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 E258EC2FC18 for ; Thu, 17 Aug 2023 09:06:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349281AbjHQJGE (ORCPT ); Thu, 17 Aug 2023 05:06:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57722 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349328AbjHQJFt (ORCPT ); Thu, 17 Aug 2023 05:05:49 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7871E7C; Thu, 17 Aug 2023 02:05:47 -0700 (PDT) Received: from dggpemm500005.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4RRJtZ5Mj7zFr28; Thu, 17 Aug 2023 17:02:46 +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; Thu, 17 Aug 2023 17:05:45 +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> <06e89203-9eaf-99eb-99de-e5209819b8b3@huawei.com> From: Yunsheng Lin Message-ID: Date: Thu, 17 Aug 2023 17:05:38 +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: dggems704-chm.china.huawei.com (10.3.19.181) 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 2023/8/17 1:01, Ilias Apalodimas wrote: > On Wed, 16 Aug 2023 at 15:49, Yunsheng Lin wrote: >> >> 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. > > Shouldn't we be grepping for CONFIG_ARCH_DMA_ADDR_T_64BIT and > PHYS_ADDR_T_64BIT to find the affected platforms? Why LPAE? I used the key in the original report: https://www.spinics.net/lists/netdev/msg779890.html >> Please see the bisection report below about a boot failure on >> rk3288-rock2-square which is pointing to this patch. The issue >> appears to only happen with CONFIG_ARM_LPAE=y. grepping the 'CONFIG_PHYS_ADDR_T_64BIT' seems to be more common? https://elixir.free-electrons.com/linux/v6.4-rc6/K/ident/CONFIG_PHYS_ADDR_T_64BIT > >> >>> >>>> >>>> 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. > > Yes, that happens *because* of this patchset. I am not against the > change. In fact, I'll have a closer look tomorrow. I am just trying > to figure out if we really need it. When the recycling patches were > introduced into page pool we had a very specific reason. Due to the > XDP verifier we *had* to allocate a packet per page. That was Did you mean a xdp frame containing a frag page can not be passed to the xdp core? What is exact reason why the XDP verifier need a packet per page? Is there a code block that you can point me to? I wonder if it is still the case for now, as bnxt and mlx5 seems to be supporting frag page and xdp now. > expensive so we added the recycling capabilities to compensate and get > some performance back. Eventually we added page fragments and had a > very clear separation on the API. > > Regards > /Ilias >> >>> >>> Thanks >>> /Ilias >>> > . >