  We compute the topological susceptibility $\chi_t$ of lattice QCD with $2+1$
dynamical quark flavors described by the M\"obius domain wall fermion.
Violation of chiral symmetry as measured by the residual mass is kept at
$\sim$1 MeV or smaller. We measure the fluctuation of the topological charge
density in a `slab' sub-volume of the simulated lattice using the method
proposed by Bietenholz {\it et al.} The quark mass dependence of $\chi_t$ is
consistent with the prediction of chiral perturbation theory, from which the
chiral condensate is extracted as $\Sigma^{\overline{\rm MS}} (\mbox{2GeV}) =
[274(13)(29)\mbox{MeV}]^3$, where the first error is statistical and the second
one is systematic. Combining the results for the pion mass $M_\pi$ and decay
constant $F_\pi$, we obtain $\chi_t = 0.229(03)(13)M_\pi^2F_\pi^2$ at the
physical point.
