This is a big annoyance for me as well. I use jemalloc to make sure that my FFI allocations don't 'steal' this lower memory from my pure Lua allocations. It works great on Linux, but only so-so on OSX.

http://www.canonware.com/pipermail/jemalloc-discuss/2014-Feb...

https://gist.github.com/neomantra/9122165