As a threshold question, in the real world how many 4K, 1MB, and 2GB frames (for example) are and remain bit-identical duplicates of each other in a "typical" operating machine? What percentage of total memory does that duplication represent? Do IBM's processor cache algorithms already "de-duplicate"? How much paging overhead does memory duplication cause?
I'd have to imagine IBM has at least given some thought to these questions and (probably) has run some performance assessments along these lines. Though I'd also assume this is something of a moving target as cache hierarchies, processor designs, memory sizes, and workload mixes change over time. Ceteris paribus, to the extent anyone worries about this issue it'd be with "relatively big" consumers of memory -- "memory hogs," if one prefers. I don't think anybody ought to be worried about a couple or a few duplicate 4K frames in today's "typical" machine, for example. Also, it might be a very good thing from a performance point of view to have duplicated memory -- one copy per processor book, for example. If there are some real world benefits in doing something more in this area -- non-trivial performance benefits, notably -- then at least in principle I'd be in favor, if I get a vote. -------------------------------------------------------------------------------------------------------- Timothy Sipples IT Architect Executive, zEnterprise Industry Solutions, AP/GCG/MEA E-Mail: [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
