On Mon, Jul 15, 2024 at 11:00:34AM -0400, Waiman Long wrote: > Cgroup subsystem state (CSS) is an abstraction in the cgroup layer to > help manage different structures in various cgroup subsystems by being > an embedded element inside a larger structure like cpuset or mem_cgroup. > > The /proc/cgroups file shows the number of cgroups for each of the > subsystems. With cgroup v1, the number of CSSes is the same as the > number of cgroups. That is not the case anymore with cgroup v2. The > /proc/cgroups file cannot show the actual number of CSSes for the > subsystems that are bound to cgroup v2. > > So if a v2 cgroup subsystem is leaking cgroups (usually memory cgroup), > we can't tell by looking at /proc/cgroups which cgroup subsystems may > be responsible. > > As cgroup v2 had deprecated the use of /proc/cgroups, the hierarchical > cgroup.stat file is now being extended to show the number of live and > dying CSSes associated with all the non-inhibited cgroup subsystems that > have been bound to cgroup v2. The number includes CSSes in the current > cgroup as well as in all the descendants underneath it. This will help > us pinpoint which subsystems are responsible for the increasing number > of dying (nr_dying_descendants) cgroups. > > The CSSes dying counts are stored in the cgroup structure itself > instead of inside the CSS as suggested by Johannes. This will allow > us to accurately track dying counts of cgroup subsystems that have > recently been disabled in a cgroup. It is now possible that a zero > subsystem number is coupled with a non-zero dying subsystem number. > > The cgroup-v2.rst file is updated to discuss this new behavior. > > With this patch applied, a sample output from root cgroup.stat file > was shown below. ... Applied to cgroup/for-6.12. Thanks. -- tejun
