swap on FC1

[Tommy Reynolds]

Uttered "Pierre De Boeck" <pierre.deboeck at skynet.be>, spake thus:

> I have 512MB of RAM and 1GB of swap file. What I observed when
> I have not started any application (except some deamons) is that
> 
> 1) the "used memory" is 370 of 502
> 2) the used swap is 0 of 1020
> 
> And when I launch 2 or 3 apps like emacs or mozilla the
> used swap is ALWAYS 0 of 1020.
>
> Is it normal? Will the swap be only used when the used 
> memory will reach the full capacity available?

Yes, this is normal.  Swap areas will be used only when the current
working set (program images and data) cannot fit into real memory.
Seeing no free memory is actually quite a good thing, because it
means the kernel is making maximal use of system memory for disk I/O
buffering and caching.
 
The kernel will actually do a bit of anticipatory swapping: it will
migrate some older disk buffers from memory to the swap area, just to
make more room for a future demand burst, so it's also common to see
some swap activity on a lightly loaded system.

So: don't get excited if you see all of memory in use.  Instead, get
excited if you see swap filling up.

Continual heavy swap I/O activity (you get to define "heavy"
according to your needs) may indicate a need for more real memory,
but keep in mind that the kernel buffers as much as it can, so even
extra real memory will get used very quickly (read that as: as soon
as you plug it in ;-) so just watch the swap I/O activity.
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