Re: [Xen-users] New user question...

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> > -- In the VWware ESX server product, identical memory pages among
> > similar domains can be transparently consolidated to free up more
> > physical RAM for the domains to use.  Is this also the case in Xen?
>
> I'm not sure, but AFAIK it is not. Xen is designed with hosting
> companies in mind. They want to charge users for the amount of memory
> (etc.) they use, and sharing the memory like that would make that much
> harder. It would also cause problems when domains wish to make changes
> to transparently shared pages if there is not enough free memory to copy
> them apart.

The Xen philosophy is to expose the real resources to domains, where possible.  
So you just allocate memory to a domain and say "This is how much RAM you 
have, please do all your own swapping".  For greater flexibility you can also 
change domain memory allocations at runtime as the workloads in the domains 
change.

A number of people are looking at new ways to implement sharing on Xen: one 
group is trying to run thousands of virtual machines on one system (by 
sharing *loads* of memory!), meanwhile with XenFS I'm trying to share the 
memory taken up by disk IO.

Cheers,
Mark

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