One would certainly hope that "copying" an address space for purposes of fork() would not require paging it all in. That would be horrible, and I seriously doubt that it works that way.
On Fri, Aug 23, 2019 at 12:26 PM Paul Gilmartin < [email protected]> wrote: > On Fri, 23 Aug 2019 10:41:55 -0500, Kirk Wolf <[email protected]> > wrote: > > >I agree! > > > >FWIW - debugging performance of forked Unix process startup/overhead is a > >mess - we had one customer who was seeing terrible performance when > >fork/execing tiny little shell processes that did practically nothing. > It > >was only happening on one of their LPARs. The IBM Support center was > >involved for a really long time, and I don't know if they ever really > >figured out what was wrong. > > > Indeed. Ouch! > > But I wonder how this plays with deferred loading of program objects > (I forget the proper term). Suppose a parent whose execution image > is only partially loaded forks a child which accesses pages never loaded > in the parent ...? > > So every page in the parent's execution image must be brought into > storage so it can be copied to the child. > > >On Fri, Aug 23, 2019 at 8:24 AM Jerry Callen wrote: > > > >> According to the "Summary of changes for z/OS UNIX System Services > >> Planning for Version 2 Release 4 (V2R4)" (see > >> > https://www.ibm.com/support/knowledgecenter/SSLTBW_2.4.0/com.ibm.zos.v2r4.bpxb200/bpxb2soc24.htm > >> copy on write for fork() has been removed from z/OS. It will be > interesting > >> to benchmark the performance of fork() between 2.3 and 2.4 on a variety > of > >> processes. > >> > >> I wonder why this was done? (Hi, Peter Relson -- hint, hint...) > > -- gil > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
