java - 'MaxRAM' JVM 参数表示什么？

Question

我正在查看在 Linux 服务器上运行的 JVM 的配置。当我运行时

java -XX:+PrintFlagsFinal | less | grep -iE 'MaxRam'

这似乎基本上打印出了 JDK 知道的几乎所有参数

我明白了

uint64_t MaxRAM = 137438953472  {pd product}

但我似乎找不到关于此标志的太多文档。

我发现 "{pd product}" 表示 "Platform Dependent Product: An officially supported, internal JVM option"

任何人都知道这个参数的确切含义，或者我可以在哪里阅读有关平台特定 JVM 标志的更多详细信息？

其他详细信息:

Java 版本: .

java version "1.6.0_35" Java(TM) SE Runtime Environment (build 1.6.0_35-b10) Java HotSpot(TM) 64-Bit Server VM (build 20.10-b01, mixed mode)

uname -a

Linux [SERVERNAME] 2.6.32-431.17.1.el6.x86_64 #1 [DATE] x86_64 x86_64 x86_64 GNU/Linux

Answer 1

根据 Standard Edition HotSpot Virtual Machine Garbage Collection Tuning Guide文档 MaxRAM 中的值用于计算默认堆大小，如果未指定初始堆大小和最大堆大小并且包含如前所述

Default Heap Size
Unless the initial and maximum heap sizes are specified on the command line, they are calculated based on the amount of memory on the machine. The proportion of memory to use for the heap is controlled by the command-line options InitialRAMFraction and MaxRAMFraction
[...]
The value of MaxRAM is platform-dependent.

指的是 Java Virtual机器规范堆的大小可以改变，这取决于 JVM 的实现。

The heap may be of a fixed size or may be expanded as required by the computation and may be contracted if a larger heap becomes unnecessary. The memory for the heap does not need to be contiguous. A Java Virtual Machine implementation may provide the programmer or the user control over the initial size of the heap, as well as, if the heap can be dynamically expanded or contracted, control over the maximum and minimum heap size.

并回答您的特定于平台的 JVM 标志问题:
Java HotSpot VM Options