[PATCH v4 7/7] cgroup: document cgroup v2 freezer interface

From: Roman Gushchin
Date: Fri Nov 30 2018 - 18:48:07 EST

Describe cgroup v2 freezer interface in the cgroup v2 admin guide.

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: kernel-team@xxxxxx
Documentation/admin-guide/cgroup-v2.rst | 27 +++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 07e06136a550..f8335e26b362 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -864,6 +864,8 @@ All cgroup core files are prefixed with "cgroup."
1 if the cgroup or its descendants contains any live
processes; otherwise, 0.
+ frozen
+ 1 if the cgroup is frozen; otherwise, 0.

A read-write single value files. The default is "max".
@@ -897,6 +899,31 @@ All cgroup core files are prefixed with "cgroup."
A dying cgroup can consume system resources not exceeding
limits, which were active at the moment of cgroup deletion.

+ cgroup.freeze
+ A read-write single value file which exists on non-root cgroups.
+ Allowed values are "0" and "1". The default is "0".
+ Writing "1" to the file causes freezing of the cgroup and all
+ descendant cgroups. This means that all belonging processes will
+ be stopped and will not run until the cgroup will be explicitly
+ unfrozen. Freezing of the cgroup may take some time; when this action
+ is completed, the "frozen" value in the cgroup.events control file
+ will be updated to "1" and the corresponding notification will be
+ issued.
+ A cgroup can be frozen either by its own settings, or by settings
+ of any ancestor cgroups. If any of ancestor cgroups is frozen, the
+ cgroup will remain frozen.
+ Processes in the frozen cgroup can be killed by a fatal signal.
+ They also can enter and leave a frozen cgroup: either by an explicit
+ move by a user, or if freezing of the cgroup races with fork().
+ If a process is moved to a frozen cgroup, it stops. If a process is
+ moved out of a frozen cgroup, it becomes running.
+ Frozen status of a cgroup doesn't affect any cgroup tree operations:
+ it's possible to delete a frozen (and empty) cgroup, as well as
+ create new sub-cgroups.