Re: [PATCH 1/8] cgroup: implement cgroup_is_ancestor()

Michal Hocko
2013-04-08T14:47:57Z

On Mon 08-04-13 16:20:11, Li Zefan wrote:
[...]
> @@ -5299,6 +5300,26 @@ struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
> return css ? css : ERR_PTR(-ENOENT);
> }
>
> +/**
> + * cgroup_is_ancestor - test "root" cgroup is an ancestor of "child"
> + * @child: the cgroup to be tested.
> + * @root: the cgroup supposed to be an ancestor of the child.
> + *
> + * Returns true if "root" is an ancestor of "child" in its hierarchy.
> + */
> +bool cgroup_is_ancestor(struct cgroup *child, struct cgroup *root)
> +{
> + int depth = child->depth;

Is this functionality helpful for other controllers but memcg?
css_is_ancestor is currently used only by memcg code AFAICS and we can
get the same functionality easily by using something like:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d195f40..37bbbff 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1472,11 +1472,13 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
struct mem_cgroup *memcg)
{
- if (root_memcg == memcg)
- return true;
- if (!root_memcg->use_hierarchy || !memcg)
- return false;
- return css_is_ancestor(&memcg->css, &root_memcg->css);
+ struct mem_cgroup *parent = memcg;
+ do {
+ if (parent == root_memcg)
+ return true;
+ } while ((parent = parent_mem_cgroup(parent)));
+
+ return false;
}

static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,

In both cases we have to go up the hierarchy.

> +
> + if (depth < root->depth)
> + return false;
> +
> + while (depth-- != root->depth)
> + child = child->parent;
> +
> + return (child == root);
> +}
> +
> #ifdef CONFIG_CGROUP_DEBUG
> static struct cgroup_subsys_state *debug_css_alloc(struct cgroup *cont)
> {
> --
> 1.8.0.2
> --
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--
Michal Hocko
SUSE Labs