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    SubjectRe: [PATCH 01/17] writeback: introduce .tagged_sync for the WB_SYNC_NONE sync stage
    On Thu, May 12, 2011 at 09:57:07PM +0800, Wu Fengguang wrote:
    > sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
    > WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do
    > livelock prevention for it, too.
    > Note that writeback_inodes_sb() is called by not only sync(), they are
    > treated the same because the other callers also need livelock prevention.
    > Impact: It changes the order in which pages/inodes are synced to disk.
    > Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
    > until finished with the current inode.

    What about all the filesystems that implement their own
    .writepages()/write_cache_pages() functions or have
    have special code that checks WB_SYNC_ALL in .writepages (e.g. gfs2,
    ext4, btrfs and perhaps others). Don't they all need to be aware of
    this tagged_sync field?


    Dave Chinner

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