, length, ppos); 805 if (dirty_writeback_interval) 806 mod_timer(&wb_timer, jiffies + 807 msecs_to_jiffies(dirty_writeback_interval * 10)); 808 else 809 del_timer(&wb_timer); 810 return 0; 811} 812 813static void wb_timer_fn(unsigned long unused) 814{ 815 if (pdflush_operation(wb_kupdate, 0) < 0) 816 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 817} 818 819static void laptop_flush(unsigned long unused) 820{ 821 sys_sync(); 822} 823 824static void laptop_timer_fn(unsigned long unused) 825{ 826 pdflush_operation(laptop_flush, 0); 827} 828 829/* 830 * We've spun up the disk and we're in laptop mode: schedule writeback 831 * of all dirty data a few seconds from now. If the flush is already scheduled 832 * then push it back - the user is still using the disk. 833 */ 834void laptop_io_completion(void) 835{ 836 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 837} 838 839/* 840 * We're in laptop mode and we've just synced. The sync's writes will have 841 * caused another writeback to be scheduled by laptop_io_completion. 842 * Nothing needs to be written back anymore, so we unschedule the writeback. 843 */ 844void laptop_sync_completion(void) 845{ 846 del_timer(&laptop_mode_wb_timer); 847} 848 849/* 850 * If ratelimit_pages is too high then we can get into dirty-data overload 851 * if a large number of processes all perform writes at the same time. 852 * If it is too low then SMP machines will call the (expensive) 853 * get_writeback_state too often. 854 * 855 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 856 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 857 * thresholds before writeback cuts in. 858 * 859 * But the limit should not be set too high. Because it also controls the 860 * amount of memory which the balance_dirty_pages() caller has to write back. 861 * If this is too large then the caller will block on the IO queue all the 862 * time. So limit it to four megabytes - the balance_dirty_pages() caller 863 * will write six megabyte chunks, max. 864 */ 865 866void writeback_set_ratelimit(void) 867{ 868 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 869 if (ratelimit_pages < 16) 870 ratelimit_pages = 16; 871 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 872 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 873} 874 875static int __cpuinit 876ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 877{ 878 writeback_set_ratelimit(); 879 return NOTIFY_DONE; 880} 881 882static struct notifier_block __cpuinitdata ratelimit_nb = { 883 .notifier_call = ratelimit_handler, 884 .next = NULL, 885}; 886 887/* 888 * Called early on to tune the page writeback dirty limits. 889 * 890 * We used to scale dirty pages according to how total memory 891 * related to pages that could be allocated for buffers (by 892 * comparing nr_free_buffer_pages() to vm_total_pages. 893 * 894 * However, that was when we used "dirty_ratio" to scale with 895 * all memory, and we don't do that any more. "dirty_ratio" 896 * is now applied to total non-HIGHPAGE memory (by subtracting 897 * totalhigh_pages from vm_total_pages), and as such we can't 898 * get into the old insane situation any more where we had 899 * large amounts of dirty pages compared to a small amount of 900 * non-HIGHMEM memory. 901 * 902 * But we might still want to scale the dirty_ratio by how 903 * much memory the box has.. 904 */ 905void __init page_writeback_init(void) 906{ 907 int shift; 908 909 mod_timer(&wb_timer, 910 jiffies + msecs_to_jiffies(dirty_writeback_interval * 10)); 911 writeback_set_ratelimit(); 912 register_cpu_notifier(&ratelimit_nb); 913 914 shift = calc_period_shift(); 915 prop_descriptor_init(&vm_completions, shift); 916 prop_descriptor_init(&vm_dirties, shift); 917} 918 919/** 920 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 921 * @mapping: address space structure to write 922 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 923 * @writepage: function called for each page 924 * @data: data passed to writepage function 925 * 926 * If a page is already under I/O, write_cache_pages() skips it, even 927 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 928 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 929 * and msync() need to guarantee that all the data which was dirty at the time 930 * the call was made get new I/O started against them. If wbc->sync_mode is 931 * WB_SYNC_ALL then we were called for data integrity and we must wait for 932 * existing IO to complete. 