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8295319: pending_cards_at_gc_start doesn't include cards in thread buffers #10914

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@kimbarrett kimbarrett commented Oct 31, 2022

Please review this change to G1 to include the per-thread buffers in the
number of pending cards at the start of a young GC.

DCQS::concatenate_logs has been renamed to concatenate_logs_and_stats, and now
also merges the per-thread refinement stats during the thread walk to flush
buffers. That replaces the separate thread walk to merge and record these
stats earlier in the GC. The merged stats and related info don't seem to be
needed until after the buffer flushing.

Also, when abandoning dirty card buffers and stats because of a full GC, fixed
to also abandon an buffers in the paused buffers lists.

Testing:
mach5 tier1-3
performance testing found no significant changes, as expected.


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  • JDK-8295319: pending_cards_at_gc_start doesn't include cards in thread buffers

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/10914/head:pull/10914
$ git checkout pull/10914

Update a local copy of the PR:
$ git checkout pull/10914
$ git pull https://git.openjdk.org/jdk pull/10914/head

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Checkout this PR locally:
$ git pr checkout 10914

View PR using the GUI difftool:
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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/10914.diff

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👋 Welcome back kbarrett! 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.

@openjdk openjdk bot added the rfr Pull request is ready for review label Oct 31, 2022
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openjdk bot commented Oct 31, 2022

@kimbarrett The following label will be automatically applied to this pull request:

  • hotspot-gc

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the hotspot-gc hotspot-gc-dev@openjdk.org label Oct 31, 2022
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mlbridge bot commented Oct 31, 2022

Webrevs

@walulyai
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calculate_collection_set -> finalize_initial_collection_set -> finalize_young_part:
size_t pending_cards = _policy->pending_cards_at_gc_start() + _g1h->hot_card_cache()->num_entries();

called before pre_evacuate_collection_set

flush_dirty_card_logs_and_stats needs to be called before calculate_collection_set

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calculate_collection_set -> finalize_initial_collection_set -> finalize_young_part: size_t pending_cards = _policy->pending_cards_at_gc_start() + _g1h->hot_card_cache()->num_entries();

called before pre_evacuate_collection_set

flush_dirty_card_logs_and_stats needs to be called before calculate_collection_set

Sigh! Looks like I got lost while tracking down the callers and call chains.

So the use in finalize_young_part is presumably using the pending cards count from the previous
collection, which usually isn't such a bad value that it causes anything goes off the rails, so testing
didn't spot a problem.

I kind of hate some of that code, which has too many non-obvious and unchecked (and not easily
checked) ordering constraints.

Thanks for spotting this.

@kimbarrett
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calculate_collection_set -> finalize_initial_collection_set -> finalize_young_part: size_t pending_cards = _policy->pending_cards_at_gc_start() + _g1h->hot_card_cache()->num_entries();
called before pre_evacuate_collection_set
flush_dirty_card_logs_and_stats needs to be called before calculate_collection_set

Sigh! Looks like I got lost while tracking down the callers and call chains.

Fixed now.

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Lgtm!

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openjdk bot commented Nov 1, 2022

@kimbarrett 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:

8295319: pending_cards_at_gc_start doesn't include cards in thread buffers

Reviewed-by: iwalulya, tschatzl

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 no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential 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.

@openjdk openjdk bot added the ready Pull request is ready to be integrated label Nov 1, 2022
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Lgtm.

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openjdk bot commented Nov 3, 2022

@kimbarrett this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout cards-in-threads
git fetch https://git.openjdk.org/jdk master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

@openjdk openjdk bot added merge-conflict Pull request has merge conflict with target branch and removed ready Pull request is ready to be integrated labels Nov 3, 2022
@kimbarrett
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Thanks @walulyai and @tschatzl for reviews.

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/integrate

@openjdk openjdk bot added ready Pull request is ready to be integrated and removed merge-conflict Pull request has merge conflict with target branch labels Nov 3, 2022
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openjdk bot commented Nov 3, 2022

Going to push as commit 0349803.

@openjdk openjdk bot added the integrated Pull request has been integrated label Nov 3, 2022
@openjdk openjdk bot closed this Nov 3, 2022
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Nov 3, 2022
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openjdk bot commented Nov 3, 2022

@kimbarrett Pushed as commit 0349803.

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

@kimbarrett kimbarrett deleted the cards-in-threads branch November 4, 2022 00:28
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