Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!auspex!hitz
From: hitz@auspex.auspex.com (Dave Hitz)
Newsgroups: comp.unix.questions
Subject: Re: the 10% factor
Summary: C is for Code
Message-ID: <2679@auspex.auspex.com>
Date: 29 Nov 89 20:07:08 GMT
References: <21436@adm.BRL.MIL> <2643@auspex.auspex.com> <89323.004057BACON@MTUS5.BITNET>
Reply-To: hitz@auspex.auspex.com (Dave Hitz)
Organization: Auspex Systems, Santa Clara
Lines: 47


In article <89323.004057BACON@MTUS5.BITNET> BACON@MTUS5.BITNET (Jeffery Bacon) writes:
>    How does one learn this stuff?

RTFC :-)

>      At the same time, it occured to me to cut the number of inodes and the
> size of the minfree value. After all, there are only 3 files...(plus the
> . and .. directory)...I don't see anything wrong with having done that, am I
> correct?
...
>     Well, I hate to sound too stupid, but I did just this on a couple of
> swap partitions I made a couple of months ago. (Run the mkfile(8)s in
> parallel. This is on a Sun 3/260, SunOS4.0.3, 2 280MB Fujitsu's, 3 ~36Mb
> swaps on two 117MB partitions. The partitions are packed full, with about
> 500K free each.) Should I remake the swap files?

Easy one first:  There is *definitely* nothing wrong with pulling down
the number of inodes.

Hard one: Setting minfree down to 0 doesn't break anything, but *may*
cause performance problems.  To determine whether it's *actually*
causing performance problems would require an experiment or a
simulation of your exact setup.

You can make sure that minfree=0 does not hurt performance much by
starting with a completely empty partition and building swap files one
at a time using mkfile(8) *without* the -n option.

Is it worth doing this?  Figuring that out is probably harder than just
doing it.  (Why don't you run a swap-death benchmark before and after and
tell us what happens.)

My *guess* would be that unless you swap heavily, you won't notice
any difference.  If you do swap heavily, random factors will dominate.
If you swap to a part of the file that was created early, before the
partition was getting full, probably no problem.  If you swap at the
end of the file, you may get a slow down.

I'd like to emphasize that these guesses about out how disk
fragmentation is likely to affect performance are in fact guesses.  I
know how to make the problem (if there is one) go away, but I don't
know if there is one.

-- 
Dave Hitz					home: 408-739-7116
UUCP: {uunet,mips,sun,bridge2}!auspex!hitz 	work: 408-492-0900