linux-kernel - Re: [PATCH] slab: fix slab flags for archs use alignment larger 64-bit

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Message-ID: <84144f020902130205x4dc5886l70fe6a695ef050a4@mail.gmail.com>
Date:	Fri, 13 Feb 2009 12:05:43 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
Cc:	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-mm@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] slab: fix slab flags for archs use alignment larger 
	64-bit

Hi Giuseppe,

On Fri, Feb 13, 2009 at 12:46 PM, Giuseppe CAVALLARO
<peppe.cavallaro@...com> wrote:
> 1) LOG with my patch:
> root@...ux:~# cat /proc/meminfo | grep Slab
> Slab:             2612 kB
>
> 2) LOG without my patch:
> root@...ux:~# cat /proc/meminfo | grep Slab
> Slab:             2504 kB

That's not too bad. I assume it's L1_CACHE_BYTES set to 32 bytes? One
big problem with your patch is that on some MIPS configurations
ARCH_KMALLOC_MINALIGN is as big as 128. So if you're going to do this,
you can't use ARCH_KMALLOC_MINALIGN directly but add a some
SLAB_MAX_DEBUG_ALIGN which can be overridden by architecture code.

One obvious question, though, is whether all this is worth the added
complexity. I mean, we've managed "just fine" without it for years.
Paul, thoughts?

                                        Pekka
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