My system now performs very badly on this:
~# time zfs list -t all |wc -l
It was running a k8s cluster using containerd, and after several thousand container restarts it could barely create a container at all. It is zfs 0.8.3 shipped by ubuntu 20.04; I switched to another system which runs zfs 2.2.2 and uses overlay snapshotter, and that runs fine so far.
Is this a known problem, and do I simply need to avoid containerd zfs snapshotter?