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From: info-vax@ucbvax.ARPA
Newsgroups: fa.info-vax
Subject: Re: Paging [and VT's]
Message-ID: <5281@ucbvax.ARPA>
Date: Wed, 6-Mar-85 11:21:26 EST
Article-I.D.: ucbvax.5281
Posted: Wed Mar  6 11:21:26 1985
Date-Received: Thu, 7-Mar-85 05:02:32 EST
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Organization: University of California at Berkeley
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From: Mark Johnson 

Two things to look at...

  1)  I you are running your own applications (anything YOU link) then
look at the VMS Linker and the options files.  The CLUSTER line can be
used to change the page-fault-cluster for a section of memory.  If you
set it big enough, one page fault per cluster ought to bring the whole
cluster into memory.  This is in both the V3 (p 3-6) and V4 (p LINK-20)
linker documentation.

  2)  The SYSGEN parameter PFCDEFAULT could also be cranked up to make
the changes system wide.

Lets look at what would happen if you do this.  Each page fault would
bring in a large number of pages into memory.  This increases overall
access to the disk & chews up more memory.  If you run programs
infrequently and have lots of memory to spare, this should be ok.
Response time after the initial load should stay good and if the WS
parameters are set right the CPU overhead should be near NIL.

If you access a lot of programs & are running short of memory, this sort
of change would clobber the system since the I/O to the disk would go
through the roof.  I think the VMS developers assume the VAXen are
normally quite loaded so they skew the numbers away from optimal
performance on lightly loaded systems and give you the tools to put the
parameters where you need them.

I can also forsee some tradeoff's depending on what kind of disks you
use.  The MASSBUS RP07's & other MBA disks are better for fewer large
size transfers than RA81's.  Where the RA disks come out on top is lots
of smaller transfers from many jobs (so seek ordering comes into play).
Its a little late to change your disk drives now, but it is something to
consider for later improvements.

I would also check other parameters that affect your working set.  In
particular, the SYSGEN parameters WSMAX, SYSMWCNT, WSINC, WSDEC, PFRATL,
PFRATH, AWSMIN, AWSTIME, GROWLIM, and BORROWLIM make affects on the
whole system.  For individual jobs, look at the authorization file for
WSDEFAULT, WSEXTENT, and WSQUOTA.  Read the documentation carefully and
check the job with SHOW SYSTEM or something else to check your job has
all the memory you think its getting.

  --Mark