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RE: [Xen-devel] Domain save/migrate issue

  • To: "Anthony Liguori" <aliguori@xxxxxxxxxx>
  • From: "Noam Taich" <noam.taich@xxxxxxxxxxxx>
  • Date: Wed, 15 Feb 2006 00:38:16 -0800
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 15 Feb 2006 08:50:36 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcYxdsWEjhT57CQySx+jrYWuI2kiZQAkXksw
  • Thread-topic: [Xen-devel] Domain save/migrate issue

> there's a fair bit of work that would be needed to allow for 
light-weight checkpointing.  A domain has to be suspended for the 
checkpoint to finish (although presumably one could use a similar as 
live migration to get most of the way there).  
> Today, in Xen, there is no way to get out of a suspended state.

>If a domain could leave the suspended state, it would make
pretty cheap.  Also, presumably, it would simplify rebooting because 
instead of having to recreate a domain on reboot, the hypervisor could 
just reinit it.  Of course, it would need some way of knowing how to 
build the domain...


Anthony Liguori
> S.

My suggestion is NOT to bring a domain out of suspension. What I am
suggesting is bypassing the problem.
Here's the current idea:

We need the memory image of the domain to be static, So we can't allow
the domain to run. So, the first idea is to use pause/unpause instead of


Now for the next (serious) problem:
This seems to work fine (in live or non live settings) until the
xc_linux_save() function reaches the part where it checks the frame
Of the suspend record, which makes sense, because now, we have NO
suspend record. So, the second idea is to (simply?) write all that info
on the io_fd
The function gets ourselves. Just canonicalize the fns that suspend
And write the appropriate info.

The restore function does not have to change at all... it sees the same

So, what do you think, is this a good idea? Even possible? Will it
entail a lot?

One of my concerns is this: the shared pages.
Can Xen write to them while the guest is "only" paused? And if so, what 
Can it (practically) write there while the guest is paused?
Even if it CAN, is it Reasonable to expect it won't do that usually? 

I'm not really troubled by the storage issues. This feature would be
useful in many cases even with no solution to that problem.

Sorry for the multiple messages on the original subject. It was an
unfortunate misunderstanding.

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