On Fri 07-02-14 12:04:23, Johannes Weiner wrote:
> Instead of returning NULL from try_get_mem_cgroup_from_mm() when the
> mm owner is exiting, just return root_mem_cgroup. This makes sense
> for all callsites and gets rid of some of them having to fallback
> manually.
It makes sense now that css reference counting is basically for free
so we do not have to prevent reference counting on the root.
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/memcontrol.c | 18 ++++--------------
> 1 file changed, 4 insertions(+), 14 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 689fffdee471..37946635655c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1071,7 +1071,7 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
> return mem_cgroup_from_css(task_css(p, mem_cgroup_subsys_id));
> }
>
> -struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
> +struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
> {
> struct mem_cgroup *memcg = NULL;
>
> @@ -1079,7 +1079,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
> do {
> memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> if (unlikely(!memcg))
> - break;
> + memcg = root_mem_cgroup;
> } while (!css_tryget(&memcg->css));
> rcu_read_unlock();
> return memcg;
> @@ -1475,7 +1475,7 @@ bool task_in_mem_cgroup(struct task_struct *task,
>
> p = find_lock_task_mm(task);
> if (p) {
> - curr = try_get_mem_cgroup_from_mm(p->mm);
> + curr = get_mem_cgroup_from_mm(p->mm);
> task_unlock(p);
> } else {
> /*
> @@ -1489,8 +1489,6 @@ bool task_in_mem_cgroup(struct task_struct *task,
> css_get(&curr->css);
> rcu_read_unlock();
> }
> - if (!curr)
> - return false;
> /*
> * We should check use_hierarchy of "memcg" not "curr". Because checking
> * use_hierarchy of "curr" here make this function true if hierarchy is
> @@ -3649,15 +3647,7 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
> if (!current->mm || current->memcg_kmem_skip_account)
> return true;
>
> - memcg = try_get_mem_cgroup_from_mm(current->mm);
> -
> - /*
> - * very rare case described in mem_cgroup_from_task. Unfortunately there
> - * isn't much we can do without complicating this too much, and it would
> - * be gfp-dependent anyway. Just let it go
> - */
> - if (unlikely(!memcg))
> - return true;
> + memcg = get_mem_cgroup_from_mm(current->mm);
>
> if (!memcg_can_account_kmem(memcg)) {
> css_put(&memcg->css);
> --
> 1.8.5.3
>
--
Michal Hocko
SUSE Labs
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