Memory defragmentor in linux?

[Rajat Jain]

Hi,
 
As the system stays up for longer time, the physical memory becomes fragmented 
(external fragmentation) such that physically continuous pages may be difficult 
to find.Is there any kind of "memory defragmentor" mechanism built in linux 
(Like disk defragmentor) that helps solves such issues?
 
Thanks,
 
Rajat