gistfile1.txt

function! Make_vimsession()
  execute("mksession! " . g:vimsession)
endfunction

command! SS call Make_vimsession()

function! Set_vimsession()
  let cwd = getcwd()
  while ! ( isdirectory( cwd . "/.git" )  || cwd == "/" )
    let cwd = simplify( cwd . "/.." )
  endwhile
  let g:vimsession = cwd . "/.git/.vimsession"
endfunction

au VimEnter * call Set_vimsession()
au VimLeave * call Make_vimsession()
nmap ZZ :xa