0.8.2 ignores ARC min/max sysctls after kernel boot

[sempervictus]

System information

Type	Version/Name
Arch
Current
4.14.150 (grsec and linux-hardened flavors both exhibit this problem, the latter is very close to if not identical to vanilla for our purposes)
Architecture	x64
ZFS Version	0.8.2 - built into the kernel, not a module.
SPL Version	N/A

Describe the problem you're observing

Sysctls for ARC min/max appear to be ignored for all cases other than kernel command line configuration. Runtime echo $((8*1024*1024*1024)) > /sys/module/zfs/parameters/zfs_arc_max does not show new value in arcstat max size, and does not shrink ARC when the initial value is bigger than the setting. Usually the initial value is bigger as it defaults to half of all system RAM, resulting in OOMs for applications over time. This problem is also present during userspace init when sysctl.d is processed.

Describe how to reproduce the problem

Attempt to set /sys/module/zfs/parameters/zfs_arc_max or /sys/module/zfs/parameters/zfs_arc_min and watch them not change.

This happens off the clean 0.8.2 tag, with the grsec 0.8.2 patch, and with all of the metaslab related commits backported from master to permit use of the range tree code on 0.8.2. In between builds, have been using git clean -dxf as suggested by @behlendorf to keep the tree clean.

Anyone else run builtin ZFS and seeing this? I imagine it would have been flagged and fixed long ago if module users were seeing it.