  The red-giant branch bump provides valuable information for the investigation
of the internal structure of low-mass stars. Because current models are unable
to accurately predict the occurrence and efficiency of mixing processes beyond
convective boundaries, one can use the luminosity of the bump --- a diagnostic
of the maximum extension of the convective envelope during the first-dredge up
--- as a calibrator for such processes. By combining asteroseismic and
spectroscopic constraints, we expand the analysis of the bump to masses and
metallicities beyond those previously accessible using globular clusters. Our
dataset comprises nearly 3000 red-giant stars observed by {\it Kepler} and with
APOGEE spectra. Using statistical mixture models, we are able to detect the
bump in the average seismic parameters $\nu_{\rm max}$ and $\langle \Delta \nu
\rangle$, and show that its observed position reveals general trends with mass
and metallicity in line with expectations from models. Moreover, our analysis
indicates that standard stellar models underestimate the depth of efficiently
mixed envelopes. The inclusion of significant overshooting from the base of the
convective envelope, with an efficiency that increases with decreasing
metallicity, allows to reproduce the observed location of the bump.
Interestingly, this trend was also reported in previous studies of globular
clusters.
