ext4: pass context information to jbd2__journal_start()

So we can better understand what bits of ext4 are responsible for
long-running jbd2 handles, use jbd2__journal_start() so we can pass
context information for logging purposes.

The recommended way for finding the longer-running handles is:

   T=/sys/kernel/debug/tracing
   EVENT=$T/events/jbd2/jbd2_handle_stats
   echo "interval > 5" > $EVENT/filter
   echo 1 > $EVENT/enable

   ./run-my-fs-benchmark

   cat $T/trace > /tmp/problem-handles

This will list handles that were active for longer than 20ms.  Having
longer-running handles is bad, because a commit started at the wrong
time could stall for those 20+ milliseconds, which could delay an
fsync() or an O_SYNC operation.  Here is an example line from the
trace file describing a handle which lived on for 311 jiffies, or over
1.2 seconds:

postmark-2917  [000] ....   196.435786: jbd2_handle_stats: dev 254,32 
   tid 570 type 2 line_no 2541 interval 311 sync 0 requested_blocks 1
   dirtied_blocks 0

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

1 files changed, 5 insertions, 5 deletions

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 8eefb636beb8..c7f4d7584669 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -466,7 +466,7 @@ static int setup_new_flex_group_blocks(struct super_block *sb,
 	meta_bg = EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG);
 
 	/* This transaction may be extended/restarted along the way */
-	handle = ext4_journal_start_sb(sb, EXT4_MAX_TRANS_DATA);
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, EXT4_MAX_TRANS_DATA);
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);
 
@@ -1031,7 +1031,7 @@ static void update_backups(struct super_block *sb, int blk_off, char *data,
 	handle_t *handle;
 	int err = 0, err2;
 
-	handle = ext4_journal_start_sb(sb, EXT4_MAX_TRANS_DATA);
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, EXT4_MAX_TRANS_DATA);
 	if (IS_ERR(handle)) {
 		group = 1;
 		err = PTR_ERR(handle);
@@ -1412,7 +1412,7 @@ static int ext4_flex_group_add(struct super_block *sb,
 	 * modify each of the reserved GDT dindirect blocks.
 	 */
 	credit = flex_gd->count * 4 + reserved_gdb;
-	handle = ext4_journal_start_sb(sb, credit);
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, credit);
 	if (IS_ERR(handle)) {
 		err = PTR_ERR(handle);
 		goto exit;
@@ -1624,7 +1624,7 @@ static int ext4_group_extend_no_check(struct super_block *sb,
 	/* We will update the superblock, one block bitmap, and
 	 * one group descriptor via ext4_group_add_blocks().
 	 */
-	handle = ext4_journal_start_sb(sb, 3);
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, 3);
 	if (IS_ERR(handle)) {
 		err = PTR_ERR(handle);
 		ext4_warning(sb, "error %d on journal start", err);
@@ -1788,7 +1788,7 @@ static int ext4_convert_meta_bg(struct super_block *sb, struct inode *inode)
 		credits += 3;	/* block bitmap, bg descriptor, resize inode */
 	}
 
-	handle = ext4_journal_start_sb(sb, credits);
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, credits);
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);