RFR: 8319650: Improve heap dump performance with class metadata caching [v5]

[Aleksey Shipilev]

> See the rationale and some profiles in the bug.
> 
> This PR implements simple caching for object instance dumping, which is overwhelmingly hottest path in heap dumping code. This allows to put the cache straight in `HeapObjectDumper`, which is effectively thread local. A simple hash table would then work to cache the class metadata.
> 
> Given a simple workload from the bug, these are the motivational improvements and historical perspective:
> 
> 
> $ for I in `seq 1 3`; do java -XX:+UseParallelGC -XX:+HeapDumpAfterFullGC -Xms8g -Xmx8g HeapDump.java 2>&1 | grep created; rm *.hprof; done
> 
> # Baseline JDK 8u382
> Heap dump file created [1440865228 bytes in 5.492 secs]
> Heap dump file created [1440865228 bytes in 5.460 secs]
> Heap dump file created [1440865228 bytes in 5.471 secs]
> 
> # Baseline JDK 11.0.21
> Heap dump file created [1446043070 bytes in 5.088 secs]
> Heap dump file created [1446042039 bytes in 5.096 secs]
> Heap dump file created [1446042835 bytes in 5.081 secs]
> 
> # Baseline JDK 17.0.10
> Heap dump file created [1446841531 bytes in 3.276 secs]
> Heap dump file created [1446841673 bytes in 3.342 secs]
> Heap dump file created [1446841590 bytes in 3.323 secs]
> 
> # Baseline JDK 21.0.2 EA
> Heap dump file created [1447828697 bytes in 5.516 secs]
> Heap dump file created [1447829756 bytes in 5.461 secs]
> Heap dump file created [1447829539 bytes in 5.435 secs]
> 
> # Baseline JDK 22
> Heap dump file created [1447285149 bytes in 5.232 secs]
> Heap dump file created [1447285149 bytes in 5.211 secs]
> Heap dump file created [1447284813 bytes in 5.222 secs]
> 
> # Patched JDK 22
> Heap dump file created [1447285087 bytes in 1.071 secs]
> Heap dump file created [1447285149 bytes in 1.073 secs]
> Heap dump file created [1447285073 bytes in 1.058 secs]
> 
> 
> This amounts to 5x improvement, 1.2 GB/sec dump rate (somewhat I/O limited), and the best heap dump performance across all JDK releases. I am planning to backport this patch where possible: at least to JDK 21u, but hopefully to JDK 17u as well.
> 
> There are other simple improvements, but this one is the top bottleneck.

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Drop StackObj

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/16545/files
  - new: https://git.openjdk.org/jdk/pull/16545/files/fb3b32ce..562fbb6d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16545&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16545&range=03-04

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16545.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16545/head:pull/16545

PR: https://git.openjdk.org/jdk/pull/16545