Summary: This version adds two new filesystem, the distributed filesystem Ceph and LogFS, a filesystem for flash devices. Other features are a driver for almost-native KVM network performance, the VMware ballon driver, the "kprobes jump" optimization for dynamic probes, new perf features (the "perf lock" tool, cross-platform analysis support), support for GPU switching, several Btrfs improvements, RCU lockdep, Generalized TTL Security Mechanism (RFC 5082) and private VLAN proxy arp (RFC 3069) support, asynchronous suspend/resume, several new drivers and many other small improvements.
1. Prominent features (the cool stuff)
1.1. Ceph filesystem
Linux-mag article: Ceph: The Distributed File System Creature from the Object Lagoon
IBM Developerworks article: Ceph: A Linux petabyte-scale distributed file system
LWN article: The Ceph filesystem
Ceph is a distributed network filesystem. It is built from the ground up to seamlessly and gracefully scale from gigabytes to petabytes and beyond. Scalability is considered in terms of workload as well as total storage. Ceph is designed to handle workloads in which tens thousands of clients or more simultaneously access the same file, or write to the same directory–usage scenarios that bring typical enterprise storage systems to their knees.
Seamless scaling: A Ceph filesystem can be seamlessly expanded by simply adding storage nodes (OSDs), and proactively migrates data onto new devices in order to maintain a balanced distribution of data.
Adaptive MDS: The Ceph metadata server (MDS) is designed to dynamically adapt its behavior to the current workload. As the size and popularity of the file system hierarchy changes over time, that hierarchy is dynamically redistributed among available metadata servers in order to balance load and most effectively use server resources. Similarly, if thousands of clients suddenly access a single file or directory, that metadata is dynamically replicated across multiple servers to distribute the workload.
Project web site: ceph.newdream.net
Recommended LWN article: LogFS
LogFS is a filesystem designed for storage devices based on flash memory (SDD hard disks, USB sticks, etc). It is aimed to scale efficiently to large devices. In comparison to JFFS2, it offers significantly faster mount times and potentially less RAM usage. In its current state it is still experimental.
Project web site: www.logfs.org
1.3. Vhost net: fast KVM networking
vhost net is a kernel-level backend for virtio networking. The main motivation for vhost is to reduce virtualization overhead for virtio-net by moving the task of converting virtio descriptors to skbs and back from qemu userspace to the vhost net driver. For virtio-net this means removing up to 4 system calls per packet: vm exit for kick, reentry for kick, iothread wakeup for packet, interrupt injection for packet. This was shown to reduce latency by a factor of 5, and improve bandwidth to almost-native performance. Existing virtio net code is used in guests without modification.
Project web site: http://www.linux-kvm.org/page/VhostNet