bug#67810: 29.1; fonts use synthetic bold on Linux / pgtk

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Stefan Kangas <stefankangas@gmail.com> writes:

> I'll take your word for it.  Do you understand why this happens?

Each time an SVG image is loaded, a bitmap the size of the scaled image
is allocated and cached, then copied onto the frame whenever the SVG
must be displayed.  This bitmap is retained for 300 seconds, during
which any number of other bitmaps might be allocated, which eventually
come to occupy most available X server memory.

The same goes for other image formats in principle, but in practice SVG
images are the most susceptible to runaway memory consumption, since the
dimensions of the bitmap cached in the course of displaying an SVG image
match its dimensions on-screen, which can be quite the beast on dense
displays or when scale factors are enabled for related reasons.

> What can we do to improve the situation?

A shorter default image cache retention time, without question, and
perhaps better criteria for deciding when to flush it.