8027959: Early reclamation of large objects in G1

Try to reclaim humongous objects at every young collection after doing a conservative estimate of its liveness.

Reviewed-by: brutisso, mgerdin

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -1926,6 +1926,8 @@ G1CollectedHeap::G1CollectedHeap(G1CollectorPolicy* policy_) :
   _secondary_free_list("Secondary Free List", new SecondaryFreeRegionListMtSafeChecker()),
   _old_set("Old Set", false /* humongous */, new OldRegionSetMtSafeChecker()),
   _humongous_set("Master Humongous Set", true /* humongous */, new HumongousRegionSetMtSafeChecker()),
+  _humongous_is_live(),
+  _has_humongous_reclaim_candidates(false),
   _free_regions_coming(false),
   _young_list(new YoungList(this)),
   _gc_time_stamp(0),
@@ -2082,6 +2084,7 @@ jint G1CollectedHeap::initialize() {
   _g1h = this;
 
   _in_cset_fast_test.initialize(_g1_reserved.start(), _g1_reserved.end(), HeapRegion::GrainBytes);
+  _humongous_is_live.initialize(_g1_reserved.start(), _g1_reserved.end(), HeapRegion::GrainBytes);
 
   // Create the ConcurrentMark data structure and thread.
   // (Must do this late, so that "max_regions" is defined.)
@@ -2177,6 +2180,11 @@ void G1CollectedHeap::stop() {
   }
 }
 
+void G1CollectedHeap::clear_humongous_is_live_table() {
+  guarantee(G1ReclaimDeadHumongousObjectsAtYoungGC, "Should only be called if true");
+  _humongous_is_live.clear();
+}
+
 size_t G1CollectedHeap::conservative_max_heap_alignment() {
   return HeapRegion::max_region_size();
 }
@@ -3771,6 +3779,61 @@ size_t G1CollectedHeap::cards_scanned() {
   return g1_rem_set()->cardsScanned();
 }
 
+bool G1CollectedHeap::humongous_region_is_always_live(uint index) {
+  HeapRegion* region = region_at(index);
+  assert(region->startsHumongous(), "Must start a humongous object");
+  return oop(region->bottom())->is_objArray() || !region->rem_set()->is_empty();
+}
+
+class RegisterHumongousWithInCSetFastTestClosure : public HeapRegionClosure {
+ private:
+  size_t _total_humongous;
+  size_t _candidate_humongous;
+ public:
+  RegisterHumongousWithInCSetFastTestClosure() : _total_humongous(0), _candidate_humongous(0) {
+  }
+
+  virtual bool doHeapRegion(HeapRegion* r) {
+    if (!r->startsHumongous()) {
+      return false;
+    }
+    G1CollectedHeap* g1h = G1CollectedHeap::heap();
+
+    uint region_idx = r->hrs_index();
+    bool is_candidate = !g1h->humongous_region_is_always_live(region_idx);
+    // Is_candidate already filters out humongous regions with some remembered set.
+    // This will not lead to humongous object that we mistakenly keep alive because
+    // during young collection the remembered sets will only be added to.
+    if (is_candidate) {
+      g1h->register_humongous_region_with_in_cset_fast_test(region_idx);
+      _candidate_humongous++;
+    }
+    _total_humongous++;
+
+    return false;
+  }
+
+  size_t total_humongous() const { return _total_humongous; }
+  size_t candidate_humongous() const { return _candidate_humongous; }
+};
+
+void G1CollectedHeap::register_humongous_regions_with_in_cset_fast_test() {
+  if (!G1ReclaimDeadHumongousObjectsAtYoungGC) {
+    g1_policy()->phase_times()->record_fast_reclaim_humongous_stats(0, 0);
+    return;
+  }
+
+  RegisterHumongousWithInCSetFastTestClosure cl;
+  heap_region_iterate(&cl);
+  g1_policy()->phase_times()->record_fast_reclaim_humongous_stats(cl.total_humongous(),
+                                                                  cl.candidate_humongous());
+  _has_humongous_reclaim_candidates = cl.candidate_humongous() > 0;
+
+  if (_has_humongous_reclaim_candidates) {
+    clear_humongous_is_live_table();
+  }
+}
+
 void
 G1CollectedHeap::setup_surviving_young_words() {
   assert(_surviving_young_words == NULL, "pre-condition");
@@ -4058,6 +4121,8 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
 
         g1_policy()->finalize_cset(target_pause_time_ms, evacuation_info);
 
