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From: Pete French <petefrench@ticketswitch.com>
Date: Thu, 25 Sep 2008 16:10:07 +0100
Cc: freebsd-stable@freebsd.org
Subject: Re: vm.kmem_size settings doesn't affect loader?
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> These are the tuning settings I use:
>
> vm.kmem_size="1536M"
> vm.kmem_size_max="1536M"
> vfs.zfs.arc_min="16M"
> vfs.zfs.arc_max="64M"

>
> The entire copying process took almost 2 hours.  Not once did I
> experience kmem exhaustion.  I can *guarantee* that I would have crashed
> the box numerous times had I not tuned the machine with the values
> above.

I am interested in the last two values you have there - I also use ZFS and
tune to prevent memory exhaustion. I tune kmem_size, but I have not bothered
toi set the arc_min - and the default appears to be 16M anyway. The arc_max
value I do set, but I got dreadful performance when I had it at 6M, so
I upped it to 128M. This has not resulted in any panics, and gives much better
performance. As I understand it there is only one ARC, and it comes from
kernel space too, so setting it to an extra 64 meg should not use that much
more memory, yes ?

My setup is:

vm.kmem_size="1024M"
vm.kmem_size_max="1024M"
vfs.zfs.arc_max="128M"
vfs.zfs.prefetch_disable=1

This is on a 2gb amd64 machine, and works beautifully, with no out of
memory errors and panics. I have been trying to panic this for a few
days. I will probably chnage the kmem size to 1536 which is what I use on
other machines though.

-pete.