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                         if (page->mapping)
  85                                 set_bit(AS_EIO, &page->mapping->flags);
  86                 }
  87                 end_page_writeback(page);
  88         } while (bvec >= bio->bi_io_vec);
  89         bio_put(bio);
  90         return 0;
  91 }
  92
  93 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
  94 {
  95         bio->bi_end_io = mpage_end_io_read;
  96         if (rw == WRITE)
  97                 bio->bi_end_io = mpage_end_io_write;
  98         submit_bio(rw, bio);
  99         return NULL;
 100 }
 101
 102 static struct bio *
 103 mpage_alloc(struct block_device *bdev,
 104                 sector_t first_sector, int nr_vecs,
 105                 unsigned int __nocast gfp_flags)
 106 {
 107         struct bio *bio;
 108
 109         bio = bio_alloc(gfp_flags, nr_vecs);
 110
 111         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
 112                 while (!bio && (nr_vecs /= 2))
 113                         bio = bio_alloc(gfp_flags, nr_vecs);
 114         }
 115
 116         if (bio) {
 117                 bio->bi_bdev = bdev;
 118                 bio->bi_sector = first_sector;
 119         }
 120         return bio;
 121 }
 122
 123 /*
 124  * support function for mpage_readpages.  The fs supplied get_block might
 125  * return an up to date buffer.  This is used to map that buffer into
 126  * the page, which allows readpage to avoid triggering a duplicate call
 127  * to get_block.
 128  *
 129  * The idea is to avoid adding buffers to pages that don't already have
 130  * them.  So when the buffer is up to date and the page size == block size,
 131  * this marks the page up to date instead of adding new buffers.
 132  */
 133 static void
 134 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
 135 {
 136         struct inode *inode = page->mapping->host;
 137         struct buffer_head *page_bh, *head;
 138         int block = 0;
 139
 140         if (!page_has_buffers(page)) {
 141                 /*
 142                  * don't make any buffers if there is only one buffer on
 143                  * the page and the page just needs to be set up to date
 144                  */
 145                 if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
 146                     buffer_uptodate(bh)) {
 147                         SetPageUptodate(page);
 148                         return;
 149                 }
 150                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 151         }
 152         head = page_buffers(page);
 153         page_bh = head;
 154         do {
 155                 if (block == page_block) {
 156                         page_bh->b_state = bh->b_state;
 157                         page_bh->b_bdev = bh->b_bdev;
 158                         page_bh->b_blocknr = bh->b_blocknr;
 159                         break;
 160                 }
 161                 page_bh = page_bh->b_this_page;
 162                 block++;
 163         } while (page_bh != head);
 164 }
 165
 166 static struct bio *
 167 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 168                         sector_t *last_block_in_bio, get_block_t get_block)
 169 {
 170         struct inode *inode = page->mapping->host;
 171         const unsigned blkbits = inode->i_blkbits;
 172         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 173         const unsigned blocksize = 1 << blkbits;
 174         sector_t block_in_file;
 175         sector_t last_block;
 176         sector_t blocks[MAX_BUF_PER_PAGE];
 177         unsigned page_block;
 178         unsigned first_hole = blocks_per_page;
 179         struct block_device *bdev = NULL;
 180         struct buffer_head bh;
 181         int length;
 182         int fully_mapped = 1;
 183
 184         if (page_has_buffers(page))
 185                 goto confused;
 186
 187         block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
 188         last_block = (i_size_read(inode) + blocksize - 1) >> blkbits;
 189
 190         bh.b_page = page;
 191         for (page_block = 0; page_block < blocks_per_page;
 192                                 page_block++, block_in_file++) {
 193                 bh.b_state = 0;
 194                 if (block_in_file < last_block) {
 195                         if (get_block(inode, block_in_file, &bh, 0))
 196                                 goto confused;
 197                 }
 198
 199                 if (!buffer_mapped(&bh)) {
 200                         fully_mapped = 0;
 201                         if (first_hole == blocks_per_page)
 202                                 first_hole = page_block;
 203                         continue;
 204                 }
 205
