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

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Message-Id: <20120110143330.44cf1ccf.akpm@linux-foundation.org>
Date:	Tue, 10 Jan 2012 14:33:30 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Dave Chinner <david@...morbit.com>,
	nowhere <nowhere@...kenden.ath.cx>,
	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 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.
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