8311978: Shenandoah: Create abstraction over heap metrics for heuristics

Reviewed-by: ysr, phh, shade

src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp

@@ -54,8 +54,8 @@ const double ShenandoahAdaptiveHeuristics::HIGHEST_EXPECTED_AVAILABLE_AT_END = 0
 const double ShenandoahAdaptiveHeuristics::MINIMUM_CONFIDENCE = 0.319; // 25%
 const double ShenandoahAdaptiveHeuristics::MAXIMUM_CONFIDENCE = 3.291; // 99.9%
 
-ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics() :
-  ShenandoahHeuristics(),
+ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics(ShenandoahSpaceInfo* space_info) :
+  ShenandoahHeuristics(space_info),
   _margin_of_error_sd(ShenandoahAdaptiveInitialConfidence),
   _spike_threshold_sd(ShenandoahAdaptiveInitialSpikeThreshold),
   _last_trigger(OTHER) { }
@@ -84,7 +84,7 @@ void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(Shenand
   // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
   // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
 
-  size_t capacity    = ShenandoahHeap::heap()->soft_max_capacity();
+  size_t capacity    = _space_info->soft_max_capacity();
   size_t max_cset    = (size_t)((1.0 * capacity / 100 * ShenandoahEvacReserve) / ShenandoahEvacWaste);
   size_t free_target = (capacity / 100 * ShenandoahMinFreeThreshold) + max_cset;
   size_t min_garbage = (free_target > actual_free ? (free_target - actual_free) : 0);
@@ -128,7 +128,7 @@ void ShenandoahAdaptiveHeuristics::record_cycle_start() {
 void ShenandoahAdaptiveHeuristics::record_success_concurrent() {
   ShenandoahHeuristics::record_success_concurrent();
 
-  size_t available = ShenandoahHeap::heap()->free_set()->available();
+  size_t available = _space_info->available();
 
   _available.add(available);
   double z_score = 0.0;
@@ -196,11 +196,10 @@ static double saturate(double value, double min, double max) {
 }
 
 bool ShenandoahAdaptiveHeuristics::should_start_gc() {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-  size_t max_capacity = heap->max_capacity();
-  size_t capacity = heap->soft_max_capacity();
-  size_t available = heap->free_set()->available();
-  size_t allocated = heap->bytes_allocated_since_gc_start();
+  size_t max_capacity = _space_info->max_capacity();
+  size_t capacity = _space_info->soft_max_capacity();
+  size_t available = _space_info->available();
+  size_t allocated = _space_info->bytes_allocated_since_gc_start();
 
   // Make sure the code below treats available without the soft tail.
   size_t soft_tail = max_capacity - capacity;

src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.hpp

@@ -26,6 +26,7 @@
 #define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHADAPTIVEHEURISTICS_HPP
 
 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
+#include "gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp"
 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
 #include "utilities/numberSeq.hpp"
 
@@ -51,9 +52,20 @@ class ShenandoahAllocationRate : public CHeapObj<mtGC> {
   TruncatedSeq _rate_avg;
 };
 
+/*
+ * The adaptive heuristic tracks the allocation behavior and average cycle
+ * time of the application. It attempts to start a cycle with enough time
+ * to complete before the available memory is exhausted. It errors on the
+ * side of starting cycles early to avoid allocation failures (degenerated
+ * cycles).
+ *
+ * This heuristic limits the number of regions for evacuation such that the
+ * evacuation reserve is respected. This helps it avoid allocation failures
+ * during evacuation. It preferentially selects regions with the most garbage.
+ */
 class ShenandoahAdaptiveHeuristics : public ShenandoahHeuristics {
 public:
-  ShenandoahAdaptiveHeuristics();
+  ShenandoahAdaptiveHeuristics(ShenandoahSpaceInfo* space_info);
 
   virtual ~ShenandoahAdaptiveHeuristics();
 
@@ -99,11 +111,12 @@ public:
   void adjust_margin_of_error(double amount);
   void adjust_spike_threshold(double amount);
 
+protected:
   ShenandoahAllocationRate _allocation_rate;
 
   // The margin of error expressed in standard deviations to add to our
   // average cycle time and allocation rate. As this value increases we
-  // tend to over estimate the rate at which mutators will deplete the
+  // tend to overestimate the rate at which mutators will deplete the
   // heap. In other words, erring on the side of caution will trigger more
   // concurrent GCs.
   double _margin_of_error_sd;

src/hotspot/share/gc/shenandoah/heuristics/shenandoahAggressiveHeuristics.cpp

@@ -31,7 +31,8 @@
 #include "logging/logTag.hpp"
 #include "runtime/os.hpp"
 