933 */ 934int write_cache_pages(struct address_space *mapping, 935 struct writeback_control *wbc, writepage_t writepage, 936 void *data) 937{ 938 struct backing_dev_info *bdi = mapping->backing_dev_info; 939 int ret = 0; 940 int done = 0; 941 struct pagevec pvec; 942 int nr_pages; 943 pgoff_t uninitialized_var(writeback_index); 944 pgoff_t index; 945 pgoff_t end; /* Inclusive */ 946 pgoff_t done_index; 947 int cycled; 948 int range_whole = 0; 949 long nr_to_write = wbc->nr_to_write; 950 951 if (wbc->nonblocking && bdi_write_congested(bdi)) { 952 wbc->encountered_congestion = 1; 953 return 0; 954 } 955 956 pagevec_init(&pvec, 0); 957 if (wbc->range_cyclic) { 958 writeback_index = mapping->writeback_index; /* prev offset */ 959 index = writeback_index; 960 if (index == 0) 961 cycled = 1; 962 else 963 cycled = 0; 964 end = -1; 965 } else { 966 index = wbc->range_start >> PAGE_CACHE_SHIFT; 967 end = wbc->range_end >> PAGE_CACHE_SHIFT; 968 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 969 range_whole = 1; 970 cycled = 1; /* ignore range_cyclic tests */ 971 } 972retry: 973 done_index = index; 974 while (!done && (index <= end)) { 975 int i; 976 977 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 978 PAGECACHE_TAG_DIRTY, 979 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); 980 if (nr_pages == 0) 981 break; 982 983 for (i = 0; i < nr_pages; i++) { 984 struct page *page = pvec.pages[i]; 985 986 /* 987 * At this point, the page may be truncated or 988 * invalidated (changing page->mapping to NULL), or 989 * even swizzled back from swapper_space to tmpfs file 990 * mapping. However, page->index will not change 991 * because we have a reference on the page. 992 */ 993 if (page->index > end) { 994 /* 995 * can't be range_cyclic (1st pass) because 996 * end == -1 in that case. 997 */ 998 done = 1; 999 break; 1000 } 1001 1002 done_index = page->index + 1; 1003 1004 lock_page(page); 1005 1006 /* 1007 * Page truncated or invalidated. We can freely skip it 1008 * then, even for data integrity operations: the page 1009 * has disappeared concurrently, so there could be no 1010 * real expectation of this data interity operation 1011 * even if there is now a new, dirty page at the same 1012 * pagecache address. 1013 */ 1014 if (unlikely(page->mapping != mapping)) { 1015continue_unlock: 1016 unlock_page(page); 1017 continue; 1018 } 1019 1020 if (!PageDirty(page)) { 1021 /* someone wrote it for us */ 1022 goto continue_unlock; 1023 } 1024 1025 if (PageWriteback(page)) { 1026 if (wbc->sync_mode != WB_SYNC_NONE) 1027 wait_on_page_writeback(page); 1028 else 1029 goto continue_unlock; 1030 } 1031 1032 BUG_ON(PageWriteback(page)); 1033 if (!clear_page_dirty_for_io(page)) 1034 goto continue_unlock; 1035 1036 ret = (*writepage)(page, wbc, data); 1037 if (unlikely(ret)) { 1038 if (ret == AOP_WRITEPAGE_ACTIVATE) { 1039 unlock_page(page); 1040 ret = 0; 1041 } else { 1042 /* 1043 * done_index is set past this page, 1044 * so media errors will not choke 1045 * background writeout for the entire 1046 * file. This has consequences for 1047 * range_cyclic semantics (ie. it may 1048 * not be suitable for data integrity 1049 * writeout). 1050 */ 1051 done = 1; 1052 break; 1053 } 1054 } 1055 1056 if (nr_to_write > 0) { 1057 nr_to_write--; 1058 if (nr_to_write == 0 && 1059 wbc->sync_mode == WB_SYNC_NONE) { 1060 /* 1061 * We stop writing back only if we are 1062 * not doing integrity sync. In case of 1063 * integrity sync we have to keep going 1064 * because someone may be concurrently 1065 * dirtying pages, and we might have 1066 * synced a lot of newly appeared dirty 1067 * pages, but have not synced all of the 1068 * old dirty pages. 1069 */ 1070 done = 1; 1071 break; 1072 } 1073 } 1074 1075 if (wbc->nonblocking && bdi_write_congested(bdi)) { 1076 wbc->encountered_congestion = 1; 1077 done = 1; 1078 break; 1079 } 1080 } 1081 pagevec_release(&pvec); 1082 cond_resched(); 1083 } 1084 if (!cycled && !done) { 1085 /* 1086 * range_cyclic: 1087 * We hit the last page and there is more work to be done: wrap 1088 * back to the start of the file 1089 */ 1090 cycled = 1; 1091 index = 0; 1092 end = writeback_index - 1; 1093 goto retry; 1094 } 1095 if (!wbc->no_nrwrite_index_update) { 1096 if (wbc->range_cyclic || (range_whole && nr_to_write > 0)) 1097 mapping->writeback_index = done_index; 1098 wbc->nr_to_write = nr_to_write; 1099 } 1100 1101 return ret; 1102} 1103EXPORT_SYMBOL(write_cache_pages); 1104 1105/* 1106 * Function used by generic_writepages to call the real writepage 1107 * function and set the mapping flags on error 1108 */ 1109static int __writepage(struct page *page, struct writeback_control *wbc, 1110 void *data) 1111{ 1112 struct address_space *mapping = data; 1113 int ret = mapping->a_ops->writepage(page, wbc); 1114 mapping_set_error(mapping, ret); 1115 return ret; 1116} 1117 1118/** 1119 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 1120 * @mapping: address space structure to write 1121 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 1122 * 1123 * This is a library function, which implements the writepages() 1124 * address_space_operation. 1125 */ 1126int generic_writepages(struct address_space *mapping, 1127 struct writeback_control *wbc) 1128{ 1129 /* deal with chardevs and other special file */ 1130 if (!mapping->a_ops->writepage) 1131 return 0; 1132 1133 return write_cache_pages(mapping, wbc, __writepage, mapping); 1134} 1135 1136EXPORT_SYMBOL(generic_writepages); 1137 1138int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 1139{ 1140 int ret; 1141 1142 if (wbc->nr_to_write <= 0) 1143 return 0; 1144 wbc->for_writepages = 1; 1145 if (mapping->a_ops->writepages) 1146 ret = mapping->a_ops->writepages(mapping, wbc); 1147 else 1148 ret = generic_writepages(mapping, wbc); 1149 wbc->for_writepages = 0; 1150 return ret; 1151} 1152 1153/** 1154 * write_one_page - write out a single page and optionally wait on I/O 1155 * @page: the page to write 1156 * @wait: if true, wait on writeout 1157 * 1158 * The page must be locked by the caller and will be unlocked upon return. 1159 * 1160 * write_one_page() returns a negative error code if I/O failed. 1161 */ 1162int write_one_page(struct page *page, int wait) 1163{ 1164 struct address_space *mapping = page->mapping; 1165 int ret = 0; 1166 struct writeback_control wbc = { 1167 .sync_mode = WB_SYNC_ALL, 1168 .nr_to_write = 1, 1169 }; 1170 1171 BUG_ON(!PageLocked(page)); 1172 1173 if (wait) 1174 wait_on_page_writeback(page); 1175 1176 if (clear_page_dirty_for_io(page)) { 1177 page_cache_get(page); 1178 ret = mapping->a_ops->writepage(page, &wbc); 1179 if (ret == 0 && wait) { 1180 wait_on_page_writeback(page); 1181 if (PageError(page)) 1182 ret = -EIO; 1183 } 1184 page_cache_release(page); 1185 } else { 1186 unlock_page(page); 1187 } 1188 return ret; 1189} 1190EXPORT_SYMBOL(write_one_page); 1191 1192/* 1193 * For address_spaces which do not use buffers nor write back. 1194 */ 1195int __set_page_dirty_no_writeback(struct page *page) 1196{ 1197 if (!PageDirty(page)) 1198 SetPageDirty(page); 1199 return 0; 1200} 1201 1202/* 1203 * Helper function for set_page_dirty family. 1204 * NOTE: This relies on being atomic wrt interrupts. 