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Date: Fri, 12 Mar 2010 11:01:29 +0100
From: Andrea Righi <arighi@develer.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
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       linux-mm@kvack.org
Subject: Re: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v6)
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On Fri, Mar 12, 2010 at 08:52:44AM +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 12 Mar 2010 00:27:09 +0100
> Andrea Righi <arighi@develer.com> wrote:
> 
> > On Thu, Mar 11, 2010 at 10:03:07AM -0500, Vivek Goyal wrote:
> 
> > > I am still setting up the system to test whether we see any speedup in
> > > writeout of large files with-in a memory cgroup with small memory limits.
> > > I am assuming that we are expecting a speedup because we will start
> > > writeouts early and background writeouts probably are faster than direct
> > > reclaim?
> > 
> > mmh... speedup? I think with a large file write + reduced dirty limits
> > you'll get a more uniform write-out (more frequent small writes),
> > respect to few and less frequent large writes. The system will be more
> > reactive, but I don't think you'll be able to see a speedup in the large
> > write itself.
> > 
> Ah, sorry. I misunderstood something. But it's depends on dirty_ratio param.
> If
> 	background_dirty_ratio = 5
> 	dirty_ratio	       = 100
> under 100M cgroup, I think background write-out will be a help.

Right, in this case background flusher threads will help a lot to
write-out the cgroup dirty memory and it'll get better performance.

-Andrea