From owner-cvs-all@FreeBSD.ORG Mon Mar 31 00:14:07 2003 Return-Path: Delivered-To: cvs-all@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id F422337B404; Mon, 31 Mar 2003 00:14:06 -0800 (PST) Received: from k6.locore.ca (k6.locore.ca [198.96.117.170]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9474E43FAF; Mon, 31 Mar 2003 00:14:05 -0800 (PST) (envelope-from jake@k6.locore.ca) Received: from k6.locore.ca (localhost.locore.ca [127.0.0.1]) by k6.locore.ca (8.12.8/8.12.8) with ESMTP id h2V8KUxS036462; Mon, 31 Mar 2003 03:20:30 -0500 (EST) (envelope-from jake@k6.locore.ca) Received: (from jake@localhost) by k6.locore.ca (8.12.8/8.12.8/Submit) id h2V8KUoK036461; Mon, 31 Mar 2003 03:20:30 -0500 (EST) Date: Mon, 31 Mar 2003 03:20:30 -0500 From: Jake Burkholder To: Peter Jeremy Message-ID: <20030331082030.GD32298@locore.ca> References: <200303300524.h2U5Ora7061852@repoman.freebsd.org> <20030330061301.GC21973@locore.ca> <20030330070723.GE21973@locore.ca> <20030330012410.I3292@odysseus.silby.com> <20030330201113.GA32298@locore.ca> <20030330152920.D6586@odysseus.silby.com> <20030330232030.GB32298@locore.ca> <20030331071239.GA27585@cirb503493.alcatel.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030331071239.GA27585@cirb503493.alcatel.com.au> User-Agent: Mutt/1.4i cc: cvs-src@FreeBSD.org cc: src-committers@FreeBSD.org cc: cvs-all@FreeBSD.org Subject: Re: HEADS UP Re: cvs commit: src/sys/conf options.i386 src/sys/i386/i386 bios.c locore.s machdep.c mpboot.s pmap.c vm86bios.s vm_machdep.c src/sys/i386/include _types.h bus_at386.h param.h pmap. X-BeenThere: cvs-all@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: CVS commit messages for the entire tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 31 Mar 2003 08:14:10 -0000 Apparently, On Mon, Mar 31, 2003 at 05:12:39PM +1000, Peter Jeremy said words to the effect of; > On Sun, Mar 30, 2003 at 06:20:30PM -0500, Jake Burkholder wrote: > >Apparently, On Sun, Mar 30, 2003 at 03:30:52PM -0600, > > Mike Silbersack said words to the effect of; > >> Is it practically possible with PAE and busdma'd drivers that such a > >> configuration could work? > > > >I'm not sure I understand the question, you mean is it possible to use > >separate address spaces for the kernel and userland, giving a full 4G each? > >Yes it is possible, but it is not practical. > > Why do you say "not practical"? Unix spent most of its formative > years with kernel and userland in separate address spaces. I don't > think the code exists in 4BSD but it's definitely still functional > in 2BSD (which is under a BSD license now-a-days). x86 just doesn't lend itself well to doing this. The sparc64 port uses separate address spaces because it is easy there. Its not a matter of the os supporting it, its what you can do realistically with the hardware. > > > It would be prohibitively expensive and ugly. > > I'll accept "ugly" and "expensive". The "prohibitively" is more of a > value judgement. Currently FreeBSD needs to trade KVA against UVA for > large RAM configurations. If you have an application that needs lots > of KVA and lots of UVA then FreeBSD on x86 isn't currently an option. > Wearing the overheads on system calls, copyin and copyout may be > cheaper than the alternatives. Don't let me stop you from implementing it. Jake