From patchwork Thu Apr 1 03:13:36 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matt Corallo X-Patchwork-Id: 12177017 X-Patchwork-Delegate: kuba@kernel.org 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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,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 76B39C433ED for ; Thu, 1 Apr 2021 03:15:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22A09600D1 for ; Thu, 1 Apr 2021 03:15:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232763AbhDADO4 (ORCPT ); Wed, 31 Mar 2021 23:14:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232994AbhDADOl (ORCPT ); Wed, 31 Mar 2021 23:14:41 -0400 X-Greylist: delayed 61 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Wed, 31 Mar 2021 20:14:41 PDT Received: from mail.as397444.net (mail.as397444.net [IPv6:2620:6e:a000:dead:beef:15:bad:f00d]) by lindbergh.monkeyblade.net (Postfix) with UTF8SMTPS id 2324FC0613E6 for ; Wed, 31 Mar 2021 20:14:41 -0700 (PDT) Received: by mail.as397444.net (Postfix) with UTF8SMTPSA id 9870450AC2E for ; Thu, 1 Apr 2021 03:13:36 +0000 (UTC) X-DKIM-Note: Keys used to sign are likely public at https://as397444.net/dkim/ DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bluematt.me; s=1617244862; t=1617246816; bh=xN/rVOY63VaNmaYocf9pUPpZ5ZOM5G3OiapUGD3CPIo=; h=Date:To:From:Subject:From; b=laVL7Z6o6rEgV5kbOQ92F9wD5H2KlPnNyvdOz0P5gbFpuTLWntzlf2lAvUeaQ7atV jlcsijd+nQevWVe9L01lWZmffZGNW8Ue5f/V2HOjq6WEB+evwrGWTSjAVarTX9JtBf nHYmnq/nYxup6F8DB/qy3u/+f6nFsVsjIr0/FpLdi80GvQDJS6eA86TAnfk08NAZrD bOy5XKu6D9ITVqZhR9K+202I9PW4KyJJNRFbonj5FtDAVYH+IFHYMmEVYkvvy1KbkK 4lPvxQW9xGlPESglfITRM4NZhVVlfl0HDXem8o85XLwo+eYHbZBGQNxeTMfwtyiPwo pU/Ulf6PPc57A== Message-ID: <5d8c685d-471c-852c-46bd-f0c80f82e416@bluematt.me> Date: Wed, 31 Mar 2021 23:13:36 -0400 MIME-Version: 1.0 Content-Language: en-US To: "netdev@vger.kernel.org" From: Matt Corallo Subject: [PATCH] Reduce IP_FRAG_TIME fragment-reassembly timeout to 1s, from 30s Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org The default IP reassembly timeout of 30 seconds predates git history (and cursory web searches turn up nothing related to it). The only relevant source cited in net/ipv4/ip_fragment.c is RFC 791 defining IPv4 in 1981. RFC 791 suggests allowing the timer to increase on the receipt of each fragment (which Linux deliberately does not do), with a default timeout for each fragment of 15 seconds. It suggests 15s to cap a 10Kb/s flow to a 150Kb buffer of fragments. When Linux receives a fragment, if the total memory used for the fragment reassembly buffer (across all hosts) exceeds net.ipv4.ipfrag_high_thresh (or the equivalent for IPv6), it silently drops all future fragments fragments until the timers on the original expire. All the way in 2021, these numbers feel almost comical. The default buffer size for fragmentation reassembly is hard-coded at 4MiB as `net->ipv4.fqdir->high_thresh = 4 * 1024 * 1024;` capping a host at 1.06Mb/s of lost fragments before all fragments received on the host are dropped (with independent limits for IPv6). Reducing the default fragment timeout to 1sec gives us 32Mb/s of fragments before we drop all fragments, which is certainly more in line with today's network speeds than 1.06Mb/s, though an optimal value may be still lower. Sadly, reducing it further requires a change to the sysctl interface, as net.ipv4.ipfrag_time is only specified in seconds. --- include/net/ip.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/ip.h b/include/net/ip.h index 2d6b985d11cc..f1473ac5a27c 100644 --- a/include/net/ip.h +++ b/include/net/ip.h @@ -135,7 +135,7 @@ struct ip_ra_chain { #define IP_MF 0x2000 /* Flag: "More Fragments" */ #define IP_OFFSET 0x1FFF /* "Fragment Offset" part */ -#define IP_FRAG_TIME (30 * HZ) /* fragment lifetime */ +#define IP_FRAG_TIME (1 * HZ) /* fragment lifetime */ struct msghdr; struct net_device;