quoted

So I think for the sake of readability and maintainability, we'd
better split cgroup.c into smaller pieces:

I agree that splitting is necessary but IMHO splitting usually tends
to go too far.  Maybe we can split it into two and think about further
splitting later on?  e.g. internal logic vs. userland interfacing.

This isn't feasible. The feasible way is to split by functionality,
which I think was the way taken by perf developers.