With >1 mio individual mappings (which may happen, e.g. when using ZGC), NMT detail report becomes unusable slow (I stopped my fastdebug JVM after 90 minutes).

We burn all the time here:

```
- 96,63% 96,16% Attach Listener libjvm.so [.] VirtualMemoryAllocationWalker::do_allocation_site
      - VirtualMemoryAllocationWalker::do_allocation_site
         - VirtualMemoryAllocationWalker::do_allocation_site
           SortedLinkedList<ReservedMemoryRegion, &(compare_virtual_memory_base(ReservedMemoryRegion const&, ReservedMemoryRegion const&)), (AnyObj::allocation_type)2, (MEMFLAGS)12, (AllocFailStrategy::AllocFailEnum)1>::add (inlined)
           LinkedListImpl<ReservedMemoryRegion, (AnyObj::allocation_type)2, (MEMFLAGS)12, (AllocFailStrategy::AllocFailEnum)1>::add (inlined)
         - SortedLinkedList<ReservedMemoryRegion, &(compare_virtual_memory_base(ReservedMemoryRegion const&, ReservedMemoryRegion const&)), (AnyObj::allocation_type)2, (MEMFLAGS)12, (AllocFailStrategy::AllocFailEnum)1>::add (inlined)
            - compare_virtual_memory_base (inlined)
            - VirtualMemoryRegion::compare (inlined)
                 45,79% VirtualMemoryRegion::overlap_region (inlined)
                 4,32% VirtualMemoryRegion::compare (inlined)
```

.. doing a sorted insert into the target array, which is O(n^2):

```
(gdb) bt
#0 0x00007efc894c13f9 in VirtualMemoryRegion::overlap_region (sz=4096, addr=0x7efb788bf000 "", this=0x7efaae2f6918) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/nmt/virtualMemoryTracker.hpp:201
#1 VirtualMemoryRegion::compare (rgn=..., this=0x7efaae2f6918) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/nmt/virtualMemoryTracker.hpp:251
#2 compare_virtual_memory_base (r2=..., r1=...) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/nmt/memBaseline.cpp:115
#3 SortedLinkedList<ReservedMemoryRegion, &(compare_virtual_memory_base(ReservedMemoryRegion const&, ReservedMemoryRegion const&)), (AnyObj::allocation_type)2, (MEMFLAGS)12, (AllocFailStrategy::AllocFailEnum)1>::add (node=0x7efaae87f700, this=0x7efac9af8f18)
    at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/utilities/linkedlist.hpp:394
#4 LinkedListImpl<ReservedMemoryRegion, (AnyObj::allocation_type)2, (MEMFLAGS)12, (AllocFailStrategy::AllocFailEnum)1>::add (e=..., this=0x7efac9af8f18) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/utilities/linkedlist.hpp:167
#5 SortedLinkedList<ReservedMemoryRegion, &(compare_virtual_memory_base(ReservedMemoryRegion const&, ReservedMemoryRegion const&)), (AnyObj::allocation_type)2, (MEMFLAGS)12, (AllocFailStrategy::AllocFailEnum)1>::add (e=..., this=0x7efac9af8f18)
    at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/utilities/linkedlist.hpp:375
#6 VirtualMemoryAllocationWalker::do_allocation_site (rgn=<optimized out>, this=0x7efac9af8f10) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/nmt/memBaseline.cpp:130
#7 VirtualMemoryAllocationWalker::do_allocation_site (this=0x7efac9af8f10, rgn=<optimized out>) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/nmt/memBaseline.cpp:128
#8 0x00007efc89adfb86 in VirtualMemoryTracker::walk_virtual_memory (walker=walker@entry=0x7efac9af8f10) at /shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/nmt/virtualMemoryTracker.cpp:677
```