For those unfamiliar with THP, see the transparent huge-page Linux tests conducted in the past. The Transparent Huge Page cache code consists of 30 patches and initially provides support for RAMFS, since it's the most simple file-system from a page cache perspective. There's also some early support for LIBFS too.
The set of thirty THP cache patches currently in their second revision (v1 came in January) are currently residing on the kernel mailing list. Depending upon feedback, this is potential material for the Linux 3.10 kernel.