RES column in top(1) output

[Dmitry Sivachenko]

On 21.05.2013, at 22:40, Charles Swiger <cswiger at mac.com> wrote:
>> 
>> Mem: 55G Active, 23G Inact, 11G Wired, 3729M Cache, 9838M Buf, 97M Free
>> Swap: 49G Total, 14M Used, 49G Free
>> 
>> 
>> PID USERNAME      THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU COMMAND
>> 93273 username        103  52    0   141G   115G uwait  22  25:37 19.82% XXX
>> 
>> So I have a machine with 96GB of RAM, no swap is used and my process's resident size is 115G (more than physical memory).
> 
> Memory that has been allocated but not written to is associated with the process address space in terms of accounting, but does not actually consume physical memory.  There's also copy-on-write memory (used for the program executable code itself, which is also typically also marked read-only), mmap()ing big sparse files or device special files like a video framebuffer (ie, an X11 server), and probably a few other things which can reserve lots of resident memory without actually consuming physical memory.
> 


Okay, I see.

What is the correct way to obtain the amount of physical memory used by a process?

Thanks!