[jdk21u-dev] RFR: 8315923: pretouch_memory by atomic-add-0 fragments huge pages unexpectedly

[Liming Liu]

This pull request ports JDK-8315923 back to JDK-21, as JDK-21 still uses atomic-add-0 to pretouch memory and results fragmented huge pages. This backport has the following differences with its original version:

- TestTransparentHugePageUsage.java gets deleted as it was deleted in JDK-8324776;
- nullptr is adopted in pretouch_thp_and_use_concurrent, as it is a part of  JDK-8327171;
- JDK-8324781 is included, as JDK-8324781 only makes changes to testcases.

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Commit messages:
 - 8324781: runtime/Thread/TestAlwaysPreTouchStacks.java failed with Expected a higher ratio between stack committed and reserved 8325218: gc/parallel/TestAlwaysPreTouchBehavior.java fails
 - 8315923: pretouch_memory by atomic-add-0 fragments huge pages unexpectedly

Changes: https://git.openjdk.org/jdk21u-dev/pull/825/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=825&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315923
  Stats: 120 lines in 11 files changed: 98 ins; 8 del; 14 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/825.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/825/head:pull/825

PR: https://git.openjdk.org/jdk21u-dev/pull/825