Message-ID: <417728B0.3070006@yahoo.com.au>
Date: Thu, 21 Oct 2004 13:10:40 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Andrea Arcangeli <andrea@novell.com>
CC: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: ZONE_PADDING wastes 4 bytes of the new cacheline
References: <20041021011714.GQ24619@dualathlon.random>
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Andrea Arcangeli wrote:
> I don't see why this 'int x' exists, alignment should really work fine
> even with empty structure (works with my compiler with an userspace
> test, please double check).
> 
> Index: linux-2.5/include/linux/mmzone.h
> ===================================================================
> RCS file: /home/andrea/crypto/cvs/linux-2.5/include/linux/mmzone.h,v
> retrieving revision 1.67
> diff -u -p -r1.67 mmzone.h
> --- linux-2.5/include/linux/mmzone.h	19 Oct 2004 14:58:00 -0000	1.67
> +++ linux-2.5/include/linux/mmzone.h	21 Oct 2004 01:14:20 -0000
> @@ -35,7 +35,6 @@ struct pglist_data;
>   */
>  #if defined(CONFIG_SMP)
>  struct zone_padding {
> -	int x;
>  } ____cacheline_maxaligned_in_smp;
>  #define ZONE_PADDING(name)	struct zone_padding name;
>  #else

Perhaps to keep old compilers working? Not sure.

I think it is common to use a zero length array...?

	int x[0];

Although that maybe that is only used when one requires a
handle on the address.

Nick
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