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Subject[v7 4/5] mm, oom, docs: describe the cgroup-aware OOM killer
Update cgroups v2 docs.

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 | 56 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 56 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index a86f3cb88125..5d21bd2e7d55 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -44,6 +44,7 @@ CONTENTS
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
@@ -799,6 +800,33 @@ 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 kill all processes attached to the cgroup
+ if selected as an OOM victim.
+ 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.
+ memory.oom_priority
+ A read-write single value file which exists on non-root
+ cgroups. The default is "0".
+ An integer number, which defines the order in which
+ the OOM killer selects victim memory cgroups.
+ OOM killer prefers memory cgroups with larger priority if they
+ are populated with eligible tasks.
+ The oom_priority value is compared within sibling cgroups.
+ The root cgroup has the oom_priority 0, which cannot be changed.

A read-only flat-keyed file which exists on non-root cgroups.
@@ -1028,6 +1056,34 @@ POSIX_FADV_DONTNEED to relinquish the ownership of memory areas
belonging to the affected files to ensure correct memory ownership.

+5-2-4. 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, hierarchically looking for a cgroup with the
+largest oom_priority. If sibling cgroups have the same priority,
+the OOM killer selects one which is the largest memory consumer.
+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 oom_group option. If set, it causes the OOM killer
+to kill all processes attached to the cgroup.
+Tasks in the root cgroup are treated as independent memory consumers,
+and are compared with other memory consumers (memory cgroups and
+other tasks in root cgroup).
+The root cgroup doesn't support the oom_group feature.
+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.
+If there are no cgroups with the enabled memory controller,
+the OOM killer is using the "traditional" process-based approach.
5-3. IO

The "io" controller regulates the distribution of IO resources. This
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