pages in segment ranges that are read only cannot be changed even by host function, like the CP STORE command. OK, this is from CMS, but it still illustrates architecture:
q segment Space Name Location Length Loaded Attribute CMSVMLIB DMSRTSEG 0179CDE8 00042DC8 YES SYSTEM CMSVMLIB VMLIB 01700000 0009CDA8 YES SYSTEM CMSPIPES RXSOCKET 01897630 000105B8 YES SYSTEM CMSPIPES PIPES 01800000 000975F0 YES SYSTEM INSTSEG CMSINST 01400000 002038C0 YES SYSTEM Ready; T=0.01/0.01 11:50:27 d k1800000 R01800000 TO 018007FF KEY = E4 Ready; T=0.01/0.01 11:50:34 st k1800000 04 HCPSTG2611E Key cannot be stored into a read-only page. Ready(02611); T=0.01/0.01 11:50:44 The CP STORE command, which supersedes instructions like ISKE, (it's emulating "HMC" functions), still doesn't work -> the architecture won't allow it. Back in the day, like HPO5, you could do this! And get a private write copy of any segment - including those created r/o! And have additional usable space. But no more - David Kreuter -----Original Message----- From: Alan Altmark To: [EMAIL PROTECTED] Sent: 3/4/2004 11:20 AM Subject: Re: Using DCSS for extra memory On Thursday, 03/04/2004 at 01:57 CET, Arnd Bergmann <[EMAIL PROTECTED]> wrote: > There is an ongoing discussion about adding support for > hotplugging memory (both adding and removing to/from a > running system) to linux-2.7 and there are patches that > can do this on some other architectures with linux-2.6. > > However, this will not be possible with DCSS segments, > because pages in memory segments do not have a usable storage > key (i.e. referenced/change bits). Not usable in what way, Arnd? Every page in a DCSS has valid reference and change bits in its storage key. If one or more pages in a DCSS are read-only, then a guest may not store into those pages so the change bit will never be set. If it is shared-write, then the change bit will be set if anyone changes the page, and ISKE will show that the page has changed (no matter who changed it). Alan Altmark Sr. Software Engineer IBM z/VM Development
