From: Stefan Monnier <monnier@iro.umontreal.ca>
 Cc: Dmitry Gutov <dgutov@yandex.ru>, Eli Zaretskii <eliz@gnu.org>,
   56682@debbugs.gnu.org
 Date: Fri, 12 Aug 2022 22:01:54 -0400
 
 > I can only repeat that the only ways to improve font locking in a non-local
 > way (or at least, the only ways that were identified in the discussions so
 > far) are either to improve the speed of syntax-ppss by an order of
 > magnitude, in which case it would perhaps become feasible to allow
 > syntax-ppss to have access to the whole buffer, or to equip syntax-ppss with
 > heuristics to make it work "as well as possible" even when it only has
 > access to a portion of the buffer.
 
 But the locked narrowing is applied based on the presence of long-lines
 rather than based on the total size of the buffer.

That's true, but the two are closely related: a buffer with very long
lines tends also to be a large buffer.