[PATCH] cgroup: document cgroup_no_v1=

[Johannes Weiner]

Add cgroup_no_v1= to kernel-parameters.txt, and a small blurb to
cgroup-v2.txt section about transitioning from cgroup to cgroup2.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 Documentation/cgroup-v2.txt         | 6 ++++++
 Documentation/kernel-parameters.txt | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index e2f4e7948a66..e892c7ab39ef 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -132,6 +132,12 @@ strongly discouraged for production use.  It is recommended to decide
 the hierarchies and controller associations before starting using the
 controllers after system boot.
 
+During transition to v2, system management software might still
+automount the v1 cgroup filesystem and so hijack all controllers
+during boot, before manual intervention is possible. To make testing
+and experimenting easier, the kernel parameter cgroup_no_v1= allows
+disabling controllers in v1 and make them always available in v2.
+
 
 2-2. Organizing Processes
 
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 444bff30e1cf..150173f47115 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -608,6 +608,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			cut the overhead, others just disable the usage. So
 			only cgroup_disable=memory is actually worthy}
 
+	cgroup_no_v1=	[KNL] Disable one, multiple, all cgroup controllers in v1
+			Format: { controller[,controller...] | "all" }
+			Like cgroup_disable, but only applies to cgroup v1;
+			the blacklisted controllers remain available in cgroup2.
+
 	cgroup.memory=	[KNL] Pass options to the cgroup memory controller.
 			Format: <string>
 			nosocket -- Disable socket memory accounting.
-- 
2.7.1