Three-Space Nursery Garbage Collector for Reducing Object Promotion
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Solution Overview
Problem
Current nursery collection techniques in virtual machine environments, such as Java Virtual Machines, unnecessarily promote objects that could have been released if young collection had been performed later, leading to performance issues and increased memory bandwidth costs.
Innovation Solution
Implementing a three-space nursery system with a larger body and two tails within the virtual machine's memory space, where the nursery garbage collector collects two of the three spaces to reduce the promotion rate, and using an old space garbage collector to manage promoted objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nursery collection is performed to manage memory in virtual machine environments, then memory management is improved, but objects are unnecessarily promoted leading to increased memory bandwidth costs and performance issues
Solution Approach 1:
The nursery space is segmented into three separate spaces (nursery0, nursery1, nursery2) instead of a single nursery space. This segmentation allows the garbage collector to selectively collect only two out of three spaces, leaving one space with potentially useful objects that can be reused, thereby reducing unnecessary object promotions and memory bandwidth usage while maintaining effective memory management.
2Productivity
If objects are promoted from nursery to old space, then memory is reused for new objects, but performance issues arise due to unnecessary promotions
Solution Approach 1:
By dividing the nursery into three spaces and collecting only two during each nursery collection, the system reduces the number of objects unnecessarily promoted to old space. Objects in the uncollected nursery space remain in memory and can be reused, reducing pause times associated with object promotion while maintaining efficient object allocation through the segmented structure.
3Productivity
If nursery size is increased to reduce promotions, then performance improves, but memory usage increases
Solution Approach 1:
The three-space nursery segmentation allows the system to achieve better performance without increasing total nursery size. By selectively collecting two out of three spaces, the system reduces unnecessary promotions while reusing objects in the uncollected space, thereby improving performance without allocating additional memory beyond the original nursery capacity.
Solution Approach 2:
Instead of increasing nursery size to reduce promotions, the system discards the idea of collecting all nursery spaces and recovers memory by reusing objects in the uncollected nursery space. This approach improves performance by reducing promotions while maintaining the same total memory footprint, as objects are recovered and reused within the existing nursery structure.
Data Source
AI summary
A system for generational garbage collection in a virtual machine environment, comprising a virtual machine for executing a software application; a memory space for use by the virtual machine in storing software objects and pointers as part of the software application, divided into a three space nursery and an old space heap; a nursery garbage collector that can collect two out of the three spaces to reduce the promotion rate; and an old space garbage collector.