9:49 a.m.
On 05/27/2015 02:19 PM, CrÃstian Deives wrote:
On 27-05-2015 12:39, Rodrigo Trujillo wrote:
> Hi Cristian,
>
> "why create memdevides ?"
> this is all about the way libvirt and memory hotplug works. Let me
> try to explain:
> - it is possible to set in guest xml two elements: <memory> and
> <currentmemory>. The first is the max amount of memory allocated to
> guest when libvirt starts it, the second is the memory the guest will
> "see". You can increase and decrease currentmemory with guest
> running, but you are not actually hotadding memory, you are using the
> ballooning module of the guest.
Changes to a VM's XML configuration are not applied to a running
system, so changing the memory value via XML on a running VM isn't
expected to update the VM memory, only after reboot.
Yes, yes, you are correct. Actually I mentioned <memory> and
<currentMemory> but did not say that we have to use "setMemoryFlags" and
"setMaxMemory" to update this values in a running system. Change the XML
is not an option to memory hotplug.
> - on the other side, we can attach (hotplug) a memory device to the
> guest (like attach a network device), this is different then using
> the ballooning. And values can higher than <memory>. In fact, this is
> the only way to increase <memory> on running guests.
It's not. You can use the function "dom.setMemory[Flags]", which seems
like a much easier way of implementing this feature.
Yes, we can use the setMemory, but you can only increase the running
guest memory up to the value set in <memory>. And, yes, this is way easier
to implement, but we would have to set <memory> to a high value and
<currentMemory> to a value that the user wants to start the guest. So user
will have an interval between <currentMemory> and <memory> to increase.
Today, Kimchi uses <memory> and <currentMemory> as the same.
I think you are mixing the concepts (I did this too), the feature I am
proposing in hotplug memory, like install new memory module in a
physical machine.
This way you can increase the guest value for a higher value, than the
previously set in <memory>. In other words, we don't want to use ballooning.
And even if you really need to attach a memory device to a VM,
wouldn't it be simpler for the user to just set a memory value? Then
Kimchi will add/remove devices as needed.
This can be done in the front-end
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