RFR: 8291718: Remove mark_for_deoptimization from klass unloading [v5]

[Axel Boldt-Christmas]

On Thu, 4 Aug 2022 13:36:51 GMT, Axel Boldt-Christmas <duke at openjdk.org> wrote:

>> @stefank suggested creating a separate issue for this part of [JDK-8291237](https://bugs.openjdk.org/browse/JDK-8291237) 
>> 
>> Description from the original issue: 
>>> The klass unloading code currently sets the mark for deoptimzation flag on nmethods that depend on the klass being unloaded. That however is all it does, there is no guarantee that those nmethods will become not entrant and make_deoptimized. The current implementation may if some future deoptimization happens to trigger see these marks as it scans the whole code cache, but it is never triggered from klass unloading. 
>>> 
>>> Me and [~eosterlund] discussed this and this behaviour seems like some leftover from earlier versions of klass unloading. There should be no reason to eliminate the nmethods that depend on unloaded klasses except to eliminate dead code. It is probably better to let other mechanisms decide if an nmethod with dead code should be deoptimized than the klass unloading. 
>>> 
>>> It might be a future improvement to have some stats which record that an nmethod had some dependency to an unloaded klass which might effect the heuristic for selecting what methods are deoptimized.
>> 
>> Testing: Tier 1-7
>
> Axel Boldt-Christmas has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove double counting _perf_total_buckets_deallocated_count

The perf counters were double counting some deallocations. The release and purge code was already handling it. This code would just double count any `not_unloading` dependencies.

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PR: https://git.openjdk.org/jdk/pull/9713