 206                 /* some filesystems will copy data into the page during
 207                  * the get_block call, in which case we don't want to
 208                  * read it again.  map_buffer_to_page copies the data
 209                  * we just collected from get_block into the page's buffers
 210                  * so readpage doesn't have to repeat the get_block call
 211                  */
 212                 if (buffer_uptodate(&bh)) {
 213                         map_buffer_to_page(page, &bh, page_block);
 214                         goto confused;
 215                 }
 216
 217                 if (first_hole != blocks_per_page)
 218                         goto confused;          /* hole -> non-hole */
 219
 220                 /* Contiguous blocks? */
 221                 if (page_block && blocks[page_block-1] != bh.b_blocknr-1)
 222                         goto confused;
 223                 blocks[page_block] = bh.b_blocknr;
 224                 bdev = bh.b_bdev;
 225         }
 226
 227         if (first_hole != blocks_per_page) {
 228                 char *kaddr = kmap_atomic(page, KM_USER0);
 229                 memset(kaddr + (first_hole << blkbits), 0,
 230                                 PAGE_CACHE_SIZE - (first_hole << blkbits));
 231                 flush_dcache_page(page);
 232                 kunmap_atomic(kaddr, KM_USER0);
 233                 if (first_hole == 0) {
 234                         SetPageUptodate(page);
 235                         unlock_page(page);
 236                         goto out;
 237                 }
 238         } else if (fully_mapped) {
 239                 SetPageMappedToDisk(page);
 240         }
 241
 242         /*
 243          * This page will go to BIO.  Do we need to send this BIO off first?
 244          */
 245         if (bio && (*last_block_in_bio != blocks[0] - 1))
 246                 bio = mpage_bio_submit(READ, bio);
 247
 248 alloc_new:
 249         if (bio == NULL) {
 250                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 251                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
 252                                 GFP_KERNEL);
 253                 if (bio == NULL)
 254                         goto confused;
 255         }
 256
 257         length = first_hole << blkbits;
 258         if (bio_add_page(bio, page, length, 0) < length) {
 259                 bio = mpage_bio_submit(READ, bio);
 260                 goto alloc_new;
 261         }
 262
 263         if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
 264                 bio = mpage_bio_submit(READ, bio);
 265         else
 266                 *last_block_in_bio = blocks[blocks_per_page - 1];
 267 out:
 268         return bio;
 269
 270 confused:
 271         if (bio)
 272                 bio = mpage_bio_submit(READ, bio);
 273         if (!PageUptodate(page))
 274                 block_read_full_page(page, get_block);
 275         else
 276                 unlock_page(page);
 277         goto out;
 278 }
 279
 280 /**
 281  * mpage_readpages - populate an address space with some pages, and
 282  *                       start reads against them.
 283  *
 284  * @mapping: the address_space
 285  * @pages: The address of a list_head which contains the target pages.  These
 286  *   pages have their ->index populated and are otherwise uninitialised.
 287  *
 288  *   The page at @pages->prev has the lowest file offset, and reads should be
 289  *   issued in @pages->prev to @pages->next order.
 290  *
 291  * @nr_pages: The number of pages at *@pages
 292  * @get_block: The filesystem's block mapper function.
 293  *
 294  * This function walks the pages and the blocks within each page, building and
 295  * emitting large BIOs.
 296  *
 297  * If anything unusual happens, such as:
 298  *
 299  * - encountering a page which has buffers
 300  * - encountering a page which has a non-hole after a hole
 301  * - encountering a page with non-contiguous blocks
 302  *
 303  * then this code just gives up and calls the buffer_head-based read function.
 304  * It does handle a page which has holes at the end - that is a common case:
 305  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
 306  *
 307  * BH_Boundary explanation:
 308  *
 309  * There is a problem.  The mpage read code assembles several pages, gets all
 310  * their disk mappings, and then submits them all.  That's fine, but obtaining
 311  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 312  *
 313  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 314  * submitted in the following order:
 315  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 316  * because the indirect block has to be read to get the mappings of blocks
 317  * 13,14,15,16.  Obviously, this impacts performance.
