On Tue, 2 Jul 2002, daRcmaTTeR wrote:

> don't ya think thats a bit ridiculous though when you stop to think about 
> just how stinkin big that swap space is gonna be? unless this machine is 
> going to be doing heavy graphics or audio processing it's never even oging 
> to use the swap space. it'll just sit there.

No, I wouldn't say it's all that ridiculous. Of course these things are
relative: what you do with your machines may not require you to ever
drop into swap. Kernels around 2.4.10 and earlier had serious problems
with memory, and requiring a few extra meg of memory would not
necessarily mean a few meg of swap got used. The system would end up
swapping entire processes and possibly lead to thrashing if the swap
space was not large enough. In fact, the earlier kernels would not add
swap space to memory, so 256M of RAM + 512M of swap would only yield
512M of working memory. This changed on/around 2.4.10 (don't remember
exactly) with the new VM. If you also consider the ratio of swap/total
disk space, you'll see that 512M or even a Gig of swap is actually
smaller than on older machines. Again, it's all relative and depends on
your usage patterns.
So how do you decide? One thing you might try is profiling your memory
usage as I suggested originally. Some folks recommend 1.5x this size for
the swap space. But you should also consider what would happen if you
run out of swap space. Hint: it's not pretty.
Now I wouldn't consider the demands on my machine as particularly heavy
but I do use 60-100M of swap when under what I consider light usage.
E.g., I'll run Gimp, mozilla, several kterms with vi and ssh sessions, 
xmms, and sometimes VMWare to see what my pages look like in Internet
Exploder. If I'm really busy I'll add POVRay, blender, and several
instances of gv as I create my TeX documentation. At this load I'll have
sometimes 300-400M swapped.
In any case, it's somewhat ridiculous to say that you won't ever use
that swap space without knowing what the machine is used for.
> 
> besides...i'm not aware of any kernel versions that would care one way or 
> the other if the swap space adds up to at least twice the physical ram 
> size. i know plenty of home users that might choke on that, but not the 
> kernel. 

These problems are well documented in the Linux kernel archives.
> 
> 


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