Compressed oops are remarkably important for lots of services. Unfortunately, there is no clear way to enforce their use, especially on heaps closer to 32GB. The exact boundary depends on a few factors, notably the choice of GC.

Counter-intuitively, even when users supply -XX:+UseCompressedOops explicitly, VM configured with incompatible heap size just silently disables UseCompressedOops and continues:
https://github.com/openjdk/jdk/blob/c8e64cb7a578f1a32b48f76649fe19900ba6d040/src/hotspot/share/runtime/arguments.cpp#L1415-L1418.

I think we can improve UX on that part: if user supplied -XX:+UseCompressedOops, and JVM cannot do it, exit right away with the error message. Something like this:

```
diff --git a/src/hotspot/share/runtime/arguments.cpp b/src/hotspot/share/runtime/arguments.cpp
index 0d0b58412ae..37463407c8a 100644
--- a/src/hotspot/share/runtime/arguments.cpp
+++ b/src/hotspot/share/runtime/arguments.cpp
@@ -1407,14 +1407,16 @@ void Arguments::set_use_compressed_oops() {
   // to use UseCompressedOops are InitialHeapSize and MinHeapSize.
   size_t max_heap_size = MAX3(MaxHeapSize, InitialHeapSize, MinHeapSize);
 
- if (max_heap_size <= max_heap_for_compressed_oops()) {
+ size_t max_heap_size_coops = max_heap_for_compressed_oops();
+ if (max_heap_size <= max_heap_size_coops) {
     if (FLAG_IS_DEFAULT(UseCompressedOops)) {
       FLAG_SET_ERGO(UseCompressedOops, true);
     }
   } else {
     if (UseCompressedOops && !FLAG_IS_DEFAULT(UseCompressedOops)) {
- warning("Max heap size too large for Compressed Oops");
- FLAG_SET_DEFAULT(UseCompressedOops, false);
+ vm_exit_during_initialization(err_msg("Compressed oops are requested, but configured max heap size ("
+ PROPERFMT ") is larger than max heap size for compressed oops (" PROPERFMT ")",
+ PROPERFMTARGS(max_heap_size), PROPERFMTARGS(max_heap_size_coops)));
     }
   }
 #endif // _LP64
```