bug#59151: Major performance issues in dired over ssh (Tramp) when remote directory contains symlinks

[Mikhail Pomaznoy <mikpom@mikpom.ru>]

Greetings emacs devs, or to whom it may concern!

I am having troubles with dired listings of remote directories 
containing many files and symlinks. When I scroll through such a dired 
buffer Emacs lags (over a second) on every page-down scroll.

The problem is easily reproducible with -Q if the directory contains a 
hundred files and a hundred symbolic links to some other hundred files 
somewhere on the filesystem. If I kill the links in the dired buffer 
(without deleting any actual files or links) then everything scrolls 
smoothly as usual.

Could you please check if thats a real issue in your setting? ssh 
connection I am using is not so slow...

Kind regards,

-Mikhail


In GNU Emacs 28.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.34, 
cairo version 1.17.6)

  of 2022-09-12 built on frederik
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Arch Linux

Configured using:
  'configure --with-x-toolkit=gtk3 --with-native-compilation
  --sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
  --localstatedir=/var --with-cairo --with-harfbuzz --with-libsystemd
  --with-modules 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt
  -fexceptions -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security
  -fstack-clash-protection -fcf-protection -g
  -ffile-prefix-map=/build/emacs/src=/usr/src/debug -flto=auto'
  'LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -flto=auto''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
   value of $LANG: en_US.UTF-8
   locale-coding-system: utf-8-unix

Major mode: Dired by name

Minor modes in effect:
   shell-dirtrack-mode: t
   tooltip-mode: t
   global-eldoc-mode: t
   show-paren-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   buffer-read-only: t
   line-number-mode: t
   indent-tabs-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec epa
derived epg rfc6068 epg-config gnus-util rmail rmail-loaddefs
text-property-search mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils dired-aux dired dired-loaddefs tramp-sh
tramp-cache tramp tramp-loaddefs trampver tramp-integration files-x
tramp-compat shell pcomplete comint ansi-color ring parse-time iso8601
time-date ls-lisp format-spec auth-source cl-seq eieio eieio-core
cl-macs eieio-loaddefs cl-loaddefs cl-lib password-cache json subr-x map
seq byte-opt gv bytecomp byte-compile cconv iso-transl tooltip eldoc
paren electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice
button loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 103629 9492)
  (symbols 48 8400 0)
  (strings 32 27457 1311)
  (string-bytes 1 928685)
  (vectors 16 17653)
  (vector-slots 8 390979 10629)
  (floats 8 27 45)
  (intervals 56 2626 0)
  (buffers 992 14))