1. A method for a storage operating system implemented in a storage system to concurrently perform readahead operations for a plurality of different read streams established in one or more files, directories, vdisks or luns stored in the storage system, the method comprising: receiving a client read request at the storage system, the client read request indicating client-requested data for the storage operating system to retrieve from a file, directory, vdisk or lun stored in the storage system; determining whether the received client read request matches any of a plurality of readset data structures (“readsets”) allocated for the file, directory, vdisk or lun containing the client-requested data; and performing readahead operations in accordance with a set of readahead metadata stored in a readset that is determined to match the received client read request.