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    SubjectStalls during writeback for mmaped I/O on XFS in 3.0
    I've got a workload that is latency sensitive that writes data to a
    memory mapped file on XFS. With the 3.0 kernel I'm seeing stalls of
    up to 100ms that occur during writeback that we did not see with older
    kernels. I've traced the stalls and it looks like they are blocking
    on wait_on_page_writeback() introduced in
    d76ee18a8551e33ad7dbd55cac38bc7b094f3abb "fs: block_page_mkwrite
    should wait for writeback to finish"

    Reading the commit description doesn't really explain to me why this
    change was needed. Can someone explain what "This is needed to
    stabilize pages during writeback for those two filesystems." means in
    the context of that commit? Is this a problem for older kernels as
    well? Should this have been backported to the stable kernels? What
    are the downsides of reverting this commit?

    Assuming this change is required are there any alternatives solutions
    to avoid these stalls with mmaped I/O on XFS?


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      Last update: 2011-09-15 16:51    [W:0.020 / U:17.132 seconds]
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