linux-kernel - Re: [PATCH -mm 00/16] VM pageout scalability improvements (V8)

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Message-ID: <483D46CE.2020507@linux.vnet.ibm.com>
Date:	Wed, 28 May 2008 17:19:34 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Rik van Riel <riel@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Kosaki Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mm 00/16] VM pageout scalability improvements (V8)

Rik van Riel wrote:
> On Mon, 26 May 2008 23:54:55 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
>> Rik van Riel wrote:
>>> On large memory systems, the VM can spend way too much time scanning
>>> through pages that it cannot (or should not) evict from memory. Not
>>> only does it use up CPU time, but it also provokes lock contention
>>> and can leave large systems under memory presure in a catatonic state.
>> Hi, Rik,
>>
>> This patchset looks good (I did a brief scan). I'll go ahead and play with it?
>> What is a good memory size to test the patches on (to see improvements).
> 
> The larger, the better.  One known problem with the current upstream
> VM is large numbers of anonymous pages, or a mix of mlocked and anon
> pages.
> 
> Once the system needs to swap something out, every single anon page
> will have the referenced bit set and the system needs to do lots of
> scanning before it can evict the first page.  This scanning causes
> multiple CPUs to pile up and things slow down exponentially and/or
> catastrophically :)
> 
> Unfortunately the largest system I have access to on a regular basis
> has "only" 16GB of RAM :(
> 
> I am also making 2.6.25 based kernel RPMs available with the split LRU
> patch set, at http://people.redhat.com/riel/splitvm/
> 
> The most recently posted patches are newer, though...
> 

Rik,

I've run into a case where with the splitvm patches the memory controller
immediately OOMs a task in the cgroup on exceeding it's limit. I am going to try
and find the root cause for it.



-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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