Implemented Region. Arena allocator now uses Region for OS specific allocation and page management.

CMakeLists.txt

@@ -10,6 +10,7 @@ set(PUBLIC_HEADERS
   include/arena.h
   include/block.h
   include/heap.h
+  include/region.h
   include/util.h
 )
 
@@ -18,6 +19,7 @@ set(SRCS
   src/block.cpp
   src/heap.cpp
   src/mimir.cpp
+  src/region.cpp
   src/util.cpp
 )
 

include/arena.h

@@ -33,6 +33,8 @@
 
 #include <cstddef>
 
+#include "region.h"
+
 namespace mimir {
 class Arena
 {
@@ -53,14 +55,13 @@ public:
   // Reset the arena, potentially also releasing committed pages
   void reset();
 private:
-  std::byte* m_data;
+  Region m_region;
   size_t m_minSize;
-  size_t m_maxSize;
-  size_t m_committedSize;
   size_t m_usedSize;
 
   static const size_t kWatermarkLen = 8;
   size_t m_watermark[kWatermarkLen];
+
 }; // class Arena
 
 } // namespace mimir

include/mimir.h

@@ -34,6 +34,7 @@
 #include "arena.h"
 #include "block.h"
 #include "heap.h"
+#include "region.h"
 #include "util.h"
 
 namespace mimir {

include/region.h

@@ -0,0 +1,55 @@
+//
+//  region.h
+//  Kraken Engine / Mimir
+//
+//  Copyright 2026 Kearwood Gilbert. All rights reserved.
+//
+//  Redistribution and use in source and binary forms, with or without modification, are
+//  permitted provided that the following conditions are met:
+//
+//  1. Redistributions of source code must retain the above copyright notice, this list of
+//  conditions and the following disclaimer.
+//
+//  2. Redistributions in binary form must reproduce the above copyright notice, this list
+//  of conditions and the following disclaimer in the documentation and/or other materials
+//  provided with the distribution.
+//
+//  THIS SOFTWARE IS PROVIDED BY KEARWOOD GILBERT ''AS IS'' AND ANY EXPRESS OR IMPLIED
+//  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+//  FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL KEARWOOD GILBERT OR
+//  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+//  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+//  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+//  ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+//  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+//  ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//  The views and conclusions contained in the software and documentation are those of the
+//  authors and should not be interpreted as representing official policies, either expressed
+//  or implied, of Kearwood Gilbert.
+//
+
+#pragma once
+
+#include <cstddef>
+
+namespace mimir {
+class Region
+{
+public:
+  Region();
+  ~Region();
+
+  bool init(size_t maxSize = 1ULL << 32);
+  bool resize(size_t size);
+  size_t getSize() const;
+  size_t getMaxSize() const;
+  std::byte* getAddress() const;
+
+private:
+  std::byte* m_data;
+  size_t m_committedSize;
+  size_t m_maxSize;
+};
+
+} // namespace mimir

src/arena.cpp

@@ -40,10 +40,7 @@ namespace mimir {
 
 Arena::Arena()
   : m_minSize(0)
-  , m_maxSize(0)
-  , m_data(nullptr)
   , m_usedSize(0)
-  , m_committedSize(0)
 {
   for (size_t i = 0; i < kWatermarkLen; i++) {
     m_watermark[i] = 0;
@@ -52,73 +49,31 @@ Arena::Arena()
 
 Arena::~Arena()
 {
-  if (m_data) {
-#if defined(_WIN32) || defined(_WIN64)
-    if (!VirtualFree((void*)m_data, 0, MEM_RELEASE)) {
-      ReportWindowsLastError("VirtualAlloc");
-    }
-#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
-    munmap(m_data, KRAKEN_MEM_ROUND_UP_PAGE(m_maxSize));
-#else
-    static_assert(false, "Not Implemented");
-#endif
-  }
 }
 
 bool Arena::init(size_t minSize, size_t maxSize)
 {
   assert(maxSize >= minSize);
-  assert(m_data == nullptr);
   assert(m_usedSize == 0);
-  assert(m_committedSize == 0);
 
