Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!ICDC.LLNL.GOV!OBERMAN From: OBERMAN@ICDC.LLNL.GOV ("Kevin Oberman, LLNL, 422-6955, L-156", 415) Newsgroups: comp.os.vms Subject: RE: MPW_HILIMIT Message-ID: <8806251239.AA29648@ucbvax.Berkeley.EDU> Date: 21 Jun 88 15:07:00 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 39 >I have been reading the VMS Tuning Guide provided (free) from Touch Technol- >ogies (they market the Dynamic Load Balancer). The guide advises setting >MPW_HILIMIT (limit at which VMS starts writing pages from the modified page >list to disk. Sets a limit on the MP list size) at 15 percent of the size of >physical memory. The claim is made that the loss of physical memory is more >than compensated by a reduced paged I/O activity. > >This seems like a rather large number for this sysgen parameter, as DEC set the >default at 500 pages. Has anyone followed Touch's advise? Have you noticed a >significant performance improvement? We run large images, use large pagefiles >and often encounter applications where much paging is required even with large >WSEXT values. I am thus trying to evaluate whether increasing MPW_HILIMIT (and >MPW_WAITLIMIT) is a reasonable thing to do (our current setting is 655, >physical memory is 32768 pages and VMS already uses 4400+ of these). Any >comments or other rules of thumb? 15% is about whrer we keep our MPW_HILIMIT. We did this to reduce pagging I/O activity, and it was very effective. The Modified Page List is a cache of pages released from working sets which are different from the page originally loaded from disk. If the pages have not been actually written to disk, they may be restored to the original working set if needed. We do ray-tracing and as a result move through large arrays in a nearly random pattern. This results in trmendous paging activity. An enlarged MPW greatly reduces the disk activity. Not to mention speding up the execution of the code. Since VMS will force a modified page write if the free list gets too small, increasing the MPW_HILIMIT seemed a reasonably painless method of decreasing paging I/O at only a moderate impact if memory ran low. And since we have a lot of memory, that is unlikely. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything.