Re: [v10 3/6] mm, oom: cgroup-aware OOM killer

[Shakeel Butt]

> +
> +static void select_victim_memcg(struct mem_cgroup *root, struct oom_control *oc)
> +{
> +       struct mem_cgroup *iter;
> +
> +       oc->chosen_memcg = NULL;
> +       oc->chosen_points = 0;
> +
> +       /*
> +        * The oom_score is calculated for leaf memory cgroups (including
> +        * the root memcg).
> +        */
> +       rcu_read_lock();
> +       for_each_mem_cgroup_tree(iter, root) {
> +               long score;
> +
> +               if (memcg_has_children(iter))
> +                       continue;

&& iter != root_mem_cgroup ?

> +
> +               score = oom_evaluate_memcg(iter, oc->nodemask, oc->totalpages);
> +
> +               /*
> +                * Ignore empty and non-eligible memory cgroups.
> +                */
> +               if (score == 0)
> +                       continue;
> +
> +               /*
> +                * If there are inflight OOM victims, we don't need
> +                * to look further for new victims.
> +                */
> +               if (score == -1) {
> +                       oc->chosen_memcg = INFLIGHT_VICTIM;
> +                       mem_cgroup_iter_break(root, iter);
> +                       break;
> +               }
> +

Shouldn't there be a CSS_ONLINE check? Also instead of css_get at the
end why not css_tryget_online() here and css_put for the previous
selected one.

> +               if (score > oc->chosen_points) {
> +                       oc->chosen_points = score;
> +                       oc->chosen_memcg = iter;
> +               }
> +       }
> +
> +       if (oc->chosen_memcg && oc->chosen_memcg != INFLIGHT_VICTIM)
> +               css_get(&oc->chosen_memcg->css);
> +
> +       rcu_read_unlock();
> +}
> +