1.3 Unbreakable Enterprise Kernel Release 3

1.3.1 Notable New Features of UEK R3

The Unbreakable Enterprise Kernel Release 3 (UEK R3) is based on the upstream kernel 3.8.13 stable source tree. For more information about UEK R3, see the Oracle Linux Unbreakable Enterprise Kernel Release 3 Release Notes.

A very large number of changes have taken place in mainline Linux between 3.0.x, on which UEK R2 is based, and 3.8.13, on which UEK R3 is based. For details of all these changes, see the kernel change logs that the Linux Kernel Newbies maintain at http://kernelnewbies.org/LinuxVersions.

1.3.1 Notable New Features of UEK R3

UEK R3 includes the following major improvements over UEK R2:

  • Integrated DTrace support in the UEK R3 kernel and user-space tracing of DTrace-enabled applications.

  • Device mapper support for an external, read-only device as the origin for a thinly-provisioned volume.

  • The loop driver provides the same I/O functionality as dm-nfs by extending the AIO interface to perform direct I/O. To create the loopback device, use the losetup command instead of dmsetup. The dm-nfs module is not provided with UEK R3.

  • Btrfs send and receive subcommands allow you to record the differences between two subvolumes, which can either be snapshots of the same subvolume or parent and child subvolumes.

  • Btrfs quota groups (qgroups) allow you to set different size limits for a volume and its subvolumes.

  • Btrfs supports replacing devices without unmounting or otherwise disrupting access to the file system.

  • Ext4 quotas are enabled as soon as the file system is mounted.

  • TCP controlled delay management (CoDel) is a new active queue management algorithm that is designed to handle excessive buffering across a network connection (bufferbloat). The algorithm is based on for how long packets are buffered in the queue rather than the size of the queue. If the minimum queuing time rises above a threshold value, the algorithm discards packets and reduces the transmission rate of TCP.

  • TCP connection repair implements process checkpointing and restart, which allows a TCP connection to be stopped on one host and restarted on another host. Container virtualization can use this feature to move a network connection between hosts.

  • TCP and STCP early retransmit allows fast retransmission (under certain conditions) to reduce the number of duplicate acknowledgements.

  • TCP fast open (TFO) can speed up the opening of successive TCP connections between two endpoints by eliminating one round time trip (RTT) from some TCP transactions.

  • The TCP small queue algorithm is another mechanism intended to help deal with bufferbloat. The algorithm limits the amount of data that can be queued for transmission by a socket.

  • The secure computing mode feature (seccomp) is a simple sandbox mechanism that, in strict mode, allows a thread to transition to a state where it cannot make any system calls except from a very restricted set (_exit(), read(), sigreturn(), and write()) and it can only use file descriptors that were already open. In filter mode, a thread can specify an arbitrary filter of permitted systems calls that would be forbidden in strict mode. Access to this feature is by using the prctl() system call. For more information, see the prctl(2) manual page.

  • The OpenFabrics Enterprise Distribution (OFED) 2.0 stack supports the following protocols:

    • SCSI RDMA Protocol (SRP) enables access to remote SCSI devices via remote direct memory access (RDMA)

    • iSCSI Extensions for remote direct memory access (iSER) provide access to iSCSI storage devices

    • Reliable Datagram Sockets (RDS) is a high-performance, low-latency, reliable connectionless protocol for datagram delivery

    • Sockets Direct Protocol (SDP) supports stream sockets for RDMA network fabrics

    • Ethernet over InfiniBand (EoIB)

    • IP encapsulation over InfiniBand (IPoIB)

    • Ethernet tunneling over InfiniBand (eIPoIB)

    The OFED 2.0 stack also supports the following RDS features:

    • Async Send (AS)

    • Quality of Service (QoS)

    • Automatic Path Migration (APM)

    • Active Bonding (AB)

    • Shared Request Queue (SRQ)

    • Netfilter (NF)

  • Paravirtualization support has been enabled for Oracle Linux guests on Windows Server 2008 Hyper-V or Windows Server 2008 R2 Hyper-V.

  • The Virtual Extensible LAN (VXLAN) tunneling protocol overlays a virtual network on an existing Layer 3 infrastructure to allow the transfer of Layer 2 Ethernet packets over UDP. This feature is intended for use by a virtual network infrastructure in a virtualized environment. Use cases include virtual machine migration and software-defined networking (SDN).

Note

The kernel version in UEK R3 is based on the mainline Linux kernel version 3.8.13. Low-level system utilities that expect the kernel version to start with 2.6 can run without change if they use the UNAME26 personality (for example, by using the uname26 wrapper utility, which is available in the uname26 package).

For more information about the new functionality that UEK R3 provides, see the Oracle Linux Unbreakable Enterprise Kernel Release 3 Release Notes.