We looked at this a lot (it was a lot of money at our scale). A cgroup itself is just a few small data structures. And a reasonable process inside will only ever have a small amount of dirty memory it won’t ever use. Even then you can’t be sure of it packing neatly into whole pages.

So, the typical saving is tiny, and the cost in unpredictable performance is quite bad.

If you really do have an issue with “lost” dirty memory, your time is best spent addressing that directly.