Slight growth of memory detected

Start by reproducing the supplied memory test with get_active_devices and get_interfaces_info, including the invalid interface name case. Trace these entry points through the repository's Python bindings and native implementation, then repeat the measurements after any investigation. Done means repeated calls no longer show measurable memory growth.

Get this script (GPLv2 Copyright (c) 2011 Red Hat):

import ethtool
import subprocess, sys, os

max = int(sys.argv[1])
nic = sys.argv[2]
total = 0

def memory():
    """ Get current memory usage in MB """
    command = "ps --no-header -o rss -p %s" % os.getpid()
    p = subprocess.Popen(command.split(), stdout=subprocess.PIPE)
    stdout, stderr = p.communicate()
    return int(stdout) / 1024

def measure(fun, arg):
    """ Run given function on given arg max times """
    global total
    print("\n%s on %s" % (fun, arg))
    start = None

    for i in range(max + 1):
        result = fun(arg)
        if i % (max / 10) == 0:
            current = memory()
            # note the memory after the first round warm-up
            if start is None:
                start = current
            print("%s %% ... %s MB" % \
                    (str(100 * i / max).rjust(3), str(current).rjust(3)))
    increase = current - start
    print("Memory increase: %s MB" % increase)
    total += increase

measure(ethtool.get_active_devices, None)
measure(ethtool.get_interfaces_info, nic)
measure(ethtool.get_interfaces_info, 'bad interface name')

print("\nTotal memory increase: %s MB" % total)
if total > 0:
    sys.exit(1)

And run:

$ python3.6 ~/tmp/memory.py 1000000 ens3
<built-in function get_active_devices> on None
0.0 % ... 10.1328125 MB
10.0 % ... 10.13671875 MB
20.0 % ... 10.13671875 MB
30.0 % ... 10.13671875 MB
40.0 % ... 10.13671875 MB
50.0 % ... 10.13671875 MB
60.0 % ... 10.13671875 MB
70.0 % ... 10.13671875 MB
80.0 % ... 10.13671875 MB
90.0 % ... 10.13671875 MB
100.0 % ... 10.13671875 MB
Memory increase: 0.00390625 MB

<built-in function get_interfaces_info> on ens3
0.0 % ... 10.13671875 MB
10.0 % ... 10.13671875 MB
20.0 % ... 10.13671875 MB
30.0 % ... 10.13671875 MB
40.0 % ... 10.13671875 MB
50.0 % ... 10.13671875 MB
60.0 % ... 10.13671875 MB
70.0 % ... 10.13671875 MB
80.0 % ... 10.13671875 MB
90.0 % ... 10.140625 MB
100.0 % ... 10.140625 MB
Memory increase: 0.00390625 MB

<built-in function get_interfaces_info> on bad interface name
0.0 % ... 10.140625 MB
10.0 % ... 10.140625 MB
20.0 % ... 10.140625 MB
30.0 % ... 10.140625 MB
40.0 % ... 10.140625 MB
50.0 % ... 10.140625 MB
60.0 % ... 10.140625 MB
70.0 % ... 10.140625 MB
80.0 % ... 10.140625 MB
90.0 % ... 10.140625 MB
100.0 % ... 10.140625 MB
Memory increase: 0.0 MB

Total memory increase: 0.0078125 MB