Improving Garbage Collection Performance with Region Pinning in OpenJDK

After a thorough review process, JEP 423, also known as Region Pinning for G1, has been successfully integrated into JDK 22. This Java Enhancement Proposal aims to significantly reduce garbage collection (GC) latency by introducing region pinning to the G1 garbage collector.

What is Region Pinning?

Region pinning is a technique that allows specific memory regions to be pinned during both major and minor collection operations in the G1 garbage collector. By pinning these regions, the garbage collection process can be carried out without disabling or pausing the application, especially when implementing Java Native Interface (JNI) calls.

The Need for Region Pinning

Traditionally, in the G1 garbage collector, the entire Java heap is divided into multiple regions. During garbage collection, these regions are scanned and potentially reclaimed. However, when JNI calls are made, and regions are modified or deallocated, the garbage collection process needs to be temporarily disabled to avoid memory integrity issues. This pause in the application can result in increased latency, affecting performance and responsiveness.

How Region Pinning Helps

With the introduction of region pinning, G1 allows developers to specify specific regions that should be pinned, even during garbage collection. These pinned regions remain unaffected by the collection process, ensuring that JNI modifications or deallocations do not disrupt the garbage collector's operation. This improvement significantly reduces GC pauses, leading to enhanced application performance and reduced latency.

Advantages of Region Pinning

Region pinning brings several benefits to the G1 garbage collector and OpenJDK:

• Reduced GC Latency: By avoiding the need to disable the garbage collection process, region pinning minimizes pauses, resulting in lower latency and improved application responsiveness.
• Better Integration with JNI: Pinning specific regions facilitates seamless integration of JNI, allowing efficient modifications and deallocations without interrupting the garbage collector's operation.
• Enhanced Performance: With reduced GC pauses, applications can run more smoothly, achieving higher throughput and optimal resource utilization.
• Improved User Experience: Faster response times and fewer hiccups due to garbage collection pauses lead to an overall improved user experience for Java applications.

Implementation Details

To implement region pinning, modifications have been made to the G1 garbage collector in OpenJDK. The garbage collector now supports the pinning of arbitrary regions during both major and minor collection operations. This flexibility allows developers to selectively pin regions based on their specific application requirements.

Conclusion

JEP 423, Region Pinning for G1, introduces a significant improvement to the G1 garbage collector in OpenJDK. By enabling developers to pin specific memory regions, the garbage collection process can continue without interruptions caused by JNI modifications. This enhancement reduces GC latency, leading to better application performance and an improved user experience. With JEP 423 integrated into JDK 22, developers can take full advantage of these performance optimizations and build more efficient Java applications.

By A N M Bazlur Rahman