linux-kernel - Re: [rfc][patch 2/3] slab: introduce SMP alignment

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Message-ID: <20080307043700.GI21185@wotan.suse.de>
Date:	Fri, 7 Mar 2008 05:37:00 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	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 2/3] slab: introduce SMP alignment

On Mon, Mar 03, 2008 at 01:31:14PM -0800, Christoph Lameter wrote:
> On Mon, 3 Mar 2008, Nick Piggin wrote:
> 
> > And maybe the VSMP guys will want to blow this out to their internode
> > alignment?
> > 
> > max(!CONFIG_TINY && num_possible_cpus() > 1 ? (is_vsmp ? internode_alignemnt : cache_line_size()) : 0, mandatory_alignment)
> 
> No the slab allocators were optimized for VSMP so that the 
> internode_alignment is not necessary there. That was actually one of the 
> requirements that triggered the slab numa work.

BTW. can you explain this incredible claim that the slab allocators
do not need internode_alignment to avoid false sharing of allocated
objects on VSMP? I don't understand how that would work at all.

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