Re: [Xen-devel] Xen memory allocation

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> " We are considering implementing a shared buffer cache, but haven't
> 
> A memory management scheme that would be useful here is a lowater/hiwater
> setting for memory allocatation to each domain.
> This would allow phys memory to be oversubscribed by the domains.
> Then xen could slosh memory between domains based on demand.
> 
> It seems like the balloon driver system would have had the groundwork for 
> this.
> I know that bit of things has rotted, but when it worked it ought to have
> demonstrated the mechansisms needed for a  lowater/hiwater policy.

The balloon driver enables a domain to give back physical memory
pages or request new memory. Unlike e.g. vmware this isn't
transparent to the guest OS, but there are actually good reasons
why you don't want it to be transparent (the guest OS is in a
much better position to make sensible paging decisions than the
VMM).

Fixing the balloon driver should be very straight forward. We
then need to add a control interface so that domain0 can tell
other domains what their current memory allocation target is
(when reducing a domain's target dom0 should give them a few
hundred milliseconds to hand back the pages, then kill the domain
if it doesn't comply).

It would be really nice to get this in the 2.0 release. Any
volunteers to help out? ;-)


Thanks,
Ian


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