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Task-aware Garbage Collection in a Multi-Tasking Virtual Machine

Task-aware Garbage Collection in a Multi-Tasking Virtual Machine. Sunil Soman Laurent Dayn è s Chandra Krintz RACE Lab, UC Santa Barbara Sun Microsystems Labs. Outline. Introduction MVM overview Task-aware collection Performance isolation Fast, immediate resource reclamation

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Task-aware Garbage Collection in a Multi-Tasking Virtual Machine

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  1. Task-aware Garbage Collection in a Multi-Tasking Virtual Machine Sunil Soman Laurent Daynès Chandra Krintz RACE Lab, UC Santa Barbara Sun Microsystems Labs

  2. Outline • Introduction • MVM overview • Task-aware collection • Performance isolation • Fast, immediate resource reclamation • Independent allocation & young gen collection • Evaluation • Conclusion

  3. Introduction • Multi-tasking VMs • Multiple users/applications • Improved startup • Reuse & sharing • Performance isolation • Accounting & timely resource reclamation • Sharing/performance isolation conflict • Loss of scalability • Bottleneck: memory management system

  4. MVM overview • Multiple isolated instances in same VM • Implements Isolates API (JSR 121) • Safety & isolation guaranteed • Task re-entrance • Class sharing • Separate task-dependent parts, rest shared • Accessed thru table indexed by unique task id • Based on Hotspot VM • Generational mark-compact GC

  5. MVM Garbage Collection • Shared generational heap • Scavenged young gen (eden & survivor spaces) • 4 phase mark-compact collected old generation • Card table for tracking mature to young pointers eden young from to old permanent

  6. MVM Garbage Collection • Lack of “task awareness” • Scalability & performance isolation • Space occupied by dead tasks reclaimed on GC • Parameter virtualization

  7. Task-aware collection • Performance isolation • Hybrid heap layout • Task-concurrent scavenging • Fast, immediate resource reclamation • Without requiring full or partial GC

  8. Hybrid heap layout eden from to old permanent eden to from Per-task . . eden to from

  9. Hybrid heap layout: young gen

  10. Hybrid heap layout: Old gen • Promotion Area Buffers • Per-task old generation regions • Allocated on demand • Adjusted on full heap GC • Used for scavenging & pretenuring • Provide • Performance isolation • GC-less reclamation on task termination • Per-task card table scanning • Enabled due to precise accounting of old gen

  11. Task 3 Allocation top Allocation top Allocation top Allocation top Resource Reclamation Task 1 Task 2 Free PABs . . . . .

  12. Task-concurrent Scavenging • Leverages hybrid heap design • Mutators can execute during scavenge • Concurrent old gen direct allocation • Synchronization • Threads belonging to GC initiator stopped • Threads poll on protected page • Suspended on access fault • Threads belonging to other tasks not suspended

  13. Evaluation • Experimental setup • Dual UltraSPARC 1.5GHz, Solaris 10 • Dacapo & Spec98 benchmarks long app short app … time • Throughput & Response time • # short apps & average pause time • Hybrid heap layout vs Shared heap

  14. Results: Thruput & resp. time Short (javac w/small input) + long running program (jess, jack, ps)

  15. Evaluation • Concurrent execution performance • Hybrid heap + task-conc. scavenging vs shared • Instances of same task run concurrently • 1 thru 5 instances • GC time & # GCs • End-to-end execution time

  16. Concurrent Exec: GC Time 62% 54% 100%

  17. Concurrent Exec: Change in GCs

  18. Concurrent Exec: Exec. Time

  19. Related Work • Prior MVM • Thread-local heaps [Domani ’02, Steensgaard ’00] • Isolation [Back ’05] • Card table/remset opt [Azagury ’98, Detlefs ’02]

  20. Summary • Task-aware collection • Performance isolation • Immediate, GC-free reclamation • Heap layout, mechanisms & perf. evaluation • Significantly improves overall execution, throughput & response time

  21. Future Work • Better multi-tasking workloads • Old generation collection • Independent collection of PABs • Different collection policies • Automatic performance tuning • Per-application tuning of GC parameters • Global management

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