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

[Thomas Schatzl]

On Wed, 17 Nov 2021 14:58:21 GMT, Vishal Chand <duke at openjdk.java.net> wrote:

>>> @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.

Hi @vish-chan - I changed the name of the CR to "Configurable card table card size" because we are done with the investigation :) No, honestly, "investigate xyz" is a bad title for a specification change (CSR) and a release note.
You need to update the title of the PR accordingly. Only you as creator can do that. Thanks.

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