Subject: Re: [patch 3/3] arch_rebalance_pgtables call
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reply-To: benh@kernel.crashing.org
To: schwidefsky@de.ibm.com
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, akpm@linux-foundation.org,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
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References: <20071112143009.425807965@de.ibm.com>
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	 <200711132333.38086.nickpiggin@yahoo.com.au>
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Date: Wed, 14 Nov 2007 21:06:36 +1100
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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.


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