top command question

[Javier Ortiz Guajardo]

i??m reading the top manual and i don??t understand what means the column
RES.
Resident size of the process in kilobytes.The resident size information is, at best,an approximate value.

Resident where? (in memory i suppose)

how can i summarize it?
the SIZE process + RES = Total size process? (i guess no)
or RES is other size resident in memory?

i must summarize the size RES like memory usage).

Thanks?
Thanks.

[A. Clay Stephenson · Accepted solution]

The reason that the value is approximate is that memory calculations are very tricky because of shared libraries and shared memory segments. Consider the simple case of the shell: There might be hundreds of instances of sh running each with it's own private data segment but sharing a common text segment - the executable code and sharing functions in shared libraries. How many times should that memory usage be counted? It's even possible for the total memory to greatly exceed the virtual memory of the box but that's an illusion because of the sharing of memory segments.

[S.K. Chan]

In addition read the HP Memory Mgt Whitepaper.
http://docs.hp.com/hpux/onlinedocs/os/11i/mem_mgt.html

[James R. Ferguson]

Hi:

To add to the information already given, a recent 11.0 patch corrected an incongruous reporting of memory usage by 'top'.

Without PHCO_26020, 'top' could sometimes show the RESident size of a process as larger than its SIZE. This was due to the inclusion private uarea, shared memory, mmap regions in addition to the resident data, stack and text allocated, in the calculation of RES. The patch "resolves" the anomoly by adding these values to the SIZE. Again, this emphasizes why the RESident value is only an approximation.

Regards!

...JRF...