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From: | Dmitry Gutov |
Subject: | bug#56682: Fix the long lines font locking related slowdowns |
Date: | Mon, 1 Aug 2022 01:42:24 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 |
On 01.08.2022 01:23, Gregory Heytings wrote:
Yes, I wasn't clear enough, I should have written "when the file is large enough (say 1 GB), even without long lines".What kind of scenario are you thinking of that would exhibit this slowness in a 1 GB file?If we're talking about syntax-ppss only, regular editing operations (typing and deleting code) limited to, say, one screen should trigger only a rescan of a limited area inside such buffer.That's true, but with such big files, the initial scan is slow. So the scenario is simple: you open a big enough file, type M->, and C-p. M-> will be instantaneous, and C-p will take a while, because of syntax-ppss.
Yeah, ok. If you are going to visit EOB, a single full scan seems unavoidable. I don't think 'M->' should be instantaneous, though: to display the last page, you need to fontify it, and font-lock depends on syntax-ppss.
But one big slow scan (and how slow it is actually depends on a particular major mode) followed by responsive editing sounds much better than what we've had before.
So I would recommend against trying to solve this part right now. And yes, some faster approximations of syntax-propertize-rules are possible, especially if we ask individual language modes to provide "simpler" syntax rules.
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