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

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Date:	Mon, 21 May 2012 08:12:26 +0100
From:	Richard Davies <richard.davies@...stichosts.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.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

Hi Satoru,

Rik van Riel wrote:
> KOSAKI Motohiro wrote:
> > Richard Davies 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.

Now that 3.4 is out with Rik's fixes, I'm keen to start testing with and
without this extra patch.

Satoru - should I just apply your original patch (most likely), or do you
need to update for the final released kernel?

Thanks,

Richard.
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