KVM Memballoon add support for Free Page Reporting and autodeflate

[bradh352]

The required feature described as a wish

Current versions of libvirt support additional memory ballooning options of Free Page Reporting and autodeflate which in theory can help VMs effectively share physical memory. At least with KVM, its not clear why memory overprovisioning toggles exist since this feature isn't enabled in the libvirt xml so no automatic ballooning will occur.

Openstack's nova recently made this same change: openstack/nova@cd401c5

This feature was introduced all the way back in libvirt v6.9.0 (2020-11-02), so its not exactly a new feature.

While this may not be of a benefit to true production workloads, we have a use-case where developers are spinning up environments to run large, but infrequent builds with VMs set to 256G+ memory, but they consume less than 1G most of the time. It would be great to be able to better utilize the hardware resources for this usecase.

[weizhouapache]

good catch @bradh352
added to 4.22.1 milestone

[bradh352]

I threw together a quick code change here #11932 that I haven't had the chance to test yet.