LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090702.mp3

For Thursday, July 2nd 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: cgroups, kmemleak, OOM, VFAT, and the return of the Zero Page.

Cgroups. Paul Menage posted an RFC patch series intended to add Hierarchy Extensions to Cgroups. With the patch series applied, one gets named cgroup hierarchies, cgroup hieracrchies with no bound subsystems, and cgroup subsystems that be bound to multiple hierarchies. A number of example use cases are included in the patch series which contains a total of 9 patches.

Kmemleak. In an effort to reduce false positive warnings, Catalin Marinas posted a patch that would better handle objects allocated during a kmemleak scan. With the patch applied, kmemleak will check to see if an allocation happened after it began scanning a list. If so, it will re-scan the list again and repeat the allocation test before reporting any problems. If the system is simply too busy to never scan the list without it changing kmemleak gives up after a certain number of passes (25 in the posted patch). With these patches applied (and perhaps some others also – it was not specified which), Catalin is finding a lot of reports of iwlwifi leaking memory and is not sure whether these reports are still noise, or a legimate bug that needs some attention. Catalin adds “I’m not familiar with this code so any help is greatly appreciated”. Perhaps someone will help take a look at that driver.

OOM. Minchan Kim followed up to the ongoing debate about why exactly a specific patch (intended to affect only non-swap machines) had caused so many OOM-type of situation, with a theory that the patch actually improved performance of page reclaim to the point where the specific tests being used would subsequently expose the system to a fork bomb. Minchan contended that David Howells had merely been “lucky” in his previous use of an unnecessary routine and informed us that Rik van Riel is currently working on a throttling version of page reclaim which should help.

VFAT. Discussion continues about the VFAT implementation. James Bottomley and Alan Cox had a debate concerning the ways in which vendors do and do not carry patches out-of-tree. Alan’s point was largely that vendors always carry patches regardless of the wishes of the kernel community, so one more isn’t a big deal, whereas James counter-argued that this went against the general notion that the kernel community was against long-lived out-of-tree bits. James defended the involvement of the Linux Foundation against what he described as “conspiracy theories” of anything more sinister going on. Later, Jan Engelhardt, Ted T’so, and Andrew Tridgell had a dialog concerning a number of devices Jan had found that broken when given filesystems modified using the various VFAT patches currently going around.

Zero Page (again). Kamezawa Hiroyu posted concerning the removal (in 2.6.24, back in October of 2007) of zero page support (essentially allowing things like sparse unbacked array allocations in userspace that are otherwise contiguous), noting that many customers and users of his haven’t really noticed that it was removed because they’re still using kernels like the 2.6.18 kernel in Red Hat Enterprise Linux 5. Recently, he has also seen an uptick in intentional users of zero page (to which Avi Kivity later added KVM in terms of its migration process) and so suggests a re-implementation that fixes many of the reference-counting and other problems from the old one.

In today’s miscellaneous items: Alek Du posted version 2 of his GPIO driver for Intel Moorestown, Catalin Marinas experienced a problem fixing an issue with kmemleak in which piped reads from the kmemleak debugfs interface would result in a lock being held on return to userspace, fread later, but obviously generating a warning from the lockdep. Gregory Haskins posted version 9 of his irqfd patch series, including fixes and rebasing on a more recent KVM. Justin P. Mattock posted a bunch of SELinux updates (some labeled “non-trivial”, some simply typos and things of that nature), Vivek Goyal posted version 6 of his IO Scheduler based IO Controller patches (including mostly split out patches and some fixes), Doug Graham posted (with a Nortel address), a V3 Minix filesystem fix for big endian systems (or those with >64K inodes) – turns out someone does still use Minix – and several other generic fixes, Venkatesh Pallipadi posted some fixes to Dave Jones for cpufreq lockdep warnings, James Bottomley posted a small number of SCSI fixes against 2.6.31-rc1, Jonathan Cameron posted version 4 of his Industrial I/O Subsystem patches (which seem to include yet another ring buffer implementation? I didn’t check yet), Alan Cox followed up to Lennart Poettering’s previous VT_WAITACTIVE patch with a more generic event interface for Virtual Terminals, and Chris Mason posted a series of btrfs updates (mostly small bug fixes, but also a first step toward snapshot deletion from Yan Zheng), intended to still make it into 2.6.31-rc2.

Finally today. Kumar Gala posted asking Alan Cox if he had some good examples of users of the tty later to use as a reference in bringing an out-of-tree serial driver for the Avocent ESP-16 MI Serial Hubs (serial over Ethernet) up to scratch for mainline inclusion.

In today’s announcements: Karel Zak posted RC2 of util-linux-ng v2.16. It includes the moving of the libuuid library from e2fsprogs into util-linux-ng. Kay Sievers noted that it fails to build in a clean chroot due to an install hook hack that moves some files around during the build. And Jaswinder Singh Rajput helpfully mailed a number of people concerning various feature removal dates that were previously committed to and have lapsed or are pending. At least one of these reminders has resulted in the related feature being killed by a subsequent patch, and will hopefully lead others to contemplate likewise.

Ryo Tsuruta announced the IO Controller Mini-Summit in Japan in October, which will immediately precede the Linux Kernel Summit. This is an event that was hinted at previously, although details remain “sketchy” and it’s not entirely sure who will be there at this time.

The latest kernel release is 2.6.31-rc1, which was released by Linus last week.

Andrew Morton posted an mm-of-the-moment for 2009-07-02-19-57. Meanwhile, various users of the previous mm-of-the-moment have reported a few glitches.

Greg Kroah-Hartman announced releases 2.6.27.26, 2.6.29.6, and 2.6.30.1 of the kernel. He strongly encourages users to upgrade, and notes that the .29 update will be the last so users should migrate to 2.6.30 as soon as possible.

Stephen Rothwell posted a linux-next tree for July 2nd. Since Wednesday, the “sfi” tree is still dropped, the tree still hates powerpc allyesconfig, and several conflicts went away also. The total sub-tree count in the latest compose stands at a respectible 132 trees.

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