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Published in Phillip A. Laplante, Dictionary of Computer Science, Engineering, and Technology, 2017
clock replacement algorithm a page replacement algorithm described as follows: A circular list of page entries corresponding to the pages in the memory is formed. Each entry has a use bit which is set to a 1 when the corresponding page has been referenced. A pointer identifies a page entry. If the use bit of the page entry is set to a 1, the use bit is reset to a 0 and the pointer advances to the next entry. The process is repeated until an entry is found with its use bit already reset, which identifies the page to be replaced. The pointer advances to the next page entry for the next occasion that the algorithm is required. The word “clock” comes from viewing the pointer as an arm of a clock. Also known as a first-in-not-used-first-out replacement algorithm.
Challenges in Design, Data Placement, Migration and Power-Performance Trade-offs in DRAM-NVM-based Hybrid Memory Systems
Published in IETE Technical Review, 2023
Sadhana Rai, Basavaraj Talawar
Page Replacement Policies for Hybrid Memory: Conventional DRAM, page replacement policies provide sub-optimal performance in hybrid memory. They would benefit from performance or power-aware page replacement policies which place the page in one of the available memories based on the desired trade-off point. A major role of the page replacement algorithm for hybrid memory should be to reduce the writes in NVM while maintaining a good hit ratio as the write operation is costlier in NVM than DRAM in terms of time and energy. The page replacement policy should encompass a good allocation policy, read-write access pattern identification and a migration policy. Broadly the page replacement algorithms can be classified as LRU-based or CLOCK-based algorithms. Page replacement is an important issue to be addressed in hybrid memory. In this section, we discuss the issues and possible solutions in handling page faults in DRAM-NVM-based hybrid memories. Problems that are faced by existing page fault handling techniques are: