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Date:      Wed, 02 Oct 1996 07:32:51 -0700
From:      David Greenman <>
To:        Craig Huckabee <>
Cc: (FreeBSD Questions)
Subject:   Re: Optimizing system performance w/ large scale system 
Message-ID:  <>
In-Reply-To: Your message of "Wed, 02 Oct 1996 09:50:24 EDT." <> 

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>  512MB of RAM, 512K of cache
>  1) With this much RAM are there any special tweaks I should make to the
>     kernel config file (other than the 'options "MAXMEM=(512*1024)"' line)
>     to improve performance and get the most out of the machine?
>  2) Are there any other special tweaks I should consider?  This machine will
>     hopefully provide shell accounts, ftp access, web service, and possibly
>     POP mail service for a large number of people (>500).

   You may have to increase the size of your kernel virtual address space
depending on how many simultaneous TCP connections you have and how much
kernel memory these consume. This is done by moving the kernel start address
down in memory by 256MB. I've done this for wcarchive, but it's somewhat
difficult due to the need to rebuild a large number of utilities after making
the change. Figuring out whether or not you need to do this is also difficult.
I was able to figure it out by carefully analyzing the free virtual address
space during system startup (using kernel printfs in key places) and then
accounting for a few variables. We need to make the out-of-VM detection more
   All of this isn't an issue for machines with 256MB of RAM or less, but
starts to become an issue for >256MB. We haven't moved the kernel start
address by default due to BSD/OS compatibility considerations (which would
break if we made such a change)...and too many people enjoy using Netscape.
   On the other hand, it may not be a problem for you; this depends entirely
on your application mix, total number of processes, total number of mbuf
clusters, etc., during peak periods. It was a problem for wcarchive, but then
noone else is serving 1200 FTP users simultaneously like we do. YMMV.


David Greenman
Core-team/Principal Architect, The FreeBSD Project

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