From: Michal Hocko <mhocko@suse.com>
To: Muchun Song <songmuchun@bytedance.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: [PATCH 2/7] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm
Date: Wed, 14 Apr 2021 11:24:34 +0200 [thread overview]
Message-ID: <YHa00lx7ACWcS1/h@dhcp22.suse.cz> (raw)
In-Reply-To: <20210413065153.63431-3-songmuchun@bytedance.com>
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?
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
> ---
> mm/memcontrol.c | 21 ++++++++++-----------
> 1 file changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f229de925aa5..9cbfff59b171 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -901,20 +901,19 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
> if (mem_cgroup_disabled())
> return NULL;
>
> + /*
> + * Page cache insertions can happen without an
> + * actual mm context, e.g. during disk probing
> + * on boot, loopback IO, acct() writes etc.
> + */
> + if (unlikely(!mm))
> + return root_mem_cgroup;
> +
> rcu_read_lock();
> do {
> - /*
> - * Page cache insertions can happen without an
> - * actual mm context, e.g. during disk probing
> - * on boot, loopback IO, acct() writes etc.
> - */
> - if (unlikely(!mm))
> + memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> + if (unlikely(!memcg))
> memcg = root_mem_cgroup;
> - else {
> - memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> - if (unlikely(!memcg))
> - memcg = root_mem_cgroup;
> - }
> } while (!css_tryget(&memcg->css));
> rcu_read_unlock();
> return memcg;
> --
> 2.11.0
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-04-14 9:24 UTC|newest]
Thread overview: 32+ 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 [this message]
2021-04-14 10:04 ` [External] " Muchun Song
2021-04-14 10:15 ` Michal Hocko
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 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 17:57 ` Roman Gushchin
2021-04-14 9:44 ` Michal Hocko
2021-04-14 10:00 ` [External] " Muchun Song
2021-04-14 17:49 ` Johannes Weiner
2021-04-15 7:08 ` Michal Hocko
2021-04-15 10:01 ` Muchun Song
2021-04-13 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 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 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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