Force file write delay ( a special filesys using physical memory )

Is there any way to force write delay for specical files in
UNIX system ? It should be something like
fopen(myfilename, rw, "Not_Write_To_HardDisk").

I meant if the system programmer know the file(s) is a frequently used, frequently changed ( not necessary to flash to HardDisk ) one, can he do something to interfere with the file system swapping ?

Or can we allocate a small physical memory area, setup a filesystem on it, then let several programs read/write data file from/to it. That will just like a RAM disk in PC, a small never_swap_out file system.

I think it will be a fast & easy way for several processes to share some public data. Those processes may be designed by different programmers, for different purpose. But no one need to worry about the share memory stuff,  and  file read/write/lock are easy to handle.

PS, it's very useful for hot imgs/pages in web server. Can proxy server do the job (cache specific file in physical memory) ?

Any sugguestion or successful story ?  Thanx.