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

[Rik van Riel <riel@redhat.com>]

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