1 /* 2 * mm/page-writeback.c 3 * 4 * Copyright (C) 2002, Linus Torvalds. 5 * 6 * Contains functions related to writing back dirty pages at the 7 * address_space level. 8 * 9 * 10Apr2002 akpm@zip.com.au 10 * Initial version 11 */ 12 13 #include <linux/kernel.h> 14 #include <linux/module.h> 15 #include <linux/spinlock.h> 16 #include <linux/fs.h> 17 #include <linux/mm.h> 18 #include <linux/swap.h> 19 #include <linux/slab.h> 20 #include <linux/pagemap.h> 21 #include <linux/writeback.h> 22 #include <linux/init.h> 23 #include <linux/backing-dev.h> 24 #include <linux/task_io_accounting_ops.h> 25 #include <linux/blkdev.h> 26 #include <linux/mpage.h> 27 #include <linux/rmap.h> 28 #include <linux/percpu.h> 29 #include <linux/notifier.h> 30 #include <linux/smp.h> 31 #include <linux/sysctl.h> 32 #include <linux/cpu.h> 33 #include <linux/syscalls.h> 34 #include <linux/buffer_head.h> 35 #include <linux/pagevec.h> 36 37 /* 38 * The maximum number of pages to writeout in a single bdflush/kupdate 39 * operation. We do this so we don't hold I_LOCK against an inode for 40 * enormous amounts of time, which would block a userspace task which has 41 * been forced to throttle against that inode. Also, the code reevaluates 42 * the dirty each time it has written this many pages. 43 */ 44 #define MAX_WRITEBACK_PAGES 1024 45 46 /* 47 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited 48 * will look to see if it needs to force writeback or throttling. 49 */ 50 static long ratelimit_pages = 32; 51 52 static int dirty_exceeded __cacheline_aligned_in_smp; /* Dirty mem may be over limit */ 53 54 /* 55 * When balance_dirty_pages decides that the caller needs to perform some 56 * non-background writeback, this is how many pages it will attempt to write. 57 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably 58 * large amounts of I/O are submitted. 59 */ 60 static inline long sync_writeback_pages(void) 61 { 62 return ratelimit_pages + ratelimit_pages / 2; 63 } 64 65 /* The following parameters are exported via /proc/sys/vm */ 66 67 /* 68 * Start background writeback (via pdflush) at this percentage 69 */ 70 int dirty_background_ratio = 5; 71 72 /* 73 * The generator of dirty data starts writeback at this percentage 74 */ 75 int vm_dirty_ratio = 10; 76 77 /* 78 * The interval between `kupdate'-style writebacks, in jiffies 79 */ 80 int dirty_writeback_interval = 5 * HZ; 81 82 /* 83 * The longest number of jiffies for which data is allowed to remain dirty 84 */ 85 int dirty_expire_interval = 30 * HZ; 86 87 /* 88 * Flag that makes the machine dump writes/reads and block dirtyings. 89 */ 90 int block_dump; 91 92 /* 93 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: 94 * a full sync is triggered after this time elapses without any disk activity. 95 */ 96 int laptop_mode; 97 98 EXPORT_SYMBOL(laptop_mode); 99 100 /* End of sysctl-exported parameters */ 101 102 103 static void background_writeout(unsigned long _min_pages); 104 105 /* 106 * Work out the current dirty-memory clamping and background writeout 107 * thresholds. 108 * 109 * The main aim here is to lower them aggressively if there is a lot of mapped 110 * memory around. To avoid stressing page reclaim with lots of unreclaimable 111 * pages. It is better to clamp down on writers than to start swapping, and 112 * performing lots of scanning. 113 * 114 * We only allow 1/2 of the currently-unmapped memory to be dirtied. 115 * 116 * We don't permit the clamping level to fall below 5% - that is getting rather 117 * excessive. 118 * 119 * We make sure that the background writeout level is below the adjusted 120 * clamping level. 121 */ 122 123 static unsigned long highmem_dirtyable_memory(unsigned long total) 124 { 125 #ifdef CONFIG_HIGHMEM 126 int node; 127 unsigned long x = 0; 128 129 for_each_online_node(node) { 130 struct zone *z = 131 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; 132 133 x += zone_page_state(z, NR_FREE_PAGES) 134 + zone_page_state(z, NR_INACTIVE) 135 + zone_page_state(z, NR_ACTIVE); 136 } 137 /* 138 * Make sure that the number of highmem pages is never larger 139 * than the number of the total dirtyable memory. This can only 140 * occur in very strange VM situations but we want to make sure 141 * that this does not occur. 