Josh Boyer — member of the Fedora Kernel Team and FESCo — talked at Flock about the State of the Fedora Kernel, including some of the changes and updates for Fedora 21. The plan with for the Kernel in Fedora 21 is to release kernel 3.16 (or 3.17 at release, depending on scheduling.) During the Fedora 21 process, the kernel maintenance has actually been fairly calm, despite a set of new packaging changes.
During the Fedora.next process, the Fedora Cloud Working Group made requests of the kernel team to shrink down its size. There are a lot of optional components built into the kernel and many of these weren’t actually needed in a cloud environment. So the kernel team went and broke out the available modules into a core set and a common set above that. This made the minimal installation set much smaller and reduced the space on the cloud images substantially. In addition to this, they found ways to compress the kernel modules so the storage on disk shrank quite a bit as well.
Another useful feature that was added to packaging in Fedora 21 is support for automatically-generated RPM “Provides” listing the set of modules that are present in each of the packages. This will make it easier for packagers to specify dependencies on the appropriate package (and will continue working if modules move around).
The last major change in Fedora 21 is support for 64-bit ARM hardware (aarch64), which as was noted by an audience member is now available for general purchase. It works fairly well (thanks in large part to a herculean effort by Red Hat ARM engineers) and may be promoted to a primary architecture in Fedora 22 or 23. As a side-effect of this work, it’s going to be possible to replace the slow armv7hl builders in Koji with the new aarch64 builders that will be vastly more performant.
Josh then moved on to discuss the new kernel Playground, which is a new unsupported COPR containing some new experimental features. It tracks Fedora Rawhide and 21 and provides today the Overlayfs v23 (a union filesystem) and kdbus (the high-performance kernel D-BUS implementation). These are fairly stable patches to the kernel that are still out of the main tree and therefore not really suitable for Fedora proper (yet).
In the future, it may include other features such as kpatch and kgraft (the in-kernel infrastructure for supporting live-patching the kernel).