linux-kernel - Re: [RFC][PATCH] introduce ptr

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Message-ID: <87aaoiu6z6.fsf@basil.nowhere.org>
Date:	Thu, 19 Aug 2010 14:23:09 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] introduce ptr_diff()

Namhyung Kim <namhyung@...il.com> writes:

> When I compiled allyesconfig'ed kernel with C=1, I got 1519 lines of
> following message:
>
>  include/linux/mm.h:599:16: warning: potentially expensive pointer subtraction
>
> which is around 10% of total warnings. this was caused by page_to_pfn() macro
> so I think it's worth to remove it by calculating pointer subtraction
> manually.

IMHO it would be better to simply disable the warning in sparse instead
of uglying the code just to work around sparse bogosity. It doesnt' seem
to make much sense. A subtraction followed by a shift is not expensive.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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