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Date:   Wed, 21 Aug 2019 00:19:37 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Michal Hocko <mhocko@kernel.org>, Edward Chron <echron@arista.com>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        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 Wed, 21 Aug 2019, Michal Hocko wrote:

> > vm.oom_dump_tasks is pretty useful, however, so it's curious why you 
> > haven't left it enabled :/
> 
> Because it generates a lot of output potentially. Think of a workload
> with too many tasks which is not uncommon.

Probably better to always print all the info for the victim so we don't 
need to duplicate everything between dump_tasks() and dump_oom_summary().

Edward, how about this?

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -420,11 +420,17 @@ static int dump_task(struct task_struct *p, void *arg)
  * State information includes task's pid, uid, tgid, vm size, rss,
  * pgtables_bytes, swapents, oom_score_adj value, and name.
  */
-static void dump_tasks(struct oom_control *oc)
+static void dump_tasks(struct oom_control *oc, struct task_struct *victim)
 {
 	pr_info("Tasks state (memory values in pages):\n");
 	pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
 
+	/* If vm.oom_dump_tasks is disabled, only show the victim */
+	if (!sysctl_oom_dump_tasks) {
+		dump_task(victim, oc);
+		return;
+	}
+
 	if (is_memcg_oom(oc))
 		mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
 	else {
@@ -465,8 +471,8 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
 		if (is_dump_unreclaim_slabs())
 			dump_unreclaimable_slab();
 	}
-	if (sysctl_oom_dump_tasks)
-		dump_tasks(oc);
+	if (p || sysctl_oom_dump_tasks)
+		dump_tasks(oc, p);
 	if (p)
 		dump_oom_summary(oc, p);
 }