src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.hpp

*** 299,11 ***
  
    inline static size_t required_regions(size_t bytes) {
      return (bytes + ShenandoahHeapRegion::region_size_bytes() - 1) >> ShenandoahHeapRegion::region_size_bytes_shift();
    }
  
!   inline static bool requires_humongous(size_t words) {
      return words > ShenandoahHeapRegion::RegionSizeWords;
    }
  
    inline static size_t region_count() {
      return ShenandoahHeapRegion::RegionCount;
--- 299,28 ---
  
    inline static size_t required_regions(size_t bytes) {
      return (bytes + ShenandoahHeapRegion::region_size_bytes() - 1) >> ShenandoahHeapRegion::region_size_bytes_shift();
    }
  
!   // Whether an allocation of the given word size must occupy a contiguous run of
+   // humongous regions rather than fitting in a single region.
+   //
+   // may_expand_for_hash must be set only when 'words' is the *base* size of a
+   // freshly allocated, not-yet-hashed object that could later grow by one word
+   // when an identity hash-code is injected as it is copied during GC (see
+   // oopDesc::copy_size). In that case we account for that potential growth when
+   // deciding whether the object needs the humongous path, so an object whose
+   // expanded form would overflow a region is routed to humongous from the start.
+   // It must be false for every size that is already final:
+   //   - the live size of an existing object (obj->size()), which already includes
+   //     the hash word once the object has been expanded by a prior GC copy;
+   //   - an evacuation/promotion copy size (copy_size()), which is already expanded;
+   //   - a raw LAB buffer (TLAB/GCLAB/PLAB), which never grows.
+   inline static bool requires_humongous(size_t words, bool may_expand_for_hash) {
+     if (UseCompactObjectHeaders && may_expand_for_hash) {
+       words = oopDesc::hash_expanded_size(words);
+     }
      return words > ShenandoahHeapRegion::RegionSizeWords;
    }
  
    inline static size_t region_count() {
      return ShenandoahHeapRegion::RegionCount;