From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932595AbWFTLCx (ORCPT ); Tue, 20 Jun 2006 07:02:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932596AbWFTLCx (ORCPT ); Tue, 20 Jun 2006 07:02:53 -0400 Received: from omx1-ext.sgi.com ([192.48.179.11]:64472 "EHLO omx1.americas.sgi.com") by vger.kernel.org with ESMTP id S932595AbWFTLCw (ORCPT ); Tue, 20 Jun 2006 07:02:52 -0400 Date: Tue, 20 Jun 2006 06:02:36 -0500 From: Robin Holt To: Andi Kleen Cc: Jes Sorensen , Robin Holt , linux-kernel@vger.kernel.org, Nick Piggin , Hugh Dickins , Carsten Otte , bjorn_helgaas@hp.com Subject: Re: [patch] do_no_pfn Message-ID: <20060620110236.GA3099@lnx-holt.americas.sgi.com> References: <200606201048.10545.ak@suse.de> <4497BBFE.6000703@sgi.com> <200606201135.53824.ak@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200606201135.53824.ak@suse.de> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 20, 2006 at 11:35:53AM +0200, Andi Kleen wrote: > > > One struct page for a random single page here, another for a single > > random page there. And the risk that someone will start walking the > > pages and dereference and cause data corruption. As explained before, > > it's a bad idea. > > Note sure what your point is. Why should they cause memory corruption? > > Allowing struct page less VM is worse. If you add that then people > will use it for other stuff, and eventually we got a two class > VM. All not very good. You already have that. You already stated the mapping of device memory. The only thing we are asking to do is have a block of device memory which has its pfn inserted at first touch. The device is essentially available on each node. It is not something the generic parts of the VM need to manage. What benefit are we going to get from having struct page * behind the pages when the struct page need to be marked as reserved and uncached? Thanks, Robin