linux-kernel - Re: [PATCH] fix sparse warning from include/linux/mmzone.h

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Message-ID: <alpine.LFD.1.00.0802081401410.2896@woody.linux-foundation.org>
Date:	Fri, 8 Feb 2008 14:04:55 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Harvey Harrison <harvey.harrison@...il.com>,
	viro@...IV.linux.org.uk, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: [PATCH] fix sparse warning from include/linux/mmzone.h



On Fri, 8 Feb 2008, Andrew Morton wrote:
> >  #ifdef CONFIG_HIGHMEM
> > -	int zone_idx = zone - zone->zone_pgdat->node_zones;
> > -	return zone_idx == ZONE_HIGHMEM ||
> > -		(zone_idx == ZONE_MOVABLE && zone_movable_is_highmem());
> > +	const int highmem_off = ZONE_HIGHMEM * sizeof(*zone);
> > +	const int movable_off = ZONE_MOVABLE * sizeof(*zone);
> > +
> > +	int zone_off = (unsigned long)zone - (unsigned long)zone->zone_pgdat->node_zones;
> > +	return zone_off == highmem_off ||
> > +		(zone_off == movable_off && zone_movable_is_highmem());
> 
> hrm.  For my i386 build (and that's where CONFIG_HIGHMEM really matters)
> this patch makes mm/page_alloc.o six bytes larger, and I don't think the
> change did much for readability.

Heh, yeah. That's a very odd way to write it.

It would probably make more sense to just write it as something like

	struct zone *base = zone->zone_pgdat->node_zones;

	if (zone == base + ZONE_HIGHMEM ||
		(zone == base + ZONE_MOVABLE && zone_movable_is_highmem());

instead.

The above is totally untested, of course.

		Linus
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