How much swap?

[Bruno Wolff III]

On Sun, Feb 25, 2007 at 18:18:14 +0100,
  Uno Engborg <uno at webworks.se> wrote:
> I am wondering how much swap space I need in modern Linux such as FC6.
> 
> I'm planning to set up a system Pentium Dual  Core with 8G RAM, and I 
> don't expect I need much
> more than that for my apps.
> 
> Would I need a swap anyway.  There is some old rule of thumb to have 
> twice as much virtual
> memory as you have physical RAM, but that sounds a bit ridiculous  as it 
> would take a lot
> of time to swap in/out this much memory from disk.
> 
> In some other Unixes the swap space was needed
> to preserve dump information in case of a panic, are there any such 
> considerations
> in Linux?

How much swap you need is going to be tied to your memory allocation setting.
If you are willing to let the oom killer run loose, you may not need any. If
you can't let it kill processes and you have processes that preallocate
a lot of memory (fortran programs with large static arrays are the classic
example), you may need a lot of swap space (even though it never gets used).