Michal Hocko writes:
I find this paragraph rather confusing. This is essentially an unsigned underflow when any of the memcg up the hierarchy is below the high limit, right? There doesn't really seem anything complex in such a hierarchy.
The conditions to trigger the bug itself are easy, but having it obviously visible in tests requires a moderately complex hierarchy, since in the basic case ancestor_usage is "similar enough" to the test leaf cgroup's usage.
