fs/mpage.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/mpage.c
   4  *
   5  * Copyright (C) 2002, Linus Torvalds.
   6  *
   7  * Contains functions related to preparing and submitting BIOs which contain
   8  * multiple pagecache pages.
   9  *
  10  * 15May2002    Andrew Morton
  11  *              Initial version
  12  * 27Jun2002    axboe@suse.de
  13  *              use bio_add_page() to build bio's just the right size
  14  */
  15
  16 #include <linux/kernel.h>
  17 #include <linux/export.h>
  18 #include <linux/mm.h>
  19 #include <linux/kdev_t.h>
  20 #include <linux/gfp.h>
  21 #include <linux/bio.h>
  22 #include <linux/fs.h>
  23 #include <linux/buffer_head.h>
  24 #include <linux/blkdev.h>
  25 #include <linux/highmem.h>
  26 #include <linux/prefetch.h>
  27 #include <linux/mpage.h>
  28 #include <linux/mm_inline.h>
  29 #include <linux/writeback.h>
  30 #include <linux/backing-dev.h>
  31 #include <linux/pagevec.h>
  32 #include "internal.h"
  33
  34 /*
  35  * I/O completion handler for multipage BIOs.
  36  *
  37  * The mpage code never puts partial pages into a BIO (except for end-of-file).
  38  * If a page does not map to a contiguous run of blocks then it simply falls
  39  * back to block_read_full_folio().
  40  *
  41  * Why is this?  If a page's completion depends on a number of different BIOs
  42  * which can complete in any order (or at the same time) then determining the
  43  * status of that page is hard.  See end_buffer_async_read() for the details.
  44  * There is no point in duplicating all that complexity.
  45  */
  46 static void mpage_end_io(struct bio *bio)
  47 {
  48         struct bio_vec *bv;
  49         struct bvec_iter_all iter_all;
  50
  51         bio_for_each_segment_all(bv, bio, iter_all) {
  52                 struct page *page = bv->bv_page;
  53                 page_endio(page, bio_op(bio),
  54                            blk_status_to_errno(bio->bi_status));
  55         }
  56
  57         bio_put(bio);
  58 }
  59
  60 static struct bio *mpage_bio_submit(struct bio *bio)
  61 {
  62         bio->bi_end_io = mpage_end_io;
  63         guard_bio_eod(bio);
  64         submit_bio(bio);
  65         return NULL;
  66 }
  67
  68 /*
  69  * support function for mpage_readahead.  The fs supplied get_block might
  70  * return an up to date buffer.  This is used to map that buffer into
  71  * the page, which allows read_folio to avoid triggering a duplicate call
  72  * to get_block.
  73  *
  74  * The idea is to avoid adding buffers to pages that don't already have
  75  * them.  So when the buffer is up to date and the page size == block size,
  76  * this marks the page up to date instead of adding new buffers.
  77  */
  78 static void
  79 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
  80 {
  81         struct inode *inode = page->mapping->host;
  82         struct buffer_head *page_bh, *head;
  83         int block = 0;
  84
  85         if (!page_has_buffers(page)) {
  86                 /*
  87                  * don't make any buffers if there is only one buffer on
  88                  * the page and the page just needs to be set up to date
  89                  */
  90                 if (inode->i_blkbits == PAGE_SHIFT &&
  91                     buffer_uptodate(bh)) {
  92                         SetPageUptodate(page);
  93                         return;
  94                 }
  95                 create_empty_buffers(page, i_blocksize(inode), 0);
  96         }
  97         head = page_buffers(page);
  98         page_bh = head;
  99         do {
 100                 if (block == page_block) {
 101                         page_bh->b_state = bh->b_state;
 102                         page_bh->b_bdev = bh->b_bdev;
 103                         page_bh->b_blocknr = bh->b_blocknr;
 104                         break;
 105                 }
 106                 page_bh = page_bh->b_this_page;
 107                 block++;
 108         } while (page_bh != head);
 109 }
 110
 111 struct mpage_readpage_args {
 112         struct bio *bio;
 113         struct page *page;
 114         unsigned int nr_pages;
 115         bool is_readahead;
 116         sector_t last_block_in_bio;
 117         struct buffer_head map_bh;
 118         unsigned long first_logical_block;
 119         get_block_t *get_block;
 120 };
 121
 122 /*
 123  * This is the worker routine which does all the work of mapping the disk
 124  * blocks and constructs largest possible bios, submits them for IO if the
 125  * blocks are not contiguous on the disk.
