Reducing the virtual memory overhead of swizzling

Swizzling is a mechanism used by OODBs and persistent object systems to convert pointers from their disk format to a more efficient in-memory format. Previous studies of swizzling have focused on analyzing the CPU overhead of pointer translation and studying trade-offs in different approaches to swizzling. In this paper we show that there is an additional indirect but important cost associated with swizzling: swizzling a read-only page causes it to be "dirty" with respect to the operating system. At the onset of paging, these read-only pages may be written to the swap file unnecessarily. We propose a simple modification to the operating system that reduces the impact of this overhead on application performance.