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Subject: Re: [PATCH] fix sparse warning from include/linux/mmzone.h
From: Harvey Harrison <harvey.harrison@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, viro@ZenIV.linux.org.uk,
       linux-kernel@vger.kernel.org, mingo@elte.hu
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Date: Fri, 08 Feb 2008 14:17:58 -0800
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On Fri, 2008-02-08 at 14:04 -0800, Linus Torvalds wrote:
> 
> 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.

As long as you read 'odd' as 'rather dumb'

> 
> 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());

s/if/return/ I think.  And missing a closing brace.  Unless I'm (again)
missing something.

Harvey