+        register_humongous_regions_with_in_cset_fast_test();
+
         _cm->note_start_of_gc();
         // We should not verify the per-thread SATB buffers given that
         // we have not filtered them yet (we'll do so during the
@@ -4108,6 +4173,9 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
                                  true  /* verify_fingers */);
 
         free_collection_set(g1_policy()->collection_set(), evacuation_info);
+
+        eagerly_reclaim_humongous_regions();
+
         g1_policy()->clear_collection_set();
 
         cleanup_surviving_young_words();
@@ -4608,7 +4676,9 @@ void G1ParCopyClosure<barrier, do_mark_object>::do_oop_work(T* p) {
 
   assert(_worker_id == _par_scan_state->queue_num(), "sanity");
 
-  if (_g1->in_cset_fast_test(obj)) {
+  G1CollectedHeap::in_cset_state_t state = _g1->in_cset_state(obj);
+
+  if (state == G1CollectedHeap::InCSet) {
     oop forwardee;
     if (obj->is_forwarded()) {
       forwardee = obj->forwardee();
@@ -4627,6 +4697,9 @@ void G1ParCopyClosure<barrier, do_mark_object>::do_oop_work(T* p) {
       do_klass_barrier(p, forwardee);
     }
   } else {
+    if (state == G1CollectedHeap::IsHumongous) {
+      _g1->set_humongous_is_live(obj);
+    }
     // The object is not in collection set. If we're a root scanning
     // closure during an initial mark pause then attempt to mark the object.
     if (do_mark_object == G1MarkFromRoot) {
@@ -5450,12 +5523,21 @@ class G1KeepAliveClosure: public OopClosure {
 public:
   G1KeepAliveClosure(G1CollectedHeap* g1) : _g1(g1) {}
   void do_oop(narrowOop* p) { guarantee(false, "Not needed"); }
-  void do_oop(      oop* p) {
+  void do_oop(oop* p) {
     oop obj = *p;
 
-    if (_g1->obj_in_cs(obj)) {
+    G1CollectedHeap::in_cset_state_t cset_state = _g1->in_cset_state(obj);
+    if (obj == NULL || cset_state == G1CollectedHeap::InNeither) {
+      return;
+    }
+    if (cset_state == G1CollectedHeap::InCSet) {
       assert( obj->is_forwarded(), "invariant" );
       *p = obj->forwardee();
+    } else {
+      assert(!obj->is_forwarded(), "invariant" );
+      assert(cset_state == G1CollectedHeap::IsHumongous,
+             err_msg("Only allowed InCSet state is IsHumongous, but is %d", cset_state));
+      _g1->set_humongous_is_live(obj);
     }
   }
 };
@@ -5485,7 +5567,7 @@ public:
   template <class T> void do_oop_work(T* p) {
     oop obj = oopDesc::load_decode_heap_oop(p);
 
-    if (_g1h->obj_in_cs(obj)) {
+    if (_g1h->is_in_cset_or_humongous(obj)) {
       // If the referent object has been forwarded (either copied
       // to a new location or to itself in the event of an
       // evacuation failure) then we need to update the reference
@@ -6435,6 +6517,147 @@ void G1CollectedHeap::free_collection_set(HeapRegion* cs_head, EvacuationInfo& e
   policy->phase_times()->record_non_young_free_cset_time_ms(non_young_time_ms);
 }
 
