64位操作系统上32位JVM的最大Java堆大小
问题不在于32位操作系统上的最大堆大小，因为32位OSes的最大可寻址内存大小为4 4GB，并且JVM的最大堆大小取决于可以保留多少连续的空闲内存。
我更感兴趣的是知道在64位操作系统中运行的32位JVM的最大堆大小(理论上和实际上都可以实现)。基本上，我正在寻找类似于the figures in a related question on SO的答案。
至于为什么使用32位JVM而不是64位JVM，原因不是技术原因，而是管理/官僚作风-在生产环境中安装64位JVM可能为时已晚。
回答 8
Stack Overflow用户
发布于 2009-09-16 19:02:05
64位操作系统上32位JVM的限制与32位操作系统上32位JVM的限制完全相同。毕竟，32位JVM将在32位虚拟机上运行(在虚拟化意义上)，因此它不会知道它正在64位操作系统/机器上运行。
与在32位操作系统上运行32位JVM相比，在64位操作系统上运行32位JVM的一个优点是您可以拥有更多的物理内存，因此不会经常遇到交换/分页。然而，只有当您有多个进程时，这一优势才能真正充分实现。
Stack Overflow用户
发布于 2011-12-11 18:23:56
Oracle当前拥有的JROCKIT JVM支持非连续堆使用，因此当JVM在64位windows操作系统上运行时，允许32位JVM访问超过3.8 GB的内存。(在32位操作系统上运行时为2.8 GB )。
http://blogs.oracle.com/jrockit/entry/how_to_get_almost_3_gb_heap_on_windows
JVM可以在以下地址免费下载(需要注册)
http://www.oracle.com/technetwork/middleware/jrockit/downloads/index.html
Stack Overflow用户
发布于 2013-05-04 03:03:49
以下是在Solaris和Linux 64位环境下的一些测试
Solaris10- SPARC - T5220机器，内存32 GB (空闲约9 GB )
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3750m MaxMemory
Error occurred during initialization of VM
Could not reserve space for ObjectStartArray
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3700m MaxMemory
Total Memory: 518520832 (494.5 MiB)
Max Memory: 3451912192 (3292.0 MiB)
Free Memory: 515815488 (491.91998291015625 MiB)
Current PID is: 28274
Waiting for user to press Enter to finish ...
$ java -version
java version "1.6.0_30"
Java(TM) SE Runtime Environment (build 1.6.0_30-b12)
Java HotSpot(TM) Server VM (build 20.5-b03, mixed mode)
$ which java
/usr/bin/java
$ file /usr/bin/java
/usr/bin/java: ELF 32-bit MSB executable SPARC Version 1, dynamically linked, not stripped, no debugging information available
$ prstat -p 28274
PID USERNAME SIZE RSS STATE PRI NICE TIME CPU PROCESS/NLWP
28274 user1 670M 32M sleep 59 0 0:00:00 0.0% java/35顺便说一句:显然Java在启动时并没有分配太多的实际内存。似乎每个启动的实例只需要大约100MB(我启动了10个)
Solaris10- x86 - VMWare虚拟机，8 GB内存(约3 GB可用*)
3 GB的空闲内存并不是真的。ZFS缓存使用了大量的RAM，但是我没有root访问权限来检查到底有多少
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3650m MaxMemory
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3600m MaxMemory
Total Memory: 516423680 (492.5 MiB)
Max Memory: 3355443200 (3200.0 MiB)
Free Memory: 513718336 (489.91998291015625 MiB)
Current PID is: 26841
Waiting for user to press Enter to finish ...
$ java -version
java version "1.6.0_41"
Java(TM) SE Runtime Environment (build 1.6.0_41-b02)
Java HotSpot(TM) Server VM (build 20.14-b01, mixed mode)
$ which java
/usr/bin/java
$ file /usr/bin/java
/usr/bin/java: ELF 32-bit LSB executable 80386 Version 1 [FPU], dynamically linked, not stripped, no debugging information available
$ prstat -p 26841
PID USERNAME SIZE RSS STATE PRI NICE TIME CPU PROCESS/NLWP
26841 user1 665M 22M sleep 59 0 0:00:00 0.0% java/12具有4 GB内存的RedHat 5.5 - x86 - VMWare VM (使用了约3.8 GB内存- 200 MB的缓冲区和3.1 GB的缓存，因此约3 GB可用)
$ alias java='$HOME/jre/jre1.6.0_34/bin/java'
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3500m MaxMemory
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3450m MaxMemory
Total Memory: 514523136 (490.6875 MiB)
Max Memory: 3215654912 (3066.6875 MiB)
Free Memory: 511838768 (488.1274871826172 MiB)
Current PID is: 21879
Waiting for user to press Enter to finish ...
$ java -version
java version "1.6.0_34"
Java(TM) SE Runtime Environment (build 1.6.0_34-b04)
Java HotSpot(TM) Server VM (build 20.9-b04, mixed mode)
$ file $HOME/jre/jre1.6.0_34/bin/java
/home/user1/jre/jre1.6.0_34/bin/java: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), for GNU/Linux 2.2.5, not stripped
$ cat /proc/21879/status | grep ^Vm
VmPeak: 3882796 kB
VmSize: 3882796 kB
VmLck: 0 kB
VmHWM: 12520 kB
VmRSS: 12520 kB
VmData: 3867424 kB
VmStk: 88 kB
VmExe: 40 kB
VmLib: 14804 kB
VmPTE: 96 kB同一台机器使用JRE7
$ alias java='$HOME/jre/jre1.7.0_21/bin/java'
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3500m MaxMemory
Error occurred during initialization of VM
Could not reserve enough space for object heap
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
$ java -XX:PermSize=128M -XX:MaxPermSize=256M -Xms512m -Xmx3450m MaxMemory
Total Memory: 514523136 (490.6875 MiB)
Max Memory: 3215654912 (3066.6875 MiB)
Free Memory: 511838672 (488.1273956298828 MiB)
Current PID is: 23026
Waiting for user to press Enter to finish ...
$ java -version
java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) Server VM (build 23.21-b01, mixed mode)
$ file $HOME/jre/jre1.7.0_21/bin/java
/home/user1/jre/jre1.7.0_21/bin/java: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.9, dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped
$ cat /proc/23026/status | grep ^Vm
VmPeak: 4040288 kB
VmSize: 4040288 kB
VmLck: 0 kB
VmHWM: 13468 kB
VmRSS: 13468 kB
VmData: 4024800 kB
VmStk: 88 kB
VmExe: 4 kB
VmLib: 10044 kB
VmPTE: 112 kBhttps://stackoverflow.com/questions/1434779
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