`top` process memory usage: SIZE vs RES

[Lowell Gilbert]

Jesse Guardiani <jesse at wingnet.net> writes:

> Dan Nelson wrote:
> 
> > In the last episode (Sep 11), Jesse Guardiani said:
> >> 1.) Where is my Free memory going? I can't account for it
> >>     in the SIZE and RES columns of the various processes.
> >>     These are relatively constant.
> > 
> > Disk cache.
> 
> I thought it might be something like that. My large test
> messages are being written to disk over and over and over
> as the message travels down the pipline. Makes a great case
> for installing a RAM disk. :)

No, probably not.  The OS disk-caching is probably *more* efficient
than letting the data go into a RAM disk at each stage.  Considerably
so, in fact.  

> >  
> >> 2.) What, exactly, is RES? `man top` describes it as this:
> >>     "RES is the current amount of resident memory", but does
> >>     that mean RES is included in SIZE? Or does that mean that
> >>     RES should be counted in addition to SIZE?
> > 
> > RES the amount of SIZE that it currently in core
> 
> OK. To clarify, you mean core kernel memory here?

No, it's not in kernel space.  "Core" just refers to RAM:  the term is
held over from the days when main memory was constructed out of little
magnetic cores in a wire matrix.

> If so, how is that significant? Why should I care?

If your system starts swapping heavily, that will often be the clue
that tells you why.  Just one example.