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=-2.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,PDS_BAD_THREAD_QP_64, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 16323C433B4 for ; Fri, 16 Apr 2021 07:33:10 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 459F161153 for ; Fri, 16 Apr 2021 07:33:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 459F161153 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4FM7Gq60gpz30hc for ; Fri, 16 Apr 2021 17:33:07 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=aculab.com (client-ip=185.58.85.151; helo=eu-smtp-delivery-151.mimecast.com; envelope-from=david.laight@aculab.com; receiver=) Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4FM7GQ580lz3000 for ; Fri, 16 Apr 2021 17:32:43 +1000 (AEST) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-212-Pz1ohOP9MbWLWc7zHXrlbA-1; Fri, 16 Apr 2021 08:32:36 +0100 X-MC-Unique: Pz1ohOP9MbWLWc7zHXrlbA-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 16 Apr 2021 08:32:35 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.012; Fri, 16 Apr 2021 08:32:35 +0100 From: David Laight To: 'Matthew Wilcox' Subject: RE: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Thread-Topic: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Thread-Index: AQHXMXYmwdfrgigLI0exh4xFUSZq9Kq0jZ3ggAFYFFmAAC15oIAABLSAgACoXgA= Date: Fri, 16 Apr 2021 07:32:35 +0000 Message-ID: References: <20210411103318.GC2531743@casper.infradead.org> <20210412011532.GG2531743@casper.infradead.org> <20210414101044.19da09df@carbon> <20210414115052.GS2531743@casper.infradead.org> <20210414211322.3799afd4@carbon> <20210414213556.GY2531743@casper.infradead.org> <20210415200832.32796445@carbon> <20210415182155.GD2531743@casper.infradead.org> <5179a01a462f43d6951a65de2a299070@AcuMS.aculab.com> <20210415222211.GG2531743@casper.infradead.org> In-Reply-To: <20210415222211.GG2531743@casper.infradead.org> Accept-Language: en-GB, 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 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Arnd Bergmann , Grygorii Strashko , "netdev@vger.kernel.org" , Ilias Apalodimas , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-mm@kvack.org" , Jesper Dangaard Brouer , Matteo Croce , "linuxppc-dev@lists.ozlabs.org" , Christoph Hellwig , "linux-arm-kernel@lists.infradead.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Matthew Wilcox > Sent: 15 April 2021 23:22 >=20 > On Thu, Apr 15, 2021 at 09:11:56PM +0000, David Laight wrote: > > Isn't it possible to move the field down one long? > > This might require an explicit zero - but this is not a common > > code path - the extra write will be noise. >=20 > Then it overlaps page->mapping. See emails passim. The rules on overlaps make be wonder if every 'long' should be in its own union. The comments would need to say when each field is used. It would, at least, make these errors less common. That doesn't solve the 64bit dma_addr though. Actually rather that word-swapping dma_addr on 32bit BE could you swap over the two fields it overlays with. That might look messy in the .h, but it doesn't require an accessor function to do the swap - easily missed. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)