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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: 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
This commit is contained in:
Roman Gushchin 2017-08-02 17:55:31 +01:00 committed by Tejun Heo
parent 1a926e0bba
commit ec39225cca
2 changed files with 34 additions and 0 deletions
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18
Documentation/cgroup-v2.txt
View File

@ -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
===========

16
kernel/cgroup/cgroup.c
View File

@ -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 */
};