linux-kernel - Re: [patch 2/2] slab: always consider arch mandated alignment

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Date:	Wed, 26 Jul 2006 13:05:43 +0300 (EEST)
From:	Pekka J 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,
	linux-mm@...ck.org, Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [patch 2/2] slab: always consider arch mandated alignment

On Wed, 26 Jul 2006, Heiko Carstens wrote:
> Since ARCH_KMALLOC_MINALIGN didn't work on s390 I tried ARCH_SLAB_MINALIGN
> instead, just to find out that it didn't work too.
> In case of CONFIG_DEBUG_SLAB kmem_cache_create() creates caches with an
> alignment lesser than ARCH_SLAB_MINALIGN, which it shouldn't according to
> this comment in mm/slab.c :

[snip]

> Index: linux-2.6/mm/slab.c
> ===================================================================
> --- linux-2.6.orig/mm/slab.c	2006-07-26 09:55:54.000000000 +0200
> +++ linux-2.6/mm/slab.c	2006-07-26 09:57:07.000000000 +0200
> @@ -2103,6 +2103,9 @@
>  		if (ralign > BYTES_PER_WORD)
>  			flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
>  	}
> +	if (BYTES_PER_WORD < ARCH_SLAB_MINALIGN)
> +		flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
> +
>  	/* 3) caller mandated alignment: disables debug if necessary */
>  	if (ralign < align) {
>  		ralign = align;

This is similar to my patch and should be enough to fix the problem. The 
first patch seems bogus and I don't really understand why you would need 
it.

					Pekka
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