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

[SendaoYan]

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

-------------

Commit messages:
 - Fix import bug
 - 8343340: Swapping checking do not work for MetricsMemoryTester failcount

Changes: https://git.openjdk.org/jdk/pull/27823/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27823&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343340
  Stats: 9 lines in 2 files changed: 2 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27823.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27823/head:pull/27823

PR: https://git.openjdk.org/jdk/pull/27823