Re: Ownership of machine pages: Was: [Xen-devel] Essay on an important Xen decision (long)

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 11 Jan 2006, at 22:49, Magenheimer, Dan (HP Labs Fort Collins) wrote:

> > Extra
> > context switches are added for any page related operation.
> Hmmm... not really.  Page operations (such as alloc and free)
> are relatively rare and can be batched (e.g. at domain startup).
> And domU's are not going to be making policy decisions...
> If dom0 is making policy decisions (e.g. this stick of RAM is
> about to die, who do I steal memory from?), dom0 ownership
> of the pages may even reduce context switches.
In a literal/extreme form of your model, any address space 
access/update would need to be translated and/or validated by domain0. 
That's certainly going to be a significant overhead. I believe that 
there is a balance to be struck between sufficient mechanism in Xen to 
ensure good performance while allowing flexible policy expression in 
the control plane. I think talking about this at the summit would be 
very interesting -- are your ideas solidified enough perhaps even for a 
short presentation?
 -- Keir


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