jbd2: don't wake kjournald unnecessarily

Don't send an extra wakeup to kjournald in the case where we
already have the proper target in j_commit_request, i.e. that
transaction has already been requested for commit.

commit deeeaf13 "jbd2: fix fsync() tid wraparound bug" changed
the logic leading to a wakeup, but it caused some extra wakeups
which were found to lead to a measurable performance regression.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
[tytso@mit.edu: reworked check to make it clearer]
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index dbf41f9452db602efdebb778f86cf544b28d0399..1a80e3146a59f0cba8435783b207a7aa16b96bae 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -513,6 +513,10 @@ int __jbd2_log_space_left(journal_t *journal)
  */
 int __jbd2_log_start_commit(journal_t *journal, tid_t target)
 {
+       /* Return if the txn has already requested to be committed */
+       if (journal->j_commit_request == target)
+               return 0;
+
        /*
         * The only transaction we can possibly wait upon is the
         * currently running transaction (if it exists).  Otherwise,