LCOV - code coverage report
Current view: top level - fs - mpage.c (source / functions) Hit Total Coverage
Test: Real Lines: 98 238 41.2 %
Date: 2020-10-17 15:46:16 Functions: 0 11 0.0 %
Legend: Neither, QEMU, Real, Both Branches: 0 0 -

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

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