BUG #18450: The memory usage of the postgresql12.6 walsender process is abnormally high.

The following bug has been logged on the website:

Bug reference:      18450
Logged by:          Melody Liu
Email address:      melody_xiaodi@sina.com
PostgreSQL version: 12.6
Operating system:   CentOS Linux release 7.9.2009
Description:

In my PostgreSQL 12.6 database, the memory usage of the walsender process
continues to rise, even during periods of low business activity. According
to current monitoring results, the walsender process can occupy up to 61G of
memory and is still increasing. Only after restarting the walsender process
can the server memory be released.

Configuration description of postgresql12.6: The OS has set hugepages with a
maximum limit of 165G, and shared_buffers is set to 150G. My server
configuration is as follows: CPU: 64core, MEM: 256G.