Online documentation for zfs kernel module tuning is out of date

[stuartthebruce]

System information

Type	Version/Name
Distribution Name	Rocky Linux
Distribution Version	9.5
Kernel Version	5.14.0-503.34.1.el9_5.x86_64
Architecture	x86_64
OpenZFS Version	2.3.1

Describe the problem you're observing

Online documentation at https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html is out of date. It also doesn't indicate what old version of ZFS it corresponds to, or how to select a specific version.

Describe how to reproduce the problem

Browse to https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html#zfs-arc-max and note,

However, recent releases like 2.3.1 appear to have switched Linux to use the previous FreeBSD algorithm, which is noted in the release bundled man pages, e.g.,

[root@ldas-pcdev15 ~]# man 4 zfs | grep -A8 zfs_arc_max
     zfs_arc_max=0B (u64)
             Max size of ARC in bytes.  If 0, then the max size of ARC is determined by the amount of sys‐
             tem memory installed.  The larger of all_system_memory - 1 GiB and 5/8 × all_system_memory
             will be used as the limit.  This value must be at least 67108864B (64 MiB).

             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.

and in the online man pages at https://openzfs.github.io/openzfs-docs/man/v2.3/4/zfs.4.html#zfs_arc_max

[gmelikov]

You're right, it's a long-standing issue openzfs/openzfs-docs#491 , unfortunately this doc is totally hand-made, I dream to make some check-params script for it, but not sure when I'll get to this.