From LWN.net: "One of the changes that is now in the 2.4.3 prepatch is
a new memory map locking scheme implemented by Rik van Riel. The memory map semaphore
controls access to the various virtual memory areas and page tables used by a process; it is
intended to keep concurrent activities, such as page faults, memory map changes, and
informational queries from stepping on each other. It is a fundamental part of how the virtual
memory system works."
March 23, 2001