hammer: MAP_32BIT

[Ulrich Drepper <drepper@redhat.com>]

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To allocate stacks for the threads in nptl we currently use MAP_32BIT to
make sure we get <4GB addresses for faster context switching time.  But
once the address space is allocated we have to resort to not using the
flag.  This means we have to make 2 mmap() calls, one with MAP_32BIT and
if it fails another one without.

It would be much better if there would also be a MAP_32PREFER flag with
the appropriate semantics.  The failing mmap() calls seems to be quite
expensive so programs with many threads are really punished a lot.

- -- 
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Ulrich Drepper \    ,-----------------'   \ Mountain View, CA 94041 USA
Red Hat         `--' drepper at redhat.com `---------------------------
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