Re: [tlug] A Swap Question

[Joe Larabell <fred62@example.com>]

On Mon, 5 Nov 2007, Daniel A. Ramaley wrote:

> For new installs on new hardware (with 1GB or more RAM), i usually
> allocate 1/2 GB swap. My rationale is that on a server if the swap is
> being hit even that much than the battle is already lost; the machine
> will be so busy swapping (rather than serving) that it is effectively
> offline.

That may not always be true. The comments equating swap usage to bad 
performance assume all the swap is being eaten up by one overzealous 
process. In that case, you're likely going to feel the pain. But it really 
does depend on exactly what you plan to do with the machine.

For example, it's not unusual for me to get into some gimp session with 
several high-res photos loaded and then run out of time before I'm done. 
Usually I just leave the process open but idle -- sometimes for days. In 
that case, the gimp and all it's memory-hogging buffers can effectively be 
swapped out so long as I have enough swap space. In the meantime I can use 
the machine for other things -- with the same available RAM I would have 
had without the gimp program loaded and no appreciable performance hits. 
The more swap, the more of these elephantine programs I can have loaded 
but idle before the performance starts to suffer.

If you never leave large-footprint programs open like that, I agree with 
the comments so far. But, on the other hand, the first time you lose a few 
hours work due to an out-of-memory condition you'll wonder whether saving 
those few gigs of cheap disk was really worth it ;-)...

Besides, if I understand right, Linux uses unallocated swap pages as disk 
cache buffers so a larger swap *may* equate to a slightly faster machine 
even if you never load any large programs.

---
Joseph L (Joe) Larabell            Never fight with a dragon
http://larabell.org                     for thou art crunchy
                                  and goest well with cheese.