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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