xfs: trace AIL manipulations

I debugging a log tail issue on a RHEL6 kernel, I added these trace
points to trace log items being added, moved and removed in the AIL
and how that affected the log tail LSN that was written to the log.
They were very helpful in that they immediately identified the cause
of the problem being seen. Hence I'd like to always have them
available for use.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_log.c

@@ -1076,6 +1076,7 @@ xlog_assign_tail_lsn_locked(
 		tail_lsn = lip->li_lsn;
 	else
 		tail_lsn = atomic64_read(&log->l_last_sync_lsn);
+	trace_xfs_log_assign_tail_lsn(log, tail_lsn);
 	atomic64_set(&log->l_tail_lsn, tail_lsn);
 	return tail_lsn;
 }

fs/xfs/xfs_trace.h

@@ -31,8 +31,8 @@ struct xfs_da_args;
 struct xfs_da_node_entry;
 struct xfs_dquot;
 struct xfs_log_item;
-struct xlog_ticket;
 struct xlog;
+struct xlog_ticket;
 struct xlog_recover;
 struct xlog_recover_item;
 struct xfs_buf_log_format;
@@ -938,6 +938,63 @@ DEFINE_LOG_ITEM_EVENT(xfs_ail_pinned);
 DEFINE_LOG_ITEM_EVENT(xfs_ail_locked);
 DEFINE_LOG_ITEM_EVENT(xfs_ail_flushing);
 
+DECLARE_EVENT_CLASS(xfs_ail_class,
+	TP_PROTO(struct xfs_log_item *lip, xfs_lsn_t old_lsn, xfs_lsn_t new_lsn),
+	TP_ARGS(lip, old_lsn, new_lsn),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(void *, lip)
+		__field(uint, type)
+		__field(uint, flags)
+		__field(xfs_lsn_t, old_lsn)
+		__field(xfs_lsn_t, new_lsn)
+	),
+	TP_fast_assign(
+		__entry->dev = lip->li_mountp->m_super->s_dev;
+		__entry->lip = lip;
+		__entry->type = lip->li_type;
+		__entry->flags = lip->li_flags;
+		__entry->old_lsn = old_lsn;
+		__entry->new_lsn = new_lsn;
+	),
+	TP_printk("dev %d:%d lip 0x%p old lsn %d/%d new lsn %d/%d type %s flags %s",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->lip,
+		  CYCLE_LSN(__entry->old_lsn), BLOCK_LSN(__entry->old_lsn),
+		  CYCLE_LSN(__entry->new_lsn), BLOCK_LSN(__entry->new_lsn),
+		  __print_symbolic(__entry->type, XFS_LI_TYPE_DESC),
+		  __print_flags(__entry->flags, "|", XFS_LI_FLAGS))
+)
+
+#define DEFINE_AIL_EVENT(name) \
+DEFINE_EVENT(xfs_ail_class, name, \
+	TP_PROTO(struct xfs_log_item *lip, xfs_lsn_t old_lsn, xfs_lsn_t new_lsn), \
+	TP_ARGS(lip, old_lsn, new_lsn))
+DEFINE_AIL_EVENT(xfs_ail_insert);
+DEFINE_AIL_EVENT(xfs_ail_move);
+DEFINE_AIL_EVENT(xfs_ail_delete);
+
+TRACE_EVENT(xfs_log_assign_tail_lsn,
+	TP_PROTO(struct xlog *log, xfs_lsn_t new_lsn),
+	TP_ARGS(log, new_lsn),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(xfs_lsn_t, new_lsn)
+		__field(xfs_lsn_t, old_lsn)
+		__field(xfs_lsn_t, last_sync_lsn)
+	),
+	TP_fast_assign(
+		__entry->dev = log->l_mp->m_super->s_dev;
+		__entry->new_lsn = new_lsn;
+		__entry->old_lsn = atomic64_read(&log->l_tail_lsn);
+		__entry->last_sync_lsn = atomic64_read(&log->l_last_sync_lsn);
+	),
+	TP_printk("dev %d:%d new tail lsn %d/%d, old lsn %d/%d, last sync %d/%d",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  CYCLE_LSN(__entry->new_lsn), BLOCK_LSN(__entry->new_lsn),
+		  CYCLE_LSN(__entry->old_lsn), BLOCK_LSN(__entry->old_lsn),
+		  CYCLE_LSN(__entry->last_sync_lsn), BLOCK_LSN(__entry->last_sync_lsn))
+)
 
 DECLARE_EVENT_CLASS(xfs_file_class,
 	TP_PROTO(struct xfs_inode *ip, size_t count, loff_t offset, int flags),

fs/xfs/xfs_trans_ail.c

@@ -659,11 +659,13 @@ xfs_trans_ail_update_bulk(
 			if (XFS_LSN_CMP(lsn, lip->li_lsn) <= 0)
 				continue;
 
+			trace_xfs_ail_move(lip, lip->li_lsn, lsn);
 			xfs_ail_delete(ailp, lip);
 			if (mlip == lip)
 				mlip_changed = 1;
 		} else {
 			lip->li_flags |= XFS_LI_IN_AIL;
+			trace_xfs_ail_insert(lip, 0, lsn);
 		}
 		lip->li_lsn = lsn;
 		list_add(&lip->li_ail, &tmp);
@@ -732,6 +734,7 @@ xfs_trans_ail_delete_bulk(
 			return;
 		}
 
+		trace_xfs_ail_delete(lip, mlip->li_lsn, lip->li_lsn);
 		xfs_ail_delete(ailp, lip);
 		lip->li_flags &= ~XFS_LI_IN_AIL;
 		lip->li_lsn = 0;