Re: [patch 3/3] arch_rebalance_pgtables call

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2007-11-14 at 10:26 +0100, Martin Schwidefsky wrote:
> That patch allows processes to have different number of page table
> levels, 31 bit processes have 2 levels (2GB), normal 64 bit processes
> have 3 levels (4TB) and really big 64 bit processes can have 4 levels
> (8PB). The downgrade of a page table to use less levels than the
> parent
> process is done in arch_pick_mmap_layout. The upgrade is done by using
> the arch_rebalance_pgtables call. I've considered using the
> arch_get_unmapped_area but got scared by the indirection in
> get_unmapped_area:
> 
>         get_area = current->mm->get_unmapped_area;
>         if (file && file->f_op && file->f_op->get_unmapped_area)
>                 get_area = file->f_op->get_unmapped_area;
>         addr = get_area(file, addr, len, pgoff, flags);

Don't be, it's really only hugetlb and other arch specific stuff that
hook in here on platforms with an MMU (It's also used by /dev/mem etc...
for mmu-less platforms but you don't care).

Ben.