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

[Markus Grönlund]

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

Yes, thank you, I took a look at those fields too. Unfortunately, there is no value that bears directly on "current in-use". The reserved and committed will not be updated. If there was a value that could reflect the current usage, even if it means adding it to both EventCodeCacheFull and the JIT restart, that would be perfect. EventCodeCacheFull because in-use is x, JIT restart because in-use is now y. There are some statistics-related properties in the CodeHeap, like for example heap->unallocated_capacity(); et al. Could some of those expose this running value perhaps?

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