cgroup: replace "cgroup.populated" with "cgroup.events"

memcg already uses "memory.events" for event reporting and other
controllers may need event reporting too.  Let's standardize on
"$SUBSYS.events" interface file for reporting events which don't
happen too frequently and thus can share event notification.

"cgroup.populated" is replaced with "populated" field in
"cgroup.events" and documentation is updated accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index c5d41c3..d95cc88 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -226,7 +226,7 @@
 
 	struct kernfs_node *kn;		/* cgroup kernfs entry */
 	struct kernfs_node *procs_kn;	/* kn for "cgroup.procs" */
-	struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */
+	struct kernfs_node *events_kn;	/* kn for "cgroup.events" */
 
 	/*
 	 * The bitmask of subsystems enabled on the child cgroups.