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

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Message-ID: <Pine.LNX.4.64.0607261126030.6690@schroedinger.engr.sgi.com>
Date:	Wed, 26 Jul 2006 11:28:44 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Manfred Spraul <manfred@...orfullife.com>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	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 Wed, 26 Jul 2006, Manfred Spraul wrote:

> There are two different types of alignment:
> - SLAB_HWCACHE_ALIGN: it's a recommendation, it's regularly ignored.
> - the align parameter, or ARCH_SLAB_MINALIGN: It's mandatory. For example the
> pgd structures must be 4 kB aligned, it's required by the hardware. And I
> think there was (is?) a structure where ptr & ~(size-1) was used to find the
> start of the structure.

I agree with the above if there is an issue there then lets fix it.

> Thus the patch is correct, it's a bug in the slab allocator. If HWCACHE_ALIGN
> is set, then the allocator ignores align or ARCH_SLAB_MINALIGN.

But then Heiko does not want to set ARCH_SLAB_MINALIGN at all. This is not 
the issue we are discussing. In the DEBUG case he wants 
ARCH_KMALLOC_MINALIGN to be enforced even if ARCH_SLAB_MINALIGN is not 
set.
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