1. An Implementation of User-level Distributed Shared Memory
Wei Zhang & Shu Liu

2. DSM: Shared Memory + Distributed Memory
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3. Problems & Solutions Problems Solutions Granularity
Use 4-Kbyte Page as the unit of sharing
Data location/Mapping
Centralized server
Communication
MPI (Message Passing Interface)
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4. Cont. Problems Solutions Memory Coherence in parallelism
a: each page has one dynamic owner
b: multi readers (make copies)
c: single writer (only owner can write the page)
d: lock & barrier (synchronize page operation)
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5. Design Overview
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6. For a read
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7. For a write
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8. Implementation Data structures: Important system calls
Page Table in each node
Pageinfo in server
Important system calls
mmap()
mprotect()
SIGSEGV signal: handle page fault
pthread: receive page fault request and send data
At first, all the shared memory is allocated in server
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9. Cont. MPI: create a cluster and be responsible for communication
#include ”dsm.h”: a simple yet powerful API
Name
Function
dsm_startup()
initialization
dsm_malloc (int size)
allocate shared memory for the process
dsm_barrier ()
global synchronization
dsm_clock()
count elapsed time
dsm_lock()
page synchronization
dsm_exit()
clean up and shut DSM down
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10. Cont. Include dsm header file Start dsm system Allocate shared memory
Synchronize
Free shared memory
Exit
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11. Evaluation Assumptions: Benchmarks:
server congestion is not the bottleneck
network is reliable
Benchmarks:
Jacobi: partial differential equations: Ax=b
MM: parallel matrix multiply: C=AB
Scan: multi-iteration scan program
Focus: multi-iteration write program
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12. Cont.
Speedup
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13. Cont.
Page Fault
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14. Conclusion & Future work
Achieved what we claimed
Improvement:
Blocking Communication-> Non-blocking Communication
Other Memory Consistency Model (MRMW)
Decrease network communication

15. Thank you!
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