From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: TCP many-connection regression between 4.7 and 4.13 kernels. Date: Mon, 22 Jan 2018 10:16:06 -0800 Message-ID: <1516644966.3478.10.camel@gmail.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit To: Ben Greear , netdev Return-path: Received: from mail-pf0-f182.google.com ([209.85.192.182]:44466 "EHLO mail-pf0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751102AbeAVSQI (ORCPT ); Mon, 22 Jan 2018 13:16:08 -0500 Received: by mail-pf0-f182.google.com with SMTP id m26so7694914pfj.11 for ; Mon, 22 Jan 2018 10:16:08 -0800 (PST) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2018-01-22 at 09:28 -0800, Ben Greear wrote: > My test case is to have 6 processes each create 5000 TCP IPv4 connections to each other > on a system with 16GB RAM and send slow-speed data. This works fine on a 4.7 kernel, but > will not work at all on a 4.13. The 4.13 first complains about running out of tcp memory, > but even after forcing those values higher, the max connections we can get is around 15k. > > Both kernels have my out-of-tree patches applied, so it is possible it is my fault > at this point. > > Any suggestions as to what this might be caused by, or if it is fixed in more recent kernels? > > I will start bisecting in the meantime... > Hi Ben Unfortunately I have no idea. Are you using loopback flows, or have I misunderstood you ? How loopback connections can be slow-speed ?