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Improving Locality of Improving Locality of Reference in a Garbage-Reference in a Garbage-Collecting Memory Collecting Memory Management SystemManagement System
Written by: ROBERT COURTS
Presented by: SHAHAR GOLAN
About the ArticleAbout the Article
• Written in 1988
• Temporal Copying GC
• LISP Oriented
THE END THE END
Basic Copying GCBasic Copying GC
3 Logical Address Spaces:
• from space
• scavenge space
• new space
After a flip,I’m all there is!
I may point,where ever I like!I never point
into the red zone!
1,1
3,3
0,0
2,2GENERATION
Basic Temporal CGCBasic Temporal CGC
2,1
3,03,13,2
2,0
1,0VOLATILITY
• Classify by age
• Classify by volatility
Where are the objects?
1,1
3,3
0,0
2,2
5% 95%
Basic Temporal CGCBasic Temporal CGC
• Collecting the 0th. Generation
Indirection Cells are not folded!
2,1
1,1
3,03,13,23,3
0,0
2,02,2
1,0VOLATILITY
GENERATION
2,1
1,1
3,03,13,23,3
0,0
2,02,2
1,0
2,1
1,1
3,03,13,23,3
0,0
2,02,2
1,0
• Collecting the 1st. Generation
Indirection Cells are folded.
ReferencReferencee
Related Work• Garbage Collection in a Large Lisp System
D.A. MOON 1984
• Improving Locality of Reference in a Garbage-Collecting Memory Management System
ROBERT COURTS, 1988
• Effective ’Static-Graph’ Recognition to Improve Locality in Garbage-Collecting Systems
• Object Type Directed Garbage Collection to Improve Locality
PAUL R. WILSON, MICHAEL S. LAM & THOMAS G. MOHLER, 1991-1992
• Using Generational Garbage Collection to Implement Cache-Conscious Data Placement
TRISHUL M. CHILIMBI & JAMES R. LARUS, Oct. 1998
Improving Locality of Improving Locality of Reference in a Garbage-Reference in a Garbage-Collecting Memory Collecting Memory Management SystemManagement System
Written by: ROBERT COURTS
Presented by: SHAHAR GOLAN
Locality ofLocality of
Locality of ReferenceLocality of ReferenceWatershed Experiment
• Flip the entire system to FROM Space• Inhibit the scavenger• Use the system• Copy objects to NEW Space by need
Observed results:• 4MB/30MB (only 13%) where copied.• Paging activity has dramatically
declined.
Locality of ReferenceLocality of ReferenceAdaptive Training
• Flip a generation• Copy objects by need• Activate scavenger• Reclaim FROM SPACE
Major drawback: We hardly learn about the dynamic objects in the higher generations.
Locality of ReferenceLocality of ReferenceAdaptive Training
2,1
1,1
3,03,13,23,3
0,0
2,02,2
1,0VOLATILITY
GENERATION
3,3 3,3
2,2
1,1
3,3
2,2
ACTIVITY
3 2 1 0
Scavenger Access
Mutator Access
From the Watershed Experiment we may conclude that a good caching scheme should be sufficient for most memory management systems. GC may be done infrequently on a ‘stop the world’ basis. (e.g., once every three months.)
Dead objects will stay on large disks but will quickly disappear from cache and memory, freeing the space to live and frequently used ones.
GC GC -- Personal View Personal View
,,Court’s dynamic regrouping technique takes advantage of specialized hardware to provide incremental garbage collection, which tends to move objects to TO space in program access order, and this can dramatically reduce the number of page faults.’’
Chilimbi & Larus (Oct. 1998)
//
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