From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 63B0BC31E4B for ; Fri, 14 Jun 2019 15:01:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 45D7621537 for ; Fri, 14 Jun 2019 15:01:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726599AbfFNPB2 convert rfc822-to-8bit (ORCPT ); Fri, 14 Jun 2019 11:01:28 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:40564 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725812AbfFNPB2 (ORCPT ); Fri, 14 Jun 2019 11:01:28 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-6-Ae-vvi9EMKOPr28p6sbQQA-1; Fri, 14 Jun 2019 16:01:23 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b::d117) by AcuMS.aculab.com (fd9f:af1c:a25b::d117) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 14 Jun 2019 16:01:22 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 14 Jun 2019 16:01:22 +0100 From: David Laight To: 'Christoph Hellwig' CC: Maarten Lankhorst , Maxime Ripard , Sean Paul , David Airlie , Daniel Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , "Ian Abbott" , H Hartley Sweeten , Intel Linux Wireless , "moderated list:ARM PORT" , "dri-devel@lists.freedesktop.org" , "intel-gfx@lists.freedesktop.org" , "linux-rdma@vger.kernel.org" , "linux-media@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linux-s390@vger.kernel.org" , "devel@driverdev.osuosl.org" , "linux-mm@kvack.org" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH 16/16] dma-mapping: use exact allocation in dma_alloc_contiguous Thread-Topic: [PATCH 16/16] dma-mapping: use exact allocation in dma_alloc_contiguous Thread-Index: AQHVIrfpTFjppS25RkWUhwqPPyqZ4qabLzdw///7eICAABIeYA== Date: Fri, 14 Jun 2019 15:01:22 +0000 Message-ID: References: <20190614134726.3827-1-hch@lst.de> <20190614134726.3827-17-hch@lst.de> <20190614145001.GB9088@lst.de> In-Reply-To: <20190614145001.GB9088@lst.de> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: Ae-vvi9EMKOPr28p6sbQQA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org From: 'Christoph Hellwig' > Sent: 14 June 2019 15:50 > To: David Laight > On Fri, Jun 14, 2019 at 02:15:44PM +0000, David Laight wrote: > > Does this still guarantee that requests for 16k will not cross a 16k boundary? > > It looks like you are losing the alignment parameter. > > The DMA API never gave you alignment guarantees to start with, > and you can get not naturally aligned memory from many of our > current implementations. Hmmm... I thought that was even documented. I'm pretty sure there is a lot of code out there that makes that assumption. Without it many drivers will have to allocate almost double the amount of memory they actually need in order to get the required alignment. So instead of saving memory you'll actually make more be used. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)