The two main items from the first EXT4 merge for Linux 3.12 include:
- Support for aggressive extent caching using the extent status tree. For end-users, Ted says this can lead to less memory usage for read-mostly workloads and improvements to asynchronous I/O.
- Improved recovery after corrupted allocation bitmaps when using the errors=ignore mount option.
There's also many other bug-fixes and other changes to find with this EXT4 file-system update for the Linux 3.12 kernel.