mm/sparse: refine usemap_size() a little

The current implementation calculates usemap_size in two steps:
    * calculate number of bytes to cover these bits
    * calculate number of "unsigned long" to cover these bytes

It would be more clear by:
    * calculate number of "unsigned long" to cover these bits
    * multiple it with sizeof(unsigned long)

This patch refine usemap_size() a little to make it more easy to
understand.

Link: http://lkml.kernel.org/r/20170310043713.96871-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 4 deletions

diff --git a/mm/sparse.c b/mm/sparse.c
index db6bf3c97ea2..6903c8fc3085 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -248,10 +248,7 @@ static int __meminit sparse_init_one_section(struct mem_section *ms,
 
 unsigned long usemap_size(void)
 {
-        unsigned long size_bytes;
-        size_bytes = roundup(SECTION_BLOCKFLAGS_BITS, 8) / 8;
-        size_bytes = roundup(size_bytes, sizeof(unsigned long));
-        return size_bytes;
+        return BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS) * sizeof(unsigned long);
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG