RFR: 7903455: JMH: Add "mempool" profiler [v2]

[Eric Caspole]

> I started off to show only the code cache related size, but I don't see any reason to not print all the available mbean pool info. We often adapt app or library code to run as JMH, to use all its benefits. In those cases seeing the code cache stats is more interesting than say, for a regular JDK API JMH benchmark. I verified the CodeHeap stats match well with +PrintCodeCache. There is mbean pool data for all the GCs as well.
> 
> Example output:
> 
> Benchmark                                                              (iterations)  Mode  Cnt      Score   Error  Units
> SpillCode.testSpillForManyInts                                                   10  avgt    5    705.433 ± 9.570  ns/op
> SpillCode.testSpillForManyInts:·CodeHeap 'non-nmethods'.used                     10  avgt    5   1139.000             kB
> SpillCode.testSpillForManyInts:·CodeHeap 'non-profiled nmethods'.used            10  avgt    5    209.750             kB
> SpillCode.testSpillForManyInts:·CodeHeap 'profiled nmethods'.used                10  avgt    5    924.875             kB
> SpillCode.testSpillForManyInts:·Compressed Class Space.used                      10  avgt    5    403.375             kB
> SpillCode.testSpillForManyInts:·G1 Eden Space.used                               10  avgt    5   8192.000             kB
> SpillCode.testSpillForManyInts:·G1 Old Gen.used                                  10  avgt    5   8160.000             kB
> SpillCode.testSpillForManyInts:·G1 Survivor Space.used                           10  avgt    5        ≈ 0             kB
> SpillCode.testSpillForManyInts:·Metaspace.used                                   10  avgt    5   3617.320             kB
> SpillCode.testSpillForManyInts:·Total CodeHeap.used                              10  avgt    5   2267.000             kB
> SpillCode.testSpillForManyInts:·Total MemPools.used                              10  avgt    5  22639.695             kB

Eric Caspole has updated the pull request incrementally with one additional commit since the last revision:

  Add newline at end of file

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Changes:
  - all: https://git.openjdk.org/jmh/pull/99/files
  - new: https://git.openjdk.org/jmh/pull/99/files/01d175d7..72c014a2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmh&pr=99&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmh&pr=99&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmh/pull/99.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/99/head:pull/99

PR: https://git.openjdk.org/jmh/pull/99