On 23/10/2025 08:44, Nguyễn Hữu Khôi wrote:
> Hello,
>
> This topic looks like it will be asked many times but I am curious why
> it won't be implemented. Does it have impacts on the system?

|It is not generally well supported in the hypervisors. For example, in
Libvirt to do a live resize, you have to pre-allocate the CPUs and DIMM
slots in the CPU topology in the initial VM. You can't simply add and
remove cores as you see fit while the VM is running. That would mean you
would have to do something like adding hw:max_cpus=64 to the initial
flavor. Then you could resize to a flavor with up to 64 cores, but only
if the NUMA and the virtual hardware topology of the VM did not change.
The same is true for RAM. You need to allocate empty DIMM slots upfront
to enable the hotplug. In general, this is a very complex feature to do
correctly and it does not really fit with a cloud model where VMs are
intended to be easily replaceable. Nova is not a virtualization platform
where this feature is more common. Even on such virt platforms, This is
rarely done at runtime and still has the same requirement to
pre-configure the max CPUs and memory that would be allocated. so the
short verison is its hard and it does nto really fit with the intended
usage model of nova. it could be done but its a very non trivial ask.|


>
> I see that will be an useful feature.
>
> Nguyen Huu Khoi