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From: ewa@csdgwy.csd.unsw.oz
Newsgroups: comp.os.vms
Subject: Re: MPW_HILIMIT
Message-ID: <522@csdgwy.csd.unsw.oz>
Date: 5 Jul 88 09:53:47 GMT
References: <2022*kenw@noah.arc.cdn>
Organization: University of New South Wales
Lines: 37

In article <2022*kenw@noah.arc.cdn>, kenw%noah.arc.CDN@ean.ubc.ca (Ken Wallewein) writes:
>    I've been following this discussion, and it's encouraged me to do a bit of 
> digging.
> 
>   We've been running memory-rich in the past, althought that's changing. 
> MPW_HILIMIT is at 6000, and MPW_LOLIMIT at 3000.
> 
>   However, one thing is bothering me: I can't seem to get the modified list 
> above about 600 pages, and it's usually somewhere between 50 and 300.  With 
> the free list running around 16,000 blocks, it just doesn't seem right.
> 

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. 

I never found any reference to it in any documentation, but my observation
of the multiple VAX/VMS systems confirm this. On many ocassions I actually
saw a zero-size modified list. An additional concern regarding a large modified
page list is, that when it is all written back to disk, all processes with
pages in it will hard-pagefault at the same time. This introduces rather
undesirable oscillating system behaviour.

Regards,

   +----------------------------------------------------------------------+
   |  E.Z. Bem,			       ASCnet: ewa@csdgwy.csd.unsw.oz     |
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