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Re: [Xen-devel] About resource reclamation

To: Xuxian Jiang <jiangx@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] About resource reclamation
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 10 Oct 2003 18:05:15 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
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> I believe Xen has the similar primitives for requesting resources from
> GuestOS side. And it seems reasonable and practical to add the reverse
> functionality rescinding resource usage back from GuestOS. Such approach
> may not be possible considering UML or VMWare, but with Xen, it should be
> possible since modification on GuestOS can be made.

Absolutely -- that's one of the big wins of para-virtualization.

For example, I'm looking forward to being able to send a message
from domain 0 to another domain saying "I wish you to release 4MB
of memory as I have another domain that is prepared to pay more
for it. You have 100ms to comply, or be terminated with extreme
prejudice." ;-)

> In one situation, where several domains have been created using overbooked
> resources, would it be nice to have some resouce reclamation capability
> which requires the cooperation between Xen and supported GuestOS?

The general plan is to avoid overbooking "guaranteed" resources
to domains, but allow domains some additional resources on a best
effort proportional share basis.

For example, we've got plans to add support for a shared buffer
cache using 'unused' memory, along with a 'swap cache' to speed
up swapping.

Volunteers welcome ;-)


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