Why does my control group show no memory usage in cgget and systemd-cgtop, despite containing a process using significant memory?

Question

I'm trying to implement a solution to this problem using control groups, which I have never worked with before. As a first step, I thought I would create a control group, add a process to it, and view its memory usage.

I ran the following code:

sudo apt install cgroup-tools
sudo cgcreate -g memory:/jupyterHub
sudo cgclassify -g memory:/jupyterHub --sticky 805

805 here is the jupyterhub process. Ultimately, I want to limit the memory usage of 805 and all of its children, so that the OOM-killer is invoked when the memory usage is too high. When I run

sudo ps -o cgroup 805

it shows the jupyterHub group as expected.

However, when I run

sudo cgget -g memory:/jupyterHub

it reports 4KB of memory usage, which is definitely wrong and I'm pretty sure corresponds to the process using zero memory.

systemd-cgtop

gives the same result. How can I create a control group containing jupyterhub and its children that will report the correct amount of memory usage?

Also, please tell me if I'm doing something dangerous here (although I'm already planning on creating a duplicate server for testing so that I don't bork up the production one).