8357053: ZGC: Improved utility for ZPageAge

Co-authored-by: Axel Boldt-Christmas <aboldtch@openjdk.org>
Reviewed-by: sjohanss, stefank

Author: jsikstro

src/hotspot/share/gc/z/zAllocator.cpp

@@ -23,6 +23,7 @@
 
 #include "gc/z/zAllocator.hpp"
 #include "gc/z/zObjectAllocator.hpp"
+#include "gc/z/zPageAge.inline.hpp"
 
 ZAllocatorEden*          ZAllocator::_eden;
 ZAllocatorForRelocation* ZAllocator::_relocation[ZAllocator::_relocation_allocators];
@@ -47,7 +48,7 @@ ZPageAge ZAllocatorForRelocation::install() {
   for (uint i = 0; i < ZAllocator::_relocation_allocators; ++i) {
     if (_relocation[i] == nullptr) {
       _relocation[i] = this;
-      return static_cast<ZPageAge>(i + 1);
+      return to_zpageage(i + 1);
     }
   }
 

src/hotspot/share/gc/z/zAllocator.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2025, 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
@@ -35,7 +35,7 @@ class ZPage;
 
 class ZAllocator {
 public:
-  static constexpr uint _relocation_allocators = static_cast<uint>(ZPageAge::old);
+  static constexpr uint _relocation_allocators = ZPageAgeCount - 1;
 
 protected:
   ZObjectAllocator _object_allocator;

src/hotspot/share/gc/z/zAllocator.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2025, 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
@@ -28,13 +28,14 @@
 
 #include "gc/z/zAddress.inline.hpp"
 #include "gc/z/zHeap.hpp"
+#include "gc/z/zPageAge.inline.hpp"
 
 inline ZAllocatorEden* ZAllocator::eden() {
   return _eden;
 }
 
 inline ZAllocatorForRelocation* ZAllocator::relocation(ZPageAge page_age) {
-  return _relocation[static_cast<uint>(page_age) - 1];
+  return _relocation[untype(page_age - 1)];
 }
 
 inline ZAllocatorForRelocation* ZAllocator::old() {

src/hotspot/share/gc/z/zGeneration.cpp

@@ -41,6 +41,7 @@
 #include "gc/z/zHeap.inline.hpp"
 #include "gc/z/zJNICritical.hpp"
 #include "gc/z/zMark.inline.hpp"
+#include "gc/z/zPageAge.inline.hpp"
 #include "gc/z/zPageAllocator.hpp"
 #include "gc/z/zRelocationSet.inline.hpp"
 #include "gc/z/zRelocationSetSelector.inline.hpp"
@@ -699,11 +700,10 @@ uint ZGenerationYoung::compute_tenuring_threshold(ZRelocationSetSelectorStats st
   uint last_populated_age = 0;
   size_t last_populated_live = 0;
 
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
-    const ZPageAge age = static_cast<ZPageAge>(i);
+  for (ZPageAge age : ZPageAgeRange()) {
     const size_t young_live = stats.small(age).live() + stats.medium(age).live() + stats.large(age).live();
     if (young_live > 0) {
-      last_populated_age = i;
+      last_populated_age = untype(age);
       last_populated_live = young_live;
       if (young_live_last > 0) {
         young_life_expectancy_sum += double(young_live) / double(young_live_last);
@@ -842,8 +842,8 @@ void ZGenerationYoung::mark_start() {
 
   // Retire allocating pages
   ZAllocator::eden()->retire_pages();
-  for (ZPageAge i = ZPageAge::survivor1; i <= ZPageAge::survivor14; i = static_cast<ZPageAge>(static_cast<uint>(i) + 1)) {
-    ZAllocator::relocation(i)->retire_pages();
+  for (ZPageAge age : ZPageAgeRangeSurvivor) {
+    ZAllocator::relocation(age)->retire_pages();
   }
 
   // Reset allocated/reclaimed/used statistics

src/hotspot/share/gc/z/zPageAge.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2025, 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
@@ -24,6 +24,7 @@
 #ifndef SHARE_GC_Z_ZPAGEAGE_HPP
 #define SHARE_GC_Z_ZPAGEAGE_HPP
 
