RFR: 8236176: Parallel GC SplitInfo comment should be updated for shadow regions

[Thomas Schatzl]

On Fri, 20 Aug 2021 06:48:18 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Hi all,
> 
> Please review this small change to add a high-level description of how shadow regions are utilized during the compact phase of the parallel GC. There is no special handling of Splitinfo by the shadow regions; the destination computation and the handling of partial_objects are done during the summary phase while the shadow regions optimization only applies to compaction. 
> 
> Additionally, some unused variables are cleaned up.

Lgtm apart from my comments about some comment typos.

src/hotspot/share/gc/parallel/psParallelCompact.hpp line 964:

> 962: // region that can be put on the ready list.  The regions are atomically added
> 963: // and removed from the ready list.
> 964: //

This commentactually refers to the sentence: "// An alternate strategy is being investigated for this deferral of updating." above.

This sentence should be removed as this offers no information about the current algorithm. Fwiw I do not know that actually anyone is working on that, and if so, a CR in JIRA would be more appropriate. I could not find anything in JIRA about work on this, and given that comment is pretty old, this is just confusing.

src/hotspot/share/gc/parallel/psParallelCompact.hpp line 968:

> 966: // destination regions may also be source regions themselves.  Consequently, the
> 967: // destination regions are not available for processing until all live objects
> 968: // within them are evacuated to their destinations. These dependencies lead to

There is a mix of one and two spaces after a full stop (5 times I think) in this and the next paragraph. I recommend using two spaces like in the above paragraphs for uniformity.

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Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5195