Re: hammer: MAP_32BIT

[H. Peter Anvin]

Followup to:  <20030509113845.GA4586@averell>
By author:    Andi Kleen <[e-mail]>
In newsgroup: linux.dev.kernel
>
> 
> On Fri, May 09, 2003 at 01:28:11PM +0200, [e-mail] wrote:
> > I have a potential use for mmap()ing in the low 4GB on x86_64.
> 
> Just use MAP_32BIT
> 
> > 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.
>  

How about this: since the address argument is basically unused anyway
unless MAP_FIXED is set, how about a MAP_MAXADDR which interprets the
address argument as the highest permissible address (or lowest
nonpermissible address)?

	-hpa
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