On Wed, 30 Mar 2016 11:24:38 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> On Wed 30-03-16 13:43:42, Chanho Min wrote:
> > The is_highmem() is can be simplified by use of is_highmem_idx().
> > This patch removes redundant code and will make it easier to maintain
> > if the zone policy is changed or a new zone is added.
> >
> > Signed-off-by: Chanho Min <chanho.min@xxxxxxx>
> > ---
> > include/linux/mmzone.h | 5 +----
> > 1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index e23a9e7..9ac90c3 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -817,10 +817,7 @@ static inline int is_highmem_idx(enum zone_type idx)
> > static inline int is_highmem(struct zone *zone)
> > {
> > #ifdef CONFIG_HIGHMEM
> > - int zone_off = (char *)zone - (char *)zone->zone_pgdat->node_zones;
> > - return zone_off == ZONE_HIGHMEM * sizeof(*zone) ||
> > - (zone_off == ZONE_MOVABLE * sizeof(*zone) &&
> > - zone_movable_is_highmem());
> > + return is_highmem_idx(zone_idx(zone));
>
> This will reintroduce the pointer arithmetic removed by ddc81ed2c5d4
> ("remove sparse warning for mmzone.h") AFAICS. I have no idea how much
> that matters though. The mentioned commit doesn't tell much about saves
> except for
> "
> On X86_32 this saves a sar, but code size increases by one byte per
> is_highmem() use due to 32-bit cmps rather than 16 bit cmps.
> "
The patch shrinks my i386 allmodconfig page_alloc.o by 50 bytes, and
that has just two is_highmem() callsites. So I think it's OK from a
code-size and performance piont of view
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