Add tracing to track changes to i_conv_pending_ios count.

Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
---
 fs/ext4/inode.c             | 11 ++++++++++-
 include/trace/events/ext4.h | 24 ++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 280ba3d359e3..8b5cb37cdd6d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -673,7 +673,16 @@ static void _ext4_conv_pending_mod(struct inode *inode, int n)
 {
 	struct ext4_inode_info *ei = EXT4_I(inode);
 
-	atomic_add(n, &ei->i_conv_pending_ios);
+	/*
+	 * Only use the full ordering variant when tracing is needed.
+	 */
+	if (trace_ext4_conv_pending_ios_enabled()) {
+		int new_ios = atomic_add_return(n, &ei->i_conv_pending_ios);
+
+		trace_ext4_conv_pending_ios(inode, n > 0, new_ios - n, new_ios);
+	} else {
+		atomic_add(n, &ei->i_conv_pending_ios);
+	}
 }
 
 /*
diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index 7d255c47c446..f1754b2e836c 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -3367,6 +3367,30 @@ TRACE_EVENT(ext4_block_zero_eof,
 		  __entry->i_disksize, __entry->did_zero, __entry->zero_written)
 );
 
+/* i_conv_pending_ios accounting tracepoint */
+TRACE_EVENT(ext4_conv_pending_ios,
+	TP_PROTO(struct inode *inode, bool add, int old_ios, int new_ios),
+	TP_ARGS(inode, add, old_ios, new_ios),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(u64, ino)
+		__field(bool, add)
+		__field(int, old_ios)
+		__field(int, new_ios)
+	),
+	TP_fast_assign(
+		__entry->dev = inode->i_sb->s_dev;
+		__entry->ino = inode->i_ino;
+		__entry->add = add;
+		__entry->old_ios = old_ios;
+		__entry->new_ios = new_ios;
+	),
+	TP_printk("dev %d:%d ino %llu %s i_conv_pending_ios %d -> %d",
+		  MAJOR(__entry->dev), MINOR(__entry->dev), __entry->ino,
+		  __entry->add ? "inc" : "dec",
+		  __entry->old_ios, __entry->new_ios)
+);
+
 #endif /* _TRACE_EXT4_H */
 
 /* This part must be outside protection */

-- 
2.55.0