+class G1FreeHumongousRegionClosure : public HeapRegionClosure {
+ private:
+  FreeRegionList* _free_region_list;
+  HeapRegionSet* _proxy_set;
+  HeapRegionSetCount _humongous_regions_removed;
+  size_t _freed_bytes;
+ public:
+
+  G1FreeHumongousRegionClosure(FreeRegionList* free_region_list) :
+    _free_region_list(free_region_list), _humongous_regions_removed(), _freed_bytes(0) {
+  }
+
+  virtual bool doHeapRegion(HeapRegion* r) {
+    if (!r->startsHumongous()) {
+      return false;
+    }
+
+    G1CollectedHeap* g1h = G1CollectedHeap::heap();
+
+    // The following checks whether the humongous object is live are sufficient.
+    // The main additional check (in addition to having a reference from the roots
+    // or the young gen) is whether the humongous object has a remembered set entry.
+    //
+    // A humongous object cannot be live if there is no remembered set for it
+    // because:
+    // - there can be no references from within humongous starts regions referencing
+    // the object because we never allocate other objects into them.
+    // (I.e. there are no intra-region references that may be missed by the
+    // remembered set)
+    // - as soon there is a remembered set entry to the humongous starts region
+    // (i.e. it has "escaped" to an old object) this remembered set entry will stay
+    // until the end of a concurrent mark.
+    //
+    // It is not required to check whether the object has been found dead by marking
+    // or not, in fact it would prevent reclamation within a concurrent cycle, as
+    // all objects allocated during that time are considered live.
+    // SATB marking is even more conservative than the remembered set.
+    // So if at this point in the collection there is no remembered set entry,
+    // nobody has a reference to it.
+    // At the start of collection we flush all refinement logs, and remembered sets
+    // are completely up-to-date wrt to references to the humongous object.
+    //
+    // Other implementation considerations:
+    // - never consider object arrays: while they are a valid target, they have not
+    // been observed to be used as temporary objects.
+    // - they would also pose considerable effort for cleaning up the the remembered
+    // sets.
+    // While this cleanup is not strictly necessary to be done (or done instantly),
+    // given that their occurrence is very low, this saves us this additional
+    // complexity.
+    uint region_idx = r->hrs_index();
+    if (g1h->humongous_is_live(region_idx) ||
+        g1h->humongous_region_is_always_live(region_idx)) {
+
+      if (G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
+        gclog_or_tty->print_cr("Live humongous %d region %d with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is dead-bitmap %d live-other %d obj array %d",
+                               r->isHumongous(),
+                               region_idx,
+                               r->rem_set()->occupied(),
+                               r->rem_set()->strong_code_roots_list_length(),
+                               g1h->mark_in_progress() && !g1h->g1_policy()->during_initial_mark_pause(),
+                               g1h->humongous_is_live(region_idx),
+                               oop(r->bottom())->is_objArray()
+                              );
+      }
+
+      return false;
+    }
+
+    guarantee(!((oop)(r->bottom()))->is_objArray(),
+              err_msg("Eagerly reclaiming object arrays is not supported, but the object "PTR_FORMAT" is.",
+                      r->bottom()));
+
+    if (G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
+      gclog_or_tty->print_cr("Reclaim humongous region %d start "PTR_FORMAT" region %d length "UINT32_FORMAT" with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is dead-bitmap %d live-other %d obj array %d",
+                             r->isHumongous(),
+                             r->bottom(),
+                             region_idx,
+                             r->region_num(),
+                             r->rem_set()->occupied(),
+                             r->rem_set()->strong_code_roots_list_length(),
+                             g1h->mark_in_progress() && !g1h->g1_policy()->during_initial_mark_pause(),
+                             g1h->humongous_is_live(region_idx),
+                             oop(r->bottom())->is_objArray()
+                            );
+    }
+    _freed_bytes += r->used();
+    r->set_containing_set(NULL);
+    _humongous_regions_removed.increment(1u, r->capacity());
+    g1h->free_humongous_region(r, _free_region_list, false);
+
+    return false;
+  }
+
+  HeapRegionSetCount& humongous_free_count() {
+    return _humongous_regions_removed;
+  }
+
+  size_t bytes_freed() const {
+    return _freed_bytes;
+  }
+
+  size_t humongous_reclaimed() const {
+    return _humongous_regions_removed.length();
+  }
+};
+
+void G1CollectedHeap::eagerly_reclaim_humongous_regions() {
+  assert_at_safepoint(true);
+
+  if (!G1ReclaimDeadHumongousObjectsAtYoungGC || !_has_humongous_reclaim_candidates) {
+    g1_policy()->phase_times()->record_fast_reclaim_humongous_time_ms(0.0, 0);
+    return;
+  }
+
+  double start_time = os::elapsedTime();
+
+  FreeRegionList local_cleanup_list("Local Humongous Cleanup List");
+
+  G1FreeHumongousRegionClosure cl(&local_cleanup_list);
+  heap_region_iterate(&cl);
+
+  HeapRegionSetCount empty_set;
+  remove_from_old_sets(empty_set, cl.humongous_free_count());
+
+  G1HRPrinter* hr_printer = _g1h->hr_printer();
+  if (hr_printer->is_active()) {
+    FreeRegionListIterator iter(&local_cleanup_list);
+    while (iter.more_available()) {
+      HeapRegion* hr = iter.get_next();
+      hr_printer->cleanup(hr);
+    }
+  }
+
+  prepend_to_freelist(&local_cleanup_list);
+  decrement_summary_bytes(cl.bytes_freed());
+
+  g1_policy()->phase_times()->record_fast_reclaim_humongous_time_ms((os::elapsedTime() - start_time) * 1000.0,
+                                                                    cl.humongous_reclaimed());
+}
+
 // This routine is similar to the above but does not record
 // any policy statistics or update free lists; we are abandoning
 // the current incremental collection set in preparation of a

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp

@@ -197,16 +197,6 @@ public:
   bool do_object_b(oop p);
 };
 
-// Instances of this class are used for quick tests on whether a reference points
-// into the collection set. Each of the array's elements denotes whether the
-// corresponding region is in the collection set.
-class G1FastCSetBiasedMappedArray : public G1BiasedMappedArray<bool> {
- protected:
-  bool default_value() const { return false; }
- public:
-  void clear() { G1BiasedMappedArray<bool>::clear(); }
-};
-
 class RefineCardTableEntryClosure;
 
 class G1CollectedHeap : public SharedHeap {
@@ -237,6 +227,7 @@ class G1CollectedHeap : public SharedHeap {
   friend class EvacPopObjClosure;
   friend class G1ParCleanupCTTask;
 
