BUG #14606: Memory usage continue to increase

The following bug has been logged on the website:

Bug reference: 14606
Logged by: sam dai
Email address: sam(dot)dai(at)servicemax(dot)com
PostgreSQL version: 9.6.1
Operating system: Ubuntu
Description:

I have a java application that uses postgresSQL 9.6.1, found the memory
usage continue to increase over time, the details is as below:
(1) At the beginning, the memory usage is Postgresql is 178.3 MB.
(2) Run performance testing(concurrent user 1800) on this application, when
active user is 1800 in performance testing, the memory usage of this
Postgresql is 1.413 GB. After the performance testing is finished, the
memory usage of this Postgresql is 344.1 MB.
(3) Wait for 8 hours and don't do anything on this application during this
time, the memory usage of this container is 360.2 MB after 8 hours. Even I
restart this application and wait for 2 hours, the memory usage of this
Postgresql is 350 MB.
(4)Run this performance testing for 20 times in 20 days, found memory usage
of this Postgresql is 3.5 GB. If restart Postgres, the memory usage will
back to about 178.3 MB.

It looks like the memory usage of Postgres increases every time we run
performance testing, not sure if it's a bug or not.