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