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

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Date:	Tue, 27 May 2008 21:40:25 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
CC:	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kosaki Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mm 00/16] VM pageout scalability improvements (V8)

Lee Schermerhorn wrote:
> On Mon, 2008-05-26 at 15:33 -0400, 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...
>>
> 
> I tested Rik's previous patch set with my noreclaim/mlock patches over
> the long weekend on 32GB systems--one ia64 [16cpu x 4 nodes] and one
> x86_64 [8 core x 4 nodes] on 26-rc2-mm1.  A fairly heavy stress load ran
> for 92-93 hours on each system w/o error.  Stats tracked throughout, no
> leaked pages, ...  
> 
> Since Balbir is starting to look at this, I need to ask about
> interaction with the memory controller.  It is currently unaware of the
> noreclaim list.  I'm not sure what will happen if/when the memory
> controller tries to reclaim a page that system has moved to the
> noreclaim list.  Something we'll need to address.  It's on my list, but
> I won't get to it for a couple of weeks.

I have not looked at the patches, but thanks for the heads up. I intend to start
looking at it in the spare bandwidth I have.

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