Linux Weather Forecast

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Welcome to the Linux Weather Forecast

This page is an attempt to track ongoing developments in the Linux development community that have a good chance of appearing in a mainline kernel and/or major distributions sometime in the near future. Your "chief meteorologist" is Jonathan Corbet, Executive Editor at If you have suggestions on improving the forecast (and particularly if you have a project or patchset that you think should be tracked), please add your comments to the Discussion page. There's a blog that reports on the main changes to the forecast. You can view it directly or use a feed reader to subscribe to the blog feed. You can also subscribe directly to the changes feed for this page to see feed all forecast edits.

Forecast Summaries

Current conditions: the 3.14 kernel was released on March 30, 2014.  It contains quite a few new features, including:

  • User-space lockdep makes the kernel's advanced tools for lock debugging available to user-space programs.
  • The Android ION memory allocator has been merged; this was, by far, the largest chunk of Android code that remained outside of the mainline kernel.
  • Event triggers enhance the tracing subsystem with a trigger mechanism allowing users to more easily zero in on the time when something interesting is happening.
  • Networking performance should be improved with the addition of "TCP autocorking" (a way of delaying small packets briefly to allow them to be coalesced with others), the "heavy hitter filter" for traffic scheduling, and the "Proportional integral controller enhanced" scheduler which takes aim at bufferbloat problems.

This development cycle featured the work of over 1400 developers who contributed 12,311 changes.  See this article for details on where the contributions to 3.14 came from.  As always, the KernelNewbies 3.14 page contains lots of details about the release itself.

Short-term forecast: the 3.15 kernel can be expected around the end of May.  Features that have been merged for this release include:

  • A significant memory management change can be found in the form of the active/inactive list balancing patch set.  For some workloads, this work should significantly reduce paging traffic, improving performance.
  • There is a new system call called renameat2().  It allows the addition of advanced features to the file rename operation; its original reason for existence is to allow two files to be atomically exchanged for each other.
  • File-private POSIX locks provide improved file locking semantics while remaining mostly compatible with standard POSIX locks.

As of this writing, the 3.15 development cycle looks to be one of the busiest ever.  Despite the large patch volume, though, the list of significant new features is relatively short; a great deal of the work this time is (as usual) dedicated to internal cleanups, additional hardware support, and changes aimed at supporting long-term improvement plans.

Longer-term forecasts

As with the weather, there are no certainties about what may be merged into the Linux kernel going forward; every change is evaluated on both its merits and its long-term maintenance costs.  Here are a few things on the horizon that are worth watching, though.

The Android kernel patches.  There has been much gnashing of teeth about the out-of-tree Android patches over the years.  At this point, though, the bulk of that code has been merged upstream.  In some cases, including the infamous wakelocks, an alternative solution was developed upstream and Android has migrated over to it.  The biggest remaining piece is the ION memory allocator; that code has now found its way into the staging tree for the 3.14 release. 

The Btrfs filesystem is taking longer than anybody might have liked to reach production readiness, but things are getting closer.  Important features, like RAID5/6 support have been merged, and bugs are being squashed.  We may well see at least one major distribution adopt Btrfs by default in 2014.

Control groups are the mechanism by which the kernel gathers processes into hierarchical groups; it can then apply policies and resource usage limits to those groups.  This feature remains under intensive development, and a lot of changes can be expected over the course of the next year.  See this article for a description of some of the ongoing issues in this area.

NUMA scheduling.  Non-uniform memory access (NUMA) machines will only perform well if running processes and their memory are kept on the same nodes; otherwise the cross-node memory accesses will slow things down considerably.  NUMA scheduling performance on Linux is not as good as users think it should be.  The good news is that quite a bit of development effort has gone into solving this problem over the course of the last year.  The 3.9 kernel included some new infrastructure, and 3.13 includes a much improved scheduler for NUMA systems.

Power-aware scheduling.  On systems with multiple cores (and even cellphones are multi-core these days), quite a bit of power savings can be had by shutting down CPUs when they are not needed.  Overly aggressive powering down can make things worse, though, so care is needed.  There are several patch sets out there, but there are still significant disagreements over how this problem should be solved.  That said, expect significant progress in this area in the 2014 time frame.



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