vim: keep undo when moving a file?

I have a file that I keep using for quite a long while, it's convenient to keep the editing history forever, so if something gone wrong I can always undo back and locate the issue.

today I moved the file to another folder and all undo history gone.

I tried to rename my original undo file according to the new location , but still not work...

anyone has a good solution?

this is my undo related config in .vimrc , I'm running latest vim 7.4..

set udf

if exists("+undofile")

  " undofile - This allows you to use undos after exiting and restarting

  " This, like swap and backups, uses .vim-undo first, then ~/.vim/undo

  " :help undo-persistence

  " This is only present in 7.3+

  if isdirectory($HOME . '/.vim/undo') == 0

    :silent !mkdir -p ~/.vim/undo > /dev/null 2>&1

  endif

  set undodir=./.vim-undo//

  set undodir+=~/.vim/undo//

  set undofile

"  set undolevels=1000         " maximum number of changes that can be undone

  set undoreload=10000        " maximum number lines to save for undo on a buffer reload

endif

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