TiDB OOM after created about 6.5M tables

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

TiDB is 16c32g(about 27.3G usable to the pod), we are creating 500K DB with 9M tables total with split-table disabled, after created about 6.5M table, ddl owner OOM

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

keep running

3. What did you see instead (Required)

OOM

4. What is your TiDB version? (Required)

master aec0fc5