We have a Mongodb sharded cluster consisting of one router server, one config server and two shard servers. The swap space in the shard servers keeps growing up even though there are plenty of available RAM. The speed is about tens of megabyte a week.

System of shard server:
operating system: Ubuntu 16,
CPU: 4 core 3.4GHZ,
RAM:16GB,
database: Mongodb 3.4.2 Community version

There is no error in the Mongodb log file. The swap space in router and config server are always zero.
Please let me know anything else you need. I appreciate your support so much!

John Wang