1. A method comprising: in response to a job submitted by an application, obtaining a dynamically loadable namespace (DLN) portion of a global single namespace of a file system, wherein said DLN is associated with the job and is maintained in a capacity tier of object storage of a storage system; obtaining one or more filtering directives from a user; reducing, using at least one processing device, said DLN based on said one or more filtering directives by removing one or more files from said DLN that do not satisfy one or more requirements of said one or more filtering directives to generate a filtered DLN, wherein the reducing comprises traversing a directory tree associated with said DLN and, for each entry in said DLN, creating an entry in a directory tree associated with said filtered DLN when said entry satisfies said one or more requirements of said one or more filtering directives; and dynamically loading, using said at least one processing device, the filtered DLN, including the metadata only for the filtered DLN, from the capacity tier of object storage into a performance tier of storage of the storage system for processing by said application.