RFR: 8331572: Allow using OopMapCache outside of STW GC phases [v2]

[Aleksey Shipilev]

On Wed, 15 May 2024 22:02:55 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> > This looks good but one question for ZGC, does ZGC need an OopMapCache::cleanup_old_entries() ?
> 
> We still call `OopMapCache::cleanup_old_entries() ` after STW pause, but now concurrent phase also can accumulate old entries, should we unify them? e.g. all depend on service thread to clean up old entries?

Yes. I think the post-GC cleanup is opportunistic after this patch: it is not necessary, since service thread is supposed to catch up with cleanups, but we might still do it after the phases that we know might generate lots of old entries. This is why I left current calls to `cleanup_old_entries()` in current paths, and we might consider adding those for ZGC paths as well. I don't see a strong pressure to do it here, though.

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PR Comment: https://git.openjdk.org/jdk/pull/19229#issuecomment-2114328579