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

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Date:	Mon, 3 Mar 2008 21:06:13 +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 1/3] slub: fix small HWCACHE_ALIGN alignment

On Mon, Mar 03, 2008 at 11:08:44AM -0800, Christoph Lameter wrote:
> On Mon, 3 Mar 2008, Nick Piggin wrote:
> 
> > SLUB should pack even small objects nicely into cachelines if that is what
> > has been asked for. Use the same algorithm as SLAB for this.
> 
> Why? SLAB does not cacheline align objects smaller than cache_line_size() 
> /2.

It still doesn't after this patch.

> If they are already not cache line aligned then we can make them as 
> dense as possible. That is what SLUB does.

Because when you specify HWCACHE_ALIGN, it means that you want the object
not to cross cacheline boundaries for at least cache_line_size() bytes.
SLAB does this. SLUB does not without this patch.

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