8336463: Parallel: Add PSOldGen::expand_and_allocate

Reviewed-by: iwalulya, zgu

src/hotspot/share/gc/parallel/mutableSpace.cpp

@@ -189,7 +189,12 @@ bool MutableSpace::cas_deallocate(HeapWord *obj, size_t size) {
 
 // Only used by oldgen allocation.
 bool MutableSpace::needs_expand(size_t word_size) const {
-  assert_lock_strong(PSOldGenExpand_lock);
+#ifdef ASSERT
+  // If called by VM thread, locking is not needed.
+  if (!Thread::current()->is_VM_thread()) {
+    assert_lock_strong(PSOldGenExpand_lock);
+  }
+#endif
   // Holding the lock means end is stable.  So while top may be advancing
   // via concurrent allocations, there is no need to order the reads of top
   // and end here, unlike in cas_allocate.

src/hotspot/share/gc/parallel/mutableSpace.hpp

@@ -129,7 +129,7 @@ class MutableSpace: public CHeapObj<mtGC> {
   // Return true if this space needs to be expanded in order to satisfy an
   // allocation request of the indicated size.  Concurrent allocations and
   // resizes may change the result of a later call.  Used by oldgen allocator.
-  // precondition: holding PSOldGenExpand_lock
+  // precondition: holding PSOldGenExpand_lock if not VM thread
   bool needs_expand(size_t word_size) const;
 
   // Iteration.

src/hotspot/share/gc/parallel/parallelScavengeHeap.cpp

@@ -434,8 +434,7 @@ HeapWord* ParallelScavengeHeap::expand_heap_and_allocate(size_t size, bool is_tl
 
   result = young_gen()->allocate(size);
   if (result == nullptr && !is_tlab) {
-    // auto expand inside
-    result = old_gen()->allocate(size);
+    result = old_gen()->expand_and_allocate(size);
   }
   return result;   // Could be null if we are out of space.
 }

src/hotspot/share/gc/parallel/psOldGen.cpp

@@ -120,6 +120,18 @@ void PSOldGen::initialize_performance_counters(const char* perf_data_name, int l
                                       _object_space, _gen_counters);
 }
 
+HeapWord* PSOldGen::expand_and_allocate(size_t word_size) {
+  assert(SafepointSynchronize::is_at_safepoint(), "precondition");
+  assert(Thread::current()->is_VM_thread(), "precondition");
+  if (object_space()->needs_expand(word_size)) {
+    expand(word_size*HeapWordSize);
+  }
+
+  // Reuse the CAS API even though this is VM thread in safepoint. This method
+  // is not invoked repeatedly, so the CAS overhead should be negligible.
+  return cas_allocate_noexpand(word_size);
+}
+
 size_t PSOldGen::num_iterable_blocks() const {
   return (object_space()->used_in_bytes() + IterateBlockSize - 1) / IterateBlockSize;
 }
@@ -170,9 +182,13 @@ bool PSOldGen::expand_for_allocate(size_t word_size) {
 }
 
 bool PSOldGen::expand(size_t bytes) {
-  assert_lock_strong(PSOldGenExpand_lock);
+#ifdef ASSERT
+  if (!Thread::current()->is_VM_thread()) {
+    assert_lock_strong(PSOldGenExpand_lock);
+  }
   assert_locked_or_safepoint(Heap_lock);
   assert(bytes > 0, "precondition");
+#endif
   const size_t alignment = virtual_space()->alignment();
   size_t aligned_bytes  = align_up(bytes, alignment);
   size_t aligned_expand_bytes = align_up(MinHeapDeltaBytes, alignment);
@@ -208,8 +224,6 @@ bool PSOldGen::expand(size_t bytes) {
 }
 
 bool PSOldGen::expand_by(size_t bytes) {
-  assert_lock_strong(PSOldGenExpand_lock);
-  assert_locked_or_safepoint(Heap_lock);
   assert(bytes > 0, "precondition");
   bool result = virtual_space()->expand_by(bytes);
   if (result) {
@@ -244,9 +258,6 @@ bool PSOldGen::expand_by(size_t bytes) {
 }
 
 bool PSOldGen::expand_to_reserved() {
-  assert_lock_strong(PSOldGenExpand_lock);
-  assert_locked_or_safepoint(Heap_lock);
-
   bool result = false;
   const size_t remaining_bytes = virtual_space()->uncommitted_size();
   if (remaining_bytes > 0) {

src/hotspot/share/gc/parallel/psOldGen.hpp

@@ -118,6 +118,7 @@ class PSOldGen : public CHeapObj<mtGC> {
   // Calculating new sizes
   void resize(size_t desired_free_space);
 
+  // Invoked by mutators and GC-workers.
   HeapWord* allocate(size_t word_size) {
     HeapWord* res;
     do {
@@ -127,6 +128,9 @@ class PSOldGen : public CHeapObj<mtGC> {
     return res;
   }
 
+  // Invoked by VM thread inside a safepoint.
+  HeapWord* expand_and_allocate(size_t word_size);
+
   // Iteration.
   void oop_iterate(OopIterateClosure* cl) { object_space()->oop_iterate(cl); }
   void object_iterate(ObjectClosure* cl) { object_space()->object_iterate(cl); }