bcachefs: Add a time_stat for blocked on key cache flush

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -447,6 +447,7 @@ BCH_DEBUG_PARAMS_DEBUG()
 	x(blocked_journal_low_on_space)		\
 	x(blocked_journal_low_on_pin)		\
 	x(blocked_journal_max_in_flight)	\
+	x(blocked_key_cache_flush)		\
 	x(blocked_allocate)			\
 	x(blocked_allocate_open_bucket)		\
 	x(blocked_write_buffer_full)		\

fs/bcachefs/btree_trans_commit.c

@@ -973,9 +973,13 @@ int bch2_trans_commit_error(struct btree_trans *trans, unsigned flags,
 		bch2_trans_unlock(trans);
 
 		trace_and_count(c, trans_blocked_journal_reclaim, trans, trace_ip);
+		track_event_change(&c->times[BCH_TIME_blocked_key_cache_flush], true);
 
 		wait_event_freezable(c->journal.reclaim_wait,
 				     (ret = journal_reclaim_wait_done(c)));
+
+		track_event_change(&c->times[BCH_TIME_blocked_key_cache_flush], false);
+
 		if (ret < 0)
 			break;