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Subject[v5 4/4] 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: David Rientjes <>
Cc: Tejun Heo <>
Documentation/cgroup-v2.txt | 62 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 62 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index dec5afdaa36d..22108f31e09d 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. Cgroup-aware OOM Killer
5-3. IO
5-3-1. IO Interface Files
5-3-2. Writeback
@@ -1002,6 +1003,37 @@ 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_kill_all_tasks
+ A read-write single value file which exits on non-root
+ cgroups. The default is "0".
+ Defines whether the OOM killer should treat the cgroup
+ as a single entity during the victim selection.
+ If set, OOM killer will kill all belonging tasks in
+ corresponding cgroup is selected as an OOM victim.
+ Be default, OOM killer respect /proc/pid/oom_score_adj value
+ -1000, and will never kill the task, unless oom_kill_all_tasks
+ is set.
+ memory.oom_priority
+ A read-write single value file which exits on non-root
+ cgroups. The default is "0".
+ An integer number within the [-10000, 10000] range,
+ 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 elegible 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.
The following entries are defined. Unless specified
@@ -1206,6 +1238,36 @@ POSIX_FADV_DONTNEED to relinquish the ownership of memory areas
belonging to the affected files to ensure correct memory ownership.

+Cgroup-aware OOM Killer
+Cgroup v2 memory controller implements a cgroup-aware OOM killer.
+It means that it treats memory cgroups as first class OOM entities.
+Under OOM conditions the memory controller tries to make the best
+choise of a victim, hierarchically looking for the largest memory
+consumer. By default, it will look for the biggest task in the
+biggest leaf cgroup.
+Be default, all cgroups have oom_priority 0, and OOM killer will
+chose the largest cgroup recursively on each level. For non-root
+cgroups it's possible to change the oom_priority, and it will cause
+the OOM killer to look athe the priority value first, and compare
+sizes only of cgroups with equal priority.
+But a user can change this behavior by enabling the per-cgroup
+oom_kill_all_tasks option. If set, it causes the OOM killer treat
+the whole cgroup as an indivisible memory consumer. In case if it's
+selected as on OOM victim, all belonging tasks will be killed.
+Tasks in the root cgroup are treated as independent memory consumers,
+and are compared with other memory consumers (e.g. leaf cgroups).
+The root cgroup doesn't support the oom_kill_all_tasks 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.

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