Java in a Container: Difference between revisions
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<code>-XX:+UseCGroupMemoryLimitForHeap</code> configures the JVM to read [[Linux_cgroups#Memory_Limit|CGroups memory limit]] from /sys/fs/cgroup/memory/memory.limit_in_bytes and use it as a base when setting the max heap. Effectively, this option sets -XX:MaxRAM to the CGroups limit. By default, without any other configuration, the max heap is set to 1/4 of the CGroups value. To initialize max heap to a different value, use <code>-XX:MaxRAMFraction</code>, according to the formula: | <code>-XX:+UseCGroupMemoryLimitForHeap</code> configures the JVM to read [[Linux_cgroups#Memory_Limit|CGroups memory limit]] from /sys/fs/cgroup/memory/memory.limit_in_bytes and use it as a base when setting the max heap. Effectively, this option sets -XX:MaxRAM to the CGroups limit. By default, without any other configuration, the max heap is set to 1/4 of the CGroups value. To initialize max heap to a different value, use <code>-XX:MaxRAMFraction</code>, according to the formula: | ||
MaxRAM | |||
max_heap = ------------- | max_heap = ------------- | ||
MaxRAMFraction | MaxRAMFraction | ||
Revision as of 20:35, 6 November 2019
External
- https://developers.redhat.com/blog/2017/03/14/java-inside-docker/
- https://blog.softwaremill.com/docker-support-in-new-java-8-finally-fd595df0ca54
- https://stackoverflow.com/questions/54292282/clarification-of-meaning-new-jvm-memory-parameters-initialrampercentage-and-minr/54297753#54297753
Internal
- Docker Container Best Practices
- Java Memory
- Kubernetes Resources Management Concepts
- Docker Resources Management Concepts
Overview
When running java in a container, the max heap should always be explicitly set with -Xmx, based on the application needs and the container limits.
Java max heap limit can also be calculated based on the container limits.
Generic script that correlates JVM memory settings to the container limits: https://github.com/fabric8io-images/run-java-sh, https://github.com/fabric8io-images/run-java-sh/blob/master/fish-pepper/run-java-sh/fp-files/run-java.sh.
Let JVM Adjust Memory Relative to CGroups Limits
Experimental Options
Java 1.8.0_181
(since Java 1.8.0_131)
java -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -XX:MaxRAMFraction=50 -XX:+PrintFlagsFinal -version | grep MaxHeapSize
-XX:+UseCGroupMemoryLimitForHeap configures the JVM to read CGroups memory limit from /sys/fs/cgroup/memory/memory.limit_in_bytes and use it as a base when setting the max heap. Effectively, this option sets -XX:MaxRAM to the CGroups limit. By default, without any other configuration, the max heap is set to 1/4 of the CGroups value. To initialize max heap to a different value, use -XX:MaxRAMFraction, according to the formula:
MaxRAM
max_heap = -------------
MaxRAMFraction
Java 1.8.0_221
java -XX:MaxRAMPercentage=20.0 -XX:+PrintFlagsFinal -version | grep MaxHeapSize
Other flags:
-XX:InitialRAMPercentage
-XX:MinRAMPercentage