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Linux Kernel 4.9 Released

Honglin Su
Sr. Director of Product Management

Linux Kernel 4.9, "the biggest release we've ever had",  was recently announced by Linus Torvalds. With more than 200 companies contributing to the Linux Kernel 4.9 release, Oracle is one of the top enterprise employers and contributed 14,425 lines of code in the 4.9 release. Oracle's strong support of Linux is evidenced by our numerous, on-going technical contributions to the Linux community.

Among the extensive list of features and enhancements in the Linux Kernel 4.9, here are a few that are noteworthy:

  • The XFS filesystem has gained support for shared extents — ranges of file data that can be shared between multiple owners — and a copy-on-write mechanism to manage modifications to those extents. That, in turn, allows XFS to support copy_file_range() along with other nice features like reflink and data deduplication.
  • SELinux now has support for overlay filesystems to secure container deployments.
  • Xen features and fixes such as switching to new CPU hotplug mechanism and support driver_override in pciback.
  • The virtually mapped kernel stacks work has been merged. This changes how kernel stacks are implemented on the x86 architecture, allowing the kernel to detect stack overflows and respond accordingly for improved security and better diagnostic output.
  • The system calls for the memory protection keys available on new Intel processors have been merged. These are a user-controllable, coarse-grained protection mechanism, allowing a program to deny certain types of access to ranges of memory. 
  • new set of resource limits has been added to control how many namespaces may be created within any given user namespace. The primary purpose of these limits is to stop programs that malfunction and attempt to create a huge number of objects before the malfunction becomes a system-wide problem.
  • The perf tool can break a function down to "basic blocks" and track events on each.
  • The NFS server now supports the NFS4.2 COPY operation, allowing file data to be copied without traveling to the client and back.
  • The build system can also perform dead code and data elimination. This option is potentially hazardous, since, without some extra effort, the linker may see some needed code as being dead, but it can also reduce the resulting image size considerably.
  • A new set of files under /sys/kernel/irq describe the interrupt lines on the system. They are a replacement for /proc/interrupts and are meant to be easier for programs to parse.
  • The bottleneck bandwidth and RTT (BBR) congestion control algorithm has been merged to get better results in a network characterized by wireless links, meddling middleboxes, and bufferbloat.
  • The netfilter module supports a new "quota" mechanism designed to enable the enforcement of byte quotas. There's also a new random-number generation module intended to enable the random distribution of packets (across multiple queues, for example).
  • The filesystems in user space (FUSE) module now support POSIX access-control lists.
  • The hardware latency tracer (which seeks to flush out latencies caused by the hardware itself) has moved into the mainline from the realtime tree. The tracer hwlat_detector is a special purpose tracer that is used to detect large system latencies induced by the behavior of certain underlying hardware or firmware, independent of Linux itself.
  • The watchdog subsystem has a new "pretimeout" mechanism to allow the system to respond just prior to the expiration of a timer. Two new "governors" are provided; one simply prints a log message, while the other will panic the system in the goal of generating more useful information for debugging the problem.
  • Read the announcement from Linus Torvalds for a full list of changes merged into the Linux Kernel 4.9.

We do upstream Linux Kernel development with enhancements that benefit Oracle Database, middleware, applications and hardware, as well as our broad partner ecosystem. These enhancements are distributed to customers through the Unbreakable Enterprise Kernel for Oracle Linux. Some of the innovations from upstream may come sooner into an enterprise Linux distribution such as Oracle Linux. You can read the recent announcement about the Unbreakable Enterprise Kernel Release 4 for Oracle Linux 6 and Oracle Linux 7.

For more information about Oracle Linux and Virtualization, visit oracle.com/linux.

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