As Konstantin Belousov recently posted on the mailing lists (https://lists.freebsd.org/pipermail/freebsd-fs/2017-April/024684.html) the 64-bit inode (ino64) patch is ready for testing and review.
Further details on the ino64 project and instructions for testing and applying the patch can be found in the mailing list posting at the link above.
Inodes are data structures corresponding to objects in a file system, such as files and directories. FreeBSD has historically used 32-bit values to identify inodes, which limits file systems to somewhat under 2^32 objects. Many modern file systems internally use 64-bit identifiers and FreeBSD needs to follow suit to properly and fully support these file systems.
Further details on the ino64 project and instructions for testing and applying the patch can be found in the mailing list posting at the link above.