More on flexibility: Storage above the bar can be set to specific storage keys when being acquired, and can use page table entries that map 1MB per entry rather than 4KB per entry.
Bill Fairchild Nolensville, TN ----- Original Message ----- From: "Kenneth Wilkerson" <[email protected]> To: [email protected] Sent: Monday, January 20, 2014 5:43:10 PM Subject: Re: Dataspace versus common area above the bar Because I've used memory objects for so long, I have not had a reason for IARVSERV. I read both the description in the macro reference and in the authorized assembler guide and there seems to be a ton of restrictions and quirks (such as TPROT). The most notable restriction is the sharing limit of 16 pages for an unauthorized address space. However, this limit can be changed. But because of the ESQA considerations created because the page tables can map different virtual address for the shared pages, I'm not sure what would be a practical limit. It does appear to address guard and to some extent page protection . It also offers the ability to share 31 bit storage with 24 bit applications (a key point). Shared and common memory objects do not have any of IARVSERV restrictions and do not change my conclusion that performance is NOT the reason to convert to a memory object. It's the advanced functionality. One reason I use a common memory object is so I can avoid using CSA and SQA particularly for code. With the 16 page restriction it would be impractical to share code with IARVSERV. And common data spaces cannot execute code. There are no limits to the flexibility offered by memory objects. I can share any number of pages. With shared memory objects I can determine which address spaces have access and which do not. With common memory I can create my own CSA and even SQA with some restrictions. As Jim affirmed, there is probably little if any performance difference between data spaces and memory objects. Chose the one best suited to your architecture. Kenneth -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Jim Mulder Sent: Monday, January 20, 2014 4:13 PM To: [email protected] Subject: Fw: Dataspace versus common area above the bar >> Memory objects are much more flexible than data spaces. Data spaces >> are limited to 2GB. Memory objects are only limited by the auxiliary storage. >> Memory objects can be guarded and can also be page protected. Data spaces >> cannot. Code can execute in memory object but not in data spaces. I started >> using memory objects 10 years ago and have nearly forgotten how to >> use a >> data space. > Guard pages and protected pages can be created in data spaces using >IARV64 with TAGET_VIEW=HIDDEN and TARGET_VIEW=READONLY I meant IARVSERV, not IARV64 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 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
