Garbage Collector Remembered Set Segmentation for Reduced Scanning Delay
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Solution Overview
Problem
Conventional garbage collection techniques, especially space-incremental collectors, introduce significant delays due to the time-consuming scanning of large remembered sets, which is disruptive in real-time and interactive systems, as they suspend non-collection threads during the collection process.
Innovation Solution
Modifying the remembered set to classify reference locations by their origin, allowing regions to be constrained and merged into equivalence classes based on reference thresholds, thereby reducing the size of remembered sets and the time required for scanning, and implementing constraints to optimize collection order and data structure management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If space-incremental collection techniques are used to allow independent collection of object subsets, then collection flexibility is improved, but remembered set size increases leading to longer scanning delays
Solution Approach 1:
The patent segments the remembered set into multiple smaller remembered sets, each associated with a specific region in the heap. Instead of maintaining a single large remembered set that tracks all references to collected objects, the system divides it into region-specific subsets. This segmentation reduces the size of each individual remembered set, thereby decreasing the time required to scan them during collection operations, while still providing the flexibility of space-incremental collection.
2Reliability
If conventional garbage collection techniques are used to reclaim unused memory, then memory reclamation is achieved, but normal processing must be suspended causing long and unpredictable delays
Solution Approach 1:
The patent implements preliminary action by maintaining region-specific remembered sets that are updated incrementally as objects are allocated and referenced. Before collection operations begin, the remembered sets are already organized and ready, allowing collection to proceed without requiring full heap scans. This preliminary organization enables concurrent collection activities while minimizing suspension of normal processing, thus reducing unpredictable delays.
3Reliability
If remembered sets track all reference locations to objects in a region, then collection completeness is ensured, but the size and scanning time of remembered sets increases
Solution Approach 1:
The patent applies local quality by creating remembered sets with properties tailored to their specific regions. Each region-specific remembered set contains only the references relevant to that region, rather than maintaining a universal remembered set with all references. This localized approach ensures that each remembered set is optimized for its specific collection needs, maintaining collection completeness for each region while improving overall collection efficiency by reducing redundant scanning.
Data Source
AI summary
A remembered set for a memory heap region in a garbage-collected computer system is modified to classify reference locations stored therein by the heap region from which the references originate so that the number of references originating from a given region can be easily determined. If the number of remembered set entries for references from a second region to a first region reaches a predetermined threshold, the second region is constrained so that it will be collected at the same time as, or before, the first region. Then, all entries in the remembered set associated with the first region for references from the second region to the first region can be deleted, and no such entries need be entered in the future thereby reducing the size of that remembered set and the time required to scan it.