To augment the need for running background operations, the kernel spawns threads (similar to processes). These kernel threads are similar to regular processes, in that they are represented by a task structure and assigned a PID. Unlike user processes, they do not have any address space mapped, and run exclusively in kernel mode, which makes them non-interactive. Various kernel subsystems use kthreads to run periodic and asynchronous operations.
All kernel threads are descendants of kthreadd (pid 2), which is spawned by the kernel (pid 0) during boot. The kthreadd enumerates other kernel threads; it provides interface routines through which other kernel threads can be dynamically spawned at runtime by kernel services. Kernel ...
