GNU bug report logs - #56682
Fix the long lines font locking related slowdowns

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Message #236 received at 56682 <at> debbugs.gnu.org (full text, mbox):

From: Dmitry Gutov <dgutov <at> yandex.ru>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: gerd.moellmann <at> gmail.com, 56682 <at> debbugs.gnu.org, gregory <at> heytings.org,
 monnier <at> iro.umontreal.ca
Subject: Re: bug#56682: Fix the long lines font locking related slowdowns
Date: Tue, 26 Jul 2022 23:52:35 +0300

On 26.07.2022 14:45, Eli Zaretskii wrote:
>> Perhaps it's due to font-lock logic in that it has to match from the
>> beginning of a line (not sure we'd want to abandon that promise,
>> though). Or maybe something else.
> It isn't font-lock, at least not in all major modes.  It's the display
> engine itself that sometimes needs to go to the beginning of the line.
> When it does, going back gets slower with font-lock than without.
> This is why you see slower redisplay when you go deeper into a long
> line.

Makese sense: the text only has to be fontified once, but all redisplays 
are slowed down (on master), not just the first one.

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