[v7 5/5] mm, oom: allow disabling cgroup-aware OOM killer

[Roman Gushchin]

Introducing of cgroup-aware OOM killer changes the victim selection
algorithm used by default: instead of picking the largest process,
it will pick the largest memcg and then the largest process inside.

This affects only cgroup v2 users.

To provide a way to use cgroups v2 if the old OOM victim selection
algorithm is preferred for some reason, the cgroup.memory=nogroupoom
boot option is added.

If set, the OOM selection is performed in a "traditional" per-process
way. Both oom_priority and oom_group memcg knobs are ignored.

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 Documentation/admin-guide/kernel-parameters.txt | 1 +
 mm/memcontrol.c                                 | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 28f1a0f84456..07891f1030aa 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -489,6 +489,7 @@
 			Format: <string>
 			nosocket -- Disable socket memory accounting.
 			nokmem -- Disable kernel memory accounting.
+			nogroupoom -- Disable cgroup-aware OOM killer.
 
 	checkreqprot	[SELINUX] Set initial checkreqprot flag value.
 			Format: { "0" | "1" }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d7dd293897ca..6a8235dc41f6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -87,6 +87,9 @@ static bool cgroup_memory_nosocket;
 /* Kernel memory accounting disabled? */
 static bool cgroup_memory_nokmem;
 
+/* Cgroup-aware OOM  disabled? */
+static bool cgroup_memory_nogroupoom;
+
 /* Whether the swap controller is active */
 #ifdef CONFIG_MEMCG_SWAP
 int do_swap_account __read_mostly;
@@ -2822,6 +2825,9 @@ bool mem_cgroup_select_oom_victim(struct oom_control *oc)
 	if (mem_cgroup_disabled())
 		return false;
 
+	if (cgroup_memory_nogroupoom)
+		return false;
+
 	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
 		return false;
 
@@ -6188,6 +6194,8 @@ static int __init cgroup_memory(char *s)
 			cgroup_memory_nosocket = true;
 		if (!strcmp(token, "nokmem"))
 			cgroup_memory_nokmem = true;
+		if (!strcmp(token, "nogroupoom"))
+			cgroup_memory_nogroupoom = true;
 	}
 	return 0;
 }
-- 
2.13.5