By default ctrlp will look for the root of your repo (by looking for a .git, .hg, .svn or .bzr file) and then start searching for files in that folder. For the project I’m currently working on that has too many files (Probably millions) I prefer that ctrlp only searches inside the folder were I started vim. This can be done with this setting in .vimrc:

let g:ctrlp_working_path_mode = 'a'
[ productivity  vim  ]
Spell and Grammar checking on vim vim productivity
Disable expandtab in Vim productivity vim
Adjusting the width of Nerdtree navigator productivity vim
Temporarily disable Syntastic on Vim productivity vim
Quick Vim setup vim productivity