[ops][nova] How to make sure that on a hypervisor there is room for a VM with a specific flavor

Dear all I have the following use case: I defined a flavor F for VMS with 10 VCPUs, 20 GB of RAM, 30 GB of root disk, 1 GPU XYZ. I use PCI passthrough to manage GPUs. I have only a XYZ GPU on my cluster (on a H hypervisor), so a VM using this flavor F must be "placed" to the compute node H (and this is not a problem: I know how to do that). H is very large: it has a lot of RAM and cores, so it can host other VMs that do not use GPUs. How can I make it so that VMs without GPU can go on H, but there must be room for a VM with flavor F (if it doesn't already exist)? Thanks, and happy new year ! Cheers, Massimo