This patch refines Parallel's sizing strategy to improve overall memory management and performance.
The young generation layout has been reconfigured from the previous `eden-from/to` arrangement to a new `from/to-eden` order. This new layout facilitates young generation resizing, since we perform resizing after a successful young GC when all live objects are located at the beginning of the young generation. Previously, resizing was often inhibited by live objects residing in the middle of the young generation (from-space). The new layout is illustrated in `parallelScavengeHeap.hpp`. `NumberSeq` is now used to track various runtime metrics, such as minor/major GC pause durations, promoted/survived bytes after a young GC, highest old generation usage, etc. This tracking primarily lives in `AdaptiveSizePolicy` and its subclass `PSAdaptiveSizePolicy`. GC overhead checking, which was previously entangled with adaptive resizing logic, has been extracted and is now largely encapsulated in `ParallelScavengeHeap::is_gc_overhead_limit_reached`. ## Performance evaluation - SPECjvm2008-Compress shows ~8% improvement on Linux/AArch64 and Linux/x64 (restoring the regression reported in [JDK-8332485](https://bugs.openjdk.org/browse/JDK-8332485) and [JDK-8338689](https://bugs.openjdk.org/browse/JDK-8338689)). - Fixes the surprising behavior when using a non-default (smaller) value of `GCTimeRatio` with Heapothesys/Hyperalloc, as discussed in [this thread](https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-November/050146.html). - Performance is mostly neutral across other tested benchmarks: **DaCapo**, **SPECjbb2005**, **SPECjbb2015**, **SPECjvm2008**, and **CacheStress**. The number of young-gc sometimes goes up a bit and the total heap-size decreases a bit, because promotion-size-to-old-gen goes down with the more effective eden/survivor-space resizing. PS: I have opportunistically set the obsolete/expired version to 25/26 for now. I will update them accordingly before merging. Test: tier1-8 ------------- Commit messages: - pgc-size-policy Changes: https://git.openjdk.org/jdk/pull/25000/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25000&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8338977 Stats: 4365 lines in 29 files changed: 521 ins; 3446 del; 398 mod Patch: https://git.openjdk.org/jdk/pull/25000.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/25000/head:pull/25000 PR: https://git.openjdk.org/jdk/pull/25000
