mm/bootmem.c: cleanup on addition to bootmem data list

The objects of "struct bootmem_data_t" are linked together to form
double-linked list sequentially based on its minimal page frame number.

The current implementation implicitly supports the following cases,
which means the inserting point for current bootmem data depends on how
"list_for_each" works.  That makes the code a little hard to read.
Besides, "list_for_each" and "list_entry" can be replaced with
"list_for_each_entry".

        - The linked list is empty.
        - There has no entry in the linked list, whose minimal page
          frame number is bigger than current one.
Signed-off-by: NGavin Shan <shangw@linux.vnet.ibm.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/bootmem.c

@@ -77,16 +77,16 @@ unsigned long __init bootmem_bootmap_pages(unsigned long pages)
  */
 static void __init link_bootmem(bootmem_data_t *bdata)
 {
-	struct list_head *iter;
-
-	list_for_each(iter, &bdata_list) {
 	bootmem_data_t *ent;
 
-		ent = list_entry(iter, bootmem_data_t, list);
-		if (bdata->node_min_pfn < ent->node_min_pfn)
-			break;
+	list_for_each_entry(ent, &bdata_list, list) {
+		if (bdata->node_min_pfn < ent->node_min_pfn) {
+			list_add_tail(&bdata->list, &ent->list);
+			return;
 		}
-	list_add_tail(&bdata->list, iter);
+	}
+
+	list_add_tail(&bdata->list, &bdata_list);
 }
 
 /*