[PATCH 5/5] jbd2: Speedup jbd2_journal_dirty_metadata()

[Jan Kara <jack@suse.cz>]

It is often the case that we mark buffer as having dirty metadata when
the buffer is already in that state (frequent for bitmaps, inode table
blocks, superblock). Thus it is unnecessary to contend on grabbing
journal head reference and bh_state lock. Avoid that by checking whether
any modification to the buffer is needed before grabbing any locks or
references.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/jbd2/transaction.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index a91f639af6c3..ad10ca8fb9ef 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1290,8 +1290,6 @@ void jbd2_buffer_abort_trigger(struct journal_head *jh,
 	triggers->t_abort(triggers, jh2bh(jh));
 }
 
-
-
 /**
  * int jbd2_journal_dirty_metadata() -  mark a buffer as containing dirty metadata
  * @handle: transaction to add buffer to.
@@ -1325,12 +1323,25 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	WARN_ON(!transaction);
 	if (is_handle_aborted(handle))
 		return -EROFS;
-	journal = transaction->t_journal;
-	jh = jbd2_journal_grab_journal_head(bh);
-	if (!jh) {
+	if (!buffer_jbd(bh)) {
 		ret = -EUCLEAN;
 		goto out;
 	}
+	/*
+	 * We don't grab jh reference here since the buffer must be part
+	 * of the running transaction.
+	 */
+	jh = bh2jh(bh);
+	J_ASSERT_JH(jh, jh->b_transaction == transaction ||
+			jh->b_next_transaction == transaction);
+	if (jh->b_modified == 1) {
+		/* If it's in our transaction it must be in BJ_Metadata list */
+		J_ASSERT_JH(jh, jh->b_transaction != transaction ||
+				jh->b_jlist == BJ_Metadata);
+		goto out;
+	}
+
+	journal = transaction->t_journal;
 	jbd_debug(5, "journal_head %p\n", jh);
 	JBUFFER_TRACE(jh, "entry");
 
@@ -1421,7 +1432,6 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	spin_unlock(&journal->j_list_lock);
 out_unlock_bh:
 	jbd_unlock_bh_state(bh);
-	jbd2_journal_put_journal_head(jh);
 out:
 	JBUFFER_TRACE(jh, "exit");
 	return ret;
-- 
2.1.4