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    SubjectRe: [PATCH v7.1] block: Coordinate flush requests
    From
    2011/1/16 Tejun Heo <tj@kernel.org>:
    > Hello,
    >
    > On Fri, Jan 14, 2011 at 09:00:22AM +0800, Shaohua Li wrote:
    >> it appears we can easily implement this in blk_do_flush, I had
    >> something at my hand too, passed test but no data yet.
    >
    >> Task1: ...FS.....C
    >> Task2: ....F......S...C
    >> Task3: ......F.........S..C
    >> F means a flush is queued, S means a flush is dispatched, C means the flush
    >> is completed. In above, when Task2's flush is completed, we actually can
    >> make Task3 flush complete, as Task2's flush is dispatched after Task3's flush
    >> is queued. With the same reason, we can't merge Task2 and Task3's flush with
    >> Task1's.
    >
    > I think this is the correct direction but we can take it further.  The
    > only thing block layer has to guarantee is (ignoring FUA support),
    >
    > * If the flush request is empty, at least one flush is executed upon
    >  its completion.
    >
    > * If the flush request is not empty, the payload is written only after
    >  a preceding flush and follwed by another flush if requested.
    >
    > So, if we can combine N flushes with or without data,
    >
    >  PREFLUSH -> N flush data payloads -> POSTFLUSH
    This makes sense. would it possible N flush data payloads delay the
    first request?

    > The following is something I hacked past few hours.  I just made it
    > compile so it's definitely horridly broken.  Please don't try to even
    > test it, but it should still give an idea about the direction.  I'll
    > try to finish this early next week.
    I'm looking forward to seeing it.

    Thanks,
    Shaohua
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