jbd2: don't wake kjournald unnecessarily

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 <[email protected]>
[[email protected]: reworked check to make it clearer]
Signed-off-by: "Theodore Ts'o" <[email protected]>