git.oblomov.eu Git - linux-2.6/blob - fs/mpage.c

   1 /*
   2  * fs/mpage.c
   3  *
   4  * Copyright (C) 2002, Linus Torvalds.
   5  *
   6  * Contains functions related to preparing and submitting BIOs which contain
   7  * multiple pagecache pages.
   8  *
   9  * 15May2002    akpm@zip.com.au
  10  *              Initial version
  11  * 27Jun2002    axboe@suse.de
  12  *              use bio_add_page() to build bio's just the right size
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/module.h>
  17 #include <linux/mm.h>
  18 #include <linux/kdev_t.h>
  19 #include <linux/bio.h>
  20 #include <linux/fs.h>
  21 #include <linux/buffer_head.h>
  22 #include <linux/blkdev.h>
  23 #include <linux/highmem.h>
  24 #include <linux/prefetch.h>
  25 #include <linux/mpage.h>
  26 #include <linux/writeback.h>
  27 #include <linux/backing-dev.h>
  28 #include <linux/pagevec.h>
  29
  30 /*
  31  * I/O completion handler for multipage BIOs.
  32  *
  33  * The mpage code never puts partial pages into a BIO (except for end-of-file).
  34  * If a page does not map to a contiguous run of blocks then it simply falls
  35  * back to block_read_full_page().
  36  *
  37  * Why is this?  If a page's completion depends on a number of different BIOs
  38  * which can complete in any order (or at the same time) then determining the
  39  * status of that page is hard.  See end_buffer_async_read() for the details.
  40  * There is no point in duplicating all that complexity.
  41  */
  42 static int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, int err)
  43 {
  44         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  45         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
  46
  47         if (bio->bi_size)
  48                 return 1;
  49
  50         do {
  51                 struct page *page = bvec->bv_page;
  52
  53                 if (--bvec >= bio->bi_io_vec)
  54                         prefetchw(&bvec->bv_page->flags);
  55
  56                 if (uptodate) {
  57                         SetPageUptodate(page);
  58                 } else {
  59                         ClearPageUptodate(page);
  60                         SetPageError(page);
  61                 }
  62                 unlock_page(page);
  63         } while (bvec >= bio->bi_io_vec);
  64         bio_put(bio);
  65         return 0;
  66 }
  67
  68 static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err)
  69 {
  70         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  71         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
  72
  73         if (bio->bi_size)
  74                 return 1;
  75
  76         do {
  77                 struct page *page = bvec->bv_page;
  78
  79                 if (--bvec >= bio->bi_io_vec)
  80                         prefetchw(&bvec->bv_page->flags);
  81
  82                 if (!uptodate)
  83                         SetPageError(page);
  84                 end_page_writeback(page);
  85         } while (bvec >= bio->bi_io_vec);
  86         bio_put(bio);
  87         return 0;
  88 }
  89
  90 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
  91 {
  92         bio->bi_end_io = mpage_end_io_read;
  93         if (rw == WRITE)
  94                 bio->bi_end_io = mpage_end_io_write;
  95         submit_bio(rw, bio);
  96         return NULL;
  97 }
  98
  99 static struct bio *
 100 mpage_alloc(struct block_device *bdev,
 101                 sector_t first_sector, int nr_vecs,
 102                 unsigned int __nocast gfp_flags)
 103 {
 104         struct bio *bio;
 105
 106         bio = bio_alloc(gfp_flags, nr_vecs);
 107
 108         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
 109                 while (!bio && (nr_vecs /= 2))
 110                         bio = bio_alloc(gfp_flags, nr_vecs);
 111         }
 112
 113         if (bio) {
 114                 bio->bi_bdev = bdev;
 115                 bio->bi_sector = first_sector;
 116         }
 117         return bio;
 118 }
 119
 120 /*
 121  * support function for mpage_readpages.  The fs supplied get_block might
 122  * return an up to date buffer.  This is used to map that buffer into
 123  * the page, which allows readpage to avoid triggering a duplicate call
 124  * to get_block.
 125  *
 126  * The idea is to avoid adding buffers to pages that don't already have
 127  * them.  So when the buffer is up to date and the page size == block size,
 128  * this marks the page up to date instead of adding new buffers.
