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    SubjectRe: [PATCH 1/2] aio: add vectored I/O support
    Joel Becker wrote:

    >>I think what happened was that the number of iocbs submitted (64 iocbs
    >>of 4K each) did not merge because the device queue depth was very large;
    >>no queuing occured because (I imagine) merging happens while a request
    >>is waiting for disk readiness.
    >>
    >>
    >
    > Why did you submit 64 iocbs of 4K? Was every page virtually
    >discontiguous, or did you arbitrarily decide to create a worst-case?
    >
    >
    The application (a userspace filesystem with its own cache) manages
    memory in 4K pages, but can perform much larger I/Os, for example during
    readahead and after merging writes. After a very short while memory is
    completely fragmented.


    --
    Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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