 126  *
 127  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 128  * represent the validity of its disk mapping and to decide when to do the next
 129  * get_block() call.
 130  */
 131 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 132 {
 133         struct page *page = args->page;
 134         struct inode *inode = page->mapping->host;
 135         const unsigned blkbits = inode->i_blkbits;
 136         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 137         const unsigned blocksize = 1 << blkbits;
 138         struct buffer_head *map_bh = &args->map_bh;
 139         sector_t block_in_file;
 140         sector_t last_block;
 141         sector_t last_block_in_file;
 142         sector_t blocks[MAX_BUF_PER_PAGE];
 143         unsigned page_block;
 144         unsigned first_hole = blocks_per_page;
 145         struct block_device *bdev = NULL;
 146         int length;
 147         int fully_mapped = 1;
 148         int op = REQ_OP_READ;
 149         unsigned nblocks;
 150         unsigned relative_block;
 151         gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
 152
 153         if (args->is_readahead) {
 154                 op |= REQ_RAHEAD;
 155                 gfp |= __GFP_NORETRY | __GFP_NOWARN;
 156         }
 157
 158         if (page_has_buffers(page))
 159                 goto confused;
 160
 161         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
 162         last_block = block_in_file + args->nr_pages * blocks_per_page;
 163         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 164         if (last_block > last_block_in_file)
 165                 last_block = last_block_in_file;
 166         page_block = 0;
 167
 168         /*
 169          * Map blocks using the result from the previous get_blocks call first.
 170          */
 171         nblocks = map_bh->b_size >> blkbits;
 172         if (buffer_mapped(map_bh) &&
 173                         block_in_file > args->first_logical_block &&
 174                         block_in_file < (args->first_logical_block + nblocks)) {
 175                 unsigned map_offset = block_in_file - args->first_logical_block;
 176                 unsigned last = nblocks - map_offset;
 177
 178                 for (relative_block = 0; ; relative_block++) {
 179                         if (relative_block == last) {
 180                                 clear_buffer_mapped(map_bh);
 181                                 break;
 182                         }
 183                         if (page_block == blocks_per_page)
 184                                 break;
 185                         blocks[page_block] = map_bh->b_blocknr + map_offset +
 186                                                 relative_block;
 187                         page_block++;
 188                         block_in_file++;
 189                 }
 190                 bdev = map_bh->b_bdev;
 191         }
 192
 193         /*
 194          * Then do more get_blocks calls until we are done with this page.
 195          */
 196         map_bh->b_page = page;
 197         while (page_block < blocks_per_page) {
 198                 map_bh->b_state = 0;
 199                 map_bh->b_size = 0;
 200
 201                 if (block_in_file < last_block) {
 202                         map_bh->b_size = (last_block-block_in_file) << blkbits;
 203                         if (args->get_block(inode, block_in_file, map_bh, 0))
 204                                 goto confused;
 205                         args->first_logical_block = block_in_file;
 206                 }
 207
 208                 if (!buffer_mapped(map_bh)) {
 209                         fully_mapped = 0;
 210                         if (first_hole == blocks_per_page)
 211                                 first_hole = page_block;
 212                         page_block++;
 213                         block_in_file++;
 214                         continue;
 215                 }
 216
 217                 /* some filesystems will copy data into the page during
 218                  * the get_block call, in which case we don't want to
 219                  * read it again.  map_buffer_to_page copies the data
 220                  * we just collected from get_block into the page's buffers
 221                  * so readpage doesn't have to repeat the get_block call
 222                  */
 223                 if (buffer_uptodate(map_bh)) {
 224                         map_buffer_to_page(page, map_bh, page_block);
 225                         goto confused;
 226                 }
 227
 228                 if (first_hole != blocks_per_page)
 229                         goto confused;          /* hole -> non-hole */
 230
 231                 /* Contiguous blocks? */
 232                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
 233                         goto confused;
 234                 nblocks = map_bh->b_size >> blkbits;
 235                 for (relative_block = 0; ; relative_block++) {
 236                         if (relative_block == nblocks) {
 237                                 clear_buffer_mapped(map_bh);
 238                                 break;
 239                         } else if (page_block == blocks_per_page)
 240                                 break;
 241                         blocks[page_block] = map_bh->b_blocknr+relative_block;
 242                         page_block++;
 243                         block_in_file++;
 244                 }
 245                 bdev = map_bh->b_bdev;
 246         }
 247
 248         if (first_hole != blocks_per_page) {
 249                 zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
 250                 if (first_hole == 0) {
 251                         SetPageUptodate(page);
 252                         unlock_page(page);
 253                         goto out;
 254                 }
 255         } else if (fully_mapped) {
 256                 SetPageMappedToDisk(page);
 257         }
 258
 259         /*
 260          * This page will go to BIO.  Do we need to send this BIO off first?