 129  */
 130 static void
 131 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
 132 {
 133         struct inode *inode = page->mapping->host;
 134         struct buffer_head *page_bh, *head;
 135         int block = 0;
 136
 137         if (!page_has_buffers(page)) {
 138                 /*
 139                  * don't make any buffers if there is only one buffer on
 140                  * the page and the page just needs to be set up to date
 141                  */
 142                 if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
 143                     buffer_uptodate(bh)) {
 144                         SetPageUptodate(page);
 145                         return;
 146                 }
 147                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 148         }
 149         head = page_buffers(page);
 150         page_bh = head;
 151         do {
 152                 if (block == page_block) {
 153                         page_bh->b_state = bh->b_state;
 154                         page_bh->b_bdev = bh->b_bdev;
 155                         page_bh->b_blocknr = bh->b_blocknr;
 156                         break;
 157                 }
 158                 page_bh = page_bh->b_this_page;
 159                 block++;
 160         } while (page_bh != head);
 161 }
 162
 163 static struct bio *
 164 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 165                         sector_t *last_block_in_bio, get_block_t get_block)
 166 {
 167         struct inode *inode = page->mapping->host;
 168         const unsigned blkbits = inode->i_blkbits;
 169         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 170         const unsigned blocksize = 1 << blkbits;
 171         sector_t block_in_file;
 172         sector_t last_block;
 173         sector_t blocks[MAX_BUF_PER_PAGE];
 174         unsigned page_block;
 175         unsigned first_hole = blocks_per_page;
 176         struct block_device *bdev = NULL;
 177         struct buffer_head bh;
 178         int length;
 179         int fully_mapped = 1;
 180
 181         if (page_has_buffers(page))
 182                 goto confused;
 183
 184         block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
 185         last_block = (i_size_read(inode) + blocksize - 1) >> blkbits;
 186
 187         bh.b_page = page;
 188         for (page_block = 0; page_block < blocks_per_page;
 189                                 page_block++, block_in_file++) {
 190                 bh.b_state = 0;
 191                 if (block_in_file < last_block) {
 192                         if (get_block(inode, block_in_file, &bh, 0))
 193                                 goto confused;
 194                 }
 195
 196                 if (!buffer_mapped(&bh)) {
 197                         fully_mapped = 0;
 198                         if (first_hole == blocks_per_page)
 199                                 first_hole = page_block;
 200                         continue;
 201                 }
 202
 203                 /* some filesystems will copy data into the page during
 204                  * the get_block call, in which case we don't want to
 205                  * read it again.  map_buffer_to_page copies the data
 206                  * we just collected from get_block into the page's buffers
 207                  * so readpage doesn't have to repeat the get_block call
 208                  */
 209                 if (buffer_uptodate(&bh)) {
 210                         map_buffer_to_page(page, &bh, page_block);
 211                         goto confused;
 212                 }
 213
 214                 if (first_hole != blocks_per_page)
 215                         goto confused;          /* hole -> non-hole */
 216
 217                 /* Contiguous blocks? */
 218                 if (page_block && blocks[page_block-1] != bh.b_blocknr-1)
 219                         goto confused;
 220                 blocks[page_block] = bh.b_blocknr;
 221                 bdev = bh.b_bdev;
 222         }
 223
 224         if (first_hole != blocks_per_page) {
 225                 char *kaddr = kmap_atomic(page, KM_USER0);
 226                 memset(kaddr + (first_hole << blkbits), 0,
 227                                 PAGE_CACHE_SIZE - (first_hole << blkbits));
 228                 flush_dcache_page(page);
 229                 kunmap_atomic(kaddr, KM_USER0);
 230                 if (first_hole == 0) {
 231                         SetPageUptodate(page);
 232                         unlock_page(page);
 233                         goto out;
 234                 }
 235         } else if (fully_mapped) {
 236                 SetPageMappedToDisk(page);
 237         }
 238
 239         /*
 240          * This page will go to BIO.  Do we need to send this BIO off first?
 241          */
 242         if (bio && (*last_block_in_bio != blocks[0] - 1))
 243                 bio = mpage_bio_submit(READ, bio);
 244
 245 alloc_new:
 246         if (bio == NULL) {
 247                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 248                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
 249                                 GFP_KERNEL);
 250                 if (bio == NULL)
 251                         goto confused;
 252         }
 253
 254         length = first_hole << blkbits;
 255         if (bio_add_page(bio, page, length, 0) < length) {
 256                 bio = mpage_bio_submit(READ, bio);
 257                 goto alloc_new;
 258         }
 259
 260         if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
 261                 bio = mpage_bio_submit(READ, bio);
 262         else
 263                 *last_block_in_bio = blocks[blocks_per_page - 1];
 264 out:
 265         return bio;
 266
 267 confused:
 268         if (bio)
 269                 bio = mpage_bio_submit(READ, bio);
 270         if (!PageUptodate(page))
 271                 block_read_full_page(page, get_block);
 272         else
 273                 unlock_page(page);
 274         goto out;
 275 }
 276
 277 /**
 278  * mpage_readpages - populate an address space with some pages, and
 279  *                       start reads against them.
