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

[Aleksey Shipilev]

On Fri, 15 Nov 2024 21:35:03 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Currently, Shenandoah uncommits regions from its control thread. The control thread is responsible for starting GC cycles in a timely fashion. Uncommitting memory from this thread may introduce unwanted delays in the control thread's response to GC pressure.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Prevent uncommit thread from running during GC

I like it, thanks!

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.

src/hotspot/share/gc/shenandoah/shenandoahUncommitThread.cpp line 189:

> 187: void ShenandoahUncommitThread::allow_uncommit() {
> 188:   _uncommit_allowed.set();
> 189: }

New line at the end of file here.

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22019#pullrequestreview-2445178952
PR Review Comment: https://git.openjdk.org/jdk/pull/22019#discussion_r1848181197
PR Review Comment: https://git.openjdk.org/jdk/pull/22019#discussion_r1848183019