It seems Linux will swap something sooner or later, even when it is swapping the only application out to disk. So your performance will plummet. But you can not disable the swap partition or go without one (according to their experiences, not mine). However, there is a simply sweet "solution" or work-around: create a small swapdisk on a RAM disk! Read more details and a howto in Don's article.
Of course, the article is about MySQL. But Oracle RDBMS is also a single-use application. At least in our data center. And I have been getting reports of some Siebel apps showing weird performance problems. This may be it!