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

On 7/22/06, Heiko Carstens <heiko.carstens@de.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