The question was asked on the lkml whether or not memory allocated by kmalloc and vmalloc is swappable. Rik van Reil offered a clear explanation as to why it is not, "unswappable kernel memory is simpler and faster," adding, "there really is no good reason for swapping kernel memory nowadays." He went on to explain:

"Over the last 15 years, the memory requirements of the Linux kernel have grown maybe a factor 10, while the memory of computers has grown by a factor of 1000.

"The data structures that grow with memory (mostly the mem_map[] array of page structs) has actually gotten smaller since the 2.4 kernel and now takes under 1% of memory even on x86-64."