Good day.

After upgrading to 4.0 we've encountered some sort of memory leak in 2 cases:

1) In cluster environment described in SERVER-43038. I don't have diagnostic.data from that time, but possibly can extract some logs from our logging system.
Memory leak occured after we've shutdown our slaveDelay instances and lasted until we've started them again.

2) Recently in replica set configuration (i attached mongodb memory graphs from two servers (each one was primary at some time), server logs, diagnostic.data and configuration file).

Spike around 2-3pm 19.09 on db1-1 was restoration of 'drive' database with mongorestore. Also i did a rs.stepdown() and restart server intance db1-1 at 4:30pm 21.09 due to memory pressure (memory leak has moved to the new primary). At 11:25pm 21.09 we've disabled most of the processes that work with that replica set.

After i've started workload again i cannot reproduce memory leak. On the contrary you can see resident memory decreases on db1-2 from 3pm 23.09 and up to date)