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

[Rik van Riel]

On 04/26/2012 11:41 AM, KOSAKI Motohiro wrote:
> On Thu, Apr 26, 2012 at 10:26 AM, Richard Davies
> <richard.davies@xxxxxxxxxxxxxxxx>  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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