RFR: 8302215: G1: Last-ditch Full GC should do serial compaction for tail regions in per thread compaction points. [v3]

[Ivan Walulya]

On Wed, 15 Feb 2023 16:09:14 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> I also prefer the sort. Common case, the number of regions in serial == ~no of threads.
>
>> Fwiw, I tend to prefer the sort call as it is least amount of code that achieves the goal well enough. All these other suggestions seem to be optimizations for little gain that need lots of extra code/helper data structures for something not (time) critical.
> 
> I think what I suggested requires less code than the sorting approach.
> 
>> Common case, the number of regions in serial == ~no of threads
> 
> True for now, but when humongous regions can be moved, this number can go up.

After discussions with @albertnetymk, we settled for the latest solution that iterates the `_region_attr_table`.

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

PR: https://git.openjdk.org/jdk/pull/12529