On 02/06/2013 10:08 PM, Eli Zaretskii wrote:

>> Date: Wed, 06 Feb 2013 11:37:30 +0400
>> From: Dmitry Antipov <dmantipov@yandex.ru>
>> CC: emacs-devel@gnu.org
>>
>> On 02/05/2013 10:01 PM, Eli Zaretskii wrote:
>>
>>> In any case, the potential for problems is still there, because now
>>> w->base_line_pos gets reset to zero in many more places than it was
>>> before.  Previously, only xdisp.c would manipulate this attribute in a
>>> few well-defined places.  Now it can be reset by any function that
>>> calls adjust_window_count, including wset_buffer, which is called from
>>> many primitives, most of them outside xdisp.c.  Therefore, it's quite
>>> possible that we will now have to count from the beginning of the
>>> buffer much more frequently than we did before.  In large buffers,
>>> this could be quite a hit.
>>
>> Hm. I'll try to reproduce such a situation and check what happens.
>> Maybe we should invalidate window_end_valid and base_line_pos only
>> if either window is really switched to another buffer or buffer
>> is changed.
>
> That'd be hard, because there are many places that switch to another
> buffer temporarily, and they all call adjust_window_count.

What about this?

Dmitry