1RCU Concepts    4The basic idea behind RCU (read-copy update)
is to split destructive    5operations into two parts, one that
prevents anyone from seeing the data    6item being destroyed,
and one that actually carries out the destruction.    7A "grace
period" must elapse between the two parts, and this grace period
8must be long enough that any readers accessing the item being
deleted have    9since dropped their references.  For example,
an RCU-protected deletion   10from a linked list would first
remove the item from the list, wait for   11a grace period to
elapse, then free the element.  See the listRCU.txt   12file for
more information on using RCU with linked lists.   15Frequently
Asked Questions   17o       Why would anyone want to use RCU?
19        The advantage of RCU's two-part approach is that RCU
readers need   20        not acquire any locks, perform any
atomic instructions, write to   21        shared memory, or (on
CPUs other than Alpha) execute any memory   22        barriers.
The fact