 261          */
 262         if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
 263                 args->bio = mpage_bio_submit(args->bio);
 264
 265 alloc_new:
 266         if (args->bio == NULL) {
 267                 if (first_hole == blocks_per_page) {
 268                         if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
 269                                                                 page))
 270                                 goto out;
 271                 }
 272                 args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), op,
 273                                       gfp);
 274                 if (args->bio == NULL)
 275                         goto confused;
 276                 args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 277         }
 278
 279         length = first_hole << blkbits;
 280         if (bio_add_page(args->bio, page, length, 0) < length) {
 281                 args->bio = mpage_bio_submit(args->bio);
 282                 goto alloc_new;
 283         }
 284
 285         relative_block = block_in_file - args->first_logical_block;
 286         nblocks = map_bh->b_size >> blkbits;
 287         if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
 288             (first_hole != blocks_per_page))
 289                 args->bio = mpage_bio_submit(args->bio);
 290         else
 291                 args->last_block_in_bio = blocks[blocks_per_page - 1];
 292 out:
 293         return args->bio;
 294
 295 confused:
 296         if (args->bio)
 297                 args->bio = mpage_bio_submit(args->bio);
 298         if (!PageUptodate(page))
 299                 block_read_full_folio(page_folio(page), args->get_block);
 300         else
 301                 unlock_page(page);
 302         goto out;
 303 }
 304
 305 /**
 306  * mpage_readahead - start reads against pages
 307  * @rac: Describes which pages to read.
 308  * @get_block: The filesystem's block mapper function.
 309  *
 310  * This function walks the pages and the blocks within each page, building and
 311  * emitting large BIOs.
 312  *
 313  * If anything unusual happens, such as:
 314  *
 315  * - encountering a page which has buffers
 316  * - encountering a page which has a non-hole after a hole
 317  * - encountering a page with non-contiguous blocks
 318  *
 319  * then this code just gives up and calls the buffer_head-based read function.
 320  * It does handle a page which has holes at the end - that is a common case:
 321  * the end-of-file on blocksize < PAGE_SIZE setups.
 322  *
 323  * BH_Boundary explanation:
 324  *
 325  * There is a problem.  The mpage read code assembles several pages, gets all
 326  * their disk mappings, and then submits them all.  That's fine, but obtaining
 327  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 328  *
 329  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 330  * submitted in the following order:
 331  *
 332  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 333  *
 334  * because the indirect block has to be read to get the mappings of blocks
 335  * 13,14,15,16.  Obviously, this impacts performance.
 336  *
 337  * So what we do it to allow the filesystem's get_block() function to set
 338  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 339  * after this one will require I/O against a block which is probably close to
 340  * this one.  So you should push what I/O you have currently accumulated.
 341  *
 342  * This all causes the disk requests to be issued in the correct order.