   m_minSize = KRAKEN_MEM_ROUND_UP_PAGE(minSize);
-  m_maxSize = KRAKEN_MEM_ROUND_UP_PAGE(maxSize);
+  return m_region.init(maxSize);
-
-#if defined(_WIN32) || defined(_WIN64)
-  m_data = (std::byte*)VirtualAlloc(NULL, KRAKEN_MEM_ROUND_UP_PAGE(m_maxSize), MEM_RESERVE, PAGE_NOACCESS);
-  if (m_data == nullptr) {
-    ReportWindowsLastError("VirtualAlloc");
-    return false;
-  }
-#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
-  m_data = (std::byte*)mmap(NULL, KRAKEN_MEM_ROUND_UP_PAGE(m_maxSize), PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-  if (m_data == MAP_FAILED) {
-    return false;
-  }
-#else
-  static_assert(false, "Not Implemented");
-#endif
-  return true;
 }
 
 std::byte* Arena::alloc(size_t size)
 {
   size_t neededSize = m_usedSize + size;
-  if (neededSize > m_committedSize)
+  if (neededSize > m_region.getSize())
   {
+    // Increase the size exponentially when we run out
     size_t newSize = std::bit_ceil(neededSize) << 1;
     if (newSize < m_minSize) {
       newSize = m_minSize;
     }
-    newSize = KRAKEN_MEM_ROUND_UP_PAGE(newSize);
+    m_region.resize(newSize);
+  }
 
-#if defined(_WIN32) || defined(_WIN64)
+  std::byte* ret = m_region.getAddress() + m_usedSize;
-    if(VirtualAlloc(m_data + m_committedSize, newSize - m_committedSize, MEM_COMMIT, PAGE_READWRITE) == nullptr) {
-      ReportWindowsLastError("VirtualAlloc");
-      return nullptr;
-    }
-#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
-    if (mprotect(m_data + m_committedSize, newSize - m_committedSize, PROT_READ | PROT_WRITE) != 0) {
-      return nullptr;
-    }
-#else
-    static_assert(false, "Not Implemented");
-#endif
-    m_committedSize = newSize;
-  } // if (neededSize > m_committedSize)
-
-  std::byte* ret = m_data + m_usedSize;
   m_usedSize = neededSize;
   return ret;
 }
@@ -131,7 +86,7 @@ std::byte* Arena::allocA16(size_t size)
     return nullptr;
   }
 
-  return m_data + nextByte;
+  return m_region.getAddress() + nextByte;
 }
 
 std::byte* Arena::allocA64(size_t size)
@@ -142,7 +97,7 @@ std::byte* Arena::allocA64(size_t size)
     return nullptr;
   }
 
-  return m_data + nextByte;
+  return m_region.getAddress() + nextByte;
 }
 
 void Arena::reset()
@@ -161,28 +116,8 @@ void Arena::reset()
     targetSize = m_minSize;
   }
   size_t thresholdSize = targetSize << 1; // The threshold for shrinking is greater than the target to implement hysteresis
-  if (m_committedSize > thresholdSize) {
+  if (m_region.getSize() > thresholdSize) {
-    size_t newSize = KRAKEN_MEM_ROUND_UP_PAGE(targetSize);
+    m_region.resize(targetSize);
-
-    std::byte* rangeStart = m_data + newSize;
-    size_t rangeLen = m_committedSize - newSize;
-#if defined(_WIN32) || defined(_WIN64)
-    if (!VirtualAlloc(rangeStart, rangeLen, MEM_RESET, PAGE_NOACCESS)) {
-      ReportWindowsLastError("VirtualAlloc");
-    } else {
-      m_committedSize = newSize;
-    }
-#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
-    if (madvise(rangeStart, rangeLen, MADV_DONTNEED) != 0) {
-      // TODO - Log Error or debug build assert
-    }
-    if (mprotect(rangeStart, rangeLen, PROT_NONE) != 0) {
-      // TODO - Log Error or debug build assert
-    }
-#else
-    static_assert(false, "Not Implemented");
-#endif
-    m_committedSize = newSize;
   }
 
   m_usedSize = 0;

