FreeNAS is full of secrets, and some of its log messages are quite cryptic, even for the more experienced part of the community. The most recent one I have stumbled upon myself is the Freed UMA keg message, always followed by something along the lines of Lost n pages of memory.

For reference, this is the extract from the email sent by my FreeNAS server last night:

Freed UMA keg (udp_inpcb) was not empty (20 items). Lost 2 pages of memory.
Freed UMA keg (udpcb) was not empty (336 items). Lost 2 pages of memory.
Freed UMA keg (tcptw) was not empty (100 items). Lost 2 pages of memory.
Freed UMA keg (tcp_inpcb) was not empty (40 items). Lost 4 pages of memory.
Freed UMA keg (tcpcb) was not empty (24 items). Lost 6 pages of memory.

Luckily, there seems to be nothing to worry about in this case. While I haven’t been able to find a clear explanation of what this means, it seems to be related to jail management: in my case, this happened right after restarting a Plex jail on this FreeNAS machine.

Because everything is working perfectly fine now after the reboot, I am going to label this as innocuous and go on with my life.