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 4.0 kernel was released on April 12. Some features merged for this release include:
- Basic support for applying patches to a running kernel, allowing the application of fixes without the need to reboot the system. There is still work to be done to get to a fully featured live-patching system, but the foundation is there in 4.0.
- The remap_file_pages() system call has been removed. Emulation of its functionality remains, though, so applications should not break.
- The kernel's support for large nonvolatile memory devices has improved considerably.
- The lazytime mount option allows for more efficient and accurate tracking of file access times.
- The kernel address sanitizer (KASan) is an important new development tool for ensuring that the kernel is not accessing memory that it shouldn't.
The major-number change for this release does not carry any information other than the 3.x minor numbers were getting too large. In terms of patch volume, 4.0 one of the slowest development cycles for a couple of years. But, as can be seen above, it still includes a number of important new features.
Short-term forecast: the most likely release date for the 4.1 kernel is June 14. As of this writing, the merge window for this release is still open, so the feature set is not yet complete. Features merged thus far include:
- File and directory encryption for the ext4 filesystem. This feature was developed for use with the Android system but should be applicable elsewhere as well.
- Extended BPF functionality in the kernel's "traffic control" subsystem, allowing for a great deal of flexibility in classification and modification of network packets as they move through the system.
- The persistent memory block driver, providing basic access to non-volatile RAM devices.
The merge window should close around April 26; this page will be updated to reflect any other features that are added before then.
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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