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authorRoman Gushchin <guro@fb.com>2017-08-02 17:55:31 +0100
committerTejun Heo <tj@kernel.org>2017-08-02 12:05:20 -0700
commitec39225cca42c05ac36853d11d28f877fde5c42e (patch)
tree7291a1c4befe3cd890a28802fce26c0f7e6e81f5
parent1a926e0bbab83bae8207d05a533173425e0496d1 (diff)
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: Roman Gushchin <guro@fb.com> Suggested-by: Tejun Heo <tj@kernel.org> Signed-off-by: Tejun 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
-rw-r--r--Documentation/cgroup-v2.txt18
-rw-r--r--kernel/cgroup/cgroup.c16
2 files changed, 34 insertions, 0 deletions
diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 46ec3f76211c..dc44785dc0fa 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -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
===========
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 0fd9134e1720..a06755a610e1 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -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 */
};