On Mon, Jul 12, 1999 at 10:53:49PM +0400, Dmitrij Tejblum wrote:
>
> I don't see how MAP_ANON is better than MAP_STACK.
>
It consumes fewer resources. Each time you grow the stack, it adds
another vm_map_entry to the vm_map and (eventually) allocates another
vm_object. Using MAP_ANON, there is at most one vm_object and one
vm_map_entry (until an mprotect chops it up).
> ...
>
> Anyway, what are the advantages of mmap over malloc? Especially if you change
> MAP_STACK to MAP_ANON?
>
None really. But, the real point (as I've explained on the -committers
list) is that there's no reason to use MAP_STACK in a FreeBSD-native
program.
Alan
P.S. As an aside, just once, everyone should look at the /proc/"pid"/map
of a running cvsup. Each line you see is a vm_map_entry. (What you
see is a result of Modula-3's garbage collector.) Roughly speaking,
on a page fault, if we're not faulting on the same range of addresses
as the last page fault, a linear cost search is performed
to find the correct entry.
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