linux-kernel - Re: [PATCH] powerpc/mm: Implement _PAGE_SPECIAL & pte

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Message-ID: <20080801011137.GA20407@wotan.suse.de>
Date:	Fri, 1 Aug 2008 03:11:37 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Kumar Gala <galak@...nel.crashing.org>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] powerpc/mm: Implement _PAGE_SPECIAL & pte_special() for 32-bit

On Thu, Jul 31, 2008 at 01:48:31PM -0500, Kumar Gala wrote:
> Implement _PAGE_SPECIAL and pte_special() for 32-bit powerpc. This bit will
> be used by the fast get_user_pages() to differenciate PTEs that correspond
> to a valid struct page from special mappings that don't such as IO mappings
> obtained via io_remap_pfn_ranges().
> 
> We currently only implement this on sub-arch that support SMP or will so
> in the future (6xx, 44x, FSL-BookE) and not (8xx, 40x).
> 
> Signed-off-by: Kumar Gala <galak@...nel.crashing.org>

Cool

> ---
> Nick, do you forsee using _PAGE_SPECIAL for other applications that would
> be of interested to non-SMP hw?
> 
> We can look at adding it into 8xx and 40x, but was being lazy as I assume
> there is no point.

I don't forsee it being used for anything else, but it is possible I guess.

We currently will also use it in the VM (vm_normal_page), turning
that function into a much more compact and simple version. It doesn't
do a great deal for performance, but you _may_ want to consider using it
just so the entire powerpc architecture takes this same path.

Not a big deal though.
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