[PATCH] JBD: journal_dirty_metadata() speedup

Before taking the highly-taken j_list_lock, take a peek to seem if this
buffer is already journalled and in the appropriate state.

diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
index b08c36640ff5b1a814dd63983eccf2e1f3275634..30d526c0a3b57c5057a06dac8a6926ca3fe4dd0a 100644 (file)
--- a/fs/jbd/transaction.c
+++ b/fs/jbd/transaction.c
@@ -1100,6 +1100,22 @@ int journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
                goto out;
        
        jbd_lock_bh_state(bh);
+
+       /*
+        * fastpath, to avoid expensive locking.  If this buffer is already
+        * on the running transaction's metadata list there is nothing to do.
+        * Nobody can take it off again because there is a handle open.
+        * I _think_ we're OK here with SMP barriers - a mistaken decision will
+        * result in this test being false, so we go in and take the locks.
+        */
+       if (jh->b_transaction == handle->h_transaction &&
+                                       jh->b_jlist == BJ_Metadata) {
+               JBUFFER_TRACE(jh, "fastpath");
+               J_ASSERT_JH(jh, jh->b_transaction ==
+                                       journal->j_running_transaction);
+               goto out_unlock_bh;
+       }
+
        spin_lock(&journal->j_list_lock);
        set_buffer_jbddirty(bh);
 
@@ -1120,7 +1136,7 @@ int journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
                /* And this case is illegal: we can't reuse another
                 * transaction's data buffer, ever. */
                /* FIXME: writepage() should be journalled */
-               goto done_locked;
+               goto out_unlock_list;
        }
 
        /* That test should have eliminated the following case: */
@@ -1129,8 +1145,9 @@ int journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
        JBUFFER_TRACE(jh, "file as BJ_Metadata");
        __journal_file_buffer(jh, handle->h_transaction, BJ_Metadata);
 
-done_locked:
+out_unlock_list:
        spin_unlock(&journal->j_list_lock);
+out_unlock_bh:
        jbd_unlock_bh_state(bh);
 out:
        JBUFFER_TRACE(jh, "exit");