linux-kernel - Re: [PATCH memcg 2/3] memcg: remove charge forcinig for dying tasks

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Message-ID: <YXAOjQO5r1g/WKmn@dhcp22.suse.cz>
Date:   Wed, 20 Oct 2021 14:41:49 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Uladzislau Rezki <urezki@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Shakeel Butt <shakeelb@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH memcg 2/3] memcg: remove charge forcinig for dying tasks

On Wed 20-10-21 15:13:46, Vasily Averin wrote:
> ToDo: should we keep task_is_dying() in mem_cgroup_out_of_memory() ?
> 
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> ---
>  mm/memcontrol.c | 20 +++++++-------------
>  1 file changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6da5020a8656..74a7379dbac1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -239,7 +239,7 @@ enum res_type {
>  	     iter != NULL;				\
>  	     iter = mem_cgroup_iter(NULL, iter, NULL))
>  
> -static inline bool should_force_charge(void)
> +static inline bool task_is_dying(void)
>  {
>  	return tsk_is_oom_victim(current) || fatal_signal_pending(current) ||
>  		(current->flags & PF_EXITING);
> @@ -1575,7 +1575,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	 * A few threads which were not waiting at mutex_lock_killable() can
>  	 * fail to bail out. Therefore, check again after holding oom_lock.
>  	 */
> -	ret = should_force_charge() || out_of_memory(&oc);
> +	ret = task_is_dying() || out_of_memory(&oc);

Why are you keeping the task_is_dying check here? IIRC I have already
pointed out that out_of_memory already has some means to do a bypass
when needed.
-- 
Michal Hocko
SUSE Labs