OK, there definitely is a problem with Oracle and btrfs
Database creation with ext4 as a filesystem is MUCH faster, and filesystemio_options do apply without a problem
(Action) really wonders why
It really shows, iowait time is negligible
And filesystemio_options is not even applicable with ext4!
The problem is elsewhere, it seems
Oracle uses too old APIs, maybe
It certainly is since when I select either of these options, there's a syscall by Oracle by which Linux answers -EINVAL