 280  *
 281  * @mapping: the address_space
 282  * @pages: The address of a list_head which contains the target pages.  These
 283  *   pages have their ->index populated and are otherwise uninitialised.
 284  *
 285  *   The page at @pages->prev has the lowest file offset, and reads should be
 286  *   issued in @pages->prev to @pages->next order.
 287  *
 288  * @nr_pages: The number of pages at *@pages
 289  * @get_block: The filesystem's block mapper function.
 290  *
 291  * This function walks the pages and the blocks within each page, building and
 292  * emitting large BIOs.
 293  *
 294  * If anything unusual happens, such as:
 295  *
 296  * - encountering a page which has buffers
 297  * - encountering a page which has a non-hole after a hole
 298  * - encountering a page with non-contiguous blocks
 299  *
 300  * then this code just gives up and calls the buffer_head-based read function.
 301  * It does handle a page which has holes at the end - that is a common case:
 302  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
 303  *
 304  * BH_Boundary explanation:
 305  *
 306  * There is a problem.  The mpage read code assembles several pages, gets all
 307  * their disk mappings, and then submits them all.  That's fine, but obtaining
 308  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 309  *
 310  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 311  * submitted in the following order:
 312  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 313  * because the indirect block has to be read to get the mappings of blocks
 314  * 13,14,15,16.  Obviously, this impacts performance.
 315  *
 316  * So what we do it to allow the filesystem's get_block() function to set
 317  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 318  * after this one will require I/O against a block which is probably close to
 319  * this one.  So you should push what I/O you have currently accumulated.
 320  *
 321  * This all causes the disk requests to be issued in the correct order.
 322  */
 323 int
 324 mpage_readpages(struct address_space *mapping, struct list_head *pages,
 325                                 unsigned nr_pages, get_block_t get_block)
 326 {
 327         struct bio *bio = NULL;
 328         unsigned page_idx;
 329         sector_t last_block_in_bio = 0;
 330         struct pagevec lru_pvec;
 331
 332         pagevec_init(&lru_pvec, 0);
 333         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 334                 struct page *page = list_entry(pages->prev, struct page, lru);
 335
 336                 prefetchw(&page->flags);
 337                 list_del(&page->lru);
 338                 if (!add_to_page_cache(page, mapping,
 339                                         page->index, GFP_KERNEL)) {
 340                         bio = do_mpage_readpage(bio, page,
 341                                         nr_pages - page_idx,
 342                                         &last_block_in_bio, get_block);
 343                         if (!pagevec_add(&lru_pvec, page))
 344                                 __pagevec_lru_add(&lru_pvec);
 345                 } else {
 346                         page_cache_release(page);
 347                 }
 348         }
 349         pagevec_lru_add(&lru_pvec);
 350         BUG_ON(!list_empty(pages));
 351         if (bio)
 352                 mpage_bio_submit(READ, bio);
 353         return 0;
 354 }
 355 EXPORT_SYMBOL(mpage_readpages);
 356
 357 /*
 358  * This isn't called much at all
 359  */
 360 int mpage_readpage(struct page *page, get_block_t get_block)
 361 {
 362         struct bio *bio = NULL;
 363         sector_t last_block_in_bio = 0;
 364
 365         bio = do_mpage_readpage(bio, page, 1,
 366                         &last_block_in_bio, get_block);
 367         if (bio)
 368                 mpage_bio_submit(READ, bio);
 369         return 0;
 370 }
 371 EXPORT_SYMBOL(mpage_readpage);
 372
 373 /*
 374  * Writing is not so simple.
 375  *
 376  * If the page has buffers then they will be used for obtaining the disk
 377  * mapping.  We only support pages which are fully mapped-and-dirty, with a
 378  * special case for pages which are unmapped at the end: end-of-file.
 379  *
 380  * If the page has no buffers (preferred) then the page is mapped here.
 381  *
 382  * If all blocks are found to be contiguous then the page can go into the
 383  * BIO.  Otherwise fall back to the mapping's writepage().
 384  *
 385  * FIXME: This code wants an estimate of how many pages are still to be
 386  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 387  * just allocate full-size (16-page) BIOs.
