Downsides to enabling NUMA / hotplug memory and/or CPU?

[Colin 't Hart]

I use Proxmox extensively in my homelab where I have virtual machines for many of my clients (I'm a freelance Postgres DBA and need to keep development / scratch machines separate).

It would be nice to be able to grow and shrink resource usage even more and it got me wondering about hotplug memory and CPU. I discovered that NUMA needs to be enabled in order for this to work. The help indicates that performance can actually improve with NUMA enabled, but I wonder, are their any downsides? If there are none, why isn't it enabled by default?

 

[Weehooey-HSS]

Hello!

To my knowledge, enabling NUMA on a device with just one NUMA node or socket presents no disadvantages. This configuration informs the guest of the host's NUMA topology, allowing the guest to allocate resources more strategically.

In rare instances where NUMA is enabled on a system with multi-socket or multiple NUMA node CPUs, there could be a slight performance decrease if NUMA misses occur frequently.

https://pve.proxmox.com/pve-docs/chapter-qm.html#_numa

Thanks!