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

[Minchan Kim <minchan@kernel.org>]

On 05/08/2012 05:09 AM, Rik van Riel wrote:

> 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.
> 


I agree Rik's opinion absolutely.

-- 
Kind regards,
Minchan Kim