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, 6 insertions, 5 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index db55c62e1f01..b6b54d658dc2 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2656,7 +2656,7 @@ static int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start,
 	ext_debug("truncate since %u to %u\n", start, end);
 
 	/* probably first extent we're gonna free will be last in block */
-	handle = ext4_journal_start(inode, depth + 1);
+	handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, depth + 1);
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);
 
@@ -4287,7 +4287,7 @@ void ext4_ext_truncate(struct inode *inode)
 	 * probably first extent we're gonna free will be last in block
 	 */
 	err = ext4_writepage_trans_blocks(inode);
-	handle = ext4_journal_start(inode, err);
+	handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, err);
 	if (IS_ERR(handle))
 		return;
 
@@ -4454,7 +4454,8 @@ retry:
 	while (ret >= 0 && ret < max_blocks) {
 		map.m_lblk = map.m_lblk + ret;
 		map.m_len = max_blocks = max_blocks - ret;
-		handle = ext4_journal_start(inode, credits);
+		handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS,
+					    credits);
 		if (IS_ERR(handle)) {
 			ret = PTR_ERR(handle);
 			break;
@@ -4532,7 +4533,7 @@ int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
 	while (ret >= 0 && ret < max_blocks) {
 		map.m_lblk += ret;
 		map.m_len = (max_blocks -= ret);
-		handle = ext4_journal_start(inode, credits);
+		handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, credits);
 		if (IS_ERR(handle)) {
 			ret = PTR_ERR(handle);
 			break;
@@ -4710,7 +4711,7 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
 	inode_dio_wait(inode);
 
 	credits = ext4_writepage_trans_blocks(inode);
-	handle = ext4_journal_start(inode, credits);
+	handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
 	if (IS_ERR(handle)) {
 		err = PTR_ERR(handle);
 		goto out_dio;