On Wed, Apr 14, 2021 at 6:15 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Wed 14-04-21 18:04:35, Muchun Song wrote: > > On Wed, Apr 14, 2021 at 5:24 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > On Tue 13-04-21 14:51:48, Muchun Song wrote: > > > > When mm is NULL, we do not need to hold rcu lock and call css_tryget for > > > > the root memcg. And we also do not need to check !mm in every loop of > > > > while. So bail out early when !mm. > > > > > > mem_cgroup_charge and other callers unconditionally drop the reference > > > so how come this does not underflow reference count? > > > > For the root memcg, the CSS_NO_REF flag is set, so css_get > > and css_put do not get or put reference. > > Ohh, right you are. I must have forgot about that special case. I am > pretty sure I (and likely few more) will stumble over that in the future > again. A small comment explaining that the reference can be safely > ignore would be helpful. OK. Will do. > > Anyway > Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks. > > Thanks! > > -- > Michal Hocko > SUSE Labs
