RFR: 8267833: Improve G1CardSetInlinePtr::add()

[Kim Barrett]

On Tue, 10 Aug 2021 13:02:26 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Hi all,
> 
> Please review this cleanup change to reduce the number of comparisons made when adding entries to an inline pointer cardset container. We allow the find to restart from a previously known index.
> 
> Testing: Tier 1-3

Changes requested by kbarrett (Reviewer).

src/hotspot/share/gc/g1/g1CardSetContainers.inline.hpp line 54:

> 52:     uint num_elems = num_cards_in(_value);
> 53:     if (num_elems > 0) {
> 54:       cur_idx = find(card_idx, bits_per_card, cur_idx, num_elems);

I found the naming here a bit confusing, with `num_elems` here but `end_at` in the find function.  Similarly in `contains`.

src/hotspot/share/gc/g1/g1CardSetContainers.inline.hpp line 95:

> 93: }
> 94: 
> 95: inline bool G1CardSetInlinePtr::contains(uint card_idx, uint bits_per_card) {

I think `contains` previously didn't use it's `card_idx` argument.  Is it needed by any callers?  Or was the previous non-use just a performance bug?

src/hotspot/share/gc/g1/g1CardSetContainers.inline.hpp line 97:

> 95: inline bool G1CardSetInlinePtr::contains(uint card_idx, uint bits_per_card) {
> 96:   uint num_elems = num_cards_in(_value);
> 97:   if(num_elems == 0) {

Space after `if`

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PR: https://git.openjdk.java.net/jdk/pull/5067