linux-kernel - Re: [PATCH 24/27] Convert gfp_zone() to use a table of precalculated values

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Message-ID: <alpine.DEB.1.10.0903191413560.17408@qirst.com>
Date:	Thu, 19 Mar 2009 14:15:32 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 24/27] Convert gfp_zone() to use a table of precalculated
 values

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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