On Fri 11-01-13 13:45:27, Glauber Costa wrote:
> We were deferring the kmemcg static branch increment to a later time,
> due to a nasty dependency between the cpu_hotplug lock, taken by the
> jump label update, and the cgroup_lock.
>
> Now we no longer take the cgroup lock, and we can save ourselves the
> trouble.
What a relief.
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@suse>
> ---
> mm/memcontrol.c | 31 +++++++------------------------
> 1 file changed, 7 insertions(+), 24 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5f3adbc..f87d6d2 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4926,8 +4926,6 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
> {
> int ret = -EINVAL;
> #ifdef CONFIG_MEMCG_KMEM
> - bool must_inc_static_branch = false;
> -
> struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
> /*
> * For simplicity, we won't allow this to be disabled. It also can't
> @@ -4958,7 +4956,13 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
> res_counter_set_limit(&memcg->kmem, RESOURCE_MAX);
> goto out;
> }
> - must_inc_static_branch = true;
> + static_key_slow_inc(&memcg_kmem_enabled_key);
> + /*
> + * setting the active bit after the inc will guarantee no one
> + * starts accounting before all call sites are patched
> + */
> + memcg_kmem_set_active(memcg);
> +
> /*
> * kmem charges can outlive the cgroup. In the case of slab
> * pages, for instance, a page contain objects from various
> @@ -4970,27 +4974,6 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
> ret = res_counter_set_limit(&memcg->kmem, val);
> out:
> mutex_unlock(&memcg_mutex);
> -
> - /*
> - * We are by now familiar with the fact that we can't inc the static
> - * branch inside cgroup_lock. See disarm functions for details. A
> - * worker here is overkill, but also wrong: After the limit is set, we
> - * must start accounting right away. Since this operation can't fail,
> - * we can safely defer it to here - no rollback will be needed.
> - *
> - * The boolean used to control this is also safe, because
> - * KMEM_ACCOUNTED_ACTIVATED guarantees that only one process will be
> - * able to set it to true;
> - */
> - if (must_inc_static_branch) {
> - static_key_slow_inc(&memcg_kmem_enabled_key);
> - /*
> - * setting the active bit after the inc will guarantee no one
> - * starts accounting before all call sites are patched
> - */
> - memcg_kmem_set_active(memcg);
> - }
> -
> #endif
> return ret;
> }
> --
> 1.7.11.7
>
--
Michal Hocko
SUSE Labs
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