virtio-mem with virt-install to share memory between guest and host on-demand

Hi I'm trying to Passthrough a GPU to a VM and have it still share its free memory with the host (just like it would with virtio-balloon). Is this something virtio-mem is capable of? I've tried to run it, but it immediately took over 9GB of memory: virt-install --name test --cpu cell0.cpus=0,cell0.memory=4194304,cell1.cpus=1,cell1.memory=4194304 --memory maxMemory=65536,maxMemory.slots=8 --memdev model=virtio-mem,target.node=0,target.block=2048,target.size=1000 --disk size=400 --network network=ai --location=/tmp/debian-12.1.0-amd64-netinst.iso --os-variant=debian11 --graphics none --extra-args "console=ttyS0 Best wishes, Daniel