Cloning a VM and copy-on-write deduplicating memory using CoW page sharing in Xen 4+

Cloning a VM and copy-on-write deduplicating memory using CoW page sharing in Xen 4+

[Patrick Wilbur]

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Hey all,
Hey Andres,

I'm looking to clone a VM into several extremely-similar VMs, and I'm
hoping to also make use of your lovely new CoW page sharing capabilities in
Xen 4.

>From my understanding of a previous thread where Andres described the
process of sharing/coalescing memory between VMs, it sounds like I will
need to "manually" coalesce each page using a homebrew tool of mine.  The
issue I have with doing this is it seems like I'd need to pause, save mem,
load mem in a new VM, coalesce, and resume two VMs, which seems painful and
wasteful of a process for cloning!

Is there an easier way to do this, or should we add a new feature for CoW
cloning of VMs in Xen via a userspace tool?

Thanks,
Pat Wilbur & team


--
Patrick F. Wilbur
Researcher, Consultant, Educator,
Computer Science Graduate at Clarkson University

DONE RIGHT THE FIRST TIME: Consulting and hiring information:
http://pdub.net/consulting/ & http://pdub.net/hiring/

patrick.wilbur@gmail.com
wilburpf@clarkson.edu

Check out our book: http://runningxen.com
My website: http://pdub.net

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Re: Cloning a VM and copy-on-write deduplicating memory using CoW page sharing in Xen 4+

[Andres Lagar-Cavilla]

> Hey all,
> Hey Andres,
>
> I'm looking to clone a VM into several extremely-similar VMs, and I'm
> hoping to also make use of your lovely new CoW page sharing capabilities
> in
> Xen 4.
>
> From my understanding of a previous thread where Andres described the
> process of sharing/coalescing memory between VMs, it sounds like I will
> need to "manually" coalesce each page using a homebrew tool of mine.  The
> issue I have with doing this is it seems like I'd need to pause, save mem,
> load mem in a new VM, coalesce, and resume two VMs, which seems painful
> and
> wasteful of a process for cloning!

Patrick,
that is indeed painful and wasteful. That is why we added
xc_memshr_add_to_physmap. Now you can do Potemkin-/SnowFlock-like cloning
in a few lines of code. You still want the source VM to be paused,
obviously.

Yuengling is my favourite US beer ;)

Andres

>
> Is there an easier way to do this, or should we add a new feature for CoW
> cloning of VMs in Xen via a userspace tool?
>
> Thanks,
> Pat Wilbur & team
>
>
> --
> Patrick F. Wilbur
> Researcher, Consultant, Educator,
> Computer Science Graduate at Clarkson University
>
> DONE RIGHT THE FIRST TIME: Consulting and hiring information:
> http://pdub.net/consulting/ & http://pdub.net/hiring/
>
> patrick.wilbur@gmail.com
> wilburpf@clarkson.edu
>
> Check out our book: http://runningxen.com
> My website: http://pdub.net
>