+#include "utilities/enumIterator.hpp"
 #include "utilities/globalDefinitions.hpp"
 
 enum class ZPageAge : uint8_t {
@@ -45,6 +46,19 @@ enum class ZPageAge : uint8_t {
   old
 };
 
-constexpr uint ZPageAgeMax = static_cast<uint>(ZPageAge::old);
+constexpr uint ZPageAgeCount = static_cast<uint>(ZPageAge::old) + 1;
+constexpr ZPageAge ZPageAgeLastPlusOne = static_cast<ZPageAge>(ZPageAgeCount);
+
+ENUMERATOR_RANGE(ZPageAge,
+                 ZPageAge::eden,
+                 ZPageAge::old);
+
+using ZPageAgeRange = EnumRange<ZPageAge>;
+
+constexpr ZPageAgeRange ZPageAgeRangeEden = ZPageAgeRange::create<ZPageAge::eden, ZPageAge::survivor1>();
+constexpr ZPageAgeRange ZPageAgeRangeYoung = ZPageAgeRange::create<ZPageAge::eden, ZPageAge::old>();
+constexpr ZPageAgeRange ZPageAgeRangeSurvivor = ZPageAgeRange::create<ZPageAge::survivor1, ZPageAge::old>();
+constexpr ZPageAgeRange ZPageAgeRangeRelocation = ZPageAgeRange::create<ZPageAge::survivor1, ZPageAgeLastPlusOne>();
+constexpr ZPageAgeRange ZPageAgeRangeOld = ZPageAgeRange::create<ZPageAge::old, ZPageAgeLastPlusOne>();
 
 #endif // SHARE_GC_Z_ZPAGEAGE_HPP

src/hotspot/share/gc/z/zPageAge.inline.hpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2025, 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.
+ */
+
+#ifndef SHARE_GC_Z_ZPAGEAGE_INLINE_HPP
+#define SHARE_GC_Z_ZPAGEAGE_INLINE_HPP
+
+#include "gc/z/zPageAge.hpp"
+
+#include "utilities/checkedCast.hpp"
+
+#include <type_traits>
+
+inline uint untype(ZPageAge age) {
+  return static_cast<uint>(age);
+}
+
+inline ZPageAge to_zpageage(uint age) {
+  assert(age < ZPageAgeCount, "Invalid age");
+  return static_cast<ZPageAge>(age);
+}
+
+inline ZPageAge operator+(ZPageAge age, size_t size) {
+  const auto size_value = checked_cast<std::underlying_type_t<ZPageAge>>(size);
+  return to_zpageage(untype(age) + size_value);
+}
+
+inline ZPageAge operator-(ZPageAge age, size_t size) {
+  const auto size_value = checked_cast<std::underlying_type_t<ZPageAge>>(size);
+  return to_zpageage(untype(age) - size_value);
+}
+
+#endif // SHARE_GC_Z_ZPAGEAGE_INLINE_HPP

src/hotspot/share/gc/z/zRelocate.cpp

@@ -488,11 +488,11 @@ class ZRelocateMediumAllocator {
   }
 
   ZPage* shared(ZPageAge age) {
-    return _shared[static_cast<uint>(age) - 1];
+    return _shared[untype(age - 1)];
   }
 
   void set_shared(ZPageAge age, ZPage* page) {
-    _shared[static_cast<uint>(age) - 1] = page;
+    _shared[untype(age - 1)] = page;
   }
 
   ZPage* alloc_and_retire_target_page(ZForwarding* forwarding, ZPage* target) {
@@ -570,11 +570,11 @@ class ZRelocateWork : public StackObj {
 
 
   ZPage* target(ZPageAge age) {
-    return _target[static_cast<uint>(age) - 1];
+    return _target[untype(age - 1)];
   }
 
   void set_target(ZPageAge age, ZPage* page) {
-    _target[static_cast<uint>(age) - 1] = page;
+    _target[untype(age - 1)] = page;
   }
 
   size_t object_alignment() const {
@@ -1232,12 +1232,12 @@ ZPageAge ZRelocate::compute_to_age(ZPageAge from_age) {
     return ZPageAge::old;
   }
 
