LWN.net has posted this week's

In recent O(1) scheduler releases, an optimization was made that removed schedule_tail from UP kernels. This causes the initial preempt_count of a new task, which starts at 1, to never decrement to zero and thus never become preemptible. Users of 2.4+O(1)+preempt (i.e. -ac) should use this patch.

Alan has added the O(1) scheduler to his -ac branch of 2.4 kernels, saying of the latest 2.4.19-pre2ac1, "This one is a bit more experimental. I've avoided putting too much in so we can see how the O(1) scheduler pans out".

KernelTraffic (a weekly lkml digest) #156 for March 4 is out. get it here

LWN.net has posted the kernel update for this week.

Andrea Arcangeli, the author of the current 2.4 VM, has released 2.4.19pre1aa1. It contains his vm-28 which he hopes to push into the 2.4.19pre kernels. If you're feeling adventurous, download his patches, test it out, and provide Andrea with some feedback...

Alan Cox's infamous -ac tree has been ressurected in recent months, taking in lots of stabalizing patches above and beyond Marcelo's main 2.4 kernel tree. In a recent email to the lkml, he refers to 73 emails he sent to Marcelo, each with a different patch he feels is ready to be merged into the main tree.

Alan's email follows, with the complete changelog. Each patch is preceded by a symbol, indicating the status of this patch:

     + indicates stuff that went to Marcelo
     o stuff that has not
     * indicates stuff that is merged in mainstreem now
     X stuff that proved bad and was dropped out

Marcello released the 2.4.18-final kernel today, then twenty minutes later apologized, "Ok, DAMN. I missed the -rc4 patch in 2.4.18. Real sorry about that". A steady stream of email began flooding the lkml, full of numerous suggestions on how to resolve "the problem". The story was quickly picked up by Slashdot, which only added to the confusion.

In reality, it was nothing more than a relatively minor mistake. 2.4.18-rc4, which quickly followed 2.4.18-rc3 (see this earlier story) included a small patch (to 'fs/binfmt_elf.c') that was then not included in the final 2.4.18. In other words, 2.4.18-final is 2.4.18-rc3, not 2.4.18-rc4 as intended. The missing patch (which you can add yourself here) was a fix for a bug introduced recently, around -pre6, affecting non-x86 ports. In Marcelo's words, "The patch which I missed only breaks static apps on _some_ architectures (not including x86)".

Some of the relevant emails follow, as does the 2.4.19-pre1 changelog. Released today, this -pre patch includes the fix dropped from 2.4.18-final, and many other changes.

Alan Cox released the 2.2.21-pre3 kernel patch today, building toward a targeted final release of the stable 2.2.21 kernel on March 10th. The changelog for this current -pre patch includes a fairly large set of fixes and updates, catching up with a backlog. Alan goes on to point out that -pre4 will include several more important fixes.

Alan's announcement email follows, including the full changelog.

Zack Brown's Kernel Traffic #155 for February 25th is online.

Robert Love posted a small patch to the lkml, providing an i386 only IRQ-safe atomic counter without locks. The conversation that followed between Robert and Andrew Morton is quite interesting, offering a little perspective into the complexities of dealing with multiple processors and the many Linux ports.

Jeff Garzik recently posted a BitKeeper Kernel Hacking HOWTO (titled Doing the BK Thing, Penguin-Style) to the lkml. Now that Linus is using BitKeeper to manage the 2.5 development kernel tree, many other Linux kernel hackers are beginning to use the tool. The HOWTO, a work in progress, provides an excellent overview of BitKeeper, helping a person use the tool to provide patches to Linus. The actual user's guide can be found here.