Date: Thu, 19 Mar 2009 14:15:32 -0400 (EDT)
From: Christoph Lameter <cl@linux-foundation.org>
To: Mel Gorman <mel@csn.ul.ie>
cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Linux Memory Management List <linux-mm@kvack.org>,
       Pekka Enberg <penberg@cs.helsinki.fi>, Rik van Riel <riel@redhat.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Johannes Weiner <hannes@cmpxchg.org>, Nick Piggin <npiggin@suse.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Lin Ming <ming.m.lin@intel.com>,
       Zhang Yanmin <yanmin_zhang@linux.intel.com>,
       Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 24/27] Convert gfp_zone() to use a table of precalculated
 values
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On Thu, 19 Mar 2009, Mel Gorman wrote:

> I ran into exactly that problem and ended up shoving the table into
> page_alloc.c but then there is no benefits from having the table statically
> declared because there is no constant folding.

Right. The table must be defined in the .h file. Just a matter of figuring
out how to convince the compiler/linker to do the right thing.

> > +	if (__builtin_constant_p(zone))
> > +		BUILD_BUG_ON(zone == BAD_ZONE);
> > +#ifdef CONFIG_DEBUG_VM
> > +	else
> > +		BUG_ON(zone == BAD_ZONE);
> >  #endif
>
> That could be made a bit prettier with
>
> 	if (__builtin_constant_p(zone))
> 		BUILD_BUG_ON(zone == BAD_ZONE);
> 	VM_BUG_ON(zone == BAD_ZONE);

VM_BUG_ON is not available here. It has to be that ugly.
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