From owner-freebsd-current@FreeBSD.ORG Thu May 24 05:03:03 2007 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 0BADE16A47D; Thu, 24 May 2007 05:03:03 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from fallbackmx03.syd.optusnet.com.au (fallbackmx03.syd.optusnet.com.au [211.29.133.136]) by mx1.freebsd.org (Postfix) with ESMTP id 2176413C448; Thu, 24 May 2007 05:02:58 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from mail31.syd.optusnet.com.au (mail31.syd.optusnet.com.au [211.29.132.102]) by fallbackmx03.syd.optusnet.com.au (8.12.11.20060308/8.12.11) with ESMTP id l4NBlsmw007666; Wed, 23 May 2007 21:47:54 +1000 Received: from besplex.bde.org (c211-30-216-190.carlnfd3.nsw.optusnet.com.au [211.30.216.190]) by mail31.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id l4NBjE4x001436 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 23 May 2007 21:45:15 +1000 Date: Wed, 23 May 2007 21:45:16 +1000 (EST) From: Bruce Evans X-X-Sender: bde@besplex.bde.org To: Kris Kennaway In-Reply-To: <20070523100631.GA30143@xor.obsecurity.org> Message-ID: <20070523212559.V10628@besplex.bde.org> References: <20070410003505.GA8189@nowhere> <20070410003837.GB8189@nowhere> <20070410011125.GB38535@xor.obsecurity.org> <20070410013034.GC8189@nowhere> <20070410014233.GD8189@nowhere> <4651BD6F.5050301@unsane.co.uk> <20070522083112.GA5136@hub.freebsd.org> <4652B15D.5060505@unsane.co.uk> <20070523085532.GA27542@hub.freebsd.org> <20070523093231.GA29797@xor.obsecurity.org> <20070523100631.GA30143@xor.obsecurity.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Mailman-Approved-At: Thu, 24 May 2007 11:31:28 +0000 Cc: Craig Boston , Pawel Jakub Dawidek , freebsd-fs@freebsd.org, freebsd-current@freebsd.org, Darren Reed , Vince Subject: Re: ZFS committed to the FreeBSD base. X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 24 May 2007 05:03:03 -0000 On Wed, 23 May 2007, Kris Kennaway wrote: > On Wed, May 23, 2007 at 05:32:31AM -0400, Kris Kennaway wrote: > >> I would actually be interested to know how Solaris gets away with >> this. It sounds like there must be less of a distinction between >> memory allocated to the kernel and to userland, and the ability for >> memory to flow between these two with some form of backpressure when >> userland wants memory that is currently gobbled by up solaris ZFS. >> >> This kind of system probably makes good sense (although maybe there >> are trade-offs), but anyway it's not how FreeBSD does it. > > After some further thought I guess the difference is just that on a > 64-bit kernel you don't have KVA issues and can indeed map all of > physical RAM into the kernel for caching. This should probably happen for 64-bit kernels in FreeBSD too. FreeBSD sizes the buffer map part of KVA in the same way on all arches, to squeeze it into the limited available space on i386's, and has large complexity and some loss of performance in the buffer cache in order to work with the limited KVA. (Very old versions had less complexity and a large loss of performance.) Bruce