 388  */
 389 static struct bio *
 390 __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 391         sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
 392         writepage_t writepage_fn)
 393 {
 394         struct address_space *mapping = page->mapping;
 395         struct inode *inode = page->mapping->host;
 396         const unsigned blkbits = inode->i_blkbits;
 397         unsigned long end_index;
 398         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 399         sector_t last_block;
 400         sector_t block_in_file;
 401         sector_t blocks[MAX_BUF_PER_PAGE];
 402         unsigned page_block;
 403         unsigned first_unmapped = blocks_per_page;
 404         struct block_device *bdev = NULL;
 405         int boundary = 0;
 406         sector_t boundary_block = 0;
 407         struct block_device *boundary_bdev = NULL;
 408         int length;
 409         struct buffer_head map_bh;
 410         loff_t i_size = i_size_read(inode);
 411
 412         if (page_has_buffers(page)) {
 413                 struct buffer_head *head = page_buffers(page);
 414                 struct buffer_head *bh = head;
 415
 416                 /* If they're all mapped and dirty, do it */
 417                 page_block = 0;
 418                 do {
 419                         BUG_ON(buffer_locked(bh));
 420                         if (!buffer_mapped(bh)) {
 421                                 /*
 422                                  * unmapped dirty buffers are created by
 423                                  * __set_page_dirty_buffers -> mmapped data
 424                                  */
 425                                 if (buffer_dirty(bh))
 426                                         goto confused;
 427                                 if (first_unmapped == blocks_per_page)
 428                                         first_unmapped = page_block;
 429                                 continue;
 430                         }
 431
 432                         if (first_unmapped != blocks_per_page)
 433                                 goto confused;  /* hole -> non-hole */
 434
 435                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 436                                 goto confused;
 437                         if (page_block) {
 438                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
 439                                         goto confused;
 440                         }
 441                         blocks[page_block++] = bh->b_blocknr;
 442                         boundary = buffer_boundary(bh);
 443                         if (boundary) {
 444                                 boundary_block = bh->b_blocknr;
 445                                 boundary_bdev = bh->b_bdev;
 446                         }
 447                         bdev = bh->b_bdev;
 448                 } while ((bh = bh->b_this_page) != head);
 449
 450                 if (first_unmapped)
 451                         goto page_is_mapped;
 452
 453                 /*
 454                  * Page has buffers, but they are all unmapped. The page was
 455                  * created by pagein or read over a hole which was handled by
 456                  * block_read_full_page().  If this address_space is also
 457                  * using mpage_readpages then this can rarely happen.
 458                  */
 459                 goto confused;
 460         }
 461
 462         /*
 463          * The page has no buffers: map it to disk
 464          */
 465         BUG_ON(!PageUptodate(page));
 466         block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
 467         last_block = (i_size - 1) >> blkbits;
 468         map_bh.b_page = page;
 469         for (page_block = 0; page_block < blocks_per_page; ) {
 470
 471                 map_bh.b_state = 0;
 472                 if (get_block(inode, block_in_file, &map_bh, 1))
 473                         goto confused;
 474                 if (buffer_new(&map_bh))
 475                         unmap_underlying_metadata(map_bh.b_bdev,
 476                                                 map_bh.b_blocknr);
 477                 if (buffer_boundary(&map_bh)) {
 478                         boundary_block = map_bh.b_blocknr;
 479                         boundary_bdev = map_bh.b_bdev;
 480                 }
 481                 if (page_block) {
 482                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 483                                 goto confused;
 484                 }
 485                 blocks[page_block++] = map_bh.b_blocknr;
 486                 boundary = buffer_boundary(&map_bh);
 487                 bdev = map_bh.b_bdev;
 488                 if (block_in_file == last_block)
 489                         break;
 490                 block_in_file++;
 491         }
 492         BUG_ON(page_block == 0);
 493
 494         first_unmapped = page_block;
 495
 496 page_is_mapped:
 497         end_index = i_size >> PAGE_CACHE_SHIFT;
 498         if (page->index >= end_index) {
 499                 /*
 500                  * The page straddles i_size.  It must be zeroed out on each
 501                  * and every writepage invokation because it may be mmapped.
 502                  * "A file is mapped in multiples of the page size.  For a file
 503                  * that is not a multiple of the page size, the remaining memory
 504                  * is zeroed when mapped, and writes to that region are not
 505                  * written out to the file."
