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

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Date:	Thu, 19 Aug 2010 06:40:17 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Namhyung Kim <namhyung@...il.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] introduce ptr_diff()

On Thu, Aug 19, 2010 at 02:23:09PM +0200, Andi Kleen wrote:
> 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.

What makes you think it's a shift?  struct page isn't necessarily a
power of two in size.  The original poster said "allyesconfig" which is
going to add in KMEMCHECK and WANT_PAGE_DEBUG_FLAGS.  I think that makes
it 76 bytes on x86-32, so sparse is right to warn.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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