Using a custom version of collectd (based on 5.4.3) with libmongoc-1.6.3, I found some memory leaks and some of them are in the libmongoc, specially on:
From mongoc-cluster.c
1473 if (stream) { 1474 sd = mongoc_topology_server_by_id (topology, server_id, error); 1475 1476 if (!sd) { 1477 return NULL; 1478 } 1479 } else {