Hello, Michal.

On Wed, Nov 07, 2012 at 05:54:57PM +0100, Michal Hocko wrote:

quoted

+struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
+					  struct cgroup *cgroup)
+{
+	struct cgroup *next;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
+	/* if first iteration, pretend we just visited @cgroup */
+	if (!pos) {
+		if (list_empty(&cgroup->children))
+			return NULL;
+		pos = cgroup;
+	}

Is there any specific reason why the root of the tree is excluded?
This is bit impractical because you have to special case the root
in the code.

Yeah, thought about including it but decided against it for two
reasons.

* To be consistent with cgroup_for_each_children() - it's a bit weird
  for descendants to include self when children don't.

* Iteration root is likely to require different treatment anyway.
  e.g. for cgroup_freezer, the root is updated to the specified config
  while all the descendants inherit config from its immediate parent.
  They are different.

Thanks.

-- 
tejun