For *my* information? Contents Supervisor uses GETMAIN to obtain module storage. VSM is quite happy to allocate partial pages. It has been thus since before my time at IBM (42 years).
I have to go with what Jor-el says at time 0:43 in this clip: https://www.youtube.com/watch?v=zUmMeS2c4Uw Jim Mulder z/OS Diagnosis, Design, Development, Test IBM Corp. Poughkeepsie NY "IBM Mainframe Discussion List" <IBM-MAIN@LISTSERV.UA.EDU> wrote on 08/30/2021 11:29:35 PM: > From: "CM Poncelet" <ponce...@bcs.org.uk> > To: IBM-MAIN@LISTSERV.UA.EDU > Date: 08/31/2021 12:26 PM > Subject: Re: RENT binder option > Sent by: "IBM Mainframe Discussion List" <IBM-MAIN@LISTSERV.UA.EDU> > > FWIW and FYI. > > A 31-bit instrucion is a 4-byte fullword address, as e.g. say at virtual > (DAT) address x'71234568'. > > The first 3 nybles (x'712') indicate the segment from which the LMOD's > storage/address has been allocated. > The next 2 nybles (x'34') are the offset to the page within the segment > that is allocated to the LMOD's address. > The last 3 nybles (x'568') are the offset within the allocated page of > the LMOD's instruction address, within the segment. > So a page, in nybles, is 16 x 16 x 16 = 4096 bytes or 4K - which is then > used to build the LMOD's virtual (DAT) address. > > Hence, the OS allocates whole - not partial - 4K pages to a load module > (LMOD). If the size of a REFR LMOD is < 8K but > 4K then the OS > allocates two 4K pages to it (both of which are then REFR protected). If > a page were partially occupied by a REFR LMOD but otherwise also > occupied by another LMOD, this would lead to situations where, say, a > 31-bit instruction at address x'71234568' could be part of a REFR LMOD > but at address x'71234800' could be part of some other LMOD - and would > imply that a same page had been allocated to more than one LMOD, which > from an addressability point of view would be absurd. > > In other words, pages are either fully allocated/occupied to or by a > REFR LMOD's code or they are not occupied by a REFR LMOD's code at all. > > HTH Cheers. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
