Re: [PATCH-cgroup v5] cgroup: Show # of subsystem CSSes in cgroup.stat

[Kamalesh Babulal <kamalesh.babulal@oracle.com>]

On 7/11/24 7:07 PM, 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 as long as it is not zero.  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 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.
> 
> 	nr_descendants 55
> 	nr_dying_descendants 35
> 	nr_subsys_cpuset 1
> 	nr_subsys_cpu 40
> 	nr_subsys_io 40
> 	nr_subsys_memory 55
> 	nr_dying_subsys_memory 35
> 	nr_subsys_perf_event 56
> 	nr_subsys_hugetlb 1
> 	nr_subsys_pids 55
> 	nr_subsys_rdma 1
> 	nr_subsys_misc 1
> 
> Another sample output from system.slice/cgroup.stat was:
> 
> 	nr_descendants 32
> 	nr_dying_descendants 33
> 	nr_subsys_cpu 30
> 	nr_subsys_io 30
> 	nr_subsys_memory 32
> 	nr_dying_subsys_memory 33
> 	nr_subsys_perf_event 33
> 	nr_subsys_pids 32
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> Acked-by: Roman Gushchin <roman.gushchin@linux.dev>

Reviewed-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>

-- 
Thanks,
Kamalesh