linux-kernel - Re: [RFC][PATCH] avoid swapping out with swappiness==0

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Message-ID: <4FA82C11.2030805@redhat.com>
Date:	Mon, 07 May 2012 16:09:53 -0400
From:	Rik van Riel <riel@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	Richard Davies <richard.davies@...stichosts.com>,
	Satoru Moriya <satoru.moriya@....com>,
	Jerome Marchand <jmarchan@...hat.com>,
	"jweiner@...hat.com" <jweiner@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	"shaohua.li@...el.com" <shaohua.li@...el.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [RFC][PATCH] avoid swapping out with swappiness==0

On 04/26/2012 11:41 AM, KOSAKI Motohiro wrote:
> On Thu, Apr 26, 2012 at 10:26 AM, Richard Davies
> <richard.davies@...stichosts.com>  wrote:
>> Satoru Moriya wrote:
>>>> I have run into problems with heavy swapping with swappiness==0 and
>>>> was pointed to this thread (
>>>> http://marc.info/?l=linux-mm&m=133522782307215 )
>>>
>>> Did you test this patch with your workload?
>>
>> I haven't yet tested this patch. It takes a long time since these are
>> production machines, and the bug itself takes several weeks of production
>> use to really show up.
>>
>> Rik van Riel has pointed out a lot of VM tweaks that he put into 3.4:
>> http://marc.info/?l=linux-mm&m=133536506926326
>>
>> My intention is to reboot half of our machines into plain 3.4 once it is
>> out, and half onto 3.4 + your patch.
>>
>> Then we can compare behaviour.
>>
>> Will your patch apply cleanly on 3.4?
>
> Note. This patch doesn't solve your issue. This patch mean,
> when occuring very few swap io, it change to 0. But you said
> you are seeing eager swap io. As Dave already pointed out, your
> machine have buffer head issue.
>
> So, this thread is pointless.

Running KVM guests directly off block devices results in a lot
of buffer cache.

I suspect that this patch will in fact fix Richard's issue.

The patch is small, fairly simple and looks like it will fix
people's problems.  It also makes swappiness=0 behave the way
most people seem to imagine it would work.

If it works for a few people (test results), I believe we
might as well merge it.

Yes, for cgroups we may need additional logic, but we can
sort that out as we go along.

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