 318  *
 319  * So what we do it to allow the filesystem's get_block() function to set
 320  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 321  * after this one will require I/O against a block which is probably close to
 322  * this one.  So you should push what I/O you have currently accumulated.
 323  *
 324  * This all causes the disk requests to be issued in the correct order.
 325  */
 326 int
 327 mpage_readpages(struct address_space *mapping, struct list_head *pages,
 328                                 unsigned nr_pages, get_block_t get_block)
 329 {
 330         struct bio *bio = NULL;
 331         unsigned page_idx;
 332         sector_t last_block_in_bio = 0;
 333         struct pagevec lru_pvec;
 334
 335         pagevec_init(&lru_pvec, 0);
 336         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 337                 struct page *page = list_entry(pages->prev, struct page, lru);
 338
 339                 prefetchw(&page->flags);
 340                 list_del(&page->lru);
 341                 if (!add_to_page_cache(page, mapping,
 342                                         page->index, GFP_KERNEL)) {
 343                         bio = do_mpage_readpage(bio, page,
 344                                         nr_pages - page_idx,
 345                                         &last_block_in_bio, get_block);
 346                         if (!pagevec_add(&lru_pvec, page))
 347                                 __pagevec_lru_add(&lru_pvec);
 348                 } else {
 349                         page_cache_release(page);
 350                 }
 351         }
 352         pagevec_lru_add(&lru_pvec);
 353         BUG_ON(!list_empty(pages));
 354         if (bio)
 355                 mpage_bio_submit(READ, bio);
 356         return 0;
 357 }
 358 EXPORT_SYMBOL(mpage_readpages);
 359
 360 /*
 361  * This isn't called much at all
 362  */
 363 int mpage_readpage(struct page *page, get_block_t get_block)
 364 {
 365         struct bio *bio = NULL;
 366         sector_t last_block_in_bio = 0;
 367
 368         bio = do_mpage_readpage(bio, page, 1,
 369                         &last_block_in_bio, get_block);
 370         if (bio)
 371                 mpage_bio_submit(READ, bio);
 372         return 0;
 373 }
 374 EXPORT_SYMBOL(mpage_readpage);
 375
 376 /*
 377  * Writing is not so simple.
 378  *
 379  * If the page has buffers then they will be used for obtaining the disk
 380  * mapping.  We only support pages which are fully mapped-and-dirty, with a
 381  * special case for pages which are unmapped at the end: end-of-file.
 382  *
 383  * If the page has no buffers (preferred) then the page is mapped here.
 384  *
 385  * If all blocks are found to be contiguous then the page can go into the
 386  * BIO.  Otherwise fall back to the mapping's writepage().
 387  *
 388  * FIXME: This code wants an estimate of how many pages are still to be
 389  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 390  * just allocate full-size (16-page) BIOs.
