2016-03-30 04:43:55

by Chanho Min

Subject: [PATCH] mm/highmem: simplify is_highmem()

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 <[email protected]>
---
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));
#else
return 0;
#endif
--
1.7.9.5

2016-03-30 06:34:16

by Dan Williams

Subject: Re: [PATCH] mm/highmem: simplify is_highmem()

On Tue, Mar 29, 2016 at 9:43 PM, Chanho Min <[email protected]> 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 <[email protected]>
> ---
> 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));
> #else
> return 0;
> #endif

Yup, looks like a straightforward replacement of open coded versions
of the same routines.

Reviewed-by: Dan Williams <[email protected]>

2016-03-30 09:24:43

by Michal Hocko

Subject: Re: [PATCH] mm/highmem: simplify is_highmem()

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 <[email protected]>
> ---
> 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.
"

> #else
> return 0;
> #endif
> --
> 1.7.9.5
>

--
Michal Hocko
SUSE Labs

2016-03-31 22:38:09

by Andrew Morton

Subject: Re: [PATCH] mm/highmem: simplify is_highmem()

On Wed, 30 Mar 2016 11:24:38 +0200 Michal Hocko <[email protected]> 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 <[email protected]>
> > ---
> > 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