[PATCH V2] Documentation: cgroups: Add notes on removing PIDs from tasks and cgroups requiring setup

[Eric B Munson]

The cgroup documentation does not specify how a process can be removed from a
particular group.  This patch adds a note at the end of the simple example
about how this is done.  Also, some cgroups (like cpusets) require user input
before a new group can be used.  This is noted in the patch as well.

Signed-off-by: Eric B Munson <emunson@xxxxxxxxx>
---
Changes from V1:
 Rework the note about removing a process from a cgroup
 Add note about ns cgroup causing failure when moving processes between groups

 Documentation/cgroups/cgroups.txt |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 44b8b7a..cbdfb7d 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -349,6 +349,10 @@ To mount a cgroup hierarchy with all available subsystems, type:
 The "xxx" is not interpreted by the cgroup code, but will appear in
 /proc/mounts so may be any useful identifying string that you like.
 
+Note: Some subsystems do not work without some user input first.  For instance,
+if cpusets are enabled the user will have to populate the cpus and mems files
+for each new cgroup created before that group can be used.
+
 To mount a cgroup hierarchy with just the cpuset and memory
 subsystems, type:
 # mount -t cgroup -o cpuset,memory hier1 /dev/cgroup
@@ -426,6 +430,14 @@ You can attach the current shell task by echoing 0:
 
 # echo 0 > tasks
 
+Note: Since every task is always a member of exactly one cgroup in each
+mounted hierarchy, to remove a task from its current cgroup you must
+move it into a new cgroup (possibly the root cgroup) by writing to the
+new cgroup's tasks file.
+
+Note: If the ns cgroup is active, moving a process to another cgroup can
+fail.
+
 2.3 Mounting hierarchies by name
 --------------------------------
 
-- 
1.7.1

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