linux-kernel - Re: [slubllv7 06/17] slub: Add cmpxchg_double

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Message-ID: <4E1C952D.6010902@zytor.com>
Date:	Tue, 12 Jul 2011 11:40:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [slubllv7 06/17] slub: Add cmpxchg_double_slab()

On 07/12/2011 09:47 AM, Christoph Lameter wrote:
> On Tue, 12 Jul 2011, Eric Dumazet wrote:
> 
>> Le mardi 12 juillet 2011 à 10:59 -0500, Christoph Lameter a écrit :
>>
>>> We do not need to have _count included. This is just there because the
>>> field is in the way on 64 bit and we can only do 2x 64 bit cmpxchges.  On
>>> 32 bi we can drop _count from "counters".
>>
>> OK, thanks for clarification.
> 
> Still I'd like to get some ideas on how to make the whole thing much
> cleaner. Isnt there some way to convert a struct to an unsigned long
> without going through a union? And a way to convert a struct + 32 bit
> atomic_t into a 64 bit unsigned long? Would simplify things significantly.

If you know it is in memory you can cast ("pun") the pointer.

If it's not in memory that can be inefficient, though.

	-hpa
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