Hinted mmap(2) without MAP_FIXED can fail prematurely

[PHO <pho%cielonegro.org@localhost>]

I'm not sure if this is a bug or not, but on NetBSD/amd64 9.2, hinted 
mmap(2) without MAP_FIXED can fail prematurely with ENOMEM if all the 
regions below the given hint address are occupied.

The man page for mmap(2) suggests that the hint is just a hint. 
Shouldn't mmap(2) also search for available regions above the hint then?

Test code:
https://gist.github.com/depressed-pho/a629247b48b3e6178e35a14c62e9d44f#file-mmap-with-hint-c

Test result:
https://gist.github.com/depressed-pho/a629247b48b3e6178e35a14c62e9d44f#file-gistfile1-txt