From owner-freebsd-arch@FreeBSD.ORG Thu Nov 11 03:16:41 2004 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from green.homeunix.org (freefall.freebsd.org [216.136.204.21]) by hub.freebsd.org (Postfix) with ESMTP id 4187116A4CE for ; Thu, 11 Nov 2004 03:16:41 +0000 (GMT) Received: from green.homeunix.org (green@localhost [127.0.0.1]) by green.homeunix.org (8.13.1/8.13.1) with ESMTP id iAB3GeAG010347 for ; Wed, 10 Nov 2004 22:16:40 -0500 (EST) (envelope-from green@green.homeunix.org) Received: (from green@localhost) by green.homeunix.org (8.13.1/8.13.1/Submit) id iAB3GeTN010346 for arch@FreeBSD.ORG; Wed, 10 Nov 2004 22:16:40 -0500 (EST) (envelope-from green) Date: Wed, 10 Nov 2004 22:16:39 -0500 From: Brian Fundakowski Feldman To: arch@FreeBSD.ORG Message-ID: <20041111031639.GC997@green.homeunix.org> References: <20041111030035.GA70923@VARK.MIT.EDU> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20041111030035.GA70923@VARK.MIT.EDU> User-Agent: Mutt/1.5.6i Subject: Re: U Area Removal X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 11 Nov 2004 03:16:41 -0000 On Wed, Nov 10, 2004 at 10:00:35PM -0500, David Schultz wrote: > Over the years, the amount of data we have stored in each process' U > area has eroded to the point where all we have left are the following: > > - A struct kinfo_proc that is only used for a.out core dumps. > This can be reconstructed at the time of the core dump, so > it doesn't need to be there. > > - The struct pstats for the process, which takes a mere 216 bytes > on i386. > > In exchange for the ability to swap out this 216-byte structure, we > keep around a 4096-byte page, a 132-byte vm_object, and a couple of > pointers. Moreover, there is a small amount of runtime overhead > associated with this, and developers need to remember to PHOLD() and > PRELE() the process as appropriate.[1] > > I propose to remove the ability to swap the U area, allocating p_stats > from malloced memory instead. Medium-term scheduling and swapping of > kernel stacks would be retained. Here are the patches; !i386 testers > wanted: > > http://www.freebsd.org/~das/patches/upages.diff > > > [1] Most of the instances of PHOLD() and PRELE() right now never > needed to be there or have been unnecessary ever since the PCB > was moved out of the U area. I am not going to get a chance to review this soon (which I'd like to) but I'm going to make sure I also voice support for removing this extra avenue for system instability due to media failure. I am happy to see you having the desire to take this step! -- Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\ <> green@FreeBSD.org \ The Power to Serve! \ Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\