[v5 4/4] mm, oom, docs: describe the cgroup-aware OOM killer

[Roman Gushchin]

Update cgroups v2 docs.

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: Tejun Heo <tj@xxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 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.
+
   memory.events
 	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.
+
 IO
 --
 
-- 
2.13.5