linux-kernel - Re: [rfc][patch 1/3] slub: fix small HWCACHE

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Date:	Thu, 6 Mar 2008 03:49:04 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	yanmin_zhang@...ux.intel.com, David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment

On Wed, Mar 05, 2008 at 12:56:33PM -0800, Christoph Lameter wrote:
> On Wed, 5 Mar 2008, Nick Piggin wrote:
> 
> > It started out as a SLUB regression that was exposing poor code in the
> > percpu allocator due to different SLUB kmalloc alignments. That prompted
> 
> That was due to SLUB's support for smaller allocation sizes. AFAICT has 
> nothing to do with alignment.

The smaller sizes meant objects were less often aligned on cacheline
boundaries.

 
> > The SMP flag was just an RFC. I think some people (like Christoph) were
> > being confused about the HWCACHE_ALIGN flag being for avoiding false
> > sharing on SMP systems. It would actually be also generally useful to
> > have the SMP flag (eg. see the sites I added it to in patch #3).
> 
> Hmmm. We could define a global constant for that? Determine it on bootup 
> and then pass it as an alignment parameter?
  
We could, but I'd rather just use the flag.

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