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Subject[v9 5/5] mm, oom, docs: describe the cgroup-aware OOM killer
Document the cgroup-aware OOM killer.

Signed-off-by: Roman Gushchin <>
Cc: Michal Hocko <>
Cc: Vladimir Davydov <>
Cc: Johannes Weiner <>
Cc: Tetsuo Handa <>
Cc: Andrew Morton <>
Cc: David Rientjes <>
Cc: Tejun Heo <>
Documentation/cgroup-v2.txt | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 3f8216912df0..936dd60b8d6a 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -48,6 +48,7 @@ v1 is available under Documentation/cgroup-v1/.
5-2-1. Memory Interface Files
5-2-2. Usage Guidelines
5-2-3. Memory Ownership
+ 5-2-4. OOM Killer
5-3. IO
5-3-1. IO Interface Files
5-3-2. Writeback
@@ -1043,6 +1044,21 @@ PAGE_SIZE multiple when read back.
high limit is used and monitored properly, this limit's
utility is limited to providing the final safety net.

+ memory.oom_group
+ A read-write single value file which exists on non-root
+ cgroups. The default is "0".
+ If set, OOM killer will consider the memory cgroup and all
+ descendant cgroups as indivisible memory consumers and compare
+ them with other memory consumers by their memory footprint.
+ If such memory cgroup is selected as an OOM victim, all
+ processes belonging to it or it's descendants will be killed.
+ OOM killer respects the /proc/pid/oom_score_adj value -1000,
+ and will never kill the unkillable task, even if memory.oom_group
+ is set.
A read-only flat-keyed file which exists on non-root cgroups.
The following entries are defined. Unless specified
@@ -1246,6 +1262,34 @@ to be accessed repeatedly by other cgroups, it may make sense to use
POSIX_FADV_DONTNEED to relinquish the ownership of memory areas
belonging to the affected files to ensure correct memory ownership.

+OOM Killer
+Cgroup v2 memory controller implements a cgroup-aware OOM killer.
+It means that it treats cgroups as first class OOM entities.
+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
+memory.oom_group option set, which are considered to be an indivisible
+memory consumers.
+By default, OOM killer will kill the biggest task in the selected
+memory cgroup. A user can change this behavior by enabling
+the per-cgroup memory.oom_group option. If set, it causes
+the OOM killer to kill all processes attached to the cgroup,
+except processes with oom_score_adj set to -1000.
+This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM
+the memory controller considers only cgroups belonging to the sub-tree
+of the OOM'ing cgroup.
+The root cgroup is treated as a leaf memory cgroup, so it's compared
+with other leaf memory cgroups and cgroups with oom_group option set.
+If there are no cgroups with the enabled memory controller,
+the OOM killer is using the "traditional" process-based approach.

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