[jdk21u-dev] RFR: 8315503: G1: Code root scan causes long GC pauses due to imbalanced iteration

[Goetz Lindenmaier]

On Mon, 8 Apr 2024 20:00:14 GMT, Goetz Lindenmaier <goetz at openjdk.org> wrote:

> I backport this for parity with 21.0.4-oracle.
> 
> I had to resolve 3 files:
> 
> src/hotspot/share/gc/g1/heapRegion.cpp
> Hunk #1 had to be resolved. "8140326: G1: Consider putting regions where evacuation failed into next collection set" is not in 21.
> It adds the "keep_tracked" argument.
> 
> src/hotspot/share/gc/g1/heapRegionRemSet.cpp
> Resolved hunk #2 because of "8140326: G1: Consider putting regions where evacuation failed into next collection set".
> Resolved hunk #4 because "8313202: MutexLocker should disallow null Mutexes" is not in 21
> (other Mutex class).
> 
> src/hotspot/share/gc/g1/heapRegionRemSet.cpp
> Resulved hunk #2, dual to hunk #2 in .cpp file.
> 
> Resolved hunks are in a commit of their own.
> 
> I include the two direct follow ups 
> 8317440: Lock rank checking fails when code root set is modified with the Servicelock held after JDK-8315503
> 8318720: G1: Memory leak in G1CodeRootSet after JDK-8315503
> 
> Both apply clean on top.
> 
> I'll backport the third follow-up
> 8323685: PrintSystemDictionaryAtExit has mutex rank assert
> as dependend backport on top of these. It also applies clean,
> but I think it is too large to merge it in here.

That's what I thought, too. 
We discussed this, and decided we want to have the whole set of changes addressing the class unloading issue in 21 following Oracle.  To reduce the risk we ask for extra reviews :)
It will run through our testing tonight.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/476#issuecomment-2044614479