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    SubjectRe: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains
    On Thu, Feb 01, 2001 at 09:25:08PM +0000, Stephen C. Tweedie wrote:
    > > No. Just allow passing the multiple of the devices blocksize over
    > > ll_rw_block.
    >
    > That was just one example: you need the sub-ios just as much when
    > you split up an IO over stripe boundaries in LVM or raid0, for
    > example.

    IIRC that's why you designed (and I thought of independandly) clone-kiobufs.

    > Secondly, ll_rw_block needs to die anyway: you can expand
    > the blocksize up to PAGE_SIZE but not beyond, whereas something like
    > ll_rw_kiobuf can submit a much larger IO atomically (and we have
    > devices which don't start to deliver good throughput until you use
    > IO sizes of 1MB or more).

    Completly agreed.

    > If I've got a vector (page X, offset 0, length PAGE_SIZE) and I want
    > to split it in two, I have to make two new vectors (page X, offset 0,
    > length n) and (page X, offset n, length PAGE_SIZE-n). That implies
    > copying both vectors.
    >
    > If I have a page vector with a single offset/length pair, I can build
    > a new header with the same vector and modified offset/length to split
    > the vector in two without copying it.

    You just say in the higher-level structure ignore from x to y even if
    they have an offset in their own vector.

    Christoph

    --
    Of course it doesn't work. We've performed a software upgrade.
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