cgroup: document how cgroup IDs are assigned
As cgroup id has been used in netprio cgroup and will be used in memcg,
it's important to make it clear how a cgroup id is allocated.
For example, in netprio cgroup, the id is used as index of anarray.
Signed-off-by: Li Zefan <lizefan@huwei.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index cca570e..4dfcd0e 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -161,7 +161,13 @@
struct cgroup {
unsigned long flags; /* "unsigned long" so bitops work */
- int id; /* idr allocated in-hierarchy ID */
+ /*
+ * idr allocated in-hierarchy ID.
+ *
+ * The ID of the root cgroup is always 0, and a new cgroup
+ * will be assigned with a smallest available ID.
+ */
+ int id;
/*
* We link our 'sibling' struct into our parent's 'children'.