[v3 3/6] mm, oom: cgroup-aware OOM killer debug info

[Roman Gushchin]

Dump the cgroup oom badness score, as well as the name
of chosen victim cgroup.

Here how it looks like in dmesg:
[   18.824495] Choosing a victim memcg because of the system-wide OOM
[   18.826911] Cgroup /A1: 200805
[   18.827996] Cgroup /A2: 273072
[   18.828937] Cgroup /A2/B3: 51
[   18.829795] Cgroup /A2/B4: 272969
[   18.830800] Cgroup /A2/B5: 52
[   18.831890] Chosen cgroup /A2/B4: 272969

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 mm/memcontrol.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bdb5103..4face20 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2669,7 +2669,15 @@ bool mem_cgroup_select_oom_victim(struct oom_control *oc)
 
 	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
 		return false;
+
+	pr_info("Choosing a victim memcg because of the %s",
+		oc->memcg ?
+		"memory limit reached of cgroup " :
+		"system-wide OOM\n");
 	if (oc->memcg) {
+		pr_cont_cgroup_path(oc->memcg->css.cgroup);
+		pr_cont("\n");
+
 		chosen_memcg = oc->memcg;
 		parent = oc->memcg;
 	}
@@ -2683,6 +2691,10 @@ bool mem_cgroup_select_oom_victim(struct oom_control *oc)
 
 			points = mem_cgroup_oom_badness(iter, oc->nodemask);
 
+			pr_info("Cgroup ");
+			pr_cont_cgroup_path(iter->css.cgroup);
+			pr_cont(": %ld\n", points);
+
 			if (points > chosen_memcg_points) {
 				chosen_memcg = iter;
 				chosen_memcg_points = points;
@@ -2731,6 +2743,10 @@ bool mem_cgroup_select_oom_victim(struct oom_control *oc)
 			oc->chosen_memcg = chosen_memcg;
 		}
 
+		pr_info("Chosen cgroup ");
+		pr_cont_cgroup_path(chosen_memcg->css.cgroup);
+		pr_cont(": %ld\n", oc->chosen_points);
+
 		/*
 		 * Even if we have to kill all tasks in the cgroup,
 		 * we need to select the biggest task to start with.
@@ -2739,7 +2755,9 @@ bool mem_cgroup_select_oom_victim(struct oom_control *oc)
 		 */
 		oc->chosen_points = 0;
 		mem_cgroup_scan_tasks(chosen_memcg, oom_evaluate_task, oc);
-	}
+	} else if (oc->chosen)
+		pr_info("Chosen task %s (%d) in root cgroup: %ld\n",
+			oc->chosen->comm, oc->chosen->pid, oc->chosen_points);
 
 	rcu_read_unlock();
 
-- 
2.7.4