[libvirt] [PATCH 0/8] logically memory hotplug via guest agent

[Jiri Denemark]

On Thu, Jun 11, 2015 at 09:38:24 +0800, zhang bo wrote:
> On 2015/6/10 17:31, Daniel P. Berrange wrote:
> 
> > On Wed, Jun 10, 2015 at 10:28:08AM +0100, Daniel P. Berrange wrote:
> >> On Wed, Jun 10, 2015 at 05:24:50PM +0800, zhang bo wrote:
> >>> On 2015/6/10 16:39, Vasiliy Tolstov wrote:
> >>>
> >>>> 2015-06-10 11:37 GMT+03:00 Daniel P. Berrange <berrange at redhat.com>:
> >>>>> The udev rules are really something the OS vendor should setup, so
> >>>>> that it "just works"
> >>>>
> >>>>
> >>>> I think so, also for vcpu hotplug this also covered by udev. May be we
> >>>> need something to hot remove memory and cpu, because in guest we need
> >>>> offline firstly.
> >>>>
> >>>
> >>>
> >>> In fact ,we also have --guest option for 'virsh sevvcpus' command, which also
> >>> uses qga commands to do the logical hotplug/unplug jobs, although udev rules seems
> >>> to cover the vcpu logical hotplug issue.
> >>>
> >>> virsh # help setvcpus
> >>> .........................
> >>>     --guest          modify cpu state in the guest
> >>>
> >>>
> >>> BTW: we didn't see OSes with udev rules for memory-hotplug-event setted by vendors, 
> >>> and adding such rules means that we have to *interfere within the guest*, It seems 
> >>> not a good option.
> >>
> >> I was suggesting that an RFE be filed with any vendor who doesn't do it
> >> to add this capability, not that we add udev rules ourselves.
> > 
> > Or actually, it probably is sufficient to just send a patch to the upstream
> > systemd project to add the desired rule to udev. That way all Linux distros
> > will inherit the feature when they update to new udev.
> > 
> 
> Then, here comes the question: how to deal with the guests that are already in use?
> I think it's better to operate them at the host side without getting into the guest.
> That's the advantage of qemu-guest-agent, why not take advantage of it?

Such guests would need an update qemu-guest-agent anyway. And installing
a new version of qemu-guest-agent is not any easier than installing an
updated udev or a new udev rule. That is, I don't think the
qemu-guest-agent way has any benefits over a udev rule. It's rather the
opposite.

Jirka