From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <ian.campbell@citrix.com>
Subject: Re: [PATCH 0/2] Bulk mem-share identical domains
Date: Tue, 6 Oct 2015 15:26:19 +0100
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To: Tamas K Lengyel <tamas@tklengyel.com>, xen-devel@lists.xenproject.org
Cc: Wei Liu <wei.liu2@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, George Dunlap <george.dunlap@eu.citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Jan Beulich <jbeulich@suse.com>, Keir Fraser <keir@xen.org>
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On Sun, 2015-10-04 at 14:25 -0600, Tamas K Lengyel wrote:
> The following patches add a convenience memop to the mem_sharing system,
> allowing for the rapid deduplication of memory pages between identical
> domains.
> 
> The envisioned use-case for this is the following:
> 1) Create two domains from the same snapshot using xl.
>    This step can also be performed by piping an existing domain's memory
> with
>         "xl save -c <domain> <pipe> | xl restore -p <new_cfg> <pipe>"
>    It is up for the user to create the appropriate configuration for the
> clone,
>    including setting up a CoW-disk as well. 
> 2) Enable memory sharing on both domains
> 3) Execute bulk dedup between the domains.

This is a neat trick, but has the downside of first shovelling all the data
over a pipe and then needing to allocate it transiently before dedupping it
again.

Have you looked at the possibility of doing the save+restore in the same
process with a cut through for the RAM part which just dups the page into
the target domain?

Once upon a time (migr v1) that would certainly have been impossibly hard,
but with migr v2 it might be a lot easier to integrate something like that
(although surely not as easy as what you've done here!).

Just an idea, and not intended at all as an argument for not taking this
series or anything.

Ian.