RFR: 8342444: Shenandoah: Uncommit regions from a separate, STS aware thread [v7]

[William Kemper]

On Wed, 20 Nov 2024 09:26:19 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Yeah, at least restore the log format and add `gc+start` log as well.
>
> This one is still not addressed, unfortunately ^

Yes, I spent some time trying to resurrect `ShenandoahConcurrentPhase` for uncommit here, but it really doesn't want to be used outside of a gc cycle. Also, previously it was logging heap _usage_, which isn't quite what we want here (this may actually increase during this phase, which makes it seem as though nothing is being uncommitted).

I've restored the original logging format, but instead of logging heap usage it is now logging heap committed before and after. Here is an excerpt from specjbb2015 with `-Xms5g -Xmx10g`:


[2024-11-20T20:02:25.056+0000][97.396s][22293][info][gc,start       ] Concurrent uncommit
[2024-11-20T20:02:25.072+0000][97.412s][22293][info][gc             ] Concurrent uncommit 5424M->5120M(5120M) 15.988ms
[2024-11-20T20:05:17.916+0000][270.255s][22293][info][gc,start       ] Concurrent uncommit
[2024-11-20T20:05:18.169+0000][270.508s][22293][info][gc             ] Concurrent uncommit 10240M->5120M(5120M) 253.048ms
[2024-11-20T20:06:45.329+0000][357.668s][22293][info][gc,start       ] Concurrent uncommit
[2024-11-20T20:06:45.596+0000][357.935s][22293][info][gc             ] Concurrent uncommit 10240M->5120M(5120M) 267.144ms
[2024-11-20T20:06:57.147+0000][369.486s][22293][info][gc,start       ] Concurrent uncommit
[2024-11-20T20:06:57.148+0000][369.487s][22293][info][gc             ] Concurrent uncommit 5456M->5440M(5440M) 1.189ms

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PR Review Comment: https://git.openjdk.org/jdk/pull/22019#discussion_r1850939713