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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_MED,USER_IN_DEF_DKIM_WL 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 63F12C46462 for ; Mon, 30 Jul 2018 02:28:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02AF720892 for ; Mon, 30 Jul 2018 02:28:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="mSilinzX" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 02AF720892 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com 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 S1725858AbeG3EAe (ORCPT ); Mon, 30 Jul 2018 00:00:34 -0400 Received: from mail-it0-f67.google.com ([209.85.214.67]:51438 "EHLO mail-it0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725756AbeG3EAd (ORCPT ); Mon, 30 Jul 2018 00:00:33 -0400 Received: by mail-it0-f67.google.com with SMTP id e14-v6so15220520itf.1 for ; Sun, 29 Jul 2018 19:27:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=rxrODUfCHY8gwZ3lQcckjgac4zgpf3MBpEqTQqjMots=; b=mSilinzXNY93k0SJSpI6ztZSCB2X+lQyGbZbQ3qWfK4na9Qigum8qqEL2dD0R2jrJM E+y1SRvym7goNL30HcdbTXrEcyeEcj8WdHfUy+vpdohnnqAPCryIYMIKbTHhLRag1P+6 mUyocOi0qhYDpwx/6kA117Z0tIa6mrJbUbjwWj8oX+RHFC8fzmguuju1+SI1cFcfTdhf RyJ+oldvCqg7XUHvjH0oVOdvWRk9zmpLwlFiJvWm+Aeby/iIrq85CAn60LqdoOUxyUHJ XJsoJ0ElryrTnagMVU7NH7RykIGOyJj94aGal3YBNfvT3VV2Ig2HBTXK5EaX8Dp5nEvQ jIOw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=rxrODUfCHY8gwZ3lQcckjgac4zgpf3MBpEqTQqjMots=; b=pQR2dcdyyvysOMi/LW5wokG9LIxQJu3ZS1QH1qzeu2BVvcfIra9V4kg/Z9RyjtnCSW a0FlaKBknjeVQua9lxZniuedxL1wGTwFsI3S+I1kPPQTqpYC9CT1KNqeoo7bQOfQVyub ucmoLSl4eWVKYcD6nLcybYhVyuzfxC8qotsyH7ypCFOlVFQ58qcmdX/KOsSk4pHGtvWc L3wgYEIRlVTQE/XqPcuyr1hsFKoA3UsbOSaNCDc3+08qztqTTSMAXIT1bJPP8YRN0F9z UFl49bIcaCuP7yeqJtolcWjDi1rFUcQG9+zz1TqXeAkmsLWAY7yJ0RMZUNQAxFn6yJ55 xylA== X-Gm-Message-State: AOUpUlFEEnupcXjQBMxNs/m+tp6z5hSYZV5fuMtzxAB0rBlaabxYdS9+ O+ItDmpKwyKq0cwPzykJ4tm/hdipp0JbMPVkidTaeQ== X-Google-Smtp-Source: AAOMgpcQfCpxLxYtt2IugbDjaar+pDLdo0uypDDdnRPLAzPaLTAbmAsplpl5azMd3lyHkhzfAPTgpbFhmkPkHX8sdL8= X-Received: by 2002:a24:6f0e:: with SMTP id x14-v6mr12888363itb.139.1532917670071; Sun, 29 Jul 2018 19:27:50 -0700 (PDT) MIME-Version: 1.0 References: <1532746900-11710-1-git-send-email-laoar.shao@gmail.com> In-Reply-To: From: Eric Dumazet Date: Sun, 29 Jul 2018 19:27:38 -0700 Message-ID: Subject: Re: [PATCH net-next 1/2] tcp: call tcp_drop() in tcp collapse To: Yafang Shao Cc: David Miller , netdev , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 29, 2018 at 7:06 PM Yafang Shao wrote: > > On Sun, Jul 29, 2018 at 12:28 AM, Eric Dumazet wrote: > > On Sat, Jul 28, 2018 at 12:43 AM Yafang Shao wrote: > >> > >> On Sat, Jul 28, 2018 at 11:38 AM, Eric Dumazet wrote: > >> > On Fri, Jul 27, 2018 at 8:35 PM Yafang Shao wrote: > >> > > >> >> So what about LINUX_MIB_TCPOFOMERGE ? > >> >> Regarding LINUX_MIB_TCPOFOMERGE, a skb is already covered by another > >> >> skb, is that dropping the packet or simply lowering the memory > >> >> overhead ? > >> > > >> > What do you think ? > >> > > >> > If you receive two times the same payload, don't you have to drop one > >> > of the duplicate ? > >> > > >> > There is a a big difference between the two cases. > >> > >> If the drop caused some data lost (which may then cause retransmition > >> or something), then this is a really DROP. > >> While if the drop won't cause any data lost, meaning it is a > >> non-harmful behavior, I think it should not be defined as DROP. > >> This is my suggestion anyway. > > > > Sigh. > > > > We count drops, not because they are ' bad or something went wrong'. > > > > If TCP stack receives twice the same sequence (same payload), we > > _drop_ one of the duplicate, so we account for this event. > > > > When ' collapsing' we reorganize our own storage, not because we have > > to drop a payload, > > but for some memory pressure reason. > > Thanks for you clarification. > So what about LINUX_MIB_TCPOFODROP ? > > if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) { > NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP); > tcp_drop(sk, skb); > return; > } > > > It is also because of our own memory pressure, but we call tcp_drop() here. Yes, we _drop_ a packet. That is pretty clear that the payload is dropped, and that the sender will have to _retransmit_. > > I am not mean to disagree with you. I am just confused and want to > make it clear. Collapsing is : For (a bunch of packets) Try (to compress them in order to reduce memory overhead) No drop of payload happens here. Sender wont have to retransmit.