Linux kernel sources

control code page:
　　Control pages are special, they are the intermediaries that are needed while we copy the rest of the pages to their final resting place. As such they must not conflict with either the destination addresses or memory the kernel is already using.

　　The only case where we really need more than one of these are for architectures where we cannot disable the MMU and must instead generate an identity mapped page table for all of the memory.