linux-kernel - Re: [patch] slab: always follow arch requested alignments

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Date:	Wed, 26 Jul 2006 14:22:55 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Heiko Carstens" <heiko.carstens@...ibm.com>
Cc:	"Christoph Lameter" <clameter@....com>,
	"Andrew Morton" <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch] slab: always follow arch requested alignments

Hi Heiko,

On 7/22/06, Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> Sorry, I should have mentioned it: on s390 (32 bit) we set
> #define ARCH_KMALLOC_MINALIGN 8.
> This is needed since our common I/O layer allocates data structures that need
> to have an eight byte alignment. Now, if I turn on DEBUG_SLAB, nothing works
> anymore, simply because the slab cache code ignores ARCH_KMALLOC_MINALIGN and
> uses an BYTES_PER_WORD alignment instead, which it shouldn't:

This is the bit I missed, sorry. I thought that the s390 hardware
mandates 8 byte alignment, but it really doesn't. So you're absolutely
right, you don't need to set ARCH_SLAB_MINALIGN and the alignment
calculation in slab is indeed broken for both, architecture and caller
mandated alignments.

                                     Pekka
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