RFR: 8272773: Investigate making card table size configurable

[Thomas Schatzl]

On Fri, 8 Oct 2021 14:23:14 GMT, Vishal Chand <github.com+10235864+vish-chan at openjdk.org> wrote:

>> Another question we need to answer is whether smaller card size than 512 gains anything - if not, I recommend keeping to use 512 at minimum, as otherwise the card table will obviously use much more memory for no gain.
>
> I'm trying to identify the usecases where we can see better performance with small card sizes. Right now, I have none. So, I'll set the minimum card size to 512 right now. Intention is to have a design such that if someone finds a usecase which gives better performance with smaller cards, only the minimum card size needs to be changed in the code, nothing else. Shall I keep this current behavior of overriding card_size based on region size till there's some feedback from others? or Do I need to change this?

Let's keep the minimum card size to 512 for now, this can be investigated further separately. As you said, this can be changed easily.

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PR: https://git.openjdk.java.net/jdk/pull/5838