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

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Message-ID: <Pine.LNX.4.64.0803112316090.4794@schroedinger.engr.sgi.com>
Date:	Tue, 11 Mar 2008 23:21:58 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Nick Piggin <npiggin@...e.de>
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 Tue, 11 Mar 2008, Nick Piggin wrote:

> On Thu, Mar 06, 2008 at 09:26:24PM -0800, Christoph Lameter wrote:
> > Internode alignment is 4k. If you need an object aligned like that then it 
> > may be better to go to the page allocator.
> 
> I never got a reply about this. Again: how can the modern slab allocator
> avoid the need for internode alignment in order to prevent cacheline
> pingpong on vsmp? Because I'm going to resubmit the SMP_ALIGN patch.

You quoted my answer. Use the page allocator to allocate data that has an 
alignment requirement on a 4k boundary.

> Also, the last I heard about the HWCACHE_ALIGN from you is that it didn't
> make sense... I see it's merged now, which I appreciate, but I think it is
> really important that we're on the same page here, so let me know if it
> still doesn't make sense.

I still think that the semantics are weird because it only works sometimes 
and then performs an alignment within a cacheline that improves the 
situation somewhat in some cases but does not give the user what he 
expected.
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