Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!ucbvax!UBVMSC.CC.BUFFALO.EDU!PSYDAVE From: PSYDAVE@UBVMSC.CC.BUFFALO.EDU (Dave Straitiff) Newsgroups: comp.os.vms Subject: RE: MPW_HILIMIT Message-ID: <8806241250.AA08692@ucbvax.Berkeley.EDU> Date: 21 Jun 88 06:12:00 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 44 Dan Esbensen who wrote the Dynamic Load Balancer and the booklet you are refering to gives a couple reasons for raising MPW_HILIMIT. This parameter tells VMS to dump the whole modified page list into the page file when this number is reached. That's a lot of I/O overhead. Most of what Dan recommends is oriented towards systems with a large amount of memory. You are not really losing any memory by setting this high, but rather keeping more pages around in physical memory. The modified page list is purged to replentish the free page list. What you are doing is keeping a lot more modified pages around in the hope that MPW_HILIMIT will be reached less often and therefore prevent a number of hard page faults and I/Os. Many pages will be immediately faulted back in. The idea is to make it a soft fault and not a hard one. Testing a high number is not going to hurt you. It is worth giving a try. As in all tuning, it is based on your applications and hardware. This concept may or may not help in your environment. Too low of a value will probably hurt though. Digital's numbers are not always a good reference for what is a reasonable value. Many defaults are the same on Vax 730s and 8800s, they are usually only best guesses. The new version of autogen may correct some of this by collecting stats on a running CPU for later tuning. As the title says, "Rules of Thumb", 15% may not be the right number for you. Try it high, try it low, try it inbetween, and see what it does for you. A last note is on MPW_WAITLIMIT, it should be the same as MPW_HILIMIT. The system could deadlock if MPW_WAITLIMIT was lower than MPW_HILIMIT. Tuning can be a lot of fun and very informative, but it usually only produces a marginal increase in performance. Poor or excessive tuning may even hinder performance. I'd approach it with a little reservation. Good Luck! Dave... ============================================================================ David M. Straitiff Bitnet: PsyDave@UBvms Computer Resource Manager Internet: PsyDave@UBvms.cc.buffalo.edu Phone: (716)689-8093 Speech Research Laboratory Department of Psychology State University of New York at Buffalo Buffalo, New York 14260 ============================================================================