bug#23457: 24.5; interactive use of next-line and previous-line (holding down C-n or C-p) lag in a buffer with all spaces and newlines

[jamezmcclain@gmail.com]

This is pretty minor, but it surprised me. When a buffer is filled with
spaces going all the way to the last column without overwrapping. If one
tries to navigate by lines using C-n or C-p and holding them down, there
is noticable lag. My window-body-width is 115 and window-body-height is
60.
Recipe:
1. Open emacs         : Emacs -Q
2. Open a blank buffer: C-x b test-2
3. Fill the buffer up with spaces until it would force a linewrap, then
   use C-j to enter a newline. C-u 115 <space>
                               C-j
4. The buffer should appear blank unless you use whitespace mode, now try
   holding down C-n or C-p. Emacs will lag.

I also tested this in a tty emacs session on linux over ssh, and it
seemed the lag was also aparent over there.

The lag lasted at most around 5 seconds.

If the line has all spaces, one period, then a newline. (So if there is
one non-space character it seems) then this lag does not happen.

Frankly just curious,

James



In GNU Emacs 24.5.1 (x86_64-w64-mingw32)
 of 2015-05-16 on KAEL
Windowing system distributor `Microsoft Corp.', version 6.3.9600
Configured using:
 `configure --prefix=/z/emacs --host=x86_64-w64-mingw32
 --target=x86_64-w64-mingw32 --build=x86_64-w64-mingw32 --with-wide-int
 --with-jpeg --with-xpm --with-png --with-tiff --with-rsvg --with-xml2
 --with-gnutls --with-sound=yes --with-file-notification=yes
 --without-dbus --without-imagemagick 'CFLAGS=-O3 -fomit-frame-pointer
 -g0 -pipe' 'LDFLAGS=-static-libgcc -static-libstdc++ -static -s
 -Wl,-s''

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:
  erc-list-mode: t
  erc-menu-mode: t
  erc-autojoin-mode: t
  erc-ring-mode: t
  erc-networks-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-track-minor-mode: t
  erc-match-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-netsplit-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  tooltip-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
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Checking 57 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/eshell...
Checking 70 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/erc...
Checking 34 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/emulation...
Checking 151 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/emacs-lisp...
Checking 24 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/cedet...
Checking 57 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/calendar...
Checking 87 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/calc...
Checking 111 files in c:/ProgramData/chocolatey/lib/emacs64/tools/emacs/share/emacs/24.5/lisp/obsolete...
Checking for load-path shadows...done
Mark set [2 times]
Quit

Load-path shadows:
None found.

Features:
(shadow sort mail-extr misearch multi-isearch noutline outline
easy-mmode view emacsbug message rfc822 mml mml-sec mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mail-utils eieio-opt speedbar sb-image
ezimage dframe find-func help-mode network-stream starttls tls erc-list
erc-menu easymenu erc-join erc-ring erc-networks erc-pcomplete pcomplete
comint ansi-color ring erc-track erc-match erc-button wid-edit erc-fill
erc-stamp erc-netsplit erc-goodies erc erc-backend erc-compat
format-spec auth-source eieio byte-opt bytecomp byte-compile cl-extra
cl-loaddefs cl-lib cconv eieio-core gnus-util mm-util help-fns
mail-prsvr password-cache thingatpt pp kmacro whitespace time-date
tooltip electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
dos-w32 ls-lisp w32-common-fns disp-table w32-win w32-vars tool-bar dnd
fontset image regexp-opt fringe tabulated-list newcomment lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
w32notify w32 multi-tty emacs)

Memory information:
((conses 16 133688 22081)
 (symbols 56 23279 0)
 (miscs 48 130 422)
 (strings 32 29961 2899)
 (string-bytes 1 788055)
 (vectors 16 17076)
 (vector-slots 8 461686 8433)
 (floats 8 87 296)
 (intervals 56 1762 121)
 (buffers 960 22))