Re: 2.2.17pre9 can't allocate more than 900MB

[Mark Hahn]

> It fails in the exact same spot. I suspect something else at work here.

there's nothing "at work" here.  this is expected behavior:
small mallocs allocate from the heap, and brk/sbrk hits the 
beginning of mmaped areas at 1G.  glibc malloc will allocate
big chunks using mmap (and thus deliver around 2G); a better 
malloc would fall back to mmaped arenas when brk/sbrk fails.

I think our VM layout is somewhat unfortunate, since it's 
based on:
	- text is mapped at ~128M;
	- heap grows up from from the end of text;
	- mmap's grow up from 1G;
	- stack grows down from 3G.

I'd prefer to have only a smallish area for stack, then have mmap's
grow down towards heap.  can't we find a way for the rare program that
uses lots of stack (fortran, mostly) to signal this to ld.so?
do we still need the >3G area reserved for the system?  
for that matter, why does text start at 0x08048000?

btw, there's no problem with hacking a kernel to leave more space 
for the heap, or even to move 3G up somewhat.  I'm just suggesting
that instead of having two up-growers and a down-, we have one up
(heap) and one down (mmaps), with stack relegated to a fixed size.

regards, mark hahn.