sequence

This article will focus on the new JDK support for Docker containers

Java8 and java9

Java 8U131 and above supports CPU and memory limits for Docker.

cpu limit

That is, if no explicit -xx :ParalllelGCThreads or -xx :CICompilerCount is specified, then the JVM uses the DOCker CPU limit. If the DOCker specified CPU limit and the JVM parameter specified -xx :ParalllelGCThreads or -xx :CICompilerCount, then the specified parameter will be used.

memory limit

In java8u131 + and java9, need to add – XX: XX: + UnlockExperimentalVMOptions – + UseCGroupMemoryLimitForHeap can make -xmx perception docker memory limit.

View the parameter defaults

java -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+PrintFlagsFinal
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Part of the output

     bool UseCGroupMemoryLimitForHeap              = false                               {experimental} {default}
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Can see in java9 UseCGroupMemoryLimitForHeap or experimental parameters, off by default.

java10

     bool UseCGroupMemoryLimitForHeap              = false                               {experimental} {default}
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Java10 UseCGroupMemoryLimitForHeap still experimental, but marked as obsolete.

However, java10 introduces a new parameter

      int ActiveProcessorCount                     = -1                                       {product} {default}
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ActiveProcessorCount can be used to specify the number of cpus

java11

Java11 officially removed UseCGroupMemoryLimitForHeap, code changes to see 8194086: Remove deprecated experimental flag UseCGroupMemoryLimitForHeap

A new parameter is also introduced

     bool UseContainerSupport                      = true                                     {product} {default}
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UseContainerSupport is true by default. You can use the -xlog: OS +container=trace argument to view details. The value of -xx :ActiveProcessorCount is used if specified, even if container support is disabled with -xx: -usecontainerSupport.

summary

Parameter/Version -XX:+UseCGroupMemoryLimitForHeap -XX:ActiveProcessorCount -XX:+UseContainerSupport
java9 Experimental, false by default There is no There is no
java10 Experimental, false by default – 1 There is no
java11 remove – 1 Product, default true

doc

  • Java SE support for Docker CPU and memory limits
  • Docker CPU limits
  • Experimental support for Docker memory limits
  • Docker memory limits
  • What to Expect from Java 10 — One Developer’s View
  • Remove deprecated experimental flag UseCGroupMemoryLimitForHeap
  • 8194086: Remove deprecated experimental flag UseCGroupMemoryLimitForHeap
  • Improve docker container detection and resource configuration usage