142 */ 143 return min(x, total); 144 #else 145 return 0; 146 #endif 147 } 148 149 static unsigned long determine_dirtyable_memory(void) 150 { 151 unsigned long x; 152 153 x = global_page_state(NR_FREE_PAGES) 154 + global_page_state(NR_INACTIVE) 155 + global_page_state(NR_ACTIVE); 156 x -= highmem_dirtyable_memory(x); 157 return x + 1; /* Ensure that we never return 0 */ 158 } 159 160 static void 161 get_dirty_limits(long *pbackground, long *pdirty, 162 struct address_space *mapping) 163 { 164 int background_ratio; /* Percentages */ 165 int dirty_ratio; 166 int unmapped_ratio; 167 long background; 168 long dirty; 169 unsigned long available_memory = determine_dirtyable_memory(); 170 struct task_struct *tsk; 171 172 unmapped_ratio = 100 - ((global_page_state(NR_FILE_MAPPED) + 173 global_page_state(NR_ANON_PAGES)) * 100) / 174 available_memory; 175 176 dirty_ratio = vm_dirty_ratio; 177 if (dirty_ratio > unmapped_ratio / 2) 178 dirty_ratio = unmapped_ratio / 2; 179 180 if (dirty_ratio < 5) 181 dirty_ratio = 5; 182 183 background_ratio = dirty_background_ratio; 184 if (background_ratio >= dirty_ratio) 185 background_ratio = dirty_ratio / 2; 186 187 background = (background_ratio * available_memory) / 100; 188 dirty = (dirty_ratio * available_memory) / 100; 189 tsk = current; 190 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { 191 background += background / 4; 192 dirty += dirty / 4; 193 } 194 *pbackground = background; 195 *pdirty = dirty; 196 } 197 198 /* 199 * balance_dirty_pages() must be called by processes which are generating dirty 200 * data. It looks at the number of dirty pages in the machine and will force 201 * the caller to perform writeback if the system is over `vm_dirty_ratio'. 202 * If we're over `background_thresh' then pdflush is woken to perform some 203 * writeout. 204 */ 205 static void balance_dirty_pages(struct address_space *mapping) 206 { 207 long nr_reclaimable; 208 long background_thresh; 209 long dirty_thresh; 210 unsigned long pages_written = 0; 211 unsigned long write_chunk = sync_writeback_pages(); 212 213 struct backing_dev_info *bdi = mapping->backing_dev_info; 214 215 for (;;) { 216 struct writeback_control wbc = { 217 .bdi = bdi, 218 .sync_mode = WB_SYNC_NONE, 219 .older_than_this = NULL, 220 .nr_to_write = write_chunk, 221 .range_cyclic = 1, 222 }; 223 224 get_dirty_limits(&background_thresh, &dirty_thresh, mapping); 225 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 226 global_page_state(NR_UNSTABLE_NFS); 227 if (nr_reclaimable + global_page_state(NR_WRITEBACK) <= 228 dirty_thresh) 229 break; 230 231 if (!dirty_exceeded) 232 dirty_exceeded = 1; 233 234 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. 235 * Unstable writes are a feature of certain networked 236 * filesystems (i.e. NFS) in which data may have been 237 * written to the server's write cache, but has not yet 238 * been flushed to permanent storage. 239 */ 240 if (nr_reclaimable) { 241 writeback_inodes(&wbc); 242 get_dirty_limits(&background_thresh, 243 &dirty_thresh, mapping); 244 nr_reclaimable = global_page_state(NR_FILE_DIRTY) + 245 global_page_state(NR_UNSTABLE_NFS); 246 if (nr_reclaimable + 247 global_page_state(NR_WRITEBACK) 248 <= dirty_thresh) 249 break; 250 pages_written += write_chunk - wbc.nr_to_write; 251 if (pages_written >= write_chunk) 252 break; /* We've done our duty */ 253 } 254 congestion_wait(WRITE, HZ/10); 255 } 256 257 if (nr_reclaimable + global_page_state(NR_WRITEBACK) 258 <= dirty_thresh && dirty_exceeded) 259 dirty_exceeded = 0; 260 261 if (writeback_in_progress(bdi)) 262 return; /* pdflush is already working this queue */ 263 264 /* 265 * In laptop mode, we wait until hitting the higher threshold before 266 * starting background writeout, and then write out all the way down 267 * to the lower threshold. So slow writers cause minimal disk activity. 