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

[Dmitry Gutov]

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.