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

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Message-ID: <20080307022537.GC21185@wotan.suse.de>
Date:	Fri, 7 Mar 2008 03:25:37 +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 Thu, Mar 06, 2008 at 06:20:40PM -0800, Christoph Lameter wrote:
> On Fri, 7 Mar 2008, Nick Piggin wrote:
> 
> > > Do you have a case in mind where that would be useful? We had a 
> > 
> > Patch 3/3
> 
> Those already have SLAB_HWCACHE_ALIGN.
> 
> The point is to switch off alignment for UP? Cant we do that with 
> SLAB_HWCACHE_ALIGN too since SLOB seemed to work successfully without it 
> in the past?

See my next post to correct your understanding of HWCACHE_ALIGN.

 
> > > Note that there is also KMEM_CACHE which picks up the alignment from 
> > > the compiler.
> > 
> > Yeah, that's not quite as good either. My allocation flag is dynamic, so
> > it will not bloat things for no reason on UP machines and SMP kernels. 
> > It also aligns to the detected machine cacheline size rather than a
> > compile time constant.
> 
> Is that really a noteworthy effect?

Yes.

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