The Linux kernel, an open source project that has grown by 2.7 million lines of code over the past 16 months, thanks in part to big gun backers such as Red Hat, IBM and Novell, which remain the top contributors.

So found a report put out by the Linux Foundation. The report also shows that Linux creator Linus Torvalds has fallen out of the Top 30 individual contributors when accounting only for kernel changes. Torvalds's work in other areas including reviews and signing off on code still make him one of the top contributors to overall kernel development, the report notes.

"Linus remains an active and crucial part of the development process," the report states.

The data was reported in the a paper titled "Linux Kernel Development," which is an update to the first development report put out in April 2008 by the Linux Foundation. The most recent report is authored by Greg Kroah-Hartman from Novell, Jonathan Corbet of LWN.net and Amanda McPherson from The Linux Foundation

Since the last report in 2008, there has been roughly a 10 percent increase in the number of developers contributing to each kernel release cycle, which come every 2-3 months. In addition, the number of lines of code added to the kernel each day has nearly tripled.

The kernel now has more than 11.5 million lines of code.

Red Hat, Novell and IBM top the chart of companies whose employees contribute the most changes to the kernel. The three companies account for just over 24 percent of all changes made to the kernel in the past 16 months.

The report notes that since 2005, more than 5,000 individual developers from nearly 500 companies have contributed to the kernel.

The paper examines four years of history from version 2.6.11 through 2.6.30 of the kernel.

The first edition of the report was published in April 2008 and covered data through the 2.6.24 kernel. This most recent report adds data through the 2.6.30 kernel and highlights changes in the past 16 months that show how kernel development is expanding.

Since the April 2008 paper, changes to the kernel have exploded. The numbers include 10,923 lines of code added (a 70 percent increase), 5,547 lines removed (68 percent increase) and 2,243 lines changed (32 percent increase) per day by the development community.

The report notes that the rate of change is larger than any other public software project of any size.

The changes are aggregated within each kernel development cycle, which now averages 81 days.

To keep up with that pace, the individual development community has doubled in the past three years with the 2.6.30 kernel claiming 1,150 developers.

But the report notes that only a relatively small number of them are doing the majority of the work.