I wrote a thesis on this in 2008 (Transparent large-page support for Itanium Linux https://ts.data61.csiro.au/publications/theses_public/08/Wie...) and Matthew Wilcox was already involved in the area then. I admire his persistence, and have certainly have not kept up in the state of the art. Itanium had probably the greatest ability to select page size, probably more than any other architecture (?). On x86-64 you really only have 2mb or 4k to work with in a general purpose situation. It was difficult to show the benefits of managing all the different page sizes and, as this notes, re/writing everything to be aware of page sizes effectively. Those who had really big workloads that benefited from huge pinned mappings didn't really care that much either. It made the work hard to find traction at the time.