>> FYI: RHEL 7.3 does not suffer from this problem and appears to have ballooning enabled:
> I imagine CONFIG_XEN_BALLOON_MEMORY_HOTPLUG is set for the Ubuntu kernel?
yes exactly, CONFIG_XEN_BALLOON_MEMORY_HOTPLUG must be enabled for it to actually increase the physical memory region, which is what the problem is in this case.
>> FYI: RHEL 7.3 does not suffer from this problem and appears to have ballooning enabled: XEN_BALLOON_ MEMORY_ HOTPLUG is set for the Ubuntu kernel?
> I imagine CONFIG_
yes exactly, CONFIG_ XEN_BALLOON_ MEMORY_ HOTPLUG must be enabled for it to actually increase the physical memory region, which is what the problem is in this case.