Xen users - Jun 2009 - Live Migration and how exactly it works

Hello everybody!

I have a couple of questions regarding the live migration feature in
XEN. How exactly does it work? I have read in a paper on the Internet
that there are three phases of the live migration process:

1. Push phase: iteratively copy the memory of the VM from the old host
to the new host
2. Stop-and-copy phase: when XEN sees that there is a certain amount
of pages that get dirtied very often it freezes the VM and copies
these pages to the new host
3. Pull phase: the VM starts on the new host and if it needs any page
that was not copied, it pulls it over the network

Is this the way XEN handles Live Migration?

If so, how is the length of the Push phase determined?
When exactly does XEN say "okay, now let''s freeze the VM and copy
the memory"?
Is there maybe an upper limit of iterations and a threshold of dirty
pages after which the VM gets stopped?
Does the length of the phase depend on the amount pages which get
dirtied? How fast should the pages change so that they get dubbed
"dirty"?

I looked in the official XEN Documentation, googled around the
Internet but couldn''t find any information on the topic...

Maybe someone knows the answers?

Thanks in advance for any replies!

Best regards,
Nikola

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