query with memory usage 0 be killed

[XuHuaiyu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Queries with memory usage less than 128MB would be recorded be global memory controller.
2. But when tidb_server_memory_limit is reached, the memory usage of the query may be less than 128MB
3. We do not need to kill such queries.
   

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)