[PATCH] mm, oom, docs: document groupoom mount option

[Roman Gushchin]

Add a note that cgroup-aware OOM logic is disabled by default
and describe how to enable it.

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 Documentation/cgroup-v2.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index c80a147f94b7..ff8e92db636d 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -1049,6 +1049,9 @@ PAGE_SIZE multiple when read back.
 	and will never kill the unkillable task, even if memory.oom_group
 	is set.
 
+	If cgroup-aware OOM killer is not enabled, ENOTSUPP error
+	is returned on attempt to access the file.
+
   memory.events
 	A read-only flat-keyed file which exists on non-root cgroups.
 	The following entries are defined.  Unless specified
@@ -1258,6 +1261,12 @@ OOM Killer
 Cgroup v2 memory controller implements a cgroup-aware OOM killer.
 It means that it treats cgroups as first class OOM entities.
 
+Cgroup-aware OOM logic is turned off by default and requires
+passing the "groupoom" option on mounting cgroupfs. It can also
+by remounting cgroupfs with the following command::
+
+  # mount -o remount,groupoom $MOUNT_POINT
+
 Under OOM conditions the memory controller tries to make the best
 choice of a victim, looking for a memory cgroup with the largest
 memory footprint, considering leaf cgroups and cgroups with the
-- 
2.14.3