8371019: G1: Support heap expansion during startup

Reviewed-by: eosterlund, tschatzl

Author: kstefanj

src/hotspot/share/gc/g1/g1CollectedHeap.cpp

@@ -185,10 +185,13 @@ G1HeapRegion* G1CollectedHeap::new_region(size_t word_size,
   G1HeapRegion* res = _hrm.allocate_free_region(type, node_index);
 
   if (res == nullptr && do_expand) {
-    // Currently, only attempts to allocate GC alloc regions set
-    // do_expand to true. So, we should only reach here during a
-    // safepoint.
-    assert(SafepointSynchronize::is_at_safepoint(), "invariant");
+    // There are two situations where do_expand is set to true:
+    //  - for mutator regions during initialization
+    //  - for GC alloc regions during a safepoint
+    // Make sure we only reach here before initialization is complete
+    // or during a safepoint.
+    assert(!is_init_completed() ||
+           SafepointSynchronize::is_at_safepoint() , "invariant");
 
     log_debug(gc, ergo, heap)("Attempt heap expansion (region allocation request failed). Allocation request: %zuB",
                               word_size * HeapWordSize);
@@ -3101,7 +3104,7 @@ G1HeapRegion* G1CollectedHeap::new_mutator_alloc_region(size_t word_size,
   if (should_allocate) {
     G1HeapRegion* new_alloc_region = new_region(word_size,
                                                 G1HeapRegionType::Eden,
-                                                false /* do_expand */,
+                                                policy()->should_expand_on_mutator_allocation() /* do_expand */,
                                                 node_index);
     if (new_alloc_region != nullptr) {
       new_alloc_region->set_eden();

src/hotspot/share/gc/g1/g1Policy.cpp

@@ -1187,8 +1187,21 @@ double G1Policy::predict_region_code_root_scan_time(G1HeapRegion* hr, bool for_y
 }
 
 bool G1Policy::should_allocate_mutator_region() const {
-  uint young_list_length = _g1h->young_regions_count();
-  return young_list_length < young_list_target_length();
+  if (_g1h->young_regions_count() < young_list_target_length()) {
+    return true;
+  }
+
+  if (should_expand_on_mutator_allocation()) {
+    return true;
+  }
+
+  return false;
+}
+
+bool G1Policy::should_expand_on_mutator_allocation() const {
+  // We can't do a GC during init so allow additional mutator
+  // allocations until we can GC.
+  return !is_init_completed();
 }
 
 bool G1Policy::use_adaptive_young_list_length() const {

src/hotspot/share/gc/g1/g1Policy.hpp

@@ -367,6 +367,7 @@ class G1Policy: public CHeapObj<mtGC> {
   uint young_list_target_length() const { return AtomicAccess::load(&_young_list_target_length); }
 
   bool should_allocate_mutator_region() const;
+  bool should_expand_on_mutator_allocation() const;
 
   bool use_adaptive_young_list_length() const;