The release was originally to be known as version 3.20 but was changed after a poll conducted by Torvalds. The live kernel patching code was submitted by SUSE developer Jiri Kosina back in February. It uses code from both kpatch (Red Hat's solution) and kGraft (SUSE's solution) and was planned at last October's Linux Plumbers Conference.
Announcing the 4.0 release, Torvalds wrote that there were no big changes despite the change in version number.
"Linux 4.0 was a pretty small release both in linux-next and in final size, although obviously 'small' is all relative. It's still over 10k non-merge commits. But we've definitely had bigger releases (and judging by linux-next v4.1 is going to be one of the bigger ones)," he wrote.
"Looking at just the statistics in git, this release is not just when we cross half a million commits total, but also cross the 4 million git object limit," Torvalds wrote. "Interestingly (if you look for numeric patterns), Linux 3.0 was when we crossed a quarter (of a) million commits and two million git objects, so there's a nice (and completely unintentional) pattern there when it comes to the kernel git repository."
Git is the source code management package the Torvalds developed when he was forced to stop using the proprietary BitKeeper source code management system.
"Another quick historical numerological footnote: the old historical BK tree was getting close to the 16-bit commit limit that BK originally used to have. So that whole 'quarter of a million commits' is actually quite a lot," Torvalds wrote.
"During all of the BK years we only got 65k commits. Of course, we only used BK for three years, and we've now been on git for almost exactly ten years, but still – it shows how the whole development process has really sped up a _lot_."