i couldn't understand the comment that "the application running in user space cannot request more memory" - can someone explain whats the point of memorybalooning anywhere if an application cannot signal when the system should actually provision physical memory from the 'baloon'
The systems administrator can use ballooning to give more memory to a VM before launching a new application. This avoids the need to shut down the VM to give it a new role.
There is still a benefit to ballooning support even if it's not exposed to userspace within the VM, because VMs aren't always used purely to host a single infinitely-long-lived application without outside intervention.
