Newsgroups: comp.unix.osf.osf1,comp.unix.internals,comp.parallel,comp.parallel.pvm
From: pdf@porthos.ucs.mun.ca (Paul David Fardy)
Reply-To: pdf@morgan.ucs.mun.ca
Subject: Help: paging and large 3-dimensional fluid models
Keywords: osf1, page fault, swapping, thrashing, KAP
Organization: Memorial University of Newfoundland
Date: Tue, 30 Aug 1994 22:07:08 GMT
Message-ID: <340aic$fmf@coranto.ucs.mun.ca>

Environment: DEC OSF/1 v2.0 on DEC 3000/300lx

I've been attempting to do some tests on the paging performance
of large 3-dimensional fluid models.  While the disk seems active
pretty much constantly, the results of getrusage(2) suggest that
only minor page faults are occuring.  Apart from about 25 to 30
major page faults in initialization, there are no major page faults.

My understanding is that a minor fault occurs after the system
(the pagedaemon?) reclaims a page but before the page has actually
been reused by another memory access.  The page table entry for
the page is not valid but the page still exists, intact, in memory.
A major page fault occurs when the page must be fetched from disk.

Am I wrong or is getrusage(2) returning incorrect numbers?

My objective is to reduce the amount of paging forced on these
big models.  Even when the job is almost alone on the system
(the network daemons are also running), the job gets 2-7% of 
the CPU (according to vmstat/ps) and the CPU is 90% idle.

Will KAP optimize for memory <-> disk paging or does it only handle
cache <-> memory "paging"?  Perhaps PVM will help, though I think
of PVM as being targetted toward systems that aren't already
saturated.  I'd like to see a single process solution, perhaps with
threads to perform prefetching of memory pages.

Any pointers to literature on optimizing algorithms for locality
of reference with respect to paging would be greatly appreciated.
I'm searching the supercomputing journals, but I don't have a complete list.
I'm also not sure how much I can gain from journals geared toward
multiprocessing systems.

	Paul Fardy
--
Paul David Fardy                     Memorial University of Newfoundland
Systems Programmer                   Elizabeth Avenue
Technical Support Group              St. John's, NF  A1C 5S7
Computing and Communications         CANADA


