>> I wonder why the /dev/zero case is slower. I guess there's not much
>> algorithmic improvement possible there; it's probably the worst case
>> for the rbtree algorithm. But, it's also an uncommon case, so the
>> regular file map speedup seems to clearly outweigh that one.
>
>I guess the question is: does it hurt MAP_ANON performance the same way 
>it hurts mmap of /dev/zero performance?

isn't that a rhetorical question, since we have:

	if ((flags & MAP_ANON) == 0) {
		...
		if (vp->v_type == VCHR && vp->v_rdev == zerodev) {
			flags |= MAP_ANON;
			goto is_anon;
		}
		...
	} else {
		...
	is_anon:
		handle = NULL;
		maxprot = VM_PROT_ALL;
		pos = 0;
	}

in sys_mmap()?

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