Although distributed threads on distributed shared memory (DSM) provide an easy programming model for distributed computer systems, it is not easy to build a high performance system with them, because a software DSM system is prone to page-thrashing. One way to reduce page-thrashing is to utilize thread migration, which leads to changes in page access patterns on DSM. In this paper, we propose thread scheduling methods based upon page access information and discuss an analytical model for evaluating this information. Then, we describe our implementation of distributed threads, PARSEC (Parallel software environment for workstation cluster). Using user-level threads, PARSEC implements thread migration and thread scheduling based upon the page access information. We also measure the performance of some applications with these thread scheduling methods. These measurements indicate that the thread scheduling methods greatly reduce page-thrashing and improve total system performance.