Deduplicating TLB entries for shared pages

Abstract

Although the page sharing among different address spaces can effectively reduce the memory footprint, the corresponding address mappings still require their own TLB entries. Consequently, redundant address mappings for the shared pages reside in TLBs. Our goal in this study is to increase the TLB density by deduplicating redundant copies of address mappings into a single mapping. In virtualized servers, the case of hosting the same guest operating systems, the same third-party libraries, and the same application is commonly found. Such environments generate the multiple identical address mappings, virtual to physical address, for shared pages among different virtual machines. We exploit this unique characteristic of the virtual memory layout being analogous in the same execution environment, and explore TLB deduplication, called DeTLB, which merges redundant virtual to physical address mappings of different address spaces into a single TLB entry. To demonstrate the performance impact, we develop a QEMU based trace simulator and evaluate the number of TLB misses by running an Apache Spark ALS and a microbenchmark with the Linux KSM module. The results indicate that DeTLB can effectively reduce the number of TLB misses for both data and instructions.