As a user of the uptime fields in a serverStatus (uptime, uptimeMillis, uptimeEstimate) I would expect that these values are based off of a monotonic clock that never goes backwards in time. Our use case was trying to determine if a server has been restarted or not by seeing if the uptime decreased. However looking at the code, the uptime is based off a wall clock, which may be subject to drift corrections leading to decreases in reported uptime. Instead the uptime should use something like a steady clock which has monotonic guarantees.