src/region.cpp

@@ -0,0 +1,153 @@
+//
+//  region.cpp
+//  Kraken Engine
+//
+//  Copyright 2026 Kearwood Gilbert. All rights reserved.
+//
+//  Redistribution and use in source and binary forms, with or without modification, are
+//  permitted provided that the following conditions are met:
+//
+//  1. Redistributions of source code must retain the above copyright notice, this list of
+//  conditions and the following disclaimer.
+//
+//  2. Redistributions in binary form must reproduce the above copyright notice, this list
+//  of conditions and the following disclaimer in the documentation and/or other materials
+//  provided with the distribution.
+//
+//  THIS SOFTWARE IS PROVIDED BY KEARWOOD GILBERT ''AS IS'' AND ANY EXPRESS OR IMPLIED
+//  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+//  FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL KEARWOOD GILBERT OR
+//  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+//  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+//  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+//  ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+//  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+//  ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//  The views and conclusions contained in the software and documentation are those of the
+//  authors and should not be interpreted as representing official policies, either expressed
+//  or implied, of Kearwood Gilbert.
+//
+
+#include "../include/mimir.h"
+#include "mimir_impl.h"
+
+#include <cassert>
+#include <cstring>
+#include <bit>
+
+namespace mimir {
+
+Region::Region()
+  : m_data(nullptr)
+  , m_committedSize(0)
+  , m_maxSize(0)
+{
+
+}
+
+Region::~Region()
+{
+  if (m_data) {
+#if defined(_WIN32) || defined(_WIN64)
+    if (!VirtualFree((void*)m_data, 0, MEM_RELEASE)) {
+      ReportWindowsLastError("VirtualAlloc");
+    }
+#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
+    munmap(m_data, KRAKEN_MEM_ROUND_UP_PAGE(m_maxSize));
+#else
+    static_assert(false, "Not Implemented");
+#endif
+  }
+}
+
+bool Region::init(size_t maxSize)
+{
+  assert(m_data == nullptr);
+  assert(m_committedSize == 0);
+
+  m_maxSize = KRAKEN_MEM_ROUND_UP_PAGE(maxSize);
+
+#if defined(_WIN32) || defined(_WIN64)
+  m_data = (std::byte*)VirtualAlloc(NULL, KRAKEN_MEM_ROUND_UP_PAGE(m_maxSize), MEM_RESERVE, PAGE_NOACCESS);
+  if (m_data == nullptr) {
+    ReportWindowsLastError("VirtualAlloc");
+    return false;
+  }
+#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
+  m_data = (std::byte*)mmap(NULL, KRAKEN_MEM_ROUND_UP_PAGE(m_maxSize), PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (m_data == MAP_FAILED) {
+    return false;
+  }
+#else
+  static_assert(false, "Not Implemented");
+#endif
+  return true;
+}
+ 
+bool Region::resize(size_t size)
+{
+  size_t newSize = KRAKEN_MEM_ROUND_UP_PAGE(size);
+
+  if (newSize == m_committedSize) {
+    return true;
+  }
+
+  if (newSize > m_committedSize) {
+    // ---- Growing ----
+#if defined(_WIN32) || defined(_WIN64)
+    if (VirtualAlloc(m_data + m_committedSize, newSize - m_committedSize, MEM_COMMIT, PAGE_READWRITE) == nullptr) {
+      ReportWindowsLastError("VirtualAlloc");
+      return false;
+    }
+#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
+    if (mprotect(m_data + m_committedSize, newSize - m_committedSize, PROT_READ | PROT_WRITE) != 0) {
+      return false;
+    }
+#else
+    static_assert(false, "Not Implemented");
+#endif
+    m_committedSize = newSize;
+    return true;
+  } // if (newSize > m_committedSize)
+
+  // ---- Shrinking ----
+  std::byte* rangeStart = m_data + newSize;
+  size_t rangeLen = m_committedSize - newSize;
+#if defined(_WIN32) || defined(_WIN64)
+  if (!VirtualAlloc(rangeStart, rangeLen, MEM_RESET, PAGE_NOACCESS)) {
+    ReportWindowsLastError("VirtualAlloc");
+  } else {
+    m_committedSize = newSize;
+  }
+#elif defined(__unix__) || defined(__APPLE__) || defined(ANDROID)
+  if (madvise(rangeStart, rangeLen, MADV_DONTNEED) != 0) {
+    // TODO - Log Error or debug build assert
+  }
+  if (mprotect(rangeStart, rangeLen, PROT_NONE) != 0) {
+    // TODO - Log Error or debug build assert
+  }
+#else
+  static_assert(false, "Not Implemented");
+#endif
+  m_committedSize = newSize;
+
+  return true;
+}
+
+size_t Region::getSize() const
+{
+  return m_committedSize;
+}
+
+size_t Region::getMaxSize() const
+{
+  return m_maxSize;
+}
+
+std::byte* Region::getAddress() const
+{
+  return m_data;
+}
+
+};