From: Harvey Harrison 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 215: 83 f8 03 cmp $0x3,%eax 218: 0f 85 8f 00 00 00 jne 2ad 21e: 83 3d 00 00 00 00 02 cmpl $0x2,0x0 225: 0f 85 82 00 00 00 jne 2ad 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 214: 3d 00 18 00 00 cmp $0x1800,%eax 219: 0f 85 8f 00 00 00 jne 2ae 21f: 83 3d 00 00 00 00 02 cmpl $0x2,0x0 226: 0f 85 82 00 00 00 jne 2ae 22c: 64 a1 00 00 00 00 mov %fs:0x0,%eax Signed-off-by: Harvey Harrison Signed-off-by: Andrew Morton --- include/linux/mmzone.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff -puN include/linux/mmzone.h~remove-sparse-warning-for-mmzoneh include/linux/mmzone.h --- a/include/linux/mmzone.h~remove-sparse-warning-for-mmzoneh +++ a/include/linux/mmzone.h @@ -637,9 +637,10 @@ static inline int is_normal_idx(enum zon 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 _