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Date:	Mon, 3 Mar 2008 15:53:15 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Nick Piggin" <npiggin@...e.de>
Cc:	"Eric Dumazet" <dada1@...mosbay.com>, netdev@...r.kernel.org,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	yanmin_zhang@...ux.intel.com, "David Miller" <davem@...emloft.net>,
	"Christoph Lameter" <clameter@...r.sgi.com>
Subject: Re: [rfc][patch 3/3] use SLAB_ALIGN_SMP

Hi,

On Mon, Mar 3, 2008 at 3:46 PM, Nick Piggin <npiggin@...e.de> wrote:
>  > Maybe we need to use three flags to separate the meanings ?
>  >
>  > SLAB_HINT_SMP_ALIGN
>  > SLAB_HINT_HWCACHE_ALIGN
>  > SLAB_HWCACHE_ALIGN /* strong requirement that two objects dont share a
>  > cache line */
>
>  Possibly, but I'm beginning to prefer that strong requirements should
>  request the explicit alignment (they can even use cache_line_size() after
>  Pekka's patch to make it generic). I don't like how the name implies
>  that you get a guarantee, however I guess in practice people are using it
>  more as a hint (or because they vaguely hope it makes their code run
>  faster :))

At least historically SLAB_HWCACHE_ALIGN has been just a hint,
although slab tries very hard to satisfy it (see the comments in
mm/slab.c). Why do we need stronger guarantees than that, btw?
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