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memcg: increment static branch right after limit set 

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.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Glauber Costa 2013-02-22 16:34:56 -08:00 committed by Linus Torvalds
parent 0999821b1d
commit 692e89abd1
1 changed files with 7 additions and 24 deletions
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31
mm/memcontrol.c
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@ -4974,8 +4974,6 @@ 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
@ -5004,7 +5002,13 @@ 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
@ -5017,27 +5021,6 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
out:
mutex_unlock(&set_limit_mutex);
mutex_unlock(&memcg_create_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;
}