Re: [RFC/PATCH] prepare_unmapped_area

[Christoph Hellwig <hch@infradead.org>]

On Tue, Feb 06, 2007 at 04:04:56PM +1100, Benjamin Herrenschmidt wrote:
> Hi folks !
> 
> On Cell, I have, for performance reasons, a need to create special
> mappings of SPEs that use a different page size as the system base page
> size _and_ as the huge page size.
> 
> Due to the way the PowerPC memory management works, however, I can only
> have one page size per "segment" of 256MB (or 1T) and thus after such a
> mapping have been created in its own segment, I need to constraint
> -other- vma's to stay out of that area.
> 
> This currently cannot be done with the existing arch hooks (because of
> MAP_FIXED). However, the hugetlbfs code already has a hack in there to
> do the exact same thing for huge pages. Thus, this patch moves that hack
> into something that can be overriden by the architectures. This approach
> was choosen as the less ugly of the uglies after discussing with Nick
> Piggin. If somebody has a better idea, I'd love to hear it.
> 
> If it doesn't shoke anybody to death, I'd like to see that in -mm (and
> possibly upstream, I don't know yet if my code using that will make
> 2.6.21 or not, but it would be nice if the list of "dependent" patches
> wasn't 3 pages long anyway :-)

Eeek, this is more than fugly.  Dave Hansen suggested to move these
checks into a file operation in response to Adam Litke's hugetlb cleanups,
and this patch shows he was right :)

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