linux-kernel - [v6 4/4] mm, oom, docs: describe the cgroup-aware OOM killer

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Date:   Wed, 23 Aug 2017 17:52:01 +0100
From:   Roman Gushchin <guro@...com>
To:     <linux-mm@...ck.org>
CC:     Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        David Rientjes <rientjes@...gle.com>,
        Tejun Heo <tj@...nel.org>, <kernel-team@...com>,
        <cgroups@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [v6 4/4] mm, oom, docs: describe the cgroup-aware OOM killer

Update cgroups v2 docs.

Signed-off-by: Roman Gushchin <guro@...com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Tejun Heo <tj@...nel.org>
Cc: kernel-team@...com
Cc: cgroups@...r.kernel.org
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
---
 Documentation/cgroup-v2.txt | 62 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index dec5afdaa36d..79ac407bf5a0 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
@@ -1002,6 +1003,34 @@ 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
+
+	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.
+
+	Be default, the OOM killer respects the /proc/pid/oom_score_adj
+	value -1000, and will never kill the task, unless oom_kill_all
+	is set.
+
+  memory.oom_priority
+
+	A read-write single value file which exists 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 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.
 	The following entries are defined.  Unless specified
@@ -1206,6 +1235,39 @@ 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, hierarchically looking for the largest memory
+consumer. By default, it will look for the biggest task in the
+biggest leaf memory cgroup.
+
+By default, all memory cgroups have oom_priority 0, and OOM killer
+will choice the cgroup with the largest memory consuption 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
+at the priority value first, and compare sizes only of memory
+cgroups with equal priority.
+
+A user can change this behavior by enabling the per-cgroup
+oom_kill_all option. If set, OOM killer will kill all processes
+attached to the cgroup if selected as an OOM victim.
+
+Tasks in the root cgroup are treated as independent memory consumers,
+and are compared with other memory consumers (leaf memory cgroups).
+The root cgroup doesn't support the oom_kill_all 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.
+
 IO
 --
 
-- 
2.13.5