G1 GC是否具有最大区域大小或区域最大量？ [英] Does G1 GC have a max size of region or max amount of region?

问题描述

当我研究G1 GC时，我发现这篇文章： http： //www.oracle.com/technetwork/articles/java/g1gc-1984535.html 。在那篇文章中，有如下所示的内容：

G1 GC是一个区域化和世代的垃圾收集器，这意味着Java对象堆（堆）被分成许多相同大小的区域。启动时，Java虚拟机（JVM）设置区域大小。根据堆大小，区域大小可以从1 MB到32 MB不等。目标是不超过2048个地区。

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 HotSpot JVM来源：

  //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:

The G1 GC is a regionalized and generational garbage collector, which means that the Java object heap (heap) is divided into a number of equally sized regions. Upon startup, the Java Virtual Machine (JVM) sets the region size. The region sizes can vary from 1 MB to 32 MB depending on the heap size. The goal is to have no more than 2048 regions.

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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