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Commit ec39225c authored by Roman Gushchin's avatar Roman Gushchin Committed by Tejun Heo
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cgroup: add cgroup.stat interface with basic hierarchy stats 



A cgroup can consume resources even after being deleted by a user.
For example, writing back dirty pages should be accounted and
limited, despite the corresponding cgroup might contain no processes
and being deleted by a user.

In the current implementation a cgroup can remain in such "dying" state
for an undefined amount of time. For instance, if a memory cgroup
contains a pge, mlocked by a process belonging to an other cgroup.

Although the lifecycle of a dying cgroup is out of user's control,
it's important to have some insight of what's going on under the hood.

In particular, it's handy to have a counter which will allow
to detect css leaks.

To solve this problem, add a cgroup.stat interface to
the base cgroup control files with the following metrics:

nr_descendants		total number of visible descendant cgroups
nr_dying_descendants	total number of dying descendant cgroups

Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Suggested-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@fb.com
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
parent 1a926e0b

Documentation/cgroup-v2.txt

+18 −0
Original line number Diff line number Diff line
@@ -868,6 +868,24 @@ All cgroup core files are prefixed with "cgroup." 
	If the actual descent depth is equal or larger,

	an attempt to create a new child cgroup will fail.



  cgroup.stat

	A read-only flat-keyed file with the following entries:



	  nr_descendants

		Total number of visible descendant cgroups.



	  nr_dying_descendants

		Total number of dying descendant cgroups. A cgroup becomes

		dying after being deleted by a user. The cgroup will remain

		in dying state for some time undefined time (which can depend

		on system load) before being completely destroyed.



		A process can't enter a dying cgroup under any circumstances,

		a dying cgroup can't revive.



		A dying cgroup can consume system resources not exceeding

		limits, which were active at the moment of cgroup deletion.





Controllers

===========

kernel/cgroup/cgroup.c

+16 −0
Original line number Diff line number Diff line
@@ -3304,6 +3304,18 @@ static int cgroup_events_show(struct seq_file *seq, void *v) 
	return 0;

}



static int cgroup_stats_show(struct seq_file *seq, void *v)

{

	struct cgroup *cgroup = seq_css(seq)->cgroup;



	seq_printf(seq, "nr_descendants %d\n",

		   cgroup->nr_descendants);

	seq_printf(seq, "nr_dying_descendants %d\n",

		   cgroup->nr_dying_descendants);



	return 0;

}



static int cgroup_file_open(struct kernfs_open_file *of)

{

	struct cftype *cft = of->kn->priv;
@@ -4407,6 +4419,10 @@ static struct cftype cgroup_base_files[] = { 
		.seq_show = cgroup_max_depth_show,

		.write = cgroup_max_depth_write,

	},

	{

		.name = "cgroup.stat",

		.seq_show = cgroup_stats_show,

	},

	{ }	/* terminate */

};