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Date:      Sun, 03 Dec 2000 17:46:22 -0800
From:      David Greenman <dg@root.com>
To:        "O. Hartmann" <ohartman@ipamzlx.physik.uni-mainz.de>
Cc:        freebsd-questions@FreeBSD.ORG, freebsd-stable@FreeBSD.ORG
Subject:   Re: NSFBUFS in kernel config 
Message-ID:  <200012040146.RAA18347@implode.root.com>
In-Reply-To: Your message of "Sun, 03 Dec 2000 23:23:00 %2B0100." <Pine.BSF.4.21.0012032320210.385-100000@ipamzlx.physik.uni-mainz.de> 

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>Can anyone explain what 
>	options		NSFBUFS=1024 or =4096
>
>
>means? I played around with this option and on a 64MBytes machine,
>pushing it to 1024 caused a heavy swapping so I commented out this
>option to avoid it. What is a reasonable value for a server system
>under heavy load and what for a client, maybe a diskless one?

   This sets a value for the maximum number of sendfile buffers, which are
essentially headers for pages that have been queued for transmit, along with
a chunk of kernel virtual memory to map them. If your applications use
sendfile() heavily, then this will also have the side-effect of making those
[file] pages inelligble to be paged out. It is intended for tuning systems
that use sendfile() heavily.
   I would guess that your applications don't use sendfile(), however, and
thus tuning the above will have no effect except to wastefully allocate a lot
of kernel virtual memory for something that isn't used.
   Unless you know what you are doing, you should not set this option in
your kernel config file. Since you are setting it (and to the value that
is in the LINT kernel config file), this brings up the obvious question of
what other LINT options you have turned on. The options in the LINT config
file are only for testing the build of the kernel and should not be randomly
included in a production kernel config file. You should use the GENERIC
config file as a template to make your own, not LINT.

-DG

David Greenman
Co-founder, The FreeBSD Project - http://www.freebsd.org
President, TeraSolutions, Inc. - http://www.terasolutions.com
Pave the road of life with opportunities.


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