linux-kernel - Re: sparse -Wptr-subtraction-blows: still needed?

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Date:	02 May 2007 15:03:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Triplett <josh@...edesktop.org>,
	linux-sparse@...r.kernel.org, linux-kernel@...r.kernel.org,
	Al Viro <viro@....linux.org.uk>
Subject: Re: sparse -Wptr-subtraction-blows: still needed?

Dave Jones <davej@...hat.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)
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