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Re: [Xen-users] Memory Sizing Guidelines

To: Paul Waldo <pwaldo@xxxxxxxxxxxxx>
Subject: Re: [Xen-users] Memory Sizing Guidelines
From: Christian Horn <chorn@xxxxxxxxxxxx>
Date: Sat, 27 Oct 2007 18:06:25 +0200
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On Sat, Oct 20, 2007 at 07:27:35AM -0400, Paul Waldo wrote:
> Christian Horn wrote:
> >  
> >256MB for dom0, rest split up for the 2 domU would be my guess.
> >
> >
> >Christian
> >  
> Thanks for the reply, Christian.  The only services I plan on running on 
> dom0 are ones that support the domU, so it should be pretty light.  I 
> guess the main issue is disk caching.  Linux uses free memory to cache 
> disk, so where should that happen, the dom0 or the domU?

I think it should be done in the dom0:
imagine just one spindle of disks and some domUs running and doing i/o
on it, i.e. a bonnie benchmark.
The dom0 should be the place where

- the caching happens; imagine the domU access all the same filesystem in
a readonly-mode, they shouldnt buffer the contents but dom0, as that
reduces the memory used to buffer the same content
- the dom0 should know best about all i/o operations that the domU try
to perform, so i.e. the elevator-algorithms in the domUs should be 
disabled and the dom0 is the place to calculate that.

I havent optimized installations for this yet, would like to hear
other opinions on that...


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