Bug report

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • binaries
• Version or commit hash:
  • Crystal
• DDS implementation:
  • Fast-RTPS, RTI Connext
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

Define messages of fixed size

Array100kb.msg

byte[100000] data

Instantiate subscription to topic of this message type

#include <memory>
#include <iostream>
#include <thread>
#include <sstream>
#include "rclcpp/rclcpp.hpp"
#include "simple_memory_test/msg/array1kb.hpp"

class SimpleSubscriberNode : public rclcpp::Node {

public:
    SimpleSubscriberNode(std::string name) : Node(name)
    {
        rmw_qos_profile_t custom_qos_profile = rmw_qos_profile_default;

        _sub = this->create_subscription<simple_memory_test::msg::Array1kb>( "chatter",
            std::bind(&SimpleSubscriberNode::simple_callback, this, std::placeholders::_1),
            custom_qos_profile);
    }
private:
    void simple_callback(const simple_memory_test::msg::Array1kb::SharedPtr msg)
    {
        (void)msg;
    }
    rclcpp::Subscription<simple_memory_test::msg::Array1kb>::SharedPtr _sub;
};



int main(int argc, char ** argv)
{
    rclcpp::init(argc, argv);

    std::shared_ptr<SimpleSubscriberNode> sub_node = std::make_shared<SimpleSubscriberNode>("this_node");

    rclcpp::spin(sub_node);

    rclcpp::shutdown();

    return 0;
}

Behavior

From what I have seen, the RAM required for instantiating a subscription, it's more or less invariant to the type of messages.
Note that I'm only running a system containing that subscriber node, no other nodes are alive.

However, testing this assumption for several values I got this

The physical memory required by the previously presented code, for a message between 50KB and 500KB it's bigger than the one required for a message of size more than 1MB.
After the peak of physical memory (56MB for a message of 450KB), the amount returns to the same constant value.

For what concerns the virtual memory usage, it keeps increasing a lot reaching 1.1GB for a message of size 4MB.

This behavior does not occur when creating publishers.

This behavior does not occur when using OpenSplice DDS.

Do you have any ideas why ?
May be related to this ? #203

Here you can find the package I used for running the tests.
https://github.com/alsora/ros2-code-examples/tree/master/simple_memory_test

It creates an executable for each data point.
I am measuring the RAM usage with
ps aux | grep sub_nodes

The package also contains a plot.py file where the exact results of the tests are hardcoded and you can get plot them again to better inspect the graph.