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 59BC1EB64DA for ; Wed, 14 Jun 2023 11:55:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236408AbjFNLzh (ORCPT ); Wed, 14 Jun 2023 07:55:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244496AbjFNLzY (ORCPT ); Wed, 14 Jun 2023 07:55:24 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 053961BF3; Wed, 14 Jun 2023 04:55:23 -0700 (PDT) Received: from dggpemm500005.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Qh3hM3SHRztQq3; Wed, 14 Jun 2023 19:52:51 +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 15.1.2507.23; Wed, 14 Jun 2023 19:55:20 +0800 Subject: Re: [PATCH net-next v4 2/5] page_pool: unify frag_count handling in page_pool_is_last_frag() To: Jakub Kicinski CC: , , , , Lorenzo Bianconi , Alexander Duyck , Jesper Dangaard Brouer , Ilias Apalodimas , Eric Dumazet References: <20230612130256.4572-1-linyunsheng@huawei.com> <20230612130256.4572-3-linyunsheng@huawei.com> <20230613213317.4eb4be7c@kernel.org> From: Yunsheng Lin Message-ID: <84100dd1-b005-5b03-fe3e-838a08640b8e@huawei.com> Date: Wed, 14 Jun 2023 19:55:20 +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: <20230613213317.4eb4be7c@kernel.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) 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 2023/6/14 12:33, Jakub Kicinski wrote: > On Mon, 12 Jun 2023 21:02:53 +0800 Yunsheng Lin wrote: >> static inline void page_pool_fragment_page(struct page *page, long nr) >> { >> - atomic_long_set(&page->pp_frag_count, nr); >> + if (!PAGE_POOL_DMA_USE_PP_FRAG_COUNT) >> + atomic_long_set(&page->pp_frag_count, nr); > > why not let the driver take references on the page count in this case? > I'm not saying it's worth the effort, but a comment may be useful? I suppose page count refers to page->_refcount, right? Page pool can only hold one reference for page->_refcount, so that it can use that to decide if the netstack or other subsystem have taken additional reference on that page in __page_pool_put_page(): https://elixir.bootlin.com/linux/v6.4-rc6/source/net/core/page_pool.c#L591 > >> diff --git a/net/core/page_pool.c b/net/core/page_pool.c >> index 9c4118c62997..69e3c5175236 100644 >> --- a/net/core/page_pool.c >> +++ b/net/core/page_pool.c >> @@ -352,6 +352,14 @@ static void page_pool_set_pp_info(struct page_pool *pool, >> { >> page->pp = pool; >> page->pp_magic |= PP_SIGNATURE; >> + >> + /* Ensuring all pages have been split into one big frag initially: > > Again, I find the "one big frag" slightly confusing. > Maybe we should rename pp_frag_cnt into pp_refcnt? > After this series is looks even more like a page pool reference > count rather than some form of number of fragments. It depends on how you look at it, perhaps we can see page->pp_frag_count being one as the page being split into one frag? Using pp_refcnt may cause confusing for cases in page_pool_alloc_frag(). > >> + * page_pool_set_pp_info() is only called once for every page when it >> + * is allocated from the page allocator and page_pool_fragment_page() >> + * is dirtying the same cache line as the page->pp_magic above, so >> + * the overhead is negligible. >> + */ >> + page_pool_fragment_page(page, 1); >> if (pool->p.init_callback) >> pool->p.init_callback(page, pool->p.init_arg); >> } > > > . >