RFR: JDK-8302820: Remove costs for NMTPreInit when NMT is off [v4]

[Thomas Stuefe]

On Thu, 2 Mar 2023 12:12:18 GMT, Andrew Dinn <adinn at openjdk.org> wrote:

> Hi Thomas,
> 
> I fully agree with the arguments you provided in https://bugs.openjdk.org/browse/JDK-8299196 for retaining NMT pre init tracking. So, I think this change is a necessary improvement.
> 
> However, I also agree with Justin that the cost of the leaks will be a case where the sum is greater than the parts due to fragmentation. It may well hurt more than is apparent. So, one of the three options you suggested to clear the redundant table entries should be implemented. I'd be happy to see that as a follow-up patch since:
> 
>     * this code is ready to ship and improves the status quo
> 
>     * a follow-up patch can investigate which is the best of the 3 options
> 
> 
> No nits as far as the code is concerned.

Hi @adinn,

thanks a lot for the review!

The latest version of my patch from tonight already frees the LU table nodes (see nmtPreinit.cpp 104ff). It was tested successfully tonight and in addition I ran x64 and x86 fastdebug release tests manually.

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PR: https://git.openjdk.org/jdk/pull/12642