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    SubjectRe: [RFC][PATCH] mm: stop balance_dirty_pages doing too much work
    On Thu, Jun 25 2009, Peter Zijlstra wrote:
    > On Wed, 2009-06-24 at 15:27 -0700, Andrew Morton wrote:
    > > On Wed, 24 Jun 2009 11:38:24 +0100
    > > Richard Kennedy <richard@rsk.demon.co.uk> wrote:
    > >
    > > > When writing to 2 (or more) devices at the same time, stop
    > > > balance_dirty_pages moving dirty pages to writeback when it has reached
    > > > the bdi threshold. This prevents balance_dirty_pages overshooting its
    > > > limits and moving all dirty pages to writeback.
    > > >
    > > >
    > > > Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
    > > > ---
    >
    > Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

    After doing some integration and update work on the writeback branch, I
    threw 2.6.31-rc1, 2.6.31-rc1+patch, 2.6.31-rc1+writeback into the test
    mix. The writeback series include this patch as a prep patch. Results
    for the mmap write test case:

    Kernel Throughput usr sys ctx util
    --------------------------------------------------------------
    vanilla 184MB/sec 19.51% 50.49% 12995 82.88%
    vanilla 184MB/sec 19.60% 50.77% 12846 83.47%
    vanilla 182MB/sec 19.25% 51.18% 14692 82.76%
    vanilla+patch 169MB/sec 18.08% 43.61% 9507 76.38%
    vanilla+patch 170MB/sec 18.37% 43.46% 10275 76.62%
    vanilla+patch 165MB/sec 17.59% 42.06% 10165 74.39%
    writeback 215MB/sec 22.69% 53.23% 4085 92.32%
    writeback 214MB/sec 24.31% 52.90% 4495 92.40%
    writeback 208MB/sec 23.14% 52.12% 4067 91.68%

    To be perfectly clear:

    vanilla 2.6.31-rc1 stock
    vanilla+patch 2.6.31-rc1 + bdi_thresh patch
    writeback 2.6.31-rc1 + bdi_thresh patch + writeback series

    This is just a single spindle w/ext4, nothing fancy. I'll do a 3-series
    run with the writeback and this patch backed out, to see if it makes a
    difference here. I didn't do that initially, since the results were in
    the range that I expected.

    --
    Jens Axboe



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