tunables: remove legacy FreeBSD aliases

[robn]

Motivation and Context

These are old pre-OpenZFS tunable names that have long been available via either conventional ZFS_MODULE_PARAM tunables or through kstats. It seems there's no point doubling up on them after so many years, and it's time for them to go.

I'd love an old FreeBSD hand or two to look over them though. FreeBSD generally doesn't churn much, so it wouldn't surprise me if there is critical code and documentation that relies on these to remain. I'm in no hurry to nuke anything in use; on the contrary, I'd like to find out and make sure it's properly documented and tested on our side. So please review this!

Description

Here's the list of names removed, with their "new" names on the right:

old tunable name (removed)	available as
vfs.zfs.arc_max	vfs.zfs.arc.max
vfs.zfs.arc_min	vfs.zfs.arc.min
vfs.zfs.arc_free_target	vfs.zfs.arc.free_target
vfs.zfs.arc_no_grow_shift	vfs.zfs.arc.no_grow_shift
vfs.zfs.l2arc_write_max	vfs.zfs.l2arc.write_max
vfs.zfs.l2arc_write_boost	vfs.zfs.l2arc.write_boost
vfs.zfs.l2arc_headroom	vfs.zfs.l2arc.headroom
vfs.zfs.l2arc_headroom_boost	vfs.zfs.l2arc.headroom_boost
vfs.zfs.l2arc_feed_secs	vfs.zfs.l2arc.feed_secs
vfs.zfs.l2arc_feed_min_ms	vfs.zfs.l2arc.feed_min_ms
vfs.zfs.l2arc_noprefetch	vfs.zfs.l2arc.noprefetch
vfs.zfs.l2arc_feed_again	vfs.zfs.l2arc.feed_again
vfs.zfs.l2arc_norw	vfs.zfs.l2arc.norw
vfs.zfs.zfetch.max_distance	vfs.zfs.prefetch.max_distance
vfs.zfs.zfetch.max_idistance	vfs.zfs.prefetch.max_idistance
vfs.zfs.remove_max_segment	vfs.zfs.vdev.remove_max_segment
vfs.zfs.removal_suspend_progress	vfs.zfs.vdev.removal_suspend_progress
vfs.zfs.min_auto_ashift	vfs.zfs.vdev.min_auto_ashift
vfs.zfs.max_auto_ashift	vfs.zfs.vdev.max_auto_ashift
vfs.zfs.validate_skip	vfs.zfs.vdev.validate_skip
vfs.zfs.top_maxinflight	vfs.zfs.vdev.max_active

old stat name (removed)	available as
vfs.zfs.anon_size	kstat.zfs.misc.arcstats.anon_size
vfs.zfs.anon_metadata_esize	kstat.zfs.misc.arcstats.anon_evictable_metadata
vfs.zfs.anon_data_esize	kstat.zfs.misc.arcstats.anon_evictable_data
vfs.zfs.mru_size	kstat.zfs.misc.arcstats.mru_size
vfs.zfs.mru_metadata_esize	kstat.zfs.misc.arcstats.mru_evictable_metadata
vfs.zfs.mru_data_esize	kstat.zfs.misc.arcstats.mru_evictable_data
vfs.zfs.mru_ghost_size	kstat.zfs.misc.arcstats.mru_ghost_size
vfs.zfs.mru_ghost_metadata_esize	kstat.zfs.misc.arcstats.mru_ghost_evictable_metadata
vfs.zfs.mru_ghost_data_esize	kstat.zfs.misc.arcstats.mru_ghost_evictable_data
vfs.zfs.mfu_size	kstat.zfs.misc.arcstats.mfu_size
vfs.zfs.mfu_metadata_esize	kstat.zfs.misc.arcstats.mfu_evictable_metadata
vfs.zfs.mfu_data_esize	kstat.zfs.misc.arcstats.mfu_evictable_data
vfs.zfs.mfu_ghost_size	kstat.zfs.misc.arcstats.mfu_ghost_size
vfs.zfs.mfu_ghost_metadata_esize	kstat.zfs.misc.arcstats.mfu_ghost_evictable_metadata
vfs.zfs.mfu_ghost_data_esize	kstat.zfs.misc.arcstats.mfu_ghost_evictable_data
vfs.zfs.uncached_size	kstat.zfs.misc.arcstats.uncached_size
vfs.zfs.uncached_metadata_esize	kstat.zfs.misc.arcstats.uncached_evictable_metadata
vfs.zfs.uncached_data_esize	kstat.zfs.misc.arcstats.uncached_evictable_data
vfs.zfs.l2c_only_size	kstat.zfs.misc.arcstats.l2_size

Note that there's still a handful of tunables in module/os/freebsd/zfs/sysctl_os.c that don't have "core" counterparts; those remain for the moment. I also haven't touched vfs.zfs.debugflags even though vfs.zfs.flags exists, because I think the former is a little smarter. I'll sort all these out another time.

How Has This Been Tested?

ZTS run in progress on FreeBSD 14.2-p1.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[amotin]

Appears even CI itself uses some. We need to update tunables.cfg.

[robn]

Huh, thanks. I need to fix my test rig some then, because it didn't throw those up (I mean yeah, the CI did, but I hadn't got into that yet). Cheers :)

[amotin]

I've just fixed couple things (systat and top) in FreeBSD base still using old names: https://cgit.freebsd.org/src/commit/?id=8aad1e6148d3389df100bb0391e2d3a909f26ecf .

[behlendorf]

I can't really comment on if the old names are still used anywhere, but the change itself looks good. Now would be the time to drop them before the 2.4 release.

[behlendorf]

Once https://cgit.freebsd.org/src/commit/?id=8aad1e6148d3389df100bb0391e2d3a909f26ecf lands we can go ahead and merge this.

[amotin]

Once https://cgit.freebsd.org/src/commit/?id=8aad1e6148d3389df100bb0391e2d3a909f26ecf lands we can go ahead and merge this.

@behlendorf It is in FreeBSD main already, and I'll merge it into stable branches tomorrow. Hope I'll be allowed to merge it into upcoming 14.3.

PS: Merged.

[robn]

@amotin thanks for doing that!

I asked on socials and a couple of people pointed out that they have various old-style tunables set in various boot configs and such, so I'd like to stick this on hold for a moment while I go and find the right FreeBSD people to get some advice. We might be better to provide aliases or deprecation warnings, or FreeBSD might prefer to patch it themselves, or maybe it just gets documented around for 15. I still want to do this, but I don't wanna be a jerk and surprise anyone. So I've put the "blocked" tag on this, and I'll let you know what the plan is as soon as I can.