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 RCU grace period latency to an operating system kernel-level RCU implementation, the method comprising: providing a non-expedited RCU grace period mechanism for invocation by RCU updaters when performing RCU update operations to initiate a non-expedited grace periods; providing an expedited RCU grace period mechanism for invocation by RCU updaters when performing RCU update operations to initiate expedited grace periods; providing a expedited grace period indicator in a kernel memory space for indicating whether a non-expedited RCU grace period or an expedited RCU grace period should be invoked; said non-expedited RCU grace period mechanism being adapted to check said expedited grace period indicator, and if said expedited grace period indicator indicates that an expedited RCU grace period should be invoked, to invoke said expedited 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 an expedited or non-expedited RCU grace period should be used.