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 X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50F91C433FE for ; Fri, 24 Sep 2021 07:33:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 39EFB6103B for ; Fri, 24 Sep 2021 07:33:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244381AbhIXHfa (ORCPT ); Fri, 24 Sep 2021 03:35:30 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:16291 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231921AbhIXHf2 (ORCPT ); Fri, 24 Sep 2021 03:35:28 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.56]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4HG3fV6Yr0z8tQ3; Fri, 24 Sep 2021 15:33:06 +0800 (CST) Received: from dggpemm500005.china.huawei.com (7.185.36.74) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.8; Fri, 24 Sep 2021 15:33:50 +0800 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_CBC_SHA256) id 15.1.2308.8; Fri, 24 Sep 2021 15:33:49 +0800 Subject: Re: [PATCH net-next 3/7] pool_pool: avoid calling compound_head() for skb frag page To: Ilias Apalodimas CC: "David S. Miller" , Jakub Kicinski , Networking , open list , , "Jesper Dangaard Brouer" , Jonathan Lemon , Alexander Lobakin , Willem de Bruijn , Cong Wang , Paolo Abeni , "Kevin Hao" , Aleksandr Nogikh , Marco Elver , , Eric Dumazet , Alexander Duyck , David Ahern References: <20210922094131.15625-1-linyunsheng@huawei.com> <20210922094131.15625-4-linyunsheng@huawei.com> From: Yunsheng Lin Message-ID: <39e62727-6d9f-a0db-39b2-296ebd6972b3@huawei.com> Date: Fri, 24 Sep 2021 15:33:49 +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: dggeme707-chm.china.huawei.com (10.1.199.103) 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 2021/9/23 19:47, Ilias Apalodimas wrote: > On Thu, 23 Sept 2021 at 14:24, Yunsheng Lin wrote: >> >> On 2021/9/23 16:33, Ilias Apalodimas wrote: >>> On Wed, Sep 22, 2021 at 05:41:27PM +0800, Yunsheng Lin wrote: >>>> As the pp page for a skb frag is always a head page, so make >>>> sure skb_pp_recycle() passes a head page to avoid calling >>>> compound_head() for skb frag page case. >>> >>> Doesn't that rely on the driver mostly (i.e what's passed in skb_frag_set_page() ? >>> None of the current netstack code assumes bv_page is the head page of a >>> compound page. Since our page_pool allocator can will allocate compound >>> pages for order > 0, why should we rely on it ? >> >> As the page pool alloc function return 'struct page *' to the caller, which >> is the head page of a compound pages for order > 0, so I assume the caller >> will pass that to skb_frag_set_page(). > > Yea that's exactly the assumption I was afraid of. > Sure not passing the head page might seem weird atm and the assumption > stands, but the point is we shouldn't blow up the entire network stack > if someone does that eventually. > >> >> For non-pp page, I assume it is ok whether the page is a head page or tail >> page, as the pp_magic for both of them are not set with PP_SIGNATURE. > > Yea that's true, although we removed the checking for coalescing > recyclable and non-recyclable SKBs, the next patch first checks the > signature before trying to do anything with the skb. > >> >> Or should we play safe here, and do the trick as skb_free_head() does in >> patch 6? > > I don't think the &1 will even be measurable, so I'd suggest just > dropping this and play safe? I am not sure what does '&1' mean above. The one thing I am not sure about the trick done in patch 6 is that if __page_frag_cache_drain() is right API to use here, I used it because it is the only API that is expecting a head page. > > Cheers > /Ilias >> >>> >>> Thanks >>> /Ilias >>>> >>>> Signed-off-by: Yunsheng Lin >>>> --- >>>> include/linux/skbuff.h | 2 +- >>>> net/core/page_pool.c | 2 -- >>>> 2 files changed, 1 insertion(+), 3 deletions(-) >>>> >>>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h >>>> index 6bdb0db3e825..35eebc2310a5 100644 >>>> --- a/include/linux/skbuff.h >>>> +++ b/include/linux/skbuff.h >>>> @@ -4722,7 +4722,7 @@ static inline bool skb_pp_recycle(struct sk_buff *skb, void *data) >>>> { >>>> if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle) >>>> return false; >>>> - return page_pool_return_skb_page(virt_to_page(data)); >>>> + return page_pool_return_skb_page(virt_to_head_page(data)); >>>> } >>>> >>>> #endif /* __KERNEL__ */ >>>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c >>>> index f7e71dcb6a2e..357fb53343a0 100644 >>>> --- a/net/core/page_pool.c >>>> +++ b/net/core/page_pool.c >>>> @@ -742,8 +742,6 @@ bool page_pool_return_skb_page(struct page *page) >>>> { >>>> struct page_pool *pp; >>>> >>>> - page = compound_head(page); >>>> - >>>> /* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation >>>> * in order to preserve any existing bits, such as bit 0 for the >>>> * head page of compound page and bit 1 for pfmemalloc page, so >>>> -- >>>> 2.33.0 >>>> >>> . >>> > . >