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SubjectRe: [RFC][PATCH] mm: stop balance_dirty_pages doing too much work
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Jens Axboe wrote:
> On Thu, Jun 25 2009, Al Boldi wrote:
> > Jens Axboe wrote:
> > > On Thu, Jun 25 2009, Jens Axboe wrote:
> > > > 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.
> > >
> > > Results for writeback without the bdi_thresh patch
> > >
> > > Kernel Throughput usr sys ctx util
> > > --------------------------------------------------------------
> > > wb-bdi_thresh 211MB/sec 22.71% 53.30% 4050 91.19%
> > > wb-bdi_thresh 212MB/sec 22.78% 53.55% 4809 91.51%
> > > wb-bdi_thresh 212MB/sec 22.99% 54.23% 4715 93.10%
> > >
> > > Not a lot of difference there, without more than three runs it's hard
> > > to say what is significant. Could be a small decrease in throughput, if
> > > the 208MB/sec results from above is an outlier (I think it is,
> > > ~215MB/sec is usually the most consistent result).
> >
> > What's the iowait on these runs?
>
> Not sure, I didn't check. Why do you ask?

iowait gives you an indication of seekactivity.


Thanks!

--
Al





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