[email protected] (Anne & Lynn Wheeler) writes: > The "dup" issue was if aggregate 3880-11 wasn't much larger than > processor memory, then nearly every page in 3880-11 would also in > processor memory. The converse if a page was needed not in processor > memory, then it would unlikely be in 3880-11 cache memory. Moving to > "no-dup" means that a page in processor memory would almost never be > in 3880-11 cache, so there is room for pages (not in processor memory) > that might be needed in processor memory.
re: http://www.garlic.com/~lynn/2017d.html#58 Paging subsystems in the era of bigass memory http://www.garlic.com/~lynn/2017d.html#61 Paging subsystems in the era of bigass memory dynamically switching between "dup" and "no-dup" ... "no-dup" was when total processor memory was compareable in size to disk cache for paging (or later, processor memory was compareable in size to space available for disk paging) ... then "no-dup" was sort of like treating/optimizing dynamic disk caches analogous to how the later 3090 extended store was directly treated ... a page was either in processor memory or in extended store ... but wouldn't maintain page in both places. recent posts mentioning 3090 extended store (32M-256N processor storage, 64M-2048M extended storage) http://www.garlic.com/~lynn/2017b.html#69 The ICL 2900 http://www.garlic.com/~lynn/2017d.html#4 GREAT presentation on the history of the mainframe long after all memory could be configured as straight processor memory, LPARs continued to offer option of configuring some as extended store ... apparently because system software had been so structured into supporting processor/extended split ... it took quite some time to adapt to efficiently just using large processor storage. I could also use it for (electronic disk) "1655" ... large number were bought from a vendor for paging use in internal IBM datacenters. It could ran as simulated 2305 (fixed head disk) or as "native" fixed-block device. Larger memory systems ... possibly much larger than total 1655 space, I could dynamically select "no-dup" ... however in the mid-70s I also did "page migration" (which was also included in my resource manager shipped to customers later in the 70s) ... periodically sweaping low-use pages from "fast" paging devices to slower paging devices (but had to be dragged threw memory to move between devices). For 3090 extended store, I wanted to be able to do direct I/O from 3090 extended store (when cleaning pages w/o having to drag through processor memory). (other) recent posts mentioning "1655": http://www.garlic.com/~lynn/2017b.html#68 The ICL 2900 http://www.garlic.com/~lynn/2017c.html#26 Multitasking, together with OS operations posts mentioning page management & replacement algorithms http://www.garlic.com/~lynn/subtopic.html#clock -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
