Write barrier elision for concurrent garbage collectors

ABSTRACT

Concurrent garbage collectors require write barriers to preserve consistency, but these barriers impose significant direct and indirect costs. While there has been a lot of work on optimizing write barriers, we present the first study of their elision in a concurrent collector. We show conditions under which write barriers are redundant, and describe how these conditions can be applied to both incremental update or snapshot-at-the-beginning barriers. We then evaluate the potential for write barrier elimination with a trace-based limit study, which shows that a significant percentage of write barriers are redundant. On average, 54% of incremental barriers and 83% of snapshot barriers are unnecessary.

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INDEX TERMS

Primary Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.3 Language Constructs and Features
          Subjects: Dynamic storage management

Additional Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.4 Processors
          Subjects: Memory management (garbage collection)
  D.4 OPERATING SYSTEMS
      D.4.2 Storage Management
          Subjects: Garbage collection; Allocation/deallocation strategies

General Terms:
Experimentation, Languages, Measurement, Performance

Keywords:
concurrent garbage collection, write barrier