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SubjectRe: hammer: MAP_32BIT
Andi Kleen writes:
>
> On Fri, May 09, 2003 at 01:28:11PM +0200, mikpe@csd.uu.se wrote:
> > I have a potential use for mmap()ing in the low 4GB on x86_64.
>
> Just use MAP_32BIT

Will that be corrected to use the full 4GB space? 2GB is too small.

> > Sounds like your MAP_32BIT really is MAP_31BIT :-( which is too limiting.
> > What about a more generic way of indicating which parts of the address
> > space one wants? The simplest that would work for me is a single byte
> > 'nrbits' specifying the target address space as [0 .. 2^nrbits-1].
> > This could be specified on a per-mmap() basis or as a settable process attribute.
>
> On x86-64 an mmap extension for that would be fine, but on i386 you get
> problems because mmap64() already maxes out the argument limit and you
> cannot add more.

This would only be used on x86_64. i386 compat is a non-issue.
(This is for runtime systems stuff, not applictions.)

> prctl is probably better. You really want [start; end] right ?

I just want mmap() to return addresses that fit in 32 bits.

MAP_32BIT would do nicely, if it wasn't limited to 2GB.

/Mikael
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