One thing that is known about using transparent huge pages (THPs) for
filesystems is that it is a hard problem to solve, but is there a solid first
step that
could be taken toward that goal? That is the question Song Liu asked to
open his combined
filesystem and memory-management session at
the 2019 Linux Storage, Filesystem, and Memory-Management Summit (LSFMM).
His employer, Facebook, has a solid use case for using THPs on files in
the page cache, which may provide a starting point.

Source: LWN.net – [$] Transparent huge pages for filesystems