RFR: 8343340: Swapping checking do not work for MetricsMemoryTester failcount

[Severin Gehwolf]

On Wed, 15 Oct 2025 14:18:41 GMT, SendaoYan <syan at openjdk.org> wrote:

> Hi all,
> 
> The sub-test failcount in jdk/internal/platform/docker/TestDockerMemoryMetrics.java requires swap memory enable on the test host. But the swap memory check introduced by JDK-8264524 do not work correctly, because it's missing jvm option '-XX:+AlwaysPreTouch', shows as below. This PR add jvm option '-XX:+AlwaysPreTouch' to make the swap memory check work correctly, and use jtreg.SkippedException instead of print waring when this test can not execute.
> 
> Change has been verified locally on linux-x64. Test fix only, no risk.
> 
> 
>> free -h
> total used free shared buff/cache available
> Mem: 751Gi 513Gi 229Gi 5.0Mi 8.4Gi 234Gi
> Swap: 0B 0B 0B
> 
> 
> Without jvm option -XX:+AlwaysPreTouch, the 'java -Xms128m -Xmx128m -version' can start successfully:
> 
>> docker run --rm --memory=128m jdk-internal:test-jdk-internal-platform-docker-TestDockerMemoryMetrics-metrics-memory /jdk/bin/java -Xms128m -Xmx128m -version
> openjdk version "26" 2026-03-17
> OpenJDK Runtime Environment HJDK-0 (build 26+-42b2999c)
> OpenJDK 64-Bit Server VM HJDK-0 (build 26+-42b2999c, mixed mode, sharing)
> 
> 
> With jvm option -XX:+AlwaysPreTouch, the 'java -XX:+AlwaysPreTouch -Xms128m -Xmx128m -version' can not start and killed by docker(return code is 137):
> 
>> docker run --rm --memory=128m jdk-internal:test-jdk-internal-platform-docker-TestDockerMemoryMetrics-metrics-memory /jdk/bin/java -XX:+AlwaysPreTouch -Xms128m -Xmx128m -version ; echo $?
> 137

Please amend the comment on line 114 to something like this:


        // Check whether swapping really works for this test
        // On some systems there is no swap space enabled. And running
        // 'java -Xms{mem-limit} -Xmx{mem-limit} -XX:+AlwaysPreTouch -version'
        // would fail due to swap space size being 0. Note that when swap is
        // properly enabled on the system the container gets the same amount
        // of swap as is configured for memory. Thus, 2x{mem-limit} is the actual
        // memory and swap bound for this pre-test.

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PR Review: https://git.openjdk.org/jdk/pull/27823#pullrequestreview-3345562755