clarification needed about ballooning Wiki page

[Chentoa]

The "Dynamic Memory Management" Wiki page states, about ballooning :

Memory ballooning (...) reduces the impact your guest can have on memory usage of your host by giving up unused memory back to the host.

Does that mean :

(a) that the unused memory is given back to the host to be used as it wishes, even for non-Proxmox/KVM related tasks​

OR

(b) that the unused memory is given back to the host, but only to be used by other VMs​

 

[leesteken]

It's (a), but the current implementation does not "give unused memory to the host". The host starts taking away memory when it is at 80% memory usage, even when the VM is using or needs the memory. How much memory it takes away from each VM is explained in the manual.
EDIT: The host does inform the VM that it is going to (try and) take the memory, so the operating system inside the VM can stop using it beforehand.

 

[Chentoa]

Thanks.
One last question : is that KVM's default behavior, or is it a Proxmox enhancement ?