+  friend class G1FreeHumongousRegionClosure;
   // Other related classes.
   friend class G1MarkSweep;
 
@@ -267,6 +258,9 @@ private:
   // It keeps track of the humongous regions.
   HeapRegionSet _humongous_set;
 
+  void clear_humongous_is_live_table();
+  void eagerly_reclaim_humongous_regions();
+
   // The number of regions we could create by expansion.
   uint _expansion_regions;
 
@@ -367,10 +361,25 @@ private:
   // than the current allocation region.
   size_t _summary_bytes_used;
 
-  // This array is used for a quick test on whether a reference points into
+  // Records whether the region at the given index is kept live by roots or
-  // the collection set or not. Each of the array's elements denotes whether the
+  // references from the young generation.
-  // corresponding region is in the collection set or not.
+  class HumongousIsLiveBiasedMappedArray : public G1BiasedMappedArray<bool> {
-  G1FastCSetBiasedMappedArray _in_cset_fast_test;
+   protected:
+    bool default_value() const { return false; }
+   public:
+    void clear() { G1BiasedMappedArray<bool>::clear(); }
+    void set_live(uint region) {
+      set_by_index(region, true);
+    }
+    bool is_live(uint region) {
+      return get_by_index(region);
+    }
+  };
+
+  HumongousIsLiveBiasedMappedArray _humongous_is_live;
+  // Stores whether during humongous object registration we found candidate regions.
+  // If not, we can skip a few steps.
+  bool _has_humongous_reclaim_candidates;
 
   volatile unsigned _gc_time_stamp;
 
@@ -690,10 +699,24 @@ public:
   virtual void gc_prologue(bool full);
   virtual void gc_epilogue(bool full);
 
+  inline void set_humongous_is_live(oop obj);
+
+  bool humongous_is_live(uint region) {
+    return _humongous_is_live.is_live(region);
+  }
+
+  // Returns whether the given region (which must be a humongous (start) region)
+  // is to be considered conservatively live regardless of any other conditions.
+  bool humongous_region_is_always_live(uint index);
+  // Register the given region to be part of the collection set.
+  inline void register_humongous_region_with_in_cset_fast_test(uint index);
+  // Register regions with humongous objects (actually on the start region) in
+  // the in_cset_fast_test table.
+  void register_humongous_regions_with_in_cset_fast_test();
   // We register a region with the fast "in collection set" test. We
   // simply set to true the array slot corresponding to this region.
   void register_region_with_in_cset_fast_test(HeapRegion* r) {
-    _in_cset_fast_test.set_by_index(r->hrs_index(), true);
+    _in_cset_fast_test.set_in_cset(r->hrs_index());
   }
 
   // This is a fast test on whether a reference points into the
@@ -1283,9 +1306,61 @@ public:
   virtual bool is_in(const void* p) const;
 
   // Return "TRUE" iff the given object address is within the collection
-  // set.
+  // set. Slow implementation.
   inline bool obj_in_cs(oop obj);
 
+  inline bool is_in_cset(oop obj);
+
+  inline bool is_in_cset_or_humongous(const oop obj);
+
+  enum in_cset_state_t {
+   InNeither,           // neither in collection set nor humongous
+   InCSet,              // region is in collection set only
+   IsHumongous          // region is a humongous start region
+  };
+ private:
+  // Instances of this class are used for quick tests on whether a reference points
+  // into the collection set or is a humongous object (points into a humongous
+  // object).
+  // Each of the array's elements denotes whether the corresponding region is in
+  // the collection set or a humongous region.
+  // We use this to quickly reclaim humongous objects: by making a humongous region
+  // succeed this test, we sort-of add it to the collection set. During the reference
+  // iteration closures, when we see a humongous region, we simply mark it as
+  // referenced, i.e. live.
+  class G1FastCSetBiasedMappedArray : public G1BiasedMappedArray<char> {
+   protected:
+    char default_value() const { return G1CollectedHeap::InNeither; }
+   public:
+    void set_humongous(uintptr_t index) {
+      assert(get_by_index(index) != InCSet, "Should not overwrite InCSet values");
+      set_by_index(index, G1CollectedHeap::IsHumongous);
+    }
+
+    void clear_humongous(uintptr_t index) {
+      set_by_index(index, G1CollectedHeap::InNeither);
+    }
+
+    void set_in_cset(uintptr_t index) {
+      assert(get_by_index(index) != G1CollectedHeap::IsHumongous, "Should not overwrite IsHumongous value");
+      set_by_index(index, G1CollectedHeap::InCSet);
+    }
+
+    bool is_in_cset_or_humongous(HeapWord* addr) const { return get_by_address(addr) != G1CollectedHeap::InNeither; }
+    bool is_in_cset(HeapWord* addr) const { return get_by_address(addr) == G1CollectedHeap::InCSet; }
+    G1CollectedHeap::in_cset_state_t at(HeapWord* addr) const { return (G1CollectedHeap::in_cset_state_t)get_by_address(addr); }
+    void clear() { G1BiasedMappedArray<char>::clear(); }
+  };
+
+  // This array is used for a quick test on whether a reference points into
+  // the collection set or not. Each of the array's elements denotes whether the
+  // corresponding region is in the collection set or not.
+  G1FastCSetBiasedMappedArray _in_cset_fast_test;
+
+ public:
+
+  inline in_cset_state_t in_cset_state(const oop obj);
+
   // Return "TRUE" iff the given object address is in the reserved
   // region of g1.
   bool is_in_g1_reserved(const void* p) const {
@@ -1340,6 +1415,10 @@ public:
   // Return the region with the given index. It assumes the index is valid.
   inline HeapRegion* region_at(uint index) const;
 
