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    SubjectRe: [PATCH] Implement barrier support for single device DM devices
    On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote:
    > Alasdair G Kergon wrote:
    > > On Fri, Feb 15, 2008 at 01:08:21PM +0100, Andi Kleen wrote:
    > >> Implement barrier support for single device DM devices
    > >
    > > Thanks. We've got some (more-invasive) dm patches in the works that
    > > attempt to use flushing to emulate barriers where we can't just
    > > pass them down like that.
    >
    > I wonder if it's worth the effort to try to implement this.

    DM in theory has some more knowledge for optimization. e.g. for example if
    it knows that a stream of requests hits only a single device then
    it can just pass the barriers through again and only flush when there
    is really a request dependency between different devices. File systems can't
    do it that fine grained; it's either all or nothing.

    I don't know if doing it fine grained will much difference in performance
    though. The only way to find out would be to try it.

    -Andi


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