RFR: 8336086: G1: Use one G1CardSet instance for all young regions

[Ivan Walulya]

On Mon, 22 Jul 2024 19:37:56 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Hi all,
>> 
>> Please review this change to assign a single G1CardSet to all young regions. As young regions are collected at the same, and we do not have young-to-young remembered sets, we can maintain a single G1CardSet for all young regions.
>> 
>> This reduces the memory overhead of the G1CardSets and the time taken to merge per region G1CardSets during GC pause.
>> 
>> Testing: Tier 1-5
>
> src/hotspot/share/gc/g1/g1RemSetSummary.cpp line 227:
> 
>> 225:     size_t rs_mem_sz = hrrs->mem_size();
>> 226: 
>> 227:     if (r->is_young() && hrrs->has_group_cardset()) {
> 
> When do young-regions not have group cardset? (I thought the second condition would always be true if the first is met.)

Right, second condition should be removed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20134#discussion_r1687900443