  We propose a computational method to measure the configurational entropy in
generic polydisperse glass-formers. In particular, our method resolves issues
related to the diverging mixing entropy term due to a continuous
polydispersity. The configurational entropy is measured as the difference
between the well-defined fluid entropy and a more problematic glass entropy. We
show that the glass entropy can be computed by a simple generalisation of the
Frenkel-Ladd thermodynamic integration method, which includes permutations of
the particle diameters. This approach automatically provides a physically
meaningful mixing entropy, and includes contributions that are not purely
vibrational. The proposed configurational entropy is thus devoid of conceptual
and technical difficulties due to continuous polydispersity, while being
conceptually closer and technically simpler than alternative free energy
approaches.
