fs/buffer.c: change type of max_buffer_heads to unsigned long

max_buffer_heads is calculated from nr_free_buffer_pages(), so change
its type to unsigned long in case of overflow.

Signed-off-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>

fs/buffer.c

@@ -3227,7 +3227,7 @@ static struct kmem_cache *bh_cachep __read_mostly;
  * Once the number of bh's in the machine exceeds this level, we start
  * stripping them in writeback.
  */
-static int max_buffer_heads;
+static unsigned long max_buffer_heads;
 
 int buffer_heads_over_limit;
 
@@ -3343,7 +3343,7 @@ EXPORT_SYMBOL(bh_submit_read);
 
 void __init buffer_init(void)
 {
-	int nrpages;
+	unsigned long nrpages;
 
 	bh_cachep = kmem_cache_create("buffer_head",
 			sizeof(struct buffer_head), 0,