-ShenandoahAggressiveHeuristics::ShenandoahAggressiveHeuristics() : ShenandoahHeuristics() {
+ShenandoahAggressiveHeuristics::ShenandoahAggressiveHeuristics(ShenandoahSpaceInfo* space_info) :
+  ShenandoahHeuristics(space_info) {
   // Do not shortcut evacuation
   SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahImmediateThreshold, 100);
 

src/hotspot/share/gc/shenandoah/heuristics/shenandoahAggressiveHeuristics.hpp

@@ -27,9 +27,13 @@
 
 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 
+/*
+ * This is a diagnostic heuristic that continuously runs collections
+ * cycles and adds every region with any garbage to the collection set.
+ */
 class ShenandoahAggressiveHeuristics : public ShenandoahHeuristics {
 public:
-  ShenandoahAggressiveHeuristics();
+  ShenandoahAggressiveHeuristics(ShenandoahSpaceInfo* space_info);
 
   virtual void choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
                                                      RegionData* data, size_t size,

src/hotspot/share/gc/shenandoah/heuristics/shenandoahCompactHeuristics.cpp

@@ -32,7 +32,8 @@
 #include "logging/log.hpp"
 #include "logging/logTag.hpp"
 
-ShenandoahCompactHeuristics::ShenandoahCompactHeuristics() : ShenandoahHeuristics() {
+ShenandoahCompactHeuristics::ShenandoahCompactHeuristics(ShenandoahSpaceInfo* space_info) :
+  ShenandoahHeuristics(space_info) {
   SHENANDOAH_ERGO_ENABLE_FLAG(ExplicitGCInvokesConcurrent);
   SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahImplicitGCInvokesConcurrent);
   SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahUncommit);
@@ -45,11 +46,9 @@ ShenandoahCompactHeuristics::ShenandoahCompactHeuristics() : ShenandoahHeuristic
 }
 
 bool ShenandoahCompactHeuristics::should_start_gc() {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-
-  size_t max_capacity = heap->max_capacity();
-  size_t capacity = heap->soft_max_capacity();
-  size_t available = heap->free_set()->available();
+  size_t max_capacity = _space_info->max_capacity();
+  size_t capacity = _space_info->soft_max_capacity();
+  size_t available = _space_info->available();
 
   // Make sure the code below treats available without the soft tail.
   size_t soft_tail = max_capacity - capacity;
@@ -65,7 +64,7 @@ bool ShenandoahCompactHeuristics::should_start_gc() {
     return true;
   }
 
-  size_t bytes_allocated = heap->bytes_allocated_since_gc_start();
+  size_t bytes_allocated = _space_info->bytes_allocated_since_gc_start();
   if (bytes_allocated > threshold_bytes_allocated) {
     log_info(gc)("Trigger: Allocated since last cycle (" SIZE_FORMAT "%s) is larger than allocation threshold (" SIZE_FORMAT "%s)",
                  byte_size_in_proper_unit(bytes_allocated),           proper_unit_for_byte_size(bytes_allocated),

src/hotspot/share/gc/shenandoah/heuristics/shenandoahCompactHeuristics.hpp

@@ -27,9 +27,13 @@
 
 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 
+/*
+ * This heuristic has simpler triggers than the adaptive heuristic. The
+ * size of the collection set is limited to 3/4 of available memory.
+ */
 class ShenandoahCompactHeuristics : public ShenandoahHeuristics {
 public:
-  ShenandoahCompactHeuristics();
+  ShenandoahCompactHeuristics(ShenandoahSpaceInfo* space_info);
 
   virtual bool should_start_gc();
 

src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp

@@ -42,7 +42,8 @@ int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
   else return 0;
 }
 
-ShenandoahHeuristics::ShenandoahHeuristics() :
+ShenandoahHeuristics::ShenandoahHeuristics(ShenandoahSpaceInfo* space_info) :
+  _space_info(space_info),
   _region_data(nullptr),
   _degenerated_cycles_in_a_row(0),
   _successful_cycles_in_a_row(0),

src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.hpp

@@ -25,6 +25,7 @@
 #ifndef SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHHEURISTICS_HPP
 #define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHHEURISTICS_HPP
 
