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

Jens Axboe
2009-06-25T09:10:39Z

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