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 59521C41513 for ; Wed, 16 Aug 2023 12:50:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245318AbjHPMuF (ORCPT ); Wed, 16 Aug 2023 08:50:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43398 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245327AbjHPMti (ORCPT ); Wed, 16 Aug 2023 08:49:38 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1DBE026B8; Wed, 16 Aug 2023 05:49:22 -0700 (PDT) Received: from dggpemm500005.china.huawei.com (unknown [172.30.72.56]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4RQnv22WG4zFqgH; Wed, 16 Aug 2023 20:46:22 +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; Wed, 16 Aug 2023 20:49:19 +0800 Subject: Re: [PATCH net-next v6 1/6] page_pool: frag API support for 32-bit arch with 64-bit DMA To: Ilias Apalodimas CC: , , , , , Lorenzo Bianconi , Alexander Duyck , Liang Chen , Alexander Lobakin , Saeed Mahameed , Leon Romanovsky , Eric Dumazet , Jesper Dangaard Brouer , References: <20230814125643.59334-1-linyunsheng@huawei.com> <20230814125643.59334-2-linyunsheng@huawei.com> From: Yunsheng Lin Message-ID: <06e89203-9eaf-99eb-99de-e5209819b8b3@huawei.com> Date: Wed, 16 Aug 2023 20:49:19 +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: dggems701-chm.china.huawei.com (10.3.19.178) 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 2023/8/16 19:26, Ilias Apalodimas wrote: > Hi Yunsheng > > On Mon, 14 Aug 2023 at 15:59, Yunsheng Lin wrote: >> >> Currently page_pool_alloc_frag() is not supported in 32-bit >> arch with 64-bit DMA because of the overlap issue between >> pp_frag_count and dma_addr_upper in 'struct page' for those >> arches, which seems to be quite common, see [1], which means >> driver may need to handle it when using frag API. > > That wasn't so common. IIRC it was a single TI platform that was breaking? I am not so sure about that as grepping 'ARM_LPAE' has a long list for that. > >> >> In order to simplify the driver's work when using frag API >> this patch allows page_pool_alloc_frag() to call >> page_pool_alloc_pages() to return pages for those arches. > > Do we have any use cases of people needing this? Those architectures > should be long dead and although we have to support them in the > kernel, I don't personally see the advantage of adjusting the API to > do that. Right now we have a very clear separation between allocating > pages or fragments. Why should we hide a page allocation under a > frag allocation? A driver writer can simply allocate pages for those > boards. Am I the only one not seeing a clean win here? It is also a part of removing the per page_pool PP_FLAG_PAGE_FRAG flag in this patchset. > > Thanks > /Ilias >