linux-kernel - Re: [RFC][PATCH] mm: stop balance_dirty

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Date:	Thu, 25 Jun 2009 16:46:22 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Kennedy <richard@....demon.co.uk>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] mm: stop balance_dirty_pages doing too much work

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@....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@....demon.co.uk>
> > > > > > > ---
> > > > >
> > > > > Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.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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