RFR: 8317371: GenShen: Needs improved support for humongous allocation [v3]

[Kelvin Nilsen]

On Thu, 12 Oct 2023 18:00:21 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Cosmetic improvements
>
> src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.cpp line 405:
> 
>> 403:   if (cand_idx > _last_old_collection_candidate) {
>> 404:     // Sort the regions that were initially rejected from the collection set in order of index.
>> 405:     QuickSort::sort<RegionData>(candidates + _last_old_collection_candidate, cand_idx - _last_old_collection_candidate,
> 
> What is the purpose of sorting these regions by index? How does this aid defragmentation?

I will add a comment to clarify.

> src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.cpp line 566:
> 
>> 564:     size_t first_old_region, last_old_region;
>> 565:     double density;
>> 566:     fragmentation_trigger_reason(density, first_old_region, last_old_region);
> 
> Just use the member fields here?

I'm not sure which member fields you are recommending here.

ShenandoahFreeSet remembers first and last indexes of the OldCollector free set, but the range we are interested in here includes all retired old-gen regions in addition to the free regions.

If I'm misunderstanding your suggestion, please clarify.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/336#discussion_r1357605590
PR Review Comment: https://git.openjdk.org/shenandoah/pull/336#discussion_r1357604320