9. A system for generating ranked search results, comprising: one or more processors configured to: receive a plurality of matching information items that match a search request; rank at least some of the plurality of matching information items using a linear ranking model that linearly combines a first plurality of feature values to obtain a first set of ranked results, wherein the linear ranking model combines the first plurality of feature values in a linear fashion using weight coefficients corresponding to the first plurality of feature values; rank at least some of the first set of ranked results using a nonlinear ranking model that nonlinearly combines a second plurality of feature values to obtain a second set of ranked results, wherein the nonlinear ranking model combines the second plurality of feature values in a nonlinear fashion using weight coefficients corresponding to the second plurality of feature values; and provide a search response based at least in part on the second set of ranked results; one or more memories coupled to the one or more processors, configured to provide the processors with instructions.
9. A system for generating ranked search results, comprising: one or more processors configured to: receive a plurality of matching information items that match a search request; rank at least some of the plurality of matching information items using a linear ranking model that linearly combines a first plurality of feature values to obtain a first set of ranked results, wherein the linear ranking model combines the first plurality of feature values in a linear fashion using weight coefficients corresponding to the first plurality of feature values; rank at least some of the first set of ranked results using a nonlinear ranking model that nonlinearly combines a second plurality of feature values to obtain a second set of ranked results, wherein the nonlinear ranking model combines the second plurality of feature values in a nonlinear fashion using weight coefficients corresponding to the second plurality of feature values; and provide a search response based at least in part on the second set of ranked results; one or more memories coupled to the one or more processors, configured to provide the processors with instructions. 14. The system of claim 9 , wherein at least some of the first plurality of feature values used by the linear ranking model are the same as at least some of the second plurality of feature values used by the nonlinear ranking model.