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The Remote Memory Pager

Normally the Remote Memory Pager (RMP for short) is a client which forwards the paging requests to a remote server using sockets over an Ethernet. The RMP connects to the remote memory servers using sockets over TCP/IP. One dedicated paging daemon issues pagein and pageout requests to the server and receives the data sent by them. When mirroring is used, it is responsible for selecting two servers for each paged out page and transfer the data to them. When parity logging is used, it maintains all the data structures related to page and parity group management and computes the parity pages. Security is ensured by allowing access to our device only to the superuser and by using privileged ports for the communication among the client and the servers.

RMP is also capable of forwarding the requests to the local disk using either a specified partition or a file. In the former case, it invokes a routine that places the request in the disk queue. In the later case it issues a read or write operation through the VFS layer routines. When no server can be found in order to satisfy the client's requests, paging to local disk is used.

Although the current implementation runs on top of a low bandwidth 10 Mbps Ethernet, remote paging is up to 2 times faster than using a local disk of the same bandwidth. It takes about 8.4 ms to transfer an 8KB page through the network, while transferring a page to/from the local disk takes about 17 ms. Faster networks such as ATM, or FDDI should offer even more promising performance, especially when faster communication protocols are used [26].

Evangelos Markatos
Wed Aug 7 11:36:29 EET DST 1996