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                         char *path, pathbuf[MAX_TRACE_PATHBUF_LEN];
  83
  84                         path = android_fstrace_get_pathname(pathbuf,
  85                                                     MAX_TRACE_PATHBUF_LEN,
  86                                                     first_page->mapping->host);
  87                         trace_android_fs_dataread_start(
  88                                 first_page->mapping->host,
  89                                 page_offset(first_page),
  90                                 bio->bi_iter.bi_size,
  91                                 current->pid,
  92                                 path,
  93                                 current->comm);
  94                 }
  95         }
  96         bio->bi_end_io = mpage_end_io;
  97         guard_bio_eod(rw, bio);
  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                 gfp_t 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_iter.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, i_blocksize(inode), 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 /*
 167  * This is the worker routine which does all the work of mapping the disk
 168  * blocks and constructs largest possible bios, submits them for IO if the
 169  * blocks are not contiguous on the disk.
 170  *
 171  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 172  * represent the validity of its disk mapping and to decide when to do the next
 173  * get_block() call.
 174  */
 175 static struct bio *
 176 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 177                 sector_t *last_block_in_bio, struct buffer_head *map_bh,
 178                 unsigned long *first_logical_block, get_block_t get_block,
 179                 gfp_t gfp)
 180 {
 181         struct inode *inode = page->mapping->host;
 182         const unsigned blkbits = inode->i_blkbits;
 183         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 184         const unsigned blocksize = 1 << blkbits;
 185         sector_t block_in_file;
 186         sector_t last_block;
 187         sector_t last_block_in_file;
 188         sector_t blocks[MAX_BUF_PER_PAGE];
 189         unsigned page_block;
 190         unsigned first_hole = blocks_per_page;
 191         struct block_device *bdev = NULL;
 192         int length;
 193         int fully_mapped = 1;
 194         unsigned nblocks;
 195         unsigned relative_block;
 196
 197         if (page_has_buffers(page))
 198                 goto confused;
 199
 200         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 201         last_block = block_in_file + nr_pages * blocks_per_page;
 202         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 203         if (last_block > last_block_in_file)
 204                 last_block = last_block_in_file;
 205         page_block = 0;
 206
 207         /*
 208          * Map blocks using the result from the previous get_blocks call first.
 209          */
 210         nblocks = map_bh->b_size >> blkbits;
 211         if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
 212                         block_in_file < (*first_logical_block + nblocks)) {
 213                 unsigned map_offset = block_in_file - *first_logical_block;
 214                 unsigned last = nblocks - map_offset;
 215
 216                 for (relative_block = 0; ; relative_block++) {
 217                         if (relative_block == last) {
 218                                 clear_buffer_mapped(map_bh);
 219                                 break;
 220                         }
 221                         if (page_block == blocks_per_page)
 222                                 break;
 223                         blocks[page_block] = map_bh->b_blocknr + map_offset +
 224                                                 relative_block;
 225                         page_block++;
 226                         block_in_file++;
 227                 }
 228                 bdev = map_bh->b_bdev;
 229         }
 230
 231         /*
 232          * Then do more get_blocks calls until we are done with this page.
 233          */
 234         map_bh->b_page = page;
 235         while (page_block < blocks_per_page) {
 236                 map_bh->b_state = 0;
 237                 map_bh->b_size = 0;
 238
 239                 if (block_in_file < last_block) {
 240                         map_bh->b_size = (last_block-block_in_file) << blkbits;
 241                         if (get_block(inode, block_in_file, map_bh, 0))
 242                                 goto confused;
 243                         *first_logical_block = block_in_file;
 244                 }
 245
 246                 if (!buffer_mapped(map_bh)) {
 247                         fully_mapped = 0;
 248                         if (first_hole == blocks_per_page)
 249                                 first_hole = page_block;
 250                         page_block++;
 251                         block_in_file++;
 252                         continue;
 253                 }
 254
 255                 /* some filesystems will copy data into the page during
 256                  * the get_block call, in which case we don't want to
 257                  * read it again.  map_buffer_to_page copies the data
 258                  * we just collected from get_block into the page's buffers
 259                  * so readpage doesn't have to repeat the get_block call
 260                  */
 261                 if (buffer_uptodate(map_bh)) {
 262                         map_buffer_to_page(page, map_bh, page_block);
 263                         goto confused;
 264                 }
 265
 266                 if (first_hole != blocks_per_page)
 267                         goto confused;          /* hole -> non-hole */
 268
 269                 /* Contiguous blocks? */
 270                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
 271                         goto confused;
 272                 nblocks = map_bh->b_size >> blkbits;
 273                 for (relative_block = 0; ; relative_block++) {
 274                         if (relative_block == nblocks) {
 275                                 clear_buffer_mapped(map_bh);
 276                                 break;
 277                         } else if (page_block == blocks_per_page)
 278                                 break;
 279                         blocks[page_block] = map_bh->b_blocknr+relative_block;
 280                         page_block++;
 281                         block_in_file++;
 282                 }
 283                 bdev = map_bh->b_bdev;
 284         }
 285
 286         if (first_hole != blocks_per_page) {
 287                 zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
 288                 if (first_hole == 0) {
 289                         SetPageUptodate(page);
 290                         unlock_page(page);
 291                         goto out;
 292                 }
 293         } else if (fully_mapped) {
 294                 SetPageMappedToDisk(page);
 295         }
 296
 297         if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
 298             cleancache_get_page(page) == 0) {
 299                 SetPageUptodate(page);
 300                 goto confused;
 301         }
 302
 303         /*
 304          * This page will go to BIO.  Do we need to send this BIO off first?
