From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: problems in linux-next (Was: Re: linux-next: Tree for December 1)
Date: Tue, 1 Dec 2009 17:01:19 +0100
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To: Christoph Lameter <cl@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>, Stephen Rothwell <sfr@canb.auug.org.au>, michal.simek@petalogix.com, linux-next@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, Rusty Russell <rusty@rustcorp.com.au>


* Christoph Lameter <cl@linux-foundation.org> wrote:

> On Tue, 1 Dec 2009, Tejun Heo wrote:
> 
> > The problem is that on UP configurations.  Percpu memory allocator 
> > becomes a simple wrapper around kmalloc and there's no way to 
> > specify larger alignment when requesting memory from kmalloc.
> 
> There is usually no point in aligning in UP. Alignment is typically 
> done for smp configurations to limit cache line bouncing and control 
> cache line use/

There is a natural minimum alignment for UP and it's smaller than the 
cache-line size: machine word size. All our allocators (except bootmem) 
align to machine word so there's no need to specify this explicitly.

Larger alignment than that just wastes memory - which waste UP systems 
can afford the least.

	Ingo