[jdk16u] RFR: 8259231: Epsilon: improve performance under contention during virtual space expansion

[Aleksey Shipilev]

This improves Epsilon performance under heavy contention.

Additional testing:
 - [x] Linux x86_64 fastdebug `gc/epsilon`
 - [x] Linux x86_64 release `gc/epsilon`

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

Commit messages:
 - Backport 722f23610e128991e21ba1b56ddf2b7eec99e5c2

Changes: https://git.openjdk.java.net/jdk16u/pull/66/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=66&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259231
  Stats: 39 lines in 1 file changed: 17 ins; 4 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/66.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/66/head:pull/66

PR: https://git.openjdk.java.net/jdk16u/pull/66