 391  */
 392 static struct bio *
 393 __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 394         sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
 395         writepage_t writepage_fn)
 396 {
 397         struct address_space *mapping = page->mapping;
 398         struct inode *inode = page->mapping->host;
 399         const unsigned blkbits = inode->i_blkbits;
 400         unsigned long end_index;
 401         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 402         sector_t last_block;
 403         sector_t block_in_file;
 404         sector_t blocks[MAX_BUF_PER_PAGE];
 405         unsigned page_block;
 406         unsigned first_unmapped = blocks_per_page;
 407         struct block_device *bdev = NULL;
 408         int boundary = 0;
 409         sector_t boundary_block = 0;
 410         struct block_device *boundary_bdev = NULL;
 411         int length;
 412         struct buffer_head map_bh;
 413         loff_t i_size = i_size_read(inode);
 414
 415         if (page_has_buffers(page)) {
 416                 struct buffer_head *head = page_buffers(page);
 417                 struct buffer_head *bh = head;
 418
 419                 /* If they're all mapped and dirty, do it */
 420                 page_block = 0;
 421                 do {
 422                         BUG_ON(buffer_locked(bh));
 423                         if (!buffer_mapped(bh)) {
 424                                 /*
 425                                  * unmapped dirty buffers are created by
 426                                  * __set_page_dirty_buffers -> mmapped data
 427                                  */
 428                                 if (buffer_dirty(bh))
 429                                         goto confused;
 430                                 if (first_unmapped == blocks_per_page)
 431                                         first_unmapped = page_block;
 432                                 continue;
 433                         }
 434
 435                         if (first_unmapped != blocks_per_page)
 436                                 goto confused;  /* hole -> non-hole */
 437
 438                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 439                                 goto confused;
 440                         if (page_block) {
 441                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
 442                                         goto confused;
 443                         }
 444                         blocks[page_block++] = bh->b_blocknr;
 445                         boundary = buffer_boundary(bh);
 446                         if (boundary) {
 447                                 boundary_block = bh->b_blocknr;
 448                                 boundary_bdev = bh->b_bdev;
 449                         }
 450                         bdev = bh->b_bdev;
 451                 } while ((bh = bh->b_this_page) != head);
 452
 453                 if (first_unmapped)
 454                         goto page_is_mapped;
 455
 456                 /*
 457                  * Page has buffers, but they are all unmapped. The page was
 458                  * created by pagein or read over a hole which was handled by
 459                  * block_read_full_page().  If this address_space is also
 460                  * using mpage_readpages then this can rarely happen.
 461                  */
 462                 goto confused;
 463         }
 464
 465         /*
 466          * The page has no buffers: map it to disk
 467          */
 468         BUG_ON(!PageUptodate(page));
 469         block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
 470         last_block = (i_size - 1) >> blkbits;
 471         map_bh.b_page = page;
 472         for (page_block = 0; page_block < blocks_per_page; ) {
 473
 474                 map_bh.b_state = 0;
 475                 if (get_block(inode, block_in_file, &map_bh, 1))
 476                         goto confused;
 477                 if (buffer_new(&map_bh))
 478                         unmap_underlying_metadata(map_bh.b_bdev,
 479                                                 map_bh.b_blocknr);
 480                 if (buffer_boundary(&map_bh)) {
 481                         boundary_block = map_bh.b_blocknr;
 482                         boundary_bdev = map_bh.b_bdev;
 483                 }
 484                 if (page_block) {
 485                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 486                                 goto confused;
 487                 }
 488                 blocks[page_block++] = map_bh.b_blocknr;
 489                 boundary = buffer_boundary(&map_bh);
 490                 bdev = map_bh.b_bdev;
 491                 if (block_in_file == last_block)
 492                         break;
 493                 block_in_file++;
 494         }
 495         BUG_ON(page_block == 0);
 496
 497         first_unmapped = page_block;
 498
 499 page_is_mapped:
 500         end_index = i_size >> PAGE_CACHE_SHIFT;
 501         if (page->index >= end_index) {
 502                 /*
 503                  * The page straddles i_size.  It must be zeroed out on each
 504                  * and every writepage invokation because it may be mmapped.
 505                  * "A file is mapped in multiples of the page size.  For a file
 506                  * that is not a multiple of the page size, the remaining memory
 507                  * is zeroed when mapped, and writes to that region are not
 508                  * written out to the file."
 509                  */
 510                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
 511                 char *kaddr;
 512
 513                 if (page->index > end_index || !offset)
 514                         goto confused;
 515                 kaddr = kmap_atomic(page, KM_USER0);
 516                 memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
 517                 flush_dcache_page(page);
 518                 kunmap_atomic(kaddr, KM_USER0);
 519         }
 520
 521         /*
 522          * This page will go to BIO.  Do we need to send this BIO off first?