 506                  */
 507                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
 508                 char *kaddr;
 509
 510                 if (page->index > end_index || !offset)
 511                         goto confused;
 512                 kaddr = kmap_atomic(page, KM_USER0);
 513                 memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
 514                 flush_dcache_page(page);
 515                 kunmap_atomic(kaddr, KM_USER0);
 516         }
 517
 518         /*
 519          * This page will go to BIO.  Do we need to send this BIO off first?
 520          */
 521         if (bio && *last_block_in_bio != blocks[0] - 1)
 522                 bio = mpage_bio_submit(WRITE, bio);
 523
 524 alloc_new:
 525         if (bio == NULL) {
 526                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 527                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
 528                 if (bio == NULL)
 529                         goto confused;
 530         }
 531
 532         /*
 533          * Must try to add the page before marking the buffer clean or
 534          * the confused fail path above (OOM) will be very confused when
 535          * it finds all bh marked clean (i.e. it will not write anything)
 536          */
 537         length = first_unmapped << blkbits;
 538         if (bio_add_page(bio, page, length, 0) < length) {
 539                 bio = mpage_bio_submit(WRITE, bio);
 540                 goto alloc_new;
 541         }
 542
 543         /*
 544          * OK, we have our BIO, so we can now mark the buffers clean.  Make
 545          * sure to only clean buffers which we know we'll be writing.
 546          */
 547         if (page_has_buffers(page)) {
 548                 struct buffer_head *head = page_buffers(page);
 549                 struct buffer_head *bh = head;
 550                 unsigned buffer_counter = 0;
 551
 552                 do {
 553                         if (buffer_counter++ == first_unmapped)
 554                                 break;
 555                         clear_buffer_dirty(bh);
 556                         bh = bh->b_this_page;
 557                 } while (bh != head);
 558
 559                 /*
 560                  * we cannot drop the bh if the page is not uptodate
 561                  * or a concurrent readpage would fail to serialize with the bh
 562                  * and it would read from disk before we reach the platter.
 563                  */
 564                 if (buffer_heads_over_limit && PageUptodate(page))
 565                         try_to_free_buffers(page);
 566         }
 567
 568         BUG_ON(PageWriteback(page));
 569         set_page_writeback(page);
 570         unlock_page(page);
 571         if (boundary || (first_unmapped != blocks_per_page)) {
 572                 bio = mpage_bio_submit(WRITE, bio);
 573                 if (boundary_block) {
 574                         write_boundary_block(boundary_bdev,
 575                                         boundary_block, 1 << blkbits);
 576                 }
 577         } else {
 578                 *last_block_in_bio = blocks[blocks_per_page - 1];
 579         }
 580         goto out;
 581
 582 confused:
 583         if (bio)
 584                 bio = mpage_bio_submit(WRITE, bio);
 585
 586         if (writepage_fn) {
 587                 *ret = (*writepage_fn)(page, wbc);
 588         } else {
 589                 *ret = -EAGAIN;
 590                 goto out;
 591         }
 592         /*
 593          * The caller has a ref on the inode, so *mapping is stable
 594          */
 595         if (*ret) {
 596                 if (*ret == -ENOSPC)
 597                         set_bit(AS_ENOSPC, &mapping->flags);
 598                 else
 599                         set_bit(AS_EIO, &mapping->flags);
 600         }
 601 out:
 602         return bio;
 603 }
 604
 605 /**
 606  * mpage_writepages - walk the list of dirty pages of the given
 607  * address space and writepage() all of them.
 608  *
 609  * @mapping: address space structure to write
 610  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 611  * @get_block: the filesystem's block mapper function.
 612  *             If this is NULL then use a_ops->writepage.  Otherwise, go
 613  *             direct-to-BIO.
 614  *
 615  * This is a library function, which implements the writepages()
 616  * address_space_operation.
 617  *
 618  * If a page is already under I/O, generic_writepages() skips it, even
 619  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 620  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 621  * and msync() need to guarantee that all the data which was dirty at the time
 622  * the call was made get new I/O started against them.  If wbc->sync_mode is
 623  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 624  * existing IO to complete.
