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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16007C072A2 for ; Fri, 17 Nov 2023 11:27:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345739AbjKQL1y (ORCPT ); Fri, 17 Nov 2023 06:27:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230051AbjKQL1w (ORCPT ); Fri, 17 Nov 2023 06:27:52 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9575CA6; Fri, 17 Nov 2023 03:27:48 -0800 (PST) Received: from dggpemm500005.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4SWvfX5qpSzNnw5; Fri, 17 Nov 2023 19:23:32 +0800 (CST) Received: from [10.69.30.204] (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_GCM_SHA256) id 15.1.2507.31; Fri, 17 Nov 2023 19:27:46 +0800 Subject: Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider To: David Ahern , Jason Gunthorpe , Mina Almasry CC: Jakub Kicinski , , , , , Willem de Bruijn , Kaiyuan Zhang , Jesper Dangaard Brouer , Ilias Apalodimas , Eric Dumazet , =?UTF-8?Q?Christian_K=c3=b6nig?= , Matthew Wilcox , Linux-MM References: <20231113130041.58124-1-linyunsheng@huawei.com> <20231113130041.58124-4-linyunsheng@huawei.com> <20231113180554.1d1c6b1a@kernel.org> <0c39bd57-5d67-3255-9da2-3f3194ee5a66@huawei.com> <15c404e4-8efa-cc1c-174f-0752005b6755@huawei.com> From: Yunsheng Lin Message-ID: Date: Fri, 17 Nov 2023 19:27:45 +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: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500005.china.huawei.com (7.185.36.74) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/11/16 23:58, David Ahern wrote: > On 11/16/23 4:12 AM, Yunsheng Lin wrote: >> On 2023/11/16 1:57, David Ahern wrote: >>> On 11/15/23 2:21 AM, Yunsheng Lin wrote: >>>> On 2023/11/14 21:16, Jason Gunthorpe wrote: >>>>> On Tue, Nov 14, 2023 at 04:21:26AM -0800, Mina Almasry wrote: >>>>> >>>>>> Actually because you put the 'strtuct page for devmem' in >>>>>> skb->bv_frag, the net stack will grab the 'struct page' for devmem >>>>>> using skb_frag_page() then call things like page_address(), kmap, >>>>>> get_page, put_page, etc, etc, etc. >>>>> >>>>> Yikes, please no. If net has its own struct page look alike it has to >>>>> stay entirely inside net. A non-mm owned struct page should not be >>>>> passed into mm calls. It is just way too hacky to be seriously >>>>> considered :( >>>> >>>> Yes, that is something this patchset is trying to do, defining its own >>>> struct page look alike for page pool to support devmem. >>>> >>> >>> Networking needs to be able to move away from struct page references. >>> The devmem and host memory for Rx use cases do not need to be page based. >> >> Yes, I am agreed the ultimate goal is to move away from struct page >> references. But I am not sure if we can do it right away as there >> still are different types of existing 'struct page' in the netstack, >> see: >> >> https://lore.kernel.org/all/8b7d25eb-1f10-3e37-8753-92b42da3fb34@huawei.com/ > > yes, that is the point of a blended approach -- pages and buffers (or > iov) -- leveraging the LSB of the address. That proposal is the right I am not sure leveraging the LSB of the address is necessary yet, as it does not seems to provide the type check protection, it seems to just provide a way to demux between pages(including page pool owned page and non-page pool owned page) and page pool owned buffer. That info is avaliable through the page->pp_magic and page->pp->mp_* too if we mirror the page pool specific union in 'struct page'. > direction to be moving for co-existence. Adding fake struct page > instances is the wrong direction. Perhaps a fake struct page with type check protection is the right direction? Intergrating devmem to page pool without a unified metadata between pages and buffers or without a proper abstract layer does not seems like the good direction either. > . >