Re: hammer: MAP_32BIT

[mikpe@csd.uu.se]

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