From owner-freebsd-hackers@FreeBSD.ORG Sat Sep 28 14:34:27 2013 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id D2D4BEAF for ; Sat, 28 Sep 2013 14:34:27 +0000 (UTC) (envelope-from nwhitehorn@anacreon.physics.wisc.edu) Received: from anacreon.physics.wisc.edu (unknown [IPv6:2607:f388:101c:0:216:cbff:fe39:3fae]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 9CB0F2F3E for ; Sat, 28 Sep 2013 14:34:27 +0000 (UTC) Received: from anacreon.physics.wisc.edu (localhost [127.0.0.1]) by anacreon.physics.wisc.edu (8.14.7/8.14.7) with ESMTP id r8SEYP1U069291; Sat, 28 Sep 2013 09:34:25 -0500 (CDT) (envelope-from nwhitehorn@anacreon.physics.wisc.edu) Received: from localhost (nwhitehorn@localhost) by anacreon.physics.wisc.edu (8.14.7/8.14.7/Submit) with ESMTP id r8SEYPCS069288; Sat, 28 Sep 2013 09:34:25 -0500 (CDT) (envelope-from nwhitehorn@anacreon.physics.wisc.edu) Date: Sat, 28 Sep 2013 09:34:25 -0500 (CDT) From: Nathan Whitehorn To: Peter Jeremy Subject: Re: Mixing amd64 kernel with i386 world In-Reply-To: <20130928103758.GC27231@server.rulingia.com> Message-ID: References: <20130928103758.GC27231@server.rulingia.com> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Mailman-Approved-At: Sat, 28 Sep 2013 16:09:30 +0000 Cc: freebsd-hackers@freebsd.org X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 28 Sep 2013 14:34:27 -0000 On Sat, 28 Sep 2013, Peter Jeremy wrote: > I have a system with 4GB RAM and hence need to use an amd64 kernel to use > all the RAM (I can only access 3GB RAM with an i386 kernel). OTOH, amd64 > processes are significantly (50-100%) larger than equivalent i386 processes > and none none of the applications I'll be running on the system need to be > 64-bit. > > This implies that the optimal approach is an amd64 kernel with i386 > userland (I'm ignoring PAE as a useable approach). I've successfully > run i386 jails on amd64 systems so I know this mostly works. I also > know that there are some gotchas: > - kdump needs to match the kernel > - anything accessing /dev/mem or /dev/kmem (which implies anything that > uses libkvm) probably needs to match the kernel. > For whatever it is worth, I have done this running a ppc32 userland with a ppc64 kernel (that is how ppc64 was first developed actually, before the 64-bit userland existed) and it worked just fine. -Nathan