On Thu, 12 Jun 2008 13:55:31 -0500, Wayne Driscoll wrote: >My guess as to why the OC is used is because fork will use a Copy on Write >(COW) protocol for the new address space. They run through the JPA and do >an OC on each page in order to get the modules copied over. This is >probably since they can't just re-load all the modules, since source library >info isn't saved. The sad part of this logic, is that if the program does a >FORK->EXEC (which is pretty standard), the EXEC will get rid of most of the >loaded modules. Garth Godfrey or Erin Farr would have the definitive answer >to this. > I'm mystified. What's the purpose of this? Doesn't touching every page frustrate the very purpose of COW, which is to defer the copy until the page is actually modified? And if the module is properly refreshable as marked, it should never be modified, and need never be copied -- the pages can remain shared indefinitely.
A few years ago, there was some discussion here about the complexities of the deferred fetch capabilities of Content Supervision. Is this going on because Content Supervision is incapable of dealing with modules shared between address spaces. If so, the Right Fix is a massive undertaking. >-----Original Message----- >From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf >Of Edward Jaffe > >We just opened APAR OA25468 against z/OS UNIX. If you run with REFRPROT >in PROGxx, you can be hit by this. > >IIUC, z/OS UNIX fork processing uses the OC instruction, while in PSW >key zero, to WRITE on EVERY PAGE of EVERY MODULE in the private area of >the address space! (Who designed this???!) > >That's the scary part. Now page down to the bottom to see the funny part >-- especially suggestion #2. > >|LOCAL FIX: >|1. Refrain from using the PROGxx REFRPROT parm. if possible. >| >|2. Re-link the affected module so it is not using the >| REFRESHABLE attribute. > And it seemed like such a good idea at first glance. -- gil ---------------------------------------------------------------------- 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
