bug#38345: 27.0.50; Permanent increase in memory consumption after opening images (or pdfs)

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@gmail.com>
> Cc: juri@linkov.net, 38345@debbugs.gnu.org
> Date: Fri, 29 Nov 2019 01:27:39 +0800
> 
> The behaviour you describe does not follow the docstring:
> > "*Maximum time* after which images are removed from the cache.
> > ...
> > If the cache contains
> > a large number of images, the actual eviction time may be shorter.
> > ...

The doc string assumes "normal" operation, it doesn't assume some Lisp
command runs for a long time, thus preventing redisplay.

> Also, I repeated my tests manually calling image-clear-cache every Nth
> image. Every invocation of image-clear-cache does reduce the memory
> consumption, but there is always some residual remaining unrealeased
> (see the attached images). The residual seems to scale with the number
> of images in the cache before clearing.

I think that's a simple result of how clear-image-cache is
implemented, I suggest to read the code.