Reiser4 File-System Port Updated For The Linux 5.1 + Linux 5.2 Kernels
Bringing Reiser4 to the Linux 5.1 kernel required various changes to the block layer's interface while porting to Linux 5.2 required some additional block layer interface changes. The Linux 5.2 version also has one additional bug fix as well.
Those interested in trying Reiser4 on top of a Linux 5.x kernel can find the patches via SourceForge.
As it stands now, there hasn't been any effort in recent years for trying to get Reiser4 mainlined in the Linux kernel. Reiser4 these days also faces as much competition as ever from the likes of Btrfs, F2FS, Bcachefs, and ZFS On Linux compared to the days when it was started by notorious kernel developer Hans Reiser.