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SubjectRe: [PATCH v3 02/21] memcg: make mm_match_cgroup() hirarchical
On Thu, Feb 23, 2012 at 05:51:46PM +0400, Konstantin Khlebnikov wrote:
> Check mm-owner cgroup membership hierarchically.

I think this one cat just beat up this other cat in front of my
window, yelling something about money and missing product. Anyway, I
already forgot why we want this patch. Could you describe that in the
changelog, please?

> @@ -821,6 +821,26 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
> struct mem_cgroup, css);
> }
>
> +/**
> + * mm_match_cgroup - cgroup hierarchy mm membership test
> + * @mm mm_struct to test
> + * @cgroup target cgroup
> + *
> + * Returns true if mm belong this cgroup or any its child in hierarchy
> + */
> +int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
> +{
> + struct mem_cgroup *memcg;
> +
> + rcu_read_lock();
> + memcg = mem_cgroup_from_task(rcu_dereference((mm)->owner));
> + while (memcg != cgroup && memcg && memcg->use_hierarchy)
> + memcg = parent_mem_cgroup(memcg);
> + rcu_read_unlock();
> +
> + return cgroup == memcg;
> +}

Please don't duplicate mem_cgroup_same_or_subtree()'s functionality in
a worse way. The hierarchy information is kept in a stack such that
ancestry can be detected in linear time, check out css_is_ancestor().

If you don't want to nest rcu_read_lock(), you could push the
rcu_read_lock() from css_is_ancestor() into its sole user and provide
a __mem_cgroup_is_ancestor() that assumes rcu already read-locked.

No?


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