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 B678FEB64D8 for ; Wed, 14 Jun 2023 03:51:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241942AbjFNDv6 (ORCPT ); Tue, 13 Jun 2023 23:51:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231937AbjFNDvy (ORCPT ); Tue, 13 Jun 2023 23:51:54 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C943EC3; Tue, 13 Jun 2023 20:51:53 -0700 (PDT) Received: from dggpemm500005.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QgryV6Hk2ztQdJ; Wed, 14 Jun 2023 11:49:22 +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 15.1.2507.23; Wed, 14 Jun 2023 11:51:51 +0800 Subject: Re: [PATCH net-next v3 3/4] page_pool: introduce page_pool_alloc() API To: Alexander Duyck CC: , , , , , Lorenzo Bianconi , Jesper Dangaard Brouer , Ilias Apalodimas , Eric Dumazet References: <20230609131740.7496-1-linyunsheng@huawei.com> <20230609131740.7496-4-linyunsheng@huawei.com> From: Yunsheng Lin Message-ID: <36366741-8df2-1137-0dd9-d498d0f770e4@huawei.com> Date: Wed, 14 Jun 2023 11:51:51 +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: 8bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) 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 2023/6/13 22:36, Alexander Duyck wrote: > On Fri, Jun 9, 2023 at 6:20 AM Yunsheng Lin wrote: ... >> >> +static inline struct page *page_pool_alloc(struct page_pool *pool, >> + unsigned int *offset, >> + unsigned int *size, gfp_t gfp) >> +{ >> + unsigned int max_size = PAGE_SIZE << pool->p.order; >> + struct page *page; >> + >> + *size = ALIGN(*size, dma_get_cache_alignment()); >> + >> + if (WARN_ON(*size > max_size)) >> + return NULL; >> + >> + if ((*size << 1) > max_size || PAGE_POOL_DMA_USE_PP_FRAG_COUNT) { >> + *size = max_size; >> + *offset = 0; >> + return page_pool_alloc_pages(pool, gfp); >> + } >> + >> + page = __page_pool_alloc_frag(pool, offset, *size, gfp); >> + if (unlikely(!page)) >> + return NULL; >> + >> + /* There is very likely not enough space for another frag, so append the >> + * remaining size to the current frag to avoid truesize underestimate >> + * problem. >> + */ >> + if (pool->frag_offset + *size > max_size) { >> + *size = max_size - *offset; >> + pool->frag_offset = max_size; >> + } >> + > > Rather than preventing a truesize underestimation this will cause one. > You are adding memory to the size of the page reserved and not > accounting for it anywhere as this isn't reported up to the network > stack. I would suggest dropping this from your patch. I was thinking about the driver author reporting it up to the network stack using the new API as something like below: int truesize = size; struct page *page; int offset; page = page_pool_dev_alloc(pool, &offset, &truesize); if (unlikely(!page)) goto err; skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset, size, truesize); and similiar handling for *_build_skb() case too. Does it make senses for that? or did I miss something obvious here? >