Path: utzoo!attcan!uunet!munnari!otc!metro!basser!usage!csdgwy!ewa From: ewa@csdgwy.csd.unsw.oz Newsgroups: comp.os.vms Subject: Re: MPW_HILIMIT --- and page caching Message-ID: <548@csdgwy.csd.unsw.oz> Date: 15 Jul 88 11:57:29 GMT References: <880708120821.27603e9e@LBL.Gov> Organization: University of New South Wales Lines: 40 In article <880708120821.27603e9e@LBL.Gov>, nagy%warner.hepnet@LBL.GOV (Frank J. Nagy, VAX Wizard & Guru) writes: >> According to what I've been told at one VAX/VMS performance seminar, it >> does not make sense to define a large MPW_HILIMIT. The reason is that whenever >> a process with pages in the modified list terminates, the whole list is >> written to disk, so its size gets down to zero. That's probably why it can >> never grow really big. > > This is 95+% wrong! When an image exits, most of its modified pages are > flushed to the free list since they have NOWHERE to go on the disk. The > only modified pages written back to disk are those from files mapped as > writable sections. In .EXE files, the code is read-only (99%) and so > become RO pages which are flushed to the free list on termination. > Initialized variables are usually in Copy-On-Reference sections and > unitialized variables (and ones inited to 0) in Demand-Zero sections; > in both these cases the page in memory DOES NOT get written back to the > .EXE file but has the system paging files as their backing store. When > the image exits it makes no sense (and so VMS does not do it) to write > these pages to the paging file. > > = Frank J. Nagy "VAX Guru & Wizard" > = Fermilab Research Division EED/Controls I was not referring to IMAGE exit, but to PROCESS termination, therefore the above argument is irrelevant. Also I used the term DISK in general sense, meaning page file, swap file or private file; all on disk, aren't they ... Anyway, true or not (I would be reluctant to put a percentage on it), it would be interesting to find another explanation for the modified page list on a busy system to go down to zero. +----------------------------------------------------------------------+ | E.Z. Bem, ASCnet: ewa@csdgwy.csd.unsw.oz | | VAX/VMS Systems Group, Infopsi: ewa@csdgwy.unsw.edu.au | | University of New South Wales, FAX: 61 2 662 8665 | | PO Box 1, Kensington, 2033 NSW, Phone: 61 2 697 2920 | | AUSTRALIA | | | | Daily a clever man learns something, daily a wise | | man gives up a certainty, perhaps... | +----------------------------------------------------------------------+