+#include "gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp"
 #include "gc/shenandoah/shenandoahHeap.hpp"
 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
 #include "gc/shenandoah/shenandoahSharedVariables.hpp"
@@ -58,6 +59,11 @@
 class ShenandoahCollectionSet;
 class ShenandoahHeapRegion;
 
+/*
+ * Shenandoah heuristics are primarily responsible for deciding when to start
+ * a collection cycle and choosing which regions will be evacuated during the
+ * cycle.
+ */
 class ShenandoahHeuristics : public CHeapObj<mtGC> {
   static const intx Concurrent_Adjust   = -1; // recover from penalties
   static const intx Degenerated_Penalty = 10; // how much to penalize average GC duration history on Degenerated GC
@@ -69,6 +75,9 @@ protected:
     size_t _garbage;
   } RegionData;
 
+  // Source of information about the memory space managed by this heuristic
+  ShenandoahSpaceInfo* _space_info;
+
   RegionData* _region_data;
 
   uint _degenerated_cycles_in_a_row;
@@ -93,7 +102,7 @@ protected:
   void adjust_penalty(intx step);
 
 public:
-  ShenandoahHeuristics();
+  ShenandoahHeuristics(ShenandoahSpaceInfo* space_info);
   virtual ~ShenandoahHeuristics();
 
   void record_metaspace_oom()     { _metaspace_oom.set(); }

src/hotspot/share/gc/shenandoah/heuristics/shenandoahPassiveHeuristics.cpp

@@ -31,6 +31,9 @@
 #include "logging/log.hpp"
 #include "logging/logTag.hpp"
 
+ShenandoahPassiveHeuristics::ShenandoahPassiveHeuristics(ShenandoahSpaceInfo* space_info) :
+  ShenandoahHeuristics(space_info) {}
+
 bool ShenandoahPassiveHeuristics::should_start_gc() {
   // Never do concurrent GCs.
   return false;
@@ -53,7 +56,7 @@ void ShenandoahPassiveHeuristics::choose_collection_set_from_regiondata(Shenando
 
   // Do not select too large CSet that would overflow the available free space.
   // Take at least the entire evacuation reserve, and be free to overflow to free space.
-  size_t max_capacity = ShenandoahHeap::heap()->max_capacity();
+  size_t max_capacity = _space_info->max_capacity();
   size_t available = MAX2(max_capacity / 100 * ShenandoahEvacReserve, actual_free);
   size_t max_cset  = (size_t)(available / ShenandoahEvacWaste);
 

src/hotspot/share/gc/shenandoah/heuristics/shenandoahPassiveHeuristics.hpp

@@ -27,8 +27,19 @@
 
 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 
+/*
+ * The passive heuristic is for use only with the passive mode. In
+ * the passive mode, Shenandoah only performs STW (i.e., degenerated)
+ * collections. All the barriers are disabled and there are no concurrent
+ * activities. Therefore, this heuristic _never_ triggers a cycle. It
+ * will select regions for evacuation based on ShenandoahEvacReserve,
+ * ShenandoahEvacWaste and ShenandoahGarbageThreshold. Note that it does
+ * not attempt to evacuate regions with more garbage.
+ */
 class ShenandoahPassiveHeuristics : public ShenandoahHeuristics {
 public:
+  ShenandoahPassiveHeuristics(ShenandoahSpaceInfo* space_info);
+
   virtual bool should_start_gc();
 
   virtual bool should_unload_classes();

src/hotspot/share/gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp

@@ -0,0 +1,45 @@
+/*
+ * Copyright Amazon.com Inc. 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.
+ *
+ */
+
+#ifndef SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHSPACEINFO_HPP
+#define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHSPACEINFO_HPP
+
+#include "utilities/globalDefinitions.hpp"
+
+/*
+ * The purpose of this interface is to decouple the heuristics from a
+ * direct dependency on the ShenandoahHeap singleton instance. This is
+ * done to facilitate future unit testing of the heuristics and to support
+ * future operational modes of Shenandoah in which the heap may be split
+ * into generations.
+ */
+class ShenandoahSpaceInfo {
+public:
+  virtual size_t soft_max_capacity() const = 0;
+  virtual size_t max_capacity() const = 0;
+  virtual size_t available() const = 0;
+  virtual size_t bytes_allocated_since_gc_start() const = 0;
+};
+
+#endif //SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHSPACEINFO_HPP

src/hotspot/share/gc/shenandoah/heuristics/shenandoahStaticHeuristics.cpp

@@ -32,7 +32,8 @@
 #include "logging/log.hpp"
 #include "logging/logTag.hpp"
 
