linux-kernel - Re: [patch 1/3] mm: introduce follow

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Message-Id: <20090505140517.bef78dd3.akpm@linux-foundation.org>
Date:	Tue, 5 May 2009 14:05:17 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	magnus.damm@...il.com, linux-media@...r.kernel.org,
	hverkuil@...all.nl, lethal@...ux-sh.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] mm: introduce follow_pte()

On Tue, 5 May 2009 22:38:07 +0200
Johannes Weiner <hannes@...xchg.org> wrote:

> On Tue, May 05, 2009 at 12:24:42PM -0700, Andrew Morton wrote:
> > On Mon,  4 May 2009 11:54:32 +0200
> > Johannes Weiner <hannes@...xchg.org> wrote:
> > 
> > > A generic readonly page table lookup helper to map an address space
> > > and an address from it to a pte.
> > 
> > umm, OK.
> > 
> > Is there actually some point to these three patches?  If so, what is it?
> 
> Magnus needs to check for physical contiguity of a VMAs backing pages
> to support zero-copy exportation of video data to userspace.
> 
> This series implements follow_pfn() so he can walk the VMA backing
> pages and ensure their PFNs are in linear order.
> 
> [ This patch can be collapsed with 2/3, I just thought it would be
>   easier to read the diffs when having them separate. ]
> 
> 1/3 and 2/3: factor out the page table walk from follow_phys() into
> follow_pte().
> 
> 3/3: implement follow_pfn() on top of follow_pte().

So we could bundle these patches with Magnus's patchset, or we could
consider these three patches as a cleanup or something.

Given that 3/3 introduces an unused function, I'm inclined to sit tight
and await Magnus's work.

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