可用物理内存的奇怪值

Question

I use a code library that contains a function to calculate the amount of memory avaliable.

For hosted PC's (hosted by Windows 2008 R2 x64) I sometimes see the free amount calculated in a funny way.

It gets reported as

physical memory : 1400/1400 MB (free/total)

Which cant really be true, since several applications are running. How can that happen?

My interest here is whether this phenomenon points to a memory problem. Sometimes my application runs out of memory when hosted on a VM with limited memory like 1400 MB. So when I see a bug report with the available meory wrongly reported as 1400 MB could it be that it really is zero?

Here is the code

function GetMemoryStatus : UnicodeString;
type
  TMemoryStatusEx = record
    dwLength                : dword;
    dwMemoryLoad            : dword;
    ullTotalPhys            : int64;
    ullAvailPhys            : int64;
    ullTotalPageFile        : int64;
    ullAvailPageFile        : int64;
    ullTotalVirtual         : int64;
    ullAvailVirtual         : int64;
    ullAvailExtendedVirtual : int64;
  end;
var gmse : function (var mse: TMemoryStatusEx) : bool; stdcall;
    ms   : TMemoryStatus;
    mse  : TMemoryStatusEx;
begin
  gmse := GetProcAddress(GetModuleHandle(kernel32), 'GlobalMemoryStatusEx');
  if @gmse <> nil then begin
    mse.dwLength := sizeOf(mse);
    gmse(mse);
  end else begin
    ms.dwLength := sizeOf(ms);
    GlobalMemoryStatus(ms);
    mse.ullAvailPhys := ms.dwAvailPhys;
    mse.ullTotalPhys := ms.dwTotalPhys;
  end;
  result := IntToStrExW((mse.ullAvailPhys + $80000) div $100000) + '/' +
            IntToStrExW((mse.ullTotalPhys + $80000) div $100000) + ' MB (free/total)';
end;

Thanks! Jacob

Answer 1

I can't reproduce your problem. The only difference is some changes to the calculations you're doing in the Result line, because I don't have MadExcept on the system I'm on right now (will rectify that soon). Here's the code I used:

type
  TMemoryStatusEx = record
    dwLength                : dword;
    dwMemoryLoad            : dword;
    ullTotalPhys            : int64;
    ullAvailPhys            : int64;
    ullTotalPageFile        : int64;
    ullAvailPageFile        : int64;
    ullTotalVirtual         : int64;
    ullAvailVirtual         : int64;
    ullAvailExtendedVirtual : int64;
  end;

type
  TGlobalMemoryStatusEx = function (var mse: TMemoryStatusEx) : bool; stdcall;

function GetMemoryStatus : string;
var
  GlobalMemoryStatusEX: TGlobalMemoryStatusEx;
  MemStatEx  : TMemoryStatusEx;
begin
  GlobalMemoryStatusEx := GetProcAddress(GetModuleHandle(kernel32),
                              'GlobalMemoryStatusEx');
  if @GlobalMemoryStatusEx <> nil then
  begin
    MemStatEx.dwLength := sizeOf(MemStatEx);
    GlobalMemoryStatusEx(MemStatEx);
    Result := Format('%d / %d KB (free/total), ',
                [MemStatEx.ullAvailPhys div 1024,
                 MemStatEx.ullTotalPhys div 1024 ]);
  end;
end;

procedure TForm3.FormShow(Sender: TObject);
begin
  Label1.Caption := GetMemoryStatus;
end;

Here's the output of the app (with Task Manager's Physical Memory pane beneath it for comparison), running in a Windows XP Mode virtual machine on Windows 7. The VM was set up with 1GB of RAM, and has this test app, Task Manager, and a single Windows Explorer instance running. (The app was written in D2007 on Win 7 64-bit, and then copied/pasted into the VM and started by double-clicking in Explorer.)