The region trap library: handling traps on application-defined regions of memory

• Authors: Tim Brecht;Harjinder Sandhu
• Venue: ATEC '99 Proceedings of the annual conference on USENIX Annual Technical Conference
• Year: 1999

User-level virtual memory (VM) primitives are used in many different application domains including distributed shared memory, persistent objects, garbage collection, and checkpointing. Unfortunately, VM primitives only allow traps to be handled at the granularity of fixed-sized pages defined by the operating system and architecture. In many cases, this results in a size mismatch between pages and application-defined objects that can lead to a significant loss in performance. In this paper we describe the design and implementation of a library that provides, at the granularity of application-defined regions, the same set of services that are commonly available at a page-granularity using VM primitives. Applications that employ the interface of this library, called the Region Trap Library (RTL), can create and use multiple objects with different levels of protection (i.e., invalid, read-only, or read-write) that reside on the same virtual memory page and trap only on read/write references to objects in an invalid state or write references to objects in a read-only state. All other references to these objects proceed at hardware speeds. Benchmarks of an implementation on five different OS/architecture combinations are presented along with a case study using region trapping within a distributed shared memory (DSM) system, to implement a region-based version of the lazy release consistency (LRC) coherence protocol. Together, the benchmark results and the DSM case study suggest that region trapping mechanisms provide a feasible region-granularity alternative for application domains that commonly rely on page-based virtual memory primitives.