268 * 269 * In normal mode, we start background writeout at the lower 270 * background_thresh, to keep the amount of dirty memory low. 271 */ 272 if ((laptop_mode && pages_written) || 273 (!laptop_mode && (nr_reclaimable > background_thresh))) 274 pdflush_operation(background_writeout, 0); 275 } 276 277 void set_page_dirty_balance(struct page *page) 278 { 279 if (set_page_dirty(page)) { 280 struct address_space *mapping = page_mapping(page); 281 282 if (mapping) 283 balance_dirty_pages_ratelimited(mapping); 284 } 285 } 286 287 /** 288 * balance_dirty_pages_ratelimited_nr - balance dirty memory state 289 * @mapping: address_space which was dirtied 290 * @nr_pages_dirtied: number of pages which the caller has just dirtied 291 * 292 * Processes which are dirtying memory should call in here once for each page 293 * which was newly dirtied. The function will periodically check the system's 294 * dirty state and will initiate writeback if needed. 295 * 296 * On really big machines, get_writeback_state is expensive, so try to avoid 297 * calling it too often (ratelimiting). But once we're over the dirty memory 298 * limit we decrease the ratelimiting by a lot, to prevent individual processes 299 * from overshooting the limit by (ratelimit_pages) each. 300 */ 301 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, 302 unsigned long nr_pages_dirtied) 303 { 304 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0; 305 unsigned long ratelimit; 306 unsigned long *p; 307 308 ratelimit = ratelimit_pages; 309 if (dirty_exceeded) 310 ratelimit = 8; 311 312 /* 313 * Check the rate limiting. Also, we do not want to throttle real-time 314 * tasks in balance_dirty_pages(). Period. 315 */ 316 preempt_disable(); 317 p = &__get_cpu_var(ratelimits); 318 *p += nr_pages_dirtied; 319 if (unlikely(*p >= ratelimit)) { 320 *p = 0; 321 preempt_enable(); 322 balance_dirty_pages(mapping); 323 return; 324 } 325 preempt_enable(); 326 } 327 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); 328 329 void throttle_vm_writeout(gfp_t gfp_mask) 330 { 331 long background_thresh; 332 long dirty_thresh; 333 334 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) { 335 /* 336 * The caller might hold locks which can prevent IO completion 337 * or progress in the filesystem. So we cannot just sit here 338 * waiting for IO to complete. 339 */ 340 congestion_wait(WRITE, HZ/10); 341 return; 342 } 343 344 for ( ; ; ) { 345 get_dirty_limits(&background_thresh, &dirty_thresh, NULL); 346 347 /* 348 * Boost the allowable dirty threshold a bit for page 349 * allocators so they don't get DoS'ed by heavy writers 350 */ 351 dirty_thresh += dirty_thresh / 10; /* wheeee... */ 352 353 if (global_page_state(NR_UNSTABLE_NFS) + 354 global_page_state(NR_WRITEBACK) <= dirty_thresh) 355 break; 356 congestion_wait(WRITE, HZ/10); 357 } 358 } 359 360 /* 361 * writeback at least _min_pages, and keep writing until the amount of dirty 362 * memory is less than the background threshold, or until we're all clean. 363 */ 364 static void background_writeout(unsigned long _min_pages) 365 { 366 long min_pages = _min_pages; 367 struct writeback_control wbc = { 368 .bdi = NULL, 369 .sync_mode = WB_SYNC_NONE, 370 .older_than_this = NULL, 371 .nr_to_write = 0, 372 .nonblocking = 1, 373 .range_cyclic = 1, 374 }; 375 376 for ( ; ; ) { 377 long background_thresh; 378 long dirty_thresh; 379 380 get_dirty_limits(&background_thresh, &dirty_thresh, NULL); 381 if (global_page_state(NR_FILE_DIRTY) + 382 global_page_state(NR_UNSTABLE_NFS) < background_thresh 383 && min_pages <= 0) 384 break; 385 wbc.encountered_congestion = 0; 386 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 387 wbc.pages_skipped = 0; 388 writeback_inodes(&wbc); 389 