G1 GC是否具有最大区域大小或区域最大量？

问题描述

当我研究G1 GC时，我发现这篇文章：。在那篇文章中，有如下所示的内容：

这是否意味着G1 GC可以处理的java堆内存的最大大小是2048 * 32M，如果大小超过它，会发生什么事情？

解决方案

From ：

  //最小区域大小;我们不会低于这个水平。 
 //我们可能会在将来减少这个值，以便更有效地处理小
 //堆。 
 static const size_t MIN_REGION_SIZE = 1024 * 1024; 
 
 //最大区域大小;我们不会比这更高。有一个很好的
 //有一个上限的理由。我们不希望区域获得太多的
 //大，否则清理的效率会降低，因为
 //在
 //标记之后找到完全空的区域的机会会减少。 
 static const size_t MAX_REGION_SIZE = 32 * 1024 * 1024; 
 
 //自动区域大小计算将尝试在堆中的许多区域（基于最小堆大小）周围存在这个
。 
 static const size_t TARGET_REGION_NUMBER = 2048; 
  

• MIN_REGION_SIZE （1MB）和 MAX_REGION_SIZE （32MB）是硬性限制;
  
• TARGET_REGION_NUMBER 只是用于计算默认区域大小的提示，如果它没有在JVM选项中指定的话。实际数量可能超过此值。

when i studied G1 GC, I found this article: http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html. In that article, there is something says as follow:

Does that mean the max size of java heap memory that G1 GC can deal with is 2048 * 32M, and if the size exceeds it, what will happen?

解决方案

From HotSpot JVM sources:

  // Minimum region size; we won't go lower than that.
  // We might want to decrease this in the future, to deal with small
  // heaps a bit more efficiently.
  static const size_t MIN_REGION_SIZE = 1024 * 1024;

  // Maximum region size; we don't go higher than that. There's a good
  // reason for having an upper bound. We don't want regions to get too
  // large, otherwise cleanup's effectiveness would decrease as there
  // will be fewer opportunities to find totally empty regions after
  // marking.
  static const size_t MAX_REGION_SIZE = 32 * 1024 * 1024;

  // The automatic region size calculation will try to have around this
  // many regions in the heap (based on the min heap size).
  static const size_t TARGET_REGION_NUMBER = 2048;

• MIN_REGION_SIZE (1MB) and MAX_REGION_SIZE (32MB) are hard limits;
• TARGET_REGION_NUMBER is just a hint that is used to calculate default region size if it is not specified among JVM options. The actual number may exceed this value.

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