We have a juju 2.1.3 controller handling ~500 machines, jujud is using 105G, the controller has 60G free ... which is more than enough to work properly until jujud decides to fork/exec. I do agree with Junien that this bug should be classified as high priority, and hopefully targeted to 2.3, because the only workaround is restart jujud, but in a 500 machines env (~1500 agents) produces a massive config-changed hook trigger putting a lot of pressure on the controller.

1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:00 WARNING juju.apiserver.machine machiner.go:200 not updating network config for container "1/lxd/3"
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:00 WARNING juju.apiserver.machine machiner.go:200 not updating network config for container "2/lxd/3"
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:02 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:09 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:14 WARNING juju.apiserver.machine machiner.go:200 not updating network config for container "0/lxd/1"
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:15 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:22 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:28 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:35 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:42 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:48 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:30:55 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:01 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:08 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:14 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:21 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:26 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:33 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:38 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:45 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:51 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:31:58 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:32:04 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:32:11 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory
1a6f9258-9688-40a8-88b5-a7f8260b18b4: machine-0 2017-07-25 16:32:17 ERROR juju.worker.dependency engine.go:547 "disk-manager" manifold worker returned unexpected error: cannot list block devices: lsblk failed: fork/exec /bin/lsblk: cannot allocate memory