On Sun, Oct 26, 2008 at 01:09:12 +0100 (+0100), Hugo Mills wrote:
> I believe that there were (that's *were*) good technical reasons
> for the 2*RAM recommendation, back when it was first made, related to
> the performance of the algorithms used to manage swap space. Those
> algorithms are long gone, and the recommendation no longer applies.
Certainly some OS's used to _require_ a page in swap for each in
memory I belive - so you actually needed at least as much swap as RAM.
The twice swap was then probably a sensible measure.
These days that's not needed. I always put a reasonable amount of
swap (e.g 0.5-2GB on a box with 1-8GB say). I don't see the point in
putting much more on (even if disk space is cheap and the amount of
real memory required to track swap is very small (a millionth springs
to mind from when I looked at the kernel source).
Worst I've seen is a SAP instance where they required "3 times
physical memory or 256MB - whichever is larger". The box had 24GB
memory (which was then increased to 32GB). The fact they even thought
SAP would run on 64MB RAM shows how ancient the instructions where.
Adrian
