RFR: JDK-8289524: Add JFR JIT restart event [v2]

[Lutz Schmidt]

On Tue, 5 Jul 2022 13:47:31 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> The JIT compiler restarts (see restart_compiler in NMethodSweeper::sweep_code_cache) would be a helpful addition to the JFR events. Currently we log the JIT stop operations in JFR (EventCodeCacheFull) but no restart.
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Incorporate JIT compiler restart into EventSweepCodeCache

Changes look good to me.

To get an idea of how much memory was freed in relation to what's actually available, you could evaluate CodeCache:max_capacity(). This function returns the overall size of the code heap (across all segments). The performance impact is minimal and no locks are acquired.

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Marked as reviewed by lucy (Reviewer).

PR: https://git.openjdk.org/jdk/pull/9334