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

[Matthias Baesken]

On Wed, 6 Jul 2022 12:56:03 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

> 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?

Probably we would need  CodeCache::unallocated_capacity()  (contains a number of code heaps as far as I know)  to compare freed_memory to, because from what I see we iterate the whole CodeCache in NMethodSweeper::sweep_code_cache() .
But maybe someone with better knowledge about the CodeCache should comment here.

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