-ShenandoahStaticHeuristics::ShenandoahStaticHeuristics() : ShenandoahHeuristics() {
+ShenandoahStaticHeuristics::ShenandoahStaticHeuristics(ShenandoahSpaceInfo* space_info) :
+  ShenandoahHeuristics(space_info) {
   SHENANDOAH_ERGO_ENABLE_FLAG(ExplicitGCInvokesConcurrent);
   SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahImplicitGCInvokesConcurrent);
 }
@@ -40,11 +41,9 @@ ShenandoahStaticHeuristics::ShenandoahStaticHeuristics() : ShenandoahHeuristics(
 ShenandoahStaticHeuristics::~ShenandoahStaticHeuristics() {}
 
 bool ShenandoahStaticHeuristics::should_start_gc() {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-
-  size_t max_capacity = heap->max_capacity();
-  size_t capacity = heap->soft_max_capacity();
-  size_t available = heap->free_set()->available();
+  size_t max_capacity = _space_info->max_capacity();
+  size_t capacity = _space_info->soft_max_capacity();
+  size_t available = _space_info->available();
 
   // Make sure the code below treats available without the soft tail.
   size_t soft_tail = max_capacity - capacity;

src/hotspot/share/gc/shenandoah/heuristics/shenandoahStaticHeuristics.hpp

@@ -27,9 +27,14 @@
 
 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 
+/*
+ * The static heuristic will trigger cycles if the available memory falls
+ * below ShenandoahMinFreeThreshold percentage of total capacity. This
+ * heuristic will attempt to evacuation any region with any garbage.
+ */
 class ShenandoahStaticHeuristics : public ShenandoahHeuristics {
 public:
-  ShenandoahStaticHeuristics();
+  ShenandoahStaticHeuristics(ShenandoahSpaceInfo* space_info);
 
   virtual ~ShenandoahStaticHeuristics();
 

src/hotspot/share/gc/shenandoah/mode/shenandoahIUMode.cpp

@@ -28,6 +28,7 @@
 #include "gc/shenandoah/heuristics/shenandoahCompactHeuristics.hpp"
 #include "gc/shenandoah/heuristics/shenandoahStaticHeuristics.hpp"
 #include "gc/shenandoah/mode/shenandoahIUMode.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
 #include "logging/log.hpp"
 #include "logging/logTag.hpp"
 #include "runtime/globals_extension.hpp"
@@ -67,14 +68,15 @@ ShenandoahHeuristics* ShenandoahIUMode::initialize_heuristics() const {
   if (ShenandoahGCHeuristics == nullptr) {
     vm_exit_during_initialization("Unknown -XX:ShenandoahGCHeuristics option (null)");
   }
+  ShenandoahHeap* heap = ShenandoahHeap::heap();
   if (strcmp(ShenandoahGCHeuristics, "aggressive") == 0) {
-    return new ShenandoahAggressiveHeuristics();
+    return new ShenandoahAggressiveHeuristics(heap);
   } else if (strcmp(ShenandoahGCHeuristics, "static") == 0) {
-    return new ShenandoahStaticHeuristics();
+    return new ShenandoahStaticHeuristics(heap);
   } else if (strcmp(ShenandoahGCHeuristics, "adaptive") == 0) {
-    return new ShenandoahAdaptiveHeuristics();
+    return new ShenandoahAdaptiveHeuristics(heap);
   } else if (strcmp(ShenandoahGCHeuristics, "compact") == 0) {
-    return new ShenandoahCompactHeuristics();
+    return new ShenandoahCompactHeuristics(heap);
   }
   vm_exit_during_initialization("Unknown -XX:ShenandoahGCHeuristics option");
   return nullptr;

src/hotspot/share/gc/shenandoah/mode/shenandoahPassiveMode.cpp

@@ -25,6 +25,7 @@
 #include "precompiled.hpp"
 #include "gc/shenandoah/heuristics/shenandoahPassiveHeuristics.hpp"
 #include "gc/shenandoah/mode/shenandoahPassiveMode.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
 #include "logging/log.hpp"
 #include "logging/logTag.hpp"
 #include "runtime/globals_extension.hpp"
@@ -59,5 +60,5 @@ ShenandoahHeuristics* ShenandoahPassiveMode::initialize_heuristics() const {
   if (ShenandoahGCHeuristics == nullptr) {
     vm_exit_during_initialization("Unknown -XX:ShenandoahGCHeuristics option (null)");
   }
-  return new ShenandoahPassiveHeuristics();
+  return new ShenandoahPassiveHeuristics(ShenandoahHeap::heap());
 }

