  Simulations with 2+1 flavors of domain wall fermions provide us with the
opportunity to compare the lattice data directly to the predictions of
continuum chiral perturbation theory, up to corrections from the residual
chiral symmetry breaking, $m_{res}$, and $O(a)$ lattice artefacts, which are
relatively small for domain wall fermions. We present preliminary results for
the pseudoscalar meson masses and decay constants from partially quenched
simulations and examine the next-to-leading order chiral extrapolations at
small quark masses. The simulations were carried out on two lattice volumes :
$16^3\times 32$ and $24^3\times 64$, with the lattice spacing fixed at about
0.1 fm. The subtleties of the chiral fits are discussed. We also explore the
roles of $m_{res}$ and $O(a)$ terms in the NLO chiral expansions and their
effects on the chiral extrapolations for the pseudoscalar masses and decay
constants.
