From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <andi@firstfloor.org>
Subject: Re: sparse -Wptr-subtraction-blows: still needed?
Date: 02 May 2007 15:03:59 +0200
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To: Dave Jones <davej@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Josh Triplett <josh@freedesktop.org>, linux-sparse@vger.kernel.org, linux-kernel@vger.kernel.org, Al Viro <viro@ftp.linux.org.uk>

Dave Jones <davej@redhat.com> writes:
> 
> #define __page_to_pfn(page)     ((unsigned long)((page) - mem_map) + \
>                                  ARCH_PFN_OFFSET)
> 
> looks like the other two variants of __page_to_pfn also use similar arithmatic.

No way around this. The only way to turn a page into a pfn is to do 
a constant division.  Should be fairly cheap here though.

-Andi (who thinks the sparse warning is dumb; better to look at oprofiles
of hot paths)