jbd2: add tracepoints which provide per-handle statistics

Handles which stay open a long time are problematic when it comes time
to close down a transaction so it can be committed.  These tracepoints
will help us determine which ones are the problematic ones, and to
validate whether changes makes things better or worse.

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

fs/jbd2/transaction.c

@@ -30,6 +30,8 @@
 #include <linux/bug.h>
 #include <linux/module.h>
 
+#include <trace/events/jbd2.h>
+
 static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh);
 static void __jbd2_journal_unfile_buffer(struct journal_head *jh);
 
@@ -307,6 +309,8 @@ repeat:
 	 */
 	update_t_max_wait(transaction, ts);
 	handle->h_transaction = transaction;
+	handle->h_requested_credits = nblocks;
+	handle->h_start_jiffies = jiffies;
 	atomic_inc(&transaction->t_updates);
 	atomic_inc(&transaction->t_handle_count);
 	jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
@@ -353,7 +357,8 @@ static handle_t *new_handle(int nblocks)
  * Return a pointer to a newly allocated handle, or an ERR_PTR() value
  * on failure.
  */
-handle_t *jbd2__journal_start(journal_t *journal, int nblocks, gfp_t gfp_mask)
+handle_t *jbd2__journal_start(journal_t *journal, int nblocks, gfp_t gfp_mask,
+			      unsigned int type, unsigned int line_no)
 {
 	handle_t *handle = journal_current_handle();
 	int err;
@@ -379,6 +384,11 @@ handle_t *jbd2__journal_start(journal_t *journal, int nblocks, gfp_t gfp_mask)
 		current->journal_info = NULL;
 		handle = ERR_PTR(err);
 	}
+	handle->h_type = type;
+	handle->h_line_no = line_no;
+	trace_jbd2_handle_start(journal->j_fs_dev->bd_dev,
+				handle->h_transaction->t_tid, type,
+				line_no, nblocks);
 	return handle;
 }
 EXPORT_SYMBOL(jbd2__journal_start);
@@ -386,7 +396,7 @@ EXPORT_SYMBOL(jbd2__journal_start);
 
 handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
 {
-	return jbd2__journal_start(journal, nblocks, GFP_NOFS);
+	return jbd2__journal_start(journal, nblocks, GFP_NOFS, 0, 0);
 }
 EXPORT_SYMBOL(jbd2_journal_start);
 
@@ -448,7 +458,14 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
 		goto unlock;
 	}
 
+	trace_jbd2_handle_extend(journal->j_fs_dev->bd_dev,
+				 handle->h_transaction->t_tid,
+				 handle->h_type, handle->h_line_no,
+				 handle->h_buffer_credits,
+				 nblocks);
+
 	handle->h_buffer_credits += nblocks;
+	handle->h_requested_credits += nblocks;
 	atomic_add(nblocks, &transaction->t_outstanding_credits);
 	result = 0;
 
@@ -1377,6 +1394,13 @@ int jbd2_journal_stop(handle_t *handle)
 	}
 
 	jbd_debug(4, "Handle %p going down\n", handle);
+	trace_jbd2_handle_stats(journal->j_fs_dev->bd_dev,
+				handle->h_transaction->t_tid,
+				handle->h_type, handle->h_line_no,
+				jiffies - handle->h_start_jiffies,
+				handle->h_sync, handle->h_requested_credits,
+				(handle->h_requested_credits -
+				 handle->h_buffer_credits));
 
 	/*
 	 * Implement synchronous transaction batching.  If the handle