From: Muchun Song <songmuchun@bytedance.com>
To: Michal Hocko <mhocko@suse.com>
Cc: guro@fb.com, hannes@cmpxchg.org, akpm@linux-foundation.org,
shakeelb@google.com, vdavydov.dev@gmail.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
duanxiongchun@bytedance.com, fam.zheng@bytedance.com
Subject: Re: [External] Re: [PATCH 2/7] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm
Date: Thu, 15 Apr 2021 11:13:16 +0800 [thread overview]
Message-ID: <CAMZfGtVGBW-j8_2+dmrD=Bbc2mOXUj4Hg_pjOKi0YrY_OVj1nA@mail.gmail.com> (raw)
In-Reply-To: <YHbAzL9ls6EBsB3L@dhcp22.suse.cz>
On Wed, Apr 14, 2021 at 6:15 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Wed 14-04-21 18:04:35, Muchun Song wrote:
> > On Wed, Apr 14, 2021 at 5:24 PM Michal Hocko <mhocko@suse.com> 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@suse.com>
Thanks.
>
> Thanks!
>
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2021-04-15 3:15 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 6:51 [PATCH 0/7] memcontrol code cleanup and simplification Muchun Song
2021-04-13 6:51 ` [PATCH 1/7] mm: memcontrol: fix page charging in page replacement Muchun Song
2021-04-13 17:45 ` Roman Gushchin
2021-04-14 9:20 ` Michal Hocko
2021-04-13 6:51 ` [PATCH 2/7] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm Muchun Song
2021-04-13 17:47 ` Roman Gushchin
2021-04-14 9:24 ` Michal Hocko
2021-04-14 10:04 ` [External] " Muchun Song
2021-04-14 10:04 ` Muchun Song
2021-04-14 10:15 ` Michal Hocko
2021-04-15 3:13 ` Muchun Song [this message]
2021-04-15 3:13 ` Muchun Song
2021-04-15 7:09 ` Michal Hocko
2021-04-13 6:51 ` [PATCH 3/7] mm: memcontrol: remove the pgdata parameter of mem_cgroup_page_lruvec Muchun Song
2021-04-13 13:12 ` Shakeel Butt
2021-04-13 13:12 ` Shakeel Butt
2021-04-13 17:48 ` Roman Gushchin
2021-04-14 9:27 ` Michal Hocko
2021-04-13 6:51 ` [PATCH 4/7] mm: memcontrol: simplify lruvec_holds_page_lru_lock Muchun Song
2021-04-13 13:28 ` Shakeel Butt
2021-04-13 13:28 ` Shakeel Butt
2021-04-13 17:57 ` Roman Gushchin
2021-04-14 9:44 ` Michal Hocko
2021-04-14 10:00 ` [External] " Muchun Song
2021-04-14 10:00 ` Muchun Song
2021-04-14 17:49 ` Johannes Weiner
2021-04-15 7:08 ` Michal Hocko
2021-04-15 10:01 ` Muchun Song
2021-04-15 10:01 ` Muchun Song
2021-04-13 6:51 ` [PATCH 5/7] mm: memcontrol: simplify the logic of objcg pinning memcg Muchun Song
2021-04-13 14:16 ` Shakeel Butt
2021-04-13 14:16 ` Shakeel Butt
2021-04-13 17:51 ` Roman Gushchin
2021-04-13 6:51 ` [PATCH 6/7] mm: memcontrol: move obj_cgroup_uncharge_pages() out of css_set_lock Muchun Song
2021-04-13 14:18 ` Shakeel Butt
2021-04-13 14:18 ` Shakeel Butt
2021-04-13 17:54 ` Roman Gushchin
2021-04-13 18:03 ` Johannes Weiner
2021-04-13 6:51 ` [PATCH 7/7] mm: vmscan: remove noinline_for_stack Muchun Song
2021-04-14 9:46 ` Michal Hocko
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