Linux Weather Forecast
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 LWN.net. 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.
Current conditions: The 3.15 kernel was released on June 8. Some of the more significant changes in this release include:
- The latency tolerance subsystem allows for better power management of power-aware peripheral devices.
- 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.
- Resume-from-suspend performance has been greatly improved over previous releases; see this article for a description of how this improvement was achieved.
With 13,722 non-merge changesets pulled into the mainline, 3.15 was the busiest development cycle in the history of the Linux kernel.
Short-term forecast: the 3.16 kernel can be expected sometime around the end of July or the beginning of August. Changes merged for this release include:
- The multiqueue block layer code continues to improve; with 3.16, it has been deemed to be "feature-complete and performant." This code will greatly improve the performance of block I/O, especially on larger systems; see this article for more information.
- The remap_file_pages() system call has been marked as deprecated, with an eye toward its eventual removal. If there are application developers out there who are making use of remap_file_pages(), they should make their needs known in the near future.
- The unified control group hierarchy code has been merged. This work changes the way control groups work, making them easier to manage and more maintainable over the long term.
3.16 included a notable change from previous development cycles: the merge window for this release was opened one week prior to the final 3.15 release. This change was made to suit Linus Torvalds's travel schedule and may not be repeated in the future, but it could also foreshadow more parallel development and faster release cycles in the future.
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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