btrfs: adjust the flush trace point to include the source

Since we have normal ticketed flushing and preemptive flushing, adjust
the tracepoint so that we know the source of the flushing action to make
it easier to debug problems.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/space-info.c

@@ -673,7 +673,7 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
  */
 static void flush_space(struct btrfs_fs_info *fs_info,
 		       struct btrfs_space_info *space_info, u64 num_bytes,
-		       enum btrfs_flush_state state)
+		       enum btrfs_flush_state state, bool for_preempt)
 {
 	struct btrfs_root *root = fs_info->extent_root;
 	struct btrfs_trans_handle *trans;
@@ -756,7 +756,7 @@ static void flush_space(struct btrfs_fs_info *fs_info,
 	}
 
 	trace_btrfs_flush_space(fs_info, space_info->flags, num_bytes, state,
-				ret);
+				ret, for_preempt);
 	return;
 }
 
@@ -997,7 +997,7 @@ static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
 
 	flush_state = FLUSH_DELAYED_ITEMS_NR;
 	do {
-		flush_space(fs_info, space_info, to_reclaim, flush_state);
+		flush_space(fs_info, space_info, to_reclaim, flush_state, false);
 		spin_lock(&space_info->lock);
 		if (list_empty(&space_info->tickets)) {
 			space_info->flush = 0;
@@ -1132,7 +1132,7 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 		to_reclaim >>= 2;
 		if (!to_reclaim)
 			to_reclaim = btrfs_calc_insert_metadata_size(fs_info, 1);
-		flush_space(fs_info, space_info, to_reclaim, flush);
+		flush_space(fs_info, space_info, to_reclaim, flush, true);
 		cond_resched();
 		spin_lock(&space_info->lock);
 	}
@@ -1223,7 +1223,7 @@ static void btrfs_async_reclaim_data_space(struct work_struct *work)
 	spin_unlock(&space_info->lock);
 
 	while (!space_info->full) {
-		flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE);
+		flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE, false);
 		spin_lock(&space_info->lock);
 		if (list_empty(&space_info->tickets)) {
 			space_info->flush = 0;
@@ -1236,7 +1236,7 @@ static void btrfs_async_reclaim_data_space(struct work_struct *work)
 
 	while (flush_state < ARRAY_SIZE(data_flush_states)) {
 		flush_space(fs_info, space_info, U64_MAX,
-			    data_flush_states[flush_state]);
+			    data_flush_states[flush_state], false);
 		spin_lock(&space_info->lock);
 		if (list_empty(&space_info->tickets)) {
 			space_info->flush = 0;
@@ -1309,7 +1309,8 @@ static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
 
 	flush_state = 0;
 	do {
-		flush_space(fs_info, space_info, to_reclaim, states[flush_state]);
+		flush_space(fs_info, space_info, to_reclaim, states[flush_state],
+			    false);
 		flush_state++;
 		spin_lock(&space_info->lock);
 		if (ticket->bytes == 0) {
@@ -1325,7 +1326,7 @@ static void priority_reclaim_data_space(struct btrfs_fs_info *fs_info,
 					struct reserve_ticket *ticket)
 {
 	while (!space_info->full) {
-		flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE);
+		flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE, false);
 		spin_lock(&space_info->lock);
 		if (ticket->bytes == 0) {
 			spin_unlock(&space_info->lock);

include/trace/events/btrfs.h

@@ -1113,15 +1113,16 @@ TRACE_EVENT(btrfs_trigger_flush,
 TRACE_EVENT(btrfs_flush_space,
 
 	TP_PROTO(const struct btrfs_fs_info *fs_info, u64 flags, u64 num_bytes,
-		 int state, int ret),
+		 int state, int ret, bool for_preempt),
 
-	TP_ARGS(fs_info, flags, num_bytes, state, ret),
+	TP_ARGS(fs_info, flags, num_bytes, state, ret, for_preempt),
 
 	TP_STRUCT__entry_btrfs(
 		__field(	u64,	flags			)
 		__field(	u64,	num_bytes		)
 		__field(	int,	state			)
 		__field(	int,	ret			)
+		__field(       bool,	for_preempt		)
 	),
 
 	TP_fast_assign_btrfs(fs_info,
@@ -1129,15 +1130,16 @@ TRACE_EVENT(btrfs_flush_space,
 		__entry->num_bytes	=	num_bytes;
 		__entry->state		=	state;
 		__entry->ret		=	ret;
+		__entry->for_preempt	=	for_preempt;
 	),
 
-	TP_printk_btrfs("state=%d(%s) flags=%llu(%s) num_bytes=%llu ret=%d",
+	TP_printk_btrfs("state=%d(%s) flags=%llu(%s) num_bytes=%llu ret=%d for_preempt=%d",
 		  __entry->state,
 		  __print_symbolic(__entry->state, FLUSH_STATES),
 		  __entry->flags,
 		  __print_flags((unsigned long)__entry->flags, "|",
 				BTRFS_GROUP_FLAGS),
-		  __entry->num_bytes, __entry->ret)
+		  __entry->num_bytes, __entry->ret, __entry->for_preempt)
 );
 
 DECLARE_EVENT_CLASS(btrfs__reserved_extent,