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, 2 insertions, 2 deletions

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index db8226d595fa..4e4fcfd342f8 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -456,7 +456,7 @@ int ext4_ext_migrate(struct inode *inode)
                  */
                 return retval;
 
-        handle = ext4_journal_start(inode,
+        handle = ext4_journal_start(inode, EXT4_HT_MIGRATE,
                                         EXT4_DATA_TRANS_BLOCKS(inode->i_sb) +
                                         EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3 +
                                         EXT4_MAXQUOTAS_INIT_BLOCKS(inode->i_sb)
@@ -507,7 +507,7 @@ int ext4_ext_migrate(struct inode *inode)
         ext4_set_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
         up_read((&EXT4_I(inode)->i_data_sem));
 
-        handle = ext4_journal_start(inode, 1);
+        handle = ext4_journal_start(inode, EXT4_HT_MIGRATE, 1);
         if (IS_ERR(handle)) {
                 /*
                  * It is impossible to update on-disk structures without