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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 32951C43461 for ; Sat, 17 Apr 2021 21:13:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0FCE761359 for ; Sat, 17 Apr 2021 21:13:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237100AbhDQVOT convert rfc822-to-8bit (ORCPT ); Sat, 17 Apr 2021 17:14:19 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:23816 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237088AbhDQVOR (ORCPT ); Sat, 17 Apr 2021 17:14:17 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-283-C6_jqWz5MbGPOBVz1Qeg8g-1; Sat, 17 Apr 2021 22:13:46 +0100 X-MC-Unique: C6_jqWz5MbGPOBVz1Qeg8g-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; Sat, 17 Apr 2021 22:13:46 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.015; Sat, 17 Apr 2021 22:13:45 +0100 From: David Laight To: "'Matthew Wilcox (Oracle)'" , "brouer@redhat.com" CC: "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@linaro.org" , "mcroce@linux.microsoft.com" , "grygorii.strashko@ti.com" , "arnd@kernel.org" , "hch@lst.de" , "linux-snps-arc@lists.infradead.org" , "mhocko@kernel.org" , "mgorman@suse.de" Subject: RE: [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head Thread-Topic: [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head Thread-Index: AQHXMxVsZdI9ViPPQ0K+FhC9QXmJFqq5NiYw Date: Sat, 17 Apr 2021 21:13:45 +0000 Message-ID: <2a531a42f23e4046833e0feb8faef0b5@AcuMS.aculab.com> References: <20210416230724.2519198-1-willy@infradead.org> <20210416230724.2519198-3-willy@infradead.org> In-Reply-To: <20210416230724.2519198-3-willy@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: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matthew Wilcox (Oracle) > Sent: 17 April 2021 00:07 > > The net page_pool wants to use a magic value to identify page pool pages. > The best place to put it is in the first word where it can be clearly a > non-pointer value. That means shifting dma_addr up to alias with ->index, > which means we need to find another way to indicate page_is_pfmemalloc(). > Since page_pool doesn't want to set its magic value on pages which are > pfmemalloc, we can use bit 1 of compound_head to indicate that the page > came from the memory reserves. > ... > struct { /* page_pool used by netstack */ > - /** > - * @dma_addr: might require a 64-bit value on > - * 32-bit architectures. > - */ > + unsigned long pp_magic; > + unsigned long xmi; > + unsigned long _pp_mapping_pad; > unsigned long dma_addr[2]; > }; You've deleted the comment. I also think there should be a comment that dma_addr[0] must be aliased to ->index. (Or whatever all the exact requirements are.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)