Very high memory usage on VM

[ecotechie]

Hi, just installed NixOS in a VM with GPU passthrough. Everything seems to be working fine, but the RAM usage being reported from the Proxmox dashboard seems very high. Specially compared to what the VM is reporting...





I have another VM booted with the ISO for NixOS and it shows far less usage:




Any ideas how to troubleshoot this?

 

[leesteken]

As always with PCI(e) passthrough, all VM memory must be pinned into actual host memory because of possible DMA. There is no way around that, so it does not matter what the GUI shows, all of the VM memory is used all the time while the VM is running (or being backed up).

 

[ecotechie]

As always with PCI(e) passthrough, all VM memory must be pinned into actual host memory because of possible DMA. There is no way around that, so it does not matter what the GUI shows, all of the VM memory is used all the time while the VM is running (or being backed up).

Thanks for that info, hence not using ballooning, right? I do still wonder why it shows 74.74% instead of 100%. I guess it's the unknowns that get you...

 

[ecotechie]

I'm now wondering if I'd be able to pass the GPU to an LXC container with the same results. Outputting the LXC's video to a monitor and using it as a "real" computer.

 

[rokyo401]

As always with PCI(e) passthrough, all VM memory must be pinned into actual host memory because of possible DMA. There is no way around that, so it does not matter what the GUI shows, all of the VM memory is used all the time while the VM is running (or being backed up).

Oh, this explains my own question. Good that I searched first!

I also passed through a PCIe NIC to a VM and was wondering why suddenly the RAM usage on the proxmox host is super high while the VM shows almost no memory used (except while booting, where it shows 70-100% usage out of 256GB RAM).

So, this is why.

 

[rokyo401]

Does this have any negative effects besides that you can't judge the actual RAM usage of the host from the host Summary page anymore? Like wear on the RAM or responsiveness of the host or individual VMs?

 

[BobhWasatch]

Does this have any negative effects besides that you can't judge the actual RAM usage of the host from the host Summary page anymore? Like wear on the RAM or responsiveness of the host or individual VMs?

No

 

[ecotechie]

@rokyo401 and @BobhWasatch it does lock up that RAM so it's only available to the VM though, right? Meaning on a 64gb host with a 32gb VM, using PCI passthrough, the host will only have 32gb available when the VM is running or backing up.