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Date:   Tue, 20 Aug 2019 20:25:32 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Edward Chron <echron@arista.com>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Shakeel Butt <shakeelb@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, colona@arista.com
Subject: Re: [PATCH] mm/oom: Add oom_score_adj value to oom Killed process
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On Tue, 20 Aug 2019, Edward Chron wrote:

> For an OOM event: print oom_score_adj value for the OOM Killed process to
> document what the oom score adjust value was at the time the process was
> OOM Killed. The adjustment value can be set by user code and it affects
> the resulting oom_score so it is used to influence kill process selection.
> 
> When eligible tasks are not printed (sysctl oom_dump_tasks = 0) printing
> this value is the only documentation of the value for the process being
> killed. Having this value on the Killed process message documents if a
> miscconfiguration occurred or it can confirm that the oom_score_adj
> value applies as expected.
> 
> An example which illustates both misconfiguration and validation that
> the oom_score_adj was applied as expected is:
> 
> Aug 14 23:00:02 testserver kernel: Out of memory: Killed process 2692
>  (systemd-udevd) total-vm:1056800kB, anon-rss:1052760kB, file-rss:4kB,
>  shmem-rss:0kB oom_score_adj:1000
> 
> The systemd-udevd is a critical system application that should have an
> oom_score_adj of -1000. Here it was misconfigured to have a adjustment
> of 1000 making it a highly favored OOM kill target process. The output
> documents both the misconfiguration and the fact that the process
> was correctly targeted by OOM due to the miconfiguration. Having
> the oom_score_adj on the Killed message ensures that it is documented.
> 
> Signed-off-by: Edward Chron <echron@arista.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Acked-by: David Rientjes <rientjes@google.com>

vm.oom_dump_tasks is pretty useful, however, so it's curious why you 
haven't left it enabled :/

> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index eda2e2a0bdc6..c781f73b6cd6 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -884,12 +884,13 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  	 */
>  	do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
>  	mark_oom_victim(victim);
> -	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
> +	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB oom_score_adj:%ld\n",
>  		message, task_pid_nr(victim), victim->comm,
>  		K(victim->mm->total_vm),
>  		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
>  		K(get_mm_counter(victim->mm, MM_FILEPAGES)),
> -		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
> +		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)),
> +		(long)victim->signal->oom_score_adj);
>  	task_unlock(victim);
>  
>  	/*

Nit: why not just use %hd and avoid the cast to long?