Debugging memory in OCaml: any advice?

Memory consumption chart

A server I just deployed (written in OCaml, of course) seems to eat RAM at breakfast. This is the chart of the RSS field of "ps" in the past 24h (click to enlarge). The program starts with almost 6 Mb and is now reaching 40 Mb, in a linear trend that has nothing good to say.

Any advice on how to debug the memory consumption?