RFR: 8365571: GenShen: PLAB promotions may remain disabled for evacuation threads

[William Kemper]

Mutators and GC workers have old generation LABs for promotions and old generation evacuations. Priority is given to old evacuations by using a promotion budget. Once the promotion budget is exhausted, a thread local flag is set to disable further promotions (the LAB can still be used for old evacuations). This thread local flag is meant to be cleared to allow all threads to resume promotions on the next cycle. However, this flag is only reset for workers that perform thread root evacuations, which may not be the same workers that perform subsequent evacuations. This patch clears the flag for all threads when their LABs are retired at the end of evacuation.

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Commit messages:
 - Re-enable plab promotions for all threads when plabs are retired

Changes: https://git.openjdk.org/jdk/pull/26785/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26785&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365571
  Stats: 24 lines in 2 files changed: 5 ins; 15 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26785.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26785/head:pull/26785

PR: https://git.openjdk.org/jdk/pull/26785