Re: [PATCH v4] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes

Michal Hocko
2018-01-11T10:42:39Z

On Wed 10-01-18 15:43:17, Andrey Ryabinin wrote:
[...]
> @@ -2506,15 +2480,13 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
> if (!ret)
> break;
>
> - try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, !memsw);
> -
> - curusage = page_counter_read(counter);
> - /* Usage is reduced ? */
> - if (curusage >= oldusage)
> - retry_count--;
> - else
> - oldusage = curusage;
> - } while (retry_count);
> + usage = page_counter_read(counter);
> + if (!try_to_free_mem_cgroup_pages(memcg, usage - limit,
> + GFP_KERNEL, !memsw)) {

If the usage drops below limit in the meantime then you get underflow
and reclaim the whole memcg. I do not think this is a good idea. This
can also lead to over reclaim. Why don't you simply stick with the
original SWAP_CLUSTER_MAX (aka 1 for try_to_free_mem_cgroup_pages)?

> + ret = -EBUSY;
> + break;
> + }
> + } while (true);

--
Michal Hocko
SUSE Labs