R.Tyler Ballance's blog say that he sucks at computers, yet he's been giving his readers the nitty-gritty about Mac computer. Recently, due to an inquiry by BuildFactory icon graphics designer Fernando, he explains why the kernel_task contains too many threads and takes up a high percentage of the virtual memory.

First, Tyler gives us a bit of background on Mach. He shares, "Mach is one of the more successful stories in microkernel development, Mac OS X is based around the Mach microkernel, as well as the NeXTStep of old, as well as DEC's OSF/1, and IBM's frequently deceased OS/2 (at least for RS6000 machines). In accordance with the basic concept of a microkernel, Mach manages memory, and handles inter-process communication but not much else."

After this backgrounder, Tyler start answering the question, "What exactly is a kernel_task"? Since the kernel_task is a mere "representation of the microkernel itself" it is not, therefore, really a "task". It being a PID 0, we can all assume it is not userland-related.

There may be little documentation on kernel_task but from the little info available, Tyler was able to assume that the kernel task may be the basic (virtual/)memory manager for Mac OS X on top of Mach, which is similar to L4 microkernel's sigma0 concept. He confidently declares that "kernel_task is responsible for handling the allocation of pages of memory in the Xnu kernel (Mach+IOKit+whatever else Apple threw in), which would explain why it has an amazing amount of threads".

Yet another process, dynamic_pager, shows up and it is possible that this task is the one that handles swap file for Mac OS X. If this is indeed true, what is dynamic_pager's connection with kernel_task? Tyler assumes, "It's quite possible that kernel_task and dynamic_pager work together of a Mach port, and when necessary, kernel_task runs out of available resources, it serves up memory from a swap file managed by dynamic_pager."

Although most of the info provided Tyler have no strong document back-up, and some even being mere speculation, he hopes that he was able to put some light on what kernel_task is. Check out Tyler's other article on the Mac OS X internals here.