Quantifying the Performance of Garbage Collection vs. Explicit Memory Management
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This talk answers an age-old question: is garbage collection faster/slower/the same speed as malloc/free? We introduce oracular memory management, an approach that lets us measure unaltered Java programs as if they used malloc and free. The result: a good GC can match the performance of a good allocator, but it takes 5X more space. If physical memory is tight, however, conventional garbage collectors suffer an order-of-magnitude performance penalty.
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Quantifying the Performance of Garbage Collection vs. Explicit Memory Management
- 1. Quantifying the Performance of Garbage Collection vs. Explicit Memory Management Matthew Hertz Canisius College Emery Berger University of Massachusetts Amherst
- 11. Comparing Memory Managers BDW Collector Node v = malloc(sizeof(Node)); v->data= malloc(sizeof(NodeData)); memcpy(v->data, old->data, sizeof(NodeData)); free(old->data); v->next = old->next; v->next->prev = v; v->prev = old->prev; v->prev->next = v; free(old); Using GC in C/C++ is easy:
- 12. Comparing Memory Managers BDW Collector Node v = malloc(sizeof(Node)); v->data= malloc(sizeof(NodeData)); memcpy(v->data, old->data, sizeof(NodeData)); free(old->data); v->next = old->next; v->next->prev = v; v->prev = old->prev; v->prev->next = v; free(old); … ignore calls to free .
- 13. Comparing Memory Managers Lea Allocator Node node = new Node(); node.data = new NodeData(); useNode(node); node = null; ... node = new Node(); ... node.data = new NodeData(); ... Adding malloc/free to Java: not easy…
- 14. Comparing Memory Managers Lea Allocator Node node = new Node(); node.data = new NodeData(); useNode(node); node = null; ... node = new Node(); ... node.data = new NodeData(); ... ... where should free be inserted? free(node.data)? free(node)?
- 25. Execution Time for pseudoJBB GC performance can be competitive
- 26. Footprint at Quickest Run GC uses much more memory
- 27. Footprint at Quickest Run GC uses much more memory 1.00 1.38 1.61 5.10 5.66 4.84 7.69 7.09 0.63
- 28. Avg. Relative Cycles and Footprint GC trades space for time
- 29. Javac Paging Performance Much slower in limited physical RAM
- 30. pseudoJBB Paging Performance Lifetime analysis adds little