Re: [Kimchi-devel] [PATCH 0/5] [Memory HotPlug] Implements backend of memory device hotplug
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.
- 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.
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.