 343  */
 344 void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
 345 {
 346         struct page *page;
 347         struct mpage_readpage_args args = {
 348                 .get_block = get_block,
 349                 .is_readahead = true,
 350         };
 351
 352         while ((page = readahead_page(rac))) {
 353                 prefetchw(&page->flags);
 354                 args.page = page;
 355                 args.nr_pages = readahead_count(rac);
 356                 args.bio = do_mpage_readpage(&args);
 357                 put_page(page);
 358         }
 359         if (args.bio)
 360                 mpage_bio_submit(args.bio);
 361 }
 362 EXPORT_SYMBOL(mpage_readahead);
 363
 364 /*
 365  * This isn't called much at all
 366  */
 367 int mpage_read_folio(struct folio *folio, get_block_t get_block)
 368 {
 369         struct mpage_readpage_args args = {
 370                 .page = &folio->page,
 371                 .nr_pages = 1,
 372                 .get_block = get_block,
 373         };
 374
 375         VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
 376
 377         args.bio = do_mpage_readpage(&args);
 378         if (args.bio)
 379                 mpage_bio_submit(args.bio);
 380         return 0;
 381 }
 382 EXPORT_SYMBOL(mpage_read_folio);
 383
 384 /*
 385  * Writing is not so simple.
 386  *
 387  * If the page has buffers then they will be used for obtaining the disk
 388  * mapping.  We only support pages which are fully mapped-and-dirty, with a
 389  * special case for pages which are unmapped at the end: end-of-file.
 390  *
 391  * If the page has no buffers (preferred) then the page is mapped here.
 392  *
 393  * If all blocks are found to be contiguous then the page can go into the
 394  * BIO.  Otherwise fall back to the mapping's writepage().
 395  *
 396  * FIXME: This code wants an estimate of how many pages are still to be
 397  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 398  * just allocate full-size (16-page) BIOs.
 399  */
 400
 401 struct mpage_data {
 402         struct bio *bio;
 403         sector_t last_block_in_bio;
 404         get_block_t *get_block;
 405         unsigned use_writepage;
 406 };
 407
 408 /*
 409  * We have our BIO, so we can now mark the buffers clean.  Make
 410  * sure to only clean buffers which we know we'll be writing.
 411  */
 412 static void clean_buffers(struct page *page, unsigned first_unmapped)
 413 {
 414         unsigned buffer_counter = 0;
 415         struct buffer_head *bh, *head;
 416         if (!page_has_buffers(page))
 417                 return;
 418         head = page_buffers(page);
 419         bh = head;
 420
 421         do {
 422                 if (buffer_counter++ == first_unmapped)
 423                         break;
 424                 clear_buffer_dirty(bh);
 425                 bh = bh->b_this_page;
 426         } while (bh != head);
 427
 428         /*
 429          * we cannot drop the bh if the page is not uptodate or a concurrent
 430          * read_folio would fail to serialize with the bh and it would read from
 431          * disk before we reach the platter.
 432          */
 433         if (buffer_heads_over_limit && PageUptodate(page))
 434                 try_to_free_buffers(page_folio(page));
 435 }
 436
 437 /*
 438  * For situations where we want to clean all buffers attached to a page.
 439  * We don't need to calculate how many buffers are attached to the page,
 440  * we just need to specify a number larger than the maximum number of buffers.
