So I decided to download Win32::API and run your code. My fix does indeed remove the warning at the line you mentioned. However, there are apparently more warnings, which are removed by the following: 
   my $MEMORYSTATUS = Win32::API::Struct->new('MEMORYSTATUS');
   { # Avoid warning at Struct.pm line 214
      $MEMORYSTATUS->align('auto');
   }
   { # Avoid all other warnings in Struct.pm
      $MEMORYSTATUS->{'dwLength'    } = 0;
      $MEMORYSTATUS->{'MemLoad'     } = 0;
      $MEMORYSTATUS->{'TotalPhys'   } = 0;
      $MEMORYSTATUS->{'AvailPhys'   } = 0;
      $MEMORYSTATUS->{'TotalPage'   } = 0;
      $MEMORYSTATUS->{'AvailPage'   } = 0;
      $MEMORYSTATUS->{'TotalVirtual'} = 0;
      $MEMORYSTATUS->{'AvailVirtual'} = 0;
   }

[download]

I'd like to correct myself regarding dwLength. The docs say Windows will set it for you. Very odd.

In reply to Re^3: Pesky warnings after calling Win32 API by ikegami
in thread Pesky warnings after calling Win32 API by Biff

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