Question regarding memory hotplug and numa

[skraw]

Hello,

recently I had some troubles with client vms that needed a lot more memory than expected. This brought up the idea to switch on memory hotplug for such vms. So I enabled numa and mem hotplug and tried to give the vm a bit more memory from the start. I though 128GiB are ok, so I entered "131072" and hit "Start". And then proxmox told me that with numa enabled my memory setup has to be aligned to 4096. Since then I wonder why 131072 / 4096 = 32 is not aligned...
Can anyone enlighten me?

 

[j.theisen]

Hi @skraw

thanks for posting on the forum!

So two things about that:
First you probably need to increase the max_mem_regions parameter as per [1]
Secondly as it is also linked in the docs in [1] the alignment of these memory regions is a bit finicky. So please try as stated here [2] to add another Gigabyte to the memory.

Yours sincerely
Jonas

[1] https://pve.proxmox.com/wiki/Hotplu...em_regions when hot-plugging more than 64 GiB
[2] https://forum.proxmox.com/threads/problem-with-hotplug-and-64gb-ram.73621/page-4#post-730697

 

[skraw]

Hi Jonas,

thanks for your comment and the referenced articles. From reading them and personal experience I'd say this topic needs qualified re-programming in proxmox. To me it seems obvious that hotplugging is a key-feature in virtualised environments. It should be very simple to add or remove memory from a guest vm. But it is not, it is not even easy to configure the vm so that hotplugging has a chance to work at all. I can well remember I was one of those arguing for cpu and mem hotplugging on LKML years ago. And now, though it's in the kernel, I can't use it...