[feffe]

I think most applications don't have any dependency towards a specific page size. They use malloc (C) or new (C++) to allocate memory which does not expose this constraint.

You need to care if using mmap directly to map files or other resources into the virtual memory address space. The default page size can be queried using for example sysconf() on Linux. I guess something like garbage collectors in language run-times would also use mmap directly as it's most likely to side step malloc/new.

An application would normally not use madvise, unless also using mmap for some special purpose.

It depends on the CPU architecture how flexible it is with different page sizes. For example, from what I recall, MIPS was extremely flexible and allowed any even power of two size for any TLB entry.

x86_64 only support three different page sizes, 4 kB, 2 MB and 1 GB and there are limitations wrt the number of TLB entries that can be used for the larger page sizes.

So, yea, there are bound to be regressions if just trying to switch to 2 MB as a default but I think it should be doable. Not all archs use 4 kB to begin with.