RFR: JDK-8255603: Memory/Performance regression after JDK-8210985

[Christoph Langer]

On Thu, 29 Oct 2020 18:02:47 GMT, Xue-Lei Andrew Fan <xuelei at openjdk.org> wrote:

>>> > Benchmarking is probably hard because we don't know the average occupancy of the map.
>>> 
>>> I agreed. No matter what the default value is, it will not fit perfectly in all situations. The value 1 may be fit for small workload applications, but not good for big workload applications. Applications could use the size setting APIs for the tuning. For this update, I think the impact for various workload may be limited/acceptable, but I'm not very sure of it. Benchmarking data with various workload would help us for a better sense.
>> 
>> But we did run with `1` for quite a long time without somebody complaining :)
>
>> > > Benchmarking is probably hard because we don't know the average occupancy of the map.
>> > 
>> > 
>> > I agreed. No matter what the default value is, it will not fit perfectly in all situations. The value 1 may be fit for small workload applications, but not good for big workload applications. Applications could use the size setting APIs for the tuning. For this update, I think the impact for various workload may be limited/acceptable, but I'm not very sure of it. Benchmarking data with various workload would help us for a better sense.
>> 
>> But we did run with `1` for quite a long time without somebody complaining :)
> 
> Yes, I think it is a safe update and looks good to me.  I believe the impact should be minimal.  But normally, I would like to check with a test for sure.  If no regression test, an explain with noreg tag may be needed.  External testing, like a confirmation of no performance regression any longer in an existing application,  is fine.
> 
> I don't want to block this integration, please go ahead if you are confident with it.

I added the noreg-hard label to the JBS bug. I'll wait for any further input til monday, before integration.

@XueleiFan would be nice if you could approve then, too :)

-------------

PR: https://git.openjdk.java.net/jdk/pull/937