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    SubjectRe: [PATCH] readahead:add blk_run_backing_dev
    On Wed, May 20, 2009 at 09:43:18AM +0800, Hisashi Hifumi wrote:
    >
    > At 10:07 09/05/20, KOSAKI Motohiro wrote:
    > >(cc to Wu and linux-mm)
    > >
    > >> Hi.
    > >>
    > >> I wrote a patch that adds blk_run_backing_dev on page_cache_async_readahead
    > >> so readahead I/O is unpluged to improve throughput.
    > >>
    > >> Following is the test result with dd.
    > >>
    > >> #dd if=testdir/testfile of=/dev/null bs=16384
    > >>
    > >> -2.6.30-rc6
    > >> 1048576+0 records in
    > >> 1048576+0 records out
    > >> 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s
    > >>
    > >> -2.6.30-rc6-patched
    > >> 1048576+0 records in
    > >> 1048576+0 records out
    > >> 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s
    > >>
    > >> Sequential read performance on a big file was improved.
    > >> Please merge my patch.
    > >
    > >I guess the improvement depend on readahead window size.
    > >Have you mesure random access workload?
    >
    > I tried with iozone. But there was no difference.

    It does not impact random IO because the patch only modified the
    *async* readahead path, and random IO is obviously *sync* ones.


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