mm/page_alloc.c: refine the calculation of highest possible node id

nr_node_ids records the highest possible node id, which is calculated by
scanning the bitmap node_states[N_POSSIBLE].  Current implementation
scan the bitmap from the beginning, which will scan the whole bitmap.

This patch reverses the order by scanning from the end with
find_last_bit().

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5b5240b..809e27e 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5478,11 +5478,9 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
  */
 void __init setup_nr_node_ids(void)
 {
-       unsigned int node;
-       unsigned int highest = 0;
+       unsigned int highest;
 
-       for_each_node_mask(node, node_possible_map)
-               highest = node;
+       highest = find_last_bit(node_possible_map.bits, MAX_NUMNODES);
        nr_node_ids = highest + 1;
 }
 #endif