1205 */ 1206void account_page_dirtied(struct page *page, struct address_space *mapping) 1207{ 1208 if (mapping_cap_account_dirty(mapping)) { 1209 __inc_zone_page_state(page, NR_FILE_DIRTY); 1210 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); 1211 task_dirty_inc(current); 1212 task_io_account_write(PAGE_CACHE_SIZE); 1213 } 1214} 1215 1216/* 1217 * For address_spaces which do not use buffers. Just tag the page as dirty in 1218 * its radix tree. 1219 * 1220 * This is also used when a single buffer is being dirtied: we want to set the 1221 * page dirty in that case, but not all the buffers. This is a "bottom-up" 1222 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 1223 * 1224 * Most callers have locked the page, which pins the address_space in memory. 1225 * But zap_pte_range() does not lock the page, however in that case the 1226 * mapping is pinned by the vma's ->vm_file reference. 1227 * 1228 * We take care to handle the case where the page was truncated from the 1229 * mapping by re-checking page_mapping() inside tree_lock. 1230 */ 1231int __set_page_dirty_nobuffers(struct page *page) 1232{ 1233 if (!TestSetPageDirty(page)) { 1234 struct address_space *mapping = page_mapping(page); 1235 struct address_space *mapping2; 1236 1237 if (!mapping) 1238 return 1; 1239 1240 spin_lock_irq(&mapping->tree_lock); 1241 mapping2 = page_mapping(page); 1242 if (mapping2) { /* Race with truncate? */ 1243 BUG_ON(mapping2 != mapping); 1244 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); 1245 account_page_dirtied(page, mapping); 1246 radix_tree_tag_set(&mapping->page_tree, 1247 page_index(page), PAGECACHE_TAG_DIRTY); 1248 } 1249 spin_unlock_irq(&mapping->tree_lock); 1250 if (mapping->host) { 1251 /* !PageAnon && !swapper_space */ 1252 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 1253 } 1254 return 1; 1255 } 1256 return 0; 1257} 1258EXPORT_SYMBOL(__set_page_dirty_nobuffers); 1259 1260/* 1261 * When a writepage implementation decides that it doesn't want to write this 1262 * page for some reason, it should redirty the locked page via 1263 * redirty_page_for_writepage() and it should then unlock the page and return 0 1264 */ 1265int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 1266{ 1267 wbc->pages_skipped++; 1268 return __set_page_dirty_nobuffers(page); 1269} 1270EXPORT_SYMBOL(redirty_page_for_writepage); 1271 1272/* 1273 * If the mapping doesn't provide a set_page_dirty a_op, then 1274 * just fall through and assume that it wants buffer_heads. 1275 */ 1276int set_page_dirty(struct page *page) 1277{ 1278 struct address_space *mapping = page_mapping(page); 1279 1280 if (likely(mapping)) { 1281 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 1282#ifdef CONFIG_BLOCK 1283 if (!spd) 1284 spd = __set_page_dirty_buffers; 1285#endif 1286 return (*spd)(page); 1287 } 1288 if (!PageDirty(page)) { 1289 if (!TestSetPageDirty(page)) 1290 return 1; 1291 } 1292 return 0; 1293} 1294EXPORT_SYMBOL(set_page_dirty); 1295 1296/* 1297 * set_page_dirty() is racy if the caller has no reference against 1298 * page->mapping->host, and if the page is unlocked. This is because another 1299 * CPU could truncate the page off the mapping and then free the mapping. 1300 * 1301 * Usually, the page _is_ locked, or the caller is a user-space process which 1302 * holds a reference on the inode by having an open file. 1303 * 1304 * In other cases, the page should be locked before running set_page_dirty(). 1305 */ 1306int set_page_dirty_lock(struct page *page) 1307{ 1308 int ret; 1309 1310 lock_page_nosync(page); 1311 ret = set_page_dirty(page); 1312 unlock_page(page); 1313 return ret; 1314} 1315EXPORT_SYMBOL(set_page_dirty_lock); 1316 1317/* 1318 * Clear a page's dirty flag, while caring for dirty memory accounting. 1319 * Returns true if the page was previously dirty. 1320 * 1321 * This is for preparing to put the page under writeout. We leave the page 1322 * tagged as dirty in the radix tree so that a concurrent write-for-sync 1323 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 1324 * implementation will run either set_page_writeback() or set_page_dirty(), 1325 * at which stage we bring the page's dirty flag and radix-tree dirty tag 1326 * back into sync. 1327 * 1328 * This incoherency between the page's dirty flag and radix-tree tag is 1329 * unfortunate, but it only exists while the page is locked. 