Created attachment 580826 [details] [diff] [review] patch I found that the sum of all the GC heap memory reporters was about 5% greater than the total size of the GC heap. Turns out there there two culprits: - The computation of gcHeapChunkDirtyUnused didn't account for gcHeapShapesBase. - "type-inference/object-main" was incorrectly marked as having JS_GC_HEAP_KIND. So "explicit", "gc-heap-chunk-dirty-unused", and "heap-unclassified" were all inflated slightly. I added an assertion to make sure that this mismatch will be detected if it occurs again in the future. (This assertion would also have caught the incorrect kind markings in bug 704391.) I also renamed countDecommittedArenas() because it was confusing the hell out of me.