RFR: 8199407: Skip Rebuild Remset Phase if there are no rebuild candidates [v2]

[Thomas Schatzl]

On Fri, 16 Apr 2021 10:01:33 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> Hi all,
>> 
>> Please review this change that skips the rebuild remset phase and the associated updates after rebuild, If during Remark, G1 finds that there are no remembered sets to rebuild.
>> 
>> Test: tier1-5
>
> Ivan Walulya has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:
> 
>  - Fix issues raised in Thomas review, and add test
>  - Merge remote-tracking branch 'upstream/master' into JDK-8199407
>  - remove trailing white space
>  - Merge branch 'master' into JDK-8199407
>  - variable name refactor
>  - variable name refactor
>  - skip iterations that depend on total_selected_for_rebuild
>  - skip the rebuild remembered set phase if remark did not select any regions for rebuilding

Lgtm, maybe that comment could be improved.

Forgot last check for whether the messages are at an appropriate level, so reverting back to "Request changes". Sorry.

test/hotspot/jtreg/gc/g1/TestSkipRebuildRemsetPhase.java line 85:

> 83: 
> 84:         private static Object alloc() {
> 85:             // G1MixedGCLiveThresholdPercent=20

Maybe this comment could be elaborated a bit further - i.e. "Since G1Mixed...ent is 20%, make sure to allocate something that is larger than that so that it will not be collected and the expected message printed."
Or just remove it.

-------------

Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3434Changes requested by tschatzl (Reviewer).