+  // Calculate the region index of the given address. Given address must be
+  // within the heap.
+  inline uint addr_to_region(HeapWord* addr) const;
+
   // Divide the heap region sequence into "chunks" of some size (the number
   // of regions divided by the number of parallel threads times some
   // overpartition factor, currently 4).  Assumes that this will be called

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.inline.hpp

@@ -40,6 +40,13 @@
 // Return the region with the given index. It assumes the index is valid.
 inline HeapRegion* G1CollectedHeap::region_at(uint index) const { return _hrs.at(index); }
 
+inline uint G1CollectedHeap::addr_to_region(HeapWord* addr) const {
+  assert(is_in_reserved(addr),
+         err_msg("Cannot calculate region index for address "PTR_FORMAT" that is outside of the heap ["PTR_FORMAT", "PTR_FORMAT")",
+                 p2i(addr), p2i(_reserved.start()), p2i(_reserved.end())));
+  return (uint)(pointer_delta(addr, _reserved.start(), sizeof(uint8_t)) >> HeapRegion::LogOfHRGrainBytes);
+}
+
 template <class T>
 inline HeapRegion*
 G1CollectedHeap::heap_region_containing_raw(const T addr) const {
@@ -172,12 +179,11 @@ inline bool G1CollectedHeap::isMarkedNext(oop obj) const {
   return _cm->nextMarkBitMap()->isMarked((HeapWord *)obj);
 }
 
-
 // This is a fast test on whether a reference points into the
 // collection set or not. Assume that the reference
 // points into the heap.
-inline bool G1CollectedHeap::in_cset_fast_test(oop obj) {
+inline bool G1CollectedHeap::is_in_cset(oop obj) {
-  bool ret = _in_cset_fast_test.get_by_address((HeapWord*)obj);
+  bool ret = _in_cset_fast_test.is_in_cset((HeapWord*)obj);
   // let's make sure the result is consistent with what the slower
   // test returns
   assert( ret || !obj_in_cs(obj), "sanity");
@@ -185,6 +191,18 @@ inline bool G1CollectedHeap::in_cset_fast_test(oop obj) {
   return ret;
 }
 
+bool G1CollectedHeap::is_in_cset_or_humongous(const oop obj) {
+  return _in_cset_fast_test.is_in_cset_or_humongous((HeapWord*)obj);
+}
+
+G1CollectedHeap::in_cset_state_t G1CollectedHeap::in_cset_state(const oop obj) {
+  return _in_cset_fast_test.at((HeapWord*)obj);
+}
+
+void G1CollectedHeap::register_humongous_region_with_in_cset_fast_test(uint index) {
+  _in_cset_fast_test.set_humongous(index);
+}
+
 #ifndef PRODUCT
 // Support for G1EvacuationFailureALot
 
@@ -288,4 +306,22 @@ inline bool G1CollectedHeap::is_obj_ill(const oop obj) const {
   return is_obj_ill(obj, heap_region_containing(obj));
 }
 
