linux-kernel - Re: [PATCH 3/6] mm: numa: Handle side-effects in count_vm_numa_events() for !CONFIG_NUMA

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Date:	Wed, 23 Jan 2013 09:27:58 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Simon Jeons <simon.jeons@...il.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] mm: numa: Handle side-effects in
 count_vm_numa_events() for !CONFIG_NUMA_BALANCING

On Tue, Jan 22, 2013 at 02:40:24PM -0800, Andrew Morton wrote:
> On Tue, 22 Jan 2013 17:12:39 +0000
> Mel Gorman <mgorman@...e.de> wrote:
> 
> > The current definitions for count_vm_numa_events() is wrong for
> > !CONFIG_NUMA_BALANCING as the following would miss the side-effect.
> > 
> > 	count_vm_numa_events(NUMA_FOO, bar++);
> 
> Stupid macros.
> 

I know but static inlines are unsuitable in this case.

> > There are no such users of count_vm_numa_events() but it is a potential
> > pitfall. This patch fixes it and converts count_vm_numa_event() so that
> > the definitions look similar.
> 
> Confused.  The patch doesn't alter count_vm_numa_event().  No matter.
> 

Nuts. When I wrote that line in the changelog, it
was because I had converted both to a static inline but that fails to
compile if !CONFIG_NUMA_BALANCING because NUMA_PTE_UPDATES is not
defined.

===
There are no such users of count_vm_numa_events() but this patch fixes it as
it is a potential pitfall. Ideally both would be converted to static inline
but NUMA_PTE_UPDATES is not defined if !CONFIG_NUMA_BALANCING and creating
dummy constants just to have a static inline would be similarly clumsy.
====

-- 
Mel Gorman
SUSE Labs
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