Re: Emacs manipulate files with long-lines very slowly.

[Richard Stallman]

    Now, I've a tex source file which is written on Microsoft Windows.  When I
    open it with Emacs on my Ubuntu Linux, 

Please do not call our operating system "Linux".  Ubuntu is an example
of a GNU/Linux system, basically GNU with Linux added.  Calling it
"Linux" is denying us the credit for our work.

                                           because the linefeed is different 
between
    Windows and Linux/Unix,

Emacs is supposed to recognize different end-of-line data automatically
and convert.  If that doesn't happen in your case, but sounds like a bug.

Since you provided a test case, we will be able to debug it.  Thanks.