 441  */
 442 void clean_page_buffers(struct page *page)
 443 {
 444         clean_buffers(page, ~0U);
 445 }
 446
 447 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 448                       void *data)
 449 {
 450         struct mpage_data *mpd = data;
 451         struct bio *bio = mpd->bio;
 452         struct address_space *mapping = page->mapping;
 453         struct inode *inode = page->mapping->host;
 454         const unsigned blkbits = inode->i_blkbits;
 455         unsigned long end_index;
 456         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 457         sector_t last_block;
 458         sector_t block_in_file;
 459         sector_t blocks[MAX_BUF_PER_PAGE];
 460         unsigned page_block;
 461         unsigned first_unmapped = blocks_per_page;
 462         struct block_device *bdev = NULL;
 463         int boundary = 0;
 464         sector_t boundary_block = 0;
 465         struct block_device *boundary_bdev = NULL;
 466         int length;
 467         struct buffer_head map_bh;
 468         loff_t i_size = i_size_read(inode);
 469         int ret = 0;
 470
 471         if (page_has_buffers(page)) {
 472                 struct buffer_head *head = page_buffers(page);
 473                 struct buffer_head *bh = head;
 474
 475                 /* If they're all mapped and dirty, do it */
 476                 page_block = 0;
 477                 do {
 478                         BUG_ON(buffer_locked(bh));
 479                         if (!buffer_mapped(bh)) {
 480                                 /*
 481                                  * unmapped dirty buffers are created by
 482                                  * block_dirty_folio -> mmapped data
 483                                  */
 484                                 if (buffer_dirty(bh))
 485                                         goto confused;
 486                                 if (first_unmapped == blocks_per_page)
 487                                         first_unmapped = page_block;
 488                                 continue;
 489                         }
 490
 491                         if (first_unmapped != blocks_per_page)
 492                                 goto confused;  /* hole -> non-hole */
 493
 494                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 495                                 goto confused;
 496                         if (page_block) {
 497                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
 498                                         goto confused;
 499                         }
 500                         blocks[page_block++] = bh->b_blocknr;
 501                         boundary = buffer_boundary(bh);
 502                         if (boundary) {
 503                                 boundary_block = bh->b_blocknr;
 504                                 boundary_bdev = bh->b_bdev;
 505                         }
 506                         bdev = bh->b_bdev;
 507                 } while ((bh = bh->b_this_page) != head);
 508
 509                 if (first_unmapped)
 510                         goto page_is_mapped;
 511
 512                 /*
 513                  * Page has buffers, but they are all unmapped. The page was
 514                  * created by pagein or read over a hole which was handled by
 515                  * block_read_full_folio().  If this address_space is also
 516                  * using mpage_readahead then this can rarely happen.
 517                  */
 518                 goto confused;
 519         }
 520
 521         /*
 522          * The page has no buffers: map it to disk
 523          */
 524         BUG_ON(!PageUptodate(page));
 525         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
 526         last_block = (i_size - 1) >> blkbits;
 527         map_bh.b_page = page;
 528         for (page_block = 0; page_block < blocks_per_page; ) {
 529
 530                 map_bh.b_state = 0;
 531                 map_bh.b_size = 1 << blkbits;
 532                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
 533                         goto confused;
 534                 if (buffer_new(&map_bh))
 535                         clean_bdev_bh_alias(&map_bh);
 536                 if (buffer_boundary(&map_bh)) {
 537                         boundary_block = map_bh.b_blocknr;
 538                         boundary_bdev = map_bh.b_bdev;
 539                 }
 540                 if (page_block) {
 541                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 542                                 goto confused;
 543                 }
 544                 blocks[page_block++] = map_bh.b_blocknr;
 545                 boundary = buffer_boundary(&map_bh);
 546                 bdev = map_bh.b_bdev;
 547                 if (block_in_file == last_block)
 548                         break;
 549                 block_in_file++;
 550         }
 551         BUG_ON(page_block == 0);
 552
 553         first_unmapped = page_block;
 554
 555 page_is_mapped:
 556         end_index = i_size >> PAGE_SHIFT;
 557         if (page->index >= end_index) {
 558                 /*
 559                  * The page straddles i_size.  It must be zeroed out on each
 560                  * and every writepage invocation because it may be mmapped.
 561                  * "A file is mapped in multiples of the page size.  For a file
 562                  * that is not a multiple of the page size, the remaining memory
 563                  * is zeroed when mapped, and writes to that region are not
 564                  * written out to the file."
 565                  */
 566                 unsigned offset = i_size & (PAGE_SIZE - 1);
 567
 568                 if (page->index > end_index || !offset)
 569                         goto confused;
 570                 zero_user_segment(page, offset, PAGE_SIZE);
 571         }
 572
 573         /*
 574          * This page will go to BIO.  Do we need to send this BIO off first?