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 390 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { 391 /* Wrote less than expected */ 392 congestion_wait(WRITE, HZ/10); 393 if (!wbc.encountered_congestion) 394 break; 395 } 396 } 397 } 398 399 /* 400 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back 401 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns 402 * -1 if all pdflush threads were busy. 403 */ 404 int wakeup_pdflush(long nr_pages) 405 { 406 if (nr_pages == 0) 407 nr_pages = global_page_state(NR_FILE_DIRTY) + 408 global_page_state(NR_UNSTABLE_NFS); 409 return pdflush_operation(background_writeout, nr_pages); 410 } 411 412 static void wb_timer_fn(unsigned long unused); 413 static void laptop_timer_fn(unsigned long unused); 414 415 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0); 416 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 417 418 /* 419 * Periodic writeback of "old" data. 420 * 421 * Define "old": the first time one of an inode's pages is dirtied, we mark the 422 * dirtying-time in the inode's address_space. So this periodic writeback code 423 * just walks the superblock inode list, writing back any inodes which are 424 * older than a specific point in time. 425 * 426 * Try to run once per dirty_writeback_interval. But if a writeback event 427 * takes longer than a dirty_writeback_interval interval, then leave a 428 * one-second gap. 429 * 430 * older_than_this takes precedence over nr_to_write. So we'll only write back 431 * all dirty pages if they are all attached to "old" mappings. 432 */ 433 static void wb_kupdate(unsigned long arg) 434 { 435 unsigned long oldest_jif; 436 unsigned long start_jif; 437 unsigned long next_jif; 438 long nr_to_write; 439 struct writeback_control wbc = { 440 .bdi = NULL, 441 .sync_mode = WB_SYNC_NONE, 442 .older_than_this = &oldest_jif, 443 .nr_to_write = 0, 444 .nonblocking = 1, 445 .for_kupdate = 1, 446 .range_cyclic = 1, 447 }; 448 449 sync_supers(); 450 451 oldest_jif = jiffies - dirty_expire_interval; 452 start_jif = jiffies; 453 next_jif = start_jif + dirty_writeback_interval; 454 nr_to_write = global_page_state(NR_FILE_DIRTY) + 455 global_page_state(NR_UNSTABLE_NFS) + 456 (inodes_stat.nr_inodes - inodes_stat.nr_unused); 457 while (nr_to_write > 0) { 458 wbc.encountered_congestion = 0; 459 wbc.nr_to_write = MAX_WRITEBACK_PAGES; 460 writeback_inodes(&wbc); 461 if (wbc.nr_to_write > 0) { 462 if (wbc.encountered_congestion) 463 congestion_wait(WRITE, HZ/10); 464 else 465 break; /* All the old data is written */ 466 } 467 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; 468 } 469 if (time_before(next_jif, jiffies + HZ)) 470 next_jif = jiffies + HZ; 471 if (dirty_writeback_interval) 472 mod_timer(&wb_timer, next_jif); 473 } 474 475 /* 476 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs 477 */ 478 int dirty_writeback_centisecs_handler(ctl_table *table, int write, 479 struct file *file, void __user *buffer, size_t *length, loff_t *ppos) 480 { 481 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos); 482 if (dirty_writeback_interval) { 483 mod_timer(&wb_timer, 484 jiffies + dirty_writeback_interval); 485 } else { 486 del_timer(&wb_timer); 487 } 488 return 0; 489 } 490 491 static void wb_timer_fn(unsigned long unused) 492 { 493 if (pdflush_operation(wb_kupdate, 0) < 0) 494 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */ 495 } 496 497 static void laptop_flush(unsigned long unused) 498 { 499 sys_sync(); 500 } 501 502 static void laptop_timer_fn(unsigned long unused) 503 { 504 pdflush_operation(laptop_flush, 0); 505 } 506 507 /* 508 * We've spun up the disk and we're in laptop mode: schedule writeback 509 * of all dirty data a few seconds from now. If the flush is already scheduled 510 * then push it back - the user is still using the disk. 511 */ 512 void laptop_io_completion(void) 513 { 514 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode); 515 } 516 517 /* 518 * We're in laptop mode and we've just synced. The sync's writes will have 519 * caused another writeback to be scheduled by laptop_io_completion. 