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#56682
Fix the long lines font locking related slowdowns
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On 15.08.2022 21:28, Eli Zaretskii wrote:
>> Date: Mon, 15 Aug 2022 21:17:23 +0300
>> Cc: 56682 <at> debbugs.gnu.org, gregory <at> heytings.org, monnier <at> iro.umontreal.ca
>> From: Dmitry Gutov <dgutov <at> yandex.ru>
>>
>>>> I'm pretty sure that doing all that in Lisp is a good thing, and would
>>>> be conducive to whatever improvements we might want to add later...
>>>
>>> No, because quite a few packages use jit-lock-register to run stuff
>>> that is not font-lock at all, and I don't want that to slow down
>>> redisplay when long lines are involved. And trying various values of
>>> a variable exposed to Lisp is easy enough.
>>
>> It should also be possible to move the whole invocation of the
>> fontification-functions up to Lisp
>
> How do you do that, given that these functions should be called from
> redisplay with the region of buffer text only redisplay knows about?
Something like in the attached patch.
>> Another reason I chose font-lock-fontify-region, though, is that it's
>> called from different places. It's the common entry point for font-lock.
>
> I have no problem with doing something similar in font-lock, I'm just
> saying that it cannot be the only place.
If we apply narrowing in handle_fontified_prop (or like in the
attachment), and also in font-lock-fontify-region, it seems like every
significant (*) execution path will go through two repetitions of the
same logic.
That's not ideal.
(*) Significant by the metric of having impact on Emacs's performance,
in large files especially.
>> I've never seen fontification-functions contain anything but
>> jit-lock-function, but jit-lock-functions is used by nlinum, for
>> instance. And bug-reference-mode, and goto-address-mode. Perhaps we
>> should ask Stefan's opinion on this.
>
> Stefan was and is on the CC list for the entire discussion.
>
>> And nlinum might not appreciate being narrowed. It seems to be working
>> okay without that in my 20 MB XML file. And in 200 MB one too.
>
> Why is it important what nlinum does, when we have native line numbers
> nowadays?
Just an example of a mode which uses jit-lock-functions. With an
implication that other, less known modes, might have similar needs and
behavior. There aren't too many known examples.
[run-fontification-functions.diff (text/x-patch, attachment)]
This bug report was last modified 2 years and 8 days ago.
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