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SubjectRe: [PATCH 2.6.32] memcg: warn on deeper hierarchies with use_hierarchy==0
On Wed, 19 Sep 2012, Michal Hocko wrote:

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f99f599..b61c34b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3106,6 +3106,11 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> } else {
> parent = mem_cgroup_from_cont(cont->parent);
> mem->use_hierarchy = parent->use_hierarchy;
> + WARN_ONCE(!mem->use_hierarchy && parent != root_mem_cgroup,
> + "Creating hierarchies with use_hierarchy==0 "
> + "(flat hierarchy) is considered deprecated. "
> + "If you believe that your setup is correct, "
> + "we kindly ask you to contact linux-mm@kvack.org and let us know");

When I deprecated /proc/pid/oom_adj (now removed), we did a WARN_ONCE()
and others complained that this unnecessarily alters userspace scripts
that a serious issue has occurred and Linus agreed that we shouldn't do
deprecation in this way. The alternative is to use printk_once() instead.

This applies to all three patches for this one, 3.0, and 3.2+.


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