-  const uint age = static_cast<uint>(from_age);
+  const uint age = untype(from_age);
   if (age >= ZGeneration::young()->tenuring_threshold()) {
     return ZPageAge::old;
   }
 
-  return static_cast<ZPageAge>(age + 1);
+  return to_zpageage(age + 1);
 }
 
 class ZFlipAgePagesTask : public ZTask {

src/hotspot/share/gc/z/zRelocationSetSelector.cpp

@@ -25,6 +25,7 @@
 #include "gc/z/zArray.inline.hpp"
 #include "gc/z/zForwarding.inline.hpp"
 #include "gc/z/zPage.inline.hpp"
+#include "gc/z/zPageAge.inline.hpp"
 #include "gc/z/zRelocationSetSelector.inline.hpp"
 #include "jfr/jfrEvents.hpp"
 #include "logging/log.hpp"
@@ -117,8 +118,8 @@ void ZRelocationSetSelectorGroup::select_inner() {
   const int npages = _live_pages.length();
   int selected_from = 0;
   int selected_to = 0;
-  size_t npages_selected[ZPageAgeMax + 1] = { 0 };
-  size_t selected_live_bytes[ZPageAgeMax + 1] = { 0 };
+  size_t npages_selected[ZPageAgeCount] = { 0 };
+  size_t selected_live_bytes[ZPageAgeCount] = { 0 };
   size_t selected_forwarding_entries = 0;
 
   size_t from_live_bytes = 0;
@@ -149,8 +150,8 @@ void ZRelocationSetSelectorGroup::select_inner() {
     if (diff_reclaimable > _fragmentation_limit) {
       selected_from = from;
       selected_to = to;
-      selected_live_bytes[static_cast<uint>(page->age())] += page_live_bytes;
-      npages_selected[static_cast<uint>(page->age())] += 1;
+      selected_live_bytes[untype(page->age())] += page_live_bytes;
+      npages_selected[untype(page->age())] += 1;
       selected_forwarding_entries = from_forwarding_entries;
     }
 
@@ -172,7 +173,7 @@ void ZRelocationSetSelectorGroup::select_inner() {
   _forwarding_entries = selected_forwarding_entries;
 
   // Update statistics
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
+  for (uint i = 0; i < ZPageAgeCount; ++i) {
     _stats[i]._relocate = selected_live_bytes[i];
     _stats[i]._npages_selected = npages_selected[i];
   }
@@ -200,7 +201,7 @@ void ZRelocationSetSelectorGroup::select() {
   }
 
   ZRelocationSetSelectorGroupStats s{};
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
+  for (uint i = 0; i < ZPageAgeCount; ++i) {
     s._npages_candidates += _stats[i].npages_candidates();
     s._total += _stats[i].total();
     s._empty += _stats[i].empty();
@@ -239,8 +240,8 @@ void ZRelocationSetSelector::select() {
 ZRelocationSetSelectorStats ZRelocationSetSelector::stats() const {
   ZRelocationSetSelectorStats stats;
 
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
-    const ZPageAge age = static_cast<ZPageAge>(i);
+  for (ZPageAge age : ZPageAgeRange()) {
+    const uint i = untype(age);
     stats._small[i] = _small.stats(age);
     stats._medium[i] = _medium.stats(age);
     stats._large[i] = _large.stats(age);

src/hotspot/share/gc/z/zRelocationSetSelector.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2025, 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
@@ -62,9 +62,9 @@ class ZRelocationSetSelectorStats {
   friend class ZRelocationSetSelector;
 
 private:
-  ZRelocationSetSelectorGroupStats _small[ZPageAgeMax + 1];
-  ZRelocationSetSelectorGroupStats _medium[ZPageAgeMax + 1];
-  ZRelocationSetSelectorGroupStats _large[ZPageAgeMax + 1];
+  ZRelocationSetSelectorGroupStats _small[ZPageAgeCount];
+  ZRelocationSetSelectorGroupStats _medium[ZPageAgeCount];
+  ZRelocationSetSelectorGroupStats _large[ZPageAgeCount];
 
   size_t _has_relocatable_pages;
 
