8314573: G1: Heap resizing at Remark does not take existing eden regi…

…ons into account

Backport-of: 762b652

src/hotspot/share/gc/g1/g1HeapSizingPolicy.cpp

@@ -217,7 +217,14 @@ size_t G1HeapSizingPolicy::full_collection_resize_amount(bool& expand) {
   // Capacity, free and used after the GC counted as full regions to
   // include the waste in the following calculations.
   const size_t capacity_after_gc = _g1h->capacity();
-  const size_t used_after_gc = capacity_after_gc - _g1h->unused_committed_regions_in_bytes();
+  const size_t used_after_gc = capacity_after_gc -
+                               _g1h->unused_committed_regions_in_bytes() -
+                               // Discount space used by current Eden to establish a
+                               // situation during Remark similar to at the end of full
+                               // GC where eden is empty. During Remark there can be an
+                               // arbitrary number of eden regions which would skew the
+                               // results.
+                               _g1h->eden_regions_count() * HeapRegion::GrainBytes;
 
   size_t minimum_desired_capacity = target_heap_capacity(used_after_gc, MinHeapFreeRatio);
   size_t maximum_desired_capacity = target_heap_capacity(used_after_gc, MaxHeapFreeRatio);