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    Subject[PATCH 5/4] writeback: limit write_cache_pages integrity scanning to current EOF

    sync can currently take a really long time if a concurrent writer is
    extending a file. The problem is that the dirty pages on the address
    space grow in the same direction as write_cache_pages scans, so if
    the writer keeps ahead of writeback, the writeback will not
    terminate until the writer stops adding dirty pages.

    For a data integrity sync, we only need to write the pages dirty at
    the time we start the writeback, so we can stop scanning once we get
    to the page that was at the end of the file at the time the scan

    This will prevent operations like copying a large file preventing
    sync from completing as it will not write back pages that were
    dirtied after the sync was started. This does not impact the
    existing integrity guarantees, as any dirty page (old or new)
    within the EOF range at the start of the scan will still be

    Signed-off-by: Dave Chinner <>
    mm/page-writeback.c | 15 +++++++++++++++
    1 files changed, 15 insertions(+), 0 deletions(-)

    diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    index e22af84..4ba2728 100644
    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -852,7 +852,22 @@ int write_cache_pages(struct address_space *mapping,
    if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
    range_whole = 1;
    cycled = 1; /* ignore range_cyclic tests */
    + /*
    + * If this is a data integrity sync, cap the writeback to the
    + * current end of file. Any extension to the file that occurs
    + * after this is a new write and we don't need to write those
    + * pages out to fulfil our data integrity requirements. If we
    + * try to write them out, we can get stuck in this scan until
    + * the concurrent writer stops adding dirty pages and extending
    + * EOF.
    + */
    + if (wbc->sync_mode == WB_SYNC_ALL &&
    + wbc->range_end == LLONG_MAX) {
    + end = i_size_read(mapping->host) >> PAGE_CACHE_SHIFT;
    + }
    done_index = index;
    while (!done && (index <= end)) {

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      Last update: 2010-04-20 05:43    [W:0.033 / U:5.048 seconds]
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