On Fri, 27 May 2022 02:12:32 GMT, Yi Yang <yy...@openjdk.org> wrote: >> Yes counting it twice is wrong but this is the wrong fix. The pools are not >> defined correctly. > >> Sorry for chiming in in a not very helpful way, but I am not sure what even >> the point is of this API. >> >> I'm seriously interested in who uses it, and for what. Calculating real >> memory usage is notoriously difficult. This one seems to be just an >> arbitrary selection of stuff. It leaves out C-heap usage (VM, outer JDK, and >> third party libs), native mappings, sometimes massive system library >> overhead, text segments, thread stacks... that it counts class space twice >> is probably its smallest problem... > > AFAIK, some DevOps platforms monitor JVM memory occupation by MemoryMXBean: > >  > > Users are confused about why `HeapMemory+NonHeapMemory` is not equal to > resident memory(top->res). It's still not clear what NonHeap means from `Java > Doc`, I tried to understand the definition of NonHeap in source code, then > found this bug...
"non-heap" is any memory not part of the Java heap. But it is up to an implementation to decide what kinds of non-heap memory are represented by memory pools. The JavaDoc can only give possible examples not numerate an actual required set. ------------- PR: https://git.openjdk.java.net/jdk/pull/8831
