cgroup: document cgroup v2 freezer interface

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

Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: linux-doc@vger.kernel.org
Cc: kernel-team@fb.com

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 20f92c16ffbf2c6e89ae090719d2e7225383985f..88e746074252298ecae8f0aab9db2bd1c9f4fb99 100644 (file)
--- 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."
          populated
                1 if the cgroup or its descendants contains any live
                processes; otherwise, 0.
+         frozen
+               1 if the cgroup is frozen; otherwise, 0.
 
   cgroup.max.descendants
        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.
 
 Controllers
 ===========