Kernel-User Space Separation in DRAM Memory

Abstract

Performance of software is increasingly restricted by the Memory Wall instead of CPU. Many studies focus on alleviating the DRAM latency by improving the row-buffer hit rate. But most of them treat the Kernel and User equally. Data used by Operating System and User applications spread in different rows of the same bank, leading to the contentions for the row-buffer when they access the bank successively. We find that contentions between Kernel and User make up of a great proportion of all the row-buffer misses. To alleviate the contentions between Kernel and User, we divide the united DRAM memory space into Kernel-Space and User-Space. A new page-allocation-system, the K/U-Aware page-allocation-system, is proposed to manage Kernel-Space and User-Space in DRAM memory in different address mapping schemes of DRAM memory controller. In the new system, pages are allocated from different spaces according to applicants (Kernel or User). Sizes of the two spaces increase and decrease dynamically as required. For benchmarks in PARSEC suites, the proposed system reduces the contentions of Kernel and User effectively, producing significant improvements of row-buffer hit rate. The execution time is reduced by 9.45% (max. 20.45%) and 6.51% (max. 18.05%) respectively in two typical address mapping schemes.