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

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Message-ID: <Pine.LNX.4.58.0607261532130.20519@sbz-30.cs.Helsinki.FI>
Date:	Wed, 26 Jul 2006 15:35:00 +0300 (EEST)
From:	Pekka J Enberg <penberg@...Helsinki.FI>
To:	Christoph Lameter <clameter@....com>
cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch] slab: always follow arch requested alignments

On 7/26/06, Christoph Lameter <clameter@....com> wrote:
> > > Your patch only deals with ARCH_SLAB_MINALIGN. kmem_cache_create() never
> > > uses ARCH_KMALLOC_MINALIGN only kmem_cache_init() does by passing it to
> > > kmem_cache_create.  ARCH_KMALLOC_MINALIGN will still be ignored.
 
On Wed, 26 Jul 2006, Pekka Enberg wrote:
> > Yes, in which case the caller mandated align will be, well,
> > ARCH_KMALLOC_MINALIGN. The patch changes kmem_cache_create to respect
> > caller mandated alignment too.

On Wed, 26 Jul 2006, Christoph Lameter wrote:
> As far as I understood Heiko s390 does not set ARCH_SLAB_MINALIGN
> because they do not want alignent for all caches.

Correct. Heiko sets ARCH_KMALLOC_MINALIGN which will be passed as the 
'align' parameter to kmem_cache_create -- also known as 'caller mandated 
alignment.'

My patch changes the code so that, if either architecture or 
caller mandated alignment is greater than BYTES_PER_WORD, 
kmem_cache_create will disable debugging. Do you now see why my patch is 
in fact _not_ ignoring ARCH_KMALLOC_MINALIGN, but instead respecting that.

			Pekka
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