Common/MemArena: Add LazyMemoryRegion to represent a zero-initialized memory region whose pages are only allocated on first access.

Source/Core/Common/MemArenaUnix.cpp

@@ -16,6 +16,7 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+#include "Common/Assert.h"
 #include "Common/CommonFuncs.h"
 #include "Common/CommonTypes.h"
 #include "Common/Logging/Log.h"
@@ -108,4 +109,46 @@ void MemArena::UnmapFromMemoryRegion(void* view, size_t size)
   if (retval == MAP_FAILED)
     NOTICE_LOG_FMT(MEMMAP, "mmap failed");
 }
+
+LazyMemoryRegion::LazyMemoryRegion() = default;
+
+LazyMemoryRegion::~LazyMemoryRegion()
+{
+  Release();
+}
+
+void* LazyMemoryRegion::Create(size_t size)
+{
+  ASSERT(!m_memory);
+
+  void* memory = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (!memory)
+  {
+    NOTICE_LOG_FMT(MEMMAP, "Memory allocation of {} bytes failed.", size);
+    return nullptr;
+  }
+
+  m_memory = memory;
+  m_size = size;
+
+  return memory;
+}
+
+void LazyMemoryRegion::Clear()
+{
+  ASSERT(m_memory);
+
+  mmap(m_memory, m_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+}
+
+void LazyMemoryRegion::Release()
+{
+  if (m_memory)
+  {
+    munmap(m_memory, m_size);
+    m_memory = nullptr;
+    m_size = 0;
+  }
+}
+
 }  // namespace Common