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Re: [Xen-devel] live saving of domU

To: "Anthony Liguori" <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] live saving of domU
From: "Jacob Gorm Hansen" <jacobg@xxxxxxx>
Date: Thu, 11 May 2006 10:25:00 +0200
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ewan Mellor <ewan@xxxxxxxxxxxxx>, Jayesh Salvi <jayeshsalvi@xxxxxxxxx>
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On 5/10/06, Anthony Liguori <aliguori@xxxxxxxxxx> wrote:
Moreover, you cannot dump the state of a domain after a pause and expect
it to ever run again.

Guests are aware of the physical addresses of the memory that's been
allocated to them.  Because of this, to save a domain's state in a
restorable way you need the guest to "canonicalize" itself.  The only
way to do this today is through a suspend operation which happens to be
a subop of shutdown.  Shutdowns are non-recoverable so you cannot use
this as a snapshotting mechanism.

I've gotten a lot of requests for light weight checkpointing.  AFAIK,
noone is actually working on it though.


I've got this running for xenlinux, using self-checkpointing. I solve
the canonicalization problem by having a radix-tree which maps mfns to
offsets in the pfn->mfn table, and upon resume use this to remap all
the page tables.

It works both across the network and to a block device, as long as
it's opened with O_DIRECT.

I am working on bringing the patch up to date with Xen 3.0.2 at the
moment. It would be great to have the driver model better support
resume after suspend of xenbus and devices in the same domU.


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