load a large file (say, ..../emacs/src/keyboard.c) wait for jit-lock to
    finish fontifying it in the background, then make a small change near the
    beginning of this file, needlessly refontifying ~320kBytes consumes ~55%
    of the CPU's power for 3½ minutes.

Why does a small change near the beginning refontify the whole file?
I suppose there are some small changes that might legitimately do so,
but I would not expect most small changes to do so.  What's up?

      I'm talking about the jit-lock that was
    shipped with Emacs 21.1.

Can you please try the latest version?  It is the only way to give
useful feedback.


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