linux-kernel - Re: [RFC][PATCH 0/9] rework KVM mmu

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Date:	Wed, 16 Jun 2010 08:03:16 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC][PATCH 0/9] rework KVM mmu_shrink() code

On Wed, 2010-06-16 at 11:38 +0300, Avi Kivity wrote:
> On 06/15/2010 04:55 PM, Dave Hansen wrote:
> > These seem to boot and run fine.  I'm running about 40 VMs at
> > once, while doing "echo 3>  /proc/sys/vm/drop_caches", and
> > killing/restarting VMs constantly.
> >    
> 
> Will drop_caches actually shrink the kvm caches too?  If so we probably 
> need to add that to autotest since it's a really good stress test for 
> the mmu.

I'm completely sure.  I crashed my machines several times this way
during testing.

> > Seems to be relatively stable, and seems to keep the numbers
> > of kvm_mmu_page_header objects down.
> >    
> 
> That's no necessarily a good thing, those things are expensive to 
> recreate.  Of course, when we do need to reclaim them, that should be 
> efficient.

Oh, I meant that I didn't break the shrinker completely.

> We also do a very bad job of selecting which page to reclaim.  We need 
> to start using the accessed bit on sptes that point to shadow page 
> tables, and then look those up and reclaim unreferenced pages sooner.  
> With shadow paging there can be tons of unsync pages that are basically 
> unused and can be reclaimed at no cost to future runtime.

Sounds like a good next step.

-- Dave

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