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

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Message-ID: <483EA5EF.70906@de.ibm.com>
Date:	Thu, 29 May 2008 14:47:43 +0200
From:	Carsten Otte <cotte@...ibm.com>
To:	Rik van Riel <riel@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Christian Borntraeger <CBORNTRA@...ibm.com>
Subject: Re: [PATCH -mm 00/16] VM pageout scalability improvements (V8)

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.
> 
> Against 2.6.26-rc2-mm1
> 
> This patch series improves VM scalability by:
> 
> 1) putting filesystem backed, swap backed and non-reclaimable pages
>    onto their own LRUs, so the system only scans the pages that it
>    can/should evict from memory
> 
> 2) switching to SEQ replacement for the anonymous LRUs, so the
>    number of pages that need to be scanned when the system
>    starts swapping is bound to a reasonable number
> 
> 3) keeping non-reclaimable pages off the LRU completely, so the
>    VM does not waste CPU time scanning them.  Currently only
>    ramfs and SHM_LOCKED pages are kept on the noreclaim list,
>    mlock()ed VMAs will be added later
I think I've run into #2 with kvm on s390 lately. I've tried a large 
setup with 200 guests running WebSphere. The guest memory is stored in 
anonymous pages, all guests are started up from a script so everything 
is dirty initially. I use 200gig swap with 45 gig main memory for the 
scenario. Everything runs perfect except when vmscan is triggered for 
the first time: it starts to writeback, and the whole system freezes 
until it has paged out the 15gig in the inactive list. From there on, 
everything runs smooth again with a constant swap rate.
I'd like to try your patchset to see how that behave in this scenario. 
Do you have a version that applies against current git, 2.6.26-rc3 or 
similar?
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