[Fontconfig-bugs] [Bug 64766] Make fontconfig scanning faster

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=64766

--- Comment #7 from nfxjfg at gmail.com ---
(In reply to comment #6)
> (In reply to comment #5)
> > Somehow freetype seems to spend rather a lot of effort on that. I don't know
> > how this stuff works, but to my naive eyes is looks like there's further
> > optimization possible, though possibly that would require changes in
> > freetype instead of fontconfig.
> 
> I may take a look.  We load all glyphs just to make sure the font actually
> has it, as opposed to having bogus or empty glyphs.  Maybe that level of
> paranoia is not quite needed these days...

Can't this be done when attempting to use the glyph?

> > For example, the granularity of the cache could be changed and create a new
> > cache for every 20 files or so.
> 
> Each cache file would mean one more mmap() in every fontconfig-using client.
> That's already bad enough...

Sure, you'll perhaps need more mmap calls. But that's much better than blocking
an application on font scanning. You could also create a light weight central
index (which can be easily reconstructed when a "sub"-cache changes), and map
the cache file only when it's needed. Well, I don't know what exactly the font
cache stores, but maybe this can serve as inspiration.

> > Or it could be made such that the old cache
> > is reused for files that have not changed. No doubt, these changes would be
> > intrusive to the cache code, but given the problems with font scanning
> > times, I think it would be worth it.
> >
> > Now that you have added a hash for each font, maybe it would be possible to
> > cache the results for memory fonts as well? Hashing actually makes loading a
> > font even slower, but since you're doing it anyway, maybe it could be used
> > for that purpose as well.
> 
> Yeah, maybe we can have a cache of individual fonts based on hashes.  Then
> we can rebuild directory caches based on those individual fonts much faster.
> 
> For memory fonts, is it really a big deal?  Why do people query those anyway?

Yes, it's a big deal. There are many use cases for memory fonts, such as
embedding fonts in Matroska (mkv) files, web-fonts, fonts embedded in
documents, special application-specific fonts.

By the way, I think adding font hashes just made font scanning slower for an
obscure feature that probably will have only one user at best...

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