RFR: 8312116: GenShen: make instantaneous allocation rate triggers more timely [v24]

[Kelvin Nilsen]

On Thu, 5 Feb 2026 18:18:16 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> After studying large numbers of GC logs with degenerated cycles that have resulted from "late" triggers, we propose the following general improvements:
>> 
>> 1. Track trends in GC times rather than always using the average GC time plus standard deviation.  In many situations, GC times trend upward due to, for example, increasing amounts of live data that must be marked as a workload builds up its working set of memory.
>> 2. Sample allocation rates more frequently than once every 100 ms.
>> 3. Track trends in allocation rates.  In some situations, the allocation rate trends upwards due to, for example, the start of a new phase of execution or a spike in client workload.
>> 4. When we detect acceleration of allocation rate, predict consumption of memory based on accelerated allocation rates rather than assuming constant allocation rate.
>
> Kelvin Nilsen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 91 commits:
> 
>  - Merge remote-tracking branch 'jdk/master' into accelerated-triggers
>  - Make delay of acceleration trigger shorter
>  - Delay accelerated trigger until some garbage has accumulated
>  - Remove debug instrumentation
>  - no need to set_mutator_free_after_updaterefs
>  - Merge remote-tracking branch 'jdk/master' into accelerated-triggers
>  - some cosmetic improvements
>  - Use fewer samples to detect acceleration
>  - align log messages for trigger trace
>  - remove problematic debug messages
>  - ... and 81 more: https://git.openjdk.org/jdk/compare/949370ab...d6dfa2c7

Both master and this PR have evolved significantly since performance comparisons reported above were gathered.  I have repeated the measurements with updated master vs updated PR.  SpecJBB results now show a larger increase in max-jOPS and a small decrease in critical-jOPS:
<img width="398" height="175" alt="Screenshot 2026-02-09 at 3 42 28 PM" src="https://github.com/user-attachments/assets/7a7dc8ed-aa4c-4acf-83ba-dabd942a96c4" />

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

PR Comment: https://git.openjdk.org/jdk/pull/29039#issuecomment-3874469730