fs: Move bh_cachep to the __read_mostly section

bh_cachep is only written to once on initialization, so move it to the
__read_mostly section.

Signed-off-by: Shai Fultheim <shai@scalemp.com>
Signed-off-by: Vlad Zolotarov <vlad@scalemp.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/buffer.c b/fs/buffer.c
index ad5938c..838a9cf 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3152,7 +3152,7 @@
 /*
  * Buffer-head allocation
  */
-static struct kmem_cache *bh_cachep;
+static struct kmem_cache *bh_cachep __read_mostly;
 
 /*
  * Once the number of bh's in the machine exceeds this level, we start