Re: top(1) and the meaning of columns
On Fri, Nov 03, 2006 at 10:12:11AM +0100, Matus UHLAR - fantomas wrote:
> > "Tshepang Lekhonkhobe" <tshepang@gmail.com> writes:
> > >> RES (aka RSS) is actually extremely important: if the sum of all
> > >> programs' RSS exceeds your RAM size, your system will thrash, and
> > >> thrashing is not good.
> > >
> > > What does thrashing mean?
>
> On 03.11.06 11:58, Miles Bader wrote:
> > In this case it means that the processes are trying to use more memory
> > _actively_ than will fit in RAM, and you end up with a very high page
> > fault rate, meaning your system spends much more time doing disk I/O
> > to the swap area than it does actually computing.
>
> AFAIK it's usually called 'swapping', I dunno why someone called it
> 'thrashing' :)
The explanation was right in front of you as you wrote that ;-)
Re-read the paragraph written by Miles Bader again and note the
underlined word _actively_.
Swapping, when the contents of the memory swapped will not be needed
for some time, is generally good as it can free up RAM for something
more useful (even if that is just disk cache).
Thrashing is always bad as it means you don't have enough RAM for what
the running processes need _immediately_. Disk access is several orders
of magnitude slower than RAM access.
--
David Hart <debian@tonix.org>
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