 305          */
 306         if (bio && (*last_block_in_bio != blocks[0] - 1))
 307                 bio = mpage_bio_submit(READ, bio);
 308
 309 alloc_new:
 310         if (bio == NULL) {
 311                 if (first_hole == blocks_per_page) {
 312                         if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
 313                                                                 page))
 314                                 goto out;
 315                 }
 316                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 317                                 min_t(int, nr_pages, BIO_MAX_PAGES), gfp);
 318                 if (bio == NULL)
 319                         goto confused;
 320         }
 321
 322         length = first_hole << blkbits;
 323         if (bio_add_page(bio, page, length, 0) < length) {
 324                 bio = mpage_bio_submit(READ, bio);
 325                 goto alloc_new;
 326         }
 327
 328         relative_block = block_in_file - *first_logical_block;
 329         nblocks = map_bh->b_size >> blkbits;
 330         if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
 331             (first_hole != blocks_per_page))
 332                 bio = mpage_bio_submit(READ, bio);
 333         else
 334                 *last_block_in_bio = blocks[blocks_per_page - 1];
 335 out:
 336         return bio;
 337
 338 confused:
 339         if (bio)
 340                 bio = mpage_bio_submit(READ, bio);
 341         if (!PageUptodate(page))
 342                 block_read_full_page(page, get_block);
 343         else
 344                 unlock_page(page);
 345         goto out;
 346 }
 347
 348 /**
 349  * mpage_readpages - populate an address space with some pages & start reads against them
 350  * @mapping: the address_space
 351  * @pages: The address of a list_head which contains the target pages.  These
 352  *   pages have their ->index populated and are otherwise uninitialised.
 353  *   The page at @pages->prev has the lowest file offset, and reads should be
 354  *   issued in @pages->prev to @pages->next order.
 355  * @nr_pages: The number of pages at *@pages
 356  * @get_block: The filesystem's block mapper function.
 357  *
 358  * This function walks the pages and the blocks within each page, building and
 359  * emitting large BIOs.
 360  *
 361  * If anything unusual happens, such as:
 362  *
 363  * - encountering a page which has buffers
 364  * - encountering a page which has a non-hole after a hole
 365  * - encountering a page with non-contiguous blocks
 366  *
 367  * then this code just gives up and calls the buffer_head-based read function.
 368  * It does handle a page which has holes at the end - that is a common case:
 369  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
 370  *
 371  * BH_Boundary explanation:
 372  *
 373  * There is a problem.  The mpage read code assembles several pages, gets all
 374  * their disk mappings, and then submits them all.  That's fine, but obtaining
 375  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 376  *
 377  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 378  * submitted in the following order:
 379  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 380  *
 381  * because the indirect block has to be read to get the mappings of blocks
 382  * 13,14,15,16.  Obviously, this impacts performance.
 383  *
 384  * So what we do it to allow the filesystem's get_block() function to set
 385  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 386  * after this one will require I/O against a block which is probably close to
 387  * this one.  So you should push what I/O you have currently accumulated.
 388  *
 389  * This all causes the disk requests to be issued in the correct order.
