[GitHub] [openwhisk-runtime-java] chetanmeh edited a comment on issue #74: Dynamically setting the JVM memory limit by reading the Cgroup

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chetanmeh edited a comment on issue #74: Dynamically setting the JVM memory limit by reading the Cgroup
URL: https://github.com/apache/openwhisk-runtime-java/pull/74#issuecomment-524178152
 
 
   @mrutkows Currently the java runtime uses openj9 instead of openjdk
   
   https://github.com/apache/openwhisk-runtime-java/blob/a8e666f7b38d533192fce897342037f4ca570a41/core/java8/Dockerfile#L18
   
   Open J9 does not support `-XX:+UseCGroupMemoryLimitForHeap` and instead has a different flag  [UseContainerSupport][1]. This flag is enabled by default in Docker base images we use in OpenWhisk
   
   ```
   $ docker run --rm -m 1g openwhisk/java8action /bin/bash -c 'echo $JAVA_TOOL_OPTIONS'
   -XX:+IgnoreUnrecognizedVMOptions -XX:+UseContainerSupport -XX:+IdleTuningCompactOnIdle -XX:+IdleTuningGcOnIdle
   ```
   
   See also [this blog post][2].
   
   Also j9 does not support `-XX:+PrintFlagsFinal` instead provides [few different flags to get the defaults][3]. Based on that
   
   ```
   $ docker run --rm -m 1g openwhisk/java8action sh -c "java -verbose:sizes -version"
     -Xmca32K        RAM class segment increment
     -Xmco128K       ROM class segment increment
     -Xmcrs200M      compressed references metadata initial size
     -Xmns2M         initial new space size
     -Xmnx128M       maximum new space size
     -Xms8M          initial memory size
     -Xmos6M         initial old space size
     -Xmox512M       maximum old space size
     -Xmx512M        memory maximum
     -Xmr16K         remembered set size
     -Xlp:objectheap:pagesize=4K	 large page size
                     available large page sizes:
                     4K
     -Xlp:codecache:pagesize=4K	 large page size for JIT code cache
                     available large page sizes for JIT code cache:
                     4K
     -Xmso256K       operating system thread stack size
     -Xiss2K         java thread stack initial size
     -Xssi16K        java thread stack increment
     -Xss1M          java thread stack maximum size
   openjdk version "1.8.0_181"
   OpenJDK Runtime Environment (build 1.8.0_181-b13)
   Eclipse OpenJ9 VM (build openj9-0.9.0, JRE 1.8.0 Linux amd64-64-Bit Compressed References 20180813_291 (JIT enabled, AOT enabled)
   OpenJ9   - 24e53631
   OMR      - fad6bf6e
   JCL      - a05586ac based on jdk8u181-b13)
   ```
   
   Per above `-Xmx512M        memory maximum` it appears that it is configured to use 512M when container is launched with 1 GB memory
   
   So I believe we are good here and do not need to explicitly specify memory settings for build version we are using
   
   [1]: https://www.eclipse.org/openj9/docs/xxusecontainersupport/
   [2]: https://royvanrijn.com/blog/2018/05/java-and-docker-memory-limits/#test-6-openj9-nightly
   [3]: https://github.com/eclipse/openj9/issues/527#issuecomment-497003442

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