[PATCH 3.12 005/146] mm, oom: prefer thread group leaders for display purposes

[Jiri Slaby]

From: David Rientjes <rientjes@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit d49ad9355420c743c736bfd1dee9eaa5b1a7722a upstream.

When two threads have the same badness score, it's preferable to kill
the thread group leader so that the actual process name is printed to
the kernel log rather than the thread group name which may be shared
amongst several processes.

This was the behavior when select_bad_process() used to do
for_each_process(), but it now iterates threads instead and leads to
ambiguity.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 mm/memcontrol.c | 19 ++++++++++++-------
 mm/oom_kill.c   | 12 ++++++++----
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 15429b92ff98..213d1b4aafd7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1820,13 +1820,18 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 				break;
 			};
 			points = oom_badness(task, memcg, NULL, totalpages);
-			if (points > chosen_points) {
-				if (chosen)
-					put_task_struct(chosen);
-				chosen = task;
-				chosen_points = points;
-				get_task_struct(chosen);
-			}
+			if (!points || points < chosen_points)
+				continue;
+			/* Prefer thread group leaders for display purposes */
+			if (points == chosen_points &&
+			    thread_group_leader(chosen))
+				continue;
+
+			if (chosen)
+				put_task_struct(chosen);
+			chosen = task;
+			chosen_points = points;
+			get_task_struct(chosen);
 		}
 		css_task_iter_end(&it);
 	}
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f5bed7f17463..a9b5b7ffc476 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -327,10 +327,14 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
 			break;
 		};
 		points = oom_badness(p, NULL, nodemask, totalpages);
-		if (points > chosen_points) {
-			chosen = p;
-			chosen_points = points;
-		}
+		if (!points || points < chosen_points)
+			continue;
+		/* Prefer thread group leaders for display purposes */
+		if (points == chosen_points && thread_group_leader(chosen))
+			continue;
+
+		chosen = p;
+		chosen_points = points;
 	}
 	if (chosen)
 		get_task_struct(chosen);
-- 
1.9.3

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