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. 13. The system of claim 9 , wherein the linear ranking model outputs a first ranking score and the nonlinear ranking model outputs a second ranking score.