Subject: bug#56682: Fix the long lines font locking related slowdowns

From: Dmitry Gutov <[email-masked]>
Date: Mon, 1 Aug 2022 13:46:41 +0300

On 01.08.2022 12:56, Gregory Heytings wrote:
> 
>>> Given your and Dmitry's feedback, I just tried to add an explicit 
>>> call to (syntax-ppss (point-max)), without narrowing, when the buffer 
>>> is opened (see below).
>>>
>>> The problem is that this is, as I said, slow.  On my laptop, opening 
>>> a 1 GB file takes about 6 seconds.  The call to syntax-ppss adds 70 
>>> seconds, so opening a large file becomes an order of magnitude slower 
>>> (13 times slower).  Which I think is too much for the added benefit.
>>
>> But that only has to happen when the buffer is scrolled to the bottom, 
>> right?
>>
> 
> No, it happens when the buffer is opened.  Given the importance that you 
> and Stefan seem to give to that function, it is, with the patch I sent 
> in my previous post, called once on the whole buffer (without any 
> narrowing) when the file is opened.

But if the buffer is not scrolled to the end, shouldn't it be called 
with a position that's close to the beginning?

That shouldn't force the full buffer scan, meaning this call should 
complete quickly.