520 * Nothing needs to be written back anymore, so we unschedule the writeback. 521 */ 522 void laptop_sync_completion(void) 523 { 524 del_timer(&laptop_mode_wb_timer); 525 } 526 527 /* 528 * If ratelimit_pages is too high then we can get into dirty-data overload 529 * if a large number of processes all perform writes at the same time. 530 * If it is too low then SMP machines will call the (expensive) 531 * get_writeback_state too often. 532 * 533 * Here we set ratelimit_pages to a level which ensures that when all CPUs are 534 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory 535 * thresholds before writeback cuts in. 536 * 537 * But the limit should not be set too high. Because it also controls the 538 * amount of memory which the balance_dirty_pages() caller has to write back. 539 * If this is too large then the caller will block on the IO queue all the 540 * time. So limit it to four megabytes - the balance_dirty_pages() caller 541 * will write six megabyte chunks, max. 542 */ 543 544 void writeback_set_ratelimit(void) 545 { 546 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); 547 if (ratelimit_pages < 16) 548 ratelimit_pages = 16; 549 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) 550 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; 551 } 552 553 static int __cpuinit 554 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) 555 { 556 writeback_set_ratelimit(); 557 return NOTIFY_DONE; 558 } 559 560 static struct notifier_block __cpuinitdata ratelimit_nb = { 561 .notifier_call = ratelimit_handler, 562 .next = NULL, 563 }; 564 565 /* 566 * Called early on to tune the page writeback dirty limits. 567 * 568 * We used to scale dirty pages according to how total memory 569 * related to pages that could be allocated for buffers (by 570 * comparing nr_free_buffer_pages() to vm_total_pages. 571 * 572 * However, that was when we used "dirty_ratio" to scale with 573 * all memory, and we don't do that any more. "dirty_ratio" 574 * is now applied to total non-HIGHPAGE memory (by subtracting 575 * totalhigh_pages from vm_total_pages), and as such we can't 576 * get into the old insane situation any more where we had 577 * large amounts of dirty pages compared to a small amount of 578 * non-HIGHMEM memory. 579 * 580 * But we might still want to scale the dirty_ratio by how 581 * much memory the box has.. 582 */ 583 void __init page_writeback_init(void) 584 { 585 mod_timer(&wb_timer, jiffies + dirty_writeback_interval); 586 writeback_set_ratelimit(); 587 register_cpu_notifier(&ratelimit_nb); 588 } 589 590 /** 591 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. 592 * @mapping: address space structure to write 593 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 594 * @writepage: function called for each page 595 * @data: data passed to writepage function 596 * 597 * If a page is already under I/O, write_cache_pages() skips it, even 598 * if it's dirty. This is desirable behaviour for memory-cleaning writeback, 599 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() 600 * and msync() need to guarantee that all the data which was dirty at the time 601 * the call was made get new I/O started against them. If wbc->sync_mode is 602 * WB_SYNC_ALL then we were called for data integrity and we must wait for 603 * existing IO to complete. 