JDK-8315479: GenShen: Expand old-gen while selecting collection set during GLOBAL GC #318

kdnilsen · 2023-09-01T16:49:35Z

With GenShen, the size of old generation is as small as possible in order to maximize memory available to young gen. This generally allows less frequent (and therefore more efficient) young-gen collections.

Under normal operation (concurrent marking of old followed by a series of mixed evacuations), old-gen is expanded at the end of a previous GC cycle in order to accommodate evacuation of mixed-evacuation candidates.

However, when we do a GLOBAL collection, we need to expand OLD gen during the selection of the collection set, depending on how many old-gen regions are selected to be evacuated during the GC evacuation phase. This PR makes the change.

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Issue

JDK-8315479: GenShen: Expand old-gen while selecting collection set during GLOBAL GC (Sub-task - P4)

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William Kemper (@earthling-amzn - Committer) ⚠️ Review applies to 10f8e145

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/shenandoah.git pull/318/head:pull/318
$ git checkout pull/318

Update a local copy of the PR:
$ git checkout pull/318
$ git pull https://git.openjdk.org/shenandoah.git pull/318/head

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$ git pr checkout 318

View PR using the GUI difftool:
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https://git.openjdk.org/shenandoah/pull/318.diff

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bridgekeeper · 2023-09-01T16:50:44Z

👋 Welcome back kdnilsen! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

mlbridge · 2023-09-01T17:19:46Z

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earthling-amzn

A couple of minor nits.

earthling-amzn · 2023-09-01T20:59:09Z

src/hotspot/share/gc/shenandoah/heuristics/shenandoahGlobalHeuristics.cpp

@@ -101,31 +125,50 @@ void ShenandoahGlobalHeuristics::choose_global_collection_set(ShenandoahCollecti
  for (size_t idx = 0; idx < size; idx++) {
    ShenandoahHeapRegion* r = data[idx]._region;
    if (cset->is_preselected(r->index())) {
+      assert(false, "There should be no preselected regions during GLOBAL GC");


Slightly more readable:

fatal("There should be no preselected regions during GLOBAL GC");

Thanks. I'll make this change.

earthling-amzn · 2023-09-01T21:00:20Z

src/hotspot/share/gc/shenandoah/heuristics/shenandoahGlobalHeuristics.cpp

      if ((new_cset <= max_old_cset) && (r->garbage() > garbage_threshold)) {
        add_region = true;
        old_cur_cset = new_cset;
      }
-    } else if (r->age() < tenuring_threshold) {
+    } else {
+      // r->is_young() && (r->age() < tenuring_threshold)


I'll make this change also.

kdnilsen · 2023-09-05T18:04:59Z

Though GHA checks have all passed, our internal CI pipelines have encountered a few problems:

stress_dacapo (5 of 5 runs) encounters:

#  Error: Verify init-mark remembered set violation; clean card should be dirty

This issue is being addressed under separate ticket: https://bugs.openjdk.org/browse/JDK-8315044

earthling-amzn · 2023-09-06T15:43:22Z

src/hotspot/share/gc/shenandoah/heuristics/shenandoahGlobalHeuristics.cpp

      if ((new_cset <= max_old_cset) && (r->garbage() > garbage_threshold)) {
        add_region = true;
        old_cur_cset = new_cset;
      }
-    } else if (r->age() < tenuring_threshold) {
+    } else {
+      assert(r->is_young() && (r->age() < tenuring_threshold), "DeMorgan\'s law");


Not quite DeMorgan's law because r could be unaffiliated (it isn't supposed to be, of course). Does the straight quote needs to be escaped?

I'm fixing the message here.

openjdk · 2023-09-06T15:50:02Z

@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:

8315479: GenShen: Expand old-gen while selecting collection set during GLOBAL GC

Reviewed-by: wkemper

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 2 new commits pushed to the master branch:

c4d0a24: 8315044: GenShen: Verifier detects clean card should be dirty
2d76fb1: 8315478: GenShen: Tolerate round-off errors in preselected promotion budget

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

kdnilsen · 2023-09-06T16:32:43Z

/integrate

openjdk · 2023-09-06T16:34:07Z

Going to push as commit 33a8085.
Since your change was applied there have been 2 commits pushed to the master branch:

c4d0a24: 8315044: GenShen: Verifier detects clean card should be dirty
2d76fb1: 8315478: GenShen: Tolerate round-off errors in preselected promotion budget

Your commit was automatically rebased without conflicts.

openjdk · 2023-09-06T16:34:17Z

@kdnilsen Pushed as commit 33a8085.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

kdnilsen added 3 commits August 31, 2023 22:07

Let choose_collection_set() for GLOBAL gc expand old on demand

0fac0e1

Keep promo budget at zero during GLOBAL GC

cc9e92f

Remove instrumentation

5d7d69a

Fix whitespace

ed9cba6

openjdk bot added the rfr Pull request is ready for review label Sep 1, 2023

earthling-amzn reviewed Sep 1, 2023

View reviewed changes

kdnilsen added 3 commits September 5, 2023 18:15

Respond to reviewer feedback

dde91e7

Fix typos in comment

bd2c520

More typos in comments

10f8e14

earthling-amzn reviewed Sep 6, 2023

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earthling-amzn approved these changes Sep 6, 2023

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openjdk bot added the ready Pull request is ready to be integrated label Sep 6, 2023

Fixup comment

867fcf0

openjdk bot added the integrated Pull request has been integrated label Sep 6, 2023

openjdk bot closed this Sep 6, 2023

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 6, 2023

ysramakrishna mentioned this pull request Aug 25, 2024

8338780: GenShen: Fix up some comments #484

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JDK-8315479: GenShen: Expand old-gen while selecting collection set during GLOBAL GC #318

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