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SubjectRe: [PATCH -mm 00/16] VM pageout scalability improvements (V8)
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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@linux.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.

Lee



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