5G的VIM

两种方式：
1.直接使用 `vim -u NONE file.txt` 打开大文件，省掉一些格式化的步骤。
2.在 .vimrc 中设置，检查文件大小，如果文件很大， 使用某些特殊的设定提高性能：
" file is large from 1GB
let g:LargeFile = 1024 * 1024 * 1024 * 1
augroup LargeFile
autocmd BufReadPre * let f=getfsize(expand("<afile>")) | if f > g:LargeFile || f == -2 | call LargeFile() | endif
augroup END
function LargeFile()
" no syntax highlighting etc
set eventignore+=FileType
" save memory when other file is viewed
setlocal bufhidden=unload
" is read-only (write with :w new_filename)
setlocal buftype=nowrite
" no undo possible
setlocal undolevels=-1
" display message
autocmd VimEnter * echo "The file is larger than " . (g:LargeFile / 1024 / 1024) . " MB, so some options are changed (see .vimrc for details)."
endfunction
以上的配置文件中，当文件大于 1G 时，关掉语法高亮功能，以只读方式打开，并且无法撤销操作。