RES column in top(1) output

Charles Swiger cswiger at mac.com
Tue May 21 19:40:42 UTC 2013


On May 21, 2013, at 11:03 AM, Dmitry Sivachenko <trtrmitya at gmail.com> wrote:
> Hello,
> 
> Can you please explain me the meaning of RES column in top(1) output:
> as far as I understand from man-page, it is resident portion of the process, that is the amount of memory process takes from RAM.

Yes, that's the definition.

> But I get:
> 
> 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.

Regards,
-- 
-Chuck



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