It's known thing that Oracle and Linux are nicely coupled that the scope of performance issues in Oracle is not just limited to Oracle sometimes... I stumbledupon one cool post by Riyaj (http://orainternals.wordpress.com/) in which he had explained how he troubleshooted the CPU usage issue with an optimal memory configuration.

Recent OS architectures are designed to use all available memory. Therefore, paging daemons doesn’t wake up until free memory falls below a certain threshold. It’s possible for the free memory to drop near zero and then climb up quickly as the paging/swapping daemon starts to work harder and harder. This explains why free memory went down to 78MB and rose to 4.7GB 10 minutes later.


What is using my memory though? /proc/meminfo is useful in understanding that, and it shows that the pagetable size is 5GB. How interesting!

Original post can be found here.
 
Problem was identified with paging which used BIG pagetable(due to smaller unit page file size, 4KB, and larger memory ~10GB) meaning so many pages (millions - ~ 2.6m) that machine most of the resources in managing the pages itself so nothing left for other any critical processes. He increased the page file size to 2MB and thereby decreasing the pagetable size and main bottleneck was resolved. It's a good read.
 
- Karteek