 390  */
 391 int
 392 mpage_readpages(struct address_space *mapping, struct list_head *pages,
 393                                 unsigned nr_pages, get_block_t get_block)
 394 {
 395         struct bio *bio = NULL;
 396         unsigned page_idx;
 397         sector_t last_block_in_bio = 0;
 398         struct buffer_head map_bh;
 399         unsigned long first_logical_block = 0;
 400         gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
 401
 402         map_bh.b_state = 0;
 403         map_bh.b_size = 0;
 404         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 405                 struct page *page = list_entry(pages->prev, struct page, lru);
 406
 407                 prefetchw(&page->flags);
 408                 list_del(&page->lru);
 409                 if (!add_to_page_cache_lru(page, mapping,
 410                                         page->index,
 411                                         gfp)) {
 412                         bio = do_mpage_readpage(bio, page,
 413                                         nr_pages - page_idx,
 414                                         &last_block_in_bio, &map_bh,
 415                                         &first_logical_block,
 416                                         get_block, gfp);
 417                 }
 418                 page_cache_release(page);
 419         }
 420         BUG_ON(!list_empty(pages));
 421         if (bio)
 422                 mpage_bio_submit(READ, bio);
 423         return 0;
 424 }
 425 EXPORT_SYMBOL(mpage_readpages);
 426
 427 /*
 428  * This isn't called much at all
 429  */
 430 int mpage_readpage(struct page *page, get_block_t get_block)
 431 {
 432         struct bio *bio = NULL;
 433         sector_t last_block_in_bio = 0;
 434         struct buffer_head map_bh;
 435         unsigned long first_logical_block = 0;
 436         gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
 437
 438         map_bh.b_state = 0;
 439         map_bh.b_size = 0;
 440         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
 441                         &map_bh, &first_logical_block, get_block, gfp);
 442         if (bio)
 443                 mpage_bio_submit(READ, bio);
 444         return 0;
 445 }
 446 EXPORT_SYMBOL(mpage_readpage);
 447
 448 /*
 449  * Writing is not so simple.
 450  *
 451  * If the page has buffers then they will be used for obtaining the disk
 452  * mapping.  We only support pages which are fully mapped-and-dirty, with a
 453  * special case for pages which are unmapped at the end: end-of-file.
 454  *
 455  * If the page has no buffers (preferred) then the page is mapped here.
 456  *
 457  * If all blocks are found to be contiguous then the page can go into the
 458  * BIO.  Otherwise fall back to the mapping's writepage().
 459  *
 460  * FIXME: This code wants an estimate of how many pages are still to be
 461  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 462  * just allocate full-size (16-page) BIOs.
 463  */
 464
 465 struct mpage_data {
 466         struct bio *bio;
 467         sector_t last_block_in_bio;
 468         get_block_t *get_block;
 469         unsigned use_writepage;
 470 };
 471
 472 /*
 473  * We have our BIO, so we can now mark the buffers clean.  Make
 474  * sure to only clean buffers which we know we'll be writing.
 475  */
 476 static void clean_buffers(struct page *page, unsigned first_unmapped)
 477 {
 478         unsigned buffer_counter = 0;
 479         struct buffer_head *bh, *head;
 480         if (!page_has_buffers(page))
 481                 return;
 482         head = page_buffers(page);
 483         bh = head;
 484
 485         do {
 486                 if (buffer_counter++ == first_unmapped)
 487                         break;
 488                 clear_buffer_dirty(bh);
 489                 bh = bh->b_this_page;
 490         } while (bh != head);
 491
 492         /*
 493          * we cannot drop the bh if the page is not uptodate or a concurrent
 494          * readpage would fail to serialize with the bh and it would read from
 495          * disk before we reach the platter.
