linux-kernel - Re: [PATCH v3] mm: memcontrol: reword obsolete comment of mem_cgroup_unmark_under

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Date:   Wed, 30 Sep 2020 12:48:19 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        vdavydov.dev@...il.com, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: memcontrol: reword obsolete comment of
 mem_cgroup_unmark_under_oom()

On Wed 30-09-20 05:53:36, Miaohe Lin wrote:
> Since commit 79dfdaccd1d5 ("memcg: make oom_lock 0 and 1 based rather than
> counter"), the mem_cgroup_unmark_under_oom() is added and the comment of
> the mem_cgroup_oom_unlock() is moved here.  But this comment make no sense
> here because mem_cgroup_oom_lock() does not operate on under_oom field. So
> we reword the comment as this would be helpful.
> [Thanks Michal Hocko for rewording this comment.]
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/memcontrol.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6877c765b8d0..4f0c14cb8690 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1817,8 +1817,8 @@ static void mem_cgroup_unmark_under_oom(struct mem_cgroup *memcg)
>  	struct mem_cgroup *iter;
>  
>  	/*
> -	 * When a new child is created while the hierarchy is under oom,
> -	 * mem_cgroup_oom_lock() may not be called. Watch for underflow.
> +	 * Be careful about under_oom underflows becase a child memcg
> +	 * could have been added after mem_cgroup_mark_under_oom.
>  	 */
>  	spin_lock(&memcg_oom_lock);
>  	for_each_mem_cgroup_tree(iter, memcg)
> -- 
> 2.19.1

-- 
Michal Hocko
SUSE Labs