linux-kernel - Re: problems in linux-next (Was: Re: linux-next: Tree for December 1)

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Date:	Tue, 1 Dec 2009 17:01:19 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Tejun Heo <tj@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>,
	michal.simek@...alogix.com, linux-next@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: problems in linux-next (Was: Re: linux-next: Tree for December 1)


* Christoph Lameter <cl@...ux-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
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