Jim Mulder wrote:
Although the architecture maximum is 65535 (16 bits), z/OS enforces
a maximum of 32767 (15 bits) for MAXUSER in IEASYSxx. It would be a lot
of work to track down and change all of the programs which use a LH instruction to fetch an ASID. We are not aware of any customer workloads for which a limit of 32767 address spaces is expected to become
a growth constraint.
ASCBs are allocated from SQA below the 16MB line. Each ASCB is a mere 384 bytes in length. A quick calculation shows that 32K address spaces would require 12MB of SQA below the 16MB line -- a value larger than the entire below-the-line private area available today in many installations!
It's clear that ASCBs will need to be moved above 16MB long before an address space limit approaching 32K would be feasible.
To maintain compatibility with older, non-privileged programs, it would probably be best to "capture" (to borrow terminology from IOSCAPU) the 31-bit ASCB address to a 24-bit value that would be placed into PSAAOLD by the dispatcher. That way, 24-bit programs that access their own ASCB wouldn't have to be changed. It's also likely such a "captured" address would appear to be within the same 24-bit virtual page for every address space in the system.
Using this technique, only programs that access ASCBs for address spaces other than their own would require AMODE(31|64) execution, and only those that still run AMODE(24) would be affected. No end-user programs would be affected since locking requirements imply that only privileged programs can access another ASCB with integrity (notwithstanding the fact that the ASCB for many system address spaces [e.g., *MASTER*] are not going anywhere and locking isn't really necessary for those cases.)
-- ----------------------------------------------------------------- | Edward E. Jaffe | | | Mgr, Research & Development | [EMAIL PROTECTED] | | Phoenix Software International | Tel: (310) 338-0400 x318 | | 5200 W Century Blvd, Suite 800 | Fax: (310) 338-0801 | | Los Angeles, CA 90045 | http://www.phoenixsoftware.com | -----------------------------------------------------------------
---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
