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=-2.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,PDS_BAD_THREAD_QP_64, SPF_HELO_NONE,SPF_PASS 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 9428EC43460 for ; Fri, 16 Apr 2021 07:32:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EE5276117A for ; Fri, 16 Apr 2021 07:32:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EE5276117A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0ED596B0036; Fri, 16 Apr 2021 03:32:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 09EB96B006C; Fri, 16 Apr 2021 03:32:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E804F6B0070; Fri, 16 Apr 2021 03:32:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0184.hostedemail.com [216.40.44.184]) by kanga.kvack.org (Postfix) with ESMTP id CBC5B6B0036 for ; Fri, 16 Apr 2021 03:32:42 -0400 (EDT) Received: from smtpin39.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 8B14618086588 for ; Fri, 16 Apr 2021 07:32:42 +0000 (UTC) X-FDA: 78037412964.39.9A47B47 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by imf19.hostedemail.com (Postfix) with ESMTP id 691AE90009F1 for ; Fri, 16 Apr 2021 07:32:24 +0000 (UTC) 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' CC: Jesper Dangaard Brouer , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mips@vger.kernel.org" , Ilias Apalodimas , Matteo Croce , Grygorii Strashko , Arnd Bergmann , "Christoph Hellwig" 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-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 691AE90009F1 X-Stat-Signature: sefo7n98h1tzkwnoh1noxwm1jb1pcmai Received-SPF: none (aculab.com>: No applicable sender policy available) receiver=imf19; identity=mailfrom; envelope-from=""; helo=eu-smtp-delivery-151.mimecast.com; client-ip=185.58.85.151 X-HE-DKIM-Result: none/none X-HE-Tag: 1618558344-54378 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000617, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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)