[3.13.y.z extended stable] Patch "ext4: disable synchronous transaction batching if max_batch_time==0" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ext4: disable synchronous transaction batching if max_batch_time==0

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From cbeac504046ea2385d0afa4d92d98394a8bc3afc Mon Sep 17 00:00:00 2001
From: Eric Sandeen <sandeen at redhat.com>
Date: Sat, 5 Jul 2014 19:18:22 -0400
Subject: ext4: disable synchronous transaction batching if max_batch_time==0

commit 5dd214248f94d430d70e9230bda72f2654ac88a8 upstream.

The mount manpage says of the max_batch_time option,

	This optimization can be turned off entirely
	by setting max_batch_time to 0.

But the code doesn't do that.  So fix the code to do
that.

Signed-off-by: Eric Sandeen <sandeen at redhat.com>
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ext4/super.c       | 2 --
 fs/jbd2/transaction.c | 5 ++++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a81a3da..25b327e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1519,8 +1519,6 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
 			arg = JBD2_DEFAULT_MAX_COMMIT_AGE;
 		sbi->s_commit_interval = HZ * arg;
 	} else if (token == Opt_max_batch_time) {
-		if (arg == 0)
-			arg = EXT4_DEF_MAX_BATCH_TIME;
 		sbi->s_max_batch_time = arg;
 	} else if (token == Opt_min_batch_time) {
 		sbi->s_min_batch_time = arg;
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 60bb365..f8a5d6a 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1590,9 +1590,12 @@ int jbd2_journal_stop(handle_t *handle)
 	 * to perform a synchronous write.  We do this to detect the
 	 * case where a single process is doing a stream of sync
 	 * writes.  No point in waiting for joiners in that case.
+	 *
+	 * Setting max_batch_time to 0 disables this completely.
 	 */
 	pid = current->pid;
-	if (handle->h_sync && journal->j_last_sync_writer != pid) {
+	if (handle->h_sync && journal->j_last_sync_writer != pid &&
+	    journal->j_max_batch_time) {
 		u64 commit_time, trans_time;

 		journal->j_last_sync_writer = pid;
--
1.9.1