Description of problem:
OSP13 HCI Documentation Guide Section 4.1.1 contains an explanation of the THT parameter definition for 'NovaReservedHostMemory' that appears confusing to a new user.
The NovaReservedHostMemory parameter sets how much RAM should be reserved for the Ceph OSD services and per-guest instance overhead on hyper-converged nodes.
Explanation according to the nova.conf:
# Amount of memory in MB to reserve for the host so that it is always available
# to host processes. The host resources usage is reported back to the scheduler
# continuously from nova-compute running on the compute node. To prevent the
# memory from being considered as available, this option is used to reserve
# memory for the host.
The explanation in Red Hat OSP13 documentation appears to state that 'NovaReservedHostMemory' should also reserve memory used for guests/instances in hyperconverged nodes when the purpose of that parameter is to reserve memory for host processes so that memory it is not used for instances.
Let me know if request is unclear -- Thank you.