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

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Message-ID: <cbda9b6b-3ee5-06ab-9a3b-debf361b55bb@virtuozzo.com>
Date:   Wed, 20 Oct 2021 17:21:33 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Michal Hocko <mhocko@...e.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 20.10.2021 15:41, Michal Hocko wrote:
> 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.

It was a misunderstanding.
I've been waiting for your final decision.

I have no good arguments "pro" or strong objection "contra". 
However, I prefer to keep task_is_dying() so as not to touch other tasks unnecessarily.

I can't justify why its removal is necessary,
but on the other hand, it shouldn't break anything.

I can drop it if you think it's necessary.

Thank you,
	Vasily Averin