I am planning to create a file system at boot time in RAM and download
application binaries to that and run.RAM is limited so my  requirement is
that i do not want to have two copies of data in the RAM (One in File
System i create and other one in Page Cache ).

Tmpfs and shmfs are two names for the same thing (the latter is 
deprecated), and I believe it will do what you want.  It exists in 
the pagecache, and I understand this is routinely mapped into process 
space for execution.

Ramfs creates a whole new section of memory and treats it as a block 
device, and the pagecache is used in addition to that.  This is not 
what you want, and I understand ramfs itself is discouraged since 
tmpfs is now in widespread use.  Cramfs is still useful as it uses 
compression on the "block device".

  Can i run a linux kernel disabling swapping (In my case no
 additional device for swap is available) ?

Certainly.  Simply don't provide a swap device or run swapon.  It'll 
work just fine until you run out of RAM, in which case you'd be 
screwed in any case.  :o)  I naturally assume you'll be running quite 
lean and tightly-controlled apps on that.

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