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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