RFR: 8272773: Investigate making card table size configurable [v3]

[Vishal Chand]

On Mon, 11 Oct 2021 13:47:29 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Currently I'm not scaling card size with region size, as it is not required. With current supported region sizes (1M to 32M) and card sizes (512b, 1024B), all the possible combinations of region size and card size are valid combinations. If we include 256b cards or 64M regions, then invalid combinations will be there which would need to be handled. 
>> Do you think that code/logic is needed now, or we can add if and when needed?
>
> Okay, let's leave it at that for now.
> 
> Note that all that kept me thinking over the weekend, and I found an easy way (the remembered set refactoring in 18 made that possible) to completely decouple heap region size from remembered sets.
> 
> So soon we'll be able to have heap region sizes > 32M without any restrictions. Same for card table sizes, they can be set independently of region size now (although 1024 is max as long as we fix BOT and card table size to the same).
> 
> Then we can re-introduce the option to allow smaller (probably 256, *maybe* 128) card table sizes.

Great, sounds good.

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