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Re: [Xen-devel] [PATCH 2 of 2 RFC] xl: allow for moving the domain's memory when changing vcpu affinity

On 06/07/12 14:25, Ian Campbell wrote:
On Fri, 2012-07-06 at 13:53 +0100, George Dunlap wrote:
On 06/07/12 10:54, Dario Faggioli wrote:
By introducing a new '-M' option to the `xl vcpu-pin' command. The actual
memory "movement" is achieved suspending the domain to a ttemporary file and
resuming it with the new vcpu-affinity
Hmm... this will work and be reliable, but it seems a bit clunky.  Long
term we want to be able to do node migration in the background without
shutting down a VM, right?  If that can be done in the 4.3 timeframe,
then it seems unnecessary to implement something like this.
We could do something cleverer for HVM (or hybrid) guests to migrate
pages while the guest is live but migrating a page under a PV guest's
feet requires quiescing it in the style of a migrate.

We could probably manage to make it such that you just need the
pause/frob/unpause phases without actually writing RAM to disk, and that
infrastructure might be useful for other reasons I suppose. (e.g. I
think bad page offlining currently uses a similar save/restore trick)
Yes, I think doing this chunks at a time is likely to be much preferrable to writing the whole thing to disk and reading it out again. Doing it "live" may end up with more total overhead, but it wont' require the VM being actually down for the suspend/resume cycle, which on a large guest may be tens of seconds.


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