LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090719.mp3

For the weekend of July 19th 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Fast and fine-grained clock sources, kmemleak, KSM, large disk arrays, and NX kernel data page protections.

Fast and fine-grained clock sources. John Stultz posted an RFC patch discussing the need for CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE clocks. These provide fine-grained timestamps, but only as of the last tick, and therefore save the (possibly very expensive) accessing of hardware. This is especially useful on Real Time systems when used in combination with the non-syscall heavy VDSO. The only real problem I can see is that this likely isn’t covered by any of the POSIX.4 specification(s), and yet exists in the same namespace as the other POSIX-defined clocks.

Kmemleak. Catalin Marinas posted an RFC patch implementing scanning for all kernel thread stacks. This will enhance the existing ability for kmemleak to locate memory leaks by looking for leaking pointers on the kernel stack(s). Catalin also posted a patch protecting kmemleak_seq start/next/stop with a call to rcu_read_lock() since such objects may a freed object reference.

KSM (Kernel Shared Memory). Izik Eidus reposted the KSM patches for consideration. KSM – Kernel Shared Memory – is a patch that aims to reduce the wasted (duplicated) memory footprint of virtual machines by scanning physical RAM pages for identical copies of the same data, replacing them with a single COW page intead, and various accompanying resource tracking. Andrea Arcangeli gave an excellent presentation on KSM at the 2009 Linux Symposium, the proceedings of which are now available. Those interested are encouraged to refer to the paper, and to the postings on the LKML also.

Large disk arrays. Neil Brown posted to point out that 32-bit Linux doesn’t handle devices larger than 16TB particularly well (the page cache is limited to a pgoff_t number of pages for example) and due to the prevelence of large disk devices now, one shouldn’t just assume that only 64-bit systems will have large block devices. Instead, it might be necessary to institute a policy – for example refusing to create devices larger than 16TB on 32-bit Linux.

NX kernel data page protection. Siarhei Liakh posted a patch expanding the functionality of CONFIG_DEBUG_RODATA to add protection for the main (static) kernel data area. The patch modifies several kernel linker scripts such that the kernel .text, .rodata, and .data sections always end on page boundaries.

In today’s miscellaneous items: a tracing fix (Frederic Weisbecker), a post from Barry Song removing the check for IRQ_DISABLED in interrupt thread functions (this appears to be a bad idea, and I’m waiting to see what Thomas says about it – I think it’s better to reconsider the existing code comment), a tracepoint for the timer event (Xio Guangrong), a fix to load average accounting and some tracing fixes (Thomas Gleixner), some lguest and virtio fixes (Rusty Russell), xfs tracing support (Christoph Hellwig), some sound fixes (Takashi Iwai), a PCI fix (Jesse Barnes), some ide-tape fixes (Borislav Petkov), improved rfkill support for hp-wmi (Alan Jenkins), and a question from Per Forlin as to the intended usage of the kernel DMA engine code, and how it might be extended to do the kinds of things that Per would like to do.

In today’s announcements: trace-cmd. A command line reader for ftrace. Steven Rostedt posted to announce trace-cmd, which is a command line reader for ftrace designed to be an alternative to the existing pseudo-text files. It doesn’t replace the existing interface, but complements it, and as a userspace utility is hosted in a git repository on git.kernel.org.

The latest kernel release is still 2.6.31-rc3, which was released by Linus last weekend. The biggest issue at the moment appears to be some lingering TTY issues related to ongoing cleanups, and several problem reports are ongoing.

Greg Kroah-Hartman posted a series of review patches for the 2.6.30.2 and 2.6.27.27 stable series. The former had 24 patches, while the latter had only 8. As usual, there wasn’t much time for public review – this case exascerbated by the fact that there were public security issues covered by the patches, and the fact that Greg was due to go on vacation.

Stephen Rothwell posted a linux-next tree for July 17th. Since Thursday, the tree still fails to build in an allyesconfig build configuration on powerpc, and several other build failures appeared in the tree. The total sub-tree count remains steady at 132 trees in the latest linux-next tree compose.

That’s a summary of today’s LKML traffic. For further information visit kernel.org. I’m Jon Masters.