mmap explicitly is allowed to create new maps in place of existing mappings by just freeing the underlying mapping, in fact that's one use for MAP_FIXED in saf

mmap explicitly is allowed to create new maps in place of existing mappings by just freeing the underlying mapping, in fact that's one use for MAP_FIXED in safely create circularly mapped buffers. And using MAP_IMMUTABLE with MAP_ANONYMOUS wouldn't seemingly be possible. I would think mprotect() would work, though. Since the new call works more like minherit() under the hood, he decided to just duplicate that mechanism for this.