8316299: GenShen: Reduce frequency of expedited GC

[kdnilsen]

We have found that expedited GCs too frequently yield very little benefit because they occur so soon after the previous GC that there has been no accumulation of garbage.

The primary motivation for expediting GC is to avoid a situation under which there is so much "promotion" work to be performed that the urgent need to reclaim garbage from young-generation is obstructed by this promotion work.

This PR ends the practice of expediting to support promotion in place. The effort required to promote a region in place is minimal and unlikely to contend in a major way with young collection efforts.

This PR also reduces the likelihood that we will expedite for promotion by evacuation, because it requires the amount of accumulated promo potential to exceed a particular threshold.

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Progress

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Issue

• JDK-8316299: GenShen: Reduce frequency of expedited GC (Bug - P3)

Reviewers

• Aleksey Shipilev (@shipilev - Committer) ⚠️ Review applies to 44b203a0
• William Kemper (@earthling-amzn - Committer)

Reviewing

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$ git checkout pull/325

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/shenandoah.git pull/325/head

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$ git pr checkout 325

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[bridgekeeper]

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[shipilev]

Looks okay, but I have a question:

[openjdk]

@kdnilsen This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8316299: GenShen: Reduce frequency of expedited GC

Reviewed-by: shade, wkemper

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[mlbridge]

Webrevs

• 01: Full - Incremental (de00edc3)
• 00: Full (44b203a0)

[earthling-amzn]

Can we also now delete ShenandoahHeap::get_promotion_in_place_potential and all the attendant code that maintains the value? This heuristic was the only place reading it.

[kdnilsen]

Good point. I'll do that.

[earthling-amzn]

Looks good - thanks!

[kdnilsen]

/integrate

[openjdk]

Going to push as commit aa1063f.
Since your change was applied there has been 1 commit pushed to the master branch:

• 88365d1: 8316297: GenShen: Degenerated GCs fail to make progress

Your commit was automatically rebased without conflicts.

[openjdk]

@kdnilsen Pushed as commit aa1063f.

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