jbd2: Improve scalability by not taking j_state_lock in jbd2_journal_stop()

One of the most contended locks in the jbd2 layer is j_state_lock when
running dbench.  This is especially true if using the real-time kernel
with its "sleeping spinlocks" patch that replaces spinlocks with
priority inheriting mutexes --- but it also shows up on large SMP
benchmarks.

Thanks to John Stultz for pointing this out.

Reviewed by Mingming Cao and Jan Kara.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index bfc70f5..e214d68 100644 (file)
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1311,7 +1311,6 @@ int jbd2_journal_stop(handle_t *handle)
        if (handle->h_sync)
                transaction->t_synchronous_commit = 1;
        current->journal_info = NULL;
-       spin_lock(&journal->j_state_lock);
        spin_lock(&transaction->t_handle_lock);
        transaction->t_outstanding_credits -= handle->h_buffer_credits;
        transaction->t_updates--;
@@ -1340,8 +1339,7 @@ int jbd2_journal_stop(handle_t *handle)
                jbd_debug(2, "transaction too old, requesting commit for "
                                        "handle %p\n", handle);
                /* This is non-blocking */
-               __jbd2_log_start_commit(journal, transaction->t_tid);
-               spin_unlock(&journal->j_state_lock);
+               jbd2_log_start_commit(journal, transaction->t_tid);
 
                /*
                 * Special case: JBD2_SYNC synchronous updates require us
@@ -1351,7 +1349,6 @@ int jbd2_journal_stop(handle_t *handle)
                        err = jbd2_log_wait_commit(journal, tid);
        } else {
                spin_unlock(&transaction->t_handle_lock);
-               spin_unlock(&journal->j_state_lock);
        }
 
        lock_map_release(&handle->h_lockdep_map);