parameters to find out read/write merges, iostat

[shampavman <shampavman.cg@gmail.com>]

Hi all,

In the 'iostat' code especially in the calculation of 'rrqm/s and 
wrqm/s' what is the parameter being chosen to initiate a merge?
Eg::
Reads and writes which are adjacent to each other may be merged for 
efficiency.  Thus two 4K reads may become one 8K read before it is 
ultimately handed to the disk, and so it will be counted (and queued) as 
only one I/O.
So is there a parameter like this that is predefined so that when the 
read/write reaches the 4k limit its actually merged and sent to the device?

Thanks
Shampavman