hard to understand and limit SQL max server memory usage, can anyone help?

Hello,

We have sql server enterprise edition 2008 R2 on windows 2008 R2  x86-64bit.

I set the max memory to 10GB but in windows os the sqlserver.exe exactly takes 16GB. I confirm it by using performon process - private memory use counter too.

In sql server when run select SUM(pages_allocated_count)* 8 from sys.dm_os_memory_objects, it show total around 10GB.

My question is what's the other 6GB been used for ? and how to limit total memory that SQL server can use?

Thanks,

Robin

Robin