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Re: [Xen-devel] of cows and clones: creating domains as clones of saved

To: Peri Hankey <mpah@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] of cows and clones: creating domains as clones of saved state
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 25 Nov 2004 22:36:08 +0000
Cc: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx
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> You had in fact seen this in an earlier thread: 'crash when domain is 
> restored', which was confirmed as occurring by Charles Coffing.  You 
> suggested I add instrumentation. I haven't yet had a chance to do that, 
> but I'll first try it with xen-unstable.
> But I'll be interested to hear whether you think there is any mileage in 
> my clone proposal.

It sounds rather like VM forking, except you want to be able to can
the base image for later re-instantiation. I guess you would create
the in-memory read-only base VM on demand from the canned image when
the first CoW VM is created, and garbage-collect it when the last CoW
VM is destroyed.

The idea of taking a small basic set of VM images and customising
their configuration when instantiating them is sane. For the memory
sharing we would like to investigate a more general mechanism (e.g.,
shared buffer cache indexed by content hash) which would optimise
memory usage not just in your scenario but also in a whole bunch of

 -- Keir

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