 625  */
 626 int
 627 mpage_writepages(struct address_space *mapping,
 628                 struct writeback_control *wbc, get_block_t get_block)
 629 {
 630         struct backing_dev_info *bdi = mapping->backing_dev_info;
 631         struct bio *bio = NULL;
 632         sector_t last_block_in_bio = 0;
 633         int ret = 0;
 634         int done = 0;
 635         int (*writepage)(struct page *page, struct writeback_control *wbc);
 636         struct pagevec pvec;
 637         int nr_pages;
 638         pgoff_t index;
 639         pgoff_t end = -1;               /* Inclusive */
 640         int scanned = 0;
 641         int is_range = 0;
 642
 643         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 644                 wbc->encountered_congestion = 1;
 645                 return 0;
 646         }
 647
 648         writepage = NULL;
 649         if (get_block == NULL)
 650                 writepage = mapping->a_ops->writepage;
 651
 652         pagevec_init(&pvec, 0);
 653         if (wbc->sync_mode == WB_SYNC_NONE) {
 654                 index = mapping->writeback_index; /* Start from prev offset */
 655         } else {
 656                 index = 0;                        /* whole-file sweep */
 657                 scanned = 1;
 658         }
 659         if (wbc->start || wbc->end) {
 660                 index = wbc->start >> PAGE_CACHE_SHIFT;
 661                 end = wbc->end >> PAGE_CACHE_SHIFT;
 662                 is_range = 1;
 663                 scanned = 1;
 664         }
 665 retry:
 666         while (!done && (index <= end) &&
 667                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 668                         PAGECACHE_TAG_DIRTY,
 669                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
 670                 unsigned i;
 671
 672                 scanned = 1;
 673                 for (i = 0; i < nr_pages; i++) {
 674                         struct page *page = pvec.pages[i];
 675
 676                         /*
 677                          * At this point we hold neither mapping->tree_lock nor
 678                          * lock on the page itself: the page may be truncated or
 679                          * invalidated (changing page->mapping to NULL), or even
 680                          * swizzled back from swapper_space to tmpfs file
 681                          * mapping
 682                          */
 683
 684                         lock_page(page);
 685
 686                         if (unlikely(page->mapping != mapping)) {
 687                                 unlock_page(page);
 688                                 continue;
 689                         }
 690
 691                         if (unlikely(is_range) && page->index > end) {
 692                                 done = 1;
 693                                 unlock_page(page);
 694                                 continue;
 695                         }
 696
 697                         if (wbc->sync_mode != WB_SYNC_NONE)
 698                                 wait_on_page_writeback(page);
 699
 700                         if (PageWriteback(page) ||
 701                                         !clear_page_dirty_for_io(page)) {
 702                                 unlock_page(page);
 703                                 continue;
 704                         }
 705
 706                         if (writepage) {
 707                                 ret = (*writepage)(page, wbc);
 708                                 if (ret) {
 709                                         if (ret == -ENOSPC)
 710                                                 set_bit(AS_ENOSPC,
 711                                                         &mapping->flags);
 712                                         else
 713                                                 set_bit(AS_EIO,
 714                                                         &mapping->flags);
 715                                 }
 716                         } else {
 717                                 bio = __mpage_writepage(bio, page, get_block,
 718                                                 &last_block_in_bio, &ret, wbc,
 719                                                 page->mapping->a_ops->writepage);
 720                         }
 721                         if (unlikely(ret == WRITEPAGE_ACTIVATE))
 722                                 unlock_page(page);
 723                         if (ret || (--(wbc->nr_to_write) <= 0))
 724                                 done = 1;
 725                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 726                                 wbc->encountered_congestion = 1;
 727                                 done = 1;
 728                         }
 729                 }
 730                 pagevec_release(&pvec);
 731                 cond_resched();
 732         }
 733         if (!scanned && !done) {
 734                 /*
 735                  * We hit the last page and there is more work to be done: wrap
 736                  * back to the start of the file
 737                  */
 738                 scanned = 1;
 739                 index = 0;
 740                 goto retry;
 741         }
 742         if (!is_range)
 743                 mapping->writeback_index = index;
 744         if (bio)
 745                 mpage_bio_submit(WRITE, bio);
 746         return ret;
 747 }
 748 EXPORT_SYMBOL(mpage_writepages);
 749
 750 int mpage_writepage(struct page *page, get_block_t get_block,
 751         struct writeback_control *wbc)
 752 {
 753         int ret = 0;
 754         struct bio *bio;
 755         sector_t last_block_in_bio = 0;
 756
 757         bio = __mpage_writepage(NULL, page, get_block,
 758                         &last_block_in_bio, &ret, wbc, NULL);
 759         if (bio)
 760                 mpage_bio_submit(WRITE, bio);
 761
 762         return ret;
 763 }
 764 EXPORT_SYMBOL(mpage_writepage);