604 */ 605 int write_cache_pages(struct address_space *mapping, 606 struct writeback_control *wbc, writepage_t writepage, 607 void *data) 608 { 609 struct backing_dev_info *bdi = mapping->backing_dev_info; 610 int ret = 0; 611 int done = 0; 612 struct pagevec pvec; 613 int nr_pages; 614 pgoff_t index; 615 pgoff_t end; /* Inclusive */ 616 int scanned = 0; 617 int range_whole = 0; 618 619 if (wbc->nonblocking && bdi_write_congested(bdi)) { 620 wbc->encountered_congestion = 1; 621 return 0; 622 } 623 624 pagevec_init(&pvec, 0); 625 if (wbc->range_cyclic) { 626 index = mapping->writeback_index; /* Start from prev offset */ 627 end = -1; 628 } else { 629 index = wbc->range_start >> PAGE_CACHE_SHIFT; 630 end = wbc->range_end >> PAGE_CACHE_SHIFT; 631 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) 632 range_whole = 1; 633 scanned = 1; 634 } 635 retry: 636 while (!done && (index <= end) && 637 (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, 638 PAGECACHE_TAG_DIRTY, 639 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) { 640 unsigned i; 641 642 scanned = 1; 643 for (i = 0; i < nr_pages; i++) { 644 struct page *page = pvec.pages[i]; 645 646 /* 647 * At this point we hold neither mapping->tree_lock nor 648 * lock on the page itself: the page may be truncated or 649 * invalidated (changing page->mapping to NULL), or even 650 * swizzled back from swapper_space to tmpfs file 651 * mapping 652 */ 653 lock_page(page); 654 655 if (unlikely(page->mapping != mapping)) { 656 unlock_page(page); 657 continue; 658 } 659 660 if (!wbc->range_cyclic && page->index > end) { 661 done = 1; 662 unlock_page(page); 663 continue; 664 } 665 666 if (wbc->sync_mode != WB_SYNC_NONE) 667 wait_on_page_writeback(page); 668 669 if (PageWriteback(page) || 670 !clear_page_dirty_for_io(page)) { 671 unlock_page(page); 672 continue; 673 } 674 675 ret = (*writepage)(page, wbc, data); 676 677 if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) 678 unlock_page(page); 679 if (ret || (--(wbc->nr_to_write) <= 0)) 680 done = 1; 681 if (wbc->nonblocking && bdi_write_congested(bdi)) { 682 wbc->encountered_congestion = 1; 683 done = 1; 684 } 685 } 686 pagevec_release(&pvec); 687 cond_resched(); 688 } 689 if (!scanned && !done) { 690 /* 691 * We hit the last page and there is more work to be done: wrap 692 * back to the start of the file 693 */ 694 scanned = 1; 695 index = 0; 696 goto retry; 697 } 698 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) 699 mapping->writeback_index = index; 700 return ret; 701 } 702 EXPORT_SYMBOL(write_cache_pages); 703 704 /* 705 * Function used by generic_writepages to call the real writepage 706 * function and set the mapping flags on error 707 */ 708 static int __writepage(struct page *page, struct writeback_control *wbc, 709 void *data) 710 { 711 struct address_space *mapping = data; 712 int ret = mapping->a_ops->writepage(page, wbc); 713 mapping_set_error(mapping, ret); 714 return ret; 715 } 716 717 /** 718 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. 719 * @mapping: address space structure to write 720 * @wbc: subtract the number of written pages from *@wbc->nr_to_write 721 * 722 * This is a library function, which implements the writepages() 723 * address_space_operation. 724 */ 725 int generic_writepages(struct address_space *mapping, 726 struct writeback_control *wbc) 727 { 728 /* deal with chardevs and other special file */ 729 if (!mapping->a_ops->writepage) 730 return 0; 731 732 return write_cache_pages(mapping, wbc, __writepage, mapping); 733 } 734 735 EXPORT_SYMBOL(generic_writepages); 736 737 int do_writepages(struct address_space *mapping, struct writeback_control *wbc) 738 { 739 int ret; 740 741 if (wbc->nr_to_write <= 0) 742 return 0; 743 wbc->for_writepages = 1; 744 if (mapping->a_ops->writepages) 745 ret = mapping->a_ops->writepages(mapping, wbc); 746 else 747 ret = generic_writepages(mapping, wbc); 748 wbc->for_writepages = 0; 749 return ret; 750 } 751 752 /** 753 * write_one_page - write out a single page and optionally wait on I/O 754 * @page: the page to write 755 * @wait: if true, wait on writeout 756 * 757 * The page must be locked by the caller and will be unlocked upon return. 758 * 759 * write_one_page() returns a negative error code if I/O failed. 