Discover huge page support on POSIX or Linux

I'm working on a program which needs to detect at runtime whether the system it's running on supports hugepages, and if so, what sizes are available. Ideally I'd like this to work for any POSIX platform, but a Linux-specific solution would be a start. POSIX supports [sysconf(_SC_PAGESIZE)](http://man7.org/linux/man-pages/man3/sysconf.3.html) to get the default page size on the platform, but doesn't seem to similarly support asking for any hugepage sizes. I could also potentially check by trying to [mmap](http://man7.org/linux/man-pages/man2/mmap.2.html) MAP_HUGE_2MB or MAP_HUGE_1GB arguments, but that would be slow, and in the case of 1GB huge pages, incredibly wasteful (and it could easily fail due to a lack of available memory).