避免 microVM 镜像复制占满 LXC page cache

scripts/microvm-runner-launch

@@ -45,8 +45,9 @@ test -r "$base_image"
 test -r "$firmware"
 install -d -m 0700 "$state_root/instances" "$vm_dir"
 # Cloud Hypervisor cannot open qcow2 backing chains.  Keep each disposable
-# root disk flat; reflink-capable storage still makes this copy cheap.
-cp --reflink=auto --sparse=always "$base_image" "$overlay"
+# root disk flat and bypass the LXC page cache: caching both a 5 GiB copy and
+# guest RAM can otherwise trigger the container memory limit.
+qemu-img convert -q -T none -t none -f qcow2 -O qcow2 "$base_image" "$overlay"
 
 cat >"$vm_dir/meta-data" <<EOF
 instance-id: $instance_id