Re: [RFC][PATCH] mm: stop balance_dirty_pages doing too much work

Al Boldi
2009-06-25T12:32:17Z

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?

Thanks!

--
Al