[jdk17u-dev] RFR: 8308643: Incorrect value of 'used' jvmstat counter

[Martin Doerr]

Backport of [JDK-8308643](https://bugs.openjdk.org/browse/JDK-8308643).

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Commit messages:
 - Backport 92167505b217c0e6074f58f8479be97bc4c776b3

Changes: https://git.openjdk.org/jdk17u-dev/pull/1494/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1494&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308643
  Stats: 150 lines in 5 files changed: 107 ins; 4 del; 39 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1494.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1494/head:pull/1494

PR: https://git.openjdk.org/jdk17u-dev/pull/1494