The recently-released 2.5.36 kernel now includes (among other things, like XFS) Rohit Seth's Huge TLB Pages patch (IA-32 only). This enables support for page sizes larger than 4k, but user-space apps must use special system calls to take advantage of the large pages.
Smaller pages are space-efficient, reduce memory fragmentation, and are easy to swap. They are suited for most tasks; but large pages are better-suited with shared memory, and require less page-table entries.
This patch has already been in Andrew Morton's [interview] -mm tree for some time, so it has (presumably) received some good testing.
Changelog for kernel 2.5.36: