On Wed, 31 Jul 2019, Matthew Wilcox wrote:

Christoph sent me a patch a few months ago called "XFS THP wip".
I've redone it based on current linus tree, plus the page_size() /
compound_nr() / page_shift() patches currently found in -mm.  I fixed
the logic bugs that I noticed in his patch and may have introduced some
of my own.  I have only compile tested this code.

Some references here to patches from a long time ago. Maybe there are
useful tidbits here ...

Variable page cache just for ramfs:
https://lkml.org/lkml/2007/4/19/261

Large blocksize support for XFS, ReiserFS and ext2
https://www.mail-archive.com/linux-fsdevel@vger.kernel.org/msg08730.html