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remove sparse warning for mmzone.h 

include/linux/mmzone.h:640:22: warning: potentially expensive pointer subtraction

Calculate the offset into the node_zones array rather than the index
using casts to (char *) and comparing against the index * sizeof(struct zone).

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.

Before:
 207:   2b 80 8c 07 00 00       sub    0x78c(%eax),%eax
 20d:   c1 f8 0b                sar    $0xb,%eax
 210:   83 f8 02                cmp    $0x2,%eax
 213:   74 16                   je     22b <kmap_atomic_prot+0x144>
 215:   83 f8 03                cmp    $0x3,%eax
 218:   0f 85 8f 00 00 00       jne    2ad <kmap_atomic_prot+0x1c6>
 21e:   83 3d 00 00 00 00 02    cmpl   $0x2,0x0
 225:   0f 85 82 00 00 00       jne    2ad <kmap_atomic_prot+0x1c6>
 22b:   64 a1 00 00 00 00       mov    %fs:0x0,%eax

After:
 207:   2b 80 8c 07 00 00       sub    0x78c(%eax),%eax
 20d:   3d 00 10 00 00          cmp    $0x1000,%eax
 212:   74 18                   je     22c <kmap_atomic_prot+0x145>
 214:   3d 00 18 00 00          cmp    $0x1800,%eax
 219:   0f 85 8f 00 00 00       jne    2ae <kmap_atomic_prot+0x1c7>
 21f:   83 3d 00 00 00 00 02    cmpl   $0x2,0x0
 226:   0f 85 82 00 00 00       jne    2ae <kmap_atomic_prot+0x1c7>
 22c:   64 a1 00 00 00 00       mov    %fs:0x0,%eax

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Harvey Harrison 2008-04-28 02:12:07 -07:00 committed by Linus Torvalds
parent 488514d179
commit ddc81ed2c5
1 changed files with 4 additions and 3 deletions
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7
include/linux/mmzone.h
View File

@ -637,9 +637,10 @@ static inline int is_normal_idx(enum zone_type idx)
static inline int is_highmem(struct zone *zone)
{
#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());
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());
#else
return 0;
#endif