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Re: [Xen-devel] Copy-on-write memory to allow many more xenU domains per machine



Ian Pratt wrote:
Hello

Some time ago Michael Vrable talked about copy-on-write memory to enable large numbers of nearly identical machines to run on the same physical hardware. Is this a feasible proposition? I asked a few days ago in the original thread, but no-one seems to have noticed. It seems to me that it would be a very significant feature to offer.

It's useful for honeypots and other situations where you want
very large numbers of VMs, but isn't generally a huge win.

When I was doing the live migration work I recorded fingerprints
of all VM pages that were on several systems, and didn't find a
whole lot of commonality between VMs.

I thought the idea would be to have a 'clone' primitive that would work
in a similar way to Unix fork? The clone would start off sharing all
pages, although a lot of them would get copied fairly quickly. Does
anyone have an idea of what proportion or number of pages in a Linux
system stay constant (and are not paged out) after boot?

--
David Hopwood <david.nospam.hopwood@xxxxxxxxxxxxxxxx>



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