Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756099AbYBUFCd (ORCPT ); Thu, 21 Feb 2008 00:02:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750806AbYBUFCZ (ORCPT ); Thu, 21 Feb 2008 00:02:25 -0500 Received: from cantor2.suse.de ([195.135.220.15]:58964 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750771AbYBUFCY (ORCPT ); Thu, 21 Feb 2008 00:02:24 -0500 Date: Thu, 21 Feb 2008 06:02:23 +0100 From: Nick Piggin To: Andrea Arcangeli Cc: Robin Holt , akpm@linux-foundation.org, Avi Kivity , Izik Eidus , kvm-devel@lists.sourceforge.net, Peter Zijlstra , general@lists.openfabrics.org, Steve Wise , Roland Dreier , Kanoj Sarcar , steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com, Christoph Lameter Subject: Re: [PATCH] mmu notifiers #v6 Message-ID: <20080221050223.GD15215@wotan.suse.de> References: <20080219084357.GA22249@wotan.suse.de> <20080219135851.GI7128@v2.random> <20080219231157.GC18912@wotan.suse.de> <20080220010941.GR7128@v2.random> <20080220103942.GU7128@v2.random> <20080220113313.GD11364@sgi.com> <20080220120324.GW7128@v2.random> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080220120324.GW7128@v2.random> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1284 Lines: 24 On Wed, Feb 20, 2008 at 01:03:24PM +0100, Andrea Arcangeli wrote: > If there's agreement that the VM should alter its locking from > spinlock to mutex for its own good, then Christoph's > one-config-option-fits-all becomes a lot more appealing (replacing RCU > with a mutex in the mmu notifier list registration locking isn't my > main worry and the non-sleeping-users may be ok to live with it). Just from a high level view, in some cases we can just say that no we aren't going to support this. And this may well be one of those cases. The more constraints placed on the VM, the harder it becomes to improve and adapt in future. And this seems like a pretty big restriction. (especially if we can eg. work around it completely by having a special purpose driver to get_user_pages on comm buffers as I suggested in the other mail). At any rate, I believe Andrea's patch really places minimal or no further constraints than a regular CPU TLB (or the hash tables that some archs implement). So we're kind of in 2 different leagues here. -- 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/