IBM Mainframe Discussion List <[email protected]> wrote on 06/12/2008 11:59:06 PM:
> Is x'00' better than other mask values? Why? Is TM preferable > to IC or ICM or L or LH or CLC or ...? (What's the fastest way > to clear a register?) TM with x'00' will cause an access exception, but avoids revealing anything about the contents of the storage in the condition code in the PSW, or in any register (keeping in mind that registers and PSW get saved in RBs/TCBs which are not fetch protected). That is likely not critical in the case of IEWLFORK, since subpool 251 is user key, and subpool 252 is not fetch protected. There are some other cases where it is relevant. > Was there any good rationale for a write operation rather than just > a read operation to each page? Was it just a developer's naive > presumption that the pages must be immediately copied rather than > just fetched? I think it was simply something that was easy to do in native PL/X without resorting to a GENERATE of assembler code, by a developer whose expertise was in program management, not virtual/real/aux storage management. Also at that time, program management was part of DFSMS on the west coast of the continent, while virtual/real/aux storage management was on the east coast. My experience is that geographic separation does not foster enhanced communication, despite the more recent management blathering which seems to suggest that nine women actually can produce a baby in one month if they are evenly spaced across the global time zones. > Will TM perhaps cause pages that have previously been loaded, then > paged out, to be re-fetched, perhaps unnecessarily. Yes. The OC is worse in this regard, as it will set the change bit, so that the page would be unnecessarily re-written to the aux slot if it is subsequently stolen. > What happens if the parent process LOADs a module (not necessarily > eligible for deferred page loading) prior to fork(), then after > the fork() either the parent or the child, but not both, DELETEs > that module? I suppose that if the Content Supervision entries > are copied (or COW) on the fork() things simply work. Contents Supervisor control blocks are propagated to the child by fork. 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: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
