bug#71644: 30.0.50; Severe slowdown in larger files with markers beginning in emacs 29+

[Ihor Radchenko]

Mitchell <mitchellahren@gmail.com> writes:

>> If you remove all the non-ASCII characters from the Org file, does the
>> slowdown go away?
>
> Eli, that solved it! The new test file is at
> https://gist.github.com/kings2u/2ef0e145f2b42d0a13605b0dc9b6e6e2. I
> replaced every non-ASCII character with an "a" so the file still has the
> same number of total characters, and in my emacs 30.0 50 build (as of
> 2024-05-25), doing Steps 1 to Step 7 gives me abbrev expansions that are as
> lighting fast as in emacs 28.2!

Hmm. Then, does the attached patch help?

>From 0bafd288faee8cae33fe4a122f6e3ac73ec10d60 Mon Sep 17 00:00:00 2001
Message-ID: 
<0bafd288faee8cae33fe4a122f6e3ac73ec10d60.1718950719.git.yantar92@posteo.net>
From: Ihor Radchenko <yantar92@posteo.net>
Date: Sun, 23 Apr 2023 21:31:46 +0200
Subject: [PATCH] * src/marker.c (buf_bytepos_to_charpos): Limit marker search

Limit searching across buffer markers to first 50 markers and thus
avoid performance scaling with the number of markers.

I got 5x `re-search-forward' speed improvement in my setup with this
dumb change.
---
 src/marker.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/marker.c b/src/marker.c
index f016bf9c088..4d7d6621513 100644
--- a/src/marker.c
+++ b/src/marker.c
@@ -354,8 +354,10 @@ buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t 
bytepos)
   if (b == cached_buffer && BUF_MODIFF (b) == cached_modiff)
     CONSIDER (cached_bytepos, cached_charpos);
 
-  for (tail = BUF_MARKERS (b); tail; tail = tail->next)
+  int i = 0;
+  for (tail = BUF_MARKERS (b); tail && i < 50; tail = tail->next)
     {
+      i++;
       CONSIDER (tail->bytepos, tail->charpos);
 
       /* If we are down to a range of 50 chars,
-- 
2.45.1

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>