src/hotspot/share/jfr/leakprofiler/leakProfiler.cpp

@@ -32,19 +32,21 @@
  #include "memory/iterator.hpp"
  #include "runtime/javaThread.inline.hpp"
  #include "runtime/vmThread.hpp"
  
  bool LeakProfiler::is_supported() {
-   if (UseShenandoahGC || UseZGC) {
-     // Leak Profiler uses mark words in the ways that might interfere
-     // with concurrent GC uses of them. This affects Shenandoah.
-     //
-     // Generational ZGC only does weak reference processing in the old generation.
-     // All objects that would usually die, because we are sampling stuff
-     // that immediately becomes garbage, will be artificially kept alive
-     // until an old-generation collection. This incurs a significant
-     // performance hit by causing allocation stalls.
+   if (UseCompactObjectHeaders || UseShenandoahGC || UseZGC) {
+     // 1. With a 32-bit mark word in Lilliput2, we don't have enough unused
+     //    bits to store edge index information in the mark word
+     // 2. Even without compressed object headers, with Shenandoah, we don't
+     //    have enough free bits in the mark word because of needing that
+     //    space for forwarding pointers in the evacuation & update refs phase.
+     // 3. Generational ZGC only does weak reference processing in the old generation.
+     //    All objects that would usually die, because we are sampling stuff
+     //    that immediately becomes garbage, will be artificially kept alive
+     //    until an old-generation collection. This incurs a significant
+     //    performance hit by causing allocation stalls.
      return false;
    }
    return true;
  }