[$] Remote memory control-group charging

Memory control groups exist to track and limit the amount of memory used bysets of processes. Normally, one would not expect that memory used by onegroup would be charged to another but, as Shakeel Butt described in amemory-management track session at the 2019 Linux Storage, Filesystem, andMemory-Management Summit, that does happen in a number of differentsituations. It's often a problem, but occasionally it's also a usefulfeature.