1330 */ 1331int clear_page_dirty_for_io(struct page *page) 1332{ 1333 struct address_space *mapping = page_mapping(page); 1334 1335 BUG_ON(!PageLocked(page)); 1336 1337 ClearPageReclaim(page); 1338 if (mapping && mapping_cap_account_dirty(mapping)) { 1339 /* 1340 * Yes, Virginia, this is indeed insane. 1341 * 1342 * We use this sequence to make sure that 1343 * (a) we account for dirty stats properly 1344 * (b) we tell the low-level filesystem to 1345 * mark the whole page dirty if it was 1346 * dirty in a pagetable. Only to then 1347 * (c) clean the page again and return 1 to 1348 * cause the writeback. 1349 * 1350 * This way we avoid all nasty races with the 1351 * dirty bit in multiple places and clearing 1352 * them concurrently from different threads. 1353 * 1354 * Note! Normally the "set_page_dirty(page)" 1355 * has no effect on the actual dirty bit - since 1356 * that will already usually be set. But we 1357 * need the side effects, and it can help us 1358 * avoid races. 1359 * 1360 * We basically use the page "master dirty bit" 1361 * as a serialization point for all the different 1362 * threads doing their things. 1363 */ 1364 if (page_mkclean(page)) 1365 set_page_dirty(page); 1366 /* 1367 * We carefully synchronise fault handlers against 1368 * installing a dirty pte and marking the page dirty 1369 * at this point. We do this by having them hold the 1370 * page lock at some point after installing their 1371 * pte, but before marking the page dirty. 1372 * Pages are always locked coming in here, so we get 1373 * the desired exclusion. See mm/memory.c:do_wp_page() 1374 * for more comments. 1375 */ 1376 if (TestClearPageDirty(page)) { 1377 dec_zone_page_state(page, NR_FILE_DIRTY); 1378 dec_bdi_stat(mapping->backing_dev_info, 1379 BDI_RECLAIMABLE); 1380 return 1; 1381 } 1382 return 0; 1383 } 1384 return TestClearPageDirty(page); 1385} 1386EXPORT_SYMBOL(clear_page_dirty_for_io); 1387 1388int test_clear_page_writeback(struct page *page) 1389{ 1390 struct address_space *mapping = page_mapping(page); 1391 int ret; 1392 1393 if (mapping) { 1394 struct backing_dev_info *bdi = mapping->backing_dev_info; 1395 unsigned long flags; 1396 1397 spin_lock_irqsave(&mapping->tree_lock, flags); 1398 ret = TestClearPageWriteback(page); 1399 if (ret) { 1400 radix_tree_tag_clear(&mapping->page_tree, 1401 page_index(page), 1402 PAGECACHE_TAG_WRITEBACK); 1403 if (bdi_cap_account_writeback(bdi)) { 1404 __dec_bdi_stat(bdi, BDI_WRITEBACK); 1405 __bdi_writeout_inc(bdi); 1406 } 1407 } 1408 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1409 } else { 1410 ret = TestClearPageWriteback(page); 1411 } 1412 if (ret) 1413 dec_zone_page_state(page, NR_WRITEBACK); 1414 return ret; 1415} 1416 1417int test_set_page_writeback(struct page *page) 1418{ 1419 struct address_space *mapping = page_mapping(page); 1420 int ret; 1421 1422 if (mapping) { 1423 struct backing_dev_info *bdi = mapping->backing_dev_info; 1424 unsigned long flags; 1425 1426 spin_lock_irqsave(&mapping->tree_lock, flags); 1427 ret = TestSetPageWriteback(page); 1428 if (!ret) { 1429 radix_tree_tag_set(&mapping->page_tree, 1430 page_index(page), 1431 PAGECACHE_TAG_WRITEBACK); 1432 if (bdi_cap_account_writeback(bdi)) 1433 __inc_bdi_stat(bdi, BDI_WRITEBACK); 1434 } 1435 if (!PageDirty(page)) 1436 radix_tree_tag_clear(&mapping->page_tree, 1437 page_index(page), 1438 PAGECACHE_TAG_DIRTY); 1439 spin_unlock_irqrestore(&mapping->tree_lock, flags); 1440 } else { 1441 ret = TestSetPageWriteback(page); 1442 } 1443 if (!ret) 1444 inc_zone_page_state(page, NR_WRITEBACK); 1445 return ret; 1446 1447} 1448EXPORT_SYMBOL(test_set_page_writeback); 1449 1450/* 1451 * Return true if any of the pages in the mapping are marked with the 1452 * passed tag. 1453 */ 1454int mapping_tagged(struct address_space *mapping, int tag) 1455{ 1456 int ret; 1457 rcu_read_lock(); 1458 ret = radix_tree_tagged(&mapping->page_tree, tag); 1459 rcu_read_unlock(); 1460 return ret; 1461} 1462EXPORT_SYMBOL(mapping_tagged); 1463