src/hotspot/share/gc/shenandoah/mode/shenandoahSATBMode.cpp

@@ -28,6 +28,7 @@
 #include "gc/shenandoah/heuristics/shenandoahCompactHeuristics.hpp"
 #include "gc/shenandoah/heuristics/shenandoahStaticHeuristics.hpp"
 #include "gc/shenandoah/mode/shenandoahSATBMode.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
 #include "logging/log.hpp"
 #include "logging/logTag.hpp"
 #include "runtime/globals_extension.hpp"
@@ -55,14 +56,15 @@ ShenandoahHeuristics* ShenandoahSATBMode::initialize_heuristics() const {
   if (ShenandoahGCHeuristics == nullptr) {
     vm_exit_during_initialization("Unknown -XX:ShenandoahGCHeuristics option (null)");
   }
+  ShenandoahHeap* heap = ShenandoahHeap::heap();
   if (strcmp(ShenandoahGCHeuristics, "aggressive") == 0) {
-    return new ShenandoahAggressiveHeuristics();
+    return new ShenandoahAggressiveHeuristics(heap);
   } else if (strcmp(ShenandoahGCHeuristics, "static") == 0) {
-    return new ShenandoahStaticHeuristics();
+    return new ShenandoahStaticHeuristics(heap);
   } else if (strcmp(ShenandoahGCHeuristics, "adaptive") == 0) {
-    return new ShenandoahAdaptiveHeuristics();
+    return new ShenandoahAdaptiveHeuristics(heap);
   } else if (strcmp(ShenandoahGCHeuristics, "compact") == 0) {
-    return new ShenandoahCompactHeuristics();
+    return new ShenandoahCompactHeuristics(heap);
   }
   vm_exit_during_initialization("Unknown -XX:ShenandoahGCHeuristics option");
   return nullptr;

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -662,6 +662,10 @@ size_t ShenandoahHeap::committed() const {
   return Atomic::load(&_committed);
 }
 
+size_t ShenandoahHeap::available() const {
+  return free_set()->available();
+}
+
 void ShenandoahHeap::increase_committed(size_t bytes) {
   shenandoah_assert_heaplocked_or_safepoint();
   _committed += bytes;
@@ -1899,7 +1903,7 @@ address ShenandoahHeap::gc_state_addr() {
   return (address) ShenandoahHeap::heap()->_gc_state.addr_of();
 }
 
-size_t ShenandoahHeap::bytes_allocated_since_gc_start() {
+size_t ShenandoahHeap::bytes_allocated_since_gc_start() const {
   return Atomic::load(&_bytes_allocated_since_gc_start);
 }
 

src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp

@@ -29,6 +29,7 @@
 #include "gc/shared/markBitMap.hpp"
 #include "gc/shared/softRefPolicy.hpp"
 #include "gc/shared/collectedHeap.hpp"
+#include "gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp"
 #include "gc/shenandoah/shenandoahAsserts.hpp"
 #include "gc/shenandoah/shenandoahAllocRequest.hpp"
 #include "gc/shenandoah/shenandoahLock.hpp"
@@ -116,7 +117,7 @@ typedef Stack<oop, mtGC>  ShenandoahScanObjectStack;
 // to encode forwarding data. See BrooksPointer for details on forwarding data encoding.
 // See ShenandoahControlThread for GC cycle structure.
 //
-class ShenandoahHeap : public CollectedHeap {
+class ShenandoahHeap : public CollectedHeap, public ShenandoahSpaceInfo {
   friend class ShenandoahAsserts;
   friend class VMStructs;
   friend class ShenandoahGCSession;
@@ -191,16 +192,17 @@ public:
   void decrease_committed(size_t bytes);
   void increase_allocated(size_t bytes);
 
-  size_t bytes_allocated_since_gc_start();
+  size_t bytes_allocated_since_gc_start() const override;
   void reset_bytes_allocated_since_gc_start();
 
   size_t min_capacity()      const;
   size_t max_capacity()      const override;
-  size_t soft_max_capacity() const;
+  size_t soft_max_capacity() const override;
   size_t initial_capacity()  const;
   size_t capacity()          const override;
   size_t used()              const override;
   size_t committed()         const;
+  size_t available()         const override;
 
   void set_soft_max_capacity(size_t v);