make __section_nr() more efficient

When CONFIG_SPARSEMEM_EXTREME is disabled, __section_nr can get the
section number with a subtraction directly.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Zhou Chengming <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Hanjun Guo <[email protected]>
Cc: Li Bin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/sparse.c b/mm/sparse.c
index 5d0cf45403646e54b0e92673f8855e693ad1cf84..36d7bbb80e4932ceed6887f27f9e5d15d0311b39 100644 (file)
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -100,11 +100,7 @@ static inline int sparse_index_init(unsigned long section_nr, int nid)
 }
 #endif
 
-/*
- * Although written for the SPARSEMEM_EXTREME case, this happens
- * to also work for the flat array case because
- * NR_SECTION_ROOTS==NR_MEM_SECTIONS.
- */
+#ifdef CONFIG_SPARSEMEM_EXTREME
 int __section_nr(struct mem_section* ms)
 {
        unsigned long root_nr;
@@ -123,6 +119,12 @@ int __section_nr(struct mem_section* ms)
 
        return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
 }
+#else
+int __section_nr(struct mem_section* ms)
+{
+       return (int)(ms - mem_section[0]);
+}
+#endif
 
 /*
  * During early boot, before section_mem_map is used for an actual