Common/MemArena: Add function for getting page size and alignment

Source/Core/Common/MemArena.h

@@ -115,6 +115,16 @@ public:
   ///
   void UnmapFromMemoryRegion(void* view, size_t size);
 
+  ///
+  /// Return the system's page size.
+  ///
+  size_t GetPageSize() const;
+
+  ///
+  /// Return the system's required page alignment.
+  ///
+  size_t GetPageAlignment() const;
+
 private:
 #ifdef _WIN32
   WindowsMemoryRegion* EnsureSplitRegionForMapping(void* address, size_t size);

Source/Core/Common/MemArenaAndroid.cpp

@@ -144,6 +144,16 @@ void MemArena::UnmapFromMemoryRegion(void* view, size_t size)
     NOTICE_LOG_FMT(MEMMAP, "mmap failed");
 }
 
+size_t MemArena::GetPageSize() const
+{
+  return sysconf(_SC_PAGESIZE);
+}
+
+size_t MemArena::GetPageAlignment() const
+{
+  return GetPageSize();
+}
+
 LazyMemoryRegion::LazyMemoryRegion() = default;
 
 LazyMemoryRegion::~LazyMemoryRegion()

Source/Core/Common/MemArenaDarwin.cpp

@@ -3,6 +3,8 @@
 
 #include "Common/MemArena.h"
 
+#include <unistd.h>
+
 #include "Common/Assert.h"
 #include "Common/Logging/Log.h"
 
@@ -163,6 +165,16 @@ void MemArena::UnmapFromMemoryRegion(void* view, size_t size)
   }
 }
 
+size_t MemArena::GetPageSize() const
+{
+  return getpagesize();
+}
+
+size_t MemArena::GetPageAlignment() const
+{
+  return GetPageSize();
+}
+
 LazyMemoryRegion::LazyMemoryRegion() = default;
 
 LazyMemoryRegion::~LazyMemoryRegion()

Source/Core/Common/MemArenaUnix.cpp

@@ -110,6 +110,16 @@ void MemArena::UnmapFromMemoryRegion(void* view, size_t size)
     NOTICE_LOG_FMT(MEMMAP, "mmap failed");
 }
 
+size_t MemArena::GetPageSize() const
+{
+  return sysconf(_SC_PAGESIZE);
+}
+
+size_t MemArena::GetPageAlignment() const
+{
+  return GetPageSize();
+}
+
 LazyMemoryRegion::LazyMemoryRegion() = default;
 
 LazyMemoryRegion::~LazyMemoryRegion()

Source/Core/Common/MemArenaWin.cpp

@@ -438,6 +438,26 @@ void MemArena::UnmapFromMemoryRegion(void* view, size_t size)
   UnmapViewOfFile(view);
 }
 
+size_t MemArena::GetPageSize() const
+{
+  SYSTEM_INFO si;
+  GetSystemInfo(&si);
+  return si.dwPageSize;
+}
+
+size_t MemArena::GetPageAlignment() const
+{
+  SYSTEM_INFO si;
+  GetSystemInfo(&si);
+  if (!m_memory_functions.m_address_MapViewOfFile3)
+  {
+    // In this case, we can only map pages that are 64K aligned.
+    // See https://devblogs.microsoft.com/oldnewthing/20031008-00/?p=42223
+    return std::max<size_t>(si.dwPageSize, 64 * 1024);
+  }
+  return si.dwPageSize;
+}
+
 LazyMemoryRegion::LazyMemoryRegion()
 {
   InitWindowsMemoryFunctions(&m_memory_functions);