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User-Level Distributed Shared Memory - Implementation, Characteristics, and Evaluation

This presentation provides an overview of user-level distributed shared memory (DSM), its characteristics, and its implementation. It discusses related work, system design, implementation details, fault handling, memory consistency model, and evaluation results. Future work and potential improvements are also discussed.

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User-Level Distributed Shared Memory - Implementation, Characteristics, and Evaluation

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  1. CSCS: A Concise Implementation of User-Level Distributed Shared Memory Final Presentation Zhi Zhai Feng Shen Computer Science and Engineering University of Notre Dame Dec. 11, 2009

  2. DSM Overview DSM Characteristics: • Physically: distributed memory • Logically: a single shared address space Figure 1 DSM architecture

  3. Related Work Models and Main Features: • IVY (Yale) - Divided Space: Shared & Private space • Mirage (UCLA) - Time Interval d : Avoid page thrashing • TreadMarks (Rice) - Lazy Release Consistency : Improve efficiency • SAM (Stanford)

  4. System Design Figure 2 Server/Client mode

  5. System Design • Server • Holder of metadata only • Thread-based Connection • Event-based Service

  6. System Design Figure 3 Server Process/Threads

  7. System Design • Client • Physical memory owner • UI/Work/Page Fetch Thread • Fixed-home Protocol • Not Aware of Peer Clients

  8. System Design Figure 4 Client process/thread

  9. System Design Figure 5 Sample Operation

  10. Implementation • Message Passing: TCP socket Figure 6 Message Passing

  11. Implementation • Server/Client Page Table • Server holds most up-to-date meta data • Server managers whole virtual memory space • Server records id & addresses of all nodes • Client owns the most up-to-date local memory segment • Client caches referenced pages from peer nodes

  12. Figure 7 Connection Table Figure 8 Server Page Table

  13. Implementation Figure 9 Client Page Table

  14. Implementation • Page fault handler • Client  Server • Check the access right • Fetch the page owner id/address • Update global access bits • Client  Client • Connect to the page owner • Cache the referenced page • Update local access bits

  15. Implementation • Page fault handler • Page fault type • Read remote page • Write on a page • Assumption • Reading happens more often than writing • Writing needs most-to-date copy more than reading

  16. Implementation Truly a remote reading fault? dsm call: dsm_do_wrt_page () dsm call: dsm_do_no_page () Assume reading remote page NO: double page fault YES: continue Figure 10 Page fault handler wordflow

  17. Implementation • Memory Consistency Model • Assumption Revisit • Reading happens more often than writing • Writing needs most-to-date copy more than reading • Multi-Reader/Single Writer • Snap-shot for reading • Every writing triggers page fault • Locks on pages being referenced • Semaphore-like reference counts: If ref_count > 0  Waiting/Re-random

  18. DSM Evaluation Figure 11 Parallel Computation on ASP Problem

  19. DSM Evaluation Figure 12 Execution time comparison

  20. DSM Evaluation Figure 13 Message Transmission Comparison

  21. DSM Evaluation Figure 14 Network Traffic Comparison

  22. Future Work • Enhance system robustness • Evaluate scalability boundary • Provide better programmability

  23. Thank You! Q&A

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