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

[Vishal Chand]

On Tue, 16 Nov 2021 08:26:04 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> @vish-chan : the change for PR#5909 has finally been integrated. Sorry for the delay, things like a related bug delayed its integration more than expected.
>
>> @tschatzl I tested PR#5909 and this change: The combination of 1024b card/512M region is giving 2-3% improvement over 1024b card/32M region in SPECjbb2015 on my setup. I haven't analyzed this is detail though.
> 
> Good that the changed did not optimize away the improvements.
> 
>> 
>> Shall I update the pull request with new patch by:
>> 
>>     1. Removing min_card_size code as it is not relevant now.
> 
> Please do. It is unnecessary now as there are no limitations of the combination of card size/region size for G1 any more.
> 
>> 
>>     2. Update minimum card size supported from 512 to 128/256? Need your input on the min card size value and default card size value.
> 
> I'd say keep 512 bytes default. I looked a bit through literature, and the suggestion is that the minimum size used seems 128 bytes. That might be useful for smallish heaps.
> 
> Thanks,
>   Thomas
> 
> Edit: I messed up with the default value, @vish-chan, please keep 512 default.

@tschatzl I've updated the PR with a new patch: Removed the dependency of G1 heap region and card size. Set card size in [128. 1024] with 512 as default.

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