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

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Date:	Mon, 06 Apr 2009 14:19:25 +0300
From:	Izik Eidus <ieidus@...hat.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
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

Nick Piggin wrote:
> 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.
>   

This numbers are took from such workload, it is some kind of weird 
script that keep opening Word / Excel and write there like a user...
I think in addition it open internet explorer and enter to random sites...
I can search for the script if wanted...

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

I Dont know.

>  
>   
>> 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.
>   

Agree about that, dont know their application to much, i know they had 
problems to do it.

>  
>   
>> 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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