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

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On Fri, Sep 15, 2023 at 02:41:50AM +0100, Daniel Krajnik wrote:
> 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

When using PCI device assignment, the VFIO driver requires that libvit
pin guest memory into RAM

so that's why you'll see the immediate memory usage. I dont' think there's
any way to workaround this limitation automatically. Closest you can get is
to actually hot-unplug the RAM your guest isn't using, but that needs manual
work to re-hot-plug it if the guest later needs more RAM, so that's not very

With regards,
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