LKML Summary Podcast

Audio: COMING SOON

For Thursday, September 24th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Checkpoint and restart, ksplice, and RAID.

Checkpoint and restart. Oren Laadan posted 80(!) patches implementing the latest “checkpoint and restart” code for the Linux kernel. The first 17 patches are cleanups, patch 18 adds the new system calls, while the remainder contain the actual “checkpoint and restart” (also refered to as “c/r”) code. Patch 32 contains an implementation for “deferqueue”, which is similar to workqueues but allows a process to defer work that will run in the original context of the task that scheduled it. So far, the code can checkpoint and restart interactive sessions of “screen” across a kernel reboot, which is useful for testing, but a far cry from a full implementation useful for the majority of users.

Ksplice. Tim Abbott (ksplice author extrodinaire) and Christoph Hellwig had a back and forth concerning the (currently) out-of-tree ksplice use of the each_symbol export, which was apparently originally exported for use by ksplice. A recent patch (part 3 of a 4 part patch series) from Christoph had removed that export (it was entitled “module: unexport each_symbol()) and Tim would really have prefered that it stick around. In response, Christoph sent a one line reply: “We don’t keep symbols for out of tree junk around.” Rusty Russell (the in-kernel module loader infrastructure maintainer) stated that he had expected ksplice to go in earlier and had originally applied the patch to make life easier for the eventual merge. But, in his words, “it’s a big hunk of code” [so it might not get merged in the 2.6.32 timeframe, either]. Separately, Tim sent some more linker script cleanups for ksplice preparation.

RAID. Discussion continued (in the thread entitled: “DRBD for 2.6.32″) concerning the eventual removal of the older “md” code once unification between the various in-kernel (md/dm) RAID implementations is complete. Neil Brown thought this process ought to take about 3-5 years, given the average time frame for “enterprise” releases of the kernel. Neil also suggested that the unification effort hadn’t really gotten under way yet, that there was little notion of what shape such an implementation might take, and that it might make more sense to spend time discussing that than the relative merits of merging DRBD into the 2.6.32 kernel. Fujita Tomonori pointed out some previous comments (from Christoph Hellwig) on what a new userspace visible API for RAID management might look like, on the DRBD development list.

In today’s pull requests: some bugfixes for the security subsystem from James Morris, round 2 of some hwmon updates for 2.6.32 from Jean Delvare, some md updates for 2.6.32 from Neil Brown (essentiall a ping reminder to pull), some microblaze fixes for 2.6.32 from Michal Simek, an update to the cputime tree maintained by Martin Schwidefsky (correcting the format of /proc/uptime), some module and parameter updates for 2.6.32 from Rusty Russell, some btrfs updates for 2.6.32 from Chris Mason (including various work on snapshot and subvolume deletion from Yan Zheng – and the btrfs worker threads are now more dynamic as they will die in order to be later respawned if they are not used for a while), some drm-intel updates for 2.6.32 from Eric Anholt, some MAINTAINERS cleanups from Joe Perches, some infiniband updates from Roland Dreier, version 2 of tracepoints for uses of the BKL (Big Kernel Lock) useful in detecting and removing such uses as the BKL is slowly being removed from Frederic Weisbecker (to which Ingo Molnar later noted some build problems), some cris updates for 2.6.32 from Jesper Nilsson, and some eCryptfs fixes for 2.6.32 from Tyler Hicks.

In today’s miscellaneous items: a patch reducing the overly excessive (one per CPU) “TSC is reliable” and “PAT enabled” messages on boot from Rolan Dreier, an assertion that a previous module loader fix in the usermodehelper code from Neil Horman had been incorrect and was causing another backtrace from Sebastian Andrzej Siewior (he included a replacement patch, which Neil agreed was actually the correct fix), some documentation updates for cgroups tasks and procs files from Paul Menage, some cpumask conversions and obsolescence removal patches from Rusty Russell, a suggestion from Kamezawa Hiroyuki that a new vma->vm_flags2 might be required for the overflow from vm_flags becoming full (in reply to the desire fro, Nigel Cunningham to have some room for TuxOnIce to make use of an additional bit for a status flag), some KVM patches from Zachary Amsden (moving timer initialization into an independent function), a patch from Peter Williams (following up to the previous day’s discussions with Peter Zijlstra on the topic) setting the correct normal_prio and prio values in sched_fork() (fixing some issues where some paths through sched_fork() would ignore this requirement and removing the need for a call to effective_prio() in wake_up_new_task()), a page writeback patch from Shaohua Li that effectively reconciles inode commits from the same filesystem so that they will be written together and reduce rotational media head movement (which was deemed a “Good idea!” by Fengguang Wu and immediately signed off on), an optimization removing an unnecessary call to wbinvd on Intel MP CPUs that support a C3 share cache when entering an C3 ACPI power state, an RFC patch series updating autofs4 to deal with some VFS locking changes from Ian Kent, some AMD64 EDAC fixes from Borislav Petkov, some percpu patches making allocation failure warnings more verbose from Tejun Heo, a patch fixing a buffer allocation problem in the “perf” tools from Eric Dumazet, some “immediate values” patches from Mathieu Desnoyers intending to take advantage of data-cache optimization (to which Jason Baron replied that his alternative “jump label” infrastructure had already been proposed, although Jason seemed to favor various aspects of Mathieu’s patch), a patch allowing “perf timechart” to output only power mode information from Arjan van de Ven, version 7 of the new “clone2″ system call intended to better support checkpoint and restart from Sukadev Bhattiprolu, some memory barrier commentary in the futex_wait_queue_me code from Darren Hart, version 10 of the “IO scheduler based IO controller” patches from Vivek Goyal, another round of “jump label” patches from Jason Baron (obviously prompted by Matheiu Desnoyers’ earlier posting of a – related – “immedate values” implementation), and a note from David Miller that “what’s really sad is that you [refering to Ingo Molnar] don’t attend enough conferences so that you can meet face to face with people and you (and others) would as a result avoid many unnecessary heated discussions as a result” [in the spirit of not becoming the Us Weekly of kernel traffic, I'll leave the rest of the discussion up to you to read].

Finally today, Steven Rostedt (and various others) had a somewhat lengthy discussion about the correct English (grammar) for refering to a mailing list intended for the discussion of user issues pertaining to tracing. Steven’s comment becomes the quote of the day: “Oh God, Linux is now tracing its users, but I don’t want to be traced!”.

In today’s announcements: Greg Kroah-Hartman announced the release of stable kernels 2.6.27.35, 2.6.30.8, and 2.6.31.1. He strongly encourages users of these stable kernels to upgrade.

The latest kernel release was 2.6.31.

Ingo Molnar reported a crash in the -tip tree in ibm_find_acpi_device. Daniel J. Blueman reported an NFS suspend to RAM hang when using an NFS home directory (including the full oops report) on recent kernels. Ed Tomlinson reported a “strange” ATA related freeze with 2.6.31.1-rc1.

Stephen Rothwell posted a linux-next tree for September 24th (a little later than usual). Since Wednesday, the drbd tree has been undropped, the tip tree gained a conflict, the ocfs2, jdelvare-hwmon, block, drbd, battery, and usb lost their conflicts, and Stephen applied a patch for a build failure in Linus’ git tree. The total subtree count is reported as falling to 139 in the latest compose (although that again seems a little out-of-sync). Stephen reminds everyone not to push for 2.6.33 until 2.6.32-rc1 is out.

That’s a summary of today’s Linux Kernel Mailing List traffic, for further information visit www.kernel.org. I’m Jon Masters.