Alternative kernel trees [LWN.net]

Much attention is paid to official kernel releases from Linus and Marcelo. There are, however, a number of other kernel trees out there, many of which offer different views of how the kernel should be or where its development should go. It has been a while since we've looked at the alternative kernel trees which are currently being maintained, so it is a good time for an update. We'll start with the 2.6-based trees.

Andrew Morton's -mm tree (currently at 2.6.0-test6-mm4) remains the largest staging area for code headed toward the mainline. The -mm kernels give big patches a place where they can be examined and tested without breaking the mainline kernel. This tree currently contains, beyond lots of fixes, a full set of kgdb patches, the current versions of the must-fix and should-fix lists, a bunch of VFS work from Al Viro (aimed at making hot removal of disks work properly), the CFQ disk I/O scheduler, Intel MSI and EFI support, the 4G/4G large memory patch, a lot of direct and asynchronous I/O work, and a patch called "support-zillions-of-scsi-disks."

Stephen Hemminger recently released 2.6.0-test6-osdl1. This relatively small patch has been reborn; it now concerns itself with features that will be merged after the 2.6.0 release, if ever. Thus, it includes a patch adding file extents to ext3, Ingo Molnar's ExecShield, the Linux kernel crash dump facility, the kexec system call, and a few others.

Martin Bligh continues to release occasional -mjb kernels; the latest is 2.6.0-test6-mjb1. These kernels have "mainly scalability and NUMA stuff, and anything else that stops things from irritating me." The patch currently includes a configuration option for the internal clock speed, a number of tunable parameters for the scheduler, the lockmeter patch, the object-based reverse mapping patch, and a number of NUMA-related patches.

Randy Dunlap posts an occasional -kj tree; 2.6.0-test6-kj1 was released on September 29. This is not the tree for people seeking exciting new features; its purpose is to serve as a collection area for janitorial patches that might otherwise fall through the cracks.

Alan Cox's departure from the kernel scene has left a large hole where his 2.4-base -ac tree used to be. Many distributors based their stock kernels on something close to Alan's tree. The -ac tree has technically been taken over by Bernhard Rosenkraenzer, but his last release was 2.4.23-pre4-pac2 on September 17.

Andrea Arcangeli has, of late, started announcing more of his -aa trees to the world. His latest (2.4.23pre6aa2) includes a new "desktop" boot parameter which sets several options for optimal desktop performance, run-time configurable internal clock speed, some virtual memory work, the TUX HTTP server, kgdb, the 2.6 "futex" feature, XFS version 13, Jens Axboe's "laptop mode" patch, and many others. Andrea plans to include Jeff Garzik's "libata" disk drivers soon.

James Bourne maintains a "-uv" patch series which is limited to compilation and security fixes for the current stable kernel. The latest is 2.4.22-uv2.