Re: [RFC][PATCH 3/4] memcg: fix OOM KILL under hierarchy

[Li Zefan <lizf@cn.fujitsu.com>]

> -int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
> +static int
> +mm_match_cgroup_hierarchy(struct mm_struct *mm, struct mem_cgroup *mem)
> +{
> +	struct mem_cgroup *curr;
> +	int ret;
> +
> +	if (!mm)
> +		return 0;
> +	rcu_read_lock();
> +	curr = mem_cgroup_from_task(mm->owner);

curr can be NULL ?

> +	if (mem->use_hierarchy)
> +		ret = css_is_ancestor(&curr->css, &mem->css);
> +	else
> +		ret = (curr == mem);
> +	rcu_read_unlock();
> +	return ret;
> +}
> +

...

> +void mem_cgroup_update_oom_jiffies(struct mem_cgroup *mem)
> +{
> +	struct mem_cgroup *cur;
> +	struct cgroup_subsys_state *css;
> +	int id, found;
> +
> +	if (!mem->use_hierarchy) {
> +		mem->last_oom_jiffies = jiffies;
> +		return;
> +	}
> +
> +	id = 0;
> +	rcu_read_lock();
> +	while (1) {
> +		css = css_get_next(&mem_cgroup_subsys, id, &mem->css, &found);
> +		if (!css)
> +			break;
> +		if (css_tryget(css)) {
> +			cur = container_of(css, struct mem_cgroup, css);
> +			cur->last_oom_jiffies = jiffies;
> +			css_put(css);
> +		}
> +		id = found + 1;
> +	}
> +	rcu_read_unlock();
> +	return;

redundant "return"

> +}