Improving Locality of Reference in a Garbage- Collecting Memory Management System Written by: R OBERT C OURTS Presented by: S HAHAR G OLAN

About the Article Written in 1988 Temporal Copying GC LISP Oriented

temporal adj. 1 lasting only for a time; transitory; temporary, not eternal 2 of this world; worldly, not spiritual 3 civil or secular rather than ecclesiastical 4 of or limited by time 5 Gram. expressing distinctions in time; pertaining to tense n. a temporal thing, power, etc. tem¿porally adv. Etymology [ ME < L temporalis < tempus, time: see temper ] ©1995 Zane Publishing, Inc. ©1994, 1991, 1988 Simon & Schuster, Inc.

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Basic Copying GC 3 Logical Address Spaces: from space scavenge space new space After a flip, Im all there is! I may point, where ever I like! I never point into the red zone!

scavenge vt. 1 to clean up (streets, alleys, etc.); remove rubbish, dirt, or garbage from 2 to salvage (usable goods) by rummaging through refuse or discards 3 to remove burned gases from (the cylinder of an internal- combustion engine) 4 Metallurgy to clean (molten metal) by using a substance that will combine chemically with the impurities present vi. 1 to act as a scavenger 2 to look for food Etymology [ back-form. < fol. ] ©1995 Zane Publishing, Inc. ©1994, 1991, 1988 Simon & Schuster, Inc.

1,1 3,3 0,0 2,2 GENERATION Basic Temporal CGC 2,1 3,03,13,2 2,0 1,0 VOLATILITY Classify by age Classify by volatility Where are the objects? 1,1 3,3 0,0 2,2 5% 95%

Basic Temporal CGC Collecting the 0 th. Generation Indirection Cells are not folded! 2,1 1,1 3,03,13,23,3 0,0 2,02,2 1,0 VOLATILITY 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 1 st. Generation Indirection Cells are folded.

Reference Reference Related Work Garbage Collection in a Large Lisp System D.A. M OON 1984 Improving Locality of Reference in a Garbage-Collecting Memory Management System R OBERT C OURTS, 1988 Effective Static-Graph Recognition to Improve Locality in Garbage-Collecting Systems Object Type Directed Garbage Collection to Improve Locality P AUL R. W ILSON, M ICHAEL S. L AM & T HOMAS G. M OHLER, Using Generational Garbage Collection to Implement Cache- Conscious Data Placement T RISHUL M. C HILIMBI & J AMES R. L ARUS, Oct Improving Locality of Reference in a Garbage- Collecting Memory Management System Written by: R OBERT C OURTS Presented by: S HAHAR G OLAN Locality of

Locality of Reference Locality of Reference Watershed Experiment Flip the entire system to FROM Space Inhibit the scavenger Use the system Copy objects to NEW Space by need Observed results: 4 MB /30 MB (only 13 % ) where copied. Paging activity has dramatically declined.

watershed n. 1 a ridge or stretch of high land dividing the areas drained by different rivers or river systems 2 the area drained by a river or river system 3 a crucial turning point affecting action, opinion, etc. ©1995 Zane Publishing, Inc. ©1994, 1991, 1988 Simon & Schuster, Inc.

Locality of Reference Locality of Reference Adaptive 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 Reference Locality of Reference Adaptive Training 2,1 1,1 3,03,13,23,3 0,0 2,02,2 1,0 VOLATILITY GENERATION 3,3 2,2 1,1 3,3 2,2 ACTIVITY 3210 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 - Personal View

,,Courts 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) THE END //