RFR: JDK-8293114: GC should trim the native heap [v11]

[Thomas Stuefe]

On Wed, 5 Jul 2023 18:37:41 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 41 commits:
>> 
>>  - fix windows build
>>  - Merge branch 'master' into JDK-8293114-GC-trim-native
>>  - wip
>>  - Merge branch 'master' into JDK-8293114-GC-trim-native
>>  - wip
>>  - Remove adaptive stepdown coding
>>  - Merge master
>>  - wip
>>  - Merge branch 'master' into JDK-8293114-GC-trim-native
>>  - wip
>>  - ... and 31 more: https://git.openjdk.org/jdk/compare/22e17c29...162b880a
>
> src/hotspot/share/memory/arena.cpp line 105:
> 
>> 103: 
>> 104:   static void clean() {
>> 105:     ThreadCritical tc;
> 
> Why do you need `ThreadCritical` here? I would have thought `PauseMark` handles everything right?

Unrelated to pause. I introduced an empty check on all pools, but that has to happen under lock protection too. So I moved up the 4 ThreadCriticals from the prune functions to this function.

The point is to avoid pausing if nothing is done, which is most of the time. Also, instead of 4 calls to ThreadCritical, just one.

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PR Review Comment: https://git.openjdk.org/jdk/pull/10085#discussion_r1254019061