RFR: 8287135: Calculation of jmm_GetMemoryUsage is wrong

[Ioi Lam]

On Mon, 23 May 2022 07:28:41 GMT, Yi Yang <yyang at openjdk.org> wrote:

> It seems that calculation of MemoryMXBean.getNonHeapMemoryUsage(jmm_GetMemoryUsage) is wrong.
> 
> Currently, `NonHeapUsage=CodeCache+Metaspace(ClassTypeSpace+NonClassTypeSpace)+CompressedClassSpace(ClassTypeSpace)`
> 
> ==> CodeHeap 'non-nmethods' 1532544 (Used)
> ==> CodeHeap 'profiled nmethods' 0
> ==> CodeHeap 'non-profiled nmethods' 13952
> ==> Metaspace 506696
> ==> Compressed Class Space 43312
> init = 7667712(7488K) used = 2096504(2047K) committed = 8454144(8256K) max = -1(-1K)
> 
> In this way, getNonHeapMemoryUsage is larger than it ought to be, it should be `NonHeapUsage = CodeCache + Metaspace`.

src/hotspot/share/services/management.cpp line 753:

> 751:     for (int i = 0; i < MemoryService::num_memory_pools(); i++) {
> 752:       MemoryPool* pool = MemoryService::get_memory_pool(i);
> 753:       if (pool->is_codeheap() || pool->is_metaspace()) {

Our only special case is that all the memory reported by `CompressedKlassSpacePool` are already reported by `MetaspacePool`, so shouldn't we do this:


if (pool->is_non_heap() && !pool->is_compressed_klass_space()) {
  // skip CompressedKlassSpacePool since its memory is already reported by
  // MetaspacePool

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PR: https://git.openjdk.java.net/jdk/pull/8831