 496          */
 497         if (buffer_heads_over_limit && PageUptodate(page))
 498                 try_to_free_buffers(page);
 499 }
 500
 501 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 502                       void *data)
 503 {
 504         struct mpage_data *mpd = data;
 505         struct bio *bio = mpd->bio;
 506         struct address_space *mapping = page->mapping;
 507         struct inode *inode = page->mapping->host;
 508         const unsigned blkbits = inode->i_blkbits;
 509         unsigned long end_index;
 510         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 511         sector_t last_block;
 512         sector_t block_in_file;
 513         sector_t blocks[MAX_BUF_PER_PAGE];
 514         unsigned page_block;
 515         unsigned first_unmapped = blocks_per_page;
 516         struct block_device *bdev = NULL;
 517         int boundary = 0;
 518         sector_t boundary_block = 0;
 519         struct block_device *boundary_bdev = NULL;
 520         int length;
 521         struct buffer_head map_bh;
 522         loff_t i_size = i_size_read(inode);
 523         int ret = 0;
 524         int wr = (wbc->sync_mode == WB_SYNC_ALL ?  WRITE_SYNC : WRITE);
 525
 526         if (page_has_buffers(page)) {
 527                 struct buffer_head *head = page_buffers(page);
 528                 struct buffer_head *bh = head;
 529
 530                 /* If they're all mapped and dirty, do it */
 531                 page_block = 0;
 532                 do {
 533                         BUG_ON(buffer_locked(bh));
 534                         if (!buffer_mapped(bh)) {
 535                                 /*
 536                                  * unmapped dirty buffers are created by
 537                                  * __set_page_dirty_buffers -> mmapped data
 538                                  */
 539                                 if (buffer_dirty(bh))
 540                                         goto confused;
 541                                 if (first_unmapped == blocks_per_page)
 542                                         first_unmapped = page_block;
 543                                 continue;
 544                         }
 545
 546                         if (first_unmapped != blocks_per_page)
 547                                 goto confused;  /* hole -> non-hole */
 548
 549                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 550                                 goto confused;
 551                         if (page_block) {
 552                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
 553                                         goto confused;
 554                         }
 555                         blocks[page_block++] = bh->b_blocknr;
 556                         boundary = buffer_boundary(bh);
 557                         if (boundary) {
 558                                 boundary_block = bh->b_blocknr;
 559                                 boundary_bdev = bh->b_bdev;
 560                         }
 561                         bdev = bh->b_bdev;
 562                 } while ((bh = bh->b_this_page) != head);
 563
 564                 if (first_unmapped)
 565                         goto page_is_mapped;
 566
 567                 /*
 568                  * Page has buffers, but they are all unmapped. The page was
 569                  * created by pagein or read over a hole which was handled by
 570                  * block_read_full_page().  If this address_space is also
 571                  * using mpage_readpages then this can rarely happen.
 572                  */
 573                 goto confused;
 574         }
 575
 576         /*
 577          * The page has no buffers: map it to disk
 578          */
 579         BUG_ON(!PageUptodate(page));
 580         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 581         last_block = (i_size - 1) >> blkbits;
 582         map_bh.b_page = page;
 583         for (page_block = 0; page_block < blocks_per_page; ) {
 584
 585                 map_bh.b_state = 0;
 586                 map_bh.b_size = 1 << blkbits;
 587                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
 588                         goto confused;
 589                 if (buffer_new(&map_bh))
 590                         unmap_underlying_metadata(map_bh.b_bdev,
 591                                                 map_bh.b_blocknr);
 592                 if (buffer_boundary(&map_bh)) {
 593                         boundary_block = map_bh.b_blocknr;
 594                         boundary_bdev = map_bh.b_bdev;
 595                 }
 596                 if (page_block) {
 597                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 598                                 goto confused;
 599                 }
 600                 blocks[page_block++] = map_bh.b_blocknr;
 601                 boundary = buffer_boundary(&map_bh);
 602                 bdev = map_bh.b_bdev;
 603                 if (block_in_file == last_block)
 604                         break;
 605                 block_in_file++;
 606         }
 607         BUG_ON(page_block == 0);
 608
 609         first_unmapped = page_block;
 610
 611 page_is_mapped:
 612         end_index = i_size >> PAGE_CACHE_SHIFT;
 613         if (page->index >= end_index) {
 614                 /*
 615                  * The page straddles i_size.  It must be zeroed out on each
 616                  * and every writepage invocation because it may be mmapped.
 617                  * "A file is mapped in multiples of the page size.  For a file
 618                  * that is not a multiple of the page size, the remaining memory
 619                  * is zeroed when mapped, and writes to that region are not
 620                  * written out to the file."
 621                  */
 622                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
 623
 624                 if (page->index > end_index || !offset)
 625                         goto confused;
 626                 zero_user_segment(page, offset, PAGE_CACHE_SIZE);
 627         }
 628
 629         /*
 630          * This page will go to BIO.  Do we need to send this BIO off first?
