Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY > I had a question about how z/OS handles physical memory for the same > load module that is loaded at different virtual addresses in > different virtual address spaces. > > For example, let's say on the same z/OS system I have the following: > > CICS region A that has load module B loaded at virtual address x'3F400010'. > CICS region B that has the same load module B loaded at virtual > address x'3D400020'. > > More than likely there will be some differences in that same load > module that has been loaded at different virtual addresses, since > things like ADCONs and VCONs will resolve to different virtual > addresses when the load module is brought into memory. However, > there will probably be many virtual pages that are also identical > between the two modules, if nothing in that virtual page needed to > be adjusted by the loader. > > My question is, does z/OS have any functionality to detect the > virtual pages that would be identical for these 2 load modules and > then adjust the virtual page tables for CICS region A and B to point > to the same physical frame and drop the duplicate frame? > > So for example, if the first 4k virtual page of load module B in > CICS region A at x'3F400010' and the first 4k virtual page of load > module B in CICS region B at x'3D400020' had the same data in it, > would z/OS recognize this and cause the page tables for CICS region > A at x'3F400010' and page tables for CICS region B at x'3D400020' to > be adjusted to point to the same physical frame and then drop the > other duplicate physical frame? > > I was under the impression that the answer was no, but one of the > SYSPROGs here thought that z/OS had functionality to detect > identical physical frames that hold instructions that different > address spaces might be using and then do some physical memory > savings like I am mentioning above. > > I tried doing some internet searches on this topic, and could not > find any hits. If z/OS is doing this and someone has links to where > this documented, I would appreciate a point in the right direction.
You are correct. The answer is "no". Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
