From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id B877B6B024D for ; Wed, 21 Jul 2010 03:46:00 -0400 (EDT) From: "Shilimkar, Santosh" Date: Wed, 21 Jul 2010 13:15:14 +0530 Subject: RE: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management Message-ID: 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> <20100721072837.GB6009@n2100.arm.linux.org.uk> In-Reply-To: <20100721072837.GB6009@n2100.arm.linux.org.uk> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org To: Russell King - ARM Linux 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" List-ID: > -----Original Message----- > From: Russell King - ARM Linux [mailto:linux@arm.linux.org.uk] > Sent: Wednesday, July 21, 2010 12:59 PM > 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 devic= e > memory management >=20 > 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 >=20 > ************************************************************************* > > > 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. > ************************************************************************* >=20 > > > 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. >=20 > See the first paragraph which I've highlighted above. > Sorry about missing that para Russell. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org