KVM: free page hinting

[some-admins]

Hello,

it would be nice if freeing memory inside a guest-VM would also decrease the memory consumption of the corresponding KVM process on the host.

1. Is the "free page hinting" necessary for this to work?
2. Is this feature enabled by default?
3. If not, how to enable it?

Cedric

 

[Stefan_R]

This can be done via the ballooning device. Enable it in the RAM settings on the Hardware Tab, and ensure that your guest OS supports it (Linux should by default, Windows needs corresponding virtio driver). Note that even then memory might not immediately be returned to the host, but only under certain pressure conditions.

 

[spirit]

Hi,

I have send a patch today on the pve-devel mailing list to enable it for proxmox7.
It's a new feature since qemu 5.1 (working like discard for disk), but it needed host kernel 5.7.

This is different than classic balloning, ballon don't need to be inflate/deflate by pvestatd when host memory reach 80%.