忘记干啥的，先留着吧
(setq backup-directory-alist '(("." . "~/.emacs.d/backup"))
backup-by-copying t ; Don't delink hardlinks
version-control t ; Use version numbers on backups
delete-old-versions t ; Automatically delete excess backups
kept-new-versions 20 ; how many of the newest versions to keep
kept-old-versions 5 ; and how many of the old
)