760 */ 761 int write_one_page(struct page *page, int wait) 762 { 763 struct address_space *mapping = page->mapping; 764 int ret = 0; 765 struct writeback_control wbc = { 766 .sync_mode = WB_SYNC_ALL, 767 .nr_to_write = 1, 768 }; 769 770 BUG_ON(!PageLocked(page)); 771 772 if (wait) 773 wait_on_page_writeback(page); 774 775 if (clear_page_dirty_for_io(page)) { 776 page_cache_get(page); 777 ret = mapping->a_ops->writepage(page, &wbc); 778 if (ret == 0 && wait) { 779 wait_on_page_writeback(page); 780 if (PageError(page)) 781 ret = -EIO; 782 } 783 page_cache_release(page); 784 } else { 785 unlock_page(page); 786 } 787 return ret; 788 } 789 EXPORT_SYMBOL(write_one_page); 790 791 /* 792 * For address_spaces which do not use buffers nor write back. 793 */ 794 int __set_page_dirty_no_writeback(struct page *page) 795 { 796 if (!PageDirty(page)) 797 SetPageDirty(page); 798 return 0; 799 } 800 801 /* 802 * For address_spaces which do not use buffers. Just tag the page as dirty in 803 * its radix tree. 804 * 805 * This is also used when a single buffer is being dirtied: we want to set the 806 * page dirty in that case, but not all the buffers. This is a "bottom-up" 807 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. 808 * 809 * Most callers have locked the page, which pins the address_space in memory. 810 * But zap_pte_range() does not lock the page, however in that case the 811 * mapping is pinned by the vma's ->vm_file reference. 812 * 813 * We take care to handle the case where the page was truncated from the 814 * mapping by re-checking page_mapping() insode tree_lock. 815 */ 816 int __set_page_dirty_nobuffers(struct page *page) 817 { 818 if (!TestSetPageDirty(page)) { 819 struct address_space *mapping = page_mapping(page); 820 struct address_space *mapping2; 821 822 if (!mapping) 823 return 1; 824 825 write_lock_irq(&mapping->tree_lock); 826 mapping2 = page_mapping(page); 827 if (mapping2) { /* Race with truncate? */ 828 BUG_ON(mapping2 != mapping); 829 if (mapping_cap_account_dirty(mapping)) { 830 __inc_zone_page_state(page, NR_FILE_DIRTY); 831 task_io_account_write(PAGE_CACHE_SIZE); 832 } 833 radix_tree_tag_set(&mapping->page_tree, 834 page_index(page), PAGECACHE_TAG_DIRTY); 835 } 836 write_unlock_irq(&mapping->tree_lock); 837 if (mapping->host) { 838 /* !PageAnon && !swapper_space */ 839 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); 840 } 841 return 1; 842 } 843 return 0; 844 } 845 EXPORT_SYMBOL(__set_page_dirty_nobuffers); 846 847 /* 848 * When a writepage implementation decides that it doesn't want to write this 849 * page for some reason, it should redirty the locked page via 850 * redirty_page_for_writepage() and it should then unlock the page and return 0 851 */ 852 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) 853 { 854 wbc->pages_skipped++; 855 return __set_page_dirty_nobuffers(page); 856 } 857 EXPORT_SYMBOL(redirty_page_for_writepage); 858 859 /* 860 * If the mapping doesn't provide a set_page_dirty a_op, then 861 * just fall through and assume that it wants buffer_heads. 862 */ 863 int fastcall set_page_dirty(struct page *page) 864 { 865 struct address_space *mapping = page_mapping(page); 866 867 if (likely(mapping)) { 868 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; 869 #ifdef CONFIG_BLOCK 870 if (!spd) 871 spd = __set_page_dirty_buffers; 872 #endif 873 return (*spd)(page); 874 } 875 if (!PageDirty(page)) { 876 if (!TestSetPageDirty(page)) 877 return 1; 878 } 879 return 0; 880 } 881 EXPORT_SYMBOL(set_page_dirty); 882 883 /* 884 * set_page_dirty() is racy if the caller has no reference against 885 * page->mapping->host, and if the page is unlocked. This is because another 886 * CPU could truncate the page off the mapping and then free the mapping. 887 * 888 * Usually, the page _is_ locked, or the caller is a user-space process which 889 * holds a reference on the inode by having an open file. 890 * 891 * In other cases, the page should be locked before running set_page_dirty(). 892 */ 893 int set_page_dirty_lock(struct page *page) 894 { 895 int ret; 896 897 lock_page_nosync(page); 898 ret = set_page_dirty(page); 899 unlock_page(page); 900 return ret; 901 } 902 EXPORT_SYMBOL(set_page_dirty_lock); 903 904 /* 905 * Clear a page's dirty flag, while caring for dirty memory accounting. 