[jdk16u] RFR: 8268127: Shenandoah: Heap size may be too small for region to align to large page size

[Zhengyu Gu]

I would like to backport this Shenandoah specific patch to 16u, which allows to fallback to regular pages for regions, if heap size is too small to allow regions to use large pages.

The original patch does not apply cleanly,  resolved then manually.

Test:
  Manually test to ensure large pages are used. Failed w/o the patch and passed with it.

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Commit messages:
 - Fixed merge

Changes: https://git.openjdk.java.net/jdk16u/pull/128/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=128&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268127
  Stats: 34 lines in 3 files changed: 20 ins; 1 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/128.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/128/head:pull/128

PR: https://git.openjdk.java.net/jdk16u/pull/128