This release includes support for Ext4 block sizes bigger than 4KB and up to 1MB, which improve performance with big files; btrfs has been updated with faster scrubbing, automatic backup of critical filesystem metadata and tools for manual inspection of the filesystems; the process scheduler has added support to set upper limits of CPU time; the desktop reponsiveness in presence of heavy writes has been improved, TCP has been updated to include an algorithm which speeds up the recovery of the connection after lost packets; the profiling tool "perf top" has added support for live inspection of tasks and libraries and see the annotated assembly code; the Device Mapper has added support for 'thin provisioning' of storage, and a new architecture has been added: the Hexagon DSP processor from Qualcomm. Other drivers and small improvements and fixes are also available in this release.

More detail can be read at KernelNewbies.org