 523          */
 524         if (bio && *last_block_in_bio != blocks[0] - 1)
 525                 bio = mpage_bio_submit(WRITE, bio);
 526
 527 alloc_new:
 528         if (bio == NULL) {
 529                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 530                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
 531                 if (bio == NULL)
 532                         goto confused;
 533         }
 534
 535         /*
 536          * Must try to add the page before marking the buffer clean or
 537          * the confused fail path above (OOM) will be very confused when
 538          * it finds all bh marked clean (i.e. it will not write anything)
 539          */
 540         length = first_unmapped << blkbits;
 541         if (bio_add_page(bio, page, length, 0) < length) {
 542                 bio = mpage_bio_submit(WRITE, bio);
 543                 goto alloc_new;
 544         }
 545
 546         /*
 547          * OK, we have our BIO, so we can now mark the buffers clean.  Make
 548          * sure to only clean buffers which we know we'll be writing.
 549          */
 550         if (page_has_buffers(page)) {
 551                 struct buffer_head *head = page_buffers(page);
 552                 struct buffer_head *bh = head;
 553                 unsigned buffer_counter = 0;
 554
 555                 do {
 556                         if (buffer_counter++ == first_unmapped)
 557                                 break;
 558                         clear_buffer_dirty(bh);
 559                         bh = bh->b_this_page;
 560                 } while (bh != head);
 561
 562                 /*
 563                  * we cannot drop the bh if the page is not uptodate
 564                  * or a concurrent readpage would fail to serialize with the bh
 565                  * and it would read from disk before we reach the platter.
 566                  */
 567                 if (buffer_heads_over_limit && PageUptodate(page))
 568                         try_to_free_buffers(page);
 569         }
 570
 571         BUG_ON(PageWriteback(page));
 572         set_page_writeback(page);
 573         unlock_page(page);
 574         if (boundary || (first_unmapped != blocks_per_page)) {
 575                 bio = mpage_bio_submit(WRITE, bio);
 576                 if (boundary_block) {
 577                         write_boundary_block(boundary_bdev,
 578                                         boundary_block, 1 << blkbits);
 579                 }
 580         } else {
 581                 *last_block_in_bio = blocks[blocks_per_page - 1];
 582         }
 583         goto out;
 584
 585 confused:
 586         if (bio)
 587                 bio = mpage_bio_submit(WRITE, bio);
 588
 589         if (writepage_fn) {
 590                 *ret = (*writepage_fn)(page, wbc);
 591         } else {
 592                 *ret = -EAGAIN;
 593                 goto out;
 594         }
 595         /*
 596          * The caller has a ref on the inode, so *mapping is stable
 597          */
 598         if (*ret) {
 599                 if (*ret == -ENOSPC)
 600                         set_bit(AS_ENOSPC, &mapping->flags);
 601                 else
 602                         set_bit(AS_EIO, &mapping->flags);
 603         }
 604 out:
 605         return bio;
 606 }
 607
 608 /**
 609  * mpage_writepages - walk the list of dirty pages of the given
 610  * address space and writepage() all of them.
 611  *
 612  * @mapping: address space structure to write
 613  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 614  * @get_block: the filesystem's block mapper function.
 615  *             If this is NULL then use a_ops->writepage.  Otherwise, go
 616  *             direct-to-BIO.
 617  *
 618  * This is a library function, which implements the writepages()
 619  * address_space_operation.
 620  *
 621  * If a page is already under I/O, generic_writepages() skips it, even
 622  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 623  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 624  * and msync() need to guarantee that all the data which was dirty at the time
 625  * the call was made get new I/O started against them.  If wbc->sync_mode is
 626  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 627  * existing IO to complete.
