linux-kernel - Re: [PATCH 05/12] mm: alloc_contig

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Message-ID: <20110331192650.GE14441@home.goodmis.org>
Date:	Thu, 31 Mar 2011 15:26:50 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, Michal Nazarewicz <mina86@...a86.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ankita Garg <ankita@...ibm.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Johan MOSSBERG <johan.xx.mossberg@...ricsson.com>,
	Mel Gorman <mel@....ul.ie>, Pawel Osciak <pawel@...iak.com>
Subject: Re: [PATCH 05/12] mm: alloc_contig_range() added

On Thu, Mar 31, 2011 at 09:02:41AM -0700, Dave Hansen wrote:
> On Thu, 2011-03-31 at 15:16 +0200, Marek Szyprowski wrote:
> > +       ret = 0;
> > +       while (!PageBuddy(pfn_to_page(start & (~0UL << ret))))
> > +               if (WARN_ON(++ret >= MAX_ORDER))
> > +                       return -EINVAL; 
> 
> Holy cow, that's dense.  Is there really no more straightforward way to
> do that?
> 
> In any case, please pull the ++ret bit out of the WARN_ON().  Some
> people like to do:
> 
> #define WARN_ON(...) do{}while(0)
> 
> to save space on some systems.  

That should be fixed, as the if (WARN_ON()) has become a standard in
most of the kernel. Removing WARN_ON() should be:

#define WARN_ON(x) ({0;})

But I agree, that there should be no "side effects" inside a WARN_ON(),
which that "++ret" is definitely one.

-- Steve

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