The `zfs_arc_max` setting *is* respected when I set it to a value of
`1073741824` = 1GiB

```
cat /etc/modprobe.d/zfs.conf; cat /sys/module/zfs/parameters/zfs_arc_max; cat 
/proc/spl/kstat/zfs/arcstats |grep ^size -B3
options zfs zfs_arc_max=1073741824

1073741824

c                               4    1073741824
c_min                           4    519804800
c_max                           4    1073741824
size                            4    1086124448
```

The manpage `man zfs-module-parameters` says

```
zfs_arc_max (ulong)
Max  arc  size of ARC in bytes. If set to 0 then it will consume 1/2 of system 
RAM. This value must be at least 67108864 (64 megabytes).

This value can be changed dynamically with some caveats. It cannot be
set back to 0 while running and reducing  it  below the current ARC size
will not cause the ARC to shrink without memory pressure to induce
shrinking.

Default value: 0.
```

Before I had set it to `134217728`, more than 64MiB, but it was not
respected.

I also tried setting `zfs_arc_max` to `519804800` (495.7MiB, where ever
this number comes from), the value reported as `c_min` and it *not*
respected.

So, the minimum arc size seems to be around 1GB and *not* 64MB, as the
manpage claims. (documentation lies, the code does not)

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https://bugs.launchpad.net/bugs/1854480

Title:
  zfs_arc_max not working anymore in zfs 0.8.1

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