Memory usage on Proxmox is higher than vm

[Nafr1]

Hello,

I have recently installed Proxmox VE 8.1.3. I have an OpenMediaVault 6 VM running inside Proxmox. For some reason, Proxmox always shows that OMV VM Memory usage is around 92% (even when idle), whereas inside the VM, it shows that memory usage is around 13%. Below is the screenshot for both Proxmox and OMV VM

Proxmox Memory usage:



OMV 6 Memmory Usage:




Below is the screenshots of some of the configurations I have for the VM in Proxmox

Qemu Agent (Enabled in Proxmox and inside VM):



Memory settings in Proxmox for VM:



Just for testing purposes I have tried following things to investigate the issue..

1) Changing the Memory size in Proxmox for the VM.... I initially started with 2GB RAM for the VM and the memory usage in Proxmos was reported around 90%. I change the size to 4GB and still the usage in Proxmox was around 90%. I changed the size to 8GB and still the memory usage in Proxmox was 90%. All this time, the memory usage inside OMV VM was around 500mb (way lower than what Proxmox was reporting).

2) I have other VMs running inside the same Proxmox node, which are reporting correct memory usage, both in Proxmox and inside the VM.

3) I tried removing and creating a new VM for OMV, still having the same Memory issue.

4) I created OMV 6 VM (with exact same configuration that I have in Proxmox) with Windows Hpyer-V and Hyper-V and OMV VM is reporting same Memory usage (around 600-700mb RAM usage).


I would really appreciate if someone can guide me what exactly am I missing here and how can I fix this reporting issue...

Thanks..

 

[leesteken]

It's (almost) always filesystem cache (inside the VM), which is not shown inside the VM. Please search the forum as this is asked regularly.

 

[bosquuimano]

Thanks @leesteken, then whats the suggestion is? How to determinate the optimal RAM assign? If we cannot trust guest ram consumtion, the real usage is the proxmox showed one?

In my case, linux VM, according VM 25% RAM usage, proxmox allways 95% (no matter if i increase or decrease assigned RAM, according Proxmox is always 95%).

Thanks!

 

[LnxBil]

This is an optimization problem, whereas the best value is the lowest at which the guest is not swapping to disk. This is heavily dependend on the guest OS (including version) and what services run and how often. Free RAM is always used as cache, so that it is never really free, which is a good thing.

I'm been running hundreds of Debian VMs for years and e.g. for Debian 12 Bookworm (a simple network gateway) works well with 128 MB without locales, with locales it is 256 MB.