Re: Emacs allocates unnecessary memory during scrolling

[storm@cua.dk (Kim F. Storm)]

MIYOSHI Masanori <miyoshi@meadowy.org> writes:

> Emacs 22 on Windows (and probably on other platforms) allocates
> unnecessary memory during scrolling.


Thank you for the bug report.

Chong, can you look at it, as I don't have time to dig into it right now?

Maybe a fix would be to operate with it->glyph_row = NULL as we do
elsewhere to just do "display measurements", but that's not a trivial
change to display_string and friends.


>
> The following opearaion reproduces the problem.
>
> o emacs -q
> o Evaluate (setq scroll-conservatively 10) on the scratch buffer.
> o Type `C-h' to view the HELLO file.
> o Type `C-n' on to scroll the window.
> o Emacs allocates unnecessary memory during scrolling.
>
> Large files which contains multibyte characters should be better
> for reproduction.
>
>
> Findings are:
>
> This changes seems to have revealed the problem.
>> 2006-09-06  Kim F. Storm  <storm@cua.dk>
>> 
>> 	* xdisp.c (pos_visible_p): Remove exact_mode_line_heights_p arg;
>> 	so calculate heights even when pos-visible-in-window-p is called
>> 	with partially = t.  Don't overshoot last_visible_y in move_it_to.
>> 	Return row height and row number in new rowh and vpos args.
>
> In the following call sequences, it->w->ncols_scale_factor is
> incremented a number of times.
>
> In xdisp.c:
> pos_visible_p()
> -> display_mode_line()
> -> display_mode_element() ;; case MODE_LINE_DISPLAY:
> -> display_string()
> -> PRODUCE_GLYPHS()
> -> x_produce_glyphs() ;; RIF
> -> append_glyph() ;; it->glyph_row->used[area]++
> -> IT_EXPAND_MATRIX_WIDTH() ;; it->w->ncols_scale_factor++
>
> In consequence, required_matrix_width() in dispnew.c returns a
> large number.  And adjust_glyph_matrix() in dispnew.c allocates
> unnecessary large memory for glyphs.
>
>
> YAMAMOTO Mitsuharu san says:
>
> In xdisp.c:
>> static int
>> display_mode_line (w, face_id, format)
> snip
>> {
> snip
>>   init_iterator (&it, w, -1, -1, NULL, face_id);
>>   prepare_desired_row (it.glyph_row);
>
> Before prepare_desired_row(), it.glyph_row->enabled_p happens not
> to be 0.  This might be caused by the interruption of redisplay
> during scrolling.
>
> Appending the next code before prepare_desired_row() may fix the
> problem.
>> it.glyph_row->enabled_p = 0;
> But he doesn't know the place is appropriate or not.
>
> --
> MIYOSHI Masanori

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk