`btrfs-qgroup(8)` man page contains (probably) outdated kernel v4.14 era warning

[UserlandAlchemist]

The man page for btrfs-qgroup(8) currently includes the following warning:

warning::
   Qgroup is not stable yet and will impact performance in current mainline
   kernel (v4.14).

This warning appears to be outdated:

• The referenced kernel version (v4.14) was released in 2017 and is no longer supported.
• Quota groups (qgroups) are now widely used in production, and are not marked experimental in any current kernel documentation.
• In fact, this 2022 update to the kernel docs lists "Hierarchical quota groups (subvolume and snapshot support)" as a headline feature of Btrfs.
• The later documentation for qgroups, introduced in commit c6be848 in 2022, has never included such a warning.
• Performance and stability considerations of quota usage more generally are already described in btrfs-quota(8).

If the warning is still relevant to certain workloads or older kernels, a clarifying update indicating which kernels for which it still applies might help. If not, I’d be happy to follow up with a PR to remove it.

Thanks for your work maintaining btrfs-progs.