linux-kernel - Re: [PATCH] mm: Simplify for_each_populated

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Message-ID: <alpine.DEB.2.02.1304101339260.25932@chino.kir.corp.google.com>
Date:	Wed, 10 Apr 2013 13:41:24 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: Simplify for_each_populated_zone()

On Thu, 11 Apr 2013, Srivatsa S. Bhat wrote:

> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ede2749..2489042 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -948,9 +948,7 @@ extern struct zone *next_zone(struct zone *zone);
>  	for (zone = (first_online_pgdat())->node_zones; \
>  	     zone;					\
>  	     zone = next_zone(zone))			\
> -		if (!populated_zone(zone))		\
> -			; /* do nothing */		\
> -		else
> +		if (populated_zone(zone))
>  
>  static inline struct zone *zonelist_zone(struct zoneref *zoneref)
>  {

Nack, it's written the way it is to avoid ambiguous else statements 
following it.  People do things like

	for_each_populated_zone(z)
		if (...) {
		} else (...) {
		}

and it's now ambiguous (and should warn with -Wparentheses).
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