I find the solution, so I give it here if somebody need :
by default the session option (what will be preserved) are "blank,buffers,curdir,folds,help,options,winsize"
You can define this with set sessionoptions=blank,buffers,[etc]
In my help there are no more option than the default one, but this help is not exactly for vim 7, there is another option : tabpages !!!
You only have to put this "set sessionoptions=blank,buffers,curdir,folds,help,options,resize,tabpages,winsize" in your vimrc to add this option.
YES I'VE GOT IT !!!