 575          */
 576         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
 577                 bio = mpage_bio_submit(bio);
 578
 579 alloc_new:
 580         if (bio == NULL) {
 581                 if (first_unmapped == blocks_per_page) {
 582                         if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
 583                                                                 page, wbc))
 584                                 goto out;
 585                 }
 586                 bio = bio_alloc(bdev, BIO_MAX_VECS,
 587                                 REQ_OP_WRITE | wbc_to_write_flags(wbc),
 588                                 GFP_NOFS);
 589                 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 590                 wbc_init_bio(wbc, bio);
 591         }
 592
 593         /*
 594          * Must try to add the page before marking the buffer clean or
 595          * the confused fail path above (OOM) will be very confused when
 596          * it finds all bh marked clean (i.e. it will not write anything)
 597          */
 598         wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
 599         length = first_unmapped << blkbits;
 600         if (bio_add_page(bio, page, length, 0) < length) {
 601                 bio = mpage_bio_submit(bio);
 602                 goto alloc_new;
 603         }
 604
 605         clean_buffers(page, first_unmapped);
 606
 607         BUG_ON(PageWriteback(page));
 608         set_page_writeback(page);
 609         unlock_page(page);
 610         if (boundary || (first_unmapped != blocks_per_page)) {
 611                 bio = mpage_bio_submit(bio);
 612                 if (boundary_block) {
 613                         write_boundary_block(boundary_bdev,
 614                                         boundary_block, 1 << blkbits);
 615                 }
 616         } else {
 617                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
 618         }
 619         goto out;
 620
 621 confused:
 622         if (bio)
 623                 bio = mpage_bio_submit(bio);
 624
 625         if (mpd->use_writepage) {
 626                 ret = mapping->a_ops->writepage(page, wbc);
 627         } else {
 628                 ret = -EAGAIN;
 629                 goto out;
 630         }
 631         /*
 632          * The caller has a ref on the inode, so *mapping is stable
 633          */
 634         mapping_set_error(mapping, ret);
 635 out:
 636         mpd->bio = bio;
 637         return ret;
 638 }
 639
 640 /**
 641  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
 642  * @mapping: address space structure to write
 643  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 644  * @get_block: the filesystem's block mapper function.
 645  *             If this is NULL then use a_ops->writepage.  Otherwise, go
 646  *             direct-to-BIO.
 647  *
 648  * This is a library function, which implements the writepages()
 649  * address_space_operation.
 650  *
 651  * If a page is already under I/O, generic_writepages() skips it, even
 652  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 653  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 654  * and msync() need to guarantee that all the data which was dirty at the time
 655  * the call was made get new I/O started against them.  If wbc->sync_mode is
 656  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 657  * existing IO to complete.
 658  */
 659 int
 660 mpage_writepages(struct address_space *mapping,
 661                 struct writeback_control *wbc, get_block_t get_block)
 662 {
 663         struct blk_plug plug;
 664         int ret;
 665
 666         blk_start_plug(&plug);
 667
 668         if (!get_block)
 669                 ret = generic_writepages(mapping, wbc);
 670         else {
 671                 struct mpage_data mpd = {
 672                         .bio = NULL,
 673                         .last_block_in_bio = 0,
 674                         .get_block = get_block,
 675                         .use_writepage = 1,
 676                 };
 677
 678                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
 679                 if (mpd.bio)
 680                         mpage_bio_submit(mpd.bio);
 681         }
 682         blk_finish_plug(&plug);
 683         return ret;
 684 }
 685 EXPORT_SYMBOL(mpage_writepages);
 686
 687 int mpage_writepage(struct page *page, get_block_t get_block,
 688         struct writeback_control *wbc)
 689 {
 690         struct mpage_data mpd = {
 691                 .bio = NULL,
 692                 .last_block_in_bio = 0,
 693                 .get_block = get_block,
 694                 .use_writepage = 0,
 695         };
 696         int ret = __mpage_writepage(page, wbc, &mpd);
 697         if (mpd.bio)
 698                 mpage_bio_submit(mpd.bio);
 699         return ret;
 700 }
 701 EXPORT_SYMBOL(mpage_writepage);