TiFlash meets memory leak in specific scenarios

[JaySon-Huang]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

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

TiFlash running smothly

3. What did you see instead (Required)

TiFlash meets memory leak in specific scenarios. Every 6 hour, tiflash memory usage raise servel GiB. It didn't happen in v7.1.6

4. What is your TiFlash version? (Required)

v7.5.6