What is the problem you're trying to solve
Remove the chown overhead of UserNS-remap mode.
https://github.com/containerd/containerd/blob/v1.5.0-beta.1/container_opts_unix.go#L34-L38

Describe the solution you'd like
Use idmapped mounts that was recently merged in the kernel 5.12 tree torvalds/linux@7d6beb7