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From: zazula@uazhe0.physics.arizona.edu (RALPH ZAZULA)
Newsgroups: comp.sys.next
Subject: Re: Lost pages in swapfile ?
Keywords: NeXT, swapfile
Message-ID: <1991Apr17.013649.532@arizona.edu>
Date: 17 Apr 91 06:30:00 GMT
References: <1991Apr15.153504.39750@slate.mines.colorado.edu> <332@nic.cerf.net>
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In article <332@nic.cerf.net>, benseb@nic.cerf.net (Booker Bense) writes...
>In article <1991Apr15.153504.39750@slate.mines.colorado.edu> mfriedel@slate.mines.colorado.edu (Friedel Michael) writes:
>>After I boot my NeXTstation I typed vm_stat which is supposed to list
>>the status of the virtual memory. Here is the result:
>[ vm-stat stuff deleted ]
>>
>>My system is 12meg (of which 11 meg are available, 1meg is reserved
>>by the system at boot time for buffers, so it tells me).
>>The swapfile has a size of 20971520 bytes after the machine is done
>>booting. Now no matter how I twist my math, I can't come up with 
>>enough pages that justify a 20meg swapfile.
>>So does anyone know to do the correct math, does vm_stat list incorrect
>>statistics or does the system just forget about a few pages ?
>>
> 
> 
>-RTFM %-)! if you have it %-(! , the swap file has a low water mark
>set in the file /etc/swaptab ( or something like that ). It's set so
>the swapfile is never shrunk to less than 20 MB. The rule of thumb is
>that the low water mark of the swap file should be twice the real
>memory. You can think of this a ``reserved space'' on your disk, so
>the system won't run out of swap space when it needs it.

Actually, RTFMing didn't shed any light on this for me either.
The command 'vm_stat' seems to be a misnomer.  Maybe it should
be 'rm_stat' for real-memory-statistics.  If I add up the pages
shown in a vm_stat, I get the 11 MEG that my machine (12 Meg) has
available, give or take a few K.  What *I* would like to know is the
number of pages that are in use in the swapfile.  This kind of information
would allow one to monitor the amount of swapfile space that is in use
and determine a good size for the thing.  One thing I tried was summing
the VSIZE column of a 'ps augx' display.  This added up to 70Meg...
Not quite the size of my 20Meg swapfile plus 12Meg RAM.  I'm not quite
sure what that meant...    


> 
> Now, for an 8 meg system 20 meg sounds a bit large. Since my 200 Meg
>disk is rather cramped, I'd like to ask the NeXTperts, if you think
>it'd be safe to set the low water mark lower ( like 16 meg ) . What
>kind of bad things happen to the OS when it runs out of swap disk?
> 
>- Booker C. Bense                    
>prefered: benseb@grumpy.sdsc.edu	"I think it's GOOD that everyone 
>NeXT Mail: benseb@next.sdsc.edu 	   becomes food " - Hobbes

Ralph

   |----------------------------------------------------------------------|
   | Ralph Zazula                               "Computer Addict!"        |
   | University of Arizona                 ---  Department of Physics     |
   |   UAZHEP::ZAZULA                            (DecNet/HEPNet)          |
   |   zazula@uazhe0.physics.arizona.edu         (Internet)               |
   |----------------------------------------------------------------------|
   |   "You can twist perceptions, reality won't budge."  - Neil Peart    |
   |----------------------------------------------------------------------|