A technique is described for improving throughput in a processing system, such as a network storage server. The technique provides multiple levels (e.g., a hierarchy) of parallelism of process execution within a single mutual exclusion domain, in a manner which allows certain operations on metadata to be parallelized as well as certain operations on user data. The specific parallelization scheme used in any given embodiment is based at least partly on the underlying metadata structures used by the processing system. Consequently, a high degree of parallelization possible, which improves the throughput of the processing system.