Recent improvements to the Linux kernel appear to have made it more stable and less susceptible to bug-related failures. As a result the operating system could become more attractive to corporate users planning critical applications.
It has been a rocky road for the Linux 2.4 kernel, however. It originally used a memory management system that was significantly more intricate than the one used in Linux 2.2. The new design brought a number of bugs that have proved hard to remove.
The worst problems have been suffered by users running heavy workloads that use a lot of virtual memory. In these cases, the memory manager could start swapping continuously, causing the operating system to be unresponsive for as long as several minutes. In an impressive feat of low-level coding, developer Andrea Arcangeli, who works for Linux distributor Suse, replaced the entire memory manager with a new design  one that is much simpler  and this has been accepted into the Linux kernel by Linux creator Linus Torvalds.
There has been a lot of benchmarking since then, and further rapid improvements from both Arcangeli and Rik van Riel, the main developer of the original 2.4 memory manager, who seem to be competing to create the best code. Benchmark results have not been consistent, but evidence is mounting that the simpler design is at least as fast as the code it replaces, and is more stable, more consistent under load and easier to fix.
So a battle over the Linux kernel that has divided the developer community appears to be over, at least for now. Torvalds and Red Hat Linux developer Alan Cox have both said that they will embrace the new virtual memory manager and implement it in forthcoming versions of the operating system. Cox has, until now, used the old virtual memory manager in the version of the 2.4 kernel he oversees.
The unified approach is good news for the Linux community, and for corporates who want to use Linux as an enterprise, mission-critical operating system. 'IBM and Compaq are certainly pushing in that direction. Compaq is also working on high-end, open-source clustering code,' Cox wrote in an email. 'We have folks stuffing Linux into handhelds, and version 2.5 is likely to also include work to reduce the minimal kernel size.'
The latest news is a relief for Linux kernel developers, who were being forced to support two versions of the 2.4 kernel  the variations included differing disk cache systems and incompatible quota code. The move also reduces speculation that the Linux community will fragment, causing the operating system to lose ground to rivals.
Torvalds said he will use Arcangeli's new virtual memory manager for his upcoming 2.5 development tree, and Cox said that he plans to include it in his 2.4 kernel.
'I think Linus should not have switched virtual memory manager code in a stable release, but having done so, there wasn't any point undoing it, and his prediction that the new virtual memory manager was worth the pain seems to be justified,' wrote Cox.
The detente has quieted speculation of a possible source-code divergence. Torvalds, who works for chip maker Transmeta, said, 'I'm not going to maintain 2.4.x forever. Alan will clearly be the maintainer of it. I just want to turn over 2.4.x to Alan in a shape where I'm personally happy with it  and I was not happy with the virtual memory manager before.'
Arcangeli complained that the previous virtual memory manager 'was falling apart'. In an email he wrote: 'It was running very slow, generating swap storms, and often it needed a long uptime to trigger the problem. It was just not good enough.'
Cox and Torvalds stressed they are now in accord. 'There is no rift between us; that would imply we are disagreeing about stuff big time,' Cox wrote. 'Linus and I agree on a direction for 2.4 and the 2.5 development tree on all major stuff. In fact, our biggest disagreement is on dynamic device naming in 2.5 Â and not on things like the virtual memory manager.'
Torvalds said he is close to handing over the stable 2.4 kernel to Cox and will concentrate on the 2.5 development tree. 'When I pass maintainership to Alan, I pass him everything. And I'll do the development kernels,' he commented.
