[$] Teaching the OOM killer about control groups

The kernel's out-of-memory (OOM) killer is summoned when the system runs
short of free memory and is unable to proceed without killing one or more
processes. As might be expected, the policy decisions around which
processes should be targeted have engendered controversy for as long as the
OOM killer has existed. The 4.19 development cycle is likely to include
a new OOM-killer implementation that targets control groups rather than
individual processes, but it turns out that there is significant
disagreement over how the OOM killer and control groups should interact.