The Btrfs file-system update for Linux 4.2 includes sub-volume quota updates, sysfs improvements, device management improvements, and various other changes. In total around 1,700 lines of Btrfs code were touched for this merge window.
More details via this pull request. As always, over at LinuxBenchmarking.com are daily, automated performance tests of the latest mainline Git kernel code across numerous subsystems -- there's several systems in the farm that are happily running with Btrfs for their root file-system. We'll also have our usual concise file-system tests on Phoronix.com as the Linux 4.2 release nears in the weeks ahead.