linux-ext4 - [PATCH] jbd2: don't wake kjournald unnecessarily

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Date:	Tue, 18 Dec 2012 20:59:54 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>
CC:	Dave Wysochanski <dwysocha@...hat.com>
Subject: [PATCH] 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@...hat.com>
---

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index dbf41f9..89970d5 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -518,7 +518,8 @@ int __jbd2_log_start_commit(journal_t *journal, tid_t target)
 	 * currently running transaction (if it exists).  Otherwise,
 	 * the target tid must be an old one.
 	 */
-	if (journal->j_running_transaction &&
+	if (journal->j_commit_request != target &&
+	    journal->j_running_transaction &&
 	    journal->j_running_transaction->t_tid == target) {
 		/*
 		 * We want a new commit: OK, mark the request and wakeup the
--
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