mm, vmalloc: use well-defined find_last_bit() func

Our intention in here is to find last_bit within the region to flush.
There is well-defined function, find_last_bit() for this purpose and its
performance may be slightly better than current implementation.  So change
it.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -1016,15 +1016,16 @@ void vm_unmap_aliases(void)
 
 		rcu_read_lock();
 		list_for_each_entry_rcu(vb, &vbq->free, free_list) {
-			int i;
+			int i, j;
 
 			spin_lock(&vb->lock);
 			i = find_first_bit(vb->dirty_map, VMAP_BBMAP_BITS);
-			while (i < VMAP_BBMAP_BITS) {
+			if (i < VMAP_BBMAP_BITS) {
 				unsigned long s, e;
-				int j;
-				j = find_next_zero_bit(vb->dirty_map,
-					VMAP_BBMAP_BITS, i);
+
+				j = find_last_bit(vb->dirty_map,
+							VMAP_BBMAP_BITS);
+				j = j + 1; /* need exclusive index */
 
 				s = vb->va->va_start + (i << PAGE_SHIFT);
 				e = vb->va->va_start + (j << PAGE_SHIFT);
@@ -1034,10 +1035,6 @@ void vm_unmap_aliases(void)
 					start = s;
 				if (e > end)
 					end = e;
-
-				i = j;
-				i = find_next_bit(vb->dirty_map,
-							VMAP_BBMAP_BITS, i);
 			}
 			spin_unlock(&vb->lock);
 		}