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RE: [Xen-users] Few Questions / Application of Xen

To: "'Ugo PARSI'" <ugo.parsi@xxxxxxxxx>
Subject: RE: [Xen-users] Few Questions / Application of Xen
From: "Steffen Heil" <lists@xxxxxxxxxxxxxxx>
Date: Tue, 21 Mar 2006 13:49:05 +0100
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Hi

> > You need to give every domU a certain amount of memory on startup.
> > As far as I know, you cannot change this later.
> >
> > So you NEED to give every domain as much memory as it will 
> > ever need.
> 
> Yeah that sucks (for my use) :(
> 
> No way of doing a no limit thing in order to share the RAM ?
> Like each domU can take as many RAM as it wants and so it 
> would automagically share the RAM load ?

I am also somehow new to xen, so somebody correct me if I am wrong.
But as fas as I understand:

Every domU has it's own kernel which manages it's own memory.
So every domU also has it's own drive cache.

Most OSs tend to simly use all free memory for drive caches. So does Windows
and so does linux. This makes sence for real hardware, since unused free
memory is a waste of resources and using every available memory as cache
speeds up the mashine extremely. However, if there are other systems that
share the same memory, It might be better for one system to have less cache
memory and therefor preventing another system from swaping. But to take
control of this, every system would need to know about the memory usage of
the other systems.
That would be totally against system separation.

Regards,
  Steffen

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