I see hwloc is a subproject hosted under OpenMPI but, in reading the documentation, I was unable to figure out if hwloc is a module within OpenMPI, or if some of the code base is borrowed into OpenMPI, or something else.  Is hwloc used by OpenMPI internally?  Is it a layer above libnuma?  Or is it just a project that is useful to OpenMPI in support of targeting various new platforms?