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    Subject[11/11] ext4: Implement range_cyclic in ext4_da_writepages instead of write_cache_pages
    From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Date: Sat Feb 14 10:42:58 2009 -0500
    Subject: ext4: Implement range_cyclic in ext4_da_writepages instead of write_cache_pages

    commit 2acf2c261b823d9d9ed954f348b97620297a36b5 upstream.

    With delayed allocation we lock the page in write_cache_pages() and
    try to build an in memory extent of contiguous blocks. This is needed
    so that we can get large contiguous blocks request. If range_cyclic
    mode is enabled, write_cache_pages() will loop back to the 0 index if
    no I/O has been done yet, and try to start writing from the beginning
    of the range. That causes an attempt to take the page lock of lower
    index page while holding the page lock of higher index page, which can
    cause a dead lock with another writeback thread.

    The solution is to implement the range_cyclic behavior in
    ext4_da_writepages() instead.

    http://bugzilla.kernel.org/show_bug.cgi?id=12579

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Jayson R. King <dev@jaysonking.com>

    ---
    fs/ext4/inode.c | 21 +++++++++++++++++++--
    1 file changed, 19 insertions(+), 2 deletions(-)

    diff -urNp linux-2.6.27.orig/fs/ext4/inode.c linux-2.6.27/fs/ext4/inode.c
    --- linux-2.6.27.orig/fs/ext4/inode.c 2010-02-26 14:28:11.222252883 -0600
    +++ linux-2.6.27/fs/ext4/inode.c 2010-02-26 14:28:16.190252556 -0600
    @@ -2456,6 +2456,7 @@ static int ext4_da_writepages(struct add
    struct inode *inode = mapping->host;
    int no_nrwrite_index_update;
    long pages_written = 0, pages_skipped;
    + int range_cyclic, cycled = 1, io_done = 0;
    int needed_blocks, ret = 0, nr_to_writebump = 0;
    struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);

    @@ -2493,9 +2494,15 @@ static int ext4_da_writepages(struct add
    if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
    range_whole = 1;

    - if (wbc->range_cyclic)
    + range_cyclic = wbc->range_cyclic;
    + if (wbc->range_cyclic) {
    index = mapping->writeback_index;
    - else
    + if (index)
    + cycled = 0;
    + wbc->range_start = index << PAGE_CACHE_SHIFT;
    + wbc->range_end = LLONG_MAX;
    + wbc->range_cyclic = 0;
    + } else
    index = wbc->range_start >> PAGE_CACHE_SHIFT;

    mpd.wbc = wbc;
    @@ -2509,6 +2516,7 @@ static int ext4_da_writepages(struct add
    wbc->no_nrwrite_index_update = 1;
    pages_skipped = wbc->pages_skipped;

    +retry:
    while (!ret && wbc->nr_to_write > 0) {

    /*
    @@ -2563,6 +2571,7 @@ static int ext4_da_writepages(struct add
    pages_written += mpd.pages_written;
    wbc->pages_skipped = pages_skipped;
    ret = 0;
    + io_done = 1;
    } else if (wbc->nr_to_write)
    /*
    * There is no more writeout needed
    @@ -2571,6 +2580,13 @@ static int ext4_da_writepages(struct add
    */
    break;
    }
    + if (!io_done && !cycled) {
    + cycled = 1;
    + index = 0;
    + wbc->range_start = index << PAGE_CACHE_SHIFT;
    + wbc->range_end = mapping->writeback_index - 1;
    + goto retry;
    + }
    if (pages_skipped != wbc->pages_skipped)
    printk(KERN_EMERG "This should not happen leaving %s "
    "with nr_to_write = %ld ret = %d\n",
    @@ -2578,6 +2594,7 @@ static int ext4_da_writepages(struct add

    /* Update index */
    index += pages_written;
    + wbc->range_cyclic = range_cyclic;
    if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
    /*
    * set the writeback_index so that range_cyclic

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