 631          */
 632         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
 633                 bio = mpage_bio_submit(wr, bio);
 634
 635 alloc_new:
 636         if (bio == NULL) {
 637                 if (first_unmapped == blocks_per_page) {
 638                         if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
 639                                                                 page, wbc)) {
 640                                 clean_buffers(page, first_unmapped);
 641                                 goto out;
 642                         }
 643                 }
 644                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 645                                 BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
 646                 if (bio == NULL)
 647                         goto confused;
 648
 649                 wbc_init_bio(wbc, bio);
 650         }
 651
 652         /*
 653          * Must try to add the page before marking the buffer clean or
 654          * the confused fail path above (OOM) will be very confused when
 655          * it finds all bh marked clean (i.e. it will not write anything)
 656          */
 657         wbc_account_io(wbc, page, PAGE_SIZE);
 658         length = first_unmapped << blkbits;
 659         if (bio_add_page(bio, page, length, 0) < length) {
 660                 bio = mpage_bio_submit(wr, bio);
 661                 goto alloc_new;
 662         }
 663
 664         clean_buffers(page, first_unmapped);
 665
 666         BUG_ON(PageWriteback(page));
 667         set_page_writeback(page);
 668         unlock_page(page);
 669         if (boundary || (first_unmapped != blocks_per_page)) {
 670                 bio = mpage_bio_submit(wr, bio);
 671                 if (boundary_block) {
 672                         write_boundary_block(boundary_bdev,
 673                                         boundary_block, 1 << blkbits);
 674                 }
 675         } else {
 676                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
 677         }
 678         goto out;
 679
 680 confused:
 681         if (bio)
 682                 bio = mpage_bio_submit(wr, bio);
 683
 684         if (mpd->use_writepage) {
 685                 ret = mapping->a_ops->writepage(page, wbc);
 686         } else {
 687                 ret = -EAGAIN;
 688                 goto out;
 689         }
 690         /*
 691          * The caller has a ref on the inode, so *mapping is stable
 692          */
 693         mapping_set_error(mapping, ret);
 694 out:
 695         mpd->bio = bio;
 696         return ret;
 697 }
 698
 699 /**
 700  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
 701  * @mapping: address space structure to write
 702  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 703  * @get_block: the filesystem's block mapper function.
 704  *             If this is NULL then use a_ops->writepage.  Otherwise, go
 705  *             direct-to-BIO.
 706  *
 707  * This is a library function, which implements the writepages()
 708  * address_space_operation.
 709  *
 710  * If a page is already under I/O, generic_writepages() skips it, even
 711  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 712  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 713  * and msync() need to guarantee that all the data which was dirty at the time
 714  * the call was made get new I/O started against them.  If wbc->sync_mode is
 715  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 716  * existing IO to complete.
 717  */
 718 int
 719 mpage_writepages(struct address_space *mapping,
 720                 struct writeback_control *wbc, get_block_t get_block)
 721 {
 722         struct blk_plug plug;
 723         int ret;
 724
 725         blk_start_plug(&plug);
 726
 727         if (!get_block)
 728                 ret = generic_writepages(mapping, wbc);
 729         else {
 730                 struct mpage_data mpd = {
 731                         .bio = NULL,
 732                         .last_block_in_bio = 0,
 733                         .get_block = get_block,
 734                         .use_writepage = 1,
 735                 };
 736
 737                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
 738                 if (mpd.bio) {
 739                         int wr = (wbc->sync_mode == WB_SYNC_ALL ?
 740                                   WRITE_SYNC : WRITE);
 741                         mpage_bio_submit(wr, mpd.bio);
 742                 }
 743         }
 744         blk_finish_plug(&plug);
 745         return ret;
 746 }
 747 EXPORT_SYMBOL(mpage_writepages);
 748
 749 int mpage_writepage(struct page *page, get_block_t get_block,
 750         struct writeback_control *wbc)
 751 {
 752         struct mpage_data mpd = {
 753                 .bio = NULL,
 754                 .last_block_in_bio = 0,
 755                 .get_block = get_block,
 756                 .use_writepage = 0,
 757         };
 758         int ret = __mpage_writepage(page, wbc, &mpd);
 759         if (mpd.bio) {
 760                 int wr = (wbc->sync_mode == WB_SYNC_ALL ?
 761                           WRITE_SYNC : WRITE);
 762                 mpage_bio_submit(wr, mpd.bio);
 763         }
 764         return ret;
 765 }
 766 EXPORT_SYMBOL(mpage_writepage);