Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online() fails

Glauber Costa
2013-04-02T14:33:30Z

On 04/02/2013 06:28 PM, Michal Hocko wrote:
> On Tue 02-04-13 18:20:56, Glauber Costa wrote:
>> On 04/02/2013 06:16 PM, Michal Hocko wrote:
>>> mem_cgroup_css_online
>>> memcg_init_kmem
>>> mem_cgroup_get # refcnt = 2
>>> memcg_update_all_caches
>>> memcg_update_cache_size # fails with ENOMEM
>>
>> Here is the thing: this one in kmem only happens for kmem enabled
>> memcgs. For those, we tend to do a get once, and put only when the last
>> kmem reference is gone.
>>
>> For non-kmem memcgs, refcnt will be 1 here, and will be balanced out by
>> the mem_cgroup_put() in css_free.
>
> So we need this, right?
> ---
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f608546..2ef875d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5306,6 +5306,8 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
> ret = memcg_update_cache_sizes(memcg);
> mutex_unlock(&set_limit_mutex);
> out:
> + if (ret)
> + mem_cgroup_put(memcg);
> return ret;
> }
> #endif /* CONFIG_MEMCG_KMEM */
> @@ -6417,16 +6419,6 @@ mem_cgroup_css_online(struct cgroup *cont)
>
> error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
> mutex_unlock(&memcg_create_mutex);
> - if (error) {
> - /*
> - * We call put now because our (and parent's) refcnts
> - * are already in place. mem_cgroup_put() will internally
> - * call __mem_cgroup_free, so return directly
> - */
> - mem_cgroup_put(memcg);
> - if (parent->use_hierarchy)
> - mem_cgroup_put(parent);
> - }
> return error;
> }
>
>
Yes, indeed you are very right - and thanks for looking at such depth.