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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 6788BC433B4 for ; Thu, 13 May 2021 02:15:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E24361108 for ; Thu, 13 May 2021 02:15:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230037AbhEMCQm (ORCPT ); Wed, 12 May 2021 22:16:42 -0400 Received: from szxga08-in.huawei.com ([45.249.212.255]:2305 "EHLO szxga08-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229630AbhEMCQm (ORCPT ); Wed, 12 May 2021 22:16:42 -0400 Received: from dggeml718-chm.china.huawei.com (unknown [172.30.72.55]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4FgZrx48RSz19PSm; Thu, 13 May 2021 10:11:13 +0800 (CST) Received: from dggpemm500005.china.huawei.com (7.185.36.74) by dggeml718-chm.china.huawei.com (10.3.17.129) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Thu, 13 May 2021 10:15:27 +0800 Received: from [127.0.0.1] (10.69.30.204) by dggpemm500005.china.huawei.com (7.185.36.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Thu, 13 May 2021 10:15:27 +0800 Subject: Re: [PATCH net-next v4 1/4] mm: add a signature in struct page To: Matthew Wilcox , Ilias Apalodimas CC: Matteo Croce , Networking , Linux-MM , Ayush Sawal , Vinay Kumar Yadav , "Rohit Maheshwari" , "David S. Miller" , Jakub Kicinski , Thomas Petazzoni , Marcin Wojtas , Russell King , Mirko Lindner , "Stephen Hemminger" , Tariq Toukan , Jesper Dangaard Brouer , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Boris Pismenny , Arnd Bergmann , Andrew Morton , "Peter Zijlstra (Intel)" , Vlastimil Babka , Yu Zhao , Will Deacon , Michel Lespinasse , Fenghua Yu , Roman Gushchin , Hugh Dickins , Peter Xu , Jason Gunthorpe , Jonathan Lemon , Alexander Lobakin , Cong Wang , wenxu , Kevin Hao , Jakub Sitnicki , Marco Elver , Willem de Bruijn , Miaohe Lin , Guillaume Nault , open list , , bpf , Eric Dumazet , David Ahern , Lorenzo Bianconi , Saeed Mahameed , Andrew Lunn , Paolo Abeni , Sven Auhagen References: <20210511133118.15012-1-mcroce@linux.microsoft.com> <20210511133118.15012-2-mcroce@linux.microsoft.com> From: Yunsheng Lin Message-ID: <3f9a0fb0-9cb9-686d-e89b-ea589d88ab58@huawei.com> Date: Thu, 13 May 2021 10:15:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggeme716-chm.china.huawei.com (10.1.199.112) To dggpemm500005.china.huawei.com (7.185.36.74) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2021/5/12 23:57, Matthew Wilcox wrote: > On Tue, May 11, 2021 at 05:25:36PM +0300, Ilias Apalodimas wrote: >> Nope not at all, either would work. we'll switch to that > > You'll need something like this because of the current use of > page->index to mean "pfmemalloc". > >>>From ecd6d912056a21bbe55d997c01f96b0b8b9fbc31 Mon Sep 17 00:00:00 2001 > From: "Matthew Wilcox (Oracle)" > Date: Fri, 16 Apr 2021 18:12:33 -0400 > Subject: [PATCH] mm: Indicate pfmemalloc pages in compound_head > > 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. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > include/linux/mm.h | 12 +++++++----- > include/linux/mm_types.h | 7 +++---- > 2 files changed, 10 insertions(+), 9 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index bd21864449bf..4f9b2007efad 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1670,10 +1670,12 @@ struct address_space *page_mapping(struct page *page); > static inline bool page_is_pfmemalloc(const struct page *page) > { > /* > - * Page index cannot be this large so this must be > - * a pfmemalloc page. > + * This is not a tail page; compound_head of a head page is unused > + * at return from the page allocator, and will be overwritten > + * by callers who do not care whether the page came from the > + * reserves. > */ > - return page->index == -1UL; > + return page->compound_head & 2; > } > > /* > @@ -1682,12 +1684,12 @@ static inline bool page_is_pfmemalloc(const struct page *page) > */ > static inline void set_page_pfmemalloc(struct page *page) > { > - page->index = -1UL; > + page->compound_head = 2; Is there any reason why not use "page->compound_head |= 2"? as corresponding to the "page->compound_head & 2" in the above page_is_pfmemalloc()? Also, this may mean we need to make sure to pass head page or base page to set_page_pfmemalloc() if using "page->compound_head = 2", because it clears the bit 0 and head page ptr for tail page too, right? > } > > static inline void clear_page_pfmemalloc(struct page *page) > { > - page->index = 0; > + page->compound_head = 0; > } > > /* > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 5aacc1c10a45..1352e278939b 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -96,10 +96,9 @@ struct page { > unsigned long private; > }; > struct { /* page_pool used by netstack */ > - /** > - * @dma_addr: might require a 64-bit value on > - * 32-bit architectures. > - */ > + unsigned long pp_magic; > + struct page_pool *pp; > + unsigned long _pp_mapping_pad; > unsigned long dma_addr[2]; It seems the dma_addr[1] aliases with page->private, and page_private() is used in skb_copy_ubufs()? It seems we can avoid using page_private() in skb_copy_ubufs() by using a dynamic allocated array to store the page ptr? > }; > struct { /* slab, slob and slub */ >