[PATCH] cgroup: Add missing cgroup-v2 PID controller documentation.

[PATCH] cgroup: Add missing cgroup-v2 PID controller documentation.

[Hans Ragas]

Signed-off-by: Hans Ragas <hansr@fb.com>
---
 Documentation/cgroup-v2.txt | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 4cc07ce..fdfe942 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -47,6 +47,8 @@ CONTENTS
   5-3. IO
     5-3-1. IO Interface Files
     5-3-2. Writeback
+  5-4. PID
+    5-4-1. PID Interface Files
 6. Namespace
   6-1. Basics
   6-2. The Root and Views
@@ -1119,6 +1121,45 @@ writeback as follows.
  vm.dirty[_background]_ratio.


+5-4. PID
+
+The process number controller is used to allow a cgroup to stop any
+new tasks from being fork()'d or clone()'d after a specified limit is
+reached.
+
+The number of tasks in a cgroup can be exhausted in ways which other
+controllers cannot prevent, thus warranting its own controller.  For
+example, a fork bomb is likely to exhaust the number of tasks before
+hitting memory restrictions.
+
+Note that PIDs used in this controller refer to TIDs, process IDs as
+used by the kernel.
+
+5-4-1. PID Interface Files
+
+  pids.max
+
+ A read-write single value file which exists on non-root cgroups.
+ The default is "max".
+
+ Hard limit of number of processes.
+
+  pids.current
+
+ A read-only single value file which exists on all cgroups.
+
+ The number of processes currently in the cgroup and its
+ descendants.
+
+Organisational operations are not blocked by cgroup policies, so it
+is possible to have pids.current > pids.max.  This can be done by
+either setting the limit to be smaller than pids.current, or
+attaching enough processes to the cgroup such that pids.current is
+larger than pids.max.  However, it is not possible to violate a cgroup
+PID policy through fork() or clone(). These will return -EAGAIN if the
+creation of a new process would cause a cgroup policy to be violated.
+
+
 6. Namespace

 6-1. Basics
--
2.9.3

Re: [PATCH] cgroup: Add missing cgroup-v2 PID controller documentation.

[tj-DgEjT+Ai2ygdnm+yROfE0A]

On Tue, Jan 10, 2017 at 05:42:34PM +0000, Hans Ragas wrote:
> 
> Signed-off-by: Hans Ragas <hansr-b10kYP2dOMg@public.gmane.org>

Applied to cgroup/for-4.11 with minor adjustments.

Thanks.

-- 
tejun