Use tell for prefetch

mars/services/subtask/worker/processor.py

@@ -22,13 +22,7 @@
 from .... import oscar as mo
 from ....core import ChunkGraph, OperandType, enter_mode, ExecutionError
 from ....core.context import get_context, set_context
-from ....core.operand import (
-    Fetch,
-    FetchShuffle,
-    execute,
-    MapReduceOperand,
-    OperandStage,
-)
+from ....core.operand import Fetch, FetchShuffle, execute
 from ....metrics import Metrics
 from ....optimization.physical import optimize
 from ....typing import BandType, ChunkType
@@ -426,7 +420,7 @@ async def set_chunks_meta():
         # set result data size
         self.result.data_size = result_data_size
 
-    async def push_mapper_data(self, chunk_graph):
+    async def _push_mapper_data(self, chunk_graph):
         # TODO: use task api to get reducer bands
         reducer_idx_to_band = dict()
         if not reducer_idx_to_band:
@@ -520,7 +514,7 @@ async def run(self):
 
         await self.done()
         # after done, we push mapper data to reducers in advance.
-        await self.push_mapper_data(chunk_graph)
+        await self.ref()._push_mapper_data.tell(chunk_graph)
         if self.result.status == SubtaskStatus.succeeded:
             cost_time_secs = (
                 self.result.execution_end_time - self.result.execution_start_time