From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762777Ab0GUH3i (ORCPT ); Wed, 21 Jul 2010 03:29:38 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:51094 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762749Ab0GUH3f (ORCPT ); Wed, 21 Jul 2010 03:29:35 -0400 Date: Wed, 21 Jul 2010 08:28:37 +0100 From: Russell King - ARM Linux To: "Shilimkar, Santosh" Cc: "stepanm@codeaurora.org" , "linux-arch@vger.kernel.org" , "dwalker@codeaurora.org" , "mel@csn.ul.ie" , "linux-arm-msm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , FUJITA Tomonori , "linux-mm@kvack.org" , "andi@firstfloor.org" , Zach Pfeffer , Michael Bohan , Tim HRM , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "ebiederm@xmission.com" Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management Message-ID: <20100721072837.GB6009@n2100.arm.linux.org.uk> References: <20100714220536.GE18138@n2100.arm.linux.org.uk> <20100715012958.GB2239@codeaurora.org> <20100715085535.GC26212@n2100.arm.linux.org.uk> <20100716075856.GC16124@n2100.arm.linux.org.uk> <4C449183.20000@codeaurora.org> <20100719184002.GA21608@n2100.arm.linux.org.uk> <20100720222952.GD10553@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 21, 2010 at 11:19:58AM +0530, Shilimkar, Santosh wrote: > > -----Original Message----- > > From: linux-arm-kernel-bounces@lists.infradead.org [mailto:linux-arm- > > kernel-bounces@lists.infradead.org] On Behalf Of Russell King - ARM Linux > > Sent: Wednesday, July 21, 2010 4:00 AM > > To: stepanm@codeaurora.org > > Cc: linux-arch@vger.kernel.org; dwalker@codeaurora.org; mel@csn.ul.ie; > > linux-arm-msm@vger.kernel.org; linux-kernel@vger.kernel.org; FUJITA > > Tomonori; linux-mm@kvack.org; andi@firstfloor.org; Zach Pfeffer; Michael > > Bohan; Tim HRM; linux-omap@vger.kernel.org; linux-arm- > > kernel@lists.infradead.org; ebiederm@xmission.com > > Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device > > memory management ************************************************************************* > > This is difficult to achieve without remapping kernel memory using L2 > > page tables, so we can unmap pages on 4K page granularity. That's > > going to increase TLB overhead and result in lower system performance > > as there'll be a greater number of MMU misses. ************************************************************************* > > However, one obvious case would be to use highmem-only pages for > > remapping - but you then have to ensure that those pages are never > > kmapped in any way, because those mappings will fall into the same > > unpredictable category that we're already trying to avoid. This > > may be possible, but you'll have to ensure that most of the system > > RAM is in highmem - which poses other problems (eg, if lowmem gets > > low.) > > Why can't we consider an option of removing the old mappings when > we need to create new ones with different attributes as suggested > by Catalin on similar thread previously. This will avoid the duplicate > mapping with different attributes issue on newer ARMs. See the first paragraph which I've highlighted above.