@@ -90,7 +90,7 @@ class ZRelocationSetSelectorGroup {
   ZArray<ZPage*>                   _live_pages;
   ZArray<ZPage*>                   _not_selected_pages;
   size_t                           _forwarding_entries;
-  ZRelocationSetSelectorGroupStats _stats[ZPageAgeMax + 1];
+  ZRelocationSetSelectorGroupStats _stats[ZPageAgeCount];
 
   bool is_disabled();
   bool is_selectable();

src/hotspot/share/gc/z/zRelocationSetSelector.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025, 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
@@ -29,6 +29,7 @@
 #include "gc/z/zArray.inline.hpp"
 #include "gc/z/zGlobals.hpp"
 #include "gc/z/zPage.inline.hpp"
+#include "gc/z/zPageAge.inline.hpp"
 #include "utilities/powerOfTwo.hpp"
 
 inline size_t ZRelocationSetSelectorGroupStats::npages_candidates() const {
@@ -60,15 +61,15 @@ inline bool ZRelocationSetSelectorStats::has_relocatable_pages() const {
 }
 
 inline const ZRelocationSetSelectorGroupStats& ZRelocationSetSelectorStats::small(ZPageAge age) const {
-  return _small[static_cast<uint>(age)];
+  return _small[untype(age)];
 }
 
 inline const ZRelocationSetSelectorGroupStats& ZRelocationSetSelectorStats::medium(ZPageAge age) const {
-  return _medium[static_cast<uint>(age)];
+  return _medium[untype(age)];
 }
 
 inline const ZRelocationSetSelectorGroupStats& ZRelocationSetSelectorStats::large(ZPageAge age) const {
-  return _large[static_cast<uint>(age)];
+  return _large[untype(age)];
 }
 
 inline bool ZRelocationSetSelectorGroup::pre_filter_page(const ZPage* page, size_t live_bytes) const {
@@ -113,7 +114,7 @@ inline void ZRelocationSetSelectorGroup::register_live_page(ZPage* page) {
   }
 
   const size_t size = page->size();
-  const uint age = static_cast<uint>(page->age());
+  const uint age = untype(page->age());
   _stats[age]._npages_candidates++;
   _stats[age]._total += size;
   _stats[age]._live += live;
@@ -122,7 +123,7 @@ inline void ZRelocationSetSelectorGroup::register_live_page(ZPage* page) {
 inline void ZRelocationSetSelectorGroup::register_empty_page(ZPage* page) {
   const size_t size = page->size();
 
-  const uint age = static_cast<uint>(page->age());
+  const uint age = untype(page->age());
   _stats[age]._npages_candidates++;
   _stats[age]._total += size;
   _stats[age]._empty += size;
@@ -141,7 +142,7 @@ inline size_t ZRelocationSetSelectorGroup::forwarding_entries() const {
 }
 
 inline const ZRelocationSetSelectorGroupStats& ZRelocationSetSelectorGroup::stats(ZPageAge age) const {
-  return _stats[static_cast<uint>(age)];
+  return _stats[untype(age)];
 }
 
 inline void ZRelocationSetSelector::register_live_page(ZPage* page) {
@@ -188,26 +189,23 @@ inline void ZRelocationSetSelector::clear_empty_pages() {
 
 inline size_t ZRelocationSetSelector::total() const {
   size_t sum = 0;
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
-    const ZPageAge age = static_cast<ZPageAge>(i);
+  for (ZPageAge age : ZPageAgeRange()) {
     sum += _small.stats(age).total() + _medium.stats(age).total() + _large.stats(age).total();
   }
   return sum;
 }
 
 inline size_t ZRelocationSetSelector::empty() const {
   size_t sum = 0;
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
-    const ZPageAge age = static_cast<ZPageAge>(i);
+  for (ZPageAge age : ZPageAgeRange()) {
     sum += _small.stats(age).empty() + _medium.stats(age).empty() + _large.stats(age).empty();
   }
   return sum;
 }
 
 inline size_t ZRelocationSetSelector::relocate() const {
   size_t sum = 0;
-  for (uint i = 0; i <= ZPageAgeMax; ++i) {
-    const ZPageAge age = static_cast<ZPageAge>(i);
+  for (ZPageAge age : ZPageAgeRange()) {
     sum += _small.stats(age).relocate() + _medium.stats(age).relocate() + _large.stats(age).relocate();
   }
   return sum;