On 3/17/06, O'Brien, Dennis L <Dennis.L.O'[EMAIL PROTECTED]> wrote: > Correction to item 1: z/VM 5.1 and below can support more than 2G of > central storage in the LPAR, as long as you're on zSeries hardware. > They just have to move pages below 2G when CP needs to do something with > them, such as I/O.
But there's more to expanded storage, and that applies to z/VM 5.2 as well. Memory management is a trade-off, and CP is not designed to use LRU when selecting pages for page-out. Especially with Linux it's easy to get the wrong pages. Having expanded storage reduces the penalty for taking the wrong pages, because it's cheap for the virtual machine to get them back. Migrating from expanded to paging disk *is* LRU. So for most configurations it is good to have some expanded storage, even when that means you give up the same amount of main memory for that (as is the case today). Apart from LRU, I believe there's another factor in CP paging involved that makes it attractive to have expanded storage for paging. But it takes more research to put my finger on that. Rob -- Rob van der Heij Velocity Software, Inc
