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Date: Thu, 20 Jun 1996 11:54:39 -0700 (MST)
From: Tony Jones <tony@rtd.com>
Message-Id: <199606201854.LAA04471@seagull.rtd.com>
To: khetan@iafrica.com
Subject: Re: swap problem - more information
Cc: questions@freebsd.org
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Khetan Gajjar (khetan@iafrica.com) wrote:
: The problem is that the drive pages so often, that the machine is
: unuseable. It is really, really slow. Anyone have any idea why it's so
: slow or how to speed it up so that it's as fast as my swap partition ?

Welcome to the world of Unix performance tuning :-)

The problem isn't that the 'drive pages so often', it's paging as much
as you are asking it to do :-). The problem is likely 'how' it is paging.

I'm pretty sure paging on FreeBSD is round robin, so you are hitting your 
vnode/fs swap area constantly. Especially with the VSZ requirements you have.

Going through a vnode, to the filesystem layer, to the block layer is adding
at least two levels of indirection. You have just discovered that Virtual  
memory isn't a transparent panacea. How fast you can get blocks to/from the
paging space is critical for system performance. Spinning in the idle
loop because you have no runnable processes is going to hurt your performance.
It's going to hurt even if the vnode/fs layers have been carefully optimised.

Also, I hope you don't have the vnode/fs page file on the same spindle as the
raw partition ? Rule #1 for multiple swap areas is seperate spindles.

I'd be backing up and doing a disk re-org to add another swap partition 
on a different spindle or enlarge your current area if you have only one
spindle.
    
tony