+inline void G1CollectedHeap::set_humongous_is_live(oop obj) {
+  uint region = addr_to_region((HeapWord*)obj);
+  // We not only set the "live" flag in the humongous_is_live table, but also
+  // reset the entry in the _in_cset_fast_test table so that subsequent references
+  // to the same humongous object do not go into the slow path again.
+  // This is racy, as multiple threads may at the same time enter here, but this
+  // is benign.
+  // During collection we only ever set the "live" flag, and only ever clear the
+  // entry in the in_cset_fast_table.
+  // We only ever evaluate the contents of these tables (in the VM thread) after
+  // having synchronized the worker threads with the VM thread, or in the same
+  // thread (i.e. within the VM thread).
+  if (!_humongous_is_live.is_live(region)) {
+    _humongous_is_live.set_live(region);
+    _in_cset_fast_test.clear_humongous(region);
+  }
+}
+
 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_INLINE_HPP

hotspot/src/share/vm/gc_implementation/g1/g1GCPhaseTimes.cpp

@@ -255,6 +255,10 @@ void G1GCPhaseTimes::print_stats(int level, const char* str, double value) {
   LineBuffer(level).append_and_print_cr("[%s: %.1lf ms]", str, value);
 }
 
+void G1GCPhaseTimes::print_stats(int level, const char* str, size_t value) {
+  LineBuffer(level).append_and_print_cr("[%s: "SIZE_FORMAT"]", str, value);
+}
+
 void G1GCPhaseTimes::print_stats(int level, const char* str, double value, uint workers) {
   LineBuffer(level).append_and_print_cr("[%s: %.1lf ms, GC Workers: %u]", str, value, workers);
 }
@@ -357,6 +361,14 @@ void G1GCPhaseTimes::print(double pause_time_sec) {
       _last_redirty_logged_cards_processed_cards.print(3, "Redirtied Cards");
     }
   }
+  if (G1ReclaimDeadHumongousObjectsAtYoungGC) {
+    print_stats(2, "Humongous Reclaim", _cur_fast_reclaim_humongous_time_ms);
+    if (G1Log::finest()) {
+      print_stats(3, "Humongous Total", _cur_fast_reclaim_humongous_total);
+      print_stats(3, "Humongous Candidate", _cur_fast_reclaim_humongous_candidates);
+      print_stats(3, "Humongous Reclaimed", _cur_fast_reclaim_humongous_reclaimed);
+    }
+  }
   print_stats(2, "Free CSet",
     (_recorded_young_free_cset_time_ms +
     _recorded_non_young_free_cset_time_ms));

hotspot/src/share/vm/gc_implementation/g1/g1GCPhaseTimes.hpp

@@ -157,11 +157,17 @@ class G1GCPhaseTimes : public CHeapObj<mtGC> {
   double _recorded_young_free_cset_time_ms;
   double _recorded_non_young_free_cset_time_ms;
 
+  double _cur_fast_reclaim_humongous_time_ms;
+  size_t _cur_fast_reclaim_humongous_total;
+  size_t _cur_fast_reclaim_humongous_candidates;
+  size_t _cur_fast_reclaim_humongous_reclaimed;
+
   double _cur_verify_before_time_ms;
   double _cur_verify_after_time_ms;
 
   // Helper methods for detailed logging
   void print_stats(int level, const char* str, double value);
+  void print_stats(int level, const char* str, size_t value);
   void print_stats(int level, const char* str, double value, uint workers);
 
  public:
@@ -282,6 +288,16 @@ class G1GCPhaseTimes : public CHeapObj<mtGC> {
     _recorded_non_young_free_cset_time_ms = time_ms;
   }
 
+  void record_fast_reclaim_humongous_stats(size_t total, size_t candidates) {
+    _cur_fast_reclaim_humongous_total = total;
+    _cur_fast_reclaim_humongous_candidates = candidates;
+  }
+
+  void record_fast_reclaim_humongous_time_ms(double value, size_t reclaimed) {
+    _cur_fast_reclaim_humongous_time_ms = value;
+    _cur_fast_reclaim_humongous_reclaimed = reclaimed;
+  }
+
   void record_young_cset_choice_time_ms(double time_ms) {
     _recorded_young_cset_choice_time_ms = time_ms;
   }
@@ -348,6 +364,10 @@ class G1GCPhaseTimes : public CHeapObj<mtGC> {
     return _recorded_non_young_free_cset_time_ms;
   }
 
+  double fast_reclaim_humongous_time_ms() {
+    return _cur_fast_reclaim_humongous_time_ms;
+  }
+
   double average_last_update_rs_time() {
     return _last_update_rs_times_ms.average();
   }

hotspot/src/share/vm/gc_implementation/g1/g1OopClosures.inline.hpp

@@ -44,7 +44,7 @@ template <class T>
 inline void FilterIntoCSClosure::do_oop_nv(T* p) {
   T heap_oop = oopDesc::load_heap_oop(p);
   if (!oopDesc::is_null(heap_oop) &&
-      _g1->obj_in_cs(oopDesc::decode_heap_oop_not_null(heap_oop))) {
+      _g1->is_in_cset_or_humongous(oopDesc::decode_heap_oop_not_null(heap_oop))) {
     _oc->do_oop(p);
   }
 }
@@ -67,7 +67,8 @@ inline void G1ParScanClosure::do_oop_nv(T* p) {
 
   if (!oopDesc::is_null(heap_oop)) {
     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
-    if (_g1->in_cset_fast_test(obj)) {
+    G1CollectedHeap::in_cset_state_t state = _g1->in_cset_state(obj);
+    if (state == G1CollectedHeap::InCSet) {
       // We're not going to even bother checking whether the object is
       // already forwarded or not, as this usually causes an immediate
       // stall. We'll try to prefetch the object (for write, given that
@@ -86,6 +87,9 @@ inline void G1ParScanClosure::do_oop_nv(T* p) {
 
