Before revision:  We further consider the problem under poisson arrival and general workload distribution,  M-SRPT is proved to be asymptotic optimal when the traffic intensity \rho approaches 1, if the task size is upper bound by the derived upper bound \eta{1-\rho}, if the job size distribution has bounded support, which generalizes the result in }[ .
After revision:  We further consider the problem under poisson arrival and general workload distribution, M-SRPT is proved to be asymptotic optimal when the traffic intensity \rho approaches 1, if the job size distribution has bounded support. In addition, we also present a characterization of the heavy traffic behavior of work-conserving algorithms in single-task job scheduling, and prove that the average flow time in GI/GI/1 system scales with \frac{1{1-\rho}, if the job size distribution has bounded support, which generalizes the result in }[ .