std::map vs unordered_map memory footprint for small N

For embedded system applications where memory usage is more of a concern than speed, what would be the best map container to use? std::map, std::unordered_map, or boost::flat_map? This would be for situations where N is less than, say, a hundred.

If implementation matters, then I'm concerned with the libstdc++ implementation (GCC).

If I wanted to make my own memory usage measurements, how would I go about doing this on a Linux platform?