Re: X performance suffers under emacs 21.1.1

[Richard Stallman]

It occurs to me that it could be a good idea to have a counter
that increments for each redisplay, and record for each cached image
the number of the last redisplay that used it.  Then it would be easy
to determine, for each image, how many redisplays have gone by without
using it.

By basing the cache discard criterion partly on the number of
redisplays that have gone by without using the image, we could to some
extent normalize the cache clearing criterion for things such as faster
or slower user activity, and user work-breaks.

Many redisplays don't cover all windows.  An image might go appear to
go unused for a certain number of redisplays, or a certain amount of
time, if the user does editing within some other buffer so that the
buffer containing the image never gets redisplayed.  So we might want
to make a slight change and count only full redisplays (all windows).

      Or maybe one
    could implement another idea: record where the image was displayed,
    and remove images from the cache when the buffer they were displayed
    in is killed

That seems like a good idea.