When passing-through via vfio-pci using QEMU 7.1.0 and OVMF, it appears
that qemu preallocates all guest system memory.
qemu-system-x86_64 \
-no-user-config \
-nodefaults \
-nographic \
-rtc base=utc \
-boot strict=on \
-machine pc,accel=kvm,dump-guest-core=off \
-cpu host,migratable=off \
-smp 8 \
-m size=8G \
-overcommit mem-lock=off \
-device vfio-pci,host=03:00.0 \
...
PID USER PR NI VIRT RES %CPU %MEM TIME+ S COMMAND
4151 root 20 0 13560.8m *8310.8m* 100.0 52.6 0:25.06 S
qemu-system-x86_64
If I remove just the vfio-pci device argument, it appears that qemu no
longer preallocates all guest system memory.
PID USER PR NI VIRT RES %CPU %MEM TIME+ S COMMAND
5049 root 20 0 13414.0m *762.4m* 0.0 4.8 0:27.06 S
qemu-system-x86_64
I am curious if anyone has any context on or experience with this
functionality. Does anyone know if preallocation is a requirement for VFIO
with QEMU or if preallocation can be disabled?
I am speculating that QEMU is actually preallocating as opposed to the
guest touching every page of system memory.
Thanks.
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