       _par_scan_state->push_on_queue(p);
     } else {
+      if (state == G1CollectedHeap::IsHumongous) {
+        _g1->set_humongous_is_live(obj);
+      }
       _par_scan_state->update_rs(_from, p, _worker_id);
     }
   }
@@ -97,12 +101,14 @@ inline void G1ParPushHeapRSClosure::do_oop_nv(T* p) {
 
   if (!oopDesc::is_null(heap_oop)) {
     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
-    if (_g1->in_cset_fast_test(obj)) {
+    if (_g1->is_in_cset_or_humongous(obj)) {
       Prefetch::write(obj->mark_addr(), 0);
       Prefetch::read(obj->mark_addr(), (HeapWordSize*2));
 
       // Place on the references queue
       _par_scan_state->push_on_queue(p);
+    } else {
+      assert(!_g1->obj_in_cs(obj), "checking");
     }
   }
 }

hotspot/src/share/vm/gc_implementation/g1/g1ParScanThreadState.inline.hpp

@@ -52,15 +52,20 @@ template <class T> void G1ParScanThreadState::do_oop_evac(T* p, HeapRegion* from
   // set, due to (benign) races in the claim mechanism during RSet scanning more
   // than one thread might claim the same card. So the same card may be
   // processed multiple times. So redo this check.
-  if (_g1h->in_cset_fast_test(obj)) {
+  G1CollectedHeap::in_cset_state_t in_cset_state = _g1h->in_cset_state(obj);
+  if (in_cset_state == G1CollectedHeap::InCSet) {
     oop forwardee;
     if (obj->is_forwarded()) {
       forwardee = obj->forwardee();
     } else {
       forwardee = copy_to_survivor_space(obj);
     }
-    assert(forwardee != NULL, "forwardee should not be NULL");
     oopDesc::encode_store_heap_oop(p, forwardee);
+  } else if (in_cset_state == G1CollectedHeap::IsHumongous) {
+    _g1h->set_humongous_is_live(obj);
+  } else {
+    assert(in_cset_state == G1CollectedHeap::InNeither,
+           err_msg("In_cset_state must be InNeither here, but is %d", in_cset_state));
   }
 
   assert(obj != NULL, "Must be");

hotspot/src/share/vm/gc_implementation/g1/g1_globals.hpp

@@ -289,6 +289,13 @@
           "The amount of code root chunks that should be kept at most "     \
           "as percentage of already allocated.")                            \
                                                                             \
+  experimental(bool, G1ReclaimDeadHumongousObjectsAtYoungGC, true,          \
+          "Try to reclaim dead large objects at every young GC.")           \
+                                                                            \
+  experimental(bool, G1TraceReclaimDeadHumongousObjectsAtYoungGC, false,    \
+          "Print some information about large object liveness "             \
+          "at every young GC.")                                             \
+                                                                            \
   experimental(uintx, G1OldCSetRegionThresholdPercent, 10,                  \
           "An upper bound for the number of old CSet regions expressed "    \
           "as a percentage of the heap size.")                              \

hotspot/src/share/vm/gc_implementation/g1/heapRegionRemSet.cpp

@@ -695,6 +695,9 @@ void OtherRegionsTable::scrub(CardTableModRefBS* ctbs,
   clear_fcc();
 }
 
+bool OtherRegionsTable::is_empty() const {
+  return occ_sparse() == 0 && occ_coarse() == 0 && _first_all_fine_prts == NULL;
+}
 
 size_t OtherRegionsTable::occupied() const {
   size_t sum = occ_fine();

hotspot/src/share/vm/gc_implementation/g1/heapRegionRemSet.hpp

@@ -185,6 +185,9 @@ public:
   // objects.
   void scrub(CardTableModRefBS* ctbs, BitMap* region_bm, BitMap* card_bm);
 
+  // Returns whether this remembered set (and all sub-sets) contain no entries.
+  bool is_empty() const;
+
   size_t occupied() const;
   size_t occ_fine() const;
   size_t occ_coarse() const;
@@ -269,6 +272,10 @@ public:
     return _other_regions.hr();
   }
 
