mm/memcg: add oom_group_kill memory event

Our container agent wants to know when a container exits if it was OOM
killed or not to report to the user.  We use memory.oom.group = 1 to
ensure that OOM kills within the container's cgroup kill everything.
Existing memory.events are insufficient for knowing if this triggered:

1) Our current approach reads memory.events oom_kill and reports the
   container was killed if the value is non-zero. This is erroneous in
   some cases where containers create their children cgroups with
   memory.oom.group=1 as such OOM kills will get counted against the
   container cgroup's oom_kill counter despite not actually OOM killing
   the entire container.

2) Reading memory.events.local will fail to identify OOM kills in leaf
   cgroups (that don't set memory.oom.group) within the container
   cgroup.

This patch adds a new oom_group_kill event when memory.oom.group
triggers to allow userspace to cleanly identify when an entire cgroup is
oom killed.

[schatzberg.dan@gmail.com: changes from Johannes and Chris]
  Link: https://lkml.kernel.org/r/20211213162511.2492267-1-schatzberg.dan@gmail.com

Link: https://lkml.kernel.org/r/20211203162426.3375036-1-schatzberg.dan@gmail.com
Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 2aeb7ae8b393..8269bfa240f4 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1268,6 +1268,9 @@ PAGE_SIZE multiple when read back.
 		The number of processes belonging to this cgroup
 		killed by any kind of OOM killer.
 
+          oom_group_kill
+                The number of times a group OOM has occurred.
+
   memory.events.local
 	Similar to memory.events but the fields in the file are local
 	to the cgroup i.e. not hierarchical. The file modified event
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 0c5c403f4be6..951f24f42147 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -42,6 +42,7 @@ enum memcg_memory_event {
 	MEMCG_MAX,
 	MEMCG_OOM,
 	MEMCG_OOM_KILL,
+	MEMCG_OOM_GROUP_KILL,
 	MEMCG_SWAP_HIGH,
 	MEMCG_SWAP_MAX,
 	MEMCG_SWAP_FAIL,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bfe9bdec192b..2d39d58baccf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6318,6 +6318,8 @@ static void __memory_events_show(struct seq_file *m, atomic_long_t *events)
 	seq_printf(m, "oom %lu\n", atomic_long_read(&events[MEMCG_OOM]));
 	seq_printf(m, "oom_kill %lu\n",
 		   atomic_long_read(&events[MEMCG_OOM_KILL]));
+	seq_printf(m, "oom_group_kill %lu\n",
+		   atomic_long_read(&events[MEMCG_OOM_GROUP_KILL]));
 }
 
 static int memory_events_show(struct seq_file *m, void *v)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1ddabefcfb5a..e52ce0b1465d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -994,6 +994,7 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 	 * If necessary, kill all tasks in the selected memory cgroup.
 	 */
 	if (oom_group) {
+		memcg_memory_event(oom_group, MEMCG_OOM_GROUP_KILL);
 		mem_cgroup_print_oom_group(oom_group);
 		mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member,
 				      (void *)message);