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    SubjectRe: Linux 2.6.29
    On Thu, Mar 26 2009, Hugh Dickins wrote:
    > On Thu, 26 Mar 2009, Jens Axboe wrote:
    > > On Wed, Mar 25 2009, Hugh Dickins wrote:
    > > >
    > > > Tangential question, but am I right in thinking that BIO_RW_BARRIER
    > > > similarly bars across all partitions, whereas its WRITE_BARRIER and
    > > > DISCARD_BARRIER users would actually prefer it to apply to just one?
    > >
    > > All the barriers refer to just that range which the barrier itself
    > > references.
    >
    > Ah, thank you: then I had a fundamental misunderstanding of them,
    > and need to go away and work that out some more.
    >
    > Though I didn't read it before asking, doesn't the I/O Barriers section
    > of Documentation/block/biodoc.txt give a very different impression?

    I'm sensing a miscommunication here... The ordering constraint is across
    devices, at least that is how it is implemented. For file system
    barriers (like BIO_RW_BARRIER), it could be per-partition instead. Doing
    so would involve some changes at the block layer side, not necessarily
    trivial. So I think you were asking about ordering, I was answering
    about the write guarantee :-)

    --
    Jens Axboe



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