RDS: use get_user_pages_fast()

Use the new function that is simpler and faster.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rds/rdma.c b/net/rds/rdma.c
index e390dc7..8dc83d2 100644
--- a/net/rds/rdma.c
+++ b/net/rds/rdma.c
@@ -150,10 +150,7 @@
 {
 	int ret;
 
-	down_read(&current->mm->mmap_sem);
-	ret = get_user_pages(current, current->mm, user_addr,
-			     nr_pages, write, 0, pages, NULL);
-	up_read(&current->mm->mmap_sem);
+	ret = get_user_pages_fast(user_addr, nr_pages, write, pages);
 
 	if (ret >= 0 && ret < nr_pages) {
 		while (ret--)