8288947: G1: Consolidate per-region is-humongous query in G1CollectedHeap

Reviewed-by: tschatzl, iwalulya

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

@@ -1452,7 +1452,6 @@ G1CollectedHeap::G1CollectedHeap() :
   _survivor_evac_stats("Young", YoungPLABSize, PLABWeight),
   _old_evac_stats("Old", OldPLABSize, PLABWeight),
   _monitoring_support(nullptr),
-  _humongous_reclaim_candidates(),
   _num_humongous_objects(0),
   _num_humongous_reclaim_candidates(0),
   _hr_printer(),
@@ -1684,7 +1683,6 @@ jint G1CollectedHeap::initialize() {
     size_t granularity = HeapRegion::GrainBytes;
 
     _region_attr.initialize(reserved(), granularity);
-    _humongous_reclaim_candidates.initialize(reserved(), granularity);
   }
 
   _workers = new WorkerThreads("GC Thread", ParallelGCThreads);

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

@@ -229,26 +229,6 @@ private:
   // Helper for monitoring and management support.
   G1MonitoringSupport* _monitoring_support;
 
-  // Records whether the region at the given index is (still) a
-  // candidate for eager reclaim.  Only valid for humongous start
-  // regions; other regions have unspecified values.  Humongous start
-  // regions are initialized at start of collection pause, with
-  // candidates removed from the set as they are found reachable from
-  // roots or the young generation.
-  class HumongousReclaimCandidates : public G1BiasedMappedArray<bool> {
-  protected:
-    bool default_value() const override { return false; }
-  public:
-    void clear() { G1BiasedMappedArray<bool>::clear(); }
-    void set_candidate(uint region, bool value) {
-      set_by_index(region, value);
-    }
-    bool is_candidate(uint region) {
-      return get_by_index(region);
-    }
-  };
-
-  HumongousReclaimCandidates _humongous_reclaim_candidates;
   uint _num_humongous_objects; // Current amount of (all) humongous objects found in the heap.
   uint _num_humongous_reclaim_candidates; // Number of humongous object eager reclaim candidates.
 public:
@@ -590,9 +570,6 @@ public:
   // Does the given region fulfill remembered set based eager reclaim candidate requirements?
   bool is_potential_eager_reclaim_candidate(HeapRegion* r) const;
 
-  // Modify the reclaim candidate set and test for presence.
-  // These are only valid for starts_humongous regions.
-  inline void set_humongous_reclaim_candidate(uint region, bool value);
   inline bool is_humongous_reclaim_candidate(uint region);
 
   // Remove from the reclaim candidate set.  Also remove from the

src/hotspot/share/gc/g1/g1CollectedHeap.inline.hpp

@@ -239,30 +239,20 @@ inline bool G1CollectedHeap::is_obj_dead_full(const oop obj) const {
     return is_obj_dead_full(obj, heap_region_containing(obj));
 }
 
-inline void G1CollectedHeap::set_humongous_reclaim_candidate(uint region, bool value) {
-  assert(_hrm.at(region)->is_starts_humongous(), "Must start a humongous object");
-  _humongous_reclaim_candidates.set_candidate(region, value);
-}
-
 inline bool G1CollectedHeap::is_humongous_reclaim_candidate(uint region) {
   assert(_hrm.at(region)->is_starts_humongous(), "Must start a humongous object");
-  return _humongous_reclaim_candidates.is_candidate(region);
+  return _region_attr.is_humongous(region);
 }
 
 inline void G1CollectedHeap::set_humongous_is_live(oop obj) {
   uint region = addr_to_region(cast_from_oop<HeapWord*>(obj));
-  // Clear the flag in the humongous_reclaim_candidates table.  Also
-  // reset the entry in the region attribute 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 clear the "candidate" 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 (is_humongous_reclaim_candidate(region)) {
-    set_humongous_reclaim_candidate(region, false);
+  // Reset the entry in the region attribute 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 because the transition is unidirectional, from
+  // humongous-candidate to not, and the write, in evacuation, is
+  // separated from the read, in post-evacuation.
+  if (_region_attr.is_humongous(region)) {
     _region_attr.clear_humongous(region);
   }
 }

src/hotspot/share/gc/g1/g1HeapRegionAttr.hpp

@@ -142,6 +142,10 @@ class G1HeapRegionAttrBiasedMappedArray : public G1BiasedMappedArray<G1HeapRegio
     get_ref_by_index(index)->clear_humongous();
   }
 
+  bool is_humongous(uintptr_t index) {
+    return get_ref_by_index(index)->is_humongous();
+  }
+
   void set_remset_is_tracked(uintptr_t index, bool remset_is_tracked) {
     get_ref_by_index(index)->set_remset_is_tracked(remset_is_tracked);
   }

src/hotspot/share/gc/g1/g1YoungCollector.cpp

@@ -383,12 +383,10 @@ class G1PrepareEvacuationTask : public WorkerTask {
 
       uint index = hr->hrm_index();
       if (humongous_region_is_candidate(hr)) {
-        _g1h->set_humongous_reclaim_candidate(index, true);
         _g1h->register_humongous_region_with_region_attr(index);
         _worker_humongous_candidates++;
         // We will later handle the remembered sets of these regions.
       } else {
-        _g1h->set_humongous_reclaim_candidate(index, false);
         _g1h->register_region_with_region_attr(hr);
       }
       log_debug(gc, humongous)("Humongous region %u (object size " SIZE_FORMAT " @ " PTR_FORMAT ") remset " SIZE_FORMAT " code roots " SIZE_FORMAT " marked %d reclaim candidate %d type array %d",