linux-kernel - Re: [PATCH 0/11] ksm: NUMA trees and page migration

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Message-ID: <20130129104513.GA15004@redhat.com>
Date:	Tue, 29 Jan 2013 12:45:14 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Petr Holasek <pholasek@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Anton Arapov <anton@...hat.com>, Mel Gorman <mgorman@...e.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH 0/11] ksm: NUMA trees and page migration

On Mon, Jan 28, 2013 at 05:07:15PM -0800, Hugh Dickins wrote:
> On Mon, 28 Jan 2013, Andrew Morton wrote:
> > On Fri, 25 Jan 2013 17:53:10 -0800 (PST)
> > Hugh Dickins <hughd@...gle.com> wrote:
> > 
> > > Here's a KSM series
> > 
> > Sanity check: do you have a feeling for how useful KSM is? 
> > Performance/space improvements for typical (or atypical) workloads? 
> > Are people using it?  Successfully?
> > 
> > IOW, is it justifying itself?
> 
> I have no idea!  To me it's simply a technical challenge - and I agree
> with your implication that that's not a good enough justification.
> 
> I've added Marcelo and Gleb and the KVM list to the Cc:
> my understanding is that it's the KVM guys who really appreciate KSM.
> 
KSM is used on all RH kvm deployments for memory overcommit. I asked
around for numbers and got the answer that it allows to squeeze anywhere
between 10% and 100% more VMs on the same machine depends on a type of
a guest OS and how similar workloads of VMs are. And management tries
to keep VMs with similar OSes/workloads on the same host to gain more
from KSM.

--
			Gleb.
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