That's from Federico, whose blog is one of the few tech blogs I read. It's recently been all about {X,GTK,Gnome} performance: profiling, optimization, etc. See e.g. footprint of non-shared dirty data from libraries. Recommended.
(Speaking of recommended, who else is worth reading? I'm looking for real technical content, like poor old
jeffr_tech that I'll keep mentioning in an attempt to shame another post out of him.) 