The possible demise of remap_file_pages()

There are actually some things you can do with remap_file_pages() that are just not implementable with other APIs without a fairly large performance hit: e.g. you can share a memory region with many other processes, then have any of those processes adjust its mapping *as seen by all the others*, atomically, because they all share the same VMAs: an emulation would have to adjust VMAs for every process in turn (unlikely to retain the atomicity semantics, for starters).

Now it may be that nobody depends on those semantics, but it was a *nice* IPC facility. It's just not a facility that anyone much uses :(