Memory Info in C#

MemoryInfo.cs

public static class MemoryInfo
{
	[DllImport("psapi.dll", SetLastError = true)]
	[return: MarshalAs(UnmanagedType.Bool)]
	public static extern bool GetPerformanceInfo([Out] out PerformanceInformation PerformanceInformation, [In] int Size);

	[StructLayout(LayoutKind.Sequential)]
	public struct PerformanceInformation
	{
		public int Size;
		public IntPtr CommitTotal;
		public IntPtr CommitLimit;
		public IntPtr CommitPeak;
		public IntPtr PhysicalTotal;
		public IntPtr PhysicalAvailable;
		public IntPtr SystemCache;
		public IntPtr KernelTotal;
		public IntPtr KernelPaged;
		public IntPtr KernelNonPaged;
		public IntPtr PageSize;
		public int HandlesCount;
		public int ProcessCount;
		public int ThreadCount;
	}

	public static Int64 GetPhysicalAvailableMemoryInMiB()
	{
		PerformanceInformation pi = new PerformanceInformation();
		if (GetPerformanceInfo(out pi, Marshal.SizeOf(pi)))
		{
			return Convert.ToInt64((pi.PhysicalAvailable.ToInt64() * pi.PageSize.ToInt64() / 1048576));
		}
		else
		{
			return -1;
		}

	}

	public static Int64 GetTotalMemoryInMiB()
	{
		PerformanceInformation pi = new PerformanceInformation();
		if (GetPerformanceInfo(out pi, Marshal.SizeOf(pi)))
		{
			return Convert.ToInt64((pi.PhysicalTotal.ToInt64() * pi.PageSize.ToInt64() / 1048576));
		}
		else
		{
			return -1;
		}

	}
}