906 * Returns true if the page was previously dirty. 907 * 908 * This is for preparing to put the page under writeout. We leave the page 909 * tagged as dirty in the radix tree so that a concurrent write-for-sync 910 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage 911 * implementation will run either set_page_writeback() or set_page_dirty(), 912 * at which stage we bring the page's dirty flag and radix-tree dirty tag 913 * back into sync. 914 * 915 * This incoherency between the page's dirty flag and radix-tree tag is 916 * unfortunate, but it only exists while the page is locked. 917 */ 918 int clear_page_dirty_for_io(struct page *page) 919 { 920 struct address_space *mapping = page_mapping(page); 921 922 if (mapping && mapping_cap_account_dirty(mapping)) { 923 /* 924 * Yes, Virginia, this is indeed insane. 925 * 926 * We use this sequence to make sure that 927 * (a) we account for dirty stats properly 928 * (b) we tell the low-level filesystem to 929 * mark the whole page dirty if it was 930 * dirty in a pagetable. Only to then 931 * (c) clean the page again and return 1 to 932 * cause the writeback. 933 * 934 * This way we avoid all nasty races with the 935 * dirty bit in multiple places and clearing 936 * them concurrently from different threads. 937 * 938 * Note! Normally the "set_page_dirty(page)" 939 * has no effect on the actual dirty bit - since 940 * that will already usually be set. But we 941 * need the side effects, and it can help us 942 * avoid races. 943 * 944 * We basically use the page "master dirty bit" 945 * as a serialization point for all the different 946 * threads doing their things. 947 * 948 * FIXME! We still have a race here: if somebody 949 * adds the page back to the page tables in 950 * between the "page_mkclean()" and the "TestClearPageDirty()", 951 * we might have it mapped without the dirty bit set. 952 */ 953 if (page_mkclean(page)) 954 set_page_dirty(page); 955 if (TestClearPageDirty(page)) { 956 dec_zone_page_state(page, NR_FILE_DIRTY); 957 return 1; 958 } 959 return 0; 960 } 961 return TestClearPageDirty(page); 962 } 963 EXPORT_SYMBOL(clear_page_dirty_for_io); 964 965 int test_clear_page_writeback(struct page *page) 966 { 967 struct address_space *mapping = page_mapping(page); 968 int ret; 969 970 if (mapping) { 971 unsigned long flags; 972 973 write_lock_irqsave(&mapping->tree_lock, flags); 974 ret = TestClearPageWriteback(page); 975 if (ret) 976 radix_tree_tag_clear(&mapping->page_tree, 977 page_index(page), 978 PAGECACHE_TAG_WRITEBACK); 979 write_unlock_irqrestore(&mapping->tree_lock, flags); 980 } else { 981 ret = TestClearPageWriteback(page); 982 } 983 return ret; 984 } 985 986 int test_set_page_writeback(struct page *page) 987 { 988 struct address_space *mapping = page_mapping(page); 989 int ret; 990 991 if (mapping) { 992 unsigned long flags; 993 994 write_lock_irqsave(&mapping->tree_lock, flags); 995 ret = TestSetPageWriteback(page); 996 if (!ret) 997 radix_tree_tag_set(&mapping->page_tree, 998 page_index(page), 999 PAGECACHE_TAG_WRITEBACK); 1000 if (!PageDirty(page)) 1001 radix_tree_tag_clear(&mapping->page_tree, 1002 page_index(page), 1003 PAGECACHE_TAG_DIRTY); 1004 write_unlock_irqrestore(&mapping->tree_lock, flags); 1005 } else { 1006 ret = TestSetPageWriteback(page); 1007 } 1008 return ret; 1009 1010 } 1011 EXPORT_SYMBOL(test_set_page_writeback); 1012 1013 /* 1014 * Return true if any of the pages in the mapping are marged with the 1015 * passed tag. 1016 */ 1017 int mapping_tagged(struct address_space *mapping, int tag) 1018 { 1019 unsigned long flags; 1020 int ret; 1021 1022 read_lock_irqsave(&mapping->tree_lock, flags); 1023 ret = radix_tree_tagged(&mapping->page_tree, tag); 1024 read_unlock_irqrestore(&mapping->tree_lock, flags); 1025 return ret; 1026 } 1027 EXPORT_SYMBOL(mapping_tagged); 1028