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    On Wed, Mar 07 2001, Stephen C. Tweedie wrote:
    > On Wed, Mar 07, 2001 at 07:51:52PM +0100, Jens Axboe wrote:
    > > On Wed, Mar 07 2001, Stephen C. Tweedie wrote:
    > >
    > > My bigger concern is when the journalled fs has a log on a different
    > > queue.
    >
    > For most fs'es, that's not an issue. The fs won't start writeback on
    > the primary disk at all until the journal commit has been acknowledged
    > as firm on disk.

    But do you then force wait on that journal commit?

    > Certainly for ext3, synchronisation between the log and the primary
    > disk is no big thing. What really hurts is writing to the log, where
    > we have to wait for the log writes to complete before submitting the
    > commit write (which is sequentially allocated just after the rest of
    > the log blocks). Specifying a barrier on the commit block would allow
    > us to keep the log device streaming, and the fs can deal with
    > synchronising the primary disk quite happily by itself.

    A barrier operation is sufficient then. So you're saying don't
    over design, a simple barrier is all you need?

    --
    Jens Axboe

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