skbuff size

["bunty " <bunty123_4@xxxxxxxxxxxxxx>]

Hello,
       I want to know is there any way by which skbuff size can be increased in NET STACK when packet is building after adding IP header to Payload?Is skb_realloc_headroom() is useful to me?
       Also, why following functions is used when allocating a buffer in skbuff.c file?
         size = SKB_DATA_ALIGN(size);
        Can i increase the value which i think it comes to 128 of variable size?  what is side effect of using this function skb_add_mtu ()?        
     
regards,
Parag.