Notes on slow kernel/ZFS memory leak resolved with FreeBSD-EN-16:08.zfs

[Eric A. Borisch]

To elaborate on EN-16:08: this fixes a bug where any attempt to access a
(1) previously mounted and (2) now destroyed snapshot leads to a small
kernel memory leak on each attempt. These attempts can come in via NFS,
from a local (potentially non-privileged) user, or even from within a jail,
so long as the user/service would be able to enter into valid snapshots --
they don't need to be able to create snapshots themselves. We
noticed it from repeated NFS attempts to mount an expired rolling snapshot;
due to a slow but steady retry, the leak was clearly visible over long
(multi-week) timescales.

The leaked memory will show up labeled as 'mount' in vmstat -m, and is easy
to verify as it will steadily grow with each failed attempt.

   - Eric

  - Eric