If you try to increase the amount of available memory using the obvious command it fails with an error message:

# virsh setmem <vm name> 16G --live
error: invalid argument: cannot set memory higher than max memory

The physical host in this case has 128G RAM and 32 CPUs. Plenty of capacity. To increase the maximum amount of memory that can be allocated to the VM:

# virsh setmaxmem <vm name> 16G --config

There are also –live and –current options which claim to affect the running/current domain. These options do not actually work. You have to use the –config option (changes take effect after next boot) and then power off the machine by logging in and running “poweroff”.

Once the machine is off set the actual memory with:

# virsh setmem <vm name> 16G --config

Then start the vm:

# virsh start <vm name>

Once the VM starts up it will have more memory.

Hope you find this useful.