From owner-freebsd-fs@FreeBSD.ORG  Fri Mar  4 13:41:18 2011
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 1A9901065673
	for <freebsd-fs@freebsd.org>; Fri,  4 Mar 2011 13:41:18 +0000 (UTC)
	(envelope-from mcdouga9@egr.msu.edu)
Received: from mail.egr.msu.edu (gribble.egr.msu.edu [35.9.37.169])
	by mx1.freebsd.org (Postfix) with ESMTP id E3A348FC17
	for <freebsd-fs@freebsd.org>; Fri,  4 Mar 2011 13:41:17 +0000 (UTC)
Received: from gribble (localhost [127.0.0.1])
	by mail.egr.msu.edu (Postfix) with ESMTP id 9E1FD6E9F2
	for <freebsd-fs@freebsd.org>; Fri,  4 Mar 2011 08:23:29 -0500 (EST)
X-Virus-Scanned: amavisd-new at egr.msu.edu
Received: from mail.egr.msu.edu ([127.0.0.1])
	by gribble (gribble.egr.msu.edu [127.0.0.1]) (amavisd-new, port 10024)
	with ESMTP id Bl83YsjmY0JX for <freebsd-fs@freebsd.org>;
	Fri,  4 Mar 2011 08:23:29 -0500 (EST)
Received: from [35.9.44.65] (daemon.egr.msu.edu [35.9.44.65])
	(using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits))
	(No client certificate requested) (Authenticated sender: mcdouga9)
	by mail.egr.msu.edu (Postfix) with ESMTPSA id 7A78C6E9BA
	for <freebsd-fs@freebsd.org>; Fri,  4 Mar 2011 08:23:29 -0500 (EST)
Message-ID: <4D70E7D1.5030205@egr.msu.edu>
Date: Fri, 04 Mar 2011 08:23:29 -0500
From: Adam McDougall <mcdouga9@egr.msu.edu>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US;
	rv:1.9.2.13) Gecko/20110101 Thunderbird/3.1.7
MIME-Version: 1.0
To: freebsd-fs@freebsd.org
References: <1299232133.18671.3.camel@pc286.embl.fr>
In-Reply-To: <1299232133.18671.3.camel@pc286.embl.fr>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: kmem_map too small with ZFS and 8.2-RELEASE
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 04 Mar 2011 13:41:18 -0000

On 03/04/11 04:48, Mickaël Canévet wrote:
>> I'd use vm.kmem_size="32G" (i.e. twice your RAM) and that's it.
>
> Should I also increase vfs.zfs.arc_max ?
>
> Do you have any idea why the kernel panicked at only 8GB allocated ?
>
> Thank you

I believe ARC allocations in kmem can become fragmented, so when it is 
searching for a place to store a new contiguous segment of memory, the 
remaining fragmented free spaces may all be too small.  I also set
vm.kmem_size to about twice the amount of ram to help it avoid this 
issue.  I suspect if kmem is badly fragmented then performance of ZFS 
can downgrade, so that is another reason to keep kmem bigger.