RFR: 8338440: Parallel: Improve fragmentation mitigation in Full GC

Thu Aug 15 07:05:15 UTC 2024

Extend `SplitInfo` to support more fine-grained splitting to mitigate the fragmentation issue during full GC. Added comments and diagrams in the process.

For easier review, it's best to start with `SplitInfo` and then proceed to see how it is constructed in `summarize_split_space` and consumed in `first_src_addr`. The accompanying diagrams should help create a clear mental image.

Test: tier1-8, systemgc micro bm, CacheStress, dacapo, specjbb2005, specjvm2008

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

Commit messages:
 - pgc-split-region

Changes: https://git.openjdk.org/jdk/pull/20590/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20590&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338440
  Stats: 569 lines in 2 files changed: 210 ins; 143 del; 216 mod
  Patch: https://git.openjdk.org/jdk/pull/20590.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20590/head:pull/20590

PR: https://git.openjdk.org/jdk/pull/20590