Cgroup memory.usage_in_bytes shows incorrect value

I created a Cgroup on my Linux device and noticed that the value of memory.usage_in_bytes (4325376) is bigger than the sum of RSS, CACHE and SWAP (4194304).

I read in a reliable documentation, the memory.usage_in_bytes doesn't show the exact value of memory (and swap) usage. If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP) value in memory.stat.

Does anyone have idea about this? Should I use the value of memory.usage_in_bytes?