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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 14:57, Dario Faggioli 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.

If I can ask, the idea or the implementation? :-)

term we want to be able to do node migration in the background without
shutting down a VM, right?

Definitely, and we also want to do that automatically, according to some
load/performance/whatever run-time measurement, without any user
intervention. However ...

If that can be done in the 4.3 timeframe,
then it seems unnecessary to implement something like this.

... I think something like this could still be useful.

IOW, I think it would be worthwhile to have both the automatic memory
migration happening in background and something like this explicit,
do-it-all-now, as they serve different purposes.
Well, I think you can have an explicit, do-it-now mechanism that doesn't require suspending the VM; and in fact, I think such a mechanism would be much preferable.

Compare it to vcpu pinning: if you decided you wanted to change the vcpu pinning, would you rather just be able to pin the maps while the VM was running, and have it take effect immediately (as it does now), or would you rather have to suspend and resume the VM, taking it out of commission for 10 seconds or so?

I'm not opposed to the -M option meaning, "...and please move the memory based on the new nodemask". But I don't think implementing it as suspend/resume is really that useful, except as a stopgap measure until we can get "live" memory migration working. If we can get that before 4.3, there's no need for the stopgap measure.


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