linux-kernel - Re: [PATCH v2] mm/oom_kill: count global and memory cgroup oom kills

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Date:   Mon, 5 Jun 2017 10:50:12 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Guschin <guroan@...il.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v2] mm/oom_kill: count global and memory cgroup oom kills

On Thu 25-05-17 13:28:30, Konstantin Khlebnikov wrote:
> Show count of oom killer invocations in /proc/vmstat and count of
> processes killed in memory cgroup in knob "memory.events"
> (in memory.oom_control for v1 cgroup).
> 
> Also describe difference between "oom" and "oom_kill" in memory
> cgroup documentation. Currently oom in memory cgroup kills tasks
> iff shortage has happened inside page fault.
> 
> These counters helps in monitoring oom kills - for now
> the only way is grepping for magic words in kernel log.

Yes this is less than optimal and the counter sounds like a good step
forward. I have 2 comments to the patch though.

[...]

> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 899949bbb2f9..42296f7001da 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -556,8 +556,11 @@ static inline void mem_cgroup_count_vm_event(struct mm_struct *mm,
>  
>  	rcu_read_lock();
>  	memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> -	if (likely(memcg))
> +	if (likely(memcg)) {
>  		this_cpu_inc(memcg->stat->events[idx]);
> +		if (idx == OOM_KILL)
> +			cgroup_file_notify(&memcg->events_file);
> +	}
>  	rcu_read_unlock();

Well, this is ugly. I see how you want to share the global counter and
the memcg event which needs the notification. But I cannot say this
would be really easy to follow. Can we have at least a comment in
memcg_event_item enum definition?

> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 04c9143a8625..dd30a045ef5b 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -876,6 +876,11 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
>  	/* Get a reference to safely compare mm after task_unlock(victim) */
>  	mm = victim->mm;
>  	mmgrab(mm);
> +
> +	/* Raise event before sending signal: reaper must see this */
> +	count_vm_event(OOM_KILL);
> +	mem_cgroup_count_vm_event(mm, OOM_KILL);
> +
>  	/*
>  	 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
>  	 * the OOM victim from depleting the memory reserves from the user

Why don't you count tasks which share mm with the oom victim? 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 0e2c925e7826..9a95947a60ba 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -924,6 +924,8 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 		 */
 		if (unlikely(p->flags & PF_KTHREAD))
 			continue;
+		count_vm_event(OOM_KILL);
+		count_memcg_event_mm(mm, OOM_KILL);
 		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
 	}
 	rcu_read_unlock();

Other than that looks good to me.
Acked-by: Michal Hocko <mhocko@...e.com>
-- 
Michal Hocko
SUSE Labs