使用PHP调用ajax调用后端调用PHP函数

Question

I want to call a PHP function from Ajax request. This PHP function will take more than 2 to 3 Min. to execute And user may not want to wait for 2 min. So for this I am planing to make ajax call and redirect to another page so that User can take another request. Till I did -

new Ajax.Request(reloadurl, { 
 method: 'POST', 
 data: $('edit_form').serialize(),
 parameters: $('edit_form').serialize(true)                 
    onComplete: function(transport) {
        //alert(transport.responseText);
        window.location = backurl;  
    },
    onCreate : function () {    
        alert('dsdsdsds');
        window.location = backurl;                          
    },
    onFailure: function() { 
        alert('Something went wrong...');}
    });

But Its not working.. Please help me out- Suggest me the way so that I can call another ajax request simultaneously