[v7 4/5] 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: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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 | 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.
+
   memory.events
 
 	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
-- 
2.13.5