LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090818.mp3

For Tuesday, August 18th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: AlacrityVM, Kconfig, Spinlocks, and VM.

AlacrityVM. Today’s ongoing debate about which IO implementation is the fairest of them all saw the discussion head into the realm of DMA. Specifically whether vbus supported things like RDMA and how guests are protected from DMA to random host memory on platforms like PowerPC using a real physical DMA controller with virtio, and similar topics.

Kconfig. Steven Rostedt, who I know has had his fair share of annoyances with building test kernels, posted some patches aimed at making the process of building test kernels for a particular system much easier by having a build target that will automatically select a configuration covering all modules currently loaded on the test system. Rather than having to build a distribution style test kernel (which takes time), Steven’s patches allow developers to use “make localmodconfig” and “make localyesconfig” to build test kernels featuring only modules actually in use, either built as modules or built into the kernel in the latter case. Thanks a whole bunch, Steven!

Spinlocks. Kumar Gala posted asking whether spin_is_locked behavior is broken on uniprocessor systems. As Linux Weekly News pointed out, the problem here is that, actually, the meaning of spin_is_locked on systems without actual spinlocks being present is somewhat ill-defined. The LWN article does a great job of explaining the issues, so I won’t cover it much further here except to say that it’s likely some new spinlock primitives are coming down the pipe.

VM. I wonder what he’s working on. Jan Beulich posted a range of patches. The first alters handling of num_physpages since memory allocations should depend upon the amount of usable memory, and not just the total PFN count (which may include all manner of non-RAM ranges) in a system. The second builds upon this by replacing various users of num_physpages with totalram_pages. The third migrates the PID hash table over to using alloc_large_system_hash. And the fourth patch from Jan removes use of alloc_bootmem_low where’s it not strictly required for a given system to operate, especially on large 64-bit systems.

Also on a VM note today, Mel Gorman posted a three part RFC patch series aimed at reducing the need to search within the fast path of the low level page allocator by maintaining multiple free-lists in the per-cpu structure. At the time of the original introduction of per_cpu_pages, Mel says that the per-cpu static allocation thereof (recall that dynamic per-cpu-structucture allocation was recently implemented) resulted in too much wasted memory. But now that this is no longer the case, he is able to add multiple free lists to struct per_cpu_pages, one per migratetype that can be stored on the PCP lists. For the most part, performance testing showed only marginal improvement, except in the case of netperf-udp on x86_64 and sysbench on ppc64, which were higher.

In today’s miscellaneous items: some tracing fixes (to correct broken names in ftrace filters) from Steven Rostedt, another version of Paul Menage’s cgroup memberlist enhancements that add a cgroup.procs file to each cgroup (that contains unique thread group information rather than task IDs), an implementation of ACPI 4.0 power meter support via an extended hwmon sysfs interface from Darrick J. Wong, some irq fixes from Thomas Gleixner (who confirmed that today’s tree “contains really what I want you to pull”, after yesterday’s tree inadvertedly had the wrong patch), a fix to the LSM_MMAP_MIN_ADDR (yes, that one) help text from Dave Jones that corrects the default value to 65536 rather than 65535 (which would still fall within the first page on a 4K page system), another version of Jon Hunter’s patch that catches timer wrapping in clocksources and allows 32-bit systems to sleep for longer than 2.15 seconds when using dynamic ticks, two more wireless updates from John Linville, a twelve part patch series aimed at cleaning up __build_sched_domains by making the code “less ugly and more readable” from Andreas Herrmann, version two of yesterday’s page based O_DIRECT implementation from Jens Axboe, a whole bunch of network fixes from David Miller (including a TUN ioctl race fix from Herbert Xu, and a fix to the genetlink data structure that had previously broken userland), version 2 of the patch series adding in-memory-only xattr support on sysfs files from Casey Schaufler, and a trivial “make html” fix for performance counters from Kyle McMartin.

Finally today, Mikael Pettersson posted an intriguingly excessive request. He notes that his laptop hardware “clips disk capacities to 128GB. There’s no BIOS update or BIOS setup option to fix this. Passing libata.ignore_hpa=1 allows the Linux kernel to access larger disks, so Linux does work Ok with larger disks. However the laptop dual-boots Windows (for work-related stuff), and Windows has a major problem: if an entry in the msdos partition table refers to a sector above the BIOS 128GB limit, the Windows kernel crashes an reboots early in its boot sequence”. He goes on to propose adding some kind of sub-partition type that could be somehow hidden from Windows.

In today’s announcements: 2.6.31-rc6-rt4. Thomas Gleixner announced the latest iteration of the preempt-rt patchset (he skipped -rt3 as it failed in testing). This included an update to the “ONESHOT” irq infrastructure Thomas has been working on for mainline inclusion.

The latest kernel release is 2.6.31-rc6, which was released on August 14th.

Christoph Thielecke posted an interesting hard lockup on 2.6.31-rc6, which again seemed to be related to his ongoing Xorg development build testing.

Stephen Rothwell posted a linux-next tree for August 18th. Since Monday, the xfs, fsnotify, and suspend trees gained conflicts while the usb tree lost one. The total sub-tree count remains steady at 140 trees.

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