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 <g...@fb.com>
Suggested-by: Tejun Heo <t...@kernel.org>
Cc: Tejun Heo <t...@kernel.org>
Cc: Zefan Li <lize...@huawei.com>
Cc: Waiman Long <long...@redhat.com>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: kernel-t...@fb.com
Cc: cgro...@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
---
Documentation/cgroup-v2.txt | 18 ++++++++++++++++++
kernel/cgroup/cgroup.c | 16 ++++++++++++++++
2 files changed, 34 insertions(+)
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 9d53d69e44bb..f58e1fe8bebd 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 */
};
--
2.13.3
--
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