jbd2: reduce journal_head size

Remove unused t_cow_tid field (ext4 copy-on-write support doesn't seem
to be happening) and change b_modified and b_jlist to bitfields thus
saving 8 bytes in the structure.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>

diff --git a/include/linux/journal-head.h b/include/linux/journal-head.h
index c18b46f..13a3da2 100644 (file)
--- a/include/linux/journal-head.h
+++ b/include/linux/journal-head.h
@@ -31,21 +31,14 @@ struct journal_head {
        /*
         * Journalling list for this buffer [jbd_lock_bh_state()]
         */
-       unsigned b_jlist;
+       unsigned b_jlist:4;
 
        /*
         * This flag signals the buffer has been modified by
         * the currently running transaction
         * [jbd_lock_bh_state()]
         */
-       unsigned b_modified;
-
-       /*
-        * This feild tracks the last transaction id in which this buffer
-        * has been cowed
-        * [jbd_lock_bh_state()]
-        */
-       tid_t b_cow_tid;
+       unsigned b_modified:1;
 
        /*
         * Copy of the buffer data frozen for writing to the log.