From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756110Ab3AQJLd (ORCPT ); Thu, 17 Jan 2013 04:11:33 -0500 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:56295 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755213Ab3AQJLZ (ORCPT ); Thu, 17 Jan 2013 04:11:25 -0500 Message-ID: <1358413880.2394.7.camel@dabdike.int.hansenpartnership.com> Subject: Re: [PATCH v2 1/1] block: blk-merge: don't merge the pages with non-contiguous descriptors From: James Bottomley To: Tejun Heo Cc: Subhash Jadavani , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-mmc@vger.kernel.org, linux-arm-msm@vger.kernel.org, martin.petersen@oracle.com, asias@redhat.com, linux-arm-kernel@lists.infradead.org, Russell King Date: Thu, 17 Jan 2013 09:11:20 +0000 In-Reply-To: <20130116231857.GU2668@htj.dyndns.org> References: <1358265681-25671-1-git-send-email-subhashj@codeaurora.org> <1358266794.10591.8.camel@dabdike.int.hansenpartnership.com> <50F64AC1.3040304@codeaurora.org> <1358332355.2384.11.camel@dabdike.int.hansenpartnership.com> <20130116231857.GU2668@htj.dyndns.org> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.6.2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-01-16 at 15:18 -0800, Tejun Heo wrote: > On Wed, Jan 16, 2013 at 10:32:35AM +0000, James Bottomley wrote: > > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c > > index 6b2fb87..ab88c5b 100644 > > --- a/arch/arm/mm/dma-mapping.c > > +++ b/arch/arm/mm/dma-mapping.c > > @@ -809,7 +809,7 @@ static void dma_cache_maint_page(struct page *page, unsigned long offset, > > op(vaddr, len, dir); > > } > > offset = 0; > > - page++; > > + page = pfn_to_page(page_to_pfn(page) + 1); > > Probably page = nth_page(page, 1) is the better form. It's the same thing. I'd actually prefer page = pfn_to_page(page_to_pfn(page) + 1); because it makes the code look like the hack it is. The preferred form for all iterators like this should be to iterate over the pfn instead of a pointer into the page arrays, because that will always work correctly no matter how many weird and wonderful memory schemes we come up with. James