[Devel] Re: [PATCH 5/7] shrink support for memcg kmem controller

[Suleiman Souhlal]

On Tue, Feb 21, 2012 at 3:34 AM, Glauber Costa <glommer at parallels.com> wrote:

> @@ -5055,8 +5117,21 @@ int memcg_kmem_newpage(struct mem_cgroup *memcg, struct page *page, unsigned lon
>  {
>        unsigned long size = pages << PAGE_SHIFT;
>        struct res_counter *fail;
> +       int ret;
> +       bool do_softlimit;
> +
> +       ret = res_counter_charge(memcg_kmem(memcg), size, &fail);
> +       if (unlikely(mem_cgroup_event_ratelimit(memcg,
> +                                               MEM_CGROUP_TARGET_THRESH))) {
> +
> +               do_softlimit = mem_cgroup_event_ratelimit(memcg,
> +                                               MEM_CGROUP_TARGET_SOFTLIMIT);
> +               mem_cgroup_threshold(memcg);
> +               if (unlikely(do_softlimit))
> +                       mem_cgroup_update_tree(memcg, page);
> +       }
>
> -       return res_counter_charge(memcg_kmem(memcg), size, &fail);
> +       return ret;
>  }

It seems like this might cause a lot of kernel memory allocations to
fail whenever we are at the limit, even if we have a lot of
reclaimable memory, when we don't have independent accounting.

Would it be better to use __mem_cgroup_try_charge() here, when we
don't have independent accounting, in order to deal with this
situation?

-- Suleiman