1. In a computer system having one or more processors operatively coupled to one or more memory devices, a method for supporting user mode specification of Read-Copy Update (RCU) grace period latency to an operating system kernel-level RCU implementation, the method comprising: providing a non-expedited kernel-level RCU grace period mechanism for invocation by kernel-level RCU updaters when performing kernel-level RCU update operations to initiate non-expedited kernel-level RCU grace periods; providing an expedited kernel-level RCU grace period mechanism for invocation by kernel-level RCU updaters when performing kernel-level RCU update operations to initiate expedited kernel-level RCU grace periods; providing a expedited grace period indicator in a kernel memory space for indicating whether said non-expedited kernel-level RCU grace periods or said expedited kernel-level RCU grace periods should be invoked; said non-expedited kernel-level RCU grace period mechanism being adapted to check said expedited grace period indicator, and if said expedited grace period indicator indicates that said expedited kernel-level RCU grace periods should be invoked, to invoke said expedited kernel-level RCU grace period mechanism; and providing a communication mechanism for use by a user mode application executing in a user memory space to manipulate said expedited grace period indicator in said kernel memory space and thereby control whether said expedited or non-expedited kernel-level RCU grace periods should be used.