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Re: [Xen-devel] About resource reclamation

To: Xuxian Jiang <jiangx@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] About resource reclamation
From: Steven Hand <Steven.Hand@xxxxxxxxxxxx>
Date: Fri, 10 Oct 2003 17:22:09 +0100
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> 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?

Yes; we have something like this for memory (via the balloon driver), 
although this is currently initiated totally by the guest OS. In our
'grand vision', there'll be an economic aspect to use/reservation of 
resources (of any sort) and hence guestOSes will have an incentive to 
reduce their use to the minimum acceptable level. 

> 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.

Modification is not even required with temporally multiplexed
resources (aka CPU, network tx shaping, etc) /unless/ the guestOS is 
re-exporting 'guarantees' or reservations to overlying processes. 
For spatially multiplexed things (mainly memory, disk storage, but 
also e.g. receive packet filters) it's a bit tricker, but can be 
achieved with sufficient guestOS co-operation. 

We'd be keen to have people work on this area (since it'd allow 
overbooking / yield management, and fit into our economic model 
once we've that all working).



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