I would like to reopen this issue. I installed Ubuntu 20.04.1 LTS Server
(no zfs root, 16GB RAM) and added zfs volumes. I tried to limit the arc
with

`options zfs zfs_arc_max=134217728` in `/etc/modprobe.d/zfs.conf` to
128MiB (just to try)

I updated the initial ramdisk with `update-initramfs -u` and rebooted
the machine.

Then I observe, that the arc still grows to ~6GB > 128M.

```
al@nas:~$ cat /etc/modprobe.d/zfs.conf; cat 
/sys/module/zfs/parameters/zfs_arc_max; cat /proc/spl/kstat/zfs/arcstats 

options zfs zfs_arc_max=134217728

134217728

12 1 0x01 98 26656 9388908203 858454750163
name                            type data
hits                            4    2341389
misses                          4    69038
demand_data_hits                4    409755
demand_data_misses              4    10337
demand_metadata_hits            4    1892418
demand_metadata_misses          4    11520
prefetch_data_hits              4    20609
prefetch_data_misses            4    36648
prefetch_metadata_hits          4    18607
prefetch_metadata_misses        4    10533
mru_hits                        4    332923
mru_ghost_hits                  4    0
mfu_hits                        4    1981310
mfu_ghost_hits                  4    0
deleted                         4    21
mutex_miss                      4    0
access_skip                     4    0
evict_skip                      4    99
evict_not_enough                4    0
evict_l2_cached                 4    0
evict_l2_eligible               4    201728
evict_l2_ineligible             4    34816
evict_l2_skip                   4    0
hash_elements                   4    70022
hash_elements_max               4    70117
hash_collisions                 4    2316
hash_chains                     4    1152
hash_chain_max                  4    2
p                               4    4173713920
c                               4    8316876800
c_min                           4    519804800
c_max                           4    8316876800
size                            4    6496367160
compressed_size                 4    5849741824
uncompressed_size               4    6240316928
overhead_size                   4    416625152
hdr_size                        4    23995776
data_size                       4    5993091584
metadata_size                   4    273275392
dbuf_size                       4    44426616
dnode_size                      4    120015552
bonus_size                      4    41562240
anon_size                       4    18524672
anon_evictable_data             4    0
anon_evictable_metadata         4    0
mru_size                        4    4014986752
mru_evictable_data              4    3841052672
mru_evictable_metadata          4    24693760
mru_ghost_size                  4    0
mru_ghost_evictable_data        4    0
mru_ghost_evictable_metadata    4    0
mfu_size                        4    2232855552
mfu_evictable_data              4    1694498304
mfu_evictable_metadata          4    15691264
mfu_ghost_size                  4    0
mfu_ghost_evictable_data        4    0
mfu_ghost_evictable_metadata    4    0
l2_hits                         4    0
l2_misses                       4    0
l2_feeds                        4    0
l2_rw_clash                     4    0
l2_read_bytes                   4    0
l2_write_bytes                  4    0
l2_writes_sent                  4    0
l2_writes_done                  4    0
l2_writes_error                 4    0
l2_writes_lock_retry            4    0
l2_evict_lock_retry             4    0
l2_evict_reading                4    0
l2_evict_l1cached               4    0
l2_free_on_write                4    0
l2_abort_lowmem                 4    0
l2_cksum_bad                    4    0
l2_io_error                     4    0
l2_size                         4    0
l2_asize                        4    0
l2_hdr_size                     4    0
memory_throttle_count           4    0
memory_direct_count             4    0
memory_indirect_count           4    0
memory_all_bytes                4    16633753600
memory_free_bytes               4    8671588352
memory_available_bytes          3    8411688960
arc_no_grow                     4    0
arc_tempreserve                 4    0
arc_loaned_bytes                4    0
arc_prune                       4    0
arc_meta_used                   4    503275576
arc_meta_limit                  4    6237657600
arc_dnode_limit                 4    623765760
arc_meta_max                    4    509194840
arc_meta_min                    4    16777216
async_upgrade_sync              4    3864
demand_hit_predictive_prefetch  4    33669
demand_hit_prescient_prefetch   4    0
arc_need_free                   4    0
arc_sys_free                    4    259902400
arc_raw_size                    4    0
```

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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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