i have a fix for datadata full that i used sometime before but it seems to dissapear now i.e. :
1.go to root explorer>data and name the data folder(which is inside data folder) to data 1.
2.then create a new folder there and name it to data and copy all the data 1 files to data folder(now you will have 3 folder i.e data,data1 and data2).
3.now phone will reboot itself and low memory option will be gone.if it doesnot reboot itself then manually reboot.
4.after booting go to root explorer and delete data1 folder ,,,,now you have data folder of 1.8 gb.
5.after that all the installed files will go to data folder and there will no message of low storage as data folder is now of 1.8 gb's.
there is no slowdown in performance of the phone after this.