RFR: 8342444: Shenandoah: Uncommit regions from a separate, STS aware thread [v3]

[William Kemper]

On Tue, 19 Nov 2024 11:33:51 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Prevent uncommit thread from running during GC
>
> src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp line 253:
> 
>> 251:     }
>> 252: 
>> 253:     heap->allow_uncommit();
> 
> This looks to be happening on every iteration, even if no GC happened. Should this `allow_uncommit()` go into the same block where `allow_commit()` is? Maybe it would be cleaner to make a `StackObj` mark object to manage this state -- up to you.

Hmm, good catch. I think it's a little worse than this even. The code that is meant to trigger an uncommit:

    if (ShenandoahUncommit) {
      if (heap->check_soft_max_changed()) {
        heap->notify_soft_max_changed();
      } else if (is_gc_requested) {
        heap->notify_explicit_gc_requested();
      }
    }

Will only happen when uncommit is forbidden. The notification will fall on deaf ears, as it were. I'll fix this.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22019#discussion_r1848942547