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

@@ -759,12 +759,20 @@
    RegionCount = align_up(max_heap_size, RegionSizeBytes) / RegionSizeBytes;
    guarantee(RegionCount >= MIN_NUM_REGIONS, "Should have at least minimum regions");
  
    // Limit TLAB size for better startup behavior and more equitable distribution of memory between contending mutator threads.
    guarantee(MaxTLABSizeWords == 0, "we should only set it once");
-   MaxTLABSizeWords = align_down(MIN2(RegionSizeWords, MAX2(RegionSizeWords / 32, (size_t) (256 * 1024) / HeapWordSize)),
-                                 MinObjAlignment);
+   // With compact object headers an object may grow by one word when an identity
+   // hash-code is injected during a GC copy. Never let the max TLAB equal a whole
+   // region: a region-sized TLAB could serve a region-sized object (bypassing the
+   // humongous path) and would itself be a region-sized LAB allocation request. Cap
+   // it one (object-aligned) word below the region so neither can happen.
+   size_t max_tlab_words = MIN2(RegionSizeWords, MAX2(RegionSizeWords / 32, (size_t) (256 * 1024) / HeapWordSize));
+   if (UseCompactObjectHeaders) {
+     max_tlab_words = MIN2(max_tlab_words, RegionSizeWords - align_object_size(1));
+   }
+   MaxTLABSizeWords = align_down(max_tlab_words, MinObjAlignment);
  
    guarantee(MaxTLABSizeBytes == 0, "we should only set it once");
    MaxTLABSizeBytes = MaxTLABSizeWords * HeapWordSize;
    assert (MaxTLABSizeBytes > MinTLABSize, "should be larger");