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Syed Adnan (sadnan@ucsd.edu)
Tue, 30 May 2000 01:42:21 -0700

untyped binary data, W10i_GMM.doc [Press RETURN to save to a file]
Name: Syed Adnan
Date: 5-29-00

Memory Coherence in Shared Virtual Memory System

Though it seemed like a book, paper wasn't too long. Easy to read, and nice written.
Paper talks about memory coherence problem, which is designing a shared virtual memory on loosely coupled multiprocessors. Goal was to provide a system that applications can use shared virtual memory just as they do a traditional virtual memory, except, that process could run in parallel.
Since any processor can access any memory, there are memory-mapping managers who implement the mapping between local memories and the shared virtual memory address space. Paper talks about few algorithms of how these managers are implemented that these managers are heart and soul of this idea of being able to use any memory on the system.
Paper talks about centralized manager algorithms, and distributed manager algorithms. Centralized manager reside in one processor and maintain a table called info, which has one entry for each page, and each entry has three fields. The owner field, the copy set field and lock field are the three fields in each entry keeping track of all the pages. This method is simple, but paper argues that decentralized algorithm improves the over all performance.
Distributed algorithms have fixed distributed, broadcast distributed, and dynamic distribution. Distributed are fixed number of managers, and therefore don't scale too well. Broadcast managers work well for few numbers of nodes, but for large number of nodes, this scheme doesn't work too well either. Dynamic managers are the best ones among all other algorithms that they scale well to number of nodes.
Paper talks about broadcasting before applying dynamic manager algorithm, which gives better results. I was surprise to see the results that they were impressive.