linux-kernel - Re: Kswapd in 3.2.0-rc5 is a CPU hog

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Message-Id: <20120110204245.d24ed540.akpm@linux-foundation.org>
Date:	Tue, 10 Jan 2012 20:42:45 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Nikolay S." <nowhere@...kenden.ath.cx>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan@...nel.org>,
	Dave Chinner <david@...morbit.com>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: Kswapd in 3.2.0-rc5 is a CPU hog

On Wed, 11 Jan 2012 07:25:20 +0400 "Nikolay S." <nowhere@...kenden.ath.cx> wrote:

> __ ____., 10/01/2012 __ 14:33 -0800, Andrew Morton __________:
> > On Tue, 27 Dec 2011 13:56:58 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > 
> > > Hmm, if I understand correctly,
> > > 
> > >  - dd's speed down is caused by kswapd's cpu consumption.
> > >  - kswapd's cpu consumption is enlarged by shrink_slab() (by perf)
> > >  - kswapd can't stop because NORMAL zone is small.
> > >  - memory reclaim speed is enough because dd can't get enough cpu.
> > > 
> > > I wonder reducing to call shrink_slab() may be a help but I'm not sure
> > > where lock conention comes from...
> > 
> > Nikolay, it sounds as if this problem has only recently started
> > happening?  Was 3.1 OK?
> > 
> > If so, we should work out what we did post-3.1 to cause this.
> 
> Yes, 3.1. was ok.
> Recently I have upgraded to 3.2, and I can not reproduce the problem.
> I'm now at 5 days uptime, the machine usage pattern, the software - all
> the same, but the problem is not visible anymore:
> 
>   PID USER      S %CPU %MEM    TIME+  SWAP COMMAND
> 14822 nowhere   R   30  0.2   0:01.52  10m dd
>   416 root      S    7  0.0   6:26.72    0 kswapd0
> 
> (also, kswapd run time after 5 days is only 6,5 seconds, whereas with
> -rc5 it was 22 seconds after 5 days).
> 
> I can provide similar traces to see what has changed in kswapd's
> activities (if it is of any value)

OK, thanks for the followup.  I suppose we assume this is fixed unless
someone reports it in 3.2.

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