Messages in this thread Patch in this message |  | | | Subject | [PATCH] fix sparse warning from include/linux/mmzone.h | | From | Harvey Harrison <> | | Date | Thu, 07 Feb 2008 12:52:23 -0800 |
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include/linux/mmzone.h:640:22: warning: potentially expensive pointer subtraction
The code in question was doing a pointer subtraction to find the index of the zone argument in the node_zones array. This essentially boils down to:
((unsigned long)zone - (unsigned long)zone->zone_pgdat->node_zones)/sizeof(struct zone)
Which can be expensive if struct zone is not a power of two. Instead, just calculate the offsets rather than the index in the array.
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com> --- This shows up > 30 times in an x86 allyesconfig, would be nice to get rid of it and makes the code a little more efficient. I believe this is correct, unless there is a subtlety I have missed. include/linux/mmzone.h | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 8d8d197..cb07758 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -637,9 +637,12 @@ 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()); + 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()); #else return 0; #endif -- 1.5.4.1219.g65b9
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