From owner-freebsd-current@FreeBSD.ORG Mon Nov 12 17:35:03 2007 Return-Path: Delivered-To: freebsd-current@FreeBSD.ORG Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id BFF6116A417 for ; Mon, 12 Nov 2007 17:35:03 +0000 (UTC) (envelope-from olli@lurza.secnetix.de) Received: from lurza.secnetix.de (lurza.secnetix.de [IPv6:2001:1b20:1:3::1]) by mx1.freebsd.org (Postfix) with ESMTP id 2CD1413C494 for ; Mon, 12 Nov 2007 17:35:02 +0000 (UTC) (envelope-from olli@lurza.secnetix.de) Received: from lurza.secnetix.de (localhost [127.0.0.1]) by lurza.secnetix.de (8.14.1/8.14.1) with ESMTP id lACHYsjt017747; Mon, 12 Nov 2007 18:35:00 +0100 (CET) (envelope-from oliver.fromme@secnetix.de) Received: (from olli@localhost) by lurza.secnetix.de (8.14.1/8.14.1/Submit) id lACHYsq4017746; Mon, 12 Nov 2007 18:34:54 +0100 (CET) (envelope-from olli) Date: Mon, 12 Nov 2007 18:34:54 +0100 (CET) Message-Id: <200711121734.lACHYsq4017746@lurza.secnetix.de> From: Oliver Fromme To: freebsd-current@FreeBSD.ORG, mashtizadeh@gmail.com In-Reply-To: X-Newsgroups: list.freebsd-current User-Agent: tin/1.8.3-20070201 ("Scotasay") (UNIX) (FreeBSD/6.2-STABLE-20070808 (i386)) MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-2.1.2 (lurza.secnetix.de [127.0.0.1]); Mon, 12 Nov 2007 18:35:00 +0100 (CET) Cc: Subject: Re: ZFS kmem_map too small. X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: freebsd-current@FreeBSD.ORG, mashtizadeh@gmail.com List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 12 Nov 2007 17:35:03 -0000 [Excessive Cc list cut] Ali Mashtizadeh wrote: > For ZFS KVA_PAGES=512 seems to run very stable so it's unfortunate that we > have to give up our VA space in the userland. I would personally like to see > a move to a 4-4 Memory model or at least have it as a compile time option. > Does anyone know if that's been attempted on FreeBSD? Sorry for the late reply. I haven't seen an answer to your question, so I try to give one. Using a 4-4 memory model (in 32 bit mode) means that kernel and user pages could never be active at the same time, i.e. they would have to be swapped for _every_ context switch, including syscalls and interrupts. That would be extremely expensive. And there would still be an address space limit at 4 GB, so the problem would only be pushed a little farther away, but it wouldn't be solved. A much better solution (or rather: the _real_ solution) is to use a 64bit OS (such as FreeBSD/amd64), where there's no need to worry about address space splitting at all. That's also precisely the reason why amd64 is recommended over i386 when using ZFS on FreeBSD. Practically all new hardware is 64bit-capable, so that's the way to go. Regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M. Handelsregister: Registergericht Muenchen, HRA 74606, Geschäftsfuehrung: secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün- chen, HRB 125758, Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart FreeBSD-Dienstleistungen, -Produkte und mehr: http://www.secnetix.de/bsd "And believe me, as a C++ programmer, I don't hesitate to question the decisions of language designers. After a decent amount of C++ exposure, Python's flaws seem ridiculously small." -- Ville Vainio