Subject: bug#57245: 29.0.50; M-> in a large XML file (without long lines) is slow

From: Dmitry Gutov <[email-masked]>
Date: Wed, 17 Aug 2022 14:46:46 +0300

On 17.08.2022 14:36, Eli Zaretskii wrote:
>> Date: Wed, 17 Aug 2022 01:20:38 +0300
>> Cc: Eli Zaretskii <[email-masked]>, [email-masked]
>> From: Dmitry Gutov <[email-masked]>
>>
>> Otherwise, syntax-wholeline-max seems to be doing its job fine: if I
>> comment out the narrowing code in handle_fontified_prop (or switch to
>> the branch I posted previously), two XML files -- one with long lines
>> and one without (the files differ only by addition of newlines) -- show
>> approximately the same delay on M->.
> 
> Doesn't syntax-wholeline-max only affect long lines?  Because I don't
> think I see its effect in the XML file where lines were broken by
> newlines, and then the file was duplicated 100 times.

Its purpose is to handle the slowdown which occurred specifically on 
long lines because of 
font-lock-extend-region-functions/syntax-propertize-extend-region-functions. 
Now that it works -- I don't see any particular slowdowns on long lines, 
even with narrowing disabled.

And the performance of M-> depends solely on the size of a file. In my 
XML test files, at least.