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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 B90DDC46471 for ; Mon, 6 Aug 2018 20:41:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 404B6217B7 for ; Mon, 6 Aug 2018 20:41:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 404B6217B7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=davemloft.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732945AbeHFWwD (ORCPT ); Mon, 6 Aug 2018 18:52:03 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:57858 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731432AbeHFWwD (ORCPT ); Mon, 6 Aug 2018 18:52:03 -0400 Received: from localhost (71-36-117-41.ptld.qwest.net [71.36.117.41]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 6174C136A4AA3; Mon, 6 Aug 2018 13:41:17 -0700 (PDT) Date: Mon, 06 Aug 2018 13:41:16 -0700 (PDT) Message-Id: <20180806.134116.1016660959593702560.davem@davemloft.net> To: laoar.shao@gmail.com Cc: edumazet@google.com, yanhaishuang@cmss.chinamobile.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next] tcp: fix the calculation of sysctl_max_tw_buckets in tcp_sk_init() From: David Miller In-Reply-To: <1533556020-20778-1-git-send-email-laoar.shao@gmail.com> References: <1533556020-20778-1-git-send-email-laoar.shao@gmail.com> X-Mailer: Mew version 6.7 on Emacs 26 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Mon, 06 Aug 2018 13:41:17 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yafang Shao Date: Mon, 6 Aug 2018 19:47:00 +0800 > tcp_hashinfo.ehash_mask is always an odd number, which is set in function > alloc_large_system_hash(). See bellow, > if (_hash_mask) > *_hash_mask = (1 << log2qty) - 1; <<< always odd number > > Hence the local variable 'cnt' is a even number, as a result of that it is > no difference to do the incrementation here. > > Maybe the compiler could also optimize it, but this code is a little ugly. > > Fix: fee83d09 ("ipv4: Namespaceify tcp_max_syn_backlog knob") The correct tag is "Fixes: " > @@ -2543,7 +2543,7 @@ static int __net_init tcp_sk_init(struct net *net) > net->ipv4.sysctl_tcp_tw_reuse = 2; > > cnt = tcp_hashinfo.ehash_mask + 1; > - net->ipv4.tcp_death_row.sysctl_max_tw_buckets = (cnt + 1) / 2; > + net->ipv4.tcp_death_row.sysctl_max_tw_buckets = cnt / 2; > net->ipv4.tcp_death_row.hashinfo = &tcp_hashinfo; This is completely harmless, and does no harm. You aren't "fixing" anything.