 628  */
 629 int
 630 mpage_writepages(struct address_space *mapping,
 631                 struct writeback_control *wbc, get_block_t get_block)
 632 {
 633         struct backing_dev_info *bdi = mapping->backing_dev_info;
 634         struct bio *bio = NULL;
 635         sector_t last_block_in_bio = 0;
 636         int ret = 0;
 637         int done = 0;
 638         int (*writepage)(struct page *page, struct writeback_control *wbc);
 639         struct pagevec pvec;
 640         int nr_pages;
 641         pgoff_t index;
 642         pgoff_t end = -1;               /* Inclusive */
 643         int scanned = 0;
 644         int is_range = 0;
 645
 646         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 647                 wbc->encountered_congestion = 1;
 648                 return 0;
 649         }
 650
 651         writepage = NULL;
 652         if (get_block == NULL)
 653                 writepage = mapping->a_ops->writepage;
 654
 655         pagevec_init(&pvec, 0);
 656         if (wbc->sync_mode == WB_SYNC_NONE) {
 657                 index = mapping->writeback_index; /* Start from prev offset */
 658         } else {
 659                 index = 0;                        /* whole-file sweep */
 660                 scanned = 1;
 661         }
 662         if (wbc->start || wbc->end) {
 663                 index = wbc->start >> PAGE_CACHE_SHIFT;
 664                 end = wbc->end >> PAGE_CACHE_SHIFT;
 665                 is_range = 1;
 666                 scanned = 1;
 667         }
 668 retry:
 669         while (!done && (index <= end) &&
 670                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 671                         PAGECACHE_TAG_DIRTY,
 672                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
 673                 unsigned i;
 674
 675                 scanned = 1;
 676                 for (i = 0; i < nr_pages; i++) {
 677                         struct page *page = pvec.pages[i];
 678
 679                         /*
 680                          * At this point we hold neither mapping->tree_lock nor
 681                          * lock on the page itself: the page may be truncated or
 682                          * invalidated (changing page->mapping to NULL), or even
 683                          * swizzled back from swapper_space to tmpfs file
 684                          * mapping
 685                          */
 686
 687                         lock_page(page);
 688
 689                         if (unlikely(page->mapping != mapping)) {
 690                                 unlock_page(page);
 691                                 continue;
 692                         }
 693
 694                         if (unlikely(is_range) && page->index > end) {
 695                                 done = 1;
 696                                 unlock_page(page);
 697                                 continue;
 698                         }
 699
 700                         if (wbc->sync_mode != WB_SYNC_NONE)
 701                                 wait_on_page_writeback(page);
 702
 703                         if (PageWriteback(page) ||
 704                                         !clear_page_dirty_for_io(page)) {
 705                                 unlock_page(page);
 706                                 continue;
 707                         }
 708
 709                         if (writepage) {
 710                                 ret = (*writepage)(page, wbc);
 711                                 if (ret) {
 712                                         if (ret == -ENOSPC)
 713                                                 set_bit(AS_ENOSPC,
 714                                                         &mapping->flags);
 715                                         else
 716                                                 set_bit(AS_EIO,
 717                                                         &mapping->flags);
 718                                 }
 719                         } else {
 720                                 bio = __mpage_writepage(bio, page, get_block,
 721                                                 &last_block_in_bio, &ret, wbc,
 722                                                 page->mapping->a_ops->writepage);
 723                         }
 724                         if (unlikely(ret == WRITEPAGE_ACTIVATE))
 725                                 unlock_page(page);
 726                         if (ret || (--(wbc->nr_to_write) <= 0))
 727                                 done = 1;
 728                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 729                                 wbc->encountered_congestion = 1;
 730                                 done = 1;
 731                         }
 732                 }
 733                 pagevec_release(&pvec);
 734                 cond_resched();
 735         }
 736         if (!scanned && !done) {
 737                 /*
 738                  * We hit the last page and there is more work to be done: wrap
 739                  * back to the start of the file
 740                  */
 741                 scanned = 1;
 742                 index = 0;
 743                 goto retry;
 744         }
 745         if (!is_range)
 746                 mapping->writeback_index = index;
 747         if (bio)
 748                 mpage_bio_submit(WRITE, bio);
 749         return ret;
 750 }
 751 EXPORT_SYMBOL(mpage_writepages);
 752
 753 int mpage_writepage(struct page *page, get_block_t get_block,
 754         struct writeback_control *wbc)
 755 {
 756         int ret = 0;
 757         struct bio *bio;
 758         sector_t last_block_in_bio = 0;
 759
 760         bio = __mpage_writepage(NULL, page, get_block,
 761                         &last_block_in_bio, &ret, wbc, NULL);
 762         if (bio)
 763                 mpage_bio_submit(WRITE, bio);
 764
 765         return ret;
 766 }
 767 EXPORT_SYMBOL(mpage_writepage);