Add documentation on ros2_control_node and make lock_memory false by default (backport #1890)

controller_manager/doc/userdoc.rst

@@ -262,6 +262,38 @@ The workaround for this is to specify another node name remap rule in the ``Node
       auto cm = std::make_shared<controller_manager::ControllerManager>(
         executor, "_target_node_name", "some_optional_namespace", options);
 
+Launching controller_manager with ros2_control_node
+---------------------------------------------------
+
+The controller_manager can be launched with the ros2_control_node executable. The following example shows how to launch the controller_manager with the ros2_control_node executable:
+
+.. code-block:: python
+
+    control_node = Node(
+        package="controller_manager",
+        executable="ros2_control_node",
+        parameters=[robot_controllers],
+        output="both",
+    )
+
+The ros2_control_node executable uses the following parameters from the ``controller_manager`` node:
+
+lock_memory (optional; bool; default: false for a non-realtime kernel, true for a realtime kernel)
+  Locks the memory of the ``controller_manager`` node at startup to physical RAM in order to avoid page faults
+  and to prevent the node from being swapped out to disk.
+  Find more information about the setup for memory locking in the following link : `How to set ulimit values <https://access.redhat.com/solutions/61334>`_
+  The following command can be used to set the memory locking limit temporarily : ``ulimit -l unlimited``.
+
+cpu_affinity (optional; int; default: -1)
+  Sets the CPU affinity of the ``controller_manager`` node to the specified CPU core.
+  The value of -1 means that the CPU affinity is not set.
+
+thread_priority (optional; int; default: 50)
+  Sets the thread priority of the ``controller_manager`` node to the specified value. The value must be between 0 and 99.
+
+use_sim_time (optional; bool; default: false)
+  Enables the use of simulation time in the ``controller_manager`` node.
+
 Concepts
 -----------
 

controller_manager/src/ros2_control_node.cpp

@@ -56,7 +56,8 @@ int main(int argc, char ** argv)
         cm->get_logger(), "Unable to set the CPU affinity : '%s'", affinity_result.second.c_str());
     }
   }
-  const bool lock_memory = cm->get_parameter_or<bool>("lock_memory", true);
+  const bool has_realtime = realtime_tools::has_realtime_kernel();
+  const bool lock_memory = cm->get_parameter_or<bool>("lock_memory", has_realtime);
   std::string message;
   if (lock_memory && !realtime_tools::lock_memory(message))
   {