+  bool is_empty() const {
+    return (strong_code_roots_list_length() == 0) && _other_regions.is_empty();
+  }
+
   size_t occupied() {
     MutexLockerEx x(&_m, Mutex::_no_safepoint_check_flag);
     return occupied_locked();
@@ -371,7 +378,7 @@ public:
   void strong_code_roots_do(CodeBlobClosure* blk) const;
 
   // Returns the number of elements in the strong code roots list
-  size_t strong_code_roots_list_length() {
+  size_t strong_code_roots_list_length() const {
     return _code_roots.length();
   }
 

hotspot/test/gc/g1/TestEagerReclaimHumongousRegions.java

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test TestEagerReclaimHumongousRegions
+ * @bug 8027959
+ * @summary Test to make sure that eager reclaim of humongous objects work. We simply try to fill
+ * up the heap with humongous objects that should be eagerly reclaimable to avoid Full GC.
+ * @key gc
+ * @library /testlibrary
+ */
+
+import java.util.regex.Pattern;
+import java.util.regex.Matcher;
+import java.util.LinkedList;
+
+import com.oracle.java.testlibrary.OutputAnalyzer;
+import com.oracle.java.testlibrary.ProcessTools;
+import com.oracle.java.testlibrary.Asserts;
+
+class ReclaimRegionFast {
+    public static final int M = 1024*1024;
+
+    public static LinkedList<Object> garbageList = new LinkedList<Object>();
+
+    public static void genGarbage() {
+        for (int i = 0; i < 32*1024; i++) {
+            garbageList.add(new int[100]);
+        }
+        garbageList.clear();
+    }
+
+    // A large object referenced by a static.
+    static int[] filler = new int[10 * M];
+
+    public static void main(String[] args) {
+
+        int[] large = new int[M];
+
+        Object ref_from_stack = large;
+
+        for (int i = 0; i < 100; i++) {
+            // A large object that will be reclaimed eagerly.
+            large = new int[6*M];
+            genGarbage();
+            // Make sure that the compiler cannot completely remove
+            // the allocation of the large object until here.
+            System.out.println(large);
+        }
+
+        // Keep the reference to the first object alive.
+        System.out.println(ref_from_stack);
+    }
+}
+
+public class TestEagerReclaimHumongousRegions {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+            "-XX:+UseG1GC",
+            "-Xms128M",
+            "-Xmx128M",
+            "-Xmn16M",
+            "-XX:+PrintGC",
+            ReclaimRegionFast.class.getName());
+
+        Pattern p = Pattern.compile("Full GC");
+
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+        int found = 0;
+        Matcher m = p.matcher(output.getStdout());
+        while (m.find()) { found++; }
+        System.out.println("Issued " + found + " Full GCs");
+        Asserts.assertLT(found, 10, "Found that " + found + " Full GCs were issued. This is larger than the bound. Eager reclaim seems to not work at all");
+
+        output.shouldHaveExitValue(0);
+    }
+}

hotspot/test/gc/g1/TestGCLogMessages.java

@@ -23,7 +23,7 @@
 
 /*
  * @test TestGCLogMessages
- * @bug 8035406 8027295 8035398 8019342
+ * @bug 8035406 8027295 8035398 8019342 8027959
  * @summary Ensure that the PrintGCDetails output for a minor GC with G1
  * includes the expected necessary messages.
  * @key gc
@@ -54,6 +54,7 @@ public class TestGCLogMessages {
     output.shouldNotContain("[String Dedup Fixup");
     output.shouldNotContain("[Young Free CSet");
     output.shouldNotContain("[Non-Young Free CSet");
+    output.shouldNotContain("[Humongous Reclaim");
     output.shouldHaveExitValue(0);
 
     pb = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
@@ -71,6 +72,10 @@ public class TestGCLogMessages {
     output.shouldContain("[String Dedup Fixup");
     output.shouldNotContain("[Young Free CSet");
     output.shouldNotContain("[Non-Young Free CSet");
+    output.shouldContain("[Humongous Reclaim");
+    output.shouldNotContain("[Humongous Total");
+    output.shouldNotContain("[Humongous Candidate");
+    output.shouldNotContain("[Humongous Reclaimed");
     output.shouldHaveExitValue(0);
 
     pb = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
@@ -90,6 +95,10 @@ public class TestGCLogMessages {
     output.shouldContain("[String Dedup Fixup");
     output.shouldContain("[Young Free CSet");
     output.shouldContain("[Non-Young Free CSet");
+    output.shouldContain("[Humongous Reclaim");
+    output.shouldContain("[Humongous Total");
+    output.shouldContain("[Humongous Candidate");
+    output.shouldContain("[Humongous Reclaimed");
     output.shouldHaveExitValue(0);
   }