[PATCH] mm: sparse: shift operation instead of division operation for root index

[Guo Hui <guohui@uniontech.com>]

In the function __nr_to_section,
Use shift operation instead of division operation
in order to improve the performance of memory management.
There are no functional changes.

Some performance data is as follows:
Machine configuration: Hygon 128 cores, 256M memory

Stream single core:
           with patch       without patch       promote
Copy       23376.7731       23907.1532          -1.27%
Scale      12580.2913       11679.7852          +7.71%
Add        11922.9562       11461.8669          +4.02%
Triad      12549.2735       11491.9798          +9.20%

Signed-off-by: Guo Hui <guohui@uniontech.com>
---
 include/linux/mmzone.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 5e50b78d58ea..8dde6fb56109 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1818,7 +1818,8 @@ struct mem_section {
 #define SECTIONS_PER_ROOT	1
 #endif
 
-#define SECTION_NR_TO_ROOT(sec)	((sec) / SECTIONS_PER_ROOT)
+#define SECTION_ROOT_SHIFT        (__builtin_popcount(SECTIONS_PER_ROOT - 1))
+#define SECTION_NR_TO_ROOT(sec)	((sec) >> SECTION_ROOT_SHIFT)
 #define NR_SECTION_ROOTS	DIV_ROUND_UP(NR_MEM_SECTIONS, SECTIONS_PER_ROOT)
 #define SECTION_ROOT_MASK	(SECTIONS_PER_ROOT - 1)
 
-- 
2.20.1