Redis Expiry and Memory Limit issue

Question

we have recently installed Redis Cache for our magento based sites.

we 2 websites on our server both using same redis server, our server is based on linux with centos.

the issue we are facing is that redis is consuming quite a lot of RAM, and it is growing by every day.

we have set some values on our magento local.xml file for redis

    <redis_session>    
    <host>xxxxxxx</host>                          
    <port>xxxx</port>
    <password></password>                            
    <timeout>2.5</timeout>                             
    <persistent></persistent>                            
    <db>1</db>                                          
    <compression_threshold>2048</compression_threshold>  
    <compression_lib>gzip</compression_lib>            
    <log_level>1</log_level>                           
    <max_concurrency>6</max_concurrency>               
    <break_after_frontend>5</break_after_frontend>     
    <break_after_adminhtml>30</break_after_adminhtml>
    <first_lifetime>86400</first_lifetime>               
    <bot_first_lifetime>60</bot_first_lifetime>
    <bot_lifetime>7200</bot_lifetime>           
    <disable_locking>0</disable_locking>        
    <min_lifetime>60</min_lifetime>             
    <max_lifetime>2592000</max_lifetime>
   <automatic_cleaning_factor>1</automatic_cleaning_factor>        
</redis_session>

it seems like we do not have an expire set to it, plus there is no memory usage limit either.

i know there are few instruction on internet for setting expire but there is nothing for use with magento in easy way.

all help is apreciated.