linux-kernel - Re: [PATCH 0/4] ksm - dynamic page sharing driver for linux v2

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Message-Id: <200904061704.50052.nickpiggin@yahoo.com.au>
Date:	Mon, 6 Apr 2009 17:04:49 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Izik Eidus <ieidus@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org, avi@...hat.com,
	aarcange@...hat.com, chrisw@...hat.com, mtosatti@...hat.com,
	hugh@...itas.com, kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 0/4] ksm - dynamic page sharing driver for linux v2

On Sunday 05 April 2009 01:35:18 Izik Eidus wrote:

> This driver is very useful for KVM as in cases of runing multiple guests
> operation system of the same type.
> (For desktop work loads we have achived more than x2 memory overcommit
> (more like x3))

Interesting that it is a desirable workload to have multiple guests each
running MS office.

I wonder, can windows enter a paravirtualised guest mode for KVM? And can
you detect page allocation/freeing events?

 
> This driver have found users other than KVM, for example CERN,
> Fons Rademakers:
> "on many-core machines we run one large detector simulation program per core.
> These simulation programs are identical but run each in their own process and
> need about 2 - 2.5 GB RAM.
> We typically buy machines with 2GB RAM per core and so have a problem to run
> one of these programs per core.
> Of the 2 - 2.5 GB about 700MB is identical data in the form of magnetic field
> maps, detector geometry, etc.
> Currently people have been trying to start one program, initialize the geometry
> and field maps and then fork it N times, to have the data shared.
> With KSM this would be done automatically by the system so it sounded extremely
> attractive when Andrea presented it."

They should use a shared memory segment, or MAP_ANONYMOUS|MAP_SHARED etc.
Presumably they will probably want to control it to interleave it over
all numa nodes and use hugepages for it. It would be very little work.

 
> I am sending another seires of patchs for kvm kernel and kvm-userspace
> that would allow users of kvm to test ksm with it.
> The kvm patchs would apply to Avi git tree.
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