Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262459AbVCSNC7 (ORCPT ); Sat, 19 Mar 2005 08:02:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262460AbVCSNC7 (ORCPT ); Sat, 19 Mar 2005 08:02:59 -0500 Received: from mta2.cl.cam.ac.uk ([128.232.0.14]:48261 "EHLO mta2.cl.cam.ac.uk") by vger.kernel.org with ESMTP id S262459AbVCSNC5 (ORCPT ); Sat, 19 Mar 2005 08:02:57 -0500 In-Reply-To: <20050319105632.GH31328@cl.cam.ac.uk> References: <20050319105632.GH31328@cl.cam.ac.uk> Mime-Version: 1.0 (Apple Message framework v619.2) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: Content-Transfer-Encoding: 7bit Cc: Paul Mackerras , akpm@osdl.org, "Eric W. Biederman" , Jesse Barnes , linux-kernel@vger.kernel.org, riel@redhat.com, Ian.Pratt@cl.cam.ac.uk, kurt@garloff.de From: Keir Fraser Subject: Re: [PATCH] Xen/i386 cleanups - AGP bus/phys cleanups Date: Sat, 19 Mar 2005 13:01:31 +0000 To: Christian Limpach X-Mailer: Apple Mail (2.619.2) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1507 Lines: 34 On 19 Mar 2005, at 10:56, Christian Limpach wrote: >> For this specific case there may be another resolution but could >> you please, please look at marking the missing pages PG_reserved >> and not hacking phys_to_virt. >> >> At this point anything short of explicitly introducing an intermediate >> step say virt_to_logical() logical_to_virt() will be extremely >> confusing and lead to very hard to spot bugs. Silently changing >> the semantics of functions is bad. > > We also use the additional level of indirection to implement suspend/ > resume and relocation of virtual machines between physical machines -- > you won't get the same sparse allocation of memory on the target > machine. > Also, this will make it much easier to support hot plug memory at the > hypervisor level since it will be able to substitute memory with very > little support from the OS running in the virtual machine. Also, more generally, I don't believe Linux would deal well with a highly fragmented memory map. I wonder how far Linux would boot if you PG_reserved every other page? We'd also need to deal with virtual<->lowmem not being a 1:1 mapping (at least for kernel code and data, as at least that obviously needs to be contiguous in virtual space). -- Keir - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/