On Tue, 6 Oct 2026 00:25:32 GMT, Patrick Fontanilla <[email protected]> wrote:
> ### Summary > For Shenandoah and ZGC, safepoint workers were created at startup and only > used for heap dump and heap inspection. If heap dump or heap inspection never > runs, these threads consume memory without doing any work. For G1 and > Parallel, GC pauses and non-GC safepoints share the GC worker pool, so heap > dump and heap inspection don't need a separate worker pool. The downside is > that dump and inspection work contributes to GC CPU time, which can affect > how G1 sizes its heap. > > ### Changes > Safepoint workers are replaced with a diagnostic worker pool used by heap > dump and heap inspection. The diagnostic worker pool is created on the first > heap dump or heap inspection that requests more than one thread, if the > collector supports parallel heap iteration and `os::active_processor_count()` > > 1. The pool holds at most `os::active_processor_count()` workers, and > workers stay alive until the VM exits. > > G1 and Parallel no longer lend their GC worker pool. ZGC's `ZRuntimeWorkers` > is deleted because it's no longer used. For Shenandoah, diagnostic workers > have no GCLAB and fall back to shared allocation when they evacuate objects. > > ### Testing all passed > - linux-x86_64-server-fastdebug: `hotspot:tier1_gc`, > `hotspot:tier1_serviceability`, `gc/shenandoah` > - GHA > - Internal CI pipeline > > ### Benchmarking > Running HeapDump.java from > [JDK-8319650](https://bugs.openjdk.org/browse/JDK-8319650) with 8 GB heap and > 36 CPUs > ``` > ┌───────────┬─────────────────────┬─────────────────────┐ > │ Collector │ Master │ Branch │ > ├───────────┼─────────────────────┼─────────────────────┤ > │ Serial │ 3.200, 3.197, 3.199 │ 3.231, 3.247, 3.221 │ > ├───────────┼─────────────────────┼─────────────────────┤ > │ Parallel │ 0.971, 0.953, 0.976 │ 0.957, 0.921, 0.918 │ > ├───────────┼─────────────────────┼─────────────────────┤ > │ G1 │ 0.999, 1.009, 0.985 │ 0.936, 0.948, 0.911 │ > └───────────┴─────────────────────┴─────────────────────┘ > > > > > --------- > - [x] I confirm that I make this contribution in accordance with the [OpenJDK > Interim AI Policy](https://openjdk.org/legal/ai). This pull request has now been integrated. Changeset: f921bd7c Author: Patrick Fontanilla <[email protected]> Committer: Rui Li <[email protected]> URL: https://git.openjdk.org/jdk/commit/f921bd7c9e2388673f9f1e6ba59666e9c9fc9542 Stats: 641 lines in 21 files changed: 434 ins; 152 del; 55 mod 8392050: Purge CollectedHeap::safepoint_workers() support Reviewed-by: stefank, shade, wkemper, kdnilsen ------------- PR: https://git.openjdk.org/jdk/pull/33218
