> +static unsigned long long
> +memcg_hierarchical_free_pages(struct mem_cgroup *mem)
> +{
> +     struct cgroup *cgroup;
> +     unsigned long long min_free, free;
> +
> +     min_free = res_counter_read_u64(&mem->res, RES_LIMIT) -
> +             res_counter_read_u64(&mem->res, RES_USAGE);
> +     cgroup = mem->css.cgroup;
> +     if (!mem->use_hierarchy)
> +             goto out;
> +
> +     while (cgroup->parent) {
> +             cgroup = cgroup->parent;
> +             mem = mem_cgroup_from_cont(cgroup);
> +             if (!mem->use_hierarchy)
> +                     break;
> +             free = res_counter_read_u64(&mem->res, RES_LIMIT) -
> +                     res_counter_read_u64(&mem->res, RES_USAGE);
> +             min_free = min(min_free, free);
> +     }
> +out:
> +     /* Translate free memory in pages */
> +     return min_free >> PAGE_SHIFT;
> +}
> +
I think you can simplify this function using parent_mem_cgroup().

        unsigned long free, min_free = ULLONG_MAX;

        while (mem) {
                free = res_counter_read_u64(&mem->res, RES_LIMIT) -
                        res_counter_read_u64(&mem->res, RES_USAGE);
                min_free = min(min_free, free);
                mem = parent_mem_cgroup();
        }

        /* Translate free memory in pages */
        return min_free >> PAGE_SHIFT;

And, IMHO, we should return min(global_page_state(NR_FREE_PAGES), min_free >> 
PAGE_SHIFT).
Because we are allowed to set no-limit(or a very big limit) in memcg,
so min_free can be very big if we don't set a limit against all the memcg's in 
hierarchy.


Thanks,
Dasiuke Nishimura.
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