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[73.241.150.58]) by smtp.gmail.com with ESMTPSA id u24sm25768448pfm.20.2020.08.11.08.35.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Aug 2020 08:35:09 -0700 (PDT) Subject: Re: [PATCH] net: eliminate meaningless memcpy to data in pskb_carve_inside_nonlinear() To: linmiaohe , Eric Dumazet Cc: "davem@davemloft.net" , "kuba@kernel.org" , "pshelar@ovn.org" , "martin.varghese@nokia.com" , "fw@strlen.de" , "dcaratti@redhat.com" , "edumazet@google.com" , "steffen.klassert@secunet.com" , "pabeni@redhat.com" , "shmulik@metanetworks.com" , "kyk.segfault@gmail.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <40a0b4ba22ff499686a2521998767ae5@huawei.com> From: Eric Dumazet Message-ID: <9684c26c-9f26-5a7f-3d17-d180afff432c@gmail.com> Date: Tue, 11 Aug 2020 08:35:07 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <40a0b4ba22ff499686a2521998767ae5@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/11/20 5:10 AM, linmiaohe wrote: > Eric Dumazet wrote: >> On 8/10/20 5:28 AM, Miaohe Lin wrote: >>> The skb_shared_info part of the data is assigned in the following >>> loop. It is meaningless to do a memcpy here. >>> >> >> Reminder : net-next is CLOSED. >> > > Thanks for your remind. I would wait for it open. > >> This is not correct. We still have to copy _something_ >> >> Something like : >> >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 2828f6d5ba898a5e50ccce45589bf1370e474b0f..1c0519426c7ba4b04377fc8054c4223c135879ab 100644 >> --- a/net/core/skbuff.c >> +++ b/net/core/skbuff.c >> @@ -5953,8 +5953,8 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, >> size = SKB_WITH_OVERHEAD(ksize(data)); >> >> memcpy((struct skb_shared_info *)(data + size), >> - skb_shinfo(skb), offsetof(struct skb_shared_info, >> - frags[skb_shinfo(skb)->nr_frags])); >> + skb_shinfo(skb), offsetof(struct skb_shared_info, >> + frags[0])); >> + >> if (skb_orphan_frags(skb, gfp_mask)) { >> kfree(data); >> return -ENOMEM; >> > > This looks good. Will send a patch v2 soon. May I add a suggested-by tag of you ? I would advise not using Suggested-by, as this would imply I suggested the idea of changing this function in the first place. I will